pubs.acs.org/IC Published on Web 02/01/2010 r 2010 American Chemical Society Inorg. Chem. 2010, 49, 2163–2172 2163 DOI: 10.1021/ic9019537 Syntheses and Structures of Cationic and Neutral, Homo- and Heteroleptic tert-Butoxides of the Group 4 Metals Edmond Y. Njua, † Alexander Steiner, ‡ and Lothar Stahl* ,† † Department of Chemistry, University of North Dakota, Grand Forks, North Dakota 58202-9024, and ‡ Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K. Received October 3, 2009 The utility of tri-tert-butoxystannate as a chelating tridentate ligand for group 4 metals was investigated. The highly Lewis acidic metals degraded the stannate ion in a series of tert-butoxide abstraction steps to produce a variety of group 4 tert-butoxides. A total of 1 equiv of NaSn(O t Bu) 3 reacted with cis-MCl 4 (THF) 2 [M = Zr (1), Hf (2)] in THF solutions to furnish the salts fac-{[M(O t Bu) 3 (THF) 3 ](SnCl 3 )}, which are separated ion pairs featuring weakly coordinating trichlorostannate ions. Neutral complexes, namely, [M(O t Bu) 2 Cl 2 (THF) 2 ][M = Zr (3), Hf (4)], were isolated when 2 / 3 equiv of sodium stannate was used in these reactions. Titanium tetrachloride formed analogues neither of 1 and 2 nor of 3 and 4, but Ti(O t Bu) 3 Cl reacted with silver triflate to give [Ti(O t Bu) 2 (OTf) 2 (THF) 2 ](5). Anion exchange of triflate for trichlorostannate transformed 1 to the contact ion pair fac-[Zr(O t Bu) 3 OTf(THF) 2 ](6). A total of 2 equiv of NaSn(O t Bu) 3 reacted with cis-MCl 4 (THF) 2 to give the complexes fac-[Sn(μ-O t Bu) 3 M(O t Bu) 3 ][M = Zr (7), Hf (8)]. Tri-tert-butoxystannate may be used as a selective alkoxylating agent for group 4 metals, and it can be transferred to these metals intact if their Lewis acidity is appropriately attenuated as in fac-{[M(O t Bu) 3 (THF) 3 ](SnCl 3 )}. Single- crystal X-ray studies revealed distorted octahedral coordination geometries for all compounds (1-8), with 1, 2, 7, and 8 being crystallographically C 3 symmetric. Introduction Their ready availability, steric tunability, and hard-donor properties have made alkoxides some of the most versatile σ-bonding ligands in chemistry. 1 Alkoxides are outstanding ligands for early transition metals because the electron-rich oxygen atoms complement these chemically hard, electron- poor metals exceedingly well. Consequently, alkoxides have played a prominent role in the chemistry of the group 4-6 metals, particularly as ligands for multiply metal- metal-bonded species. 2 More recently, the utility of metal alkoxides as precursors for binary or ternary metal oxides has also stimulated commercial interest in these compounds. 3 Despite their extensive synthetic and structural chemistry, early-transition-metal alkoxides were rarely used in stoichio- metric or catalytic transformations prior to 1980. This absence was largely because of the propensity of alkoxide complexes to aggregate and undergo ligand-exchange reac- tions in solution, 4 which render controlled catalytic transfor- mations with simple, early-transition-metal alkoxides difficult. Among the first to exploit the catalytic properties of early- transition-metal alkoxides were Katsuki and Sharpless, who discovered that Ti(O i Pr) 4 catalyzed the asymmetric epoxida- tion of allylic alcohols by tert-butyl hydroperoxide. 5 Almost simultaneously, Schrock and co-workers reported their semi- nal research on alkyne metathesis reactions with W(C t Bu)- (O t Bu) 3 and related catalysts. 6 Shortly thereafter, Wolczanski and co-workers 7-10 and Rothwell and co-workers 11-13 initiated systematic reactivity studies of group 4 and 5 metal *To whom correspondence should be addressed. E-mail: lstahl@chem. und.edu. (1) Bradley, D. C.; Mehrotra, E. C.; Rothwell, I. P.; Singh, A. Alkoxo and Aryloxo Derivatives of Metals; Academic Press: San Diego, 2001. (2) (a) Chisholm, M. H.; Cotton, F. A.; Extine, W. E.; Kelly, R. L. J. Am. Chem. Soc. 1978, 100, 2256–2267. (b) Chisholm, M. H.; Reichert, W. W.; Cotton, F. A.; Murillo, C. A. J. Am. Chem. Soc. 1977, 99, 1652–1654. (c) Chisholm, M. 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