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(NBu t ) 2 TiCl 2 ( 2; cycl = C n H 2 n, n = 3−5) in 2:1 or 1:1 stoichiometry yielded four-coordinate dimethyltitanium (cycl)Si(NBu t ) 2 TiMe 2 ( 3 ) and monomethyltitanium (CH 2 ) 3 Si(NBu t ) 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(NBu t ) 2 Ti(μ-OMe)Me] 2 ( 4 ) and [(cycl)Si(NBu t ) 2 Ti(μ-OMe)Cl] 2 ( 6 ). In contrast, the reaction of the titanium(IV) dichloride complex (CH 2 ) 3 Si(NBu t ) 2 TiCl 2 ( 2a ) with O 2 gives the hydrazido species [{(NBu t NBu t )(CH 2 ) 3 SiO}TiCl 2 ] 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 PhCH 2 MgBr yielded the corresponding dibenzyl (Bn 2 ) derivatives of titanium (cycl)Si(NBu t ) 2 TiBn 2 ( 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.