Organometallics 1984, 3, 977-983 The common feature to isomers a, exo, and d, endo, is to have the propyl group R only in the vicinity of the nitrosyl ligand. On the other hand, it is likely that the six other isomers (Scheme XII) undergo steric hindrance between the propyl group and either the cyclopentadienyl ring or the triphenylgermyl moiety. The mechanism leading to this isomerization is not perfectly clear at the present time and does not seem to be just a rotation of the allylic ligand like that of cyclopentadienyl rings in ferrocene. Actually Faller et have proposed an isomerization mechanism involving the decoordination of the $-allylic to an #-allylic ligand. Conclusion The reaction of anions [(05-C5H5)(CO) (L)(MaPh3)M~]with unsaturated iodides seems to be general, with some limitations however. Allyl iodides give the neutral ubonded square-pyramidal complexes in which the allyl and the group 4B metal ligands are trans to each other. These complexes may undergo thermal reaction to q2allyl complexes via v3-all 1 ones. According to the nature of MT and M4Bthe ql-, 7 -, or .r12-allyliccomplexes can be
! ’
(22) Faller, J. W.; Shvo, Y.; Chao, K.; Murray, H. H. J . Organomet. Chem. 1982,226, 251.
977
isolated. Nethertheless the reaction pathway seems to be the same in all cases, but the reaction can stop and give the 77, intermediate. u complexes bearing w-alkenyl ligands undergo thermal reaction to q3-allylicones, with isomerization of the chain. This structure is established unambiguously by an X-ray structure determination. Interestingly, among the possible isomers, the two having less steric hindrance are obtained. Acknowledgment. We are grateful to Dr. J. C. PromB, Centre de Recherche de Biochimie et de GBnBtique Cellulaires, Toulouse, for the recording and calculations of mass spectra by field desorption and to R. Astier and Dr. E. Philippot of the laboratoire de Chimie MinBrale, Chimie des MatBriaux, E.R.A. 314, UniversitB des Sciences et Techniques du Languedoc, for the help with X-ray data collection on a Nonius CAD-4 diffractometer Registry No. 1, 89958-46-3; 2,89958-47-4; 3, 89958-48-5; 4, 89975-08-6;5, 89958-49-6;6, 89958-50-9;7, 89975-09-7;8, 89958-51-0; 9,89958-52-1; 10,89958-53-2; a,exo-11,89958-54-3; d,endo-l1,90025-744; a,exo-l2,89958-55-4; d,endo-12,90129-08-1.
Supplementary Material Available: A table of vibrational thermal parameters (Table IX) and a listing of observed and calculated structure factors (Table X) (13pages). Ordering information is given on any current masthead page.
Preparation of Group 4A Complexes Containing Tri-tert-butylmethoxide (tritox), a Steric Cyclopentadienyl Equivalent Timothy V. Lubben, Peter T. Wolczanski,’ and Gregory D. Van Duyne Department of Chemisfry, Baker Laborafory, Cornell Universlv, Ithaca, New York 14853 Received January 12, 1984
Li(tritox),((CHJ3C),COLi, reacts stoichiometrically with MC14(M = Zr,Ti) to form (trito~)~ZrCl,-Li(OEg)Z (11, ( t r i t o ~ ) ~ M (M C l ~= Zr (21,Ti (4)), and (tritox)TiCl, (5). From TiC1, and Li(tritox) (1:2),a complex (3) was obtained; 3 yielded the corresponding dichloride 4 upon tentatively formulated as “(trit~x)~TiCl”
treatment with CClk Derivatization of the M(IV) chlorides with CH3Li produced (tritox),M(CH,), (M = Zr (6), Ti (7)) and (tritox)Ti(CH,), (8). Controlled alcoholysis of Zr(CH2Ph),,Zr(CH,C(CH,),),, and 6 with (tritox)H gave (tritox)Zr(CH,Ph), (91, (tritox)Zr(CH2C(CH3),),(lo), and (tritox),ZrCH, (ll),respectively. An X-ray structure determination of 1 showed the tritox units equatorially disposed in this seudo-tbp complex. Crystal data: monoclinic, E 1 / c , a = 12.946 (3)A,b = 14.026 (3)A,c = 26.257 (4) %,fi = 121.016 (12)”,2 = 4,and T = -75 “C. Standard refinement procedures yielded an R factor of 0.079 from 4346 data where pol I3uQFOI).The spatial resemblence of tritox to cyclopentadienyl(Cp) is discussed, the short Zr-0 bonds (1.895A average) and near linear Zr-0-C L’S (169”average) of 1 also suggest that tritox may function as a five-electron donor, like Cp. Introduction An important challenge confronting the organometallic chemist concerns the synthesis of complexes that are coordinatively unsaturated, since this characteristic is necessary for observation of metal-centered reactivity.l One approach to this problem involves the use of both neutral and anionic ancillary ligands that sterically “saturate” a metal center that may remain coordinatively and electronically unsaturated. For example, by using bis(trimethylsilybnide, a number of workers have prepared low (1) Parshall, G. W. ”Homogeneous Catalysis”; Wiley-Interscience: New York, 1980.
coordinate M[N(Si(CH,),),], complexes that span the periodic table.2~~ In a similar fashion, sterically comparable phosphide ligands are currently being e ~ p l o i t e d . Bulky ~ neutral ligands, principally phosphines (PR,, R = cyclohexyl, tert-butyl, etc.), have been used to prepare several (2) Bradley, D. C.; Chisholm, M. H. Acc. Chem. Res. 1976, 9, 273. (3) (a) Anderson, R. A. Znorg. Chem. 1979,18,1724. (b) Simpson, S. J.; Turner, H. W.; Anderson, R. A. Zbid. 1981,20, 2991. (c) Tilley, T. D.; Zalkin, A,; Anderson, R. A.; Templeton, D. H. Zbid. 1981, 20, 551. (d) Anderson, R. A. Zbid. 1979, 18, 2929. (4) (a) Baker, R. T.; Krusic, P. J.; Tulip, T. H.; Calabrese, J. C.; Wreford, S. S. J. Am. Chem. Soc. 1983,105,6763. (b) Jones, R. A.; Stuart, A. L.; Atwood, J. L.; Hunter, W. E. Organometallics 1983,2, 1437 and references therein.
0276-7333/84/2303-0977$01.50/0 0 1984 American Chemical Society
978 Organometallics, Vol. 3, No. 7, 1984
Lubben, Wolczanski, and Van Duyne
low coordinate group 6 and 8 complexes.6 Both types of encumbering ligands suffer some drawbacks. Bulky phosphines at times may undergo substitution reactions by typical neutral substrates (i.e., CO, olefins, etc.), thus hampering their ability to function as ancillary ligands. Although amides and phosphides may not be easily displaced by neutral donors, they, unlike the phosphines, are best viewed as occupying a wedge of space afid may pack together efficiently on a metal, thus impeding the path of small molecule substrates. In an effort to combine the best properties of the aforementioned ligands, the application of the steric saturation theme to transition-metal alkoxide chemistry may be accomplished via the utilization of tri-tert-butylmethoxidee as an ancillary ligand. Recent notable advances in the chemistry of alkoxide-containing complexes lend credence to the application of this bulky ligand; the varied reactivity displayed by hexaalkoxydimolybdenum and ditungsten complexes,' the acetylene metathesis capability of (O-t-Bu),W=C-R species? and the development of potent Nb, Ta,B and Wl0 olefin metathesis catalysts containing tert-butoxide and neopentoxide are convincing examples. Tri-tert-butyl methoxide (tritox) forms a steric
-
n
donor), the initial synthetic studies of tritox-containing complexes reported herein are modeled after known group 4 cyclopentadienyl species.15 Synthetic Studies The most straightforward route to alkoxy complexes is the displacement of halide by alkoxide.16 The tritox reagent employed in these metathetical reactions is Li(tritox), prepared as a white crystalline solid in >90% yield via deprotonation of the parent alcohol (tritox)H1' by n-butyllithium (eq 1).l8 Li(tritox) was shown to be far ((CH3)3C)3COH+ n-BuLi (tritox)H
M
more versatile than either K(tritox) or BrMg(tritox), prepared via addition of KCH2C6H5or CH3MgBr to (tritox)H, respectively, and was used exclusively. Treatment of ZrC14with 2 equiv of Li(tritox) in diethyl ether led to the isolation of white, crystalline (trit ~ x ) ~ Z r C l ~ . L i ( O (1) E b )in~ high yield (80%)according to eq 2. The bound LiCl may be removed from the coor-
ItritoxIM IICH313C13COM
conell about a metal, similar to a bulky phosphine, yet is anionic and thus akin to bis(trimethylsily1)amide. The cone angle of tritox (1250)12 approaches that of cyclopentadienyl (Cp cone angle = 136O)l1J3and models indicate that its methyl hydrogens overhang the oxygen in a manner sufficient to prevent the formation of alkoxide bridges that are prevalent for smaller RO- ligands (R= CH3, C2H5, etc.).14 In view of the steric simikity to Cp (five-electron (5) (a) Otauka, S.; Yoshida, T.; Mataumoto, M.; Nakateu, K. J. Am. Chem. SOC.1976, 98, 5850. (b) Yoshida, T.; Otauka, S. Ibid. 1977, 99, 2134. (c) Maeon, M. G.; Ibere, J. A. Ibid. 1982,104,5153. (d) Kubae, G. J. J.Chem. SOC.,Chem. Commun. 1980,61 and references therein. (e)
mer, P. G.; Bradley, D. C.; Hurethouee,M. B.; Meek, D. W. Coord. Chem. Reu. 1977, 24, 1. (6) To avoid confusing RO. terminology, alkoxidea (formally evenelectron donors ae RO-) will be referred to ae odd-electron donors in the neutral counting sense. (7) (a) Chisholm, M. H. J. Organomet. Chem. 1982, 279, 79. (b) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Rothwell, I. P. J. Am. Chem. SOC.1982,104,4389. (c) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Rater", A. L. Inorg. Chem. 1982,21,978. (d) Chisholm, M. H.; Huffman, J. C.; Kirkpatrick, C. C. Zbid. 1983,22,1704. (e) Chisholm,M. H.; Folting, K.; Huffman, J. C.; Rothwell, I. P. Organometallics 1982,1, 251 and references therein. (8)(a) Wengrovius,J. H.;Sancho, J.; Schrock, R. R. J. Am. Chem. Soc. 1981, 103, 3932. (b) Sancho, J.; Schrock, R. R. J. Mol. Catal. 1982,15, 75. (c) Chisholm, M. H.; Huffman, J. C.; Rothwell, 1. P. J. Am. Chem. SOC.1981,103,4245. (d) Schrock, R. R.; Listemam, M. L.; Sturgeoff, L. G. Ibid. 1982,104,4291. (e) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. Inorg. Chem. 1983,22,2903. (0Chisholm, M. H.; Huffman, J. C.; Marchant, N. S. Ibid. 1983, 105, 6162. (9) Rocklage, S. M.; Fellmann, J. D.; Rupprecht, G. A.; Messerle, L. W.; Schrock, R. R. J. Am. Chem. SOC.1981,103, 1440. (10) (a) Schrock, R. R.; Rocklage, S. M.; Wengrovius, J.; Rupprecht, G.; Fellmann, J. J. Mol. Catal. 1980,8,73. (b) Wengrovius, J.; Schrock, R. R. Organometallics 1982,1,148. (c) Krees, J.; Wesolek, M.; Osbom, J. A. J.Chem. SOC.,Chem. Commun. 1982, 514. (d) Kress, J.; Wesolek, M.; Le Ny, J. P.; Osborn, J. A. Zbid. 1981, 1039. (11) Tolman, C. A. Chem. Rev. 1977, 77, 313. (12) Construction of (tritox)M and CpM models using Framework Molecular Models (Prentice-Hall,Inc.) showed that both ligandsadopted cone angles of about 125O, in conflict with ref 11. (13) Lauher, J. W.; Hoffmann, R. J.Am. Chem. SOC.1976,98,1729.
hexane
((CH&C)3COLi + C4H10 (1) (tritox)Li
BLi(tritox) + ZrC1,
=
-
1
hexane
E@
(trit~x)~ZrCl,-Li(OEt~)~ + 2LiC1 (2) 1
( t r i t o ~ ) ~ Z r+ C lLiCl ~ + 2Et20
(3)
2
dination sphere of 1 via addition of hexane, yielding the (eq 3). Although dichloride ( t r i t o ~ ) ~ Z r(2) c l quantitatively ~ easily isolable, 2 decomposes in benzene solution over a 24-h period at 25 OCl9 and must be stored as a solid under nitrogen at -20 "C. With the hope of obtaining a dimer analogous to the known diamagnetic [Cp2TiC1I2complex,20 Tic&was treated with 2 equiv of Li(tritox) in diethyl ether (eq 4) over a 3.5-day period. Contrary to expectations, the 2Li(tritox)
+ TiC13
EhO
"(trit~x)~TiCl" + 2LiCl 3
(4)
pale mint green precipitate 3 that was isolated from hexane solution exhibited a clean single-line EPR spectrum at g = 1.952 (2) accompanied by 47Ti(I = 5/2) and 49Ti (I= 7/2) satellites (a(Ti) = 13 G)and is thus tentatively formulated (3).21 Surprisingly, no indication of as "(trit~x)~TiCl" (14) (a) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. 'Metal Alkoxides"; Academic Prew: New York, 1978. (b) Bradley, D. C. Adu. Znorg. Chem. Radiochem. 1972, 15, 259. (c) Mehrotra, R. C. Zbid. 1983,26, 269. (15) Wailes, P. C.; Coutta, R. S. P.; Weigold, H. "Organometallic Chemistry of Titanium, Zirconium and Hafnium"; Academic Press: New York, 1974 and references therein. (16) For other Ti and Zr alkoxy halide and alkyl complexes see: (a) Weidmann, B.; Seebach, D. Angew. Chem., Znt. Ed. Engl. 1983,22, 31. (b) Rausch, M. D.; Gordon, H. B. J. Organomet. Chem. 1974, 74,85. (c) Reetz, M. T.; Steinbach, R.; Westermann, J.; Urz, R.; Wenderoth, B.; Peter, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 135. (d) Bert, M. B.; Gervais, D. J. Organomet. Chem. 1979,165, 209 and references therein. (17) (a) Syper, L. Rocz. Chem. 1973, 47, 433. (b) Bartlett, P. D.; Lefferta, E.B. J. Am. Chem. SOC.1966, 77, 2804. (18) X-ray structural characterization of Li(tritox) indicates that it is a dimer in the solid state. Power, P. P.; private communication. (19) This decomposition appeara to be autocatalytic and occurs concomitant with either benzene alkylation or oligomerization,presumably via carbonium ion or Lewis acid catalyzed Friedel-Crafta processes; a 0.3 M benzene solution 'gels" within a 24-h Deriod. See: Benner. L. S.: Lai. Y.-H.; Vollhardt, K. 'P. C. J. Am. C h e k SOC.1981,103, 3609. (20) Coutta, R. S. P.; Wailes, P. C.; Martin, R. L. J. Organomet. Chem. I~
1973, 47, 375.
Group 4A Complexes Containing Tri-tert- butylmethoxide
trimethyl phosphite binding was observed by EPR, despite a 100-fold excess of the added ligand.22 Reactivity complimentary to [Cp2TiClI2is displayed by “(trit~x)~TiCl” (3); 3 is cleanly transformed into the dichloride (tri(4),l ~via the addition of CC14 (eq 5). The preto~)~TiC
hexane
“(trit~x)~TiCl” + CCl,(excess) 2Li(tritox) + TiC14
(tritox),TiCl, (5)
-+ EtzO
4
4
2LiC1
(6)
ferred route to the white, crystalline dichloride 4 is the metathesis reaction of TiC14 and Li(tritox) illustrated in eq 6 (51% yield). Although CH analysis of 3 indicates its purity is suspect, the transformation of 3 to the dichloride 4 was monitored by lH NMR and proceeded with minimal production (85%)from the addition of n-butyllithium to 2, its extreme solubility prevented satisfactory purification. Hindered alkyllithiums (neopentyllithium and (CH3)3SiCH2Li)react slowly with the dichloride 2, thus allowing the competitive decomposition of 2 to interfere. It has been shown that metathetical reactions leading to the preparation of bis(tritox) species proceed with no interference from the formation of mono- and tris(tritox) (21) For epr studies of Cp,TiCl(THF) see: Krusic, P. J.; Tebbe, F. N. Inorg. Chem. 1982,21,2900. (22) (a) Bercaw, J. E.; Brintzinger, H. H. J. Am. Chem. SOC.1969,91, 7301. (b) Klei, E.;Teuben, J. H. J. Organomet. Chem. 1980,188, 97. (23) The probable impurities present are LiCl and/or TiC13. (24) Giannini, U.; Cesca, S. Tetrahedron Lett. 1960,14, 19.
The complexes were characterized principally via ‘H and 13C(lH)NMR spectroscopy (Table I), which proved valuable in establishing the purity of the unstable, yet crys(2),l ~ (tritox)TiCl, ( 5 ) , and (tritox)talline ( t r i t o ~ ) ~ Z r C Ti(CH3)3(8) complexes. From the spectral data, it is estimated that 2, 5, and 8 contain approximately go% HzDCC~HS. Procedures. 1. Li(tritox). To a solution of 20.1 g of (tritox)H (0.100 mol) in 150 mL of hexane at -78 "C was added 70 mL of n-butyllithium (1.55 M in hexane, 0.108 mol) via syringe. The solution was allowed to warm to 25 "C. During a 5-h period white, crystalline Li(tritox) precipitated. The slurry was then concentrated, cooled to -78 "C, and filtered to yield 18.7 g of Li(tritox) (91%). Titration of Li(tritox) indicated that the conversion to the alkoxide was complete (98.9%). 2. (tritox)zZrC13.Li(EtzO)z, 1. To a flask containing ZrC1, (500 mg, 2.15 mmol) and (tritox)Li (890 mg, 4.31 mmol) at -78 "C was added diethyl ether (40 mL) via distillation. The reaction was stirred at -78 "C for 3 h and allowed to warm to 25 "C over an 8-h period. The solution was concentrated to 30 mL and filtered twice with medium frits and once with a fine frit. Slow evaporation of the remaining diethyl ether at -20 "C yielded 1.21 g of 1 (75%). Loss of diethyl ether from solid 1 at room temperature was noted. 3. (tritox)zZrCIZ,2. To a flask containing ZrC1, (2.00 g, 8.58 mmol) and Li(tritox) (3.60 g, 17.5 mmol) was distilled 100 mL of diethyl ether at -78 "C. After slow warming to 25 "C and 7 h of stirring, the EtzO was removed and 50 mL of hexane was added at -78 "C. Filtration and crystallization gave 2.95 g of thermally sensitive white crystals (61% yield). 4. '(tritox)zTiC1", 3. To a flask containing 350 mg of TiC1, (2.27 mmol) and 935 mg of Li(tritox) (4.54 mmol) was distilled 50 mL of EtzO at -78 "C. During the 3 days of stirring at room temperature the reaction mixture changed from a colorless solution with purple/black particulate to a yellow-green solution with a grayish white precipitate. The diethyl ether was removed and 15 mL of hexane added. This mixture was stirred and the hexane removed under vacuum. This was repeated, and 30 mL of hexane was added after which the solution was filtered. Removal of hexane yielded an olive green oil to which 10 mL of hexane was added and removed by vacuum. Hexane (15 mL) was added and the solution cooled to -78 "C as the hexane was removed. The resulting mint green precipitate was filtered from the oily solution while cold and washed with 10 mL of cold hexane (660 mg, 60% based on "(tritox)2TiC1").Reprecipitation of this material (3) from cold hexane gave 300 mg of material (27%) which manifested a broad absorption (no diamagnetic material observed) at 6 1.42 (benzene-d6)with ul,Z = 153 Hz. Addition of CCl, to the NMR tube resulted in the clean formation of (tritox)zTiC12(4) (the only H-containing impurity noted was -5% EtzO). Anal. Calcd for C26H54TiOZC1: C, 64.78; H, 11.29; C1, 7.35. Found (sample no.
Organometallics, Vol. 3, No. 7, 1984 983
Group 4A Complexes Containing Tri-tert- butylmethoxide 1):C, 57.79; H, 10.32. Found (no. 2): C, 54.79; H, 9.47; C1,18.57. No 4 was detected by IR (
