by Elzbieta Stepowska - University of Toronto T-Space · 2010-11-03 · Synthesis of...

Ruthenium 4,5-diazafluorene complexes and their reactivity

by

Elzbieta Stepowska

A thesis submitted in conformity with the requirements

for the degree of Master of Science

Graduate Department of Chemistry

University of Toronto

© Copyright Elzbieta Stepowska 2009

ii

Ruthenium 4,5-diazafluorene complexes and their reactivity

Elzbieta Stepowska

Master of Science 2009

Department of Chemistry

University of Toronto

Abstract

The reaction between RuCl2(PPh3)3 and 4,5-diazafluorene (LH) produced the

orange, air sensitive RuCl2(LH)(PPh3)2 (1). Exposing this complex to air led to the

oxidation of the CH2 group on the central ring of LH to a carbonyl group.

RuCl2(LH)(dppb) (3) was synthesized but did not show the same reactivity as complex 1.

The reaction between RuHCl(LH)(PPh3)2 (4) and KOtBu produced the purple complex

RuH(N2)(L)(PPh3)2 (5), L = deprotonateed 4,5-diazafluorene. Complex 5 heterolytically

splits H2 to form RuH2(LH)(PPh3)2 (6), quantitatively. Complex 5 shows C-D bond

activation of C6D6 and is air sensitive in the solid state and in solution. Both 1 and 6

were shown to catalyze the hydrogenation of acetophenone. Bis(4,5-diazafluoren-9-

yl)methane has been synthesized and fully characterized by 1H NMR,

13C NMR and X-

ray crystallography.

iii

Acknowledgements

I would like to thank my supervisor Datong Song for all of his support and helpful

discussions. I would also like to thank my group members especially Dr. Alen Hadzovic,

Dr. Huiling Jiang for their help with everyday laboratory work and Vincent Annibale for

proof reading this thesis. Special thanks also go to Dr. Matthias Ullrich for his help with

experimental set ups and support throughout the year. I would also like to thank Dr.

Edwin Otten for his help with experiments and useful discussions. Of course I would like

to thank my parents for their continuing support. Lastly I would like to thank the

University of Toronto and the funding agencies (NSERC, CFI, and the Ontario Research

Fund) which provided the funding in order for this work to be possible.

iv

Table of Contents

Page

Abstract ii

Acknowledgements iii

Table of Contents iv

List of Tables vii

List of Figures viii

List of Schemes ix

List of Abbreviations xi

Chapter I: Introduction 1

1.1 Dihydrogen: First M-η2-H2 complex 1

1.2 H2 interaction with metal complexes 2

1.3 Examples of heterolytic H2 splitting 4

1.4 Bimetallic complexes 7

1.5 Scope of thesis 9

Chapter II: Experimental 10

2.1 Synthesis of RuCl2(PPh3)3 11

2.2 Synthesis of RuHCl(PPh3)3 11

2.3 Synthesis of RuCl2(dppb)(PPh3) 11

2.4 Synthesis of RuCl2(LH)(PPh3)2 (1) 11

v

2.5 Synthesis of RuCl2(LH)(dppb) (3) 12

2.6 Synthesis of RuHCl(LH)(PPh3)2 (4) 13

2.7 Synthesis of RuH(N2)(L)(PPh3)2 (5) 13

2.8 Synthesis of RuH2(LH)(PPh3)2 (6) 14

2.9 Synthesis of cis-cis-trans RuH(py)(L)(PPh3)2 (7) 14

2.10 Synthesis of RuH(OMe)(LH)(PPh3)2 (8) 15

2.11 Synthesis of 4,5-diazafluorene-9-one (9) 15

2.12 Synthesis of 4,5-diazafluorene (10) 15

2.13 Synthesis of bis(4,5-diazafluoren-9-yl) methane (11) 16

Chapter III: Results and Discussion 26

3.1 Synthesis and reactivity of 1 26

3.2 Synthesis and reactivity of 4 28

3.3 Synthesis of 5 29

3.4 Reactivity of 5 with H2 and D2 31

3.5 Independent synthesis of 6 33

3.6 Reversibility of H2 splitting 35

3.7 C-D bond activation of C6D6 with 5 36

3.8 Reactions of 5 and 6 with MeOH 38

3.9 Reaction of 5 with CH4 38

3.10 Transfer hydrogenation of acetophenone 39

3.11 Synthesis of 11 40

vi

Chapter IV: Conclusion and Future Outlook 42

References 44

vii

List of Tables

Page

Table 1: Crystallographic data for cis-cis-trans-RuCl2(LH)(PPh3)2 18

Table 2: Selected bond lengths (Å) and angles (deg) of RuCl2(LH)(PPh3)2 19

Table 3: Crystallographic data for RuH(N2)(L)(PPh3)2 (5) 20

Table 4: Selected bond lengths (Å) and angles (deg) of 5 21

Table 5: Crystallographic data for RuH2(LH)(PPh3)2 (6) 22

Table 6: Selected bond lengths (Å) and angles (deg) of 6 23

Table 7: Crystallographic data for bis(4,5-diazafluoren-9-yl) methane (11) 24

Table 8: Bond lengths (Å) and angles (deg) of 11 25

viii

List of Figures

Page

Chapter I: Introduction

Figure 1.1: Homolytic and heterolytic cleavage of H2 2

Figure 1.2: a) pyrazolate, b) monophenoxide, c) Pacman porphyrins 7

Figure 1.3: Examples of functionalized LH 9

Chapter III: Results and Discussion

Figure 3.1: Molecular structure of cis-cis-trans-RuCl2(LH)(PPh3)2 29

Figure 3.2: Molecular structure of 5 30

Figure 3.3: Formation of HD when 5 is placed under D2 32

Figure 3.4: UV-Vis data for reaction in Scheme 3.6 33


Figure 3.6: 1H NMR spectrum of 5 and

1H NMR spectrum of 5a 36


ix

List of Schemes

Page

Chapter I: Introduction

Scheme 1.1: Synthesis of first metal-dihydrogen complexes 1

Scheme 1.2: Synthesis of Mo(H2)(CO)(dppe)2 3

Scheme 1.3: Reaction of an Ir(III) compound with H2 5

Scheme 1.4: H2 splitting between a metal and a non-innocent ligand 5

Scheme 1.5: Reversible H2 splitting across a metal and a β-diketiminate 6

Scheme 1.6: Formation of FLPs 6

Scheme 1.7: Deprotonation of LH 8

Scheme 1.8: Synthesis of [Pd(PPh3)ClL]2 8

Chapter III: Results and Discussion

Scheme 3.1: Synthesis of 1 26

Scheme 3.2: Oxidation of 1 by air 26




Scheme 3.6: Reaction of 5 with H2 31

Scheme 3.7: Reaction of 4 with NaH 33

Scheme 3.8: Heating 6 to 60oC with excess pyridine 35


Scheme 3.10: Reversible H/D exchange 37

x

Scheme 3.11: Reactions of 5 and 6 with MeOH 38

Scheme 3.12: Transfer hydrogenation of acetophenone 39


xi

List of Abbreviations

1 RuCl2(LH)(PPh3)2

3 RuCl2(LH)(dppb)

4 RuHCl(LH)(PPh3)2

5 RuH(N2)(L)(PPh3)2

6 RuH2(LH)(PPh3)2

7 cis-cis-trans RuH(py)(L)(PPh3)2

8 RuH(OMe)(LH)(PPh3)2

9 4,5-diazafluorene-9-one

10 4,5-diazafluorene

11 bis(4,5-diazafluoren-9-yl) methane

LH 4,5-diazafluorene

L deprotonated 4,5-diazafluorene

dppb diphenylphosphine butane

dppe diphenylphosphine ethane

MeOH methanol

THF tetrahydrofuran

N2 dinitrogen

CaH2 calcium hydride

PPh3 triphenylphosphine

NaH sodium hydride

KOH potassium hydroxide

KMnO4 potassium permanganate

xii

MgSO4 magnesium sulfate

NaSO4 sodium sulfate

LiAlH4 lithium aluminum hydride

Cy cyclohexyl

Å angstrom

g gram

h hour

min minute

mmol millimole

mol mole

NMR nuclear magnetic resonance

ppm parts per million

MHz mega herz

δ chemical shift

m multiplet

t triplet

d doublet

dd doublet of doublets

s singlet

% percent

py pyridine

M metal

λmax maximum wavelength

1

CHAPTER I

INTRODUCTION

1.1 Dihydrogen: first M-η2-H2 complex

Dihydrogen is of significant importance in the chemical industry. It is used in

catalytic hydrogenations of organic compounds i.e. ketones, imines and alkenes1-7

, which

are amongst the most widely used chemical reactions in the world. The Haber process1

of making ammonia also requires the use of dihydrogen.

The importance of

understanding how the H2 molecule interacts with metal complexes has been stressed

over the years and is important in understanding hydrogenation reactions.1,8-10

It was not

until the discovery of the first stable M-dihydrogen complex by Kubas1 in 1984 that a

new understanding of the coordination of H2 was established. Kubas et al11

used an

unsaturated 16 electron complex, which was later found to have an agostic C-H

interaction stabilizing it12

, to isolate the first dihydrogen complex as shown in Scheme

1.1.

Scheme 1.1. Synthesis of metal-dihydrogen complexes

This discovery led to a new classification of bonding interactions in transition metal

complexes and was the first example of coordination of a σ bond to a metal.13

The large

1H-

2H coupling observed in the corresponding HD complexes, M(HD)(PR3)2(CO)3, (M =

Mo, W, R = Cy, iPr) was enough evidence that the sigma complex exists as a stable

2

species in solution.14

This property is now routinely used to identify dihydrogen

complexes.

1.2 H2 interaction with metal complexes

The H2 molecule has a strong two electron bond which can donate electron

density into a vacant d orbital on a metal and thus form a stable metal-dihydrogen

complex.1 This type of bonding interaction is termed σ-bonding and is described as a 2-

electron, 3-center bond similar to what can be found in bridging metal hydrides.1 This

type of interaction is the first step towards bond cleavage. Breaking the H-H bond can be

achieved in two ways, depending on the amount of electron density at the metal center as

shown in figure 1.1.1,15-17

Figure 1.1. Homolytic and heterolytic cleavage of H2.

The initial interaction of the H2 molecule is a combination of two effects; sigma donation

of the bonding electrons of the H2 molecule, and the back donation of electron density

from the metal into the empty sigma antibonding (σ*) orbital of H2.1,15

Back donation is

of great importance in stabilizing M-η2-H2 complexes.

1 The extent of back donation will

determine how the H2 molecule is split or whether a stable dihydrogen complex will

prevail. If the metal is very electron rich, there will be extensive back donation, which

over populates the σ* orbital of H2 and thus leads to the homolytic cleavage of the H-H

bond to form M-hydrides.1,15-17

On the other hand, if the metal center is electrophilic, the

3

extent of back donation is less significant. In this case the bound H2 molecule becomes

more acidic, i.e., polarized, which leads to a M-hydride and an H+.2, 15,18,19

The H+ can

then be picked up by any internal, or external, base which is termed intramolecular H2

splitting and intermolecular H2 splitting respectively.

One way to tune the electronics of the metal center is by introducing ligands with

different donating and withdrawing abilities, another being of course the choice of the

metal. It has been found that H2 activation is strongly dependent on the metal, the ligands

and the charge of the overall complex.15

Highly donating ligands, third-row metals and neutral complex charge:

Ligands that are strong donors, phosphines for example, increase the electron

density at the metal center thereby promoting back donation. Third row transition metals

have more diffuse d orbitals thereby making them better back donors than first row

metals and once again promoting back donation.15

Kubas et al20

used the previously

synthesized Mo(CO)(R2PC2H4PR2)221

where R = Ph to isolate a stable dihydrogen

complex: MoH2(CO)(Ph2PC2H4PPh2)2 as shown in Scheme 1.2.

Scheme 1.2. Synthesis of Mo(H2)(CO)(dppe)220

This complex was found to have an intact H2 molecule bound to the Mo center. Kubas et

al13

were interested in investigating how different phosphine ligands would affect the

interaction of the H2 molecule with the Mo center. They showed that when dppe was

replaced with more basic alkylphosphines, (R2PC2H4PR2) where R = Et, i-Bu, they were

4

able to isolate the Mo-dihydride complexes with 7 coordinate pentagonal bipyramidal

structures.13

The basicities when R = Et or i-Bu are similar and greater than when R = Ph.

The cone angles of PPh3 and P(i-Bu)3 are similar and larger than PEt3 and by comparing

all three complexes they were able to separate steric and electronic factors. By showing

that when R= i-Bu, they were able to isolate the dihydride it was evident that steric

factors were not as important as electronic factors when it came to splitting the H2

molecule.13

This clearly indicated that increased basicity of the ancillary ligands

influenced the interaction of H2 with the metal center.

Electron withdrawing ligands, first row metals and cationic complex charge:

An increase in the electrophilicity of the metal center decreases the amount of

back donation from the metal to the antibonding orbital of H2. Depending on the extent

of back donation, this can lead to stable M-η2-H2 complexes or to the heterolytic splitting

of the H2 molecule. One diagnostic tool used to determine the extent of back donation is

the H-H bond distance where complexes were found to have distances ranging between

0.82 to 1.5 Å.22

1.3 Examples of heterolytic H2 splitting:

As stated previously there are two forms of heterolytic splitting, intramolecular

and intermolecular, in any case there is no change to the oxidation state of the metal or to

the coordination number of the complex.

Many variations of H2 splitting have been reported between metal centers and

adjacent nucleophilic heteroatoms (N, O, S) which is facilitated by the close proximity of

the heteroatom to the metal center.15,23-25

Lee et al26

have reported an Ir(III) compound

with the 2-aminobenzoquiolinate ligand which can split H2 heterolytically. The close

5

proximity of the NH2 group allows proton abstraction to take place as shown in Scheme

1.3.

Scheme 1.3. Reaction of Ir(III) compound with H2

In 2006, Milstein et al27

reported H2 activation in an Ir(PNP), (PNP = 2,6-bis-(di-

tert-butylphosphinomethyl)pyridine) system where the splitting is facilitated by the

dearomatization/aromatization of the ligand. The splitting takes place between a metal

center and a non-adjacent carbon on the ligand as shown in Scheme 1.4.

Scheme 1.4. H2 splitting between metal and non-innocent ligand.

The authors have no direct evidence of the dearomatized intermediate but conclude that it

is a possible intermediate in the reaction. Interestingly when the authors put the Ir(PNP)

complex under D2 gas they did not obtain the dideuteride only the Ir(H)(D) species with a

deuterium atom incorporated into the benzylic side arm. This experiment supported the

proposal of the benzylic carbons involvement in H2 splitting.27

More recently Dyson et al28

have reported H2 splitting between a Ru(II) center

and the backbone of a β-diketiminate ligand. More specifically the reaction takes place

between the metal and a nucleophilic carbon center as shown in Scheme 1.5.

6

Scheme 1.5. Reversible H2 splitting across a metal and a β-diketiminate ligand

The highly reactive product in solid form readily loses H2 in the absence of a hydrogen

atmosphere.28

H2 activation is not confined to metal complexes. Stephan6,7

has described the

concept of “frustrated Lewis pairs” (FLPs) where sterically encumbered Lewis donors

and acceptors are combined as shown in Scheme 1.6.

Scheme 1.6. Formation of a FLP.

Here, we see the “nucleophilic attack by the phosphine at the more accessible,

electrophilic p-carbon of an arene ring”.6,7

Due to the steric demands of the borane and

phosphine the Lewis acidity and basicity remain unquenched and thus these centers are

available for further reactions. Recently, Ullrich et al29

, have shown the reversible, room

temperature heterolytic activation of H2 between the borane B(p-C6F4H)3 and bulky

phosphines PR3, R = t-Bu, Cy, o-C6H4Me) to form the corresponding salts:

[R3PH][HB(p-C6F4H)3].

7

2.1 Bimetallic complexes

There are many examples of enzymes having more than one metal center

incorporated into their design. Many of which have been structurally characterized.30-31

An important feature in enzymes is the ability of the protein matrix to provide different

binding sites for individual metal centers.32

Differences in binding environments lead to

different reactivity. One way to mimic mother nature is to design catalysts with more

than one binding site for individual metals. This is where ligand design becomes crucial.

An excellent review by Gavrilova and Bosnich give examples of many different types of

ligands where figure 1.2 shows only a select few.33

Figure 1.2. a) pyrazolate bridging ligand, b) monophenoxide c) “Pacman” porphyrins

Cofacial diporphyrins (figure 1.c) have attracted much attention over the years and a

binuclear cobalt complex has been shown to activate O2.34

The interest in bimetallic

complexes stems from the idea of cooperativity between metal centers. It is believed that

when two metal centers are in close proximity they can influence each other and this

property can give rise to interesting variations to reactivity in comparison to either metal

alone.35

It is our interest to design ligands with two distinct binding sites using the 4,5-

diazafluorene (LH) moiety. LH was reported over 30 years ago36

and can be viewed as a

8

cyclopentadiene (CpH) ring with two pyridine rings fused on either side.37

As shown in

Scheme 1.7, if the central ring of LH is deprotonated at the 9-position, the resulting

ligand has two different binding sites: the two nitrogens of the pyridine rings and the

carbons of Cp-:37

Scheme 1.7. Deprotonation of LH

Deprotonation of LH can be achieved by NaH in THF solution. The protons at the 9-

position shift from 3.85 ppm in LH to 5.91 ppm in L-, indicating the increased aromaticiy

of the central ring.37

Despite this interesting feature very few complexes of L- exist,

even complexes of LH are limited.37-39,42

In 2008, Jiang and Song37

have reported the

synthesis of a dimeric Pd(II) complex which depicts the bridging mode of L- as shown in

Scheme 1.8.

Scheme 1.8. Synthesis of [Pd(PPh3)ClL]2

This complex demonstrates the versatile nature of this ligand. Each L- is coordinating

with one nitrogen donor atom to one Pd(II) and with a carbon of Cp- to the other Pd(II).

9

So far no known literature example exists of a compound with a metal bound to the

central ring of L- in a η

5 binding mode, similar to how Fe binds in ferrocene. With this in

mind, one of our goals is to design ligands capable of trapping a metal at the C5 ring and

having the other coordination site open for substrate binding. One way of achieving this

is to attach an additional coordinating group to the C5 ring, which can stabilize incoming

ions in a chelating fashion. Some examples of such ligands are shown in figure 1.3.

Figure 1.3. Examples of functionalized LH ligands

Ligand A, with a picolyl functional group has previously been synthesized by members

of our group, B was not known. The synthesis of B will be presented in this thesis.

1.5 Scope of thesis

One major focus of this research was to expand the coordination chemistry of LH,

since it is rather undeveloped. Several new Ru(II) complexes have been synthesized.

One of which was found to undergo oxidation of the CH2 group of the coordinated LH

and another was found to heterolytically split the H2 molecule. Another focus of this

thesis was to functionalize the LH ligand at the 9-position. The synthesis of a new ligand

will be reported herein.

10

CHAPTER II

EXPERIMENTAL

General. All reactions were handled under argon using standard Schlenk techniques or in

a nitrogen-atmosphere glovebox from MBraun. Unless otherwise stated, all chemicals

were purchased from commercial sources and used without further purification. C6H6,

C6D6, THF and diethyl ether were dried over sodium/benzophenone, vacuum transferred

and stored over activated 4 Å sieves in the glovebox. MeOH was dried over activated 3

Å molecular sieves and vacuum transferred before use. CH2Cl2 was dried over CaH2 and

vacuum transferred before use. Pentanes, toluene and hexanes were obtained from a

solvent purification system (IT PruSolv PS-MD-6) and degassed before use. CD2Cl2 and

CDCl3 were purchased from Cambridge Isotope Laboratories, Inc., dried over CaH2 and

vacuum transferred before use.

Physical Characterization: NMR spectra were recorded on a Varian 400 spectrometer

working at 400 MHz for 1H, 162 MHz for

31P and 100 MHz for

13C or on a Varian 300

spectrometer working at 300 MHz for 1H and 121 MHz for

31P. Chemical shifts are

reported in parts per million (ppm) relative to the solvent’s residual signal. Elemental

analyses were performed at our Chemistry Department using Perkin Elmer 2400 Series II

C/H/N/S analyzer. All samples were dried under vacuum before analysis.

11

2.1 Synthesis of RuCl2(PPh3)340

:

0.200 g (0.76 mmol) of RuCl3. 3H2O was dissolved in 50 ml of MeOH under argon. A

six fold excess, 1.200 g (4.6 mmol) of triphenylphosphine was added as a solid. The

solution was allowed to reflux under argon for 4 hours. The resulting precipitate was

washed with MeOH and then diethyl ether. The product was dried under vacuum (0.597

g, 82 % yield). 31

P NMR (CDCl3, 121 MHz) δ 30.163 ppm.

2.2 Synthesis of RuHCl(PPh3)318

:

1.46 g (1.5 mmol) of RuCl2(PPh3)3 was dissolved in toluene under hydrogen. 0.74 ml

(5.3 mmol) of triethylamine was added to the reaction flask and the solution was allowed

to stir overnight. The purple precipitate was washed with EtOH and diethyl ether (1.32 g,

95 % yield). 31

P NMR (C6D6, 121 MHz ) δ 57.8 ppm (s, br). 1H NMR (C6D6, 300 MHz)

δ -17.617 ppm (2JH-P = 25.6 Hz).

2.3 Synthesis of RuCl2(dppb)(PPh3)41

:

0.400 g (0.4 mmol) of RuCl2(PPh3)3 was dissolved in 20 ml of CH2Cl2. 0.179 g (0.4

mmol) of dppb was added as a solid to the stirred solution. After the addition of the

ligand the solution changed colours from dark purple/brown to green. The solution was

allowed to stir for half an hour. The volume was reduced and dry EtOH was added to

precipitate the product (0.272 g, 79 % yield). 31

P NMR (CD2Cl2, 121 MHz) δ 26.77,

25.63, 24.46, - 4.47 ppm.

2.4 Synthesis of RuCl2(LH)(PPh3)2 (1):

0.6 g (0.62 mmol) of RuCl2(PPh3)3 was dissolved in 50 ml of THF. 0.1 g (0.62 mmol) of

LH was added as a solid and the solution allowed to stir overnight in the glovebox. The

orange precipitate was collected by filtration, washed several times with THF and dried

12

under vacuum (0.439 g, 82 % yield). 1H NMR (CD2Cl2, 400 MHz) δ 8.72 (d, 1 H,

3JH-H =

5 Hz, LH), 7.72 (t, 6 H, 3JH-H = 8 Hz, PPh3), 7.62 (d, 1 H,

3JH-H = 8 Hz, LH), 7.50 (d, 1 H,

3JH-H = 7 Hz, LH), 7.19-7.15 (m, 3 H, PPh3), 7.12-7.02 (m, 10 H, 9 H from PPh3, 1 H

from LH), 6.93 (t, 6 H, 3JH-H = 8 Hz, PPh3), 6.83 (t, 6 H,

3JH-H = 8 Hz, PPh3), 6.68 (d, 1 H,

3JH-H = 6 Hz, LH), 6.51 (dd, 1 H,

3JH-H = 5, 8 Hz, L), 4.05 (d, 1 H, J = 21 Hz, LH), 3.77 (d

1 H, J = 21 Hz, LH). 31

P NMR (CD2Cl2, 162 MHz) δ 44.61 (d, 2JP-P = 30 Hz), 42.88 (d,

2JP-P = 30 Hz).

13C NMR (CD2Cl2, 100 MHz) δ 152.07, 134.40, 14.34, 134.29, 133.85,

132.43, 129.25, 128.60, 127.44, 127.38, 127.33, 126.88, 124.52. Anal. Calcd for

C47H38Cl2N2P2Ru + 1/2 CH2Cl2: C, 62.89; H, 4.33; N, 3.09. Found: C, 62.61; H, 4.40; N,

3.05.

2.5 Synthesis of RuCl2(LH)(dppb) (3): Under nitrogen atmosphere 0.200 g (0.23

mmol) of RuCl2(dppb)PPh3 was dissolved in 5 ml of THF. 0.04 g (0.24 mmol) of 4,5-

diazafluoene was dissolved in 3 ml THF. The pale yellow 4,5-diazafluorene solution was

then added to the green ruthenium solution. With the addition of the ligand the solution

turned red. The solution was stirred at ambient temperature overnight. After overnight

stirring a red/orange precipitate was observed. The precipitate was filtered and washed

several times with THF (0.136 g, 77 % yield). 31

P NMR (CD2Cl2, 121 MHz) δ 48. 55 (d,

2JP-P = 36.3 Hz ). 38.26 (d,

2JP-P = 36.3 Hz ).

13C NMR (CD2Cl2, 100 MHz) δ 166.02,

162.19, 153.68, 148.27, 142.62, 141.07, 137.17, 136.99, 136.90, 136.74, 135.30, 135.20,

135.10, 134.34, 133.57, 132.53, 132.39, 130.64 130.45, 129.78, 129.29, 129.98, 128.23,

127.95, 127.72, 127.16, 124.10, 123.30, 68.30, 36.50, 34.97, 28.05, 27.55, 26.15, 19.89.

13

2.6 Synthesis of RuHCl(LH)(PPh3)2 (4):

1.200 g (1.3 mmol) of RuHCl(PPh3)3 was dissolved in 90 ml of THF and 0.220 g (1.3

mmol) of LH was added as a solid. The solution was allowed to stir overnight in the

glovebox. The orange precipitate was collected by filtration, washed several times with

THF and dried under vacuum (0.928 g, 86 % yield). 1H NMR (CDCl3, 300 MHz) δ 8.16

(d, 1 H, LH), 7.97 (d, 1 H, LH), 7.74-7.68 (m, 7 H, 6 H from PPh3, 1 H from LH), 7.47

(d, 1 H, LH), 7.20-6.99 (m, 13 H, 12 H from PPh3, 1 H from LH), 6.85-6.83 (m, 6 H,

PPh3), 6.79 (dd, 1 H, LH), 3.95 (d, 1 H, LH, 2JH-H= 15 Hz), 3.74 (d, 1 H, LH,

2JH-H=15

Hz), -16.32 (t, 1H, 2JH-P =27.8 Hz, Ru-H).

31P NMR (CDCl3, 162 MHz) δ 75.37 (dd,

2JP-

P= 35 Hz, 2JH-P = 20 Hz), 65.25 (dd,

2JP-P = 35 Hz,

2JH-P = 20 Hz ). Anal. Calcd for

RuP2N2ClC47H39: C, 67.99; H, 4.73; N, 3.37. Found: C, 67.57; H, 4.62; N, 3.51. 128.6,

128.7, 128.8, 128.9, 129.5, 129.7, 130.7, 132.7, 136.2, 139.4, 151.2, 159.2.

2.7 Synthesis of RuH(N2)(L)(PPh3)2 (5):

0.443 g (0.53 mmol) of RuHCl(LH)(PPh3)2 was dissolved in 50 ml of THF and 0.063 g

(0.56 mmol) of potassium t-butoxide was added as a solid. The solution was allowed to

stir overnight under nitrogen. The volume was reduced by vacuum and pentanes were

added to afford the product as a purple precipitate (0.348 g, 80% yield). Crystals suitable

for X-ray crystallographic analysis were obtained from slow diffusion of pentanes into a

concentrated solution of 5 in THF. 1H NMR (C6D6, 400 MHz) δ 7.96 (d, 1 H,

3JH-H = 4

Hz, L), 7.76 (d, 1 H, 3JH-H = 8 Hz, L), 7.56 (d, 1 H,

3JH-H = 8 Hz, L), 7.35 (m, 12 H, PPh3),

6.96 (d, 1 H, 3JH-H = 4 Hz, L), 6.85 (m, 18 H, PPh3), 6.81 (dd, 1 H,

3JH-H = 4, 8 Hz, L)

6.44 (s, 1 H, L), 6.16 (dd, 1 H, 3JH-H = 4, 8 Hz, L), -12.23 (t, 1 H,

2JP-H = 20 Hz, Ru-H).

31P NMR (C6D6, 162 MHz) δ 49.65 ppm. IR(nujol): ν(Ru-N2) 2091.61 (s) cm

-1.

13C

14

NMR (C6D6, 100 MHz) δ 141.1, 140.6, 137.8, 135.1, 134.0, 133.6, 129.7, 128.2, 127.5,

125.3, 124.6, 117.9, 117.6, 82.2. Anal. Calcd for RuC47H38N4P2 + 2[O]: C, 66.11; H,

4.49; N, 6.56. Found: C, 66.74; H, 4.79; N, 6.18.

2.8 Synthesis of RuH2(LH)(PPh3)2 (6):

0.300 g (0.36 mmol) of RuHCl(LH)(PPh3)2 was dissolved in 25 ml of THF. 0.016 g (0.4

mmol) of NaH (60 wt% dispersion in mineral oil) was added as a solid and the solution

allowed to stir overnight under nitrogen. The solution was then filtered through Celite

and the volume reduced under vacuum. Pentanes were added to obtain the product as a

purple precipitate (0.175 g, 61 % yield). Crystals suitable for X-ray crystallographic

analysis were obtained from slow diffusion of hexanes into a concentrated solution of 6

in THF. 1H NMR (C6D6, 300 MHz) δ 8.03 (d, 2 H,

3J-H-H = 6 Hz, LH), 7.80 (m, 12 H,

PPh3), 6.97 (m, 18 H, PPh3), 6.97 (d, 2 H, 3JH-H = 6 Hz, LH), 6.28 (dd, 2 H,

3JH-H = 6, 7

Hz, LH), 2.97 (s, 2 H, LH) -15.43 (t, 2 H, 2JP-H = 27 Hz, Ru-H).

31P NMR (C6D6, 121

MHz) δ 63.21. 13

C NMR (C6D6, 100 MHz) δ 162.0, 151.7, 140.9, 133.9, 133.4, 127.6,

127.4, 125.7, 123.2, 35.4 ppm. Anal. Calcd for RuC47H40N2P2 + 2[O]: C, 68.19; H, 4.87;

N, 3.38. Found: C, 68.15; H, 5.01; N, 3.31.

2.9 Synthesis of cis-cis-trans RuH(py)(L)(PPh3)2 (7): 0.129 mg (0.16 mmol) of

RuH(N2)(LH)(PPh3)2 was dissolved in 5 ml THF and 8 equivalents (100 µL) of pyridine

was added. The solution was allowed to stir at 60oC for 12 h. The volume was reduced

and pentanes added to afford a dark brown/red precipitate (0.123 g, 88 % yield). 1H

NMR (C6D6, 400 MHz) δ 8.47 (d, 2 H, py), 8.15 (d, 1 H, L), 7.89 (d, 1 H, L), 7.51 (d, 1

H, L), 7.47 (d, 1 H, L), 7.32 (m, 12 H, ortho-H of PPh3), 7.12 (q, 1 H, L), 6.89 (m, 18 H,

15

m-H and p-H of PPh3), 6.43 (s, 1 H, L), 6.31 (q, 1 H, L), 6.29 (m, 1 H, py), 5.68 (m, 2 H,

py), -16.28 (t, 2JP-H = 24 Hz, Ru-H).

31P NMR (C6D6, 400 MHz) δ 56.11 (s).

2.10 Synthesis of RuH(OMe)(LH)(PPh3)2 (8):

0.050 g (0.06 mmol) of RuH2(LH)(PPh3)2 was dissolved in 5 ml of dry MeOH under a

nitrogen atmosphere. The solution was allowed to stir for 12 h at which point the solvent

was removed, the crude product redissolved in C6H6 and pentanes added to afford the

product as a green precipitate (0.039 g, 79 % yield). 1H NMR (C6D6, 300 MHz) δ 7.98

(d, 1 H, 2JH-H = 3 Hz, LH), 7.67 (d, 1 H,

2JH-H = 9 Hz), 7.58 (d, 1 H,

2JH-H = 9 Hz, LH),

7.35 (m, 12 H, o-H of PPh3), 7.01 (d, 1 H, 2JH-H = 3 Hz, LH), 6.87 (m, 18 H, p-H and m-

H of PPh3), 6.74 (q, 1 H, 2JH-H = 6, 9 Hz), 6.24 (q, 1 H,

2JH-H = 6,9 Hz), 2.77 (s, 3 H,

OCH3), -11.57 (t, 1 H, 2JH-P = 18 Hz, Ru-H).

31P (C6D6, 121 MHz), δ 49.71 (s).

2.11 Synthesis of 4,5-diazafluorene-9-one (9) 42,43

:

10 g (0.055 mol) of 1,10-phenanthroline and 10 g (0.178 mol) of KOH were dissolved in

750 ml of water. 25.5 g (0.161mol) of KMnO4 was dissolved in 400 ml of water and

heated to 60oC. The hot KMnO4 solution was slowly added to the refluxing

phenanthroline solution over the course of three hours. The solution was then filtered hot

and allowed to come to room temperature. The solution was then extracted with CHCl3

(3 x 500 ml). The extracts were then dried over MgSO4. The solution was then filtered

and the solvent evaporated (7.94 g, 75 % yield) 1H NMR (400 MHz, CDCl3) δ 8.811 ppm

(d, 2 H, ortho-H), 8.013 ppm (d, 2 H, para-H), 7.359 ppm (dd, 2 H, meta-H).

2.12 Synthesis of 4,5-diazafluorene (10) 42,43

:

2.87 g (0.016 mol) of 4,5-diazafluorene-9-one and 20 ml (0.642 mol) of hydrazine

hydrate were heated to 180oC for 6 h in a Teflon lined bomb. After allowing the mixture

16

to come to room temperature it was extracted with CH2Cl2 (4 x 100 ml). The organic

extracts were dried over MgSO4 then filtered and the solvent removed by vacuum.

Chromatography on silica gel using ethyl acetate gave the pure compound (1.34 g, 50 %

yield) 1H NMR (CDCl3, 300 MHz) δ 8.741 ppm (d, 2 H, ortho-H), 7.876 ppm (d, 2 H,

para-H), 7.291 ppm (dd, 2 H, meta-H), 3.872 ppm (s, 2 H, CH2). 13

C NMR (CDCl3, 100

MHz) δ 159.09, 149.70, 137.44, 132.95, 122.74, 32.40.

2.13 Synthesis of bis(4,5-diazafluoren-9-yl) methane (11):

0.500 g (2.97 mmol) of 4,5 diazafluorene was dissolved in 30 ml of THF in the glove

box. 0.120 g (2.97 mmol) of NaH (60 wt% dispersion in mineral oil) was slowly added

to the stirring solution. Allowed the solution to stir for half an hour then added 105 µL

(1.48 mmol) of dibromomethane to the solution and refluxed under argon for 4 days. The

solution was then quenched with minimal water and the solvent removed under vacuum.

Chromatography on silica gel using a 3:1 ratio of ethyl acetate to MeOH gave the pure

compound (0.207 g, 40 % yield). Crystals suitable for X-ray crystallographic analysis

were obtained from slow diffusion of hexanes into a concentrated solution of 11 in

CH2Cl2. 1H NMR (CDCl3, 400 MHz) δ 8.770 ppm (d, 4 H, ortho-H), 7.820 ppm (d, 4 H,

para-H), 7.295 ppm (dd, 4 H, meta-H), 4.280 ppm (t, 2 H, CHCH2CH), 2.320 ppm (t, 2

H, CHCH2CH). 13

C NMR (CDCl3, 100 MHz) δ 158.31, 150.22, 140.80, 132.43, 122.88,

41.76, 36.58. Elemental analysis, calc. for C23H16N4 + ½ [H2O]: C, 77.29; H, 4.79; N,

15.67. Found: C, 76.91; H, 5.23; N, 15.49.

17

X-ray crystallography: All diffraction data were collected at 150 K on a Nonius Kappa-

CCD diffractometer with Mo Kα radiation (λ = 0.71073 Å), operating at 50 kV and 30

mA. The data were processed using the DENZO-SMN package.51

All structures were

solved using the direct methods and refined by full-matrix least-squares procedures on F2

using SHELXTL V6.10.52

The crystallographic data are summarized in Tables 1,3, 5 and

7. Bond lengths and angles are presented in Tables 2,4,6,8.

18

Table 1: Crystallographic data cis-cis-trans-RuCl2(LH)(PPh3)2

Table 1. Crystal data and structure refinement for es3.

Identification code es3

Empirical formula C48 H40 Cl4 N2 P2 Ru

Formula weight 949.63

Temperature 150(2) K

Wavelength 0.71073 Å

Crystal system Orthorhombic

Space group P n a 21

Unit cell dimensions a = 27.5957(16) Å = 90°.

b = 15.2404(10) Å = 90°.

c = 10.1260(5) Å = 90°.

Volume 4258.7(4) Å3

Z 4

Density (calculated) 1.481 Mg/m3

Absorption coefficient 0.732 mm-1

F(000) 1936

Crystal size 0.08 x 0.05 x 0.05 mm3

Theta range for data collection 2.41 to 27.87°.

Index ranges -36<=h<=25, -20<=k<=19, -11<=l<=13

Reflections collected 21905

Independent reflections 9235 [R(int) = 0.1165]

Completeness to theta = 27.87° 99.2 %

Absorption correction Semi-empirical from equivalents

Max. and min. transmission 0.9618 and 0.6460

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 9235 / 1 / 514

Goodness-of-fit on F2 0.967

Final R indices [I>2sigma(I)] R1 = 0.0651, wR2 = 0.0946

R indices (all data) R1 = 0.1339, wR2 = 0.1144

Absolute structure parameter -0.14(4)

Largest diff. peak and hole 0.770 and -0.627 e.Å-3

19

Table 2: Selected Bond lengths (Å) and angles (deg) of cis-cis-trans-RuCl2(LH)(PPh3)2

_____________________________________________________

Ru(1)-N(1) 2.099(6)

Ru(1)-N(2) 2.130(5)

Ru(1)-P(2) 2.371(2)

Ru(1)-P(1) 2.3753(18)

Ru(1)-Cl(2) 2.404(2)

Ru(1)-Cl(1) 2.4333(18)

C(1)-C(2) 1.411(10)

C(2)-C(3) 1.385(11)

C(3)-C(4) 1.381(10)

C(4)-C(11) 1.382(9)

C(4)-C(5) 1.533(11)

C(5)-C(6) 1.542(10)

C(7)-C(8) 1.398(10)

N(1)-Ru(1)-N(2) 82.0(2)

N(1)-Ru(1)-P(2) 91.72(18)

N(2)-Ru(1)-P(2) 92.51(16)

N(1)-Ru(1)-P(1) 91.08(18)

N(2)-Ru(1)-P(1) 88.94(17)

P(2)-Ru(1)-P(1) 177.00(8)

N(1)-Ru(1)-Cl(2) 87.49(16)

N(2)-Ru(1)-Cl(2) 169.47(16)

P(2)-Ru(1)-Cl(2) 87.39(7)

P(1)-Ru(1)-Cl(2) 91.66(7)

N(1)-Ru(1)-Cl(1) 175.29(17)

N(2)-Ru(1)-Cl(1) 94.04(16)

P(2)-Ru(1)-Cl(1) 90.99(7)

P(1)-Ru(1)-Cl(1) 86.29(7)

Cl(2)-Ru(1)-Cl(1) 96.49(7)

____________________________________________________________

Symmetry transformations used to generate equivalent atoms

20

Table 3: Crystallographic data for RuH(N2)(L)(PPh3)2 (5)

Crystal data and structure refinement for 2.

Identification code 2

Empirical formula C53 H44 N4 P2 Ru




Crystal system Monoclinic

Space group P2(1)/n


b = 9.9438(2) Å = 110.4570(10)°.

c = 25.1806(7) Å = 90°.

Volume 4321.68(19) Å3

Z 4



F(000) 1856



Index ranges -23<=h<=23, -12<=k<=11, -32<=l<=32












21

Table 4: Selected Bond lengths (Å) and angles (deg) of RuH(N2)(L)(PPh3)2 (5)

_____________________________________________________

Ru(1)-N(3) 1.9305(15)

Ru(1)-N(1) 2.1139(14)

Ru(1)-N(2) 2.2823(14)

Ru(1)-P(1) 2.3394(4)

Ru(1)-P(2) 2.3516(4)

N(3)-N(4) 1.111(2)

C(4)-C(5) 1.419(3)

C(4)-C(11) 1.438(2)

C(5)-C(6) 1.422(3)

C(6)-C(10) 1.437(2)

C(10)-C(11) 1.390(2)

N(3)-Ru(1)-N(1) 177.16(6)

N(3)-Ru(1)-N(2) 95.95(5)

N(1)-Ru(1)-N(2) 81.34(5)

N(3)-Ru(1)-P(1) 89.69(4)

N(1)-Ru(1)-P(1) 91.47(4)

N(2)-Ru(1)-P(1) 96.72(3)

N(3)-Ru(1)-P(2) 90.85(4)

N(1)-Ru(1)-P(2) 88.52(4)

N(2)-Ru(1)-P(2) 94.59(4)

P(1)-Ru(1)-P(2) 168.561(15)

N(4)-N(3)-Ru(1) 179.01(15)

_____________________________________________________________

Symmetry transformations used to generate equivalent atoms:

22

Table 5: Crystallographic data for RuH2(LH)(PPh3)2 (6)

Table 1. Crystal data and structure refinement for 6.

Identification code 6

Empirical formula C47 H40 N2 P2 Ru





Space group P2(1)/n


b = 17.7363(6) Å = 105.9974(16)°.

c = 15.9357(3) Å = 90°.

Volume 3758.57(18) Å3

Z 4



F(000) 1640



Index ranges -17<=h<=17, -20<=k<=23, -17<=l<=20












23

Table 6: Selected Bond lengths (Å) and angles (deg) of RuH2(LH)(PPh3)2 (6)

_____________________________________________________

Ru(1)-N(1) 2.198(2)

Ru(1)-N(2) 2.218(2)

Ru(1)-P(2) 2.2593(7)

Ru(1)-P(1) 2.2964(7)

Ru(1)-H(2) 1.56(3)

Ru(1)-H(1) 1.66(3)

C(4)-C(5) 1.512(5)

C(5)-C(6) 1.515(4)

C(5)-H(5A) 0.9900

C(5)-H(5B) 0.9900

C(6)-C(10) 1.385(4)

C(10)-C(11) 1.424(4)

N(1)-Ru(1)-N(2) 79.80(8)

N(1)-Ru(1)-P(2) 101.49(6)

N(2)-Ru(1)-P(2) 101.62(6)

N(1)-Ru(1)-P(1) 92.39(6)

N(2)-Ru(1)-P(1) 94.19(6)

P(2)-Ru(1)-P(1) 160.52(3)

N(1)-Ru(1)-H(2) 173.2(11)

N(2)-Ru(1)-H(2) 93.4(11)

P(2)-Ru(1)-H(2) 79.9(12)

P(1)-Ru(1)-H(2) 88.0(11)

N(1)-Ru(1)-H(1) 96.3(10)

N(2)-Ru(1)-H(1) 176.1(10)

P(2)-Ru(1)-H(1) 78.9(10)

P(1)-Ru(1)-H(1) 86.1(10)

H(2)-Ru(1)-H(1) 90.5(15)

_____________________________________________________________


24

Table 7: Crystallographic data for bis(4,5-diazafluoren-9-yl) methane (11)

Crystal data and structure refinement for es5.

Identification code es5

Empirical formula C23 H16 N4





Space group P 21/c


b = 12.1974(9) Å = 93.696(4)°.

c = 13.4442(9) Å = 90°.

Volume 1685.13(19) Å3

Z 4



F(000) 728



Index ranges -12<=h<=13, -15<=k<=15, -17<=l<=17












25

Table 8: Selected Bond lengths (Å) and angles (deg) of bis(4,5-diazafluoren-9-yl)

methane (11)

_____________________________________________________

C(1)-N(1) 1.338(3)

C(1)-C(2) 1.383(3)

C(2)-C(3) 1.387(3)

C(3)-C(4) 1.380(3)

C(4)-C(5) 1.405(2)

C(4)-C(11) 1.512(2)

C(5)-N(1) 1.340(2)

C(5)-C(6) 1.470(3)

C(6)-N(2) 1.339(2)

C(6)-C(7) 1.408(3)

C(7)-C(8) 1.387(3)

C(7)-C(11) 1.521(2)

C(8)-C(9) 1.387(3)

C(9)-C(10) 1.382(3)

C(10)-N(2) 1.351(3)

C(11)-C(12) 1.532(2)

N(1)-C(1)-C(2) 124.94(19)

C(1)-C(2)-C(3) 119.23(19)

C(4)-C(3)-C(2) 117.69(18)

C(3)-C(4)-C(5) 118.54(18)

N(1)-C(5)-C(6) 127.12(16)

C(4)-C(5)-C(6) 108.19(16)

N(2)-C(6)-C(7) 125.77(18)

N(2)-C(6)-C(5) 125.69(18)

C(7)-C(6)-C(5) 108.49(15)

C(8)-C(7)-C(6) 117.95(17)

C(8)-C(7)-C(11) 131.46(17)

C(10)-C(9)-C(8) 120.07(19)

N(2)-C(10)-C(9) 124.51(18)

C(4)-C(11)-C(7) 101.87(14)

_____________________________________________________________


26

CHAPTER III

RESULTS AND DISCUSSION

3.1 Synthesis and reactivity of RuCl2(LH)(PPh3)2

Compound 1 can be made by reacting RuCl2(PPh3)3 with LH in THF overnight.

Scheme 3.1. Synthesis of RuCl2(LH)(PPh3)2 (1)

The orange compound can be obtained in 82 % yield and was found to be stable in

chlorinated solvents. The 1H NMR in CD2Cl2 indicates an unsymmetrical structure where

there are two sets of signals for the hydrogens of LH. The 31

P NMR spectrum shows two

doublets at 44.61 (2JP-P = 30 Hz), and 42.88 (

2JP-P = 30 Hz) indicating the cis geometry of

the two PPh3 groups. We recently reported the air sensitivity of this compound as shown

in Scheme 3.2.44

Scheme 3.2. Oxidation of 1 by air

In this reaction the sp3 carbon in the C5 ring of LH gets oxidized to a carbonyl group

under mild condition. Typically such reactions require harsh conditions and many

27

transition metal catalysts have been developed to promote such reactions using O2 as the

oxidant.49

One observation to note is that the reactant has the two PPh3 cis to one another

where as they are trans in the product. One application of this reaction would be to use

compound 1 to catalytically convert LH to 4.5-diazafluorene-9-one. When LH was

dissolved in CH2Cl2 under a balloon of air with 1 mol % of 1 the formation of 4,5-

diazafluorene-9-one was not observed. This indicated that when 2 is formed the oxidized

ligand is bound tightly to the Ru(II) center due to the weak trans influence of the chlorine

ligands. If the oxidized ligand was trans to at least one PPh3 the ligand would be more

labile due to the strong trans influence of PPh3. In our efforts to explore this possibility

compound 3 was synthesized as shown in Scheme 3.3.

Scheme 3.3. Synthesis of RuCl2(LH)(dppb) (3)

Compound 3 was obtained in 77 % yield as a red/orange precipitate. The 31

P NMR

spectrum in CD2Cl2 showed two doublets at 48.55 (2JP-P = 36 Hz) and 38.26 (

2JP-P = 36

Hz) indicating the cis geometry of the dppb ligand. By using dppb, a chelating ligand,

we are forcing the two phosphorus atoms to stay cis to one another in the product. This

would force one of the nitrogen atoms of the oxidized ligand to be trans to the

phosphorus atom of dppb which would lead to a much weaker Ru-N bond. The weaker

Ru-N bond could lead to ligand dissociation which would be a requirement for the

28

catalytic conversion of LH to 4,5-diazafluorene-9-one. Compound 3 however was found

to be air stable and did not show the same type of reactivity with air as compound 1.

3.2 Synthesis and reactivity of RuHCl(LH)(PPh3)2

As shown in Scheme 3.4, reacting RuHCl(PPh3)3 with LH in THF leads to the

orange, oxygen sensitive RuHCl(LH)(PPh3)2 (4) in 86 % yield.

Scheme 3.4. Synthesis of RuHCl(LH)(PPh3)2 (4)

The 1H NMR spectrum in CDCl3 indicates an unsymmetrical structure, where the two

pyridine rings of LH show two sets of signals and the CH2 group of the central ring

shows an AB pattern, two doublets at 3.95 ppm and 3.74 ppm respectively with a

coupling constant (2JH-H) of 15 Hz. The Ru-hydride resonates at -16.32 ppm and is a

triplet with a coupling constant of (2JH-P) 28 Hz, similar to that previously reported for a

fac geometry of a {RuP2}(H) system.45

The 31

P NMR spectrum for compound 4 shows

two doublets of doublets at 75.3 ppm and 65.2 ppm with coupling constants of (2JP-P) 35

Hz and (2JH-P) 20 Hz. The

1H and

31P NMR data indicate a cis-{RuP2} and cis-RuHCl

structure in solution. The slow diffusion of hexanes into a concentrated solution of 4 in

CH2Cl2 led to the formation of cis-cis-trans-RuCl2(LH)(PPh3)3 as indicated by the crystal

structure obtained:

29

Figure 3.1. Molecular structure of cis-cis-trans-RuCl2(LH)(PPh3)2 with thermal ellipsoids plotted

at 50% probability. All hydrogen atoms except for the Ru-hydride are omitted for clarity.

Thus this compound readily reacts with chlorinated solvents.

3.3 Synthesis of RuH(N2)(L)(PPh3)2

Reacting potassium-t-butoxide with 4 in THF under a nitrogen atmosphere gives

RuH(N2)(L)(PPh3)2 (5), where L = deprotonated 4,5-diazafluorene as shown in Scheme

3.5.

Scheme 3.5. Synthesis of RuH(N2)(L)(PPh3)2 (5)

30

Recrystallization in THF/pentane affords 80 % of the compound as a purple precipitate.

Compound 5 is air sensitive both in the solid state and in solution (THF, C6H6, toluene).

The 1H NMR spectrum of compound 5 in C6D6 shows an unsymmetrical structure giving

rise to 7 peaks for the L ligand. The proton on the central ring of L resonates at 6.44 ppm

indicating an increased aromatic character.37

The Ru-hydride resonates at – 12.23 ppm

with a 2JP-H = 20 Hz. Only one peak is observed in the

31P NMR spectrum in C6D6 at

49.61 ppm. The N2 stretching frequency appears at 2091 cm-1

in the IR spectrum which

indicates only a weak activation of dinitrogen.46

The solid state structure of 5 was

confirmed by X-ray crystallography.

Figure 3.2. Molecular structure of compound 5 with thermal ellipsoids plotted

at 50% probability. All hydrogen atoms except for the Ru-hydride are omitted for clarity.

As shown in Figure 3.2 the Ru(II) center adopts a distorted octahedral geometry with

two nitrogen donor atoms from L, two phosphorus donor atoms from two

31

triphenylphosphine ligands, a hydride and an N2 molecule coordinated in an end-on

fashion occupying the six coordination sites of the metal. The N3-N4 distance is

1.111(2) Å, similar to free N2 with a bond length of 1.0975 Å, which verifies the IR data

obtained that the N2 molecule is only weakly activated.46

The Ru1–N1 bond (2.114(1) Å)

is longer than the Ru1–N2 bond (2.282(4) Å) as a result of N1 being trans to a hydride

which has a stronger trans influence than the N2 molecule. Carbons of the central ring in

L all show bond lengths which are typical for shortened single bonds, i.e. around 1.43 Å.

3.4 Reactivity of 5 with H2 and D2

When compound 5 is put under H2 gas either in C6H6 or THF, and heated to 60oC

for 1.5 h, it forms RuH2(LH)(PPh3)2 (6) in quantitative yield, as shown in Scheme 3.6.

Scheme 3.6: Reaction of 5 with H2 (1 atm).

During this reaction it is postulated that N2 is lost first, which opens up a free site on the

Ru center, such that H2 can bind. No observation of the Ru-η2-H2 has been made by

1H

solution NMR spectroscopy, where the Ru- η2-H2 would typically appear as a broad peak

in the high-field region of the proton NMR.9 Indirect evidence of its formation is

suggested by D2 experiments. When compound 5 is put under D2 gas in C6D6 there is

formation of HD gas as seen by 1H NMR spectroscopy as a triplet at 4.45 ppm due to

spin 1 for deuterium with a JH-D of 44 Hz.8 The formation of HD may be explained by

32

the coordination of D2 to the vacant site on Ru with a rapid intramolecular site exchange

between Ru-H and Ru-η2-D2.

1

4.3504.4004.4504.5004.5504.5

6

4.4

9

4.4

5

4.3

4

Figure 3.3. Formation of HD when 5 is placed under D2 gas and heated to 60oC for 45 min.

When the sample is under D2 gas it is also observed that the ortho positions of the phenyl

rings of triphenylphosphine and the central ring of LH become deuterated. The rapid

H/D exchange for the hydrides, ortho hydrogens of triphenylphosphine and hydrogens of

the central ring of LH are consistent with an equilibrium between the dihydride and

dihydrogen species, where the dihydrogen species is in too low concentration to be

detected.45

Once the H2 is bound to the Ru center the splitting of the H2 molecule occurs

in a heterolytic fashion with the formation of a Ru-hydride and a proton, where the proton

is added to the central ring of L to make the neutral ligand LH.3, 8

When an isolated

sample of complex 6 is put under D2 gas in C6H6 there is evidence of ortho-deuteration of

PPh3 as well. From the 2H NMR spectrum the peak at 7.69 ppm is assigned to the o-D of

PPh3, and the peak at -15.28 ppm to Ru-D (peaks are referenced to CD2Cl2 at 4.27 ppm).

A preliminary UV-Vis spectral time trace of the reaction in Scheme 3.6 is shown

in Figure 3.4. During the course of the reaction compound 5 (purple solution in THF

with a λmax of 430 nm) turns dark green (λmax = 580 nm) indicating the presence of

JH-D = 44 Hz

(H2)

33

compound 6. Compound 6, similar to compound 5, is air sensitive in both the solid state

and in solution.

Figure 3.4. Monitoring reaction in Scheme 3.6 by UV-Vis. Compound 5 dissolved in THF, placed under 1 atm H2 and

heated to 60oC. Reaction monitored during the course of one hour.

3.5 Independent synthesis of RuH2(LH)(PPh3)2

Compound 6 was independently synthesized by reacting 4 with one equivalent of

NaH as shown in Scheme 3.7.

Scheme 3.7. Reaction of 4 with NaH to make 6

Recrystallization out of THF/pentanes affords the product as a purple precipitate in 61 %

yield. The 1H NMR spectrum of the isolated sample of 6 shows the protons on the central

ring of LH at 2.97 ppm in C6D6, indicating the decrease in aromaticity compared to

5

4

34

compound 5. The Ru-hydride has shifted upfield to -15.43 ppm with a 2JP-H= 27 Hz and

has an integration of 2 protons. This high upfield shift and coupling constant of the Ru-

hydrides is consistent with a cis-{RuH2}.2 The

31P NMR in C6D6 shows only one peak at

63.21 ppm indicating equivalent phosphorus environments.45

The 1H and

31P NMR data

are consistent with a cis-{RuH2} and trans-{RuP2} configuration. The solid state

structure of 6 was confirmed by X-ray crystallography.

Figure 3.5. Molecular structure of compound 6 with thermal ellipsoids plotted

at 50% probability. All hydrogen atoms except for the hydrogens of C5 and Ru-hydridess are omitted for clarity.

As shown in Figure 3.5, the Ru(II) center adopts a distorted octahedral geometry with

two nitrogen donor atoms from LH, two phosphorus donor atoms from two

triphenylphosphines and two hydrides occupying the six coordination sites in a cis, trans,

cis fashion respectively. The Ru1-N1 distance (2.198(2) Å) is similar to Ru1-N2

(2.218(2) Å) since both nitrogen atoms are trans to a hydride. The distance between C4-

35

C5 has gone from 1.419(3) Å in compound 5 to 1.512(5) Å in compound 6, and C5-C6

from 1.422(3) Å to 1.515(4) Å.

The reaction in Scheme 3.6 is slowed down significantly in the presence of 15

equivalents of pyridine indicating that pyridine is competing for the same coordination

site as H2. Only 13 % of the dihydride was present after heating for 1.5 h in C6D6 under

H2 gas. Evidence of pyridine coordination is observed by 1H NMR.

3.6 Reversibility of H2 splitting

To investigate the reversibility of the reaction in Scheme 3.6 compound 6 was

heated to 60oC for 12 h under an N2 atmosphere. This led to only 12 % conversion to

compound 5. The equilibrium clearly favours compound 6. However the complete

release of H2 can be achieved in the presence of a monodentate ligand. When the

reaction was done in the presence of 8 equivalents of pyridine, it went to completion as

shown in Scheme 3.8.

Scheme 3.8. Heating 6 to 60oC in the presence of excess pyridine.

The product of the reaction was a mixture of two isomers: cis-cis-trans-

RuH(Py)(L)(PPh3)2 (29 %) and cis-cis-cis-RuH(py)(L)(PPh3)2 (71 %). The trans isomer

was synthesized independently by reacting 5 with an excess of pyridine as shown in

Scheme 3.9.

36

Scheme 3.9. Synthesis of 7

Recrystallizing in THF/pentanes gave compound 7 in 88 % yield. Only one peak was

observed in the 31

P NMR in C6D6 at 56.11 ppm. The 1H NMR spectrum in C6D6 showed

an unsymmetrical structure with 7 peaks for L with the proton on the central ring

showing up at 6.43 ppm. The Ru-H has shifted from -12 23 ppm in 5 to -16.28 ppm with

a 2JP-H = 24 Hz in 7.

3.7 C-D bond activation of C6D6 with 5

When compound 5 is heated to 60oC for 3 hours in C6D6 it converts to a species

(5ˈ) that appears as a sharp singlet at 49.15 ppm in the 31

P NMR spectrum. The 1H NMR

spectrum is very similar to that of compound 5, however there is no Ru-hydride peak

present and the peak for the ortho-H of triphenylphosphine has decreased in intensity as

shown in figure 3.6 b.

7.9

8

7.9

7

7.7

7

7.7

5

7.5

7

7.5

5

7.3

4

7.1

5

1.0

0

1.0

1

1.0

0

0.4

1

7.9

7

7.9

6

7.7

7

7.7

5

7.5

7

7.5

5

7.3

4

7.1

5

12.2

9

1.0

4

1.0

8

1.0

0

Figure 3.6. a) 1H NMR of RuH(N2)(LH)(PPh3)2 and b) 1H NMR of reaction of 5 with C6D6. Both samples in C6D6.

a) b)

ortho-H of PPh3

(LH) (LH) (LH)

37

From the IR spectrum there is evidence of N2 being bound to the Ru center in compound

5a with a ν(Ru-N2) of 2088 cm-1

(s). It is our speculation that this species is the starting

material with a Ru-D bond as a result of C-D activation of C6D6 and subsequent ortho-

deuteriation of triphenylphosphine as seen from Figure 3.6 b. Peaks at 7.33 ppm and -

12.47 ppm in the 2H NMR spectrum of 5a in C6H6 using CDCl3 as the internal reference

(6.15 ppm in benzene) were assigned to ortho-D of PPh3 and Ru-D respectively. H/D

exchange in Ru(II) compounds has been observed in literature.47,48

[Ru(IMes)(PCy3)(η2-

H2)2H2] where IMes= 1,3-dimesity-1,3-dihydro-2H-imidazol-2-ylidene and Cy =

cyclohexyl, has been reported to catalyze the H/D exchange between C6D6 and other

aromatic compounds.48

Heating 5a up to 60oC in C6H6 reverses the process, as shown in

Scheme 3.10.

Scheme 3.10. Reversible H/D exchange.

Compound 5a also converts to compound 6 when heated to 60oC under H2 gas in C6D6.

During the course of the reaction there is evidence of HD gas in the 1H NMR spectrum

giving further evidence of a Ru-D bond being present.

38

3.8 Reaction of 5 and 6 with MeOH

Dissolving either 5 or 6 in dry MeOH and heating to 60oC for 6 h leads to a new

species in solution as shown in Scheme 3.11.

Scheme 3.11. Reaction of 5 with MeOH and reaction of 6 with MeOH to form 8

When 5 is used as the starting material, the reaction may be explained by the protonation

of the 9 position by methanol, loss of the N2 ligand and coordination of the OMe- group

to the Ru(II) center. Using 6 as the starting material, compound 8 can be isolated in 79 %

yield as a green precipitate. There is only one peak in the 31

P NMR spectrum at 49.71

ppm. The 1H NMR spectrum shows an unsymmetrical structure with 7 peaks for LH and

one singlet at 2.77 ppm assigned to the protons of Ru-OCH3 upfield from free methanol

at 3.07 ppm in C6D6. The Ru-H resonates at -11.57 ppm with a 2JP-H = 18 Hz.

3.9 Reaction of 5 with CH4

The reaction of 5 with methane was investigated to see if any methane activation

could be achieved. The methane used was first passed through a LiAlH4 column to dry

the gas before introducing into the J. Young with a C6D6 solution of 5. The solution was

heated to 60oC for 5.5 h. In the

1H NMR spectrum there was evidence of a small amount

of CH3D resonating at 0.14 ppm with a 2JH-D = 1.6 Hz. This reaction did not lead to a

clean conversion to one species in solution. One possible product of the reaction could

have a Ru-CH3 group and the 9 position of L protonated as a result of methane activation,

39

however, the CH3 group could also end up on the 9 position with the formation of a new

Ru-hydride. Further studies of this reaction need to be done to identify the product of the

reaction.

3.10 Transfer hydrogenation of acetophenone

We investigated the catalytic activity of both RuCl2(LH)(PPh3)2 and RuH2(LH)(PPh3)2 in

the hydrogenation of acetophenone. The reactions were done in isopropanol at reflux

conditions under argon with a 100:20:1 ratio of substrate to potassium-t-butoxide to

catalyst as shown in Scheme 3.12:

Scheme 3.12 Transfer hydrogenation of acetophenone with 1 and 5

The hydrogenation of acetophenone went to 85 % conversion to product in 3.5 hours

when RuCl2(LH)(PPh3)2 was used, with no further conversion taking place. This was

most likely due to the air sensitivity of the catalyst.44

When RuH2(LH)(PPh3)2 was used,

the reaction went to completion in 4.5 hours under the same reaction conditions. These

two catalysts are not very significant in comparison to some of the Noyori type catalysts,

some of which have been found to catalyze the same reaction in Scheme 3.12 leading to

100 % conversion in 45 min in a water/sodium formate mixture under air and only

requiring 40oC.

50

40

3.11 Synthesis of bis(4,5-diazafluoren-9-yl) methane

The first step in functionalizing LH was to deprotonate at the 9-position and then

add an appropriate electrophile. Bis(4,5-diazafluoren-9-yl) methane was synthesized as

shown in Scheme 3.13.

Scheme 3.13. Synthesis of 11

The synthesis of LH is well established in literature which involves an oxidative ring

contraction of 1,10-phenanthroline to form 9 and subsequent reduction of the carbonyl

group to form 10.42-43

Once LH was synthesized it was dissolved in dry THF under N2

atmosphere and upon the addition of NaH (60 wt% dispersion in mineral oil) the solution

immediately turned dark pink. At this stage a lot of effervescence was observed due to

the production of H2 gas. After half an hour of stirring, the solution was attached to a

condenser under argon and half an equivalent of CH2Br2 was added. The solution was

refluxed for 4 days at which point the product was purified by column chromatography

(3:1 ratio of ethyl acetate to MeOH on silica gel) with a 40 % yield. The 1H NMR

spectrum of the purified product showed the protons of the carbon linking the two LH

41

units as two triplets one at 4.28 ppm and the other at 2.32 ppm which both integrated to 1

H. There were three peaks present in the aromatic region which all integrated to 4 H:

8.77, 7.82 and 7.29 ppm assigned to ortho-H, para-H and meta-H of LH respectively.

The structure of 11 was confirmed by X-ray crystallography as shown in figure 3. 7:

Figure 3.7 Molecular structure of compound 11 with thermal ellipsoids plotted at 50% probability.

This complex was found to be insoluble in many common solvents such as C6H6, diethyl

ether and was only sparingly soluble in THF. No bimetallic complexes have been

isolated with this ligand, although attempts have been made with ZrCl4 and RuCl2(PPh3)2.

42

CHAPTER IV

CONCLUSION AND FUTURE OUTLOOK

The coordination chemistry of 4,5-diazafluorene (LH) is an undeveloped area.

We have isolated many new Ru(II)(LH) complexes, some of which have shown

fascinating reactivity. RuCl2(LH)(PPh3)2 (1) was found to undergo a facile C-H bond

oxidation of the coordinated LH ligand by air. At this stage it is unclear as to how the

oxidation of the sp3 carbon of LH is taking place. One future direction would be to

explore the mechanism of this reaction.

Although complex 1 was able to undergo oxidation of the sp3 carbon of the

central ring of LH by air, we could not make the oxidation of LH to 4,5-diazafluorne-9-

one catalytic. The synthesis of RuCl2(LH)(dppb) (3) was established, however it was

found to be air stable and not undergo the same type of reactivity as complex 1.

We have also achieved the reversible heterolytic long-range splitting of H2 in

RuH(N2)(L)(PPh3)2 (5). Complex 5 can also activate C-D bonds in C6D6. This complex

was also shown to activate CH4 to a certain extent and future studies need to be done to

verify the products of the reaction.

Preliminary kinetics studies to monitor the reaction of complex 5 with H2 were

done. However, it would be desirable to obtain the rate law for this reaction in order to

better understand how this reaction is taking place.

The idea of using the deprotonated version of LH to form bimetallic complexes is

also an undeveloped area which has the potential of isolating novel bimetallic complexes

that may be capable of small molecule activation.

43

The synthesis of bis(4,5-diazafluoren-9-yl) methane was achieved, however no

bimetallic complexes of this ligand were isolated. As a future direction, increasing the

solubility of the ligands in common organic solvents would be desirable.

44

REFERENCES:

1. Kubas, G.J. Chem. Rev. 2007, 107, 4152-4205.

2. Abdur-Rashid, K.; Clapham, S.E.; Hadzovic, A.; Harvey, J. N.; Lough, A. J.;

Morris, R. H. J. Am. Chem. Soc. 2002, 124, 15104-15118.

3. Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev. 2004, 248, 2201-

2237.

4. Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Fröhlich, R.; Erker, G. Angew.

Chem. Int. Ed. 2008, 47, 7543-7546.

5. Chase, P. A.; Welch, G.C.; Jurca, T.; Stephan, D.W. Angew. Chem. In. Ed. 2007,

46, 8050-8053.

6. Stephan, D. W. Org. Biomol. Chem. 2008, 6, 1535-1539.

7. Chase, P. A.; Gille, A.L.; Gilbert, T. M.; Stephan, D.W. Dalton Trans. 2009, 35,

7179-7188.

8. Kubas, G. J. J. Organomet. Chem. 2001, 635, 37-68.

9. Bautista, M.T.; Cappellani, E. P.; Drouin, S. D.; Morris, R. H.; Schweitzer, C. T.;

Sella, A.; Zubkowski, J. J. Am. Chem. Soc. 1991, 113, 4876-4887.

10. Matthews, S.L.; Pons, V.; Heinekey, D. M. J. Am. Chem. Soc. 2005, 127, 850-

851.

11. Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman, H. J. J.

Am. Chem. Soc. 1984, 106, 451-452.

12. Wasserman, H. J.; Kubas, G. J.; Ryan, R. R. J. Am. Chem. Soc. 1986, 108, 2294-

2301.

45

13. Kubas, G. J.; Ryan, R. R.; Unkefer, C. L. J. Am. Chem. Soc. 1987, 109, 8113-

8115.

14. Morris, R. H. Coord. Chem. Rev. 2008, 252, 2381-2394.

15. Kubas, G. J. Adv. Inorg. Chem. 2004, 56, 127.

16. Rautenstrauch, V.; Hoang-Cong, X.; Churlaud, R.; Abdur-Rashid, K.; Morris, R.

H. Chem. Eur. J. 2003, 9, 4954-4967.

17. Kubas, G. J.; Burns, C. J.; Eckert, J.; Johnson, S. W.; Larson, A. C.; Vergamini,

P. J.; Unkefer, C. J.; Khalsa, G. R. K.; Jackson, S. A.; Eisenstein, O. J. Am. Chem.

Soc., 1993, 115, 569-581.

18. Abbel, R.; Abdur-Rashid, K.; Faatz, M.; Hadzovic, A.; Lough, A. J.; Morris, R.

H. J. Am. Chem. Soc. 2005, 127, 1870-1882.

19. Ikariya, T.; Murata, K.; Noyori, R. Org. Biomol. Chem. 2006, 4, 393-406.

20. Kubas, G. J.; Ryan, R. R.; Wrobleski, D. A. J. Am. Chem. Soc. 1986, 108, 1339-

1341.

21. Sato, M.; Tatsumi, T.; Kodama, T.; Hidai, M.; Uchida, T.; Uchida, Y. J. Am.

Chem. Soc. 1978, 100, 4447-4452.

22. Ehlers, A. W.; Dapprich, S.; Vyboishchikov, S. F.; Frenking, G.

Organometallics 1996, 15, 105-117.

23. Ienco, A.; Calhorda, M. J.; Rienhold, J.; Reineri, F.; Bianchini, C.; Peruzzini,

M.; Vizza, F.; Mealli, C. J. Am. Chem. Soc. 2004, 126, 11954

24. Pascal, M.; Büttner, T.; Breher, F.; Le Floch, P.; Grützmacher, H. Angew. Chem.

Int. Ed. 2005, 44, 6318-6323.

46

25. Nagaraja, C. M.; Parameswaran, P.; Jemmis, E. D.; Jagirdar, B. R. J. Am. Chem.

Soc. 2007, 129, 5587-5596.

26. Lee, D.-H.; Patel, B.; Clot, E.; Eisenstein, O.; Crabtree, R. H. Chem. Commun.,

1999, 297-298.

27. Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2006,

128, 15390-15391.

28. Phillips, A. D.; Laurenczy, G.; Scopelliti, R.; Dyson, P. J. Organometallics 2007,

26, 1120-1122.

29. Ullrich, M.; Lough, A. J.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 52-53.

30. Nordlund, P.; Eklund, H. Curr. Opin. Struct. Biol. 1995, 5, 758-766.

31. Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. Rev. 1996, 96, 2239-2314.

32. Roth, A.; Buchholz, A.; Rudolph, M.; Schutze, E.; Kothe, E.; Plass, W. Chem.

Eur. J. 2008, 14, 1571-1583.

33. Gavrilova, A. L.; Bosnich, B. Chem, Rev. 2004, 104, 349-383.

34. Rosenthal, J.; Nocera, D. G. Acc. Chem. Res. 2007, 40, 543-553.

35. Cowie, M. Can. J. Chem. 2005, 83, 1043-1055.

36. Kloc, K.; Mlochowski, J.; Szule, Z. Heterocycles 1978, 9, 849-

37. Jiang, H.; Song, D. Organometallics 2008, 27, 3587-3592.

38. Henderson, L. J.; Fronczek, F. R.; Cherry, W. R. J. Am. Chem. Soc. 1984, 106,

5876-5879.

39. Strekas,T. C.; Gafney, H. D.; Tysoe, S. A.; Thummel, R. P.; Lefoulon, F.

Inorg.Chem. 1989, 28, 2964-2967.

40. Sharma, S. K.; Srivastava, V. K.; Jasra, R. V. J. Mol. Catal. A: Chem. 2006, 245,

47

200-209.

41. Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inogr. Chem. 1984,

23, 726-729.

42. Plater, M.J.; Kemp, S.; Lattmann, E. J. Chem. Soc., Perkin Trans. 2000, 1, 971-

979.

43. Thummel, R.P.; Lefoulon, F.; Mahadevan, R. J. Org. Chem. 1985, 50, 3824-3828.

44. Jiang, H.; Stepowska, E.; Song, D. Dalton Trans. 2008, 5879-5881.

45. Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2000, 19, 2655-

2657.

46. MacKay, B. A.; Fryzuk, M. D. Chem. Rev. 2004, 104, 385-401.

47. Bennett, M. A.; Clark, A. M.; Contel, M.; Rickard, C. E. F.; Roper, W. R.;

Wright, L. J. J. Organomet. Chem. 2000, 601, 299-304.

48. Prechtl, M. H. G.; Hölscher, M.; Ben-David, Y.; Theyssen, N.; Loschen, R.

Milstein, D.; Leitner, W. Angew. Chem. Int. Ed. 2007, 46, 2269-2272.

49. Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105, 2329-2363.

50. Cortez, N. A.; Aguirre, G.; Parra-Hake, M.; Somanathan, R. Tetrahedron:

Asymmetry 2008, 19, 1304-1309.

51. Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307-326.

52. Sheldrick, G. M. SHELXTL/PC, Version 6.1 Windows NT Version; Bruker AXS

Inc.: Madison, WI, 2001.

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