Disilyl Complexes of Zirconium,Hafnium,and Tantalum.Their Synthesis,Characterization,and Exchanges with Silyl Anions

摘要

Cyclopentadienyl-free disilyl amide complexes [(Me_2N)_3M(SiBu~tPh_2)_2]~-(M = Zr,1;Hf,2 as [Li(THF)_4]~+ salts),K(18-crown-6)_3/2{(Me_2N)_3M[(Me_3Si)_2Si-(CH_2)_2-Si(SiMe_3)_2]}(M = Zr,3;Hf,4),(Me_2N)_3Ta[Si(SiMe_3)_3]_2(5),(Me_2N)_3Ta(SiBu~tPh_2)_2(6),and(Me_2N)_3Ta(SiBu~tPh_2)[Si-(SiMe_3)_3](7)have been prepared.The structures of 1-4 have been determined by X-ray single-crystal diffraction.The two -Si(SiMe_3)_3~-ligands in(Me_2N)_3Ta[Si(SiMe_3)_3]_2(5)were replaced sequentially by the-SiBu~tPh_2~-anions to give(Me_2N)_3Ta(SiBu~tPh_2)[Si(SiMe_3)_3](7)and(Me_2N)_3Ta(SiBu~tPh_2)_2(6).The silyl ligand in(Me_2N)_3Zr-Si(SiMe_3)_3 was found to undergo a reversible exchange with SiBu~tPh_2~,probably through a disilyl intermediate,to reach the following equilibrium:(Me_2N)_3ZrSi(SiMe_3)_3 + SiBu'Phr -(Me_2N)_3ZrSiBu~tPh_2 + Si(SiMe_3)_3~-with DELTAHdeg = 4.6(0.5)kcal/mol and DELTAS~deg=-7(2)eu.A similar exchange involving [(Me_2N)_3M(SiBu~tPh_2)_2]-(M-Zr,1;Hf,2)was observed:(Me_2N)_3ZrSiBu~tPh_2 + SiBu~tPh_2-- 1 with the estimated free energy of activation DELTAG* = 14.1(0.5)kcal/mol.(Me_2N)_3Ta(Si-Bu~tPh_2)_2(6)and(Me_2N)_3Ta(SiBu~tPh_2)[Si(SiMe_3)_3](7)are thermally unstable.Kinetic studies give the activation parameters of the decomposition of 7:DELTAH* = 22.8(1.3)kcal/mol and DELTAS* =-3(5)eu.