C2-Symmetric ansa-lanthanidocene complexes. Synthesis via silylamine elimination and β-SiH agostic rigidity

3080

J. Am. Chem. Soc. 2000, 122, 3080-3096

C₂-Symmetric ansa-Lanthanidocene Complexes. Synthesis via

Silylamine Elimination and â-SiH Agostic Rigidity

Jo1rg Eppinger, Michael Spiegler, Wolfgang Hieringer, Wolfgang A. Herrmann, and

Reiner Anwander*

Contribution from the Anorganisch-chemisches Institut, Technische UniVersita¨t Mu¨nchen,

D-85747 Garching, Germany

ReceiVed August 4, 1999

Abstract: The synthesis as well as the spectroscopic and structural characterization of a new class of C₂-

symmetric, mononuclear metallocene complexes of the lanthanide elements is described. Heteroleptic

lanthanidocene silylamide complexes have been obtained ate-complex-free according to silylamine elimination

reactions of complexes Ln[N(SiHMe₂)₂]₃(THF)_x(x ) 1, Ln ) Sc; x ) 2, Ln ) Y, La, Nd, Lu) and linked,

substituted cyclopentadiene and indene systems. The molecular structure of [Me₂Si(C₅Me₄)₂]La[N(SiHMe₂)₂]

(95% isolated yield) has been determined by X-ray crystallography. Brintzinger-type, indenyl-derived

metallocene complexes have been isolated in racemic yields as high as 72%. IR and multinuclear NMR

spectroscopy (¹H, ¹³C, ²⁹Si, ⁸⁹Y) reveals the presence of an unprecedented strong diagostic interaction between

the electron-deficient metal centers and the SiH moiety of the bis(dimethylsilyl)amide ligand: SiH stretching

1

vibrations as low as 1759 cm^-1and J_Si,Hcoupling constants as low as 133 Hz indicate a distinct weakening

of the SiH bonding. X-ray structure analyses of the compounds rac-[Me₂Si(2-Me-Benz-Ind)₂]Ln[N(SiHMe₂)₂]

(Ln ) Y, Lu) and rac-[Me₂Si(2-Me-C₉H₅)₂]Ln[N(SiHMe₂)₂] (Ln ) Y, Lu) show that the structural features

of both the chelating ancillary ligands and such agostically fused metallacycles depend on the type of the

ligand and the size of the metal: bite angles Ω of approximately “U-shaped” ansa-ligands as large as 68.2(2)°

and Ln-Si and Ln-H contacts as close as 3.028(1) and 2.37(3) Å, respectively, have been detected, the latter

forcing very large Si-N-Si angles up to 160.1(2)°. The isolation of reaction intermediates such as

Y[N(SiHMe₂)₂]₃(THF) and partly exchanged [Me₂Si(2-Me-4-Ph-Ind)₂H]Y[N(SiHMe₂)₂]₂provides mechanistic

details of this peculiar silylamine elimination reaction. Additionally, the pK_avalues of various protonated

ligands including new 9-(SiHMe₂)-fluorene, 3-(SiHMe₂)-indene, and 3-(SiHMe₂)-2-Me-indene determined

according to the method of Fraser give evidence of a thermodynamically controlled ligand exchange.

Introduction

During the past decade lanthanidocene chemistry developed

into a prolific branch of metallocene research.¹Although the

first lanthanidocene complexes, “Cp₂LnR”, comprising unsub-

stituted cyclopentadienyl rings were reported as early as 1963

by Dubeck et al. (Figure 1, A),²it was the discovery of the

lanthanidocene-based “Ziegler-Natta” model which decisively

stimulated the development of this class of compounds.³

Meanwhile, several generations of rare earth metallocene

complexes form an integral part of the enantioselective synthesis

of both polymers and fine chemicals.^4,5For example, achiral

(1) (a) Burger, B. J.; Cotter, W. D.; Coughlin, E. B.; Chacon, S. T.;

Hajela, S.; Herzog, T. A.; Ko¨hn, R.; Mitchell, J.; Piers, W. E.; Shapiro, P.

J.; Bercaw, J. E. In Ziegler Catalysts; Fink, G., Mu¨hlhaupt, R., Brintzinger,

H.-H., Eds.; Springer-Verlag: Berlin, 1995; pp 317-331. (b) Edelmann,

F. T. In Metallocenes; Togni, A., Haltermann, R. L., Eds.; Wiley-VCH:

Weinheim, 1998; pp 55-110. (c) Chirik, P. J.; Bercaw, J. E. In Metal-

locenes; Togni, A., Haltermann, R. L., Eds., Wiley-VCH: Weinheim, 1998;

pp 111-152.

Figure 1. Various generations of lanthanidocene complexes.

lanthanidocene complexes of type B promote the stereoregular

polymerization of functionalized olefins such as acryl esters,⁶

while C₁-symmetric derivatives of type C selectively catalyze

a variety of olefin transformations including the hydroamination/

cyclization of R,ω-aminoolefins.⁷C₂-Symmetric yttrocene com-

(2) Maginn, R. E.; Manastyrskyj, S.; Dubeck, M. J. Am. Chem. Soc.

1963, 85, 672-676.

(3) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51-56.

(4) For recent reviews, see: Yasuda, H.; Tamai, H. Prog. Polym. Sci.

1993, 18, 1097-1139. (b) Yasuda, H. Top. Organomet. Chem. 1999, 2,

255-283. (c) Yasuda, H.; Ihara, E. AdV. Polym. Sci. 1999, 133, 53-101.

(5) For recent reviews, see: (a) Edelmann, F. T. Top. Curr. Chem. 1996,

179, 247-276. (b) Anwander, R. In Applied Homogenoeus Catalysis with

Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH

Publishers: Weinheim, 1996; pp 866-892. (c) Molander, G. A.: Dowdy,

E. C. Top. Organomet. Chem. 1999, 2, 119-154.

(6) For examples, see: (a) Yasuda, H.; Yamamoto, H.; Yokota, K.;

Miyake, S.; Nakamura, A. J. Am. Chem. Soc. 1992, 114, 4908-4910. (b)

Giardello, M. A.; Yamamoto, Y.; Brard, L.; Marks, T. J. J. Am. Chem.

Soc. 1995, 117, 3276-3279.

Published on Web 03/18/2000

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3081

plexes of type D are the only reported single-site rare earth

catalysts to be active in propene polymerization.⁸So far, salt

metathesis starting from anhydrous lanthanide chlorides con-

stitutes the only well-examined synthetic access to lanthan-

idocene derivatives of types A-D.^9,10However, this route is

encumbered by lengthy, tedious, often low-yield syntheses and

ate complex formation, resulting in alkali metal- and donor

solvent-contaminated products.^9,11

species, were successfully applied for the synthesis of linked

amidocyclopentadienyl derivatives of type F.¹⁹However, the

synthesis of the thermally labile tris(trimethylsilyl)methyl

complexes is successful for the late lanthanide elements only

and suffers from ate complexation.²⁰

Here, we report on the feasibility of our extended silylamide

route for the synthesis of C₂-symmetric ansa-lanthanidocene

complexes of type E by considering a variety of representative

ligands on the basis of steric and pK_acriteria.²¹A full account

of the synthesis as well as spectroscopic and structural features

of these complexes is presented. Companion contributions^22,23

will address (i) the strength and the features of the â-SiH

diagostic interaction from a theoretical point of view and (ii)

the kinetics and mechanism of complex racemizations as well

as the implication of this diagostic interaction for the generation

of high racemic yields.

Since metallocene-mediated stereoselective olefin transforma-

tion reactions are governed by ancillary ligand effects compris-

ing steric and electronic factors as well as the induction of

chirality, we thought it worthwhile to further investigate the

class of C₂-symmetric lanthanidocene complexes. Strangely

enough, few efforts have been made to extend the ligand

spectrum to indenyl or fluorenyl congeners,¹²considering the

benefits to research and industry which evolved from Brintz-

inger-type C₂-symmetric ansa-zirconocenes.¹³Recently, we

communicated the synthesis of the first C₂-symmetric ansa-

yttrocene complexes of type E according to an amine elimination

reaction¹⁴which utilizes specialized silylamide complexes

Ln[N(SiHMe₂)₂]₃(THF)_x(x ) 1,2) as synthetic precursors

(“extended silylamide route”).¹⁵The decreased steric bulk of

the [N(SiHMe₂)₂] ligand and THF dissociation are anticipated

to render less shielded Ln-N bonds prone to extended proton-

transfer reactions.^14,16-18In addition, the thermally very stable

“Ln[N(SiHMe₂)₂]” moiety enables ligand-exchange reactions

at elevated temperatures and participates in strong diagostic

Ln‚‚‚(SiH)₂interactions. Also recently, in situ alkane elimination

reactions, featuring Ln(CH₂SiMe₃)₃(THF)₂as the reactive

Results and Discussion

Synthesis of ansa-Lanthanidocene Amides. The applicabil-

ity of this extended silylamide route was initially probed for

the routinely employed bis(2,3,4,5-tetramethyl-1-cyclopenta-2,4-

dienyl)dimethylsilane ([Me₂Si(CpH′′)₂], 1)²⁴and subsequently

applied to fused cyclopentadienyl ring systems including 2,2-

bis(inden-1-yl)propane ([Me₂C(IndH)₂], 2), bis(2-methylinden-

1-yl)dimethylsilane ([Me₂Si(2-Me-IndH)₂], 3), bis(2-methyl-4-

phenylinden-1-yl)dimethylsilane ([Me₂Si(2-Me-4-Ph-IndH)₂],

4), bis(2-methyl-4,5-benzoinden-1-yl)dimethylsilane ([Me₂Si-

(2-Me-Benz-IndH)₂], 5), and bis(fluoren-9-yl)dimethylsilane

([Me₂Si(FluoH)₂], 6).^25,26According to Scheme 1, reaction with

the bis(dimethylsilyl)amide precursors 7a-c¹⁶gave the corre-

sponding ansa-lanthanidocene amide complexes.

(7) Arredondo, V. M.; Tian, S.; McDonald, F. E.; Marks, T. J. J. Am.

Chem. Soc. 1999, 121, 3633-3639 and references therein.

¹H NMR spectroscopy and GC-MS analysis revealed that

complete conversion is achieved only at elevated temperatures.

(8) Mitchell, J. P.; Hajela, S.; Brookhart, S. K.; Hardcastle, K. I.; Henling,

L. M.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 1045-1053.

(9) For recent organolanthanide reviews, see: (a) Schumann, H.; Meese-

Marktscheffel, J. A.; Esser, L. Chem. ReV. 1995, 95, 865-986. (b)

Edelmann, F. T. In ComprehensiVe Organometallic Chemistry II; Abel, E.

W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol.

4, pp 11-212.

(18) The amine elimination reaction as a route to zirconocene complexes

is meanwhile established: (a) Chandra, G.; Lappert, M. F. J. Chem. Soc. A

1968, 1940-1945. (b) Hughes, A. K.; Meetsma, A.; Teuben, J. H. Organo-

metallics 1993, 12, 1936-1945. (c) Herrmann, W. A.; Morawietz, M. J.

A.; Priermeier, T. Angew. Chem. 1994, 106, 2025-2028; Angew. Chem.,

Int. Ed. Engl. 1994, 33, 1946-1949. (d) Diamond, G. M.; Jordan, R. F.;

Petersen, J. L. Organometallics 1997, 16, 3044-3055 and references therein.

(19) (a) Mu, Y.; Piers, W. E.; MacQuarnie, D. C.; Zaworotko, M. J.;

Young, U. G., Jr. Organometallics 1996, 15, 2720-2726. (b) Hultzsch, K.

C.; Spaniol, T. P.; Okuda, J. Angew. Chem. 1999, 111, 163-166; Angew.

Chem., Int. Ed. Engl. 1999, 38, 227-230.

(20) (a) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,

126. (b) Schumann, H.; Mu¨ller, J. J. Organomet. Chem. 1978, 146, C5-C7.

(21) Parts of this work were already communicated: (a) Anwander, R.;

Eppinger, J., Spiegler, M. 214th National Meeting of the American Chemical

Society, September 7-11, 1997, Las Vegas, NV. (b) Eppinger, J.; Spiegler,

M.; Anwander, R. X. Workshop on Rare Earth Elements, December 3-5,

1997, Berlin, Germany.

(10) Alternative methods of preparation have only rarely been under-

taken: (a) Fischer, E. O.; Fischer, H. Angew. Chem. 1964, 76, 52. (b)

Hammel, H.; Weidlein, J. J. Organomet. Chem. 1990, 388, 75-87. (c)

Watson, P. L.; Whitney, J. F.; Harlow, R. L. Inorg. Chem. 1981, 20, 3271-

3278. (d) Stults, S. D.; Andersen, R. A.; Zalkin, A. Organometallics 1990,

9, 115-122. (e) Mu, Y.; Piers, P. E.; MacDonald, M.-A.; Zaworotko, M.

J. Can. J. Chem. 1995, 73, 2233-2238. (f) For further non-salt metathesis

routes to organolanthanide complexes, see: Schaverien, C. J. AdV. Orga-

nomet. Chem. 1994, 36, 283-362.

(11) Alkali metal ligand ate complexation was reported to markedly affect

the stereoselectivity of acrylate polymerization: Yasuda, H.; Ihara, E.

Macromol. Chem. Phys. 1995, 196, 2417-2441.

(12) (a) Deacon, G. B.; Newnham, R. H. Aust. J. Chem. 1985, 38, 1757-

1765. (b) Evans, W. J.; Gummersheimer, T. S.; Boyle, T. J.; Ziller, J. W.

Organometallics 1994, 13, 1281-1284. (c) Wang, S.; Yu, Y.; Ye, Z.; Qian,

C.; Huang, X. J. Organomet. Chem. 1994, 464, 55-58. (d) Qian, C.; Zou,

G.; Sun, J. J. Organomet. Chem. 1998, 566, 21-28. (e) Kretschmer, W.

P.; Troyanov, S. I.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics

1998, 17, 284-286.

(13) For a recent review, see: Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt,

R.; Rieger, B.; Waymouth, R. M. Angew. Chem. 1995, 107, 1255-1283;

Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.

(14) Herrmann, W. A.; Eppinger, J.; Runte, O.; Spiegler, M.; Anwander,

R. Organometallics 1997, 16, 1813-1814.

(15) Anwander, R.; Runte, O.; Eppinger, J.; Gerstberger, G.; Spiegler,

M.; Herdtweck, E. J. Chem. Soc., Dalton Trans. 1998, 847-858.

(16) Anwander, R. Top. Curr. Chem. 1996, 179, 33-112 and literature

cited therein. For examples utilizing this specialized amide precursor, see:

(a) Runte, O.; Priermeier, T.; Anwander, R. J. Chem. Soc., Chem. Commun.

1996, 1385-1386. (b) Go¨rlitzer, H. W.; Spiegler, M.; Anwander, R. Eur.

J. Inorg. Chem. 1998, 1009-1014.

(17) In contrast, efforts to synthesize lanthanidocene complexes from

Ln[N(SiMe₃)₂]₃precursor compounds were successful in moderate yields

only for derivatives featuring nonlinked cyclopentadienyl ligands and the

larger lanthanide(III) cations (Ln ) La, Ce, Sm): Booij, M.; Kiers, N. H.;

Heeres, H. J.; Teuben, J. H. J. Organomet. Chem. 1989, 364, 79-86.

(22) Hieringer, W.; Eppinger, J.; Anwander, R.; Herrmann, W. A. J.

Am. Chem. Soc., in press.

(23) (a) Eppinger, J. Ph.D. Thesis, Technische Universita¨t Mu¨nchen,

1999. (b) Eppinger, J.; Spiegler, M.; Herrmann, W. A.; Anwander, R.,

unpublished results.

(24) Jutzi, P. Dickbreder, R. Chem. Ber. 1986, 119, 1750-1754.

(25) For ligand synthesis, see the following. (a) Me₂C(IndH)₂: Nifant’ev,

I. E.; Ivchenko, P. V.; Kuz’mina, G.; Luzikov, Y. N.; Sitnikov, A. A.; Sizan,

O. E. Synthesis 1997, 469-474. (b) Me₂Si(2-Me-IndH)₂: Spaleck, W.;

Antberger, M.; Rohrmann, J.; Winter, A.; Bachmann, B.; Kiprof, P.; Behm,

J.; Herrmann, W. A. Angew. Chem. 1992, 104, 1373-1376; Angew. Chem.,

Int. Ed. Engl. 1992, 32, 1345-1347. (c) Me₂Si(2-Me-4-Ph-IndH)₂: Spaleck,

W.; Ku¨ber, F.; Winter, A.; M.; Rohrmann, J.; Bachmann, B.; Antberger,

M.; Dolle, V.; Paulus, E. P. Organometallics 1994, 13, 954-963. (d)

Me₂Si(2-Me-Benz-IndH)₂: Stehling, U.; Diebold, J.; Kirsten, R.; Roll, W.;

Brintzinger, H.-H.; Ju¨ngling, S.; Mu¨hlhaupt, R.; Langhauser, F. Organo-

metallics 1994, 13, 963-970. (e) For a comparable survey of structural

parameters in zirconocene chlorides, see: Resconi, L.; Piemontesi, F.;

Camurato, I.; Sumeijer, O.; Nifant’ev, I. E.; Ivchenko, P. V.; Kuz’mina, L.

G. J. Am Chem. Soc. 1998, 120, 2308-2321.

(26) Chen, Y.-X.; Rausch, M. D.; Chien, J. C. W. J. Organomet. Chem.

1995, 497, 1-9.

3082 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

Scheme 2. Utilization of a Linked 4,5-Substituted

Benzoindene System 5 for the Synthesis of the

ansa-Yttrocene Amide Complex 15b According to the

Extended Silylamide Route (5 ) (2-Me-Benz-IndH)₂SiMe₂;

R ) SiHMe₂)^a

Scheme 1. Synthesis of C₂-Symmetric ansa-Lanthanidocene

Amide Complexes According to the Extended Silylamide

Route

^aThe meso-isomer was detected as mono-THF adduct by NMR

spectroscopy.

La(III) cation could an ansa-complex be isolated (rac-14c). The

putative yttrium complex could not be obtained. Instead,

monocoordination of the ancillary ligand was observed to yield

[Me₂Si(2-Me-4-Ph-Ind)₂H]Y[N(SiHMe₂)₂]₂(14b), which can be

seen as a reaction intermediate of the ansa-complex formation

according to Scheme 3. The yield of the pure yttrium complex

rac-12b derived from the propylidene-bridged indenyl ligand

was also low. This can be attributed to a more opened

coordination sphere at the metal center, arising from the absence

of a methyl group in the 2-position and a short propylidene

ansa-bridge. The increased bite angle of the ligand enhances

the electron deficiency of the metal center, which disfavors

donor (THF) dissociation, the latter being a prerequisite of high

racemic yields. The attempted synthesis of the corresponding

lanthanum complex 12c is in accord with this finding: the larger

lanthanum center discourages the ansa-coordination mode,

probably forming an oligomeric product which is barely soluble

in tetrahydrofuran.

^aMonocoordination of the ansa-ligand detected only. ^bComplex

detected by NMR spectroscopy only.

Recrystallization of the crude reaction products from n-hexane

or toluene solutions afforded the pure compounds. The overall

yield of the homologous bis(dimethylsilyl)amide complexes

[SiMe₂(C₅Me₄)₂]Ln[N(SiHMe₂)₂] (11b,c) is almost double that

of the corresponding bis(trimethylsilyl)amide derivatives

[SiMe₂(C₅Me₄)₂]Ln[N(SiMe₃)₂] obtained by conventional salt

metathesis.²⁷

Crystallization of the ansa-bis(indenyl) complexes afforded

the pure rac-form in moderate to good yields. The meso-

derivatives were obtained as THF adducts which could not be

isolated in pure form. NMR spectra of the meso-isomers usually

display broad signals at room temperature.²²The yields of the

rac-isomers could be increased by prolonged thermal treatment

via consecutive refluxing in toluene and mesitylene (two-step

synthesis). This enrichment of the rac-form can be explained

in terms of donor (THF) evaporation during boiling and a rac/

meso equilibrium shift due to donor displacement.²²

In contrast, the 4,5-substituted benzoindene 5 exhibits sub-

stantially higher reactivity, and the resulting complexes 15 reveal

amazingly high racemic yields (Scheme 2). The implications

of the 4,5-benzo substitution vs the 4-phenyl substitution for

the synthetic outcome will be discussed below. The lower yield

of the lanthanum derivative 15c compared to the homologous

yttrium compound 15b probably reflects the tendency for Si-C

bond-breaking during the synthesis of these complexes at

elevated temperatures.²²Bis(fluorene) 6 gave roughly a 7% yield

1

of complex 16b as detected by H NMR.

Use of the SiMe₂-linked indene 3 carrying a methyl group

in the 2-position resulted in the isolation of the first Brintzinger-

type ansa-lanthanidocene complexes 13.¹⁶The development of

the two-step synthesis allowed the synthesis of ansa-indenyl

complexes covering the entire range of rare earth cation radii.

However, formation of derivatives of the smaller Sc(III) and

Lu(III) was hampered by long reaction times and moderate

racemic yields. The highest racemic yields were achieved for

medium-sized yttrium in complex 13b. Attempts to synthesize

the corresponding bis(trimethylsilyl)amide complex from 3 and

Y[N(SiMe₃)₂]₃failed due to decomposition reactions during

prolonged heating.^18,28This finding emphasizes the necessity

for synthetic precursors carrying sterically more flexible, readily

exchangeable amide ligands.

Elemental analyses of complexes 11, 12, 13, and 15 are

consistent with complete THF displacement at the metal center.

The enhanced thermal stability of the novel ansa-lanthanidocene

complexes is also revealed by their CI mass spectra. In addition

to the intense peaks of the parent molecular ions, fragmentation

occurred mainly due to methyl- and bis(dimethylsilyl)amide

separation. A dinuclear species was detected for the isopropyl-

idene-bridged derivative 12b, pointing out redistribution reac-

tions of the ancillary ligand.²⁹All of the isolated bis(cyclopen-

tadienyl) and rac-bis(indenyl) metallocene amide complexes

(27) Giardello, M. A.; Conticelli, V. P.; Brard, L.; Sabat, M.; Rheingold,

A. L.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10212-

10240.

(28) Addition of tetramethyldisilazane to the Y[N(SiMe₃)₂]₃reaction will

also initiate the “diene”/silylamine ligand exchange; however, this procedure

is prone to side products: Eppinger, J.; Anwander, R., unpublished results.

The reactivity of indene 4 featuring phenyl substitution in

the 4-position was markedly decreased. Only for the larger

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3083

Table 1. Selected IR and NMR Spectroscopic Data for Bis(dimethylsilyl)amide Complexes

compound

IR^aν_(SiH)(cm^-1

)

¹H NMR^bδ_(SiH)(ppm) ²⁹Si NMR^bδ_(Si)(ppm) (¹J_Si,H

)

[Me₂Si(Cp′′)₂]YN(SiHMe₂)₂(11b)

[Me₂Si(Cp′′)₂]LaN(SiHMe₂)₂(11c)

rac-[Me₂C(Ind)₂]YN(SiHMe₂)₂(rac-12b)

1789

1845

1821

2012/1793

1804

1838

1824

1759

2069/1830

1832

4.00 (dsp)

4.18 (m)

-19.9 (147)

-17.3 (150)

- (152)

3.56 (dsp)^c

2.96 (m)

rac-[Me₂Si(2-Me-Ind)₂]ScN(SiHMe₂)₂(rac-13a)

rac-[Me₂Si(2-Me-Ind)₂]YN(SiHMe₂)₂(rac-13b)

rac-[Me₂Si(2-Me-Ind)₂]LaN(SiHMe₂)₂(rac-13c)

rac-[Me₂Si(2-Me-Ind)₂]NdN(SiHMe₂)₂(rac-13d)

rac-[Me₂Si(2-Me-Ind)₂]LuN(SiHMe₂)₂(rac-13e)

[Me₂Si(2-Me-4-Ph-Ind)₂H]Y[N(SiHMe₂)₂]₂(14b)

rac-[Me₂Si(2-Me-4-Ph-Ind)₂]LaN(SiHMe₂)₂(rac-14c)

rac-[Me₂Si(2-Me-Benz-Ind)₂]YN(SiHMe₂)₂(rac-15b)

rac-[Me₂Si(2-Me-Benz-Ind)₂]LaN(SiHMe₂)₂(rac-15c) 1838

rac-[Me₂Si(2-Me-Benz-Ind)₂]LuN(SiHMe₂)₂(rac-15e) 1773

[Me₂Si(Fluo)₂]YN(SiHMe₂)₂(16b)

Ln[N(SiHMe₂)₂]₃(THF)_x(7, x ) 1, 2) (ref 16)

{ZrCl[N(SiHMe₂)₂]₂(µ-Cl)}₂(ref 30)

- (155)

2.97 (dsp)^c

3.74 (m)

- (142)

- (145)

d

-

3.29 (sp)^c

4.31 (dsp)

3.87 (m)

- (146)

- (148)

- (141)

-26.6 (133)

- (140)

- (142)

1811

2.65 (dsp)^c

3.30 (m)

2.98 (sp)^c

3.21 (sp)

e

f

-

2051-2072, 1931-1970 (sh)

4.94-5.02 (sp)

5.06 (sp)

-19.3 to -26.0 (162-171)

2136, 2093, 1948

-

^aIR spectra were recorded as Nujol mulls. ^bNMR spectra were recorded at 25 °C as C₆D₆solutions. ^cThe coupling pattern is of higher order

and rather describes the signal shape. ^dThe SiH signal could not be detected due to the paramagnetic neodymium center. ^eAs the isolation of 16b

1

failed, no IR spectrum could be recorded. ^fThe detection of the silicon sidebands was not sufficient for an accurate determination of the J_Si,H

coupling constant.

display good solubility in warm hydrocarbons, which facilitated

their spectroscopic characterization.

Spectroscopic Characterization. The IR spectra of all of

the isolated rare earth metallocene bis(dimethylsilyl)amide

complexes show a distinct shift (>200 cm^-1) of the Si-H

stretching frequency to lower energy in comparison to the

synthetic precursors 7a-c (ca. 2060 cm^-1) (see Table 1).¹⁶This

behavior is particularly pronounced for the smaller cations,

indicating the effect of enhanced Lewis acidity. The lutetium

complex rac-13e displays a shift as large as 312 cm^-1. In

general, such a distinct Si-H bond-weakening is assigned to

agostic interactions.^30-32In fact, these Si-H stretching frequen-

cies are significantly lower than those observed for â-SiH

interactions in early transition metal complexes.³²The bonding

mode seems to be even comparable to that in Mo-η²(Si-H)

Figure 2. ¹H NMR spectrum (400 MHz) of [Me₂Si(2-Me-Ind)₂]Y-

complexes (1750-1730 cm^-1).³³

[N(SiHMe₂)₂] (13b) as a solution in toluene-d₈. The solvent signals

The IR spectrum of the scandium derivative rac-13a shows

are indicated by an asterisk.

two well-separated Si-H stretching vibrations, while the spectra

of the lanthanum, yttrium, and lutetium complexes display a

interaction of the more Lewis acidic metal center. The ¹H NMR

spectrum of rac-15b shows a SiH resonance at 2.65 ppm which

less intense and broadened Si-H band, excluding a more

detailed interpretation. Interestingly, the scandium complex also

is 2.33 ppm upfield compared to the signal of 7b (Table 1).

shows a band at 1072 cm^-1attributable to a ν_as(NSi₂) stretching

Such drastic upfield shifts were also found in related zirconocene

vibration which reinforces evidence for different coordination

complexes.³²In addition, the dramatic Si-H upfield shifts seem

modes of the Ln-N(SiHMe₂)₂moiety.

to be associated with the presence of extended aromatic ring

NMR spectroscopic examinations of the diamagnetic com-

systems, increasing in the order 1 < 2, 3, 4 < 5 < 6.^34,35

plexes 11b,c, rac-12b, rac-13a-c,e, 14b, rac-14c, rac-15b,c,

and 16b were performed to clarify the significant perturbation

Examination of the SiH coupling pattern indicates the

presence of a J_Ln,Hcoupling in all of the ansa-metallocene amide

of the SiH environment. The findings are discussed for the

1

complexes. Whereas the complexes of the metals with I > /₂

(Sc, La, Lu) produce poorly resolved multiplets, the SiH

resonances of the yttrocene amide complexes resemble a nonet,

which is derived from a doublet of septets, as peak intensities

suggest. The doublet splitting in the range of 2.9 (11b)-5.0

yttrium complexes in more detail. The H NMR spectrum of

rac-13b is representatively shown in Figure 2.

A strong dependency of the SiH signal on the nature of the

metal center and the ligands was observed. In accordance with

the IR spectra, the smaller metal cations induce a larger upfield

shift of the SiH signal, correlating with an enhanced agostic

3

Hz (rac-15b) which occurs in addition to the J_H,Hcoupling

(about 2.5 Hz) can be assigned to a H‚‚‚Y‚‚‚H coupling.³⁶

Relatively small ¹H-²⁹Si coupling constants document a

significant lengthening of the SiH bond (Table 1),³⁷the value

of 133 Hz for rac-15b suggesting a considerable activation of

(29) (a) Ho¨ck, N.; Oroschin, W.; Paolucci, G.; Fischer, R. D. Angew.

Chem. 1986, 98, 748-749; Angew. Chem., Int. Ed. Engl. 1986, 25, 738-

739. (b) Stern, D.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1990, 112,

9558-9575.

(30) Herrmann, W. A.; Huber, N. W.; Behm, J. Chem. Ber. 1992, 125,

1405-1407.

(31) Rees, W. S.; Just, O.; Schumann, H.; Weimann, R. Angew. Chem.

1996, 108, 481-483; Angew. Chem., Int. Ed. Engl. 1996, 35, 419-422.

(32) Procopio, L. J.; Carrott, J. J.; Berry, D. H. J. Am. Chem. Soc. 1994,

116, 177-185.

(33) Lou, X. J.; Kubas, G. J.; Burns, C. J.; Bryan, J. C.; Unkefer, C. J.

J. Am. Chem. Soc. 1995, 117, 1159-1160.

(34) For the interpretation of analogous upfield shifts due to aromatic

ring currents, see: (a) Haigh, C. W.; Mallion, R. B. Prog. Nucl. Magn.

Reson. Spectrosc. 1980, 13, 303-344. (b) Haigh, C. W.; Mallion, R. B.

Org. Magn. Reson. 1972, 4, 203-228.

(35) Calculations on the basis of the model of Haigh and Mallion³⁴point

out that the ring current only partly contributes to the high upfield shift of

the SiH proton.

3084 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

the Si-H bond by metal coordination.^33,38,39The recorded ²⁹Si

resonances range from -26.6 (rac-11b) to -17.3 (rac-15b) and

from -32.5 (rac-11b) to -15.9 ppm (rac-15b) for N(SiHMe₂)₂

and the SiMe₂-ansa-bridge, respectively. The proton-decoupled

²⁹Si NMR spectrum of rac-15b displays two doublets due to

²⁹Si-⁸⁹Y coupling of both the dimethylsilylamide moiety (12.2

Hz) and the dimethylsilyl bridge (1.2 Hz).⁴⁰Perhaps the most

striking feature of the new ansa-metallocene amide complexes

is their rigidity in solution, as evidenced by the persistence of

1

the H‚‚‚Y‚‚‚H coupling. The H NMR spectra of complexes

13a,b and 15b in toluene-d₈reveal the absence of any significant

signal shift or change of coupling pattern in the temperature

1

range from -90 to 130 °C. The H and ¹³C resonances of the

methylsilyl(amido) group of the racemic compounds appear as

two doublets and a doubled singlet, respectively, as expected

for two methyl groups with different chemical environments.

In contrast, the C_2V-symmetric complexes 11b and 11c display

only one doublet and a singlet, respectively. However, the latter

complexes show the same SiH coupling pattern as the C₂-

symmetric derivatives, indicating that this coupling pattern

results from Ln-H coupling and not from the diastereotopy of

the two methyl groups.

Figure 3. ⁸⁹Y NMR spectra of rac-15b without (ca. 25 °C; a) and

with (30.0 ( 0.1 °C; b) temperature control.

The presence of a Y-H coupling was unequivocally proven

by ⁸⁹Y NMR spectroscopy. The ⁸⁹Y NMR spectrum of rac-

15b shows a triplet with a ⁸⁹Y-¹H coupling constant of 4.7 Hz

(Figure 3b). This relatively small coupling constant⁴¹is in good

1

agreement with the value derived from the H NMR spectrum

(J_Y,H) 5.0 Hz). The visible ²⁹Si satellites display a coupling

constant of 19.5 Hz.⁴⁰The shielding ring current of the aromatic

indenyl ligands results in a dramatic upfield shift of the ⁸⁹Y

signal to -96.7 ppm compared to that of the amide precursor

7b (δ ) 444 ppm).^16,42The distinct temperature dependency of

this chemical shift was demonstrated by measurements at ca.

25 °C (δ ) -96.7 ppm) and constant 30 °C (δ ) -93.5 ppm).

(36) The size of the coupling constant is attributable to a ³J_Y,SiHcoupling

rather than a ¹J_Y,Hone. The higher order coupling pattern of the SiH proton

in the rac-form can be assigned to coupling with two diastereotopic methyl

groups or additional through-space J_H,Hcoupling via Y.

(37) Lukevics, E.; Pudowa, O.; Sturkovich, R. Molecular Structure of

Organosilicon Compounds; Ellis-Horwood: Chichester, U.K., 1989. Silicon

1

hydrides generally display J_Si,Hvalues in the range 160-200 cm^-1

.

(38) ¹J_Si,Hvalues for M-(η²-SiH). (a) 136 Hz for M ) Cr: Driess, M.;

Reigys, M.; Pritzkow, H. Angew. Chem. 1992, 104, 1514-1516; Angew.

Chem., Int. Ed. Engl. 1992, 31, 1510-1512. (b) 92 Hz for M ) Ti: Ohff,

A.; Kosse, P.; Baumann, W.; Tillack, A.; Kempe, R.; Go¨rls, H.; Burlakov,

V. V.; Rosenthal, U. J. Am. Chem. Soc. 1995, 117, 10399-10400. (c) 20-

70 Hz for M ) Mo: Luo, X.-L.; Kubas, G. J.; Bryan, J. C.; Burns. J. C.;

Unkefer, C. J. J. Am. Chem. Soc. 1994, 116, 10312-10313. (d) Crabtree,

R. H.; Pritzkow, H. Angew. Chem. 1993, 105, 828-845; Angew. Chem.,

Int. Ed. Engl. 1993, 32, 789-805. (e) Crabtree, R. H.; Hamilton, D. G.

AdV. Organomet. Chem. 1988, 28, 299-358. (f) Schubert, H. AdV.

Organomet. Chem. 1990, 30, 151-187.

Figure 4. NOE enhancements and solid-state structure bonding

distances of the two diastereotopic methyl groups of the amide moiety

of rac-15b.

Without temperature regulation, the signal appears as a nonin-

terpretable pseudoquartet (Figure 3a).⁴³

The â-SiH agostic rigidity of the amide fragment could be

1

further corroborated by H NMR-NOE spectroscopy of rac-

(39) σ-Bond metathesis reactions involving Ln-C/Si-H transpositions

were reported to occur in hydrosilylation reactions: (a) Sakura, T.;

Lautenschlager, H.-J.; Tanaka, M. J. Chem. Soc., Chem. Commun. 1991,

40-41. (b) Molander, G. A.; Julius, M. J. Org. Chem. 1992, 57, 6347-

6351. (c) Onozawa, S.; Sakakura, T.; Tanaka, M. Tetrahedron Lett. 1994,

35, 8177-8180. (d) Ziegler, T.; Folga, E. J. Organomet. Chem. 1994, 478,

57-65. (e) Molander, G. A.; Nichols, P. J. J. Am. Chem. Soc. 1995, 117,

4415-4416. (f) Radu, N. S.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117,

5863-5864. (g) Fu, P.-F.; Brard, L.; Li, Y.; Marks, T. J. J. Am. Chem.

Soc. 1995, 117, 7157-7168. (h) Voskoboynikov, A. Z.; Parshina, I. N.;

Shestakova, A. K.; Butin, K. P.; Beletskaya, I. P.; Kuz’mina, L. G.; Howard,

J. A. K. Organometallics 1997, 16, 4041-4055.

15b. Due to the fixed arrangement, the two diastereotopic

methyl(silylamide) groups display only one intense NOE signal

between the less upfield-shifted methyl resonance and the signal

of the hydrogen atom H3 of the benzoindenyl moiety (13.5%

enhancement). All of the other enhancements resulting from

proton coupling with the amide ligand fragment are below 1%

(Figure 4). These findings are in accordance with the observed

distances in the solid-state structure which reveal a relatively

close contact of ca. 3.2 Å between the averaged methyl hydrogen

atoms of the amide ligand and the H3 hydrogen atom. This

2

(40) A J_Si,Ycoupling constant of 7.7 Hz was reported for a siloxide

complex, Y₂(OSiPh₃)₆: Coan, P. S.; Hubert-Pfalzgraf, L. G.; Caulton, K.

G. Inorg. Chem. 1992, 31, 1262-1267.

(42) For a systematic investigation of ⁸⁹Y chemical shifts in metal-

organic compounds, see: (a) Evans, W. J.; Meadows, J. H.; Kostka, A. G.;

Closs, G. L. Organometallics 1985, 4, 324-326. (b) Schaverien, C. J.

Organometallics 1994, 13, 69-82.

(41) ¹J_Y,Hcoupling constants are in the range of 15-30 Hz: Rheder, D.

In Transition Metal Nuclear Magnetic Resonance; Pregosin, P. S., Ed.;

Elsevier: Amsterdam, 1991; pp 4-51. ²J_Y,H) 3.6 Hz for the Y(µ-CH₃)Y

moiety in [(CH₃C₅H₄)₂Y(µ-CH₃)]₂: Evans, W. J.; Meadows, J. H.; Wayda,

A. L.; Hunter, W. E.; Attwood, J. L. J. Am. Chem. Soc. 1982, 104, 2008-

2014.

(43) Similar effects have been reported for ¹⁰³Rh NMR: Mann, B. E. In

Transition Metal Nuclear Magnetic Resonance; Pregosin, P. S., Ed.;

Elsevier: Amsterdam, 1991; pp 177-215.

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3085

Table 2. Selected Structural Parameters for Lanthanidocene Complexes

11c (Ln ) La)

rac-13b^c(Ln ) Y)

rac-13e^c(Ln ) Lu)

rac-15b (Ln ) Y)

rac-15e (Ln ) Lu)

Bond Distances (Å)

av. Ln1-C_Cp

min. Ln1-C_Cp

max. Ln1-C_Cp

Ln1-C_g1^a

Ln1-C_g2^a

Ln1-N1

2.799

2.663

2.614

2.666

2.627

2.738(2)

2.867(3)

2.523(1)

2.526(1)

2.449(3)

3.246(1)

3.244(1)

3.494(1)

2.70(3)

2.66(4)

1.661(3)

1.663(3)

1.39(3)

1.38(4)

2.627(3)

2.697(3)

2.371(2)

2.237(4)

3.082(1)

3.387(2)

2.54(2)

1.666(1)

1.45(2)

2.574(3)

2.651(3)

2.315(2)

2.159(4)

3.116(1)

3.347(1)

2.63(2)

1.676(2)

1.42(5)

2.609(3)

2.719(4)

2.378(2)

2.372(2)

2.274(3)

3.028(1)

3.034(1)

3.416(1)

2.37(3)

2.38(3)

1.660(3)

1.661(3)

1.45(3)

1.47(3)

2.577(6)

2.670(6)

2.328(2)

2.327(2)

2.173(5)

3.277(2)

3.041(2)

3.384(2)

3.05(2)

2.66(2)

1.656(6)

1.682(6)

1.45(2)

Ln1-Si1

Ln1-Si2

Ln1-Si3

Ln1-H1^b

Ln1-H2^b

N1-Si1

N1-Si2

Si1-H1^b

Si2-H2^b

Bond Angles (deg)

C_g1-Ln1-C_g2^a

Si1-N1-Si2

Ln1-N1-Si1

Ln1-N1-Si2

N1-Si1-H1

N1-Si2-H2

H1-Ln1-H2

118.53(2)

154.9(2)

102.6(1)

102.5(1)

103(1)

101(2)

109(1)

123.14(2)

153.3(2)

103.4(1)

100(1)

119.1(8)

125.3(2)

144.0(2)

108.0(1)

98(2)

115.6(14)

122.75(1)

160.1(2)

99.5(2)

99.7(1)

98(1)

121.4(10)

124.58(2)

139.3(4)

117.1(3)

103.4(3)

103.7

104.6

113.4

Dihedral Angles (deg)

Ln1-N1-Si1-H1

Ln1-N1-Si2-H2

-1(1)

4(2)

3(1)

-3(1)

4.3(2)

-4.3(2)

6(1)

3(1)

-11.5

-7.8

^aC_g) ring centroid. ^bLn-H and Si-H distances have to be discussed carefully due to the location of the hydrogen atoms close to two heavy

atoms. ^cAs the metallocenes rac-13b und rac-13e crystallize in a C2/c-symmetric unit cell, the atoms were labeled differently: C_g2 ) C_g1a; Si1

) Si2; Si2 ) Si2a; Si3 ) Si1; H1 ) H2; H2 ) H2a.

in an agostic manner. So far, it was the asymmetric, monoagostic

approach of one SiMe₃moiety exclusively which has been found

in heteroleptic metallocene complexes carrying silylamide as

well as silylated hydrocarbon substituents.^9,44-46Although this

series of ansa-metallocene complexes exhibits a similar mo-

lecular coordination geometry, both ansa-ligand and metal

variation have significant implications for the â-SiH agostic

interaction of the silylamide fragment. The present close

Ln‚‚‚Si contacts ranging from 3.028(1) to 3.246(1) Å already

resemble Ln-Si σ-bond distances,⁴⁷suggesting an appreciable

Figure 5. Definition of twisted geometry angles summarized in

interaction in the solid state, which remains in solution, as

Table 3.

indicated by the spectroscopic investigations discussed above.

Additionally, close Ln‚‚‚H contacts⁴⁸(2.38(3)-2.70(3) Å) at

rigidity of the silylamide moiety explains the strong dependency

the upper end of covalent Ln-H bonds⁴⁹complete the formation

of agostically fused Ln-N-Si-H four-membered rings. These

rings display only small torsional angles (1(1)-6(1)°) and are

located in a plane almost parallel to the bisector of the two

of the Si-H upfield shift on the type of ansa-ligand as described

above: the SiH group located below the shielding ring cur-

rent^34,35of the aromatic ligand is sensitive toward both a

decreasing cationic radius and extension of the fused aromatic

rings into the environment of the amide fragment.

(44) Stern, D.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1990, 112,

9558-9575.

Molecular Structures of the ansa-Lanthanidocene Amides

11c, rac-13b, rac-13e, rac-15b, and rac-15e

(45) In theoretical studies the asymmetric geometry has been attributed

to an interaction between the electron-deficient Ln(III) center and the

electron density of the Si-C bond: (a) Tatsumi, K.; Nakamura, A. J. Am.

Chem. Soc. 1987, 109, 3195-3206. (b) Bursten, B. E.; Fang, A. Inorg.

Chim. Acta 1985, 110, 153-160.

General Features. Single-crystal X-ray structural determina-

tions were carried out on selected ansa-lanthanidocene amide

complexes in order to unambiguously establish the C₂symmetry

of the bis(indenyl) complexes and to detect any systematic

structural features. For ease of comparison, key parameters of

the metallocene amide complexes are listed in Table 2. Details

of the ligand framework are described by several angles between

selected planes and compared to relevant data from the literature

(Figure 5, Table 3).

All of the complexes display an almost perfect trigonal planar

arrangement of the amide and the ansa-ligand. The C_g-Ln-

C_gangle increases slightly with decreasing cation size (C_gis

the center of the five-membered ring). In all of the molecular

structures, both of the Si-H moieties approach the Ln(III) center

(46) Correspondingly, the interactions discussed in this paper involve

the electron density of the SiH fragment: Scherer, W. Ph.D. Thesis,

Technische Universita¨t Mu¨nchen, 1993.

(47) (a) A comparable Sm-Si distance of 3.0524(8) Å was reported for

Cp*₂Sm[SiH(SiMe₃)₂]: Radu, N. S.; Tilley, T. D.; Rheingold, A. L. J. Am.

Chem. Soc. 1992, 114, 8293-8295. (b) (Me₃SiCH₂)Y[(µ-(CH₂)₂SiMe₂][(µ-

OCH₃)Li(thf)₂]₂reveals a Y-Si distance of 3.147(2) Å: Evans, W. J.; Boyle,

T. J.; Ziller, W. J. J. Organomet. Chem. 1993, 462, 141-148.

(48) All SiH hydrogens atoms were located in difference Fourier maps

and successfully refined. Of course, the usual caution regarding the accuracy

of hydrogen positions in heavy atom structures was applied. In fact, though

a lengthening of the agostically interacting Si-H bonds should be expected,

the refined SiH positions yield bond lengths of 1.43-1.47 Å, which are

even shorter than normal SiH distances in hydrosilanes (1.47-1.50 Å;

Lukevics, E.; Pudowa, O.; Sturkovich, R. Molecular Structure of Organo-

silicon Compounds; Ellis-Horwood: Chichester, U.K., 1989).

3086 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

Table 3. Selection of Twisted Geometry Parameters (deg) for Lanthanidocene Amide and Comparable Complexes

compound

R^a

â^a

γ^a

Ω^a

Θ^a

11c

102.8(1)

100.9(1)

99.7(2)

98.7(2)

98.1(3)

103.1(2)

98.2

16.6(2)/18.1(2)

19.9(2)

19.8(2)

17.9(2)/17.6(2)

18.5(3)/18.6(3)

12.3(2)/12.3(2)

16.6/15.8

-

68.2(2)

61.2(2)

59.7(2)

66.0(1)

65.6(2)

82.5(1)

66.1/69.2

45.2

2.56(8)

5.31(9)

4.5(2)

7.74(9)

11.0(7)

45.8(3)

6.7/15.0

-

rac-13b

rac-13e

rac-15b

rac-15e

1.8(2)

1.5(2)

5.5(2)/4.9(2)

5.3(3)/2.3(3)

3.0(2)/4.1(1)

rac-12b(THF) (ref 23)

[Me2Si(Cp^Menthyl)₂]Y-N(SiMe₃)₂(ref 27)

Cp*₂YN(SiMe₃)₂(ref 50)

-

15.5

14.7

-

(C₅H₄Et)₂YN(SiMe₃)₂(ref 51)

{[Me₂Si(Cp′′)₂]ThH₂}₂(ref 52)

[Me₂Si(2-Me-Ind)₂]ZrCl₂(ref 25b)

[Me₂Si(2-Me-Benz-Ind)₂]ZrCl₂(ref 25c)

-

47.19

73.3/70.6

60.2

-

b

102.6/98.5

94.4

13.1/16.2 11.2/16.8

17.4/16.8

17.0

-

2.6/5.0

1.7

1.3

0.8

94.8

61.6

^aFor angle definitions see Figure 5. ^bNo hydrogen atom positions available.

cyclopentadienyl and indenyl rings, respectively. The strong

symmetric Ln‚‚‚SiH interaction causes extremely widened Si-

N-Si angles (144.0(2)-160.1(2)°) and a concomitant significant

contraction of both Ln-N-Si angles (99.5(2)-108.0(1)°); the

range observed for the amide precursors 7 is 109.0(3)-123.2-

(2)°.¹⁶The two methyl groups of each silylamide silicon atom

are mirrored by the Si-N-Si plane. Interestingly, the lutetium

complex rac-15e features a slightly perturbated silylamide

coordination, probably as a result of peculiar steric constraints

(vide infra).

Details of the Molecular Structures. Compound [Me₂-

Si(Cp′′)₂]La[N(SiHMe₂)₂] (11c) crystallizes in the triclinic space

group P1h. The C₂-symmetric ansa-indenyl compounds exhibit

centrosymmetric unit cells of C2/c symmetry for the homolo-

gous ansa-metallocenes rac-13b and rac-13e and of P1h sym-

metry for rac-15b and rac-15e, respectively.

The molecular structure of the C_2V-symmetric complex 11c

(Figure 6) resembles those of the numerous structurally char-

acterized complexes of type “Cp₂LnX”, in particular that of

Cp*₂Y[N(SiMe₃)₂],⁵⁰adopting the typical bent metallocene

arrangement.⁹The La-C distances range from 2.738(2) to

2.786(7) Å, the ipso-carbon atom being the closest to the La-

(III) cation. The cyclopentadienyl rings are tilted against the

Si3-C_ipsoaxis toward the metal center (â ) 16.6(2)°/18.1(2)°),

while the C_ipso-Si3-C_ipsoangle is only slightly contracted (R

) 102.8(1)°) (Figure 5 and Table 3). Such a “U-shaped” (â .

0) coordination of the linked cyclopentadienyl ligand seems to

be directed by the large metal center. These angle distortions

generate an ipso carbon atom of enhanced sp³-character. In

comparable actinide and zirconocene complexes, the deviation

of the “V-shaped” (â ≈ 0) ligand coordination appears less

pronounced (Table 3). The smaller Zr(IV) centers can be

accommodated by ansa-ligands via a more contracted angle R

(94.4-94.8°) and a comparable tilt angle â (16.8-17.4°),^25b,c

whereas the larger Th(IV) complex displays tentatively less tilted

cyclopentadienyl planes (â ) 11.2-16.8°).^52,53

Figure 6. PLATON⁸⁰drawing of 11c. Atoms are represented by

thermal ellipsoids at the 50% level. Except for H(1) and H(2), all

hydrogen atoms are omitted for clarity. For selected distances and

angles, see Tables 2 and 3.

(Ω ) 73.3/70.6°) and the propylidene-bridged ansa-complex

rac-12b(THF) (Ω ) 82.5).²³Such large bite angles are assumed

to facilitate the diagostic approach of the dimethylsilylamide

moiety to the Lewis acidic metal ion. The La-N bond length

of 2.449(3) Å compares well with the La-N distances in nine-

coordinated [Cp*₂La][µ-(C₁₂H₈N₂)] (2.452(2) Å)⁵⁴and appears

markedly elongated compared to those in eight-coordinated

complex Cp*₂La(NHMe)(H₂NMe) (2.32(1) Å)⁵⁵and its five-

coordinated synthetic precursor (2.395(5)-2.416(5) Å).¹⁵The

La-Si (3.2460(9)/3.2440(9) Å) and La-H (2.70(3)/2.66(4) Å)

contacts are slightly elongated compared to those of σ-bonded

silicon⁴⁷and bridging hydride ligands,⁴⁹respectively, taking into

Despite the distinctly U-shaped ansa-ligand in 11c, the large

lanthanum cation forces a large bite angle Ω of 68.2(2)°, which

is exceeded only by those of complex {[Me₂Si(Cp′′)₂]ThH₂}₂

(51) Schumann, H.; Rosenthal, E. C. E.; Kociok-Ko¨hn, G.; Molander,

G. A.; Winterfeld, J. J. Organomet. Chem. 1995, 496, 233-240.

(52) Fendrick, C. M.; Schertz, L. D.; Day, V. W.; Marks, T. J.

Organometallics 1988, 7, 1828-1839.

52

(49) Examples of Ln-H bond lengths from X-ray diffraction data include

the following. (a) 2.19/2.17 Å in [(C₅H₄Me)₂Y(µ-H)(THF)]₂: Evans, W.

J.; Meadows, J. H.; Wayda, A. L.; Hunter, W. E.; Atwood, J. L. J. Am.

Chem. Soc. 1982, 106, 2008-2014. (b) 2.35 Å in [(C₅H₅)₂Y(µ-Cl)]₂(µ-H)-

AlH₂(OEt₂): Lobovskii, B.; Soloveichik, G. L.; Erofeev, A. B.; Bulichev,

B. M.; Bel’skii, V. K. J. Organomet. Chem. 1982, 235, 151-158. (c) 1.98/

2.13 Å in [(C₅H₅)₂Lu(µ-H)(THF)]₂: Schumann, H.; Genthe, W.; Hahn, E.;

Hossain, M. B.; van der Helm, D. J. Organomet. Chem. 1986, 299, 67-

84. (d) 2.59/2.25/2.29 Å in [(BH₃)₂La(THF)₅][(BH₃)₄La(THF)₂]: Bel’skii,

V. K.; Sobolev, A. N.; Bulychev, B. M.; Alikhanova, T. Kh.; Kurbonbekov,

A.; Mirsaidov, U. Koord. Khim. 1990, 16, 1963-1969.

(53) The more covalent dimethylsilyl-bridged ferrocenyl complexes

exhibit tilt angles â as large as 40.0°, affording a nearly planar arrangement

of both cyclopentadienyl rings: (a) Rulhuns, R.; Lough, A. J.; Mannus, I.

Angew. Chem. 1996, 108, 1929-1931; Angew. Chem., Int. Ed. Engl. 1996,

35, 1805-1807. (b) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer,

B. Angew. Chem. 1996, 108, 1927-1929; Angew. Chem., Int. Ed. Engl.

1996, 35, 1863-1864. (c) Stoeckli-Evans, H.; Osborne, A. G.; Whiteley,

R. H. HelV. Chim. Acta 1976, 59, 2402-2406.

(54) Scholz, J.; Scholz, A.; Weimann, R.; Janiak, C.; Schumann, H.

Angew. Chem. 1994, 106, 1220-1223; Angew. Chem., Int. Ed. Engl. 1994,

33, 1171-1174.

(50) Den Haan, K. H.; De Boer, J. L.; Teuben, J. H.; Speck, A. L.; Kojic-

Prodic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726-1733.

(55) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992,

114, 275-294.

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3087

Figure 7. PLATON⁸⁰drawing of rac-13e. Atoms are represented by

thermal ellipsoids at the 30% level. Except for H(2) and H(2a), all

hydrogen atoms are omitted for clarity. For selected distances and angles

see Tables 2 and 3. rac-13b is isostructural.¹⁴

Figure 9. PLATON⁸⁰drawing of rac-15e. Atoms are represented by

thermal ellipsoids at the 30% level. Except for H(1) and H(2), all

hydrogen atoms are omitted for clarity. For selected distances and angles

see Tables 2 and 3.

15b (2.274(3) Å) correlate well with the corresponding distances

in seven-coordinated yttrium amide complexes, e.g., Cp*₂-

Y[N(SiMe₃)₂] (2.274(5) Å) and {(R)-Me₂Si(Me₄C₅)[(-)-men-

thyl-C₅H₃]}Y[N(SiMe₃)₂] (2.211(8), 2.281(8) Å).^44,50Remark-

ably, complex rac-13e features a Lu-N bond length of 2.159(4)

Å, which is even shorter than that in the five-coordinate amide

precursor (7e, 2.184(3)-2.238(3) Å). The shortest Ln-N bond

reported so far was observed in the polyagostic complex Nd-

(NiPr₂)[(µ-Me)(µ-NiPr₂)AlMe₂][(µ-Me)₂AlMe₂] (2.168(2) Å).^58b

The present geometrical parameters depend on the cation size

and the type of ansa-ligand. Complexes rac-13b and rac-13e

display bite angles Ω (61.2(1)°, 59.7(2)°) in the range of those

of related zirconocene complexes.^25b,cFor comparison, the bite

angles present in nonlinked cyclopentadienyl and indene deriva-

tives Cp*₂Y[N(SiMe₃)₂],⁵⁰(C₅Me₄Et)₂Y[N(SiMe₃)₂],⁵¹and [(2,4,7-

Me₃C₉H₄)₂Y(µ-H)]₂^12eare considerably smaller (45.2/47.2/46.6/

47.8°).⁵⁰The molecular structures of the benzoindenyl-derived

complexes rac-15b and rac-15e show relatively large bite angles

of 66.0(1)° and 65.6(2)°, respectively, comparable to that of

the lanthanum complex 11c. Additionally, small but significant

differences of the geometrical parameters â, γ, and Θ (Table

3) are detected for the rac-derivatives of complexes 13 and 15.

The comparatively slightly decreased (â) and increased (γ, Θ)

values in complexes 15 are probably due to the steric interaction

of the silylamide moiety with the 4,5-benzo substituents.

Particularly, the latter parameters γ and Θ defining the curvature

of the aromatic system away from the silyl groups of the amide

(rac-15b, γ ) 5.5(2)/4.9(2)°; rac-15e, 5.3(3)/2.3(3)) and the

distortion of the silylamide plane (Θ ) 7.7(1)°, 11.0(7)°),

respectively, exceed the values of the related zirconium complex

[Me₂Si(2-Me-Benz-Ind)₂]ZrCl₂.^25c

Figure 8. PLATON⁸⁰drawing of rac-15b. Atoms are represented by

thermal ellipsoides at the 50% level. Except for H(1) and H(2), all

hydrogen atoms are omitted for clarity. For selected distances and angles

see Tables 2 and 3.

account the different cation size and coordination number.⁵⁶

Similar bonding parameters were recently detected in the single-

crystal neutron diffraction structures of the monoagostic complex

Cp*La[CH(SiMe₃)₂]₂(La‚‚‚Si, 3.35(1)-3.42(1) Å)⁵⁷and the

polyagostic complex Nd[AlMe₄]₃(Al₂Me₆)_0.5(Nd‚‚‚H, 2.65(1)

Å).^58a

The X-ray structure analyses of the bis(indenyl) complexes

rac-13b, rac-13e, rac-15b, and rac-15e reveal the trans-

coordination of the chelating ligands, which determines the C₂

symmetry of the thermodynamically more favorable rac-

complexes as presented in Figures 7-9. Their overall geometry

is analogous to that of the C_2V-symmetric metallocene amide

11c. The Y-C and Lu-C bond distances lie in the expected

range; however, the π-ancillary ligation of the benzoindenyl

system shows considerable distortions (∆Ln-C_Cp) 0.07-0.11

Å). The Y-N bond distances in rac-13b (2.237(4) Å) and rac-

The Si-N-Si angle deformation detected in the [N(Si-

HMe₂)₂] moiety originates from the strong diagostic interaction;

however, there seems to be no clear correlation between the

cation size and this intrinsic enlargement of the Si-N-Si angles.

The agostic Ln-Si and Ln-H distances decrease in the order

11c (La) > rac-13e (Lu) > rac-13b (Y) > rac-15b (Y) and

are in the range of covalent bonds for the latter one.^47,48The

angle of 153.3(2)° in rac-13b is only slightly smaller than that

of 11c, ranging between those of rac-13e (144.0(2)°) and rac-

15b (160.1(2)°). This angle expansion appears to be limited

mainly by steric interaction between the SiMe₂H groups and

(56) Shannon, R. D. Acta Crystallogr. 1976, A32, 751-767.

(57) Klooster, W. T.; Brammer, L.; Schaverien, C. J.; Budzelaar, P. H.

M. J. Am. Chem. Soc. 1999, 121, 1381-1382.

(58) (a) Klooster, W. T.; Lu, R. S.; Anwander, R.; Evans, W. J.; Koetzle,

T. F.; Bau, R. Angew. Chem. 1998, 110, 1326-1329; Angew. Chem., Int.

Ed. Engl. 1998, 37, 1268-1270. (b) Evans, B. J.; Anwander, R.; Ziller, J.

W.; Khan, S. I. Inorg. Chem. 1995, 34, 5927-5930.

3088 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

Figure 10. Disordering model of the silylamide moiety in rac-15e.

the ansa-ligand framework: the closest distance⁵⁹measured

between the amide moiety and the hydrogen atoms of the

aromatic systems are almost equal for all of the complexes and

just slightly below the sum of the van der Waals radii (11c,

1.96 Å; rac-13b, 2.16 Å; rac-13e, 2.24 Å; rac-15b, 2.10 Å;

rac-15e, 2.18 Å). For example, the bis(indenyl) complexes

feature the closest contact between the C3-H hydrogen and

the corresponding methylsilyl group. The interaction of the

silylamide moiety with the 4,5-benzo substituent is particularly

pronounced in complex rac-15e, as revealed by the compara-

tively long Lu-N bond distance of 2.173(5) Å and a crystal-

lographically disordered SiHMe₂moiety (Figure 10). Extended

embedding of the smaller lutetium center into the ligand bite

sterically disfavors a strong â-SiH diagostic interaction, which

would cause an increased interaction of the methyl groups of

the silylamide ligand and the 2-Me substituent of the ansa-

system. To reduce a sterically stressed, staggered conformation

of the SiHMe₂groups, rotation about the Si-N bond occurs.

This peculiar situation is expressed in the extreme values of γ

(5.3(3)°/2.3(3)°) and θ (11.0(7)°) and a comparatively small

Si-N-Si angle of 139.3(4)°.

A correlation between Si-N-Si angles and their pertinent

Si-N distances reveals that the electronic situation in the

agostically tensioned bis(dimethylsilyl)amide fragments cannot

be described in terms of a simple rehybridization model only

(Figure 11).

All of the nonmetallocene bis(dimethylsilyl)amide moieties

approximately fit one function (plot A), as derived from a

hybridization model.⁶⁰Although the Si-N-Si angles exhibit

enhanced flexibility, the data from both µ₁- and µ₂-coordinated

bis(dimethylsilyl)amide fragments fit considerably well. The

angle/distance correlation of the ansa-metallocene silylamide

complexes described herein can be fitted by a second, steeper

plot B. It is only the disordered SiHMe₂moiety of complex

rac-15e which significantly deviates from this plot B, even

approaching plot A. Apparently, these complexes experience

no significant change of hybridization at the nitrogen atom:

the Si-N distances remain comparable to the educt amide

Figure 11. Correlation between Si-N-Si angles and their pertinent

Si-N distances in bis(dimethylsilyl)amide complexes. The correlation

functions^57bwere derived from a hybridization model. Data points in

parentheses result from disordered bis(dimethylsilyl)amide moieties and

were not taken into account for fitting the functions.

complexes (7a-e) when the Si-N-Si angle is enlarged.

Therefore, it can be assumed that the observed Si-H diagostic

interaction not only is due to an attractive interaction between

the silicon hydrogen atoms and the metal center but also affects

the electron distribution of the entire silylamide ligand.

So far, the question remained unsolved of why these ansa-

metallocene complexes do not show the usually observed agostic

interaction of one silyl group of the amide ligand (Figure

12b)^44,50,51,57but display this unique symmetric approach of both

SiH moieties (Figure 12a).^58,61,62According to theoretical

calculations,²²the present agostic interaction is mainly ionic,

taking place via the attraction of the negative partial charge of

the SiH hydrogen atoms and the Lewis acidic Ln(III) metal

centers. However, covalent bonding contributions cannot be

neglected, as revealed by the peculiar behavior of the SiH group

in spectroscopic examinations. Such a diagostic interaction leads

to a significant decrease of the molecule’s total energy, with

the Si-N-Si angle deformation energy of 0.1-1.0 kcal/mol

being compensated by the â-SiH diagostic interaction, which

can be estimated as 6.4 kcal/mol.²²

Kinetic and Thermodynamic Limitations of the Extended

Silylamide Route

(59) As hydrogen atom locations on the basis of X-ray data are not very

reliable, the closest possible distances were calculated by a simple

trigonometric approach, assuming free rotation of the CH₃groups around

their bond axis. Calculations were done on the basis of the observed C-C

distances, combined with the following neutron diffraction data for hydrogen

atoms: C_alkyl-H ) 1.113 Å; C_aromat-H ) 1.090 Å; H-C-Si ) 107°.

The hydrogen atoms of the aromatic systems were placed on the bisector

of the C-CH-C angles.

(60) (a) The correlation between the Si-N-Si angles and the pertinent

Si-N distances was based on 72 data points, taken from 17 compounds

(data sources: CSD, refs 15, 16 and this publication). (b) Assuming a linear

correlation of the p-orbital content P in the spⁿhybrid and the Si-N distance

d (d ) S(0) + kP), from cos R ) (P - 1)/P (R ) Si-N-Si angle) the

correlation function d ) S(0) + k/(1 - cos R) can be obtained. This function

was fitted to the data points by least-squares refinement. The resulting

parameters are, for the metallocene silylamides, S(0) ) 1.440 and k ) 0.425

(rms ) 0.0132) and, for unperturbated monoagostic silylamides, S(0) )

1.300, k ) 0.881 (rms ) 0.0154). For 180° > R > 90°, theoretical Si-N

bond distances in the range 1.653 < d < 1.866 Å and 1.530 < d < 2.179

Å can be derived for metallocene silylamide complexes and for unpertur-

bated silylamide complexes, respectively.

General Considerations. The synthetic yields of the ansa-

lanthanidocene complexes presented in Scheme 1 markedly

depend on the nature of the chelating ligand. For example, the

low reactivity of the 2,4-substituted bis(indene) 4 is in contrast

to the high crystallized racemic yields obtained for the similarly

bulky bis(benzoindene) 5. In the following, both thermodynamic

and kinetic limitations of this extended silylamide route are

addressed on the basis of pK_aand steric factors. Amine

elimination reactions as described in Schemes 1 and 2 represent

(61) A diagostic interaction of a bis(dimethylsilyl)alkyl moiety has been

described recently: Sekiguchi, A.; Ichnohe, M.; Takahashi, M.; Kabuto,

C.; Sahurai, H. Angew. Chem. 1997, 109, 1577-1579; Angew. Chem., Int.

Ed. Engl. 1997, 36, 1533-1534. In contrast to the interactions described

by us, this â-SiH diagostic interaction involves two different metal centers,

Li⁺cations, and hence insignificantly increased Si-C-Si angles.

(62) For polyagostic Ln‚‚‚Me interactions, see: Tilley, T. D.; Andersen,

R. A.; Zalkin, A. Inorg. Chem. 1984, 23, 2271-2276.

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3089

Figure 12. Symmetric (a) and asymmetric (b) coordination mode of

the silylamide moiety.

Scheme 3. Reaction Mechanism Proposed for the Formation

of ansa-Metallocene Amide Complex 11b via the Extended

Silylamide Route Based on the Isolated Intermediates 17b

and 14b

Figure 13. Sterically hindered (above) and unhindered (below)

approach of 2,4-substituted ansa-indene molecules 4 and 5, respectively,

at complex Ln[N(SiHMe₂)₂]₃(THF) on the basis of MM2 calculations.

Kinetically Controlled Ligand Approach. A qualitative

description of the implications of steric hindrance for this

specialized silylamine elimination could be gained on the

basis of MM2 force field calculations. According to the

mechanism proposed above (Scheme 3), ligand approach at the

mono-THF adduct 17b was chosen as a model reaction. The

calculated geometry of reaction intermediate 17b is in good

accordance with that of the mono-dimethylimidazol-2-ylidene

adduct Y[N(SiHMe₂)₂]₃(Me₂C₃H₂N₂) reported recently.⁶³

Approach of the differently substituted linked bis(indenes) 4

and 5 was forced by a fixed CsH‚‚‚N distance of 3.20 Å.⁶⁴

The resulting structure of reaction intermediate I₁clearly shows

that steric constraints hamper the proton exchange process

(Figure 13). The pincers formed by the methyl and phenyl

substituents in the 2- and 4-positions are too small to match

the bulk of the bis(dimethylsilyl)amide ligand. In contrast, the

4,5-benzo-substituted bis(indene) seems to perfectly fit into the

void which is formed by the amide ligands of 17b. These

findings are in good accordance with the synthetic results, which

show a high crystallized yield for complexes 15 and no or

incomplete ligand exchange for complexes 14.

pK_aValue Estimation. Many pK_avalue estimations have

been carried out for amines and hydrocarbons which resulted

in a number of different pK_ascales, depending on the applied

solvent, the counterions, and the method of measure-

ment.^65-67The method introduced by Fraser et al.⁶⁵comprises

an acidity scale which seemed to be well suited to evaluate our

extended silylamide route. According to these studies, ¹³C NMR

spectroscopy is used to measure the relative concentrations of

all four species of a deprotonation/reprotonation equilibrium,

as shown in Scheme 4.

Bro¨nsted-type acid-base reactions, the approach of the protic

substrate and subsequent proton transfer to the amide nitrogen

being the key steps of the reaction. Hence, the thermodynamics

of the exchange reactions can be best understood by determining

the pK_avalues of the ligands involved. Factors such as steric

oversaturation/unsaturation are known to govern the feasibility

of ligand-exchange reactions in rare earth chemistry.¹⁶The

isolation of the reaction intermediates 14b and 17b substantiates

the presence of kinetically controlled exchange reactions under

the prevailing conditions and proposes a reaction mechanism

such as that depicted in Scheme 3. Unsuccessful or incomplete

exchange reactions utilizing the sterically more crowded

Ln[N(SiMe₃)₂]₃complexes reinforce this mechanistic scenario.

The exchange reaction is initiated by THF dissociation from

the amide precursor, affording, e.g., the mono-THF adduct Ln-

[N(SiHMe₂)₂]₃(THF) (17). The yttrium derivative 17b was

obtained independently by refluxing 7b in toluene and charac-

terized spectroscopically and by elemental analysis. The unoc-

cupied coordination site in complex 17b directs approach and

coordination of one “diene” moiety of the linked cyclopenta-

dienyl ligands to give intermediate I₁. After transfer of the

“acidic” proton onto the amide nitrogen, dissociation of the

protonated silylamine and of the second THF molecule results

in a reaction intermediate I₂comparable to complex 14b. The

final ligand association proceeds via the second proton transfer,

followed by displacement of the amine by the chelating ligand.

On the basis of this mechanism, two key limitations of the

exchange reactions are evident. First, the presence of the

dissociated THF donor molecule should slow the reactivity, as

it can be coordinated on each step of product formation and

thus block coordination sites. Second, the steric bulk of the

approaching protic molecule restricts the ligand orientation for

the following proton transfer.

(63) Herrmann, W. A.; Munck, F. C.; Artus, G. R. J.; Runte, O.;

Anwander, R. Organometallics 1997, 16, 682-688.

(64) So far, few CsH‚‚‚N distances have been reported. A relatively

strong CsH‚‚‚N hydrogen bond in methylnitrile results in a close C‚‚‚N

contact of 318 pm: Dulmage, W. J.; Lipscomb, W. N. Acta Crystallogr.

1951, 4, 330-335. For a recent discussion, see: Mascal, M. Chem. Commun.

1998, 303-304.

(65) (a) Fraser, R. R.; Besse, M.; Mansour, T. S. J. Chem. Soc., Chem.

Commun. 1983, 620-621. (b) Fraser, R. R.; Mansour, T. S.; Savard, S. J.

Org. Chem. 1985, 50, 3232-3234. (c) Fraser, R. R.; Mansour, T. S.; Savard,

S. Can. J. Chem. 1985, 63, 3505-3509 and references therein.

3090 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

Scheme 5. Problems Associated with pK_aValue

Estimations: (a) ssip/cip Equilibrium, (b) Solvation and

Coordination Isomers of the Li⁺, (c) Mono- and

Bis-deprotonation of the ansa-Ligand, and (d) Migration of

the Silyl Group

Scheme 4. pK_aValue Estimation by the Method of Fraser et

al.⁶⁵

However, application of this method to silyl-bridged bis-

(indene) and bis(fluorene) systems is hampered by different

effects. Donor solvent-dependent equilibria between solvent

separated (ssip) and contact ion pairs (cip) (a),⁶⁸different

solvation and coordination isomers of the dilithium salts of

chelating ligands present in solution (b),⁶⁹disproportionation

equilibria between mono- and bis-deprotonated species with

the neutral ligand (c), and 1,5-sigmatropic shifts of the silyl

group (d)⁷⁰contribute to signal broadening and/or signal mul-

tiplicities and hence often result in noninterpretable spectra

(Scheme 5).

To minimize these aggravating factors, monosilylated indene

and fluorene systems 8a-10a were used for the pK_avalue

determinations. The new compounds were synthesized by

silylation of the corresponding lithium salts with dimethylchlo-

rosilane as shown in Scheme 6.⁷¹A further simplification of

the system could be achieved by recording the spectra in a

solvent mixture of C₆D₆/THF-d₈(20/1), which resembles the

conditions of the extended silylamide route and counteracts ssip

formation. Silyl group shift reactions proved to be negligible:

1

according to the H NMR spectrum of 8a, in addition to the

thermodynamically favored 3-(dimethylsilyl)indene (94%) only

a small amount of the 1-substituted derivative (6%) formed.

Such small amounts are below the accuracy of the estimation

of ¹³C NMR signal intensities and therefore hardly affect the

determination of the pK_avalues. The pK_avalues estimated by

this modification of the method of Fraser et al. are presented in

Table 4.

Scheme 6. Preparation of Silylated Indene and Fluorene

Model Compounds for the pK_aValue Estimation

(66) For reviews about pK_avalue estimations, see: (a) Streitwieser, A.,

Jr.; Juaristi, E.; Nebenzahl L. L. In ComprehensiVe carbanion chemistry,

Part A; Buncel, E., Durst, T., Eds.; Elsevier-North Holland: Amsterdam,

1980; pp 323-382. (b) Reutov, O. A.; Beletskaya, I. P.; Butin, K. P. CH-

Acids; Pergamon Press: Oxford, 1978. (c) For recent advances in measure-

ment techniques, see: Bausch, M. J.; Gong, Y. J. Am. Chem. Soc. 1994,

116, 5963-5964. (d) Bordwell, F. G.; Cheng, P.-J.; Ji, G.-Z.; Satish, A.

V.; Zhang, X. J. Am. Chem. Soc. 1991, 113, 9790-9795. (e) Streitwieser,

A.; Ciula, J. C.; Krom, J. A.; Thiele, G. J. Org. Chem. 1991, 56, 1074-

1076.

(67) Matthews, W. A.; Bares, J. E.; Bartmess, J. E.; Bordwell, F. G.;

Cornforth, F. J.; Drucker, G. E.; Magolin, Z.; McCallum, R. J.; Mc. Collum,

G. J., Vanier, N. R. J. Am. Chem. Soc. 1975, 97, 7006-7014.

(68) For discussions of ssip/cip equilibria, see refs 62a,b and the

following: (a) O’Brien, D. H. In ComprehensiVe carbanion chemistry, Part

A; Buncel, E., Durst, T., Eds.; Elsevier-North Holland: Amsterdam, 1980;

pp 271-322. (b) Eiermann, M.; Hafner, K. J. Am. Chem. Soc. 1992, 114,

135-140. (c) O’Brian, H. D.; Russel, R. C.; Hart, A. J. J. Am. Chem. Soc.

1979, 101, 633-639. (d) Grutzner, J. B.; Lawlor, J. M.; Jackman, L. M. J.

Am. Chem. Soc. 1972, 64, 2306-2314.

Silylamines display a relatively low basicity attributable to

dπ-pπ interactions between the vacant d-orbitals of the silicon

atoms and the lone pairs of the amide nitrogen.⁷²For example,

the pK_avalue of the bis(trimethylsilyl)amine was determined

as 25.8 in THF.^65bAccording to our estimations, the pK_aof

bis(dimethylsilyl)amine is as low as 22.8.⁷³Three differently

performed acidity measurements of fluorene (runs 2, 3, and 5)

demonstrate the accuracy of this method. Variation of the

reference acids, the pK_avalues of which were determined first

(runs 1 and 4), resulted in pK_avalues varying within 0.1 unit.

Generally, the present values are about 1.5 units higher than

the ones obtained by other methods in DMSO. The presence of

a silyl group in the 3-position decreases the pK_avalue by 1.5

and 1.8 units for the indenyl derivatives 8a and 9a, respectively.

(69) Harder, S.; Lutz, M.; Straub, A. W. G. Organometallics 1997, 177,

107-113.

(70) 1,5-Sigmatropic shifts of silyl groups at cyclopentadienyl and indenyl

systems are well established in the literature. For recent examples, see: (a)

Stradiotto, M.; Rigby, S. S.; Hughes, D. W.; Brook, M. A.; Bain, A. D.;

McGlinchey, M. J. Organometallics 1996, 15, 5645-5652. (b) Rigby, S.

S.; Gupta, H. K.; Werstiuk, N. H.; Bain, A. D.; McGlinchey, M. J. Inorg.

Chim. Acta 1996, 251, 355-364. (c) Rigby, S. S.; Girard, L.; Bain, A. D.;

McGlinchey, M. J. Organometallics 1995, 14, 3798-3801. (d) Chen, Y.-

X.; Rausch, M. D.; Chien, J. C. W. Organometallics 1993, 12, 4607-4612.

For problems in pK_avalue determinations, caused by 1,5-sigmatropic shifts

of silyl groups, see: (e) Bordwell, F. G.; Satish, A. V. J. Am. Chem. Soc.

1992, 114, 10173-10176. (f) Zhang, S.; Zhang, X.-M.; Bordwell, F. G. J.

Am. Chem. Soc. 1995, 117, 602-606.

(71) Interestingly, the silylated indenyl compounds 8b and 9b show the

same diastereotopic signal pattern (two doublets) for the two silylmethyl

groups as the ansa-metallocene amide complexes described above. The

signals of the Si-H moieties are shaped differently, additionally emphasizing

the Ln‚‚‚HSi coupling in the rare earth metallocene complexes.

(72) d_π-p_πinteractions for silylamines have been discussed controver-

sely, see: Ebsworth, E. A. V. Volatile Silicon Compounds; Pergamon

Press: Oxford, 1963.

(73) This could be independently proven by transsilylamination reactions

of NaN(SiMe₃)₂with bis(dimethylsilyl)amine: Eppinger, J.; Herdtweck,

E.; Anwander, R. Polyhedron 1998, 17, 1195-1201.

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3091

Table 4. pK_aValues According to the Modified Method of Fraser

run

acid₁

HN(SiHMe₂)₂

fluorene

indene

ref. acid₂(pK₂)

K_eq

-log K

pK₁

lit. data

1

2

3

4

5

6

7

8

9

HN(SiMe₃)₂(25.8)^a)

HN(SiHMe₂)₂(22.8)

indene (21.7)

1.1 × 10^-3

3.0

1.7

-1.2

1.1

-2.3

-1.4

1.5

-1.5

0.3

22.8

24.2

24.0

21.7

24.0

23.1

20.2

23.1

21.4

0.020

24.4^a/22.6^b

20.1^b

16

0.080

200

25

0.032

30

0.050

fluorene

24.4^a/22.6^b

21.7^b,c

SiHMe₂-Fluo (10a)

3-(SiHMe₂)-Ind (8a)

2-Me-Ind

3-(SiHMe₂)-2-Me-Ind (9a)

^aReference 65b. ^bIn DMSO, refs 70e,f. ^cTrimethylsilyl derivative in DMSO.

This effect is less pronounced for the ligand 9-(SiMe₂)fluorene

(∆pK_a) 0.9). As expected, a methyl group in the 2-position

increases the basicity of the indene molecule by 1.5 units.

These results show that the low yields isolated for the bis-

(indenyl) complexes rac-13a and 14b are mainly due to

sterically disfavored exchange reactions (kinetic control). In

contrast, the synthesis of the silyl-linked bis(fluorenyl) com-

plexes is additionally hampered by the low pK_avalue of the

bis(fluorene) precursors. Hence, an efficient preparation of

fluorenyl-derived lanthanidocenes will require alternative amide

precursors. For comparison, the pK_acriterion is of minor

importance in related zirconocene chemistry,¹⁹where amine

elimination reactions are routinely accomplished by utilizing

more basic dialkylamide ligands (e.g, pK_a(HNiPr₂) ) 36.0).^66a

Experimental Section

General Considerations. All air- and moisture-sensitive compounds

were manipulated with the rigorous exclusion of oxygen and moisture

in flame-dried (180 °C) Schlenk-type glassware using the standard high-

vacuum technique or an argon-filled glovebox (MBraun) with O₂/H₂O

< 1 ppm. The solvents were predried, distilled from Na/K alloy, and

stored in a glovebox. Deuterated solvents were obtained from Deutero

GmbH and degassed and dried over Na/K alloy.

Fluorene and 2-methylindene were purchased from Aldrich and used

as received. Indene (90%, Aldrich) was distilled and stored under

nitrogen at -35 °C. Dimethyldichlorosilane and dimethylchlorosilane

(Aldrich) were freshly distilled from potassium carbonate prior to use.

Bis(2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)dimethylsilane (Me₂-

Si(Cp′′H)₂, 1)²⁴and bis(fluoren-9-yl)dimethylsilane (Me₂Si(FluoH)₂, 6)²⁶

were synthesized according to published procedures by reacting the

corresponding lithiated hydrocarbons with dimethyldichlorosilane.

Lithiation of the hydrocarbons indene, 2-methylindene, fluorene, and

the silylamines 1,1,1,3,3,3,-hexamethyldisilazane and 1,1,3,3,-tetram-

ethyldisilazane was carried out by adding n-butyllithium (1.6 M solution

in hexane) to an n-hexane solution at -78 °C. Tetrahydrofurantris-

[bis(dimethylsilyl)amido]scandium(III) (7a) and the trans-bis(tetrahy-

drofuran)tris[bis(dimethylsilyl)amido]lanthanoid(III) precursors 7b-e

were prepared as described recently.¹⁵Y[N(SiMe₃)₂]₃was prepared from

YCl₃(THF)₃and K[N(SiMe₃)₂] and sublimed prior to use. 2,2-Bis(inden-

1-yl)propane (Me₂C(IndH)₂, 2) and bis(2-methyl-4-phenylinden-1-yl)-

dimethylsilane (Me₂Si(2-Me-4-Ph-IndH)₂, 4) were donated by Hoechst

AG. Bis(2-methylinden-1-yl)dimethylsilane (Me₂Si(2-Me-IndH)₂, 3) and

bis(2-methyl-4,5-benzoinden-1-yl)dimethylsilane (Me₂Si(2-Me-Benz-

IndH)₂, 5) were donated by Peroxid GmbH (Laporte). For the

preparation of these ligands see ref 25.

Conclusion

A specialized silylamine elimination reaction gives access

to a wide range of achiral and C₂-symmetric metallocene

complexes of the rare earth elements, including the first

Brintzinger-type lanthanide complexes. Utilization of tailor-

made synthetic precursors such as Ln[N(SiHMe₂)₂]₃(THF)_x

seems to be the proper strategy to achieve exchange reactions

with bulky, chelating molecules such as linked and substituted

indene derivatives. The commercially available, sterically more

encumbered standard systems Ln[N(SiMe₃)₂]₃, however, do not

undergo these exchange reactions. Not only does the SiH moiety

of the [N(SiHMe₂)₂] ligands constitute an excellent spectroscopic

probe to study these ligand-exchange reactions, but the steric

and electronic peculiarities of the chelating ancillary ligands

also imply a remarkable bis(dimethylsilyl)amide bonding. This

bonding features a two-fold, strong Si-H metal coordination

which is rigid in solution within a temperature range from -90

to 130 °C. This novel â-SiH diagostic interaction forces

unprecedented large Si-N-Si angles and elongated Si-H bond

distances, as revealed by spectroscopic and structural investiga-

tions. Such interactions resemble the early step of the oxidative

addition of an Si-H bond to a metal center. Close M‚‚‚SiH

interactions (M ) rare earth metal cation) are assumed

mechanistic intermediates, e.g., in the dehydrogenative polym-

erization of hydrosilanes by lanthanidocene complexes.⁷⁴The

kinetic and thermodynamic limitations of this specialized

silylamine elimination reaction could be rationalized on the basis

of steric considerations and pK_avalue determinations. To widen

the scope of this synthetic route, i.e., better to cope with the

prevailing synthetic limitations, we are currently evaluating

additional tailor-made lanthanide amide precursors. Preliminary

catalytic examinations clearly indicate an intriguing potential

of this new generation of lanthanidocene complexes in both fine

chemical and polymer synthesis.⁷⁵

NMR spectra were recorded either on a Bruker DPX-400 (FT, 400

1

MHz H; 100 MHz ¹³C) or on a JEOL JNM-GX-400 (FT, 400 MHz

¹H; 100 MHz ¹³C; 79.5 MHz ²⁹Si) spectrometer. ¹H and ¹³C shifts are

referenced to internal solvent resonances and reported relative to TMS.

The NOE experiment was recorded on the Bruker spectrometer. ⁸⁹Y

NMR experiments were performed on the JEOL spectrometer, which

was equipped with a broad-band 10-mm probe (19.48 MHz ⁸⁹Y, 3.0

M YCl₃in D₂O as a standard, sample concentration 0.26 M in a 6:1

mixture of toluene/C₆D₆; acquisition parameters, pulse width 10 ms,

pulse delay 20 s, 3000 scans). IR spectra were recorded on a Perkin-

Elmer 1650-FTIR spectrometer as Nujol mulls. Mass spectra (CI;

ionization agent, isobutene) were obtained on a Finnigan MAT-90

spectrometer. Elemental analyses were performed in the microanalytical

laboratory of the institute.

pK_aValue Measurements. The pK_avalues of tetramethyldisilazane,

inden-1-yldimethylsilane, (2-methylinden-1-yl)dimethylsilane, and flouren-

1-yldimethylsilane were determined by a slight modification of the

procedure described by Fraser et al.⁶⁵In a glovebox, the lithiated

reference acid (lithium bis(trimethylsilyl)amide, lithium bis(dimethyl-

silyl)amide, indenyllithium, fluorenyllithium) was mixed with an

equimolar amount of the protonated acid and 0.33 equiv of hexa-

methylbenzene as an internal standard. The mixture was cooled to -35

°C and dissolved in a 20:1 mixture of C₆D₆and THF-d₈to give a 0.1

M solution. After 30 min the solution was transferred into a 10-mm

(74) (a) Forsyth, C. M.; Nolan, S. P.; Marks, T. J. Organometallics 1991,

10, 2543-2545. (b) Sakakura, T.; Lautenschlager, H.-J.; Nakajima, M.;

Tanaka, M. Chem. Lett. 1991, 913-916.

(75) Anwander R.; Go¨rlitzer, H. W.; Gerstberger, G.; Eppinger, J.,

unpublished results.

3092 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

sealable NMR tube, allowed to warm to ambient temperature, and

placed in the Bruker spectrometer operating at 25 °C. ¹³C NMR spectra

were accumulated immediately using a small pulse angle (30°) and a

2-s repetition rate (a repetition rate of 4 s did not affect the integral

ratios). Influences such as differential NOEs were eliminated by using

an empirically derived correction factor. This factor was determined

by measuring the integrals of the protonated and lithiated compounds

relative to a certain amount of hexamethylbenzene as an internal

standard. In accordance with Fraser et al.,⁶⁵we estimated the accuracy

of K, derived from the equilibrium concentrations of all species present

in the solution, to be (30%, i.e., an uncertainty of ∆pK_aof (0.2 pK_a

unit or less. The ¹³C NMR shifts were (400 MHz, 25 °C) as follow:

HN(SiMe₃)₂, δ 4.19; LiN(SiMe₃)₂, δ 3.17; HN(SiHMe₂)₂, δ 1.54; LiN-

(SiHMe₂)₂, δ 2.62; IndH, δ 144.7, 143.5, 133.8, 132.1, 126.1, 124.5,

123.6, 120.9, 39.1; Li(Ind), δ 128.4, 120.5, 115.7, 115.4, 91.9; 2-Me-

IndH, δ 146.7, 145.4, 145.0, 126.0, 125.5, 125.3, 122.8, 120.3, 46.8,

16.73; Li(2-Me-Ind), δ 128.2, 125.7, 119.4, 115.5, 92.2, 14.83; FluoH,

δ 142.2, 141.0, 127.1, 125.8, 124.2, 120.4, 40.13; Li(Fluo), δ 136.5,

121.8, 120.1, 119.3, 116.6, 109.5, 80.4; C₆Me₆, δ 131.71, 16.86.

General Procedure for the Silylation of Indenyl and Fluorenyl

Systems. Over a period of 30 min, 1.0 equiv of n-butyllithium (1.6 M

solution in hexane) was added dropwise to a solution of the corre-

sponding aromatic hydrocarbon in THF (5 mL/mmol of the reactants)

at - 78 °C. The cold reaction mixture was stirred for 2 h. Then 1.1

equiv of dimethylchlorosilane in THF (5 mL/mmol) was added

dropwise at -78 °C, and the mixture was stirred at this temperature

for 1 h. The reaction mixture was allowed to warm to ambient

temperature and stirred for another 12 h before the solvent was removed

in vacuo. The residue was suspended in n-hexane (10 mL/mmol of the

desired product) and refluxed for 30 min. After the hexane suspension

was cooled to ambient temperature, LiCl was filtered off, and the residue

was washed a second time with the same amount of n-hexane. The

pure product was obtained by removing the solvent from the combined

organic phases.

889 vs, 836 vs, 801 s, 782 s, 750 vs, 730 m, 714 s, 683 w, 647 s, 630

m, 602 m, 566 m, 477 m, 455 s, 424 w. ¹H NMR (400 MHz, C₆D₆, 25

3

°C): δ 7.34 (d, J(H,H) ) 7.7 Hz, 1 H, indenyl-H), 7.32 (d, J(H,H)

) 7.3 Hz, 1 H, indenyl-H), 7.21 (“t”, ³J(H,H) ) 7.5 Hz, 1 H, indenyl-

H), 7.11 (“dt”, ³J(H,H) ) 7.3 Hz, 1 H, ⁴J(H,H) ) 0.7 Hz, indenyl-H),

1

3

6.46 (s, 1 H, indenyl-H), 4.25 (dsept, J(Si,H) ) 190 Hz, J(H,H) )

3.6 Hz, ³J(H,H) ) 1.0 Hz, 1 H, SiH), 3.14 (d, ³J(H,H) ) 1.0 Hz, 1 H,

indenyl-H), 2.00 (s, 3 H, indenyl-CH₃), -0.08 (d, J(H,H) ) 3.6 Hz,

3

6 H, HSi(CH₃)₂(I)), -0.35 (d, ³J(H,H) ) 3.6 Hz, 6 H, HSi(CH₃)₂(II)).

¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 146.7, 145.4, 145.0, 126.0,

125.5, 123.3, 122.8, 120.3, (s, indenyl-C), 46.78 (s, R-C), 16.73 (s,

indenyl-CH₃), -6.03 (s, HSi(CH₃)₂(I)), -7.19 (s, HSi(CH₃)₂(II)). MS

(EI): m/z (relative intensity) 188 (33) [M⁺], 173 (20) [M⁺- CH₃)],

129 (45) [M⁺- SiH(CH₃)₂], 59 (100) [SiH(CH₃)₂⁺]. Anal. Calcd for

C₁₂H₁₆Si: C, 76.52; H, 8.56. Found: C, 75.16; H, 8.84.

9-(Dimethylsilyl)fluorene (10a). Following the procedure described

above, fluorene (1.662 g, 10.00 mmol), n-butyllithium (1.60 M in

hexane, 6.25 mL, 10.0 mmol), and dimethylchlorosilane (1.04 g, 11.0

mmol) yielded 10a (1.963 g, 8.75 mmol, 87%) as a white powder. IR

(Nujol, cm^-1): 3065 w, 2926 vs, 2853 vs, 2724 s, 2122 s (ν(Si-H)),

1938 w, 1901 w, 1795 w, 1615 w, 1576 w, 1460 s, 1402 w, 1377 s,

1310 w, 1298 w, 1250 m, 1186 m, 1098 w, 1055 m, 1028 w, 1005 w,

973 w, 952 w, 933 w, 885 s, 860 w, 838 w, 795 w, 738 vs, 694 w, 646

1

w, 621 m, 486 w, 426 w, 411 m. H NMR (400 MHz, C₆D₆, 25 °C):

3

4

δ 7.74 (dd, J(H,H) ) 6.6 Hz, J(H,H) ) 1.5 Hz, 2 H, fluorenyl-H),

3

4

7.42 (dd, J(H,H) ) 7.0 Hz, J(H,H) ) 1.3 Hz, 2 H, fluorenyl-H),

7.26 (“t”, ³J(H,H) ) 7.0 Hz, 2 H, fluorenyl-H), 7.22 (“dt”, ³J(H,H) )

4

1

6.5 Hz, J(H,H) ) 1.5 Hz, 2 H, fluorenyl-H), 4.26 (dsept, J(Si,H) )

184 Hz, ³J(H,H) ) 3.7 Hz, 1 H, SiH), 3.48 (s, 1 H, fluorenyl-H), -0.28

(d, ³J(H,H) ) 3.7 Hz, 12 H, HSi(CH₃)₂). ¹³C{¹H} NMR (100.5 MHz,

C₆D₆, 25 °C): δ 145.5, 143.5, 127.0, 126.6, 125.2, 120.1 (s, fluorenyl-

C), 36.91 (s, R-C), -6.42 (s, HSi(CH₃)₂). MS (EI): m/z (relative

intensity) 224 (41) [M⁺], 209 (17) [M⁺- CH₃)], 165 (43) [M⁺

-

SiHMe₂], 59 (100) [SiHMe₂⁺]. Anal. Calcd for C₁₅H₁₆Si: C, 80.29;

H, 7.19. Found: C, 81.40; H, 7.07.

Dimethylsilylindene (8a). Following the procedure described above,

indene (1.564 g, 18.17 mmol), n-butyllithium (1.60 M in hexane, 11.4

mL, 18.2 mmol), and dimethylchlorosilane (1.89 g, 20.0 mmol) yielded

8a (2.587 g, 14.84 mmol, 82%) as a pale yellow oil. IR (neat, cm^-1):

3115 w, 3065 m, 3052 m, 3015 w, 2959 m, 2901 w, 2120 vs (ν(Si-

H)), 1938 w, 1900 w, 1833 w, 1789 w, 1722 w, 1626 w, 1605 w, 1580

w, 1536 w, 1459 m, 1450 s, 1422 w, 1360 w, 1311 w, 1250 s, 1220 m,

1190 m, 1112 w, 1029 vs, 980 m, 934 m, 886 vs, 860 s, 837 s, 801 s,

766 vs, 728 m, 716 s, 675 m, 644 m, 632 m, 600 w, 564 m, 540 m,

General Procedure for the Lithiation of Silylated Indenyl and

Fluorenyl Systems. Over a period of 10 min, 1.0 equiv of n-

butyllithium (1.6 M solution in hexane) was added dropwise to a

solution of the corresponding silylated aromatic hydrocarbon in

n-hexane (5 mL/mmol of the reactants) at - 78 °C. After being stirred

for 2 h at low temperature, the reaction mixture was stirred for an

additional 2 h at ambient temperature before the insoluble product was

separated via filtration. The residue was washed with cold n-hexane (2

mL/mmol desired product) and dried in vacuo, yielding the pure

product.

1

455 s, 420 w. H NMR (400 MHz, C₆D₆, 25 °C): (a) major isomer

3

(3-dimethylsilylindene, 94 mol %): δ 7.42 (dd, J(H,H) ) 7.7 Hz,

⁴J(H,H) ) 0.9 Hz, 1 H, indenyl-H), 7.40 (dd, ³J(H,H) ) 7.7 Hz, ⁴J(H,H)

) 1.0 Hz, 1 H, indenyl-H), 7.21 (“t”, ³J(H,H) ) 7.5 Hz, 1 H, indenyl-

H), 7.15 (“t”, ³J(H,H) ) 7.3 Hz, 1 H, indenyl-H), 6.83 (dd, ³J(H,H) )

3-(Dimethylsilyl)indene Lithium (8b). Following the procedure

described above, 3-dimethylsilylindene (8a) (1.451 g, 8.32 mmol) and

n-butyllithium (1.60 M in hexane, 5.2 mL, 8.3 mmol) yielded 8b (0.934

g, 5.18 mmol, 62%) as a white powder. IR (Nujol, cm^-1): 2924 vs,

2734 w, 2094 m (ν(Si-H)), 1463 vs, 1377 s, 1318 m, 1288 w, 1257

m, 1212 m, 1155 m, 1141 w, 1033 m, 991 w, 970 m, 941 w, 894 m,

4

3

5.2 Hz, J(H,H) ) 0.7 Hz, 1 H, indenyl-H), 6.43 (dd, J(H,H) ) 5.1

3

1

Hz, J(H,H) ) 1.9 Hz, 1 H, indenyl-H), 4.26 (dsept, J(Si,H) ) 189

Hz, ³J(H,H) ) 3.4 Hz, ³J(H,H) ) 1.0 Hz, 1 H, SiH), 3.48 (d, ³J(H,H)

3

1

) 1.6 Hz, 1 H, indenyl-H), -0.17 (d, J(H,H) ) 3.6 Hz, 6 H, HSi-

868 m, 834 m, 753 sh, 722 m, 668 m, 630 w, 534 sh, 467 brm. H

(CH₃)₂(I)), -0.27 (d, ³J(H,H) ) 3.6 Hz, 6 H, HSi(CH₃)₂(II)); (b) minor

isomer (1-dimethylsilylindene, 6 mol %): δ 7.51 (dd, 1 H, indenyl-

H), 7.28 (“t”, 1 H, indenyl-H), 7.10 (“t”, 1 H, indenyl-H), 6.72 (dd, 1

H, indenyl-H), 6.23 (dd, 1 H, indenyl-H), 4.40 (sept, 1 H, SiH), 3.03

(t, 1 H, indenyl-H), 0.13 (d, 6 H, HSi(CH₃)₂(I)), -0.10 (d, 6 H, HSi-

(CH₃)₂(II)). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 145.3, 144.5,

135.0, 129.8, 125.5, 124.4, 123.0, 121.5, (s, indenyl-C), 43.80 (s, R-C),

-5.25 (s, HSi(CH₃)₂(I)), -6.46 (s, HSi(CH₃)₂(II)). MS (EI): m/z

(relative intensity) 174 (21) [M⁺], 159 (34) [M⁺- CH₃)], 115 (17)

[M⁺- SiHMe₂], 59 (100) [SiHMe₂⁺]. Anal. Calcd for C₁₁H₁₄Si: C,

75.71; H, 8.09. Found: C, 76.26; H, 8.20.

3-Dimethylsilyl-2-methylindene (9a). Following the procedure

described above, 2-methylindene (1.175 g, 9.03 mmol), n-butyllithium

(1.60 M in hexane, 5.6 mL, 9.0 mmol), and dimethylchlorosilane (0.946

g, 10.0 mmol) yielded 9a (1.460 mg, 7.75 mmol, 86%) as a pale yellow

oil. IR (neat, cm^-1): 3063 s, 3052 s, 3013 m, 2960 s, 2908 s, 2855 w,

2734 w, 2120 vs (ν(Si-H)), 1932 w, 1896 w, 1859 w, 1794 w, 1680

w, 1605 w, 1593 m, 1567 w, 1457 s, 1447 s, 1379 w, 1300 m, 1250 s,

1220 m, 1194 m, 1153 w, 1120 w, 1100 w, 1051 s, 1012 s, 930 m,

NMR (400 MHz, C₆D₆, 25 °C): δ 7.89 (m, 2 H, indenyl-H), 7.40 (dd,

³J(H,H) ) 7.7 Hz, ⁴J(H,H) ) 1.0 Hz, 1 H, indenyl-H), 7.11-7.05 (m,

3

3 H, indenyl-H), 6.49 (d, J(H,H) ) 3.5 Hz, 1 H, indenyl-H), 5.27

(sept, ¹J(Si,H) ) 176 Hz, ³J(H,H) ) 3.6 Hz, 1 H, SiH), 0.62 (d, ³J(H,H)

) 3.9 Hz, 6 H, HSi(CH₃)₂(I)). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25

°C): δ 134.9, 132.4, 127.2, 125.5, 124.2, 121.4, 116.9, 116.7, 96.4 (s,

indenyl-C), -1.08 (s, HSi(CH₃)₂). Anal. Calcd for C₁₁H₁₃LiSi: C, 73.30;

H, 7.27. Found: C, 74.23; H, 6.84.

3-Dimethylsilyl-2-methylindene Lithium (9b). Following the pro-

cedure described above, 3-dimethylsilyl-2-methylindene (9a) (1.147 g,

6.12 mmol) and n-butyllithium (1.60 M in hexane, 3.8 mL, 6.1 mmol)

yielded 9b (0.842 g, 4.33 mmol, 71%) as a white powder. IR (neat,

cm^-1): 2921 vs, 2723 w, 2083 s (ν(Si-H)), 1463 vs, 1411 w, 1377 s,

1350 m, 1336 m, 1267 m, 1244 m, 1203 w, 1153 w, 1120 w, 1052 m,

1000 w, 908 w, 881 s, 833 s, 801 s, 760 s, 734 s, 696 w, 669 w, 647

1

3

m, 483 brs. H NMR (400 MHz, C₆D₆, 25 °C): δ 7.95 (d, J(H,H) )

3

8.4 Hz, 1 H, indenyl-H), 7.33 (d, J(H,H) ) 7.5 Hz, 1 H, indenyl-H),

7.06-7.01 (m, 2 H, indenyl-H), 6.24 (s, 1 H, indenyl-H), 5.31 (sept,

¹J(Si,H) ) 180 Hz, ³J(H,H) ) 3.9 Hz, 1 H, SiH), 2.66 (s, 3 H, indenyl-

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3093

3

CH₃), 0.62 (d, J(H,H) ) 4.0 Hz, 6 H, HSi(CH₃)₂(I)). ¹³C{¹H} NMR

(SiHMe)⁺]. Anal. Calcd for C₂₄H₄₄LaNSi₃: C, 50.59; H, 7.78; N, 2.46.

Found: C, 50.47; H, 8.14; N, 2.28.

(100.5 MHz, C₆D₆, 25 °C): δ 135.8, 135.7, 131.1, 120.6, 119.6, 119.5,

116.4, 115.6, 91.6, (s, indenyl-C), 17.28 (s, indenyl-CH₃), -0.36 (s,

HSi(CH₃)₂). Anal. Calcd for C₁₂H₁₅LiSi: C, 74.19; H, 7.78. Found:

C, 73.95; H, 7.37.

9-(Dimethylsilyl)fluorene Lithium (10b). Following the procedure

described above, 9-(dimethylsilyl)fluorene (10a) (1.122 g, 5.00 mmol)

and n-butyllithium (1.60 M in hexane, 3.1 mL, 5.0 mmol) yielded 10b

(0.671 mg, 2.92 mmol, 58.3%) as a white powder. IR (Nujol, cm^-1):

2923 vs, 2854 vs, 2724 w, 2085 s (ν(Si-H)), 1577 w, 1463 vs, 1377

s, 1321 s, 1266 w, 1212 m, 1200 w, 1151 w, 1096 w, 1067 m, 1043 w,

1008 w, 988 m, 926 w, 842 w, 821 w, 770 w, 751 m, 726 s, 688 w,

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis-2,2-(inden-1-yl)propyl]-

yttrium(III) (rac-12b). Following the procedure described above, 7b

(630.1 mg, 1.000 mmol) and 2 (274.0 mg, 1.000 mmol) yielded rac-

12b (69.8 mg, 0.142 mmol, 14%) as yellow prisms (15 h of refluxing

in toluene and 5 h of refluxing in mesitylene). IR (Nujol, cm^-1): 2922

vs, 2853 vs, 2723 m, 1821 w (ν(Si-H)), 1461 vs, 1377 s, 1306 w,

1246 m, 1216 w, 1204 w, 1153 w, 1044 w, 1003 w, 915 m, 896 m,

842 m, 804 w, 766 m, 749 s, 743 m, 721 m, 685 w; 672 w, 611 w, 468

w, 454 m, 427 w. ¹H NMR (400 MHz, C₆D₆, 75 °C): δ 7.74 (d, ³J(H,H)

3

) 8.6 Hz, 2 H, H4), 7.39 (d, J(H,H) ) 8.0 Hz, 2 H, H6), 6.91 (dd,

1

3

542 m, 494 w, 429 m. H NMR (400 MHz, C₆D₆, 25 °C): δ 8.08 (d,

2× J(H,H) ) 7.5 Hz, 2 H, H5), 6.73 (dd, 2× J(H,H) ) 7.3 Hz, 2 H,

³J(H,H) ) 8.0 Hz, 2 H, fluorenyl-H), 7.76 (d, ³J(H,H) ) 7.9 Hz, 2 H,

fluorenyl-H), 7.25 (“t”, ³J(H,H) ) 8.0 Hz, 2 H, fluorenyl-H), 7.12 (“t”,

H7), 6.62 (d, ³J(H,H) ) 3.0 Hz, 2 H, H2), 6.19 (d, ³J(H,H) ) 3.1 Hz,

1

3

2 H, H3), 3.56 (dsept, J(Si,H) ) 152 Hz, J(H,H) ) 2.8 Hz, 2 H,

SiH), 2.14 (s, 6 H, C(CH₃)₂), 0.11 (d, ³J(H,H) ) 2.7 Hz, 6 H, HSiCH₃-

(I)), 0.07 (d, ³J(H,H) ) 2.7 Hz, 6 H, HSiCH₃(II)). ¹³C{¹H} NMR (100.5

MHz, C₆D₆, 60 °C): δ 126.2/125.8/123.7/123.0/121.6/118.9/114.6/

109.1/101.7 (s, indenyl-C), 40.5 (s, bridge-C), 28.9 (s, C(CH₃)₂), 2.59

(s, HSi(CH₃)₂(I)), 2.07 (s, HSi(CH₃)₂(II)). MS (CI): m/z (relative

intensity) ) 851 (6) [M⁺+ Y(Me₂CInd₂)], 845 (3) [M⁺+ Y(N(Si-

³J(H,H) ) 7.6 Hz, 2 H, fluorenyl-H), 5.53 (sept, J(Si,H) ) 168 Hz,

1

³J(H,H) ) 3.8 Hz, 1 H, SiH), 0.71 (d, J(H,H) ) 3.9 Hz, 12 H, HSi-

3

(CH₃)₂). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 142.3, 127.2,

121.7, 121.0, 119.1, 117.1, 111.5 (s, fluorenyl-C), -0.57 (s, HSi(CH₃)₂).

Anal. Calcd for C₁₅H₁₅LiSi: C, 78.23; H, 6.56. Found: C, 77.37; H,

6.81.

HMe₂)₂)₂], 491 (100) [M⁺], 476 (12) [M⁺- CH₃], 359 (14) [M⁺

-

General Procedure for the Preparation of ansa-Lanthanidocene

Amides. In a glovebox, Ln[N(SiHMe₂)₂]₃(THF)_x(7a-e) and the

equimolar amount of ligand 1-6 were dissolved in toluene (20 mL/

mmol silylamide), refluxed for the time mentioned below, and

evaporated to dryness. For the bis(indene) or bis(fluorene) 2-6, the

residue was dissolved in mesitylene (20 mL/mmol silylamide) and

refluxed a second time. After the solvent was removed in vacuo, the

resulting powder was dissolved in toluene. The filtrated solution was

cooled to -45 °C, upon which a microcrystalline precipitate formed.

After the solvent was decanted, this precipitate was dissolved in hot

n-hexane and cooled slowly to -45 °C, at which temperature pure

11b,c-16b were obtained as single crystals. This procedure could be

scaled up from 0.5 to 20 mmol.

[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2,3,4,5-tetramethylcyclopen-

tadien-1-yl)dimethylsilyl]yttrium(III) (11b). Following the procedure

described above, 7b (630.1 mg, 1.000 mmol) and 1 (300.6 mg, 1.000

mmol) yielded 11b (462.2 mg, 0.820 mmol, 82%) as colorless prisms

(15 h of refluxing in toluene). IR (Nujol, cm^-1): 2922 vs, 2853 vs,

2724 m, 1789 brw (ν(Si-H)), 1463 vs, 1377 s, 1371 sh, 1312 m, 1244

m, 1154 w, 1086 w, 1020 m, 972 w, 905 brm, 900 w, 836 w, 811 w,

N(SiHMe₂)₂], 272 (2) [Me₂CInd₂⁺], 247 (4) [M⁺- N(SiHMe₂)₂- Ind

+ 2H], 132 (4) [N(SiHMe₂)₂⁺], 118 (7) [N(SiHMe₂)(SiHMe)⁺]. Anal.

Calcd for C₂₅H₃₂NSi₂Y: C, 61.08; H, 6.56; N, 2.85. Found: C, 59.18;

H, 6.70; N, 2.48.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methylinden-1-yl)-

dimethylsilyl]scandium(III) (rac-13a). Following the procedure de-

scribed above, 7a (1028.1 mg, 2.000 mmol) and 3 (633.0 mg, 2.000

mmol) yielded rac-13a (201.4 mg, 0.410 mmol, 20%) as lemon yellow

prisms (24 h of refluxing in toluene and 12 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2924 vs, 2953 vs, 2724 w, 2012 m, 1793 brw (ν-

(Si-H)), 1460 vs, 1377 vs, 1346 w, 1304 w, 1272 w, 1245 s, 1152 w,

1072 m, 1038 brm, 1000 m, 898 s, 834 s, 806 s, 802 s, 764 m, 744 m,

1

721 w, 691 m, 654 w, 611 w, 566 w, 484 w, 455 s. H NMR (400

3

MHz, C₆D₆, 25 °C): δ 7.78 (d, J(H,H) ) 8.5 Hz, 2 H, H7), 7.49 (d,

3

³J(H,H) ) 7.5 Hz, 2 H, H4), 6.85 (dd, 2× J(H,H) ) 7.5 Hz, 2 H,

3

H6), 6.80 (dd, 2× J(H,H) ) 7.5 Hz, 2 H, H5), 6.23 (s, 2 H, H3), 2.96

1

3

(m, J(Si,H) ) 155 Hz, J(H,H) ) 2.5 Hz, 2 H, SiH), 2.27 (s, 6 H,

CH₃-indenyl), 1.12 (s, 6 H, Si(CH₃)₂), 0.11 (d, ³J(H,H) ) 2.5 Hz, 6 H,

HSiCH₃(I)), 0.060 (d, J(H,H) ) 2.5 Hz, 6 H, HSiCH₃(II)). ¹³C{¹H}

3

1

NMR (100.5 MHz, C₆D₆, 25 °C): δ 136.9/132.8/131.8/125.0/124.8/

122.9/122.8/113.2 (s, C2-C9), 100.8 (s, C1), 18.8 (s, CH₃-indenyl),

3.45 (s, HSiCH₃), 3.07 (s, SiCH₃). MS (CI): m/z (relative intensity)

491 (16) [M⁺], 476 (10) [M⁺- CH₃], 432 (12) [M⁺- SiHMe₂], 359

(10) [M⁺- N(SiHMe₂)₂], 316 (30) [SiMe₂(Me-Ind)₂H⁺], 301 (14)

[SiMe₂(Me-Ind)₂H⁺- CH₃], 187 (100) [SiMe₂(Me-Ind)H⁺], 159 (6)

[Si(Me-Ind)H₂⁺], 132 (2) [N(SiHMe₂)₂⁺]. Anal. Calcd for C₂₆H₃₆NSi₃-

Sc: C, 63.50; H, 7.38; N, 2.85. Found: C, 62.48; H, 7.33; N, 2.53.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methylinden-1-yl)-

dimethylsilyl]yttrium(III) (rac-13b). Following the procedure de-

scribed above, 7b (630.1 mg, 1.000 mmol) and 3 (316.5 mg, 1.000

mmol) yielded rac-13b (278.3 mg, 0.520 mmol, 52%) as lemon yellow

prisms (15 h of refluxing in toluene and 3 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2922 vs, 2853 vs, 2723 m, 1804 brw (ν(Si-H)),

1464 vs, 1410 w, 1379 s, 1344 m, 1333 m, 1279 m, 1246 s, 1150 m,

1037 m, 1000 m, 902 m, 876 s, 833 s, 807 s, 781 s, 765 s, 748 s, 690

m, 656 w, 644 m, 611 w, 571 w, 484 w, 460m, 449 s, 429 m. ¹H NMR

(400 MHz, C₆D₆, 25 °C): δ 7.87 (d, ³J(H,H) ) 8.5 Hz, 2 H, H7), 7.38

761 w, 722 m, 676 m, 462 w. H NMR (400 MHz, C₆D₆, 25 °C): δ

4.00 (dsept, J(Y,H) ) 2.9 Hz, J(Si,H) ) 147 Hz, J(H,H) ) 2.70

Hz, 2 H, SiH), 2.06 (s, 12 H, Cp(CH₃)(I)), 1.95 (s, 12 H, Cp(CH₃)-

1

3

(II)), 0.97 (s, 6 H, Cp′′₂Si(CH₃)₂), 0.24 (d, J(H,H) ) 2.5 Hz, 12 H,

HSi(CH₃)₂). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 127.3 (s,

C

_Cp(I)), 122.8 (s, C_Cp(II)), 108.7 (s, SiC_Cp), 14.5 (s, Cp(CH₃)(I)), 12.0

(s, Cp(CH₃)(II)), 4.33 (s, Cp′′₂Si(CH₃)₂), 3.55 (s, HSi(CH₃)₂). ²⁹Si{¹H}

NMR (79.5 MHz, C₆D₆, 25 °C): δ -19.87 (s, NSi), -32.45 (brs,

Si_bridge). MS (CI): m/z (relative intensity) 519 (14) [M⁺], 447 (8) [M⁺

- N(SiHMe₂)], 389 (3) [M⁺- N(SiHMe₂)₂+ 2H], 331 (46) [Y(Cp′′)⁺],

316 (100) [SiMe₂(Cp′′)CH₄⁺], 301 (16) [SiMe₂(Cp′′)H⁺], 179 (7)

[SiMe₂(Cp′′)⁺], 118 (2) [N(SiHMe₂)(SiHMe)⁺]. Anal. Calcd for C₂₄H₄₄-

NSi₃Y: C, 55.46; H, 8.53; N, 2.69. Found: C, 54.24; H, 8.89; N, 2.37.

[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2,3,4,5-tetramethylcyclopen-

tadien-1-yl)dimethylsilyl]lanthanum(III) (11c). Following the pro-

cedure described above, 7c (340.1 mg, 0.500 mmol) and 1 (150.3 mg,

0.500 mmol) yielded 11c (273.5 mg 0.480 mmol, 96%) as colorless

prisms (15 h of refluxing in toluene). IR (Nujol, cm^-1): 2922 vs, 2853

vs, 2723 m, 1845 brw (ν(Si-H)), 1462 vs, 1454 vs, 1377 s, 1250 m,

1161 w, 1100 w, 1092 w, 1015 w, 974 w, 928 m, 900 w, 881 w, 834

3

(d, ³J(H,H) ) 7.8 Hz, 2 H, H4), 6.91 (dd, 2× J(H,H) ) 7.6 Hz, 2 H,

3

H6), 6.84 (dd, 2× J(H,H) ) 8.5 Hz, 2 H, H5), 6.15 (s, 2 H, H3), 2.98

1

w, 801 w, 723 m, 663 w. H NMR (400 MHz, C₆D₆, 25 °C): δ 4.18

(dsept, ¹J(Y,H) ) 4.6 Hz, ¹J(Si,H) ) 142 Hz, ³J(H,H) ) 2.4 Hz, 2 H,

SiH), 2.39 (s, 6 H, CH₃-indenyl), 1.10 (s, 6 H, Si(CH₃)₂), 0.067 (d,

³J(H,H) ) 2.4 Hz, 6 H, HSiCH₃(I)), 0.034 (d, ³J(H,H) ) 2.4 Hz, 6 H,

HSiCH₃(II)). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 138.0/131.3/

131.0/123.4/123.3/122.1/121.9/108.2 (s, C2-C9), 99.3 (s, C1), 18.0

(s, CH₃-indenyl), 3.15 (s, SiCH₃), 2.66 (s, HSiCH₃(I)), 2.64 (s, HSiCH₃-

(II)). MS (CI): m/z (relative intensity) 535 (6) [M⁺], 316 (32) [SiMe₂-

(Me-Ind)₂H⁺], 187 (100) [SiMe₂(Me-Ind)H⁺], 132 (7) [N(SiHMe₂)₂⁺].

Anal. Calcd for C₂₆H₃₆NSi₃Y: C, 58.29; H, 6.77; N, 2.61. Found: C,

56.32; H, 6.80; N, 2.34.

(m, ¹J(Si,H) ) 150 Hz, 2 H, SiH), 2.18 (s, 12 H, Cp(CH₃)(I)), 1.95 (s,

3

12 H, Cp(CH₃)(II)), 0.95 (s, 6 H, Cp′′₂Si(CH₃)₂), 0.19 (d, J(H,H) )

2.5 Hz, 12 H, HSi(CH₃)₂); ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C):

δ 127.3 (s, C_Cp(I)), 126.1 (s, C_Cp(II)), 110.5 (s, SiC_Cp), 14.5 (s, Cp-

(CH₃)(I)), 11.3 (s, Cp(CH₃)(II)), 4.50 (s, Cp′′₂Si(CH₃)₂), 2.23 (s, HSi-

(CH₃)₂). ²⁹Si{¹H} NMR (79.5 MHz, C₆D₆, 25 °C): δ -17.31 (s, NSi),

-30.41 (brs, Si_bridge). MS (CI): m/z (relative intensity) 569 (85) [M⁺],

554 (15) [M⁺- CH₃], 437 (100) [M⁺- N(SiHMe₂)₂], 421 (12) [M⁺

- N(SiHMe₂)₂- CH₃], 179 (7) [SiMe₂(Cp′′)⁺], 118 (2) [N(SiHMe₂)-

3094 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methylinden-1-yl)-

dimethylsilyl]lanthanum(III) (rac-13c). Following the procedure

described above, 7c (328.8 mg, 0.483 mmol) and 3 (152.9 mg, 0.483

mmol) yielded rac-13c (137.8 mg, 0.235 mmol, 49%) as lemon yellow

prisms (9 h of refluxing in toluene and 1 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2923 vs, 2854 vs, 2724 w, 1838 brm (ν(Si-H)),

1463 vs, 1417 w, 1377 s, 1348 w, 1339 w, 1302 m, 1270 m, 1249 s,

1209 w, 1152 m, 1033 sh, 1012 m, 954 brm, 892 w, 874 m, 836 m,

806 m, 778 m, 744 m, 721 w, 685 m, 647 w, 611 w, 570 w, 482 w,

h of refluxing in toluene and 10 h of refluxing in mesitylene). IR (Nujol,

cm^-1): 2923 vs, 2853 vs, 2723 w, 2069 m, 1830 brw (ν(Si-H)), 1462

vs, 1610 w, 1410 w, 1379 s, 1344 m, 1333 m, 1279 m, 1246 s, 1150

m, 1037 m, 1000 m, 902 m, 876 s, 833 s, 807 s, 781 s, 765 s, 748 s,

1

690 m, 656 w, 644 m, 611 w, 571 w, 484 w, 460m, 449 s, 429 m. H

NMR (400 MHz, C₆D₆, 25 °C): δ 7.88 (dd, ³J(H,H) ) 8.4 Hz, ⁴J(H,H)

) 1.3 Hz, 2 H, phenyl(I)), 7.84 (d, ³J(H,H) ) 8.4 Hz, 1 H), 7.57 (dd,

³J(H,H) ) 8.4 Hz, ⁴J(H,H) ) 1.3 Hz, 2 H, phenyl(II)), 7.35-7.23 (m,

4 H, phenyl + indenyl), 7.19-7.11 (m, 5 H, phenyl), 7.02 (dd, 2×

³J(H,H) ) 7.5 Hz, 1 H), 6.94 (s, 1H, indenyl), 6.82 (s, 1 H, indenyl),

6.58 (d, ³J(H,H) ) 8.0 Hz, 1 H), 4.31 (dsept, ¹J(Si,H) ) 148 Hz,

³J(H,H) ) 2.9 Hz, 4 H, SiH), 3.66 (s, 1 H, indenyl), 2.34 (s, 3 H,

CH₃-indenyl(I)), 1.75 (s, 3 H, CH₃-indenyl(II)), 0.67 (s, 3 H, Si(CH₃)₂-

(I)), 0.48 (s, 3 H, Si(CH₃)₂(II)), 0.12 (d, ³J(H,H) ) 2.5 Hz, 24 H, HSi-

(CH₃)₂). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 162.9/148.0/

145.8/145.2/143.0/142.0/140.9/137.7/137.4/134.1/130.1/129.8/128.4/

127.9/127.2/126.6/125.6/125.4/123.2/123.1/123.0/122.8/122.2/122.1/

105.8 (s, phenyl + indenyl), 49.9 (s, indenyl-C3), 18.0 (s, CH₃-

indenyl(I)), 16.9 (s, CH₃-indenyl(I)), 2.56 (s, HSiCH₃(I)), 2.42 (s,

HSiCH₃(II)), 0.58 (s, Si(CH₃)₂(I)), -0.69 (s, Si(CH₃)₂(II)). MS (CI):

m/z (relative intensity) 821 (3) [M⁺], 689 (5) [M⁺- N(SiHMe₂)₂],

557 (45) [M⁺- 2N(SiHMe₂)₂], 468 (54) [Me₂Si(2-Me-4-Ph-Ind)₂H⁺],

263 (100) [Me₂Si(2-Me-4-Ph-Ind)H⁺], 132 (20) [N(SiHMe₂)₂⁺]. Anal.

Calcd for C₄₂H₅₉YN₂Si₅: C, 61.43; H, 7.24; N, 3.41. Found: C, 59.94;

H, 7.09; N, 3.16.

1

462 w, 441 m, 420 m. H NMR (400 MHz, C₆D₆, 25 °C): δ 7.78 (d,

3

³J(H,H) ) 8.2 Hz, 2 H, H7), 7.29 (d, J(H,H) ) 7.9 Hz, 2 H, H4),

3

6.79 (t, J(H,H) ) 7.6 Hz, 2 H, H6), 6.74 (t, J(H,H) ) 7.5 Hz, 2 H,

H5), 6.13 (s, 2 H, H3), 3.74 (m, ¹J(Si,H) ) 145 Hz, 2 H, SiH), 2.61 (s,

3

6 H, CH₃-indenyl), 1.05 (s, 6 H, Si(CH₃)₂), 0.06 (d, J(H,H) ) 2.5

3

Hz, 6 H, HSiCH₃(I)), -0.01 (d, J(H,H) ) 2.5 Hz, 6 H, HSiCH₃(II)).

¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 136.1/133.5/133.2/124.0/

121.8/ 121.4/121.0/107.1 (s, C2-C9), 104.3 (s, C1), 18.4 (s, CH₃-

indenyl), 3.16 (s, HSiCH₃(I)), 2.29 (s, HSiCH₃(II)), 1.84 (s, SiCH₃).

MS (CI): m/z (relative intensity) ) 586 (54) [M⁺], 453 (34) [M⁺

-

N(SiHMe₂)₂], 316 (47) [Me₂Si(Me-Ind)₂⁺], 301 (24) [MeSi(Me-Ind)₂⁺],

187 (100) [SiMe₂(Me-Ind)H⁺], 132 (60) [N(SiHMe₂)₂⁺], 118 (45)

[N(SiHMe₂)(SiHMe)⁺]. Anal. Calcd for C₂₆H₃₆LaNSi₃: C, 53.31; H,

6.19; N, 2.39. Found: C, 54.51; H, 6.50; N, 1.80.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methylinden-1-yl)-

dimethylsilyl]neodymium(III) (rac-13d). Following the procedure

described above, 7d (701.0 mg, 1.023 mmol) and 3 (323.8 mg, 1.023

mmol) yielded rac-13d (266.4 mg, 0.451 mmol, 44%) as green prisms

(12 h of refluxing in toluene and 2 h of refluxing in mesitylene). IR

(Nujol, cm^-1): 2922 vs, 2853 vs, 2724 w, 1824 brm (ν(Si-H)), 1463

vs, 1409 w, 1377 s, 1344 w, 1332 w, 1302 m, 1267 m, 1246 s, 1198

w, 1150 m, 1029 sh, 1000 m, 975 brm, 937 sh m, 898 w, 873 m, 833

m, 806 m, 791 w, 776 m, 748 m, 721 w, 686 m, 652 w, 643 w, 612 w,

570 w, 483 w, 462 w, 445 m, 420 m. ¹H NMR (400 MHz, C₆D₆, 20.6

°C): δ 23.6 (s, 6 H, lw ) 105 Hz), 13.7 (s, 6 H, lw ) 46 Hz), 11.5 (s,

6 H, lw ) 45 Hz), 2.2 (s, 2 H, lw ) 5 Hz), -0.4 (s, 2 H, lw ) 186

Hz), -2.1 (s, 2 H, lw ) 60 Hz), -11.1 (s, 6 H, lw ) 304 Hz), -13.4

(s, 2 H, lw ) 34 Hz), -21.7 (s, 2 H, lw ) 91 Hz); a Si-H signal

could not be detected. MS (CI): m/z (relative intensity) 591 (55)

[M⁺], 458 (30 [M⁺- N(SiHMe₂)₂], 316 (47) [SiMe₂(Me-Ind)₂H⁺],

301 (25) [MeSi(Me-Ind)₂⁺], 187 (100) [SiMe₂(Me-Ind)H⁺], 132 (55)

[N(SiHMe₂)₂⁺], 118 (49) [N(SiHMe₂)(SiHMe)⁺]. Anal. Calcd for

C₂₆H₃₆NNdSi₃: C, 52.83; H, 6.14; N, 2.37. Found: C, 52.11; H, 6.50;

N, 2.30.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methyl-4-phenylinden-

1-yl)dimethylsilyl]lanthanum(III) (rac-14c). Following the procedure

described above, 7c (340.1 mg, 0.500 mmol) and 4 (234.4 mg, 0.500

mmol) yielded rac-14c (48.0 mg, 0.065 mmol, 13%) as lemon yellow

needles (24 h of refluxing in toluene and 5 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2923 vs, 2853 vs, 2723 w, 1832 brw (ν(Si-H)),

1462 vs, 1610 w, 1410 w, 1379 s, 1344 m, 1333 m, 1279 m, 1246 s,

1150 m, 1037 m, 1000 m, 902 m, 876 s, 833 s, 807 s, 781 s, 765 s,

748 s, 690 m, 656 w, 644 m, 611 w, 571 w, 484 w, 460 m, 449 s, 429

1

3

m. H NMR (400 MHz, C₆D₆, 25 °C): δ 7.84 (d, J(H,H) ) 8.4 Hz,

3

2 H, H7), 7.42 (d, J(H,H) ) 8.0 Hz, 2 H, H5), 7.35-7.25 (m, 12 H,

3

phenyl), 6.89 (dd, 2× J(H,H) ) 7.7 Hz, 2 H, H6), 6.59 (s, 2 H, H3),

1

3.87 (m, J(Si,H) ) 141 Hz, 2 H, SiH), 2.58 (s, 6 H, CH₃-indenyl),

1.11 (s, 6 H, Si(CH₃)₂), -0.14 (d, ³J(H,H) ) 2.5 Hz, 6 H, HSi(CH₃)₂-

(I)), -0.29 (d, ³J(H,H) ) 2.5 Hz, 6 H, HSi(CH₃)₂(II)). ¹³C{¹H} NMR

(100.5 MHz, C₆D₆, 25 °C): δ 141.0/136.3/135.3/131.9/129.3/128.9/

127.5/127.2/123.1/121.3/120.5/108.4/100.6 (s, phenyl + indenyl), 18.2

(s, CH₃-indenyl), 3.22 (s, Si(CH₃)₂), 2.10 (s, HSiCH₃(I)), 1.95 (s,

HSiCH₃(II)). MS (CI): m/z (relative intensity) 738 (9) [M⁺], 468 (54)

[Me₂Si(2-Me-4-Ph-Ind)₂H⁺], 263 (100) [Me₂Si(2-Me-4-Ph-Ind)H⁺], 132

(20) [N(SiHMe₂)₂⁺]. Anal. Calcd for C₃₈H₄₄LaNSi₃: C, 61.85; H, 6.01;

N, 1.90. Found: C, 61.47; H, 6.12; N, 1.75.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methylinden-1-yl)di-

methylsilyl]lutetium(III) (rac-13e). Following the procedure described

above, 7e (716.2 mg, 1.000 mmol) and 3 (316.5 mg, 1.000 mmol)

yielded rac-13e (201.5 mg, 0.324 mmol, 32%) as lemon yellow prisms

(24 h of refluxing in toluene and 24 h of refluxing in mesitylene). IR

(Nujol, cm^-1): 2922 vs, 2853 vs, 2723 m, 1759 brw (ν(Si-H)), 1463

vs, 1409 w, 1377 s, 1341 m, 1335 m, 1269 m, 1245 s, 1150 w, 1086

sh, 1035 m, 997 w, 901 m, 833 m, 807 m, 783 s, 764 m, 746 s, 690 m,

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methyl-4,5-benzoinden-

1-yl)dimethylsilyl]yttrium(III) (rac-15b). Following the procedure

described above, 7b (630.1 mg, 1.000 mmol) and 5 (416.7 mg, 1.000

mmol) yielded rac-15b (459.7 mg, 0.723 mmol, 72%) as light yellow

prisms (18 h of refluxing in toluene and 13 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2922 vs, 2853 vs, 2724 m, 1811 brw (ν(Si-H)),

1608 w, 1462 vs, 1376 s, 1351 m, 1277 w, 1247 m, 1241 m, 1172 brs,

1096 w, 1027 m, 973 m, 938 w, 902 m, 896 w, 868 w, 836 w, 814 w,

1

658 w, 657 w, 644 m, 612 w, 570 w, 484 w, 448 s, 428 m. H NMR

(400 MHz, C₆D₆, 25 °C): δ 7.84 (d, ³J(H,H) ) 8.4 Hz, 2 H, H7), 7.42

3

(d, ³J(H,H) ) 8.0 Hz, 2 H, H4), 6.90 (dd, 2× J(H,H) ) 7.7 Hz, 2 H,

3

H6), 6.83 (dd, 2× J(H,H) ) 7.3 Hz, 2 H, H5), 6.19 (s, 2 H, H3), 3.29

1

3

1

(sept, J(Si,H) ) 146 Hz, J(H,H) ) 2.6 Hz, 2 H, SiH), 2.39 (s, 6 H,

CH₃-indenyl), 1.10 (s, 6 H, Si(CH₃)₂), 0.10 (d, ³J(H,H) ) 2.6 Hz, 6 H,

800 m, 766 s, 727 s, 682 m, 644 m, 467 m, 431 m. H NMR (400

3

MHz, C₆D₆, 25 °C): δ 7.95 (d, J(H,H) ) 7.4 Hz, 2 H, H7), 7.93 (d,

3

HSiCH₃(I)), 0.07 (d, J(H,H) ) 2.6 Hz, 6 H, HSiCH₃(II)). ¹³C{¹H}

3

4

³J(H,H) ) 7.4 Hz, 2 H, H6), 7.61 (dd, J(H,H) ) 7.7 Hz, J(H,H) )

1.3 Hz, 2 H, benzo-H), 7.27-7.18 (m, 6 H, benzo-H), 6.72 (s, 2 H,

H3), 2.65 (dsept, J(Y,H) ) 4.8 Hz, ¹J(Si,H) ) 133 Hz, ³J(H,H) ) 2.5

Hz, 2 H, SiH), 2.56 (s, 6 H, CH₃-indenyl), 1.15 (s, 6 H, Si(CH₃)₂),

NMR (100.5 MHz, C₆D₆, 25 °C): δ 136.6/130.8/130.2/123.7/123.5/

122.1/121.9/108.1 (s, C2-C9), 98.2 (s, C1), 17.91 (s, CH₃-indenyl-

(I)), 17.89 (s, CH₃-indenyl(II)), 3.06 (s, HSiCH₃), 2.78 (s, SiCH₃). MS

(CI): m/z (relative intensity) 621 (100) [M⁺- H], 605 (18) [M⁺

-

3

-0.03 (d, J(H,H) ) 2.5 Hz, 6 H, HSiCH₃(I)), -0.87 (d, J(H,H) )

2.5 Hz, 6 H, HSiCH₃(II)). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C):

δ 133.7/130.6/129.6/129.3/128.9/127.0/126.7/125.2/124.0/123.3/123.2/

109.4/104.0 (s, C-benzoindenyl), 18.2 (s, CH₃-indenyl), 3.07 (s, SiCH₃),

2.89 (s, HSiCH₃(I)), -0.10 (s, HSiCH₃(II)). ²⁹Si{¹H} NMR (79.5 MHz,

CH₃- 2H], 562 (4) [M⁺- SiHMe₂], 389 (10) [M⁺- N(SiHMe₂)₂],

316 (8) [SiMe₂(Me-Ind)₂H⁺], 310 (13) [SiMe₂(Me-Ind)₂⁺- CH₃], 187

(27) [SiMe₂(Me-Ind)H⁺], 132 (7) [N(SiHMe₂)₂⁺]. Anal. Calcd for

C₂₆H₃₆LuNSi₃: C, 50.22; H, 5.84; N, 2.26. Found: C, 50,12; H, 6.38;

N, 1.96.

1

C₆D₆, 25 °C): δ -15.90 (d, J(Y,Si) ) 1.2 Hz, Si_bridge), -26.61 (d,

Bis[bis(dimethylsilyl)amido][η⁵-bis(2-methyl-4-phenylinden-1-yl)-

dimethylsilyl]yttrium(III) (14b). Following the procedure described

above, 7b (630.1 mg, 1.000 mmol) and 4 (468.8 mg, 1.000 mmol)

yielded 14b (90.3 mg, 0.065 mmol, 11%) as lemon yellow prisms (24

¹J(Y,Si) ) 12.2 Hz, NSi). ⁸⁹Y NMR (19.48 MHz, toluene/C₆D₆, 30

°C): δ -93.5 (t, ¹J(Y,H) ) 4.7 Hz). MS (CI): m/z (relative intensity)

651 (31) [M⁺+ CH₃], 636 (31) [M⁺], 635 (60) [M⁺- H], 621 (11)

[M⁺- CH₃], 503 (28) [M⁺- N(SiHMe₂)₂], 416 (58) [SiMe₂(Me-

C₂-Symmetric ansa-Lanthanidocenes

J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3095

Table 5. X-ray Diffraction Collection Parameters for Organolanthanide Complexes

11c

rac-13b

rac-13e

rac-15b

rac-15e

formula

formula weight

crystal system

space group

a/Å

b/Å

c/Å

C₂₄H₄₄LaNSi₃

569.78

triclinic

P1h

9.529(1)

11.145(1)

13.573(1)

79.68(1)

83.26(1)

77.61(1)

1380.4(2)

2

C₂₆H₃₆YNSi₃

535.74

monoclinic

C2/c

15.110(4)

11.731(2)

15.699(5)

90

108.55(1)

90

2638.2(12)

4

1.349

23.6

1120

C₂₆H₃₆LuNSi₃

621.80

monoclinic

C2/c

15.0153(4)

11.8938(5)

15.7695(5)

90

108.145(2)

90

2676.21(16)

4

1.543

38.4

1248

C₃₄H₄₀YNSi₃‚(C₇H₈)_0.5

635.86‚46.07

triclinic

C₃₄H₄₀LuNSi₃

721.91

triclinic

P1h

11.6187(7)

12.1293(8)

13.9320(11)

78.198(8)

67.611(8)

63.935(7)

1629.1(2)

2

P1h

11.1193(6)

11.9449(5)

14.8399(8)

72.396(5)

75.824(6)

69.896(5)

1742.2(2)

2

R/deg

â/deg

γ/deg

V/Å³

Z

F

_calcd/g cm^-1

1.371

16.9

588

1.300

18.0

714

1.472

31.6

728

µ/cm^-1

F(000)

temperature/K

λ(Mo KR)/Å

diffractometer

scan type

193

163

273

193

293

0.710 73

STOE-IPDS

æ scans

1.9-24.7

12166/4365

3986

396

refined

0.0291/0.0247

0.0605

0.710 73

Nonius-CAD4

ω scans

2.2-26.0

4534/2472

2147

0.710 73

Nonius-κCCD

æ scans

4.9-25.4

4071/2203

2085

214

refined

0.0223/0.0206

0.0474

0.710 73

STOE-IPDS

æ scans

2.0-24.7

21813/5536

4525

373

mixed

0.0463/0.0358

0.0944

0.710 73

STOE-IPDS

æ scans

3.1-25.7

9550/5683

4486

365

calcd

0.0459/0.0332

0.769

θ range/deg

no. of total/unique data

no. of observed data

no of parameters

H atoms

214

refined

0.0403/0.0318

0.0742

final R1^a

final wR2^b

GOF

difference Fourier

1.037

0.91/-1.01

1.048

0.52/-0.45

1.094

0.27/-0.79

0.973

0.98/-0.45

0.916

0.74/-0.51

^aR1 ) ∑(||F_o| - |F_c||)/∑|F_o|. ^bwR2 ) [∑w(|F_o- F_c²|²)/wF_o]^1/2

2

Benz-Ind)₂H⁺], 237 (100) [SiMe₂(Me-Benz-Ind)H⁺], 221 (7) [YN-

834 w, 811 m, 800 m, 766 m, 741 m, 722 m, 683 m, 644 w, 467 m,

1

3

(SiHMe₂)₂⁺], 180 (10) [(Me-Benz-Ind)H⁺], 132 (13) [N(SiHMe₂)₂⁺],

431 w. H NMR (400 MHz, C₆D₆, 25 °C): δ 7.97 (d, J(H,H) ) 7.6

Hz, 2 H, H7), 7.89 (d, ³J(H,H) ) 9.0 Hz, 2 H, H6), 7.60 (dd, ³J(H,H)

) 7.9 Hz, ⁴J(H,H) ) 1.0 Hz, 2 H, benzo-H), 7.29-7.19 (m, 6 H, benzo-

+

118 (17) [N(SiHMe₂)₂- CH₃]. Anal. Calcd for C₃₄H₄₀NSi₃Y: C,

64.22; H, 6.34; N, 2.20. Found: C, 63.58; H, 6.37; N, 2.04.

Recrystallization of rac-15b from toluene results in incorporation of

solvent into the crystal. Anal. Calcd for C₃₄H₄₀NSi₃Y‚C₇H₈: C, 67.64;

H, 6.64; N, 1.94. Found: C, 66.54; H, 6.50; N, 1.94.

1

3

H), 6.75 (s, 2 H, H3), 2.98 (sept, J(Si,H) ) 142 Hz, J(H,H) ) 2.5

Hz, 2 H, SiH), 2.52 (s, 6 H, CH₃-indenyl), 1.14 (s, 6 H, Si(CH₃)₂),

3

-0.055 (d, J(H,H) ) 2.5 Hz, 6 H, HSiCH₃(I)), -0.77 (d, J(H,H) )

2.5 Hz, 6 H, HSiCH₃(II)). ¹³C{¹H} NMR (100.5 MHz, C₆D₆, 25 °C):

δ 132.5/130.7/129.7/128.8/126.9/126.1/125.3/124.6/124.3/123.4/123.2/

109.3/103.4 (s, C-benzoindenyl), 18.0 (s, CH₃-indenyl), 3.52 (s, SiCH₃),

2.98 (s, HSiCH₃(I)), 0.26 (s, HSiCH₃(II)). MS (CI): m/z (relative

intensity) 721 (37) [M⁺], 620 (68) [M⁺- H], 706 (20) [M⁺- CH₃],

588 (41) [M⁺- N(SiHMe₂)₂], 416 (45) [SiMe₂(Me-Benz-Ind)₂H⁺],

237 (100) [SiMe₂(Me-Benz-Ind)H⁺], 180 (17) [(Me-Benz-Ind)H⁺], 132

(14) [N(SiHMe₂)₂⁺], 118 (21) [N(SiHMe₂)₂⁺- CH₃]. Anal. Calcd for

C₃₄H₄₀NSi₃Lu: C, 56.67; H, 5.58; N, 1.94. Found: C, 66.38; H, 5.69;

N, 1.82.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methyl-4,5-benzoinden-

1-yl)dimethylsilyl]lanthanum(III) (rac-15c). Following the procedure

described above, 7c (680.1 mg, 1.000 mmol) and 5 (416.7 mg, 1.000

mmol) yielded rac-15c (320.3 mg, 0.467 mmol, 47%) as light yel-

low prisms (18 h of refluxing in toluene and 6 h of refluxing in

mesitylene). IR (Nujol, cm^-1): 2923 vs, 2853 vs, 2723 w, 1830 brw

(ν(Si-H)), 1610 w, 1462 vs, 1377 s, 1352 m, 1279 w, 1250 m, 1214

w, 1155 brs, 1096 w, 1027 m, 997 w, 974 m, 938 w, 897 m, 873 m,

834 m, 812 m, 800 m, 765 s, 724 w, 679 m, 645 w, 466 m, 432 m. ¹H

3

NMR (400 MHz, C₆D₆, 25 °C): δ 7.90 (d, J(H,H) ) 7.4 Hz, 2 H,

H7), 7.86 (d, ³J(H,H) ) 7.4 Hz, 2 H, H6), 7.61 (dd, ³J(H,H) ) 7.4 Hz,

[Bis(dimethylsilyl)amido][η⁵:η⁵-bisfluoren-9-yl-dimethylsilyl]-

yttrium(III) (16b). Following the procedure described above, 7b (945.0

mg, 1.500 mmol) and 6 (583.0 mg, 1.500 mmol) yielded 174 mg of an

orange powder (24 h of refluxing in toluene and 5 h of refluxing in

mesitylene). According to NMR spectroscopy, this powder contained

about 35% of 16b in addition to unreacted bis(fluorene) and a complex

containing a monocoordinated bis(fluorene). ¹H NMR (400 MHz, C₆D₆,

25 °C): δ 8.11 (d, ³J(H,H) ) 8.1 Hz, 4 H, fluorene-H), 8.08 (d, ³J(H,H)

) 8.3 Hz, 4 H, fluorene-H), 7.21 (t, ³J(H,H) ) 7.4 Hz, 4 H, fluorene-

H), 6.85 (t, ³J(H,H) ) 7.2 Hz, 4 H, fluorene-H), 3.21 (sept, ³J(H,H) )

⁴J(H,H) ) 1.1 Hz, 2 H, benzo-H), 7.25-7.17 (m, 6 H, benzo-H), 6.72

1

(s, 2 H, H3), 3.30 (m, J(Si,H) ) 140 Hz, 2 H, SiH), 2.53 (s, 6 H,

3

CH₃-indenyl), 1.15 (s, 6 H, Si(CH₃)₂), -0.087 (d, J(H,H) ) 2.5 Hz,

6 H, HSiCH₃(I)), -0.81 (d, ³J(H,H) ) 2.5 Hz, 6 H, HSiCH₃(II)). ¹³C-

{¹H} NMR (100.5 MHz, C₆D₆, 25 °C): δ 133.2/131.9/129.9/129.0/

128.7/127.1/126.6/124.7/123.2/123.1/122.0/108.7/104.7 (s, C-benzoin-

denyl), 17.8 (s, CH₃-indenyl), 3.12 (s, SiCH₃), 1.91 (s, HSiCH₃(I)),

-0.18 (s, HSiCH₃(II)). MS (CI): m/z (relative intensity) 686 (23) [M⁺],

685 (42) [M⁺- H], 671 (14) [M⁺- CH₃], 553 (33) [M⁺

-

N(SiHMe₂)₂], 416 (73) [SiMe₂(Me-Benz-Ind)₂H⁺], 237 (100) [SiMe₂-

(Me-Benz-Ind)H⁺], 180 (22) [(Me-Benz-Ind)H⁺], 132 (19) [N(Si-

2.5 Hz, 2 H, SiH), 0.96 (s, 6 H, Si(CH₃)₂), -0.13 (d, J(H,H) ) 2.6

3

Hz, 12 H, HSi(CH₃)₂).

+

HMe₂)₂⁺], 118 (11) [N(SiHMe₂)₂- CH₃]. Anal. Calcd for C₃₄H₄₀-

(Tetrahydrofurano)tris[bis(dimethylsilyl)amido]yttrium(III) (17b).

In a glovebox, 7b (630 mg, 1.00 mmol) was placed in a 100-mL flask

with fused reflux condenser, dissolved in 20 mL of toluene, and refluxed

under a slight argon purge for 12 h. Then the solvent was removed in

vacuo, and the residue was dried at 10^-4mbar, producing 17b as a

white powder (512 mg, 0.92 mmol, 92%). IR (Nujol, cm^-1): 2924 vs,

2854 vs, 2724 m, 2067 s, 1931 (sh) m (ν(Si-H)), 1462 vs, 1377 s,

1247 s, 1040 brvs, 897 vs, 837 s, 789 m, 784 m, 684 w, 609 w, 406 w.

LaNSi₃: C, 59.54; H, 5.88; N, 2.04. Found: C, 59.39; H, 6.14; N,

1.91.

rac-[Bis(dimethylsilyl)amido][η⁵:η⁵-bis(2-methyl-4,5-benzoinden-

1-yl)dimethylsilyl]lutetium(III) (rac-15e). Following the procedure

described above, 7e (1343.7 mg, 1.897 mmol) and 5 (790.5 mg, 1.897

mmol) yielded rac-15e (743.6 mg, 1.030 mmol, 54%) as light yellow

prisms (18 h of refluxing in toluene and 12 h of refluxing in mesitylene).

IR (Nujol, cm^-1): 2922 vs, 2853 vs, 2725 w, 1773 brw (ν(Si-H)),

1611 w, 1463 vs, 1377 s, 1351 m, 1276 w, 1249 w, 1238 m, 1162 m,

1138 w, 1095 w, 1080 w, 1041 m, 1027 m, 991 shm, 895 w, 857 w,

1

¹H NMR (400 MHz, C₆D₆, 25 °C): δ 4.94 (sept, J(Si,H) ) 162 Hz,

³J(H,H) ) 2.96 Hz, 6 H, SiH), 3.75 (brs, 4 H, THF(I)), 1.21 (m, 4 H,

3

THF(II)), 0.37 (d, J(H,H) ) 3.0 Hz, 36 H, SiCH₃). ¹³C{¹H} NMR

3096 J. Am. Chem. Soc., Vol. 122, No. 13, 2000

Eppinger et al.

(100.5 MHz, C₆D₆, 25 °C): δ 70.6 (s, THF), 24.2 (s, THF), 2.30 (s,

SiCH₃). ²⁹Si{¹H} NMR (79.5 MHz, C₆D₆, 25 °C): δ -22.39 (s). MS

(CI): m/z (relative intensity) ) 778 (13) [M⁺+ Y{N(SiMe₂H)₂}], 557

(2) [M⁺- H], 484 (44) [M⁺- THF + H], 470 (58) [M⁺- THF -

CH₃], 426 (100) [M⁺- N(SiMe₂H)₂], 353 (36) [M⁺- THF -

N(SiMe₂H)₂], 293 (69) [M⁺- 2N(SiMe₂H)₂], 132 (58) [N(SiMe₂H)₂⁺],

118 (93) [HN(HSiMe₂)(SiHMe)⁺]. Anal. Calcd for C₁₆H₅₀YN₃OSi₆:

C, 34.41; H, 9.03; N, 7.53. Found: C, 34.64; H, 8.80; N, 6.36.

X-ray Data Collection and Refinement. Single crystals of the

complexes 11c, rac-13b, rac-13e, rac-15b, and rac-15e were grown

at -35 °C from toluene/n-hexane solutions. The X-ray diffraction data

were collected on a Nonius CAD-4 diffractometer⁷⁶for complex rac-

13b, on a Nonius Kappa-CCD-system⁷⁶for rac-13e, and on a STOE-

IPDS⁷⁷for 11c, rac-15b, and rac-15e.

several electron density peaks in the vicinity of the symmetry center.

These peaks correspond to a disordered toluene solvate molecule. The

final least-squares refinement was performed using anisotropic thermal

parameters for the non-hydrogen atoms of the metal complex and

isotropic thermal parameters for the atoms of the solvate molecule.

Hydrogen atoms were located from difference Fourier maps and refined

for 11c, rac-13b, and rac-13e, refined only for Si-H in the case of

rac-15b, and placed in calculated positions for rac-15e. All details of

the data collection and the crystal and refinement parameters are

summarized in Table 5.

Acknowledgment. We thank the Deutsche Forschungsge-

meinschaft for the award of a DFG fellowship to R.A.

Preliminary positions of heavy atoms were found by direct methods,⁷⁸

while positions of the other non-hydrogen atoms were determined from

successive Fourier difference maps coupled with initial isotropic least-

squares refinement.⁷⁹All of the non-hydrogen positions were refined

anisotropically. For rac-15b, the difference Fourier synthesis showed

Supporting Information Available: Tables of crystal data,

structure solution and refinement, atomic coordinates, bond

lengths and angles, and anisotropic thermal parameters for 11c,

rac-13b, rac-13e, rac-15b, and rac-15e (PDF). X-ray crystal-

lographic data, in CIF format, are also available. This material

is available free of charge via the Internet at http://pubs.acs.org.

(76) Otwinowski, Z.; Minov, W. In Methods in Enzymology; Caster, C.

W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1996; Vol.

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stadt, Germany, 1995.

(78) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.

Crystallogr. 1998, 26, 343-350.

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(79) Sheldrick, G. M. SHELXL 93; Universita¨t Go¨ttingen, Germany,

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Article Doi

C2-Symmetric ansa-lanthanidocene complexes. Synthesis via silylamine elimination and β-SiH agostic rigidity

DOI: 10.1021/ja992786a

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