Titanium complexes incorporating 1,1-bis(tert-butylamido)-1-silacycloalkane ligands:: Generation of alkyl derivatives and reactivity toward molecular oxygen

A series of methoxy-bridged diamidotitanium dimers have been synthesized and fully characterized. Treatment of the Grignard reagent MeMgBr with (cycl)Si(NBut)(2)TiCl2 (2; cycl = CnH2n, n = 3-5) in 2:1 or 1:1 stoichiometry yielded four-coordinate dimethyltitanium (cycl)Si(NBut)(2)TiMe2 (3) and monomethyltitanium (CH2)(3)Si(NBut)(2)TiMeCl (5) complexes, respectively. Subsequent reaction of these complexes with dioxygen proceeds by insertion of an oxygen molecule into the Ti-C bond of 3 and 5, generating the respective methoxy-bridged titanium dimers [(cycl)Si(NBUt)(2)Ti(mu-OMe)Me](2) (4) and [(cycl)Si(NBut)(2)Ti(u-OMe)Cl](2) (6). In contrast, the reaction of the titanium(IV) dichloride complex (CH2)(3)Si(NBut)(2)TiCl2 (2a) with O-2 gives the hydrazido species [{((NBuNBut)-N-t)(CH2)(3)SiO}TiCl2](2) (7a) as a result of facile Si-O-Ti bond formation upon autoxidation. To our knowledge, these complexes are the first examples of methoxy-bridged diamidotitanium(IV) dimers. Reaction of 2 with 2 equiv of PhCH2MgBr yielded the corresponding dibenzyl (Bn-2) derivatives of titanium (cycl)Si(NBut)(2)TiBn2 (9). When these dibenzyl complexes were used as precursors for the conversion of monomeric to dimeric alkoxy-bridged species, oxo insertion did not occur, presumably because formation of the alkoxy-bridged dimer was hampered by the presence of bulky dibenzyl units.