Synthesis and Crystal Structures of Lithium Complexes from the

Wing-Por Leung, Queenie Wai-Yan Ip, Suk-Yu Wong, and Thomas C. W. Mak ... Wing-Por Leung, Hung Kay Lee, Lin-Hong Weng, Bao-Sheng Luo, Zhong-Yuan ...
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Organometallics 1995, 14, 4832-4836

4832

Synthesis and Crystal Structures of Lithium Complexes from the Metalation of %PicolineDerivatives Wing-Por Leung,* Ling-Hong Weng, Ru-Ji Wang, and Thomas C. W. Mak Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong Received May 22, 1995@ Metalation of the 2-picoline derivatives 2 - R W C H C 5 h N ( R = Ph, SiButMe2;R = SiMe3, (tmeda = Me2NCHzCH2NMe2) in hexane affords the organolithium complexes [2-(Me3Si>PhC(CsHY)Li(tmeda)l (l),[2-(ButMe2Si)HC(C5HY)Li(tmeda)12 (21, and [2-Ph(H)C(C,H4N)Li(tmeda)12 (3). X-ray analysis has shown that the deprotonated species [ 2 - R R C C 5 h N ] - acts as an amide rather than a n alkyl ligand. The Li atoms are bonded more strongly to the pyridyl nitrogen than to the a-carbon, as shown by the long Li-Ca bond distances. The relatively short Ca-C,, distances of 1.382, 1.385, and 1.37 A in 1-3, respectively, suggest that they have substantial double-bond character. The C-C distances within the pyridine ring are significantly different and are consistent with a nonaromatic moiety having the charge localized a t nitrogen, befitting the description of 1-3 as "enamido" types of lithium complexes.

H)with Bu"Li/tmeda

Introduction Organolithium compounds are commonly used as transfer reagents in organometallic chemistry of the anionic fragment and also as a source of base or nucleophile for organic synthesis. In recent years there has been broad interest in structural studies dealing with organolithium compounds,l which provide a rationale of their reactivity based on their degree of aggregation and the extent and nature of their solvation. Metalation of 2-picoline using various lithium reagents to yield 2-picolyllithium compounds was reported as early as 1974.2 Lithium compounds derived from metalation of 2,6-dimeth~lpyridine~ and bis(pyridy1)methyl4 have also been reported. The structures of lithium compounds derived from 2-R3-,CHnC5H4N (R = SiMe3, Ph; n = 1, 2), prepared from their reactions with Bu"Li, were described r e ~ e n t l y .The ~ versatility of these lithium compounds as transfer reagents has been demonstrated in the synthesis of a variety of metal complexes.6 In principle, three resonance structures are possible for such a picolyl anion: (a) C-centered carbanion, (b) delocalized aza-allyl ion, and (c)N-centeredenamide ion.

carbanion

q3-aza-allyl

(a)

(b)

enamide (C)

X-ray structural studies of such lithium compounds provide useful information for assigning the type of complex formed. The molecular geometries of the lithium complexes 4-7, derived from the metalation of Abstract published in Advance ACS Abstracts, September 1,1995. (1)Setzer,W. N.;Schleyer, P. v. R. Adu. Organometal. Chem. 1986, 24, 352. (2)Beumel, 0.F.;Smith, W. N., Jr.; Rybalka, B. Synthesis 1974, @

43. (3)(a) Hacker, H.; Schleyer, P. v. R.; Reber, G.; Miiller, G.; Brandsma, L. J . Organomet. Chem. 1986,316,C4. (b) Schleyer, P. v. R.; Hacker, H.; Dietrich, H.; and Mahdi, W. J . Chem. SOC.,Chem. Commun. 1985,622.

R i M SiMeo e 3 Li

Et201i.Li LidOEtp

Me3SiQ

I'

5

4

SiMe3

SiMe3 q i Li M e 3

q i M e 3

(tmeda) 6

2-R3-,CHnC5H4N (R = SiMe3; n = 1,2),were shown to be influenced by solvents and the degree of substitution a t the ipso carbons5 The lithium atom in the centrosymmetrical dinuclear complex [{2-(Me3SikC(Li)CsH}~l (4) is bonded closely to Ca of one ligand and nitrogen of the other ligand, showing it to be a C-centered type of complex. In the presence of other coordinating ligands such as ether, tmeda (tetramethylethylenediamine), and the parent picoline, novel v3-azaallyl-type structures (4) (a)Gornitzka, H.; Stalke, D. Angew. Chem., Int. Ed. Engl. 1994, 33,693.(b) Gornitzka, H.; Stalke, D. Organometallics 1994,13,4398. (5) (a) Papasergio, R. I.; Skelton, B. W.; Twiss, P.; Raston, C. L.; White, A. H.; J. Chem. SOC,Dalton Trans. 1990,1161.(b) Engelhardt, L. M.; Jacobsen, G. E.;Junk, P. C.; Raston, C. L.;White, A. H. J.Chem. SOC.,Dalton Trans. 1988,1011. (6)(a) Colgan, D.; Papasergio, R. I.; Raston, C. L.; White, A. H.J . Chem. SOC,Chem. Commun. 1984,1708.(b) Papasergio, R. I.; Raston, C. L.; White, A. H.J. Chem. SOC.,Chem. Commun. 1983,1419. (c) Chem. Papasergio, R. I.; Raston, C. L.; White, A. H.J. Chem. SOC., Commun. 1984,612.(d) Henderson, M.J.; Papasergio, R. I.; Raston, C. L.; White, A. H.; Lappert, M. F. J . Chem. SOC.,Chem. Commun. 1986,672.(e) Engelhardt, L. M. ; Jolly, B. S.; Lappert, M. F.;Raston, C. L.; White, A. H. J . Chem. SOC.,Chem. Commun. 1988,336.(0 Jones, C; Engelhardt, L. M.; Junk, P. C.; Hutchings, D. S.; Patalinghug, W. C.; Raston, C. L.; White, A. H. J . Chem. SOC.,Chem. Commun. 1991, 1560.(g) Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H. Angew. Chem., Int. Ed. Engl. 1987,26,681.

0276-733319512314-4832$09.00/0 0 1995 American Chemical Society

Metalation

of

2-Picoline Derivatives

Organometallics, Vol. 14, No. 10, 1995 4833 Scheme la

LI

(i) and (iii)

(tmeda)

Ph

Ph

9

1

3

R=H

(iv)

~

0

,SiButMez

N

CH

I

Me 10

‘SiBdMe,

11

2

a Reagents and conditions: (i)Bu”Li, tmeda, hexane/ether;(ii) Me3siC1, hexane/ether;(iii)Bu‘MezSiCl, hexane/ether; (iv) MeI, hexanelether,

5-7 were found. In 5 and 6, each lithium atom is approximately in the plane of the pyridine ring with appreciable n-bonding between. Recently, structural studies on the diphenylpyridylmethyl complexes [PhzCCsH4NLi*20Etzl @a), [PhzCC5H4NNa.3THFI (THF = tetrahydrofuran) (8b),and [Ph~CC~.&Kpmdetal (pmdeta = (Me2NCHzCHz)zNMez) (8c) showed that the alkali-metal atoms are bonded directly to the nitrogen and suggested that the negative charge on the ligand is almost totally localized at the nitrogen atom.7 In the present paper, we report the synthesis and structural results of the organolithium complexes 1-3, which are based on the picoline derivatives 2RRCHC5H4N ( R = Ph or SiButMez; R = H, SiMe3). The influence of the degree of substitution and the role of different substituents a t Ca are shown in the structures of these compounds. The charge delocalization and the coordination behavior of the anion are considered and compared with those in 4-7 and 8a.

Preparation of Compounds 1-3. The lithium complexes 1-3 and their derivatives were prepared by the reactions of BunLi/tmeda and then SiMesCl or Me1 under different conditions, as shown in Scheme 1. BunLi in conjunction with tmeda acts as an activating agent; this use has become a common practice in the metalation of organic substrates.6 It enhances the reactivity of the lithium reagent as well as increases the solubility of the compound in a low-polarity organic solvent by decreasing the degree of aggregation. Replacement of the acidic a-hydrogen of 2-picoline or 2-benzylpyridine with lithium, followed by quenching with the appropriate chlorosilane or MeI, gave the silylated derivatives 2-Ph(Me3Si)CHC&.N(9),2-(ButMe~Si)CHzC5W (lo),and 2-(ButMezSi)CH(Me)C&N(111, respectively. In the preparation of 10,no bis-silylated compound, viz. 2-(ButMe2Si)2HCC5H4N,was obtained. It has been reported earlier that the conditions for the preparation of the monosilylated picoline derivative

2-(Me3Si)CHzC5HdN from the lithiated compound are rather ~ r i t i c a l .The ~ conditions for the formation of the monosilylated compound as the major product versus a mixture of the mono- and bis-silylated compounds are dependent on the order of adding the SiMesC1. This was explained by the relative acidities of the methyl groups in 2-methylpyridine and ~ - ( M ~ ~ S ~ ) C H Zand C ~the H~N relative concentration of SiMesCl and the lithiated species in the reaction m i x t ~ r e .In ~ the present work, the possibility of forming the bis-silylated compound 2-(ButMe2Si)zHCC5HD is minimal, as the SiButMez group is comparatively more bulky than the SiMe3 group, and hence incorporating a second SiButMez group would be sterically more unfavorable. The incorporation of different substituent groups (Ph, SiMes, and SiButMez) can change the steric crowding around Ca and decreases the degree of aggregation. It also alters the lipophilicity and the solubility of the lithium compounds, significant for the isolation of crystalline compounds from a hydrocarbon solvent. The lithium complexes were isolated as extremely airsensitive crystalline solids and characterized by ‘H and 13CNMR spectroscopy and formation of derivatives by treatment with SiMesCl and MeI. The lH NMR spectra of the lithium complexes show significant upfield shies for the ring protons when compared with their signals in the conjugate acids. This is consistent with the data obtained for some deprotonated methyl-substituted pyridines which are due to the delocalization of charges.1° The methine proton signal at 2.75 ppm of the lithiated compound 2 shows a significant downfield shift when compared with the methylene proton signal a t 2.33 ppm of its conjugate acid 10. This is due to the changing of the ipso carbon from sp3to sp2hybridization, suggesting the existence of the “enamide”contribution in solution. Crystal Structures of Compounds 1-3. The results of the single-crystal structure determinations of 1-3 have shown that all the anionic ligands [2-RRCHC5H4N]- ( R = Ph, SiButMez;R = SiMe3, H) are bonded strongly t o the lithium via the nitrogen and are consistent with the amide complexes being formed.

(7) Pieper, U.; Stalke, D. Organometallics 1993,12, 1201. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol 7.

(9)Jones, C.; Kennard, C. H. L.; Raston, C. L.; Smith, G. J. Organomet. Chem. 1990,396, C39. (10)Konishi, K.; Takahashi, K. Bull. Chem. Soc. Jpn. 1977,50,2512; 1983,56,1612.

Results and Discussion

(8) Wakefield, B. J.

4834 Organometallics, Vol. 14, No. 10, 1995

Leung et al.

Table 1. Selected Intramolecular Distances (A) and Angles (deg) with Estimated Standard Deviations (Esd’s)in Parentheses for [{2-(MesSi)PhC(Cd&N)) {Li(tmeda)}l(1) molecule I

Figure 1. Perspective view of one of the two independent molecules in 1. The thermal ellipsoids are drawn at the 35% probability level, and the interaction of the Li atom with the C(7)-C(8) bond is indicated by a broken bond. C1131

CllSl

C1161

Figure 2. Perspective view of the Cp dimeric molecule in 2. The thermal ellipsoids are drawn at the 35% probability level.

Figure 1 shows the molecular structure of one of the two independent molecules of 1; Figures 2 and 3 show the molecular structures of 2 and 3, respectively. Selected intramolecular structural data are shown in Tables 1-3, respectively. The comparative selected structural data for compounds having [2-RRCHC5H4Nl- ( R = Ph, SiButMe2; R = SiMes, H) ligands are compared in Table 4. From these data, it is possible to show the extent of charge delocalization in the anionic ligand, as depicted in

1.977(9) 2.128(9) 2.13(1) 3.288(8) 2.661(8) 2.74(1) 1.379(5) 1.347(6) 1.382(6) 1.489(7) 1.443(7) 1.350(7) 1.394(6) 1.356(8) 1.38(1) 1.36(1) 1.42(1) 1.35(2) 1.28(2) 1.42(2)

Li(2)-N(4) Li(2)- N(5 ) Li(2)-N(6) Li(2)-C(3 1) Li(2)-C(37) Li(2)-C(38) N(4)-C(32) N(4)-C(36) C(31)-C(32) C(31)-C(37) C(32)-C(33) C(33)-C(34) C(34)-C(35) C(35)-C(36) C(37)-C(38) C(37)-C(42) C(38)-C(39) C(39)-C(40) C(40)-C(41) C(41)-C(42)

1.979(8) 2.11 (1) 2.14 (1) 3.293(9) 2.68 (1) 2.78(1) 1.386(6) 1.343(6) 1.390(6) 1.490(6) 1.445(5) 1.340(7) 1.386(8) 1.362(6) 1.36(1) 1.359(9) 1.38(1) 1.33(1) 1.30(1) 1.397(9)

118.8(5) 121.8(5) 86.5(3) 72.8(3) 135.5(5) 125.8(4) 126.5(4) 115.7(3) 116.7(3) 124.5(3) 118.6(4)

N(4)-Li(2)-N(5) N(4)-Li(2)-N(6) N(5)-Li(2)-N(6) N(4)-Li(2)-N(37) N(5)-Li(2)-N(37) N(6)-Li(2)-N(37) Li(2)-N(4)-N(32) Li(2)-N(4)-N(36) Si(2)-C(31)-C(32) Si(2)-C(31)-C(37) C(32)-C(31)-C(37)

118.4(4) 123.9(4) 86.5(4) 73.2(3) 132.0(4) 127.9(4) 126.1(4) 115.4(4) 124.2(3) 116.7(3) 119.1(4)

Table 2. Selected Intramolecular Distances (A) and Angles (deg) with Estimated Standard Deviations (Esd’s)in Parentheses for [{2-(ButMezSi)HC(C&N)} { Li(tmeda)}12(2) Li(l)-Li(2) Li(l)-C(2) Li(1)-N( 1) Li(1)-N(2) N(l)-C(2) C(l)-C(2) C(2)-C(3) C(4)-C(5) N(l)-Li(l)-N(2) N(l)-Li(l)-N(la) N(2)-Li(2)-N( l a ) N(2)-Li(l)-N(2a) Si(l)-C(l)-C(2)

Figure 3. Perspective view of the C2 dimer in 3. The thermal ellipsoids are drawn at the 25%probability level.

molecule I1

2.88(1) 3.202 2.181(4) 2.217(5) 1.386(5) 1.385(7) 1.437(6) 1.406(6) 99.4(2) 95.4(2) 146.3(1) 84.7(3) 129.7(3)

Li(2)-C(2) Li(2)-N( 1) Li(2)-N(3) N(WC(6) C(1)-C(7) C(3)-C(4) C(5)-C(6) N(l)-Li(2)-N(3) N(l)-Li(2)-N(la) N(3)-Li(2)-N( 1a) N(3)-Li(2)-N(3a)

3.633 2.143(8) 2.140(9) 1.354(7) 1.489(7) 1.333(8) 1.358(8) 113.2(1) 97.6(5) 125.2(2) 85.2(5)

structures a-c above, by comparison of the Li-C,, LiNPY,and Ca-Cpy distances in these complexes. The LiC(1) (i.e. Li-C,) distances of 1-3, ranging from 2.70 to 3.42 A,are too long t o be considered bonding interactions, while other complexes have shorter distances such as 2.43 A in the C-centered ligand in 4 and 2.36 A in the v3-azaallyl-type ligand in 5. The Li-N(l) (i.e. LiNpy)distances in 1-3 are in good accord with those of typical lithium amides.l’ As a consequence of the charge being largely localized at the nitrogen, the C(1)C(2) (i.e. Ca-Cpy) distances of 1-3, ranging from 1.37 to 1.38A,suggest more enhanced double-bond character than in compounds 4-7 and 8a. The geometry at C(1) also indicates that the a-carbon is sp2-hydridized. The comparatively short C(3)-C(4) and C(5)-C(6) bond (11) Gregory, K.;Schleyer, P. v. R. Ado. Organomet. Chem. 1991, 37, 67.

Organometallics, Vol. 14, No. 10,1995 4835

Metalation of 2-Picoline Derivatives

Table 3. Selected Intramolecular Distances (A) and Angles (deg) with Estimated Standard Deviations (Esd's) in Parentheses for t { 2-Ph(H)C(CSH~N) 1{Li(tmeda)112 (3) Li(1)-Li(2) Li(P)-N(l) Li(2)-N( 2 ) N(1)-C(6) C(1)-C(7) C(3)-C(4) C(5)-C(6) C(7)-C(12) C(9)-C(10) C(ll)-C(12)

2.91(3) 2.26(1) 2.21(2) 1.33(1) 1.47(1) 1.34%1) 1.37(1) 1.39(1) 1.35(2) 1.35(1)

N(l)-Li(2)-C(l) C(l)-Li(2)-N(2) C(l)-Li(2)-N(la) C(l)-Li(2)-C(la) N(2)-Li(2)-N(2a) C(2)-C(l)-C(7)

55.7(3) 106.4(3) 95.2(5) 140.7(8) 84.3(7) 128.5(7)

Li(1)-N( 1) Li(2)-C(l) N(1)-C(2) C(l)-C(2) C(2)-C(3) C(4)-C(5) C(7)-C(8) C(8)-C(9) C(lO)-C(ll) N(l)-Li(2)-N(2) N(l)-Li(2)-N(la) N(2)-Li(2)-N(la) N(2)-Li(2)-C(la) Li(l)-N(l)-Li(2)

2.09(1) 2.70(1) 1.40(1) 1.37(1) 1.43(1) 1.41(1) 1.39(1) 1.37(1) 1.37(1) 96.7(2) 90.8(7) 157.6(3) 102.5(3) 84.2(6)

Table 4. Comparative Selected Structural Data for Compounds Having [2-RRCHC&Nl-(R'= H, Ph, SiMes; R = SiBu'Mez, H) Ligands compd 1

2 3 8a 4 5

R Ph H H Ph SiMe3 H

R Li-C(l) (A) Li-N (A) C(l)-C(2) SiMe3 3.288(8) 1.977(9) 1.382(6) SiMezBu' 3.418(av) 2.181(4) 1.385(7) 2.70(1) 2.09(1) 1.37(1) Ph Ph 3.26(4) 1.972 1.405(4) 1.96(2) SiMe3 2.43(2) 2.19 SiMe3 2.36(1)

distances within the pyridine rings also suggest that they have substantial double-bond character and nonaromaticity in the pyridine ring due to charge redistribution. The crystal structures of 5-7 have been shown to have the azaallyl type of bonding, the lithium atom being bonded to both the a-carbon and the nitrogen, and hence are indicative of delocalization of charge along the CCN linkage. In compound 4, the contact ion pair type of structure shows that the Li atom is bonded closely t o the C, atom. X-ray structure determination shows that compound 1 is monomeric. There are two independent molecules in the asymmetric unit, which have the same configuration. The anion [2-MesSi(Ph)CCbH4Nl- acts as an N-centered amide ligand bonded to the lithium via nitrogen a t a distance of 1.977(9) A,similar to that of 1.972(5)8, in 8a. The Li-C(l) distance of 3.288(8) is long and hence nonbonding. The negative charge of the anion is localized at nitrogen rather than the deprotonated carbon. The C(l)-C(2) distance of 1.382(6)8, and the geometry a t C(1) (sum of valence angles 359.8") suggests the presence of an exocyclic double bond. The alternating C-C bond distances are consistent with nonaromaticity within the pyridine ring. The shortest Li-C distance in 1 (Li-C7 = 2.661(8) A,Figure 1,Table 1)is too long to be considered a bonding interaction. The dihedral angles between the pyridyl and phenyl groups in each independent molecule of 1 are 79.1 and 90.2". Compound 2 is dimeric, with a crystallographic C2 axis passing through the two lithium atoms and the centers of each ethylene group of the tmeda ligands. The lithium atoms are bridged byfhe pyridyl nitrogen atoms to form a (LiN)2 four-membered ring. Each lithium atom in a distorted-tetrahedral environment is being surrounded by the nitrogen atoms from two substituted pyridyl ligands and the chelating tmeda. The Li-.*Li distance of 2.88(1)A is longer than that in the dimeric species 4 (2.560(9) A), which bears a smaller SiMe3

A

group. The average Li-N, disltance of 2.162 8, is significantly longer than the sirtiilar distance in 1, presumably due to repulsion between the lithium atoms, and is a consequence of the intermolecular amide bridge formation. The Si atom is almost in the plane of the pyridyl ring, a feature similar tc) that in [{2-(MesSi)HC(C5H&J)Li(tmeda)}z1.5The Si( L)-C(l)-C(2) angle of 129.7", the C(l)-C(2) distance of 1.385(7) 8,, and the C-C bond distance within the pyridyl ring suggest that the anion ligand behaves as an N-centered amide type ligand. Compound 3 is also a dimer of C2 symmetry similar t o that in 2, and the anionic ligand [2-MesSi(Ph)CCsHdNI- acts as a bridging ainide for the lithium atoms, which are in different environments. Li(1) is coordinated by the tmeda ligand and the bridging pyridyl nitrogen atom in a distorted-tetrahedral geometry. The Li to ipso carbon distance of 2.70 8, is again too long to be considered a bonding interaction. The butterfly conformation is probat;ily caused by the twist of the tmeda molecules relative to the anionic ligands. The Li- *Lidistance of 2.91(3) 8, is the longest between the dimeric compound 2 and [{2-(MesSi)HC(CsHsN)Li(tmeda)}~].This is presumably clue to the weak interaction of Li(2) with C(U, which pulls it further from the opposite Li atom of the (LiN)2 four-membered ring. The two amide bridges are unsymmetrical, as shown by the different Li-N distances of 2.09 and 2.26 A, respectively. By comparison of the available structural results of the lithium complexes with the ligand [2-Ra"CHC&Nlin this work and those in the literature, it appears that the nature of lithium-ligand interactions, the electron density distribution within the ligand, and also the degree of aggregation of the co mplex depend on (i) the steric and electronic nature of the group at the ipso carbon, (ii) the degree of substitution at the ipso carbon, and (iii) the nature and the pres,enceof an ancillary base ligand such as tmeda or Et2O. The structural studies have clearly shown that the 2 -picoline derivatives are capable of ligation in Werent ways due to delocalization of charge. Surprisingly, the N-centered amide type of coordination mode seems to be more predominant, although the metal complexefa derived from these organolithium complexes are mainly metal alkyl complexes.

Experimental Section All manipulations were carried out under an inert atmosphere of argon gas by standard Schlenk techniques or in a dinitrogen glovebox. Solvents w'ere dried over and distilled from CaHz (hexane) andor Na (EtzO). 2-Picoline, 2-benzylpyridine, Bu'MezSiCl, and MesSiCl were purchased from Aldrich and used without further purification. The lH and 13C NMR spectra were recorded at 250 a n d 62.90 MHz, respectively, using a Bruker WM-250 or ARX-800 instrument. All spectra were recorded in benzene-&, a n d the chemical shifts 6 are relative to SiMe4. Preparation of 2-(ButMe~S~i)CHzC6Ha (lo), the Conjugate Acid of the Anion of 2. To a solution mixture of 2-picoline (5.70 g, 61.2 mmol) a n d tmeda (7.15 g, 61.5 mmol) in ether (70 mL) at 0 "C was slowly added a solution of BunLi in hexane (39.0 mL, 1.6 M,61.4 mmol). The solution changed from colorless to red. The red solution was added to a solution of BulMezSiCl (8.90 g, 5.91 mrnol) in ether (40 mL) at 0 "C. The resulting yellow slurry wasi stirred for 5 h at 25 "C; water

4836 Organometallics, Vol. 14, No. 10, 1995 (20 mL) was added. The organic layer was separated, and the aqueous layer was ext:racted with 2 x 60 mL of ether. The ethereal extracts were combined with the organic layer and dried over anhydrous MgSO4. The filtrate was concentrated, and the product distil1al;e of bp 59-61 oC/10-2mmHg collected was collected, corresponding to 2H (9.86 g, 80.5%). Anal. Found: C, 69.24; H, 10.21; N, 6.77. Calcd for C12H21NSi: C, 69.50; H, 10.21; N, 6.75. 'H NMR (250 MHz, C&): 6 -0.02 (s, 6H, SiMez), 0.88 (s, 9H, SiBu'), 2.33 (s, 2H, SiCHd, 6.57 (m, l H , CbH4N), 6.65 (nn, l H , C5H4N), 7.04 (m, l H , C5H4N), 8.42 (m, l H , C5H4N). I3C NMR (62.90 MHz, C&): 6 -5.93 (SiMez), 16.92 (SiCHZ), 26.60 (CMe, %But), 26.24 (C, SiBu'), 119.08 (CH, C5Ha), 122.28 (CH, C5H4N), 135.34 (CH, C5H4N), 149 (C, C5H4N). Mass spectrum ( m l z ) : 207 (P+). Preparation of 2-(rfltesSi)CHPhCsH4N,the Conjugate Acid of the Anion of It. To a solution of 2-benzylpyridine (5.00 g, 29.5 mmol) and 1;meda (4.60 mL, 30.5 mmol) in ether (30 mL) at 0 "C was slow1,yadded a solution of BunLiin hexane (18.70 mL, 30.0 mmol). 'The resulting deep red solution was warmed to room temperature and was stirred for 4 h. The red solution was then added to a solution of MesSiCl(3.40 g, 31.3 mmol) in ether (20 rnL) and was stirred at room temperature for a further 4 h. To the white suspension was added water (20 mL), and the organic layer was separated. The aqueous layer was extracted with ether (2 x 30 mL). The ethereal extracts were combined with the organic layer and dried over anhydrous MgS04. The filtrate was concentrated to a yellow viscous oil. After addition of MeOH (5 mL) and storage at -20 "C, a white crystalline solid was isolated, washed with cold MeOH, and dried under vacuum to give 1H (4.40 g, 61.7%). Anal. Found: C, 74.27; H, 7.93; N, 5.63. Calcd for C15HlgNSi: C, 74.63; H.,17.93; N, 5.80. lH NMR (250 MHz, C&): 6 0 . 1 3 ( ~9H, , SiMe3), 3.56 (S, 1H, CHI, 6.55 (m, 1H), 6.76 (d, l H , J = 7.4 Hz), 6..97(t, l H , J = 7.7 Hz), 7.03 (d, l H , J = 9.53 Hz), 7.17 (m, 2H), 7.46 (d, 2H, J = 7.65 Hz), 8.46 (d, l H , J = 3.75 Hz). 13C K'MR (62.90 MHz, C&): 6 -1.72 (SiMes), 48.71 (C-1, 120.03, 123.67, 125.28, 128.75, 135.78, 142.25, 148.92, 163.82 (arci:matic/C5H4N). Mass spectrum ( m/ 2): 241 (P+). Preparation of [{2-(Me~Si)CPhCJ&N}{Li(tmeda)}l(1). To a solution of 1H (3.72 g , 15.4 mmol) and tmeda (2.40 mL, 15.9 mmol) at 0 "C was aclded a solution of BunLi in hexane (10.0 mL, 1.6 M, 16.0 mniol). The orange solution was set aside at -20 "C for 1 day, whereafter orange crystals of the title compound 1 (5.51 g, 98.3%) were collected and dried in UUCUO. 'H NMR (500 MHz, C6D6): 6 0.38 (8,9H, SiMes), 1.23 (s, 4H, NCHz), 1.41 (9, 12H, NMeZ), 5.69 (t, l H , J = 5.5 Hz), 6.53 (t, l H , J = 7.0 Hz), 6.68 (d, l H , J = 9.0 Hz), 6.74 (t, l H , J = 8.0 Hz), 6.88 (t,2H, J = 7.5 Hz), 7.15 (s, l H ) , 7.35 (d, 2H, J = 8.0 Hz). l3cNMR (62.90 MHz, C6D6): 6 2.45 (SiMeg), 45.30 (C-)(NCHz), 56.31 (NCHz),80.34 (NMeZ),102.49, 117.55, 120.75, 125.25, 128.75, 129.114, 131.31, 133.02, 147.14, 150.22, 163.81 (aromatic/CsH4N). Preparation of [{2-(ButlMezSi)CHC&N}{Li(tmeda)}l~ (2). To a solution of 2H (2.29 g, 11.04 mmol) and tmeda (1.67 mL, 11.06 mmol) at 0 "C was added a solution of Bu"Li in hexane (6.95 mL, 1.6 M, 11.12 mmol). The orange solution was set aside at -20 "C for 1day; the orange crystals deposited were collected and dried in zi~zcuoto give the title compound 2 (3.53 g, 97%). 'H NMR (500 MHz, C&): 6, 0.35 (s, 6H, SiMez), 1.22 (s, 9H, SiBu'), 1.88 (s, 4H, NCHz), 2.12 (s, 12H, NMed, 2.75 (s, l H , SiCH), 5.51 (t, l H , J = 5.8 Hz), 6.47 (d, l H , J = 9.0 Hz), 6.55 (t, l H , e J = 7.5 Hz), 7.21 (d, l H , J = 5.0 Hz) (CsHdN). I3C NMR (62.510 MHz, C6D6): 6 -3.02, 19.89, 45.71, 57.21, 100.17, 118.24, 132.63, 147.92, 168.24. Preparation of [{2-PhCHICsH4N}{Li(tmeda)}]z (3). To a solution of 2-benzylpyridine (4.36 g, 25.8 mmol) and tmeda (4.5 mL, 30.1 mmol) at 0 "C was added a solution of Bu"Li in hexane (16.5 mL, 1.6 M, 26.4 mmol). The deep red solution was set aside at 20 "C for 1day; the resulting dark red crystals were collected and dried in UUC'UOto give the title compound 3

h u n g et al. Table 6. X-ray Crystallographic Data for 1-3 1 2 3 f'21/~(N0.14) c2 (N0.5) C ~ / (No.15) C 19.345(4) 14.009(3) 14.191(3) 11.918(2) 14.957(3) 19.153(4) b (A) c (A) 21.210(4) 11.113(2) 16.514(3) P (deg) 103.04(3) 108.97(3) lOO.OO(3) v (A)3 4764(2) 2202(1) 4420(2) z 8 2 4 density (g ~ m - ~ ) 1.014 0.994 0.963 p (mm-') 0.11 0.11 0.06 F(OO0) 1584 128 1396 2&,, (de!) 44 48 48 no. of unique data 5726 2614 3437 measd 3117 1672 1162 no. of obsd data 0.08 0.062 0.055 RF 0.079 0.061 0.054 %F (7.67 g, 98%). Crystals used for X-ray determination were obtained by recrystallization from ether. Preparation of 2-(BufMezSi)C(Me)HC&N(11)from 2. To a solution of 2 (1.35 g, 4.01 mmol) was added slowly a solution of Me1 (0.58 g, 4.09 mmol) in ether at 0 "C. The whole reaction mixture was warmed to room temperature and stirred for 4 h. To the resulting yellow mixture was added 10 mL of water, and the organic layer was separated and dried with anhydrous MgS04. It was then filtered, and the solvent was removed under vacuum to give a pale yellow oily residue (99% yield). Anal. Found: C, 69.79; H, 10.46; N, 6.20. Calcd for C13H23NSi: C, 69.33; H, 10.47; N, 6.33. 'H NMR (250 MHz, C&): 6 -0.10 (s, 3H, SiMe), 0.08 (s, 3H, SiMe), 0.86 (s, 9, SiBut), 1.48 (d, 3H, J = 7.25 Hz, CMe), 2.52 (9, l H , J = 7.38 Hz, CHI, 6.56 (t, l H , J = 5.86 Hz), 6.70 (d, l H , J = 7.93 Hz), 7.04 (t, lH, J = 7.65 Hz), 8.44 (d, l H , J = 4.72 Hz) (C5H4N). 13CNMR(62.90MH~,C&j): 6-6.75,7.05,16.15,17.69,27.10, 30.45, 119.49, 121.70, 135.34, 149.25. Mass spectrum ( m / z ) : 221 ( P - l)+. X-ray Crystallography. The crystallographic data for 1-3 are shown in Table 5. Crystals of 1 and 2 were grown from hexane and those of 3 from ether. X-ray data were collected using single crystals sealed in capillaries under dinitrogen, and raw intensities were collected on a Siemens P4PC fourcircle diffractometer at 294 K. The structures were solved by direct phase determination, and all non-hydrogen atoms were subjected to anisotropic refinement. The hydrogen atoms were generated geometrically (C-H bonds fixed at 0.96 A) and allowed to ride on their respective parent C atoms; they were assigned appropriate isotropic temperature factors and included in the structure factor calculations. In 3 there is free tmeda in the lattice cavities formed by the loose packing of the complex molecules, and its site occupancy factor was assigned to be '/z on account of its low electron density. Computations were performed using the SHELXTL PC program packageI2 on a PC 486 computer. Analytic expressions of atomic scattering factors were employed, and anomalous dispersion corrections were in~orporated.'~

ZPE

Acknowledgment. This work was supported by Hong Kong Research Grants Council Earmarked Grant CUHK 22/91. Supporting Information Available: Tables of crystal data, bond distances and angles, atomic coordinates and equivalent isotropic temperature factors, anisotropic thermal parameters, and hydrogen atom coordinates and assigned isotropic temperature factors for 1-3 (20 pages). Ordering information is given on any current masthead page. OM950373M (12) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick, G. M., Krieger, C., Goddard, R., Eds.; Oxford University Press: New York, 1985; p 175. (13)International Tables for X-Ray CrystalZography; Kynoch Press: Birmingham, U.K., 1974.