Novel derivatives of ansa-titanocenes procured from 6-phenylfulvene: a combined experimental and...

Inorganica Chimica Acta 357 (2004) 225–234

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Novel derivatives of ansa-titanocenes procured from6-phenylfulvene: a combined experimental and theoretical study

Shona Fox a, John P. Dunne a,1, Matthias Tacke a,*, John F. Gallagher b

a Chemistry Department, Centre for Synthesis and Chemical Biology (CSCB),

Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Irelandb School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

Received 25 July 2003; accepted 2 August 2003

Abstract

The previously prepared trans-[(1,2-diphenyl-1,2-dicyclopentadienyl)ethanediyl] titanium(IV) dichloride, [1,2-(Ph)2C2H2{g5-

C5H4}2]Ti(Cl)2, was synthesised using an alternative procedure, from which its crystal structure was determined. Using this

compound, a variety of other ansa-titanocene derivatives were synthesised by replacement of the chloride ligands with selected

substituents. Thus RTi(X)(Y) systems where R ¼ 1; 2-(Ph)2C2H2g5-C5H42; X¼Y¼CH3; X¼CH3, Y¼Cl; X¼Y¼NCS;

X¼Y¼NCO; X¼Y¼OPh and (X/Y)¼O have been synthesised and characterised. DFT calculations were performed on the

complexes trans-[(1,2-diphenyl-1,2-dicyclopentadienyl)-ethanediyl] titanium(IV) dichloride, bis-(6,6-diphenylfulvene)titanium and

bis-(6,6-diphenylfulvene)iron. This demonstrated the role that the metal centre plays in their formation, generating either an

ansa-metallocene, a �tucked in� fulvene complex or a metallocene coordinating fulvene anions.

� 2003 Elsevier B.V. All rights reserved.

Keywords: Titanium; ansa-Metallocenes; X-ray crystal structure; Density functional theory

1. Introduction

Since their discovery, ansa-metallocenes have played

an increasingly important role in organometallic chem-

istry, as it soon became evident that the presence of the

bridging moiety introduces interesting modificationsinto the properties of the molecules [2,3]. An example of

such a change can be seen in the tetramethylethylene

chromocene carbonyl complex. In this case the cyclo-

pentadienyl rings are tethered by a two-carbon bridge,

which produces a stable complex, unlike its unbridged

counterpart [4]. This rationale has also been applied to

the titanocene derivatives (Cp2TiX2) to improve upon

existing and develop (these include their potential to actas anti-cancer drugs) new applications. But by far the

* Corresponding author. Tel.: +35317168428; fax: +35317162127.

E-mail address: [email protected] (M. Tacke).1 Present address: Department of Chemistry, University of York,

Heslington, York YO10 5DD, UK.

0020-1693/$ - see front matter � 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0020-1693(03)00496-1

most important application is their utilisation as cata-

lysts in olefin polymerisations [5]. The placement of a

bridging moiety on the sandwich structure, thereby

generating ansa-titanocenes, enhances the activity of the

catalyst and can also change the chemical and physical

properties of the polymer [6,7]. The widespread successof this application has centred on the ansa-titanocenes

ability to promote stereospecific polymerisation [8] when

activated by a co-catalyst, e.g. MAO (methylaluminox-

ane) [9].

Numerous methods exist to bring about the reductive

dimerisation of fulvenes, which are versatile precursors

for the synthesis of ansa-metallocenes. This can be

achieved through the use of metal vapour synthesis

mail to: [email protected]

226 S. Fox et al. / Inorganica Chimica Acta 357 (2004) 225–234

techniques [10,11] or more conventionally by solution

methods such as; activated metal powders [12–14], low

valent transition metal complexes [15] and one-electron

reducing agents [4].

For the purposes of this study, we were interested in

preparing ansa-titanocene derivatives with a two-carbon

bridging unit, which distorts the cyclopentadienyl rings

out of the normal arrangement they adopt in the un-bridged analogue. The synthesis involved the reductive

dimerisation of our ligand of choice, 6-phenylfulvene

[16], with activated calcium producing an intermediate

compound, [1,2-(Ph)2C2H2{g5-C5H4}2]Ca(THF)2 (1)

[17] on which a transmetallation with 3TiCl3 �AlCl3yielded the desired complex, 2. This compound was then

used as the point of origin for the synthesis and spec-

troscopic characterisation of a variety of derivatives.Our choice of 6-phenylfulvene in these procedures was a

result of a theoretical study carried out on a series of

fulvenes using DFT methods [16]. This ascertained the

effect of varying the fulvene exocyclic substituents, on

the radical anion generated as an intermediate in these

reactions. This was further expanded here to include a

comparative study of the titanocene structures, 2 and 3,

prepared from two different fulvenes. A third calculationwas then carried out using complex 4 and this was to

study the effect of varying the metal atom on the

metallocene structure.

2. Experimental

2.1. Synthetic work – general

The preparation of 6-phenylfulvene [18] and 1 [17]

were carried out according to the literature procedures.

Solvents were purified and degassed by three-freezepump thaw cycle prior to use. Benzene-d6 was dried over

sodium and collected by vacuum transfer. Air- and

moisture-sensitive compounds were stored and handled

in an argon glove box and manipulations of these

substances were carried out using standard Schlenk

techniques.

NMR spectra were recorded on a VARIAN 300

MHz spectrometer and a JEOL GX 270 MHz spec-trometer. Chemical shifts (d) are reported in ppm and

are referenced to TMS. The mass spectra were measured

on a Finnigan MAT Incos 50 B mass spectrometer in EI

mode. X-ray data were collected on a Bruker P4

diffractometer.

2.2. Computational details

DFT calculations were performed using the GAUSS-GAUSS-

IANIAN 98 [19] programme implemented on an Origin 200

eight-processor cluster (SGI 180 MHz CPU/2 GB

RAM). These were carried out at the B3LYP level, using

the 6-31G** basis set for all atoms. A correction value,

namely the zero-point energy (ZPE), must be added on

to these values to give the overall energies (E0) of the

molecules.

2.3. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(Cl)2 (2)

3TiCl3 �AlCl3 (0.65 g, 3.25 mmol) was added under

argon to a freshly prepared solution of ansa-calcocene

[17] (1.13 g, 3.25 mmol) in dry THF, which was cooled

to )50 �C. This was allowed to slowly warm to room

temperature and was stirred for ca. 10 h. The solutionwas filtered and the filtrate was cooled to )40 �C, whilemaintaining stirring. To this cooled solution, 6 M HCl

(4 ml) was added dropwise and stirring was continued

for an hour, during which it was gradually allowed to

warm to room temperature. Dichloromethane (50 ml)

was added and the solution was dried over MgSO4. This

was removed by filtration and the deep red solution was

held at )30 �C to afford 0.902 g of a red crystallineproduct (yield of 65%). 1H NMR (CDCl3, d): 4.83 (s,

2H, 2x PhCHCp), 6.17, 6.35, 6.86 (m, 6H, C5H4), 7.17–

7.26 (m, 2H, C5H4, 10H, C6H5).13C NMR (CDCl3, d):

54.1 (PhCHCp), 109.9, 117.2, 127.5, 133.9, 137.3

(C5H4), 126.5, 127.6, 128.8, 140.1 (C6H5). Principle IR

absorptions (KBr cm�1): 3076 (m), 3030 (m), 2925 (m),

2853 (m), 1586 (m), 1492 (m), 1454 (m), 1384 (m), 1261

(w), 1106 (s), 1042 (w), 823 (s), 736 (s), 698 (s). MS (EI):m/z 428 (C24H

4820 Ti37Cl35Cl, 9.5%), 426 (Mþ, 13.6%),

391 (Mþ–Cl, 5.2%), 355 (Mþ–2Cl, 1.0%), 272 (Mþ–fulv,100%), 237 (Mþ–fulv, –Cl, 16.9%), 200 (Mþ–fulv, –2Cl,36.9%), 154.1 (fulv, 26.3%), 153.1 (fulv–Hþ, 84.0%).

UV–Vis (CH2Cl2 nm) kmax 294, 382, 520.

2.4. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(CH3)2(5)

CH3Li dissolved in diethylether (2.93 ml, 4.1 mmol)

was added to a solution of 2 (0.365 g, 0.85 mmol) in dry

toluene (30 ml). This was refluxed for 1 h to give a

musty-yellow solution. The solution was then filtered

and the toluene removed under reduced pressure to give

0.323 g (98% yield) of a bright yellow powder. 1H NMR

(CDCl3, d): 0.25 (s, 6H, 2x 2CH3), 3.64 (s, 2H, 2xPhCHCp), 5.21, 5.32, 6.85 (m, 6H, C5H4), 6.89–7.02 (m,

2H, C5H4, 10H, C6H5).13C NMR (CDCl3, d): 42.6 (2x

CH3), 52.5 (PhCHCp), 105.5, 111.0, 117.1, 121.3, 126.1

S. Fox et al. / Inorganica Chimica Acta 357 (2004) 225–234 227


absorptions (KBr cm�1): 3078 (m), 3062 (m), 3030 (m),

2879 (m), 2793 (w), 1598 (m), 1490 (m), 1425 (m), 1260

(s), 1073 (s), 1042 (s), 819 (s), 749 (m), 719 (s), 694 (s).

MS (EI): m/z 371 (Mþ–Me, 23.8%), 355 (Mþ–2Me,51.4%), 217 (Mþ–fulv, –Me, 1.1%), 200 (Mþ–fulv, –

2Me, 15.1%), 154 (fulv, 10.2%), 153 (fulv–Hþ, 15.3%).

UV–Vis (CH2Cl2 nm) kmax 297, 362, 514.

2.5. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(CH3)Cl

(6)

A solution of 5 (0.323 g, 0.83 mmol) in toluene (30ml) was treated with Me3SiCl (0.14 ml, 1.12 mmol)

followed by H2O (7� 10�3 ml, 0.41 mmol). This was

stirred for 1 h at room temperature to produce an amber

coloured solution. The solvent was removed under re-

duced pressure and the residue was washed with pentane

to afford an amber-red powder (0.321 g, 95% yield). 1H

NMR (CDCl3, d): 0.29 (s, 3H, CH3), 4.23 (s, 2H, 2xPhCHCp), 5.67, 6.69 (m, 6H, C5H4), 6.96–7.03 (m, 2H,C5H4, 10H, C6H5).

13C NMR (CDCl3, d): 44.2 (CH3),

53.6 (PhCHCp), 107.9, 115.2, 124.8, 132.5, 135.2


absorptions (KBr cm�1): 3073 (m), 3028 (w), 2922 (m),

2850 (m), 1641 (m), 1490 (s), 1453 (s), 1383 (w), 1424

(m), 1261 (s), 1094 (s), 1042 (s), 820 (s), 710 (m). MS

(EI): m/z 391 (Mþ–Me, 4.5%), 355 (Mþ–Me, –Cl, 0.8%),

252 (Mþ–fulv, 0.7%), 237 (Mþ–fulv, –Me, 22.7%), 217(Mþ–fulv, –Cl, 1.7%), 200 (Mþ–fulv, –Me, –Cl, 76.2%),

154 (fulv, 29.5%), 153 (fulv–Hþ, 100.0%). UV–Vis

(CH2Cl2 nm) kmax 295, 376, 527.

2.6. Reactions of [1,2-(Ph)2C2H2g5-C5H42]Ti(CH3)Cl

(6)

(a) A solution of 6 (0.3 g, 0.7 mmol) in dry toluene (30ml) was freshly prepared. CH3Li dissolved in dieth-

ylether (1.2 ml, 1.68 mmol) was slowly added and

the solution was refluxed for 30 min to give a

musty-yellow solution. Filtration and removal of

the solvent yielded a bright yellow powder (0.26 g,

96%), which analysis proved to be 5.

(b) To a solution of 6 (0.3 g, 0.7 mmol) in toluene (30

ml) was added Me3SiCl (0.11 ml, 0.95 mmol) fol-lowed by H2O (6� 10�3 ml, 0.34 mmol). This was

stirred at room temperature for 1 h to give a bright

red solution. The work-up is the same as for 6,

which yielded a pale red powder (0.28 g, 97%). Anal-

ysis of this compound revealed it to be 2.

2.7. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(NCS)2(7)

Complex 2 (0.124 g, 0.29 mmol) was dissolved in

THF (50 ml) and to this was added KSCN (0.062 g, 0.64

mmol). The mixture was refluxed for 2 h, filtered while

still hot and the solvent was removed in vacuo. This

gave 0.1311 g of a brick-red powder (96% yield). 1H

NMR (CDCl3, d): 4.96 (s, 2H, 2x PhCHCp), 6.17, 6.44,

6.62, 6.93 (m, 8H, C5H4), 7.17–7.25 (m, 10H, C6H5).13C

NMR (CDCl3, d): 54.5 (PhCHCp), 110.9, 117.2, 122.5,

129.4, 138.2 (C5H4), 127.6, 127.9, 128.9, 139.7 (C6H5),

122.3 (NCS). Principle IR absorptions (KBr cm�1) 3076

(w), 3028 (w), 2963 (m), 2059 (vs), 2009 (vs), 1637 (s),

1618 (s), 1490 (m), 1452 (m), 1261 (s), 1082 (s), 1042 (s),

823 (s), 801 (s), 711 (m), 694 (m). MS (EI): m/z 472 (Mþ,28.9%), 414 (Mþ–NCS, 41.2%), 355 (Mþ–(NCS)2,

6.2%), 318 (Mþ–fulv, 74.8%), 260 (Mþ–fulv, –NCS,42.8%), 200 (Mþ–fulv, –(NCS)2, 37.4%), 164 (Ti(NCS)2,

7%), 154 (fulv, 39.7%), 153 (fulv–Hþ, 100.0%). UV–Vis

(CH2Cl2 nm) kmax 283, 345, 430, 571.

2.8. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(NCO)2(8)

A solution of 2 (0.16 g, 0.38 mmol) in THF (50 ml)was prepared and to it was added freshly ground KOCN

(0.067 g, 0.83 mmol). This was refluxed for 4 h and fil-

tered while hot. Removal of the solvent under reduced

pressure gave a red powder (0.138 g, 84). 1H NMR

(C6D6, d): 4.25 (s, 2H, 2x PhCHCp), 5.38, 5.67, 6.44,

6.70 (m, 8H, C5H4), 6.91–7.10 (m, 10H, C6H5).13C

NMR (C6D6, d): 53.8 (PhCHCp), 109.1, 116.5, 126.1,

133.8, 136.4 (C5H4), 127.3, 127.8, 128.6, 140.6 (C6H5),122.4 (NCO). Principle IR absorptions (KBr cm�1) 3080

(m), 3020 (m), 2920 (w), 2222 (vs), 2204 (vs), 1602 (m),

1489 (s), 1454 (m), 1234 (w), 1086 (s), 1044 (s), 956 (w),

814 (s), 766 (m). MS (EI): m/z 440 (Mþ, 1.4%), 398

(Mþ–NCO, 0.5%), 355 (Mþ–(NCO)2, 0.3%), 286 (Mþ–fulv, 16.9%), 244 (Mþ–fulv, –NCO, 2.5%), 200 (Mþ–fulv, –(NCO)2, 89.6%), 154 (fulv, 27.9%), 153 (fulv–Hþ,100.0%). UV–Vis (CH2Cl2 nm) kmax 297, 378, 511.

2.9. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti(OPh)2(9)

The dropwise addition of LiOPh to a solution of 2

(0.16 g, 0.38 mmol) in toluene (50 ml) was carried out at

)30 �C. (LiOPh was prepared by dissolving PhOH

(0.071 g, 0.75 mmol) in benzene (15 ml) and reacting itwith nBuLi 2.0 M in Pentane (0.375 ml, 0.75 mmol) at

)10 �C). The solution was gradually warmed to room

temperature and was stirred for 18 h. After filtration, the

solvent was removed in vacuo and the beige coloured

powder was washed twice with pentane (2� 20 ml). This

produced a pale yellow powder (0.148 g, 73% yield). 1H

NMR (C6D6, d): 4.55 (s, 2H, 2x PhCHCp), 5.77, 5.91,

6.14, 6.43 (m, 8H, C5H4), 6.90–7.12 (m, 16H, 10x C6H5;6x OC6H5), 7.31–7.38 (m, 4H, 4x OC6H5).

13C NMR

(C6D6, d): 52.9 (PhCHCp), 104.7, 111.8, 118.9, 128.2,

134.1 (C5H4), 125.8, 126.9, 127.3, 140.5 (C6H5), 116.9,


118.1, 128.3, 169.4 (OC6H5). Principle IR absorptions

(KBr cm�1) 2950 (m), 2920 (w), 1586 (m), 1495 (m),

1480 (s), 1233 (w), 1213 (w), 1184 (w), 1095 (s), 1050 (w),

1014 (s), 944 (m), 868 (w), 809 (w). MS (EI): m/z 449

(Mþ–OPh, 2.9%), 388 (Mþ–fulv, 2.1%), 371 (Mþ–OPh,–Ph, 0.5%), 355 (Mþ–2OPh, 0.5%), 310 (Mþ–fulv, –Ph,1.2%), 293 (Mþ–fulv, –OPh, 3.5%), 234 [Ti(OPh)2,

2.7%], 215 (Mþ–fulv, –OPh, –Ph, 4.3%), 200 (Mþ–2OPh, 2.5%), 155 (fulv–Hþ, 100.0%), 154 (fulv, 30.4%),

153 (fulv–Hþ, 33.9%). UV–Vis (CH2Cl2 nm) kmax 286,

322, 500.

2.10. Synthesis of [1,2-(Ph)2C2H2g5-C5H42]Ti@O (10)

To a solution of 2 (0.32 g, 0.749 mmol) in THF (50

ml) was added KOH (0.11 g, 1.89 mmol). This was

treated with H2O (2 ml) and stirred for 1 h at room

temperature, to give a pale yellow solution. Following

filtration, the solvent was removed in vacuo and the

residue extracted into pentane. Removal of the pentane

gave a yellow powder (0.184 g, 66%). 1H NMR (CDCl3,d): 4.43 (s, 2H, 2x PhCHCp), 6.11, 6.19, 6.33, 6.44 (m,

8H, C5H4), 6.97–7.15 (m, 10H, C6H5). Principle IR ab-

sorptions (KBr cm�1) 3103 (m), 3062 (m), 2958 (m),

1602 (w), 1448 (m), 1442 (w), 1093 (s), 1051 (m), 1013

(s), 866 (w), 806 (s). MS (EI): m/z 372 (Mþ, 0.6%), 355

(Mþ–O, 3.1%), 310 (Mþ–Ti@O, 4.8%), 218 (Mþ–fulv,8.9%), 200 (Mþ–fulv, –O, 8.9%), 155 (fulv–Hþ, 100.0%),

154 (fulv, 33.5%), 153 (fulv–Hþ, 25.7%). UV–Vis(CH2Cl2 nm) kmax 352, 373, 505.

3. Results and discussion

3.1. Synthetic procedure for 2

The ansa-titanocene, 2, has previously preparedthrough the reduction of 6-phenylfulvene with

TiCl2 � 2THF in refluxing toluene [1]. This yielded a

mixture of cis and trans isomers in a 45:55 ratio. In an

attempt to improve the stereochemical control, we

sought an alternative route, namely the reductive di-

merisation of 6-phenylfulvene, with activated calcium at

0 �C to produce ansa-calcocene [17]. This is the most

important step in the whole process as it is here that thebridge formation occurs. There are a number of factors

Scheme 1. Synthetic p

that determine whether or not this happens, an impor-

tant factor being the type of fulvene used. This dictates

the degree to which the sole production of the bridge

occurs. Choosing a fulvene, that is easily reduced and

stable enough as a radical anion to undergo selectivedimerisation, gives the desired results. Much of the early

work in these ansa-metallocenes was carried out using

6,6-dimethylfulvene and regardless of whether the re-

action was carried out in solution [20] or using metal

vapour synthesis [10], an unbridged isopropyl impurity

was always present. Later it was revealed that, not only

was this side product present, but so too was an isop-

ropenyl metallocene [13]. From our own studies on thereducibility and selectivity of a series of fulvenes [16], we

also see the inability of this fulvene to give sole forma-

tion of the bridge and find that 6-phenylfulvene is our

ligand of choice.

Following the preparation of the ansa-calcocene, a

transmetallation was carried out at )50 �C with 3TiCl3 �AlCl3. Gradual warming to room temperature and

stirring for ca. 10 h gave a red–brown mixture, whichwas filtered to give a clear solution. An oxidation was

then carried out by first cooling the solution and then

adding the required volume of HCl. Stirring in air after

warming back to room temperature afforded the desired

product (Scheme 1). (The transmetallation can also be

carried out using TiCl4, giving the same quality of

product, but slightly lower yields, 59%.) This resulted in

an overall yield of 65% and a cis:trans ratio of 30:70.Due to the particular work-up of 2, only the trans iso-

mer is crystallised out of solution and this is evident

from both the 1H NMR and X-ray structure itself. The1H NMR exhibits three distinct multiplets, d 6.17, 6.35,

and 6.86, corresponding to three of the four-cyclopen-

tadienyl ring protons, the fourth overlaps with the

multiplet found between d 7.17 and 7.26 due to the

phenyl rings. If the cis isomer were present, additionalmultiplets would occur slightly downfield from these

values. It was upon this trans conformer that the deri-

vation reactions were carried out. Upon closer inspec-

tion of the results, we see that 2 crystallised in the trans

form with a R;R:S; S ratio of 30:70. However, the syn-

thetic route carried out by Eisch and co-workers [1],

where the MCl2 was reacted directly with 6-phenylful-

vene, produced a cis:trans ratio of 45:55 and was quotedas having high yields. Separation of these isomers was

possible using flash column chromatography.

rocedure for 2.

Fig. 1. An ORTEP view of 2with displacement ellipsoids at the 30% level using PLATON [27]; the disordered dichloromethane was omitted for clarity.

Table 2

Selected experimental bond lengths and angles in 2


3.2. Molecular structure of trans-2

The molecular structure of trans-2 was determined

using single crystal X-ray diffraction and is depicted

in Fig. 1. Crystallographic parameters are presented in

Table 1 and selected bond lengths and bond angles inTable 2, the definition of which can be found in Fig. 2.

Complex 2 crystallised in the monoclinic system in space

Table 1

Summary of crystal data and intensity collection parameters

Compound 2

Molecular formula C25H22TiCl4Molecular weight (g mol�1) 508.30

Crystal system monoclinic

Space group P21=ca (�AA) 12.2500(10)

b (�AA) 12.0902(11)

c (�AA) 16.2351(12)

a; c (�) 90

b (�) 94.805(5)

V (�AA3) 2396.0(3)

Z 4

q 1.409

l (mm�1) 0.803

F ð000Þ 1040

Index range �16 h6 15, �16 k6 14,

�20l6 20

2h (�) 52

Temperature (K) 292(2)

Reflections collected 5885

Reflections unique 4683

Reflections observed (4r) 2665

Cell weight 2033.20

Rr 0.056

wR2 0.120

Weighting scheme 0.0492a

aCalc. W ¼ 1=ðr2F 2o þ ð0:0492P Þ2 þ 1:8998P ; P ¼ ðF 2

o þ 2F 2c Þ=3.

group P21=c (No. 14). At an intermediate stage in the

refinement process (SHELXL97SHELXL97), it became obvious that

there was solvent of crystallisation present in the lattice.

Disordered CH2Cl2 {two sites with occupancies of

Bond 2 (�AA) Bond 2 (�AA)

C(1)–C(2) 1.394 C(10)–C(20) 1.387

C(2)–C(3) 1.393 C(20)–C(30) 1.405

C(3)–C(4) 1.369 C(30)–C(40) 1.357

C(4)–C(5) 1.394 C(40)–C(50) 1.394

C(5)–C(1) 1.389 C(50)–C(10) 1.402

C(1)–C(6a) 1.522 C(10)–C(60a) 1.526

C(1)–C6b 1.595 C(10)–C(60b) 1.635

C(6a)–R(1) 1.556 C(60a)–R(10) 1.549

C(6b)–R(1) 1.590 C(60b)–R(10) 1.560

C(6a)–C(60a) 1.551 C(6b)–C(60b) 1.493

M–Cl(1) 2.363 M–Cl2 2.356

M–C(1) 2.368 M–C(10) 2.383

M–C(2) 2.381 M–C(20) 2.380

M–C(3) 2.406 M–C(30) 2.421

M–C(4) 2.395 M–C(40) 2.400

M–C(5) 2.335 M–C(50) 2.334

Cl–Ti–Cl 96.39(4)�

Fig. 2. Numbering scheme for the calculated structures.


0.721(7) and 0.235(7)} was treated using soft DELU/

ISOR restraints for the anisotropic displacement pa-

rameters. Further disorder was deduced from the

bridging carbon atoms C(6)/C(60) over two sites with

occupancies of ca. 0.70:0.30 and refining to 0.708(15):0.292(15). This is not uncommon [21] in ethylene

bridged systems and in this structure is consistent with

SS (major) and RR (minor) configurations at the C(1)/

C(10) atom sites. The disorder is present due to the

fortuitous and close fit of the RR=SS systems into a

loosely packed crystal lattice.

The bridge bond lengths for the major/minor sites of

1.553(14)/1.49(3) �AA, are not significantly different, thehigh esd�s are due to the disorder and lower site occu-

pancy so that a discussion of the differences is not really

viable. The only distances that can be discussed com-

prehensively are those involving the Ti–Cl, Ti � � �Cgwhere Cg are the ring centroids and these will be dis-

cussed in more detail later on. No disorder model was

attempted for the cyclopentadienyl ring or phenyl ring

systems and the fit between the R;R and S; S is very goodfor these groups on analysis of Fourier maps through

the g5-C5 planes.

The phenyl groups adopt a trans arrangement, with

respect to one another and the metal is g5 coordinated

to the cyclopentadienyl rings (Fig. 1). However, the

structure does not adopt perfect C2 symmetry about the

Ti atom and the following torsion angles highlight this

deviation: Cl(1) � � �Ti � � �Cg(1) � � �C(11) is )123.5(3)�,Cl(1) � � �Ti � � �Cg(2) � � �C(21) is 130.9(3)�, Cl(2) � � �Ti� � �Cg(1) � � �C(11) is 134.3(3)� and finally Cl(2) � � �Ti� � �Cg(2) � � �C(21) is )126.6(3)� (Cg is a g5-C5 ring

centroid). The two Cg � � �Ti distances are 2.071(2) �AA for

Cg(1) and 2.064(2) �AA for Cg(2) and they intersect at an

Scheme 2. Synthesis of ansa-tit

angle (d) of 128.33(9)� at the Ti centre. The cyclopen-

tadienyl rings are oriented at an angle (a) of 54.75(15)�and the angle formed between the Cl(1)–Ti–C(l2) atoms

is 96.39(4)�. These results can be compared with an

unsubstituted ansa-titanocene, (CH2)2(C5H4)2TiCl2 [13].The Cg � � �Ti distances, 2.06 �AA, and resulting angle,

128.2�, are similar to 2 and the bridge length is 1.49 �AA. A

slight decrease is observed for the two angles, the ring

tilt angle (a), 51.8�, and the Cl(1)–Ti–Cl(2) angle, 94.8�.Crystallographic data have been deposited with the

Cambridge Crystallographic Data Centre as CCDC-

206414. Copies of this information may be obtained free

of charge from the Director, CCDC, 12 Union Road,Cambridge, CD21E2, UK (www.ccdc.cam.ac.uk, email:

[email protected]).

3.3. Derivatives obtained from 2

The synthesis of 2 allows formation of a new and

broad range of derivatives through ligand exchange.

Compounds 5 to 10 are a direct result (Scheme 2).The dimethyl species, 5, was obtained in a high yield

of 98% by reacting MeLi with a solution of 2 in refluxing

toluene for an hour. A variety of colour changes oc-

curred during this period, from the original red to amber

to pale yellow and finally to a musty yellow, the product

was isolated as a bright yellow solid. The effect of the

ligand exchange can be seen in the 1H NMR for 5. Here

an upfield shift occurs with the bridging hydrogens oc-curring at d 3.64 (d 4.83 for 2) and the cyclopentadienyl

hydrogens at d 5.21, 5.32, and 6.85, with the fourth

being present within the phenyl hydrogens range of d6.89–7.02. This is a result of the increased shielding ex-

perienced by the protons due to the replacement of an

anocene derivatives 5–10.

http://www.ccdc.cam.ac.uk


electron-withdrawing group with an electron releasing

one.

Derivatisation of compound 5 yielded the interme-

diary compound 6, whereby one of the methyl groups

was replaced with a chloride. This fact was demon-strated effectively in the 1H NMR, where its multiplets

lie midway between those of 2 and 5. Synthesis was

achieved by treating a solution of 5 with Me3SiCl, fol-

lowed by H2O and stirring for an hour, an amber so-

lution being the end result. In order to purify the

compound, the solvent was removed and the residue

washed twice with pentane to give an amber-red powder

(95% yield). This ligand arrangement has also beenproposed to occur during the course of olefin poly-

merisations, where a titanocene dichloride is used as a

catalyst in conjunction with methylaluminoxane

(MAO). The MAO is thought to displace one of the

chloride groups with a methyl group, which is then

followed by the removal of the final chloride to produce

an active site, from where chain propagation can occur.

From 6 it is possible to synthesise 5 or 2, simply bychoosing the required reagents. Treating 6 with MeLi,

removes the chloride and replaces it with another methyl

group. Alternatively, reacting this titanocene with

Me3SiCl, followed by an addition of H2O, displaces the

methyl group for a chloride to yield 2. A source of error

can also occur in the synthesis of 6. Adding an excess of

Me3SiCl to the original reaction with 5 yields 2 as the

final product, 6 only occurs as an intermediate, which isthen consumed to yield the dichloride derivative.

A further derivative, 7, was synthesised by refluxing a

solution of 2 in THF with KSCN for 2 h and filtering the

hot solution removed any unreactedKSCN. The addition

ofNCS groups causes slightlymore proton deshielding to

occur with respect to 2. Cyclopentadienyl hydrogens are

found in the following positions: d 6.17, 6.44, 6.62, and

6.93, in this case each ring proton is represented by adistinct multiplet. The assertion that these groups are in

fact isothiocyanate and not thiocyanates arises from

spectroscopic analysis. The carbon of the NCS group

occurs at d 122.3 in the 13C NMR, which is within the

expected isothiocyanate range and downfield from where

thiocyanates occur (d 95–115). Furthermore, two broad

and very intense absorptions occur in the IR spectrum of

7, at 2059 and 2009 cm�1 typical of isothiocyanates (range2140–1990 cm�1). Titanium bound sulphur would give

absorption bands between 2175 and 2160 cm�1.

Synthesis of 8 is similar to that already discussed for

7, with KNCO being utilised and resulting in a red

powder (84% yield). For an isocyanate bound ligand the

carbon signal was located at d 122.4, within the expected

isocyanate range. However, from this, it cannot be de-

finitively stated that bonding occurs through the nitro-gen, as this value is borderline with the cyanate range of

d 105–120. From IR data, the N-bonding is obvious, as

two intense absorptions occur at 2222 and 2204 cm�1.

Formation of the phenolate derivative, 9, was carried

out by reacting a freshly prepared solution of LiOPh

with 2 at )30 �C. This yielded a yellow/brown solution,

which after 18 h was filtered to give a beige powder.

Spectroscopic analysis confirmed this to be 9. The in-fluence of the phenoxy groups can be seen to contribute

to the deshielding of the complex, although not to the

same extent as for 2. Also peaks are visible for all the

cyclopentadienyl H atoms at d 5.77, 5.91, 6.14, and 6.43,

respectively. It is also evident in the 13C NMR that some

degree of deshielding is occurring causing a more upfield

position from those of 2, but not to the same degree as

seen in 5.The final derivative prepared was that of 10. Treat-

ment of a solution of 2 with KOH, followed by H2O

yielded a pale yellow solution, which upon workup gave

the desired compound. Unfortunately spectroscopic

analysis was more limited in this case, as due to poor

intensity levels, no 13C NMR could be determined.

However in the 1H NMR, it is apparent that the protons

are being deshielded to a greater extent than in 9 due tothe oxy group, with peaks at d 6.11, 6.19, 6.33, and 6.44.

3.4. Theoretical study on 2, 3, and 4

Density functional theory calculations were carried

out at the B3LYP level and using 6-31G�� as the basis set,results from which can be found in Table 3. The first of

these calculations was performed on compound 2 itselfand a direct comparison can be made between these re-

sults and those from X-ray diffraction. Both the experi-

mental and calculated structures show a typical bent

ansa-metallocene geometry. However, the C–C andM–C

bond length ranges are comparable, with the estimated

carbon ring bond lengths from 1.404 to 1.427�AA and Ti–C

distances of 2.369–2.454�AA. The ipso carbons are closer to

Ti, 2.369 and 2.416 �AA, whereas the other carbons havelonger Ti–C, e.g. 2.454 and 2.438 �AA. The length of the

two-carbon bridge spanning the cyclopentadienyl rings

was found to be 1.563 �AA. It has been shown that the size

of a two-carbon bridge [22] is such that its presence on a

metallocene causes a distortion away from its �natural�arrangement. In the case of titanocenes, which have a

bent structure, the bridging unit amplifies the distortion

causing the Cg � � �Ti � � �Cg angle to decrease from 131.0�[23] in the unbridged metallocene to 128.3� in 2. However

despite the fact that the complex is being pulled from its

preferred configuration, no additional strain is imposed

on the bridge. Additional strain is on the other hand

generated due to the presence of the two-phenyl groups,

with the result that the carbon–carbon single bond

lengthens, to relieve this steric strain. The calculated

bridge length of 1.563�AAdemonstrates this effect. This toohas also been seen with a variety of transition metal met-

allocenes. An analogous coboticenium species, trans-[(1,

2-diphenyl-1,2-dicyclopentadienyl) ethanediyl]–cobalt(III)

Table 3

Selected calculated bond lengths for compounds 2, 3 and 4 using the B3LYP/6-31G** level of theory

Bond Bond length (�AA) (2) Bond (�AA) (3) Bond length (�AA) (4)

M–C(1) 2.369 2.149 2.213

M–C(2) 2.438 2.290 2.061

M–C(3) 2.454 2.450 2.039

M–C(4) 2.416 2.419 2.043

M–C(5) 2.419 2.253 2.055

M–C(6) n/a 2.385 3.348

M–C(10) 2.416 2.149 2.213

M–C(20) 2.454 2.290 2.055

M–C(30) 2.438 2.450 2.043

M–C(40) 2.369 2.419 2.039

M–C(50) 2.419 2.253 2.061

M–C(60) n/a 2.385 3.348

C1–C(2) 1.427 1.448 1.458

C2–C(3) 1.422 1.410 1.418

C3–C(4) 1.404 1.414 1.427

C4–C(5) 1.424 1.417 1.418

C5–C(1) 1.416 1.449 1.461

C1–C(6) 1.514 1.454 1.411

C6–C(60) 1.563 n/a n/a

C6–C(Ph(1)) 1.525 1.512 1.478

C6–C(Ph(2)) n/a 1.503 1.470

C(10)–C(20) 1.416 1.448 1.461

C(20)–C(30) 1.424 1.410 1.418

C(30)–C(40) 1.404 1.414 1.427

C(40)–C(50) 1.422 1.417 1.418

C(50)–C(10) 1.427 1.449 1.458

C(10)–C(60) 1.514 1.454 1.411

C(6)–C(Ph(1))0 n/a 1.512 1.470

C(6)–C(Ph(2))0 1.525 1.503 1.478


hexafluorophosphate has a slightly shorter C–C bond

length than 2, of 1.540 �AA [12] while the C–C bond length

in 1,10-tetramethylethyleneferrocene has a longer bridg-ing C–C bond of 1.584 �AA [24]. This is attributed to the

increased steric crowding caused by replacing the phenyl

and hydrogen groups with methyl groups.

Varying the metal component and fulvenyl exocyclic

substituents can have an even more dramatic effect on

structure, i.e., the ansa-metallocene structure is not the

only possible outcome, two further bonding modes

could also form instead. Formation of complex 2(bonding mode a) involves the reduction of 6-phenyl-

fulvene to generate its corresponding radical anion. This

intermediate is stable enough, due to the presence of the

phenyl group, to undergo dimerisation and exclusively

yield 2, the structure of which is depicted in Scheme 5.

Increasing the steric load on the exocyclic carbon to the

extent that bridge formation is suppressed and using an

electron deficient metal, results in �tucked in� or fulvenecomplexes (bonding mode b) shown in Scheme 4. An

example of this is the 16VE titanocene derivative 3 [25].

Replacing the Ti in this complex with Fe gives yet an-

other type of structure (Scheme 3). In this case, the

presence of iron eliminates the possibility for a �tuckedin� configuration due to its higher electron count. In-

stead the fulvene ligands are reduced and complexed by

a M2þ metal centre, forming an intermediate species,

which can either dimerise or undergo hydride extraction

from the solvent. Support for this postulate was ob-

tained following the elucidation of the structure of 4, anintermediate formed during the reaction of iron atoms

with 6,6-diphenylfulvene [26]. Initial formation of this

species is thought to involve the complexation of neutral

fulvenes with an iron centre whose oxidation state is

zero (bonding mode c). Reduction of each of these li-

gands takes place as a result of electron transfer from

the metal centre. This species, then undergoes hydrogen

abstraction giving the unbridged metallocene, a routethat minimises the steric clashes between the bulky

phenyl groups (Scheme 3).

From the crystal structure of 4, the question arises as

to whether this complex exists in a singlet or triplet state.

DFT calculations obtained using B3LYP/6-31g**

showed a minimum in the singlet state. Using the X-ray

crystal structure of 4 as a starting geometry, the triplet

species failed to optimise, thereby showing that it is notan electronic state on the potential energy surface for

this system. This indicates that in 4 the radicals at the

C(6) and C(60) positions are paired, but are unable to

form a C–C bond for steric reasons.

The effect of these structural details can also be seen

in the calculated reaction enthalpies for the formation of

2, 3, and 4. The reaction between titanium atoms and

6,6-diphenylfulvene results in the most exothermic

Scheme 4. Reaction of titanium atoms with 6,6-diphenylfulvene to yield 3, whose structure depicts bonding mode b.

Scheme 5. Reaction of TiCl2 with 6-phenylfulvene to yield 2.

Scheme 6. Reaction of iron atoms with 6,6-diphenylfulvene to yield 4.

Scheme 3. Reaction mechanism for the synthesis of metallocenes, showing the role of the bis-fulvene iron complex 4.


value, )136.8 kcal/mol, out of the three complexes

(Scheme 4). The reaction enthalpy for 2 was also cal-

culated, this time from the reaction of unsolvated TiCl2with 6-phenylfulvene (Scheme 5). A lower value of

)114.4 kcal/mol was obtained. By replacing the Ti

centre with an Fe one, the reaction enthalpy for the

formation of 4 becomes )79.5 kcal/mol (Scheme 6). This

is significantly lower than the previous enthalpy of for-mation, a difference attributable to their structural

variations. Experimental and theoretical results support

the postulate that 3 adopts the �tucked in� structure.

Both of these data sources are comparable, with the

theoretical range for the cyclopentadienyl carbon–

carbon bonds being 1.410–1.449 �AA and the experimental

range being 1.377–1.455 �AA. The metal to ring carbon

range was calculated to be 2.149–2.450 �AA, while struc-

turally this is 2.121–2.400 �AA. But the most significant

bond length in this complex is that between the titanium

centre and the exocyclic carbon, 2.385 �AA theoretically,2.347 �AA experimentally. It is the presence and strength

of this bond in 3 that results in the greater exothermic

output during its formation. However, formation of an


equivalent bond in 4 is not possible, due to the increased

distance between the metal centre and the exocyclic

carbon. Theoretically, this was found to be 3.484 �AA, 0.06�AA greater than the crystallographically determined va-

lue. As for the rest of the structural arrangement in 4,again theoretical and experimental results are in good

agreement. The calculated ring carbon–carbon bonds

occupy a range of 1.418–1.458 �AA with the measured

range being 1.406–1.452 �AA. From these values, it can be

noted that the cyclopentadienyl rings have increased

aromatic character. The metal–carbon distances, theo-

retically and experimentally are found to be 2.039–2.213�AA and 2.035–2.209 �AA, respectively. Elongation has alsooccurred in the exocyclic bond, causing increased single

bond character, theoretically this was found to be 1.411�AA and experimentally to be 1.408 �AA. It is clear from

these results that the true structural nature of 4 is that of

a ferrocene derivative, in which the Fe(II) centre coor-

dinates to two fulvene anions. The complex is also found

to be in a singlet state, which shows that the spins of the

two-fulvene radical anions are paired.

4. Conclusion

A new synthetic route to the previously isolated

ansa-metallocene, trans-[(1,2-diphenyl-1,2-dicyclopenta-

dienyl)ethanediyl] titanium(IV) dichloride (2) was carried

out, in good yield. This involved the reductive dimerisa-tion of 6-phenylfulvene with activated calcium powder,

followed by transmetallation using 3TiCl3 � � �AlCl3. This

compound was then used to synthesise a variety of other

ansa-titanocene compounds, 5–10, in high yield through

ligand replacement. As the ansa-metallocene framework

remained untouched, the influence of these ligands on the

titanocene itself, could be ascertained spectroscopically.

The reaction of 6,6-diphenylfulvene with Ti atoms wascalculated using B3LYP/6-31G** and the reaction en-

thalpy for the formation of this �tucked in� titanocenedichloride, 3, was )136.8 kcal/mol. However the same

reaction involving Fe atoms had a lower reaction en-

thalpy of )79.5 kcal/mol and resulted in the formation of

a singlet ferrocene, 4, in which coordination to fulvene

anions occurred. The formation of a C2 bridged ferrocene

was not possible due to the steric load of two phenylsubstituents on each of the fulvene systems. The calcu-

lated reaction enthalpy for the reaction of TiCl2 with 6-

phenylfulvene to yield 2, an example of the third type of

structural geometry available, was found to be )114.4kcal/mol. Structural comparisons were also carried out

between each of these calculated complexes, giving fur-

ther verification of their differing geometric arrangement.

Acknowledgements

This work was supported by the Centre for High-

Performance Computing Applications at University

College Dublin, Ireland. M.T. and S.F. also wish tothank Enterprise Ireland for financial support (Grant

SC/1997/570).

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