I. Novel, One-Pot Reactions towards Molecular Alkaline Earth Species

Yuriko Takahashi

Ruhlandt Group

Syracuse University

II. Exploring Weak Interactions as Structure Determining Factors in MOCVD volatility

1

Education and Research Experience

Dept. of Engineering, Applied Chemistry, Saitam University, Japan (April 2005 - March 2007 )

B.A. Chemistry, Augustana College, SD (May 2009)

Summer Research Program at Lehigh University, PA (2008 Summer)

Summer Research Program at Syracuse University, NY (2009 Summer)

Ph.D. Candidate, Syracuse University, NY (2009 - )

I. Exploration of a benign, efficient synthetic route for alkaline earth metal compounds

II. Evaluation of influence of weak interactions on thermal properties of target compounds

2

What is involved?

Inert gas synthetic techniques

NMR (mechanistic) studies

Structural studies, crystallography

Thermogravimetric analysis (TGA)

Ligand synthesis

3

Inert Gas Synthetic Techniques

◆ All reactions are carried out under inert gas condition

◆ Solvents – dried, and degassed prior to use

◆ Starting materials - dried over CaH2 and distilled under vacuum or inert gas prior to use

Dry box Schlenk lineSolvent system

4

What is involved?

Inert gas synthetic techniques

NMR (mechanistic) studies

Structural studies, crystallography

Thermogravimetric analysis (TGA)

Ligand synthesis

5

Highly attractive reagents

Inexpensive

Earth abundant

Mg and Ca are biocompatible

Sr and Ba are found in electronic materials

Attractive substitutes for selected rare-earth metals

H

AcRaFr

LaBaCs

YSrRb

ScCaK

MgNa

BeLi

H

AcRaFr

LaBaCs

YSrRb

ScCaK

Na

BeLi

Mg

Why Alkaline Earth Metals?

6

Applications

Synthetic Chemistry Catalysis

• Hydroamination, Hydrophosphination, Hydrosilylation

Selective deprotonation agents

Polymer Chemistry Polymerization initiators

• Lactides, Caprolactone , Styrene

Material Chemistry Hydrogen storage

Synthetic bone scaffolds

MOCVD (Metal Organic Chemical Vapor Deposition) precursors

The Chemistry of Organolithium Compounds. Wiley: New York, 2004. Elschenbroich, C., Organometallics. Wiley-VCH Verlag GmbH & Co,: KGaA, Weinheim, 2006. Crimmin, M. R.; Casely, I. J.;Hill, M. S., J. Am. Chem. Soc. 2005, 127, 2042 Westerhausen, M., Coord. Chem. Rev. 1998, 176, 157. Yanagisawa, A.; Habaue, S.; Yamamoto, H., J. Am. Chem. Soc. 1991, 113, 8955. Otway, D. J.; Rees, W . S., Jr., Coord. Chem. Rev. 2000, 210, 279. Harder, S.; Feil, F.; Weeber, A., Organometallics 2001, 20, 1044.

7

H

AcRaFr

LaBaCs

YSrRb

ScCaK

MgNa

BeLi

H

AcRaFr

LaBaCs

YSrRb

ScCaK

Na

BeLi

Mg

Ba

Mg

Sr

Ca

size

Ionic Radii (Å)

0.72

1.00

1.18

1.35

CN = 4

CN = 6

CN = 6

CN = 6

High oxo- and hydrophilicity

Tendency towards aggregation and subsequently poor volatility

Challenges

Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.

I. Novel, one-pot reactions towards molecular alkaline earth species

Safe

Inexpensive

Simple

Available starting materials

Minimize environmental impact

Classic Synthetic Routes

9

Direct metallation via

anhydrous NH3(l) activation

Ae[N(SiMe3)2]2(thf)2 + 2 HL

2 KL + AeI2 Ae + 2 HL

NH3(l)

Ae = Ca, Sr, BaHL = Protonated ligand

Salt Elimination

Transamination

Ae(L)2

•Limited surface area of metal slows reaction•Work with condensed NH3

•Poor for bulky HL•Require highly acidic HL

•Prior synthesis of Ae[N(SiMe3)2]2(thf)2

•Highest quality AeI2

•Preparation of KL

Gillett-Kunnath, M. M. Doctoral Dissertation, Syracuse University, 2007

Redox Transmetallation/

10

pKa (Benzene) = 43 (in DMSO)

Ae + HgPh2 {AePh2(thf)n} + Hg

{AePh2(thf)n} + 2 HL AeL2(thf)n + 2 C6H6

Ae = Ca, Sr, Ba

THF

THF

Redox transmetallation

Ligand exchange

Torvisco, A., et al. Coord. Chem. Rev., 2011, 255, 1268. Hitzbleck, J., et al. Chem. Eur. J. 2004, 10, 3315. Deacon, G. B., et al. Dalton Trans, 2009, 4878. Deacon, G. B., et al. Organometallics, 2008, 27, 4772. Deacon, G. B., et al. Dalton Trans, 2011, 40, 1601. Hauber, S-O., et al. Angew. Chem. Int. Ed., 2005, 44, 5871. Cole, M.L., et al. Dalton Trans, 2006, 3360. Deacon, G. B., et al. N J Chem, 2010, 34, 1731.

Ligand Exchange (RTLE)

Toxicity of mercurial limits the use of this route

L = cyclopentadienide, pyrazolate, formamidinate, aryloxide

HgPh2

LD50 = 50-400 mg kg-1

oral, rat

11

HgPh2 BiPh3

LD50 = 50-400 mg kg-1 LD50 = 180 g kg-1

oral, rat oral, dog

Environmental Friendly

Hg2+/Hg Bi3+/Bi

E0(V) 0.852 0.30

Eo (V)M2+

(aq) + 2e- → M(s))

Ca2+ -2.87

Sr2+ -2.89

Ba2+ -2.90

An alternative to HgPh2

Attractive alternative synthetic route

Redox Transmetallation/

12Gillett-Kunnath, M. M.; MacLellan, J. G.; Forsyth, C. M.; Andrews, P. C.; Deacon, G. B.; Ruhlandt-Senge, K. Chem. Commun. 2008, 37, 4490.

Ligand Exchange (RTLE) using BiPh3

3 Ae(xs) + 2 BiPh3 + 6 HL 3 Ae(L)2(thf)n + 2 Bi + 6 C6H6

THF

Sonication

Advantages of RTLE utilizing BiPh3

Commercially available starting materials

One-pot; time and cost effective

Environmentally benign

Easy work-up

Good product yields

BiPh3

LD50 = 180 g kg-1

oral, dog

Ae = Ca, Sr, Ba

N NH

H

13

Objectives

SiMe3

NH

SiMe3

NH SiMe3

OH

Explore mechanism of RTLE reaction utilizing BiPh3

Demonstrate feasibility of RTLE utilizing BiPh3 for the synthesis of alkaline earth metal organometallics

Investigate/examine influence of ligands acidity (pKa) on the reaction rate

Experimental Procedure

14

NMR tube sealed with a J-Young tap •Ba metal filings (0.50 mmol, excess)• BiPh3 (0.15 mmol)• HL (0.45 mmol)• Cyclohexane (internal standard)• D8-THF (0.6 mL) anhydrous

•All reactions carried out under inert gas conditions •Sonication, T = 60 oC

•Monitored by 1H-NMR spectroscopy

Example of NMR data

15

0 h

2 h

10 h

BiPh3

C6H6

Cyclohexane(internal standard)

SiMe3

NH

SiMe3

SiMe3

N

SiMe3

HMDS

3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6

THF

Sonication

0

20

40

60

80

100

0 5 10 15

Co

nce

ntr

atio

n (

%)

Time (h)

Free ligand

Deprotonated ligand

BiPh3

Mechanistic Considerations

16

3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6

THF, N2

Sonication

SiMe3

NH

SiMe3

Kinetic Investigation

17

Heterogeneous nature of the reactions

Active area of the metal surface is unknown and is continuously changing

We get kinetic data from indirect measurements of the chemical composition of the bulk solution

Kinetic results are certainly sufficient for surveying average trends

Rogers, H. R., et al. J. Am. Chem. Soc. 1980, 102, 217. Olson, I. A., et al. J. Phys. Chem. A 2011, 115, 11001.

0

20

40

60

80

100

0 5 10 15

Co

nce

ntr

atio

n (

%)

Time (h)

Free ligand

Deprotonated ligand

BiPh3

Mechanistic Considerations

18

20% of BiPh3

left over

3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6

THF, N2

Sonication

50 % of product: t50%conv = ca. 5h

SiMe3

NH

SiMe3

Direct Metallation

19

3 Ba(xs) + 6 HN(SiMe3)2

THF, N2

Sonication

0

20

40

60

80

100

0 5 10 15 20 25 30

Co

nce

ntr

atio

n (

%)

Time (days)

Free ligand

Deprotonated ligand

Direct metallation and RTLE based BiPh3 occur simultaneously

Direct metallation was not complete

Rate for RTLE (t50%conv = 5h ) is much faster than that for direct metallation

SiMe3

NH

SiMe3

ca. 26 days

After t50%conv

product decomposition

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400 450 500

Co

nce

ntr

atio

n (

%)

Time (h)

DM

RTLE vs. Direct Metallation – HCp*

20

ca. 21 days

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400 450 500

Co

nce

ntr

atio

n (

%)

Time (h)

RTLE + DM

DM

RTLE vs. Direct Metallation – HCp*

21

ca. 22 h

ca. 21 days

RTLE vs. Direct Metallation – Ph2pzH

22

0

20

40

60

80

100

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25

Co

nce

ntr

atio

n (

%)

Time (h)

RTLE + DM

DM

N NH

H

1 h

2.5 h

Reactions between Ba metal and the pyrazole ligand are not enhanced by the BiPh3.

RTLE vs. Direct Metallation

23

pKa 5.60 ± 0.38[1] 11[2] 13.03[3] 14[4] 22.6[4] 26.1[4]

t50 % conv. 3.5 h 4 h 2.5 h 5 h 6 h 22 h

DM

t50 % conv. 25 h 4 h 1 h26

days19 days

21 days

SiMe3

NH

SiMe3

NH SiMe3

N NH

H

OH

DM

RTLE

[1]Estimated pKa values of silylamides was calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (© 1994-2012 ACD/Labs). [2]Sinha, A., et al. Organometallics, 2006, 25, 1412. [3]Aggarwal, V. K., et al. J. Org. Chem., 2003, 68, 5381. [4]Bordwell, F.A.; Bausch, M.J. Am. Chem. Soc. 1983, 105, 6188.

RTLE vs. Direct Metallation -Pyrazoles

24

[Sr(Me2pz)2(Me2pzH)4][Ca(Me2pz)2(Me2pzH)4]

Hitzbleck, J.; O'Brien, A.Y.; Forsyth, C.M.; Deacon, G.B.; Ruhlandt-Senge, K. Chem., Eur. J. 2004, 10, 3315.

Form stable complexes through hydrogen bonding

Conclusions

25

RTLE utilizing environmentally benign BiPh3 provides an excellent alternative for synthesis of organoalkaline earth complexes

Replaces organomercury

One-pot, convenient

Variety of ligands

Dramatically improves reaction rates over direct metallation

II. Exploring Weak Interactions as Structure Determining Factors in MOCVD Volatility

MOCVD process deposits thin films on a substrate Semiconductor

High temperature super conductors

Computer memory

27

H

AcRaFr

LaBaCs

YSrRb

ScCaK

MgNa

BeLi

H

AcRaFr

LaBaCs

YSrRb

ScCaK

Na

BeLi

Mg

Ba

Mg

Sr

Ca

size

Ionic Radii (Å)

0.72

1.00

1.18

1.35

CN = 4

CN = 6

CN = 6

CN = 6

High oxo- and hydrophilicity

Tendency towards aggregation and subsequently poor volatility

Challenges

Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.

28

Coordinative Saturation

Ligand bulk

Neutral co-ligands

Non-covalent interactions (secondary interactions)

Metal∙∙∙π (arene)

Agostic (M∙∙∙H－C)

Metal∙∙∙F

providing a major factor in the reactivity and physical properties of the alkaline earth organometallics

29

Metal∙∙∙F Metal∙∙∙π Agostic H-Bond

Free energies of rotation (kcal/mol)

18.7 - 19.1 19.0 13.6 - 14.6 15.0 – 40.0

Metal-ligand bonding Secondary interactions

Transition metals Strong Much smaller role

Alkaline earth metals Weak Significant role

Importance of Secondary Interactions

As alkaline earth metal compounds frequently displayweak, highly polar metal-ligand bonding, secondary interactions are an important means to provide steric saturation to the metal center

Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Ruhlandt-Senge, K. in prep.Szatylowicz, H. J. Phys. Org. Chem. 2008, 21, 897-914. Gillett-Kunnath, M.; Teng, W.; Vargas, W.; Ruhlandt-Senge, K., Inorg. Chem. 2005, 44, 4862.

30

Weak interaction of a coordinately unsaturated metal with a C—H bond

Ca[N(SiMe3)(Mes)]2(thf)2

CN = 4 + 1

Ba2(Odpp)4

Deacon, G. B., et al. Chem. Eur. J. 2009, 15, 5503. Gillett-Kunnath, M. et al., Inorg. Chem., 2005, 44, 4862

Secondary Interactions

Agostic (M∙∙∙H—C) Metal―π (arene)

Ba2: CN = 4 +4Ba1: CN = 3 + 9

31

Secondary Interactions

Metal∙∙∙F

KBa(PFTB)3(thf)4

C CF3F3C

OH

CF3

Perfluoro-t-butanolH(PFTB)

Stabilized via M-F interaction

Excellent thermal properties

Previous work with

Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55.

Ba1

C CF3F3C

OH

32

C CF3F3C

OH

CF3

1,1,1,3,3,3-Hexafluoro-2-phenyl-2-propanol

Detailed analysis of strategies to achieve steric saturation

Studies of its effect on:

Coordination pattern

Thermal properties

Possible interactions

Metal∙∙∙F Metal∙∙∙F, Metal―π, M∙∙∙H—C

H(PFTB) H(HFPP)

Evaluation of Secondary Interactions

Direct metallation via ammonia activation

Moderate to good yields with high purity

33

C CF3F3C

OH

Ae + 2THF

-78 oC, NH3 (l)

Monometallic Complexes -Synthesis

Ae = Ca, Sr, Ba

[Ae(HFPP)2(thf)4] + H2

Partial loss of THF co-ligands induced dimerization and extensive M∙∙∙F interactions to achieve coordinative saturation

34

Crystallization from THF Crystallization from toluene

CN = 6 Sr1: CN = 6 Sr2: CN = 4 + 6

Monometallic Complexes -Structures

[Sr(HFPP)2(thf)4] [Sr2(HFPP)4(thf)3]

35

Heterobimetallic Complexes -Synthesis

KH + H(HFPP) [K(HFPP)(thf)]4THF

[BaK(HFPP)3(thf)]24 [Ba(HFPP)2(thf)4] + [K(HFPP)(thf)]4THF

Combination of the two solutions of homometallic complex leads to heterobimetallic formation

36

Heterobimetallic Complexes -Structure

Ba1

36

C CF3F3C

OH

CF3

C CF3F3C

OH

KBa(HFPP)3(thf)4 KBa(PFTB)3(thf)4

1 Ba∙∙∙F 3 K∙∙∙F 0 Ba∙∙∙F 6 K∙∙∙FBuchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55.

37

Magnitude of metal∙∙∙F interactions may potentially effect volatility of alkaline earth metal compounds

Comparison of Thermal Properties by TGA

C CF3F3C

OH

CF3

C CF3F3C

OH

1 Ba∙∙∙F3 K∙∙∙F

6 K∙∙∙F

PFTB HFPP

38

Conclusion/Future work

Secondary non-covalent interactions are an important stabilizing factors

Metal∙∙∙F

Agostic

→ Isolated heterobimetallic alkaline earth metal HFPP complexes

Secondary non-covalent interactions are likely to be a key factor in volatility

Synthesis of another alkali/alkaline earth metal combination complexes is in process for direct comparison of structural features and thermal properties of two groups of compounds based on HFTB and HFPP

Extend the work to divalent lanthanide metals

Dr. Karin Ruhlandt

Dr. Glen B. Deacon

Dr. Anna O’Brien

Dr. Miriam M. Gillett-Kunnath

Dr. Ana Torvisco

Melanie Wolf

Ruhlandt Group Members

Syracuse University Department of Chemistry

NSF

Acknowledgements

39