This work presents the synthesis, structure, and reactivity of tantalum, yttrium and zirconium complexes with biphenyl and binaphthyl silylamido ligands.

The highly bent imido complex Cp*Ta[=N(C₆HC₃Me)₂NSiMe₃]Cl and the methyl derivative Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Me were prepared and characterized. Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Me reacts with xylyl isonitrile giving an insertion product, and with MeI giving a cationic complex. Reactions of Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Cl and Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Me with PhSiH₃ afford the hydrides Cp*Ta[PhSiH₂N(C₆H₃Me)₂NSiMe₃](H)Cl and Cp*Ta[PhSiH₂N(C₆H₃Me)₂NSiMe₃](H)Me via addition of the Si-H bond across the Ta=N double bond. In presence of CH₂Cl₂ and PhSiH₃, Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Cl forms the complex Cp*Ta[PhSiH₂N(C₆H₃Me)₂NSiPhHCl](H)Cl, which exhibits a nonclassical interaction between the hydride ligand and a silyl group. Reactions of PhSiH₃ and (CH₂)₃SiH₂ with Cp*Ta[=N(C₆H₃Me)₂NSiMe₃]Me follow second-order kinetics, with an inverse isotope effect for the PhSiH₃ addition. Elimination of HSiMe₃ from Cp*Ta[PhSiH₂N(C₆H₃Me)₂NSiMe₃](H)Me follows first-order kinetics, with approach to equilibrium, and exhibits inverse isotope effect. The proposed addition / elimination mechanism involves slow formation of pentacoordinate silicon intermediates, coupled with a fast hydride shift between Ta and Si.

The yttrium complex [DADMB]YCl(THF)₂ (DADMB = 2,2'-bis(tert-butyl-dimethylsilylamido)-6,6'-dimethylbiphenyl) and its alkyl derivatives [DADMB]YMe(THF)₂ and [DADMB]Y[CH(SiMe₃)₂](THF)(OEt₂) were prepared. In presence of silicone grease, reaction of [DADMB]YCl(THF)₂ with MeLi produces the trimethylsiloxide [DADMB]Y(OSiMe₃)(THF)₂. [DADMB]YMe(THF)₂ and [DADMB]Y[CH(SiMe₃)₂](THF)(OEt₂) react with phenylsilane or H₂ forming the dimeric hydride {[DADMB]Y(u-H)(THF)}₂^.C₆H₆. This hydride reacts rapidly with olefins via single insertion, and with pyridine, forming two isomeric 1,2- and 1,4-insertion products.

{[DADMB]Y(u-H)(THF)}₂ catalyzes the hydrosilylation of olefins. Catalyst reactivity and selectivity for different olefins and silanes are investigated. Aliphatic olefins exhibit high preference for terminal addition, while aromatic olefins undergo mostly 2,1 addition. Both primary and secondary silanes can be employed. Using enantiopure catalyst for enantioselective hydrosilylation of norbornene yields 90% ee. Kinetic studies support a mechanism involving fast olefin insertion into the Y-H bond, followed by slow metathesis reaction of the resulting alkyl with silane.

The zirconium complexes {[DADMB]ZrCl₂}₂, [DMBN]ZrCl₂^.THF (DMBN = 2,2'-bis(tert-butyldimethylsilylamido)-1,1'-binaphthyl), [DBMN]Zr(CH₂Ph)₂ and [DMBN]ZrMe₂^.THF were prepared. With B(C₆F₅)₃, [DBMN]Zr(CH₂Ph)₂ produces the zwitterionic complex [DMBN]Zr(CH₂Ph)^.[h⁶-PhCH₂B(C₆F₅)₃]. {[DADMB]ZrCl₂}₂ and [DMBN]ZrCl₂^.THF are moderately active ethylene polymerization catalysts. [DBMN]Zr(CH₂Ph)₂ activated with Ph₃CB(C₆F₅)₄ polymerizes 1-hexene to low molecular weight oligomers.

[PREVIOUS][TableOfContents][NEXT]