Influence of SiMe3 Substituents on Structures and Hydrosilylation Activities of ((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl

Abstract

This report examines the effect of substituents R on structures and reactivities of the complexes (R-Ind)Ni(PPh3)Cl (R-Ind = 1-Me-indenyl, 1; 1-SiMe3-indenyl, 2; 1,3-(SiMe3)2-indenyl, 3). NMR studies indicate that a relatively facile dissociation of PPh3 takes place in solutions of complex 3 (ΔG⧧ ≈ 10 kcal/mol in C6D6) but not those of complexes 1 and 2, implying that the presence of Ind substituents at the 1- and 3-positions can influence the kinetic lability of PPh3. X-ray analyses have also shown that the PPh3 ligand and the SiMe3 group adjacent to it in complex 3 experience some steric repulsion, which is manifested in angular deformations (out-of-plane bending of the SiMe3 group by about 0.56−0.65 A and 5−10° variations in the P−Ni−Cl and P−Ni−C3 angles) and a somewhat longer Ni−P bond (ca. 2.19 A). Reactivity studies have shown that complexes 1−3 are effective precatalysts for the addition of PhSiH3 to styrene in the presence of the cationic initiator NaBPh4; α-addition of the silyl moiety takes pla...