Metal-dependent stabilization of Si-S bonds to hydrolysis in iridium and rhodium silyls. Hydrolyzability as a probe for Si-H reductive elimination

The iridium (triethylthio)silyl complexes cis-(PPh(3))(2)(CO)IrH2(Si(SEt)(3)) (5), fac-(PMe(3))(3)Ir(CH3)(H)-(Si(SEt)(3) (6), and mer-(PMe(3))(3)Ir(C6F5)(H)(Si(SEt)(3)) (7) were synthesized by oxidative addition, of HSi(SEt)(3) (1) to HIr(CO)(PPh(3))(3) (2), CH(3)IrPMe(3))(4) (3), and C6F5 Ir(PMe(3))(3) (4), respectively. 4 was synthesized by the reaction between Ir(PMe(3))(4)Cl and C6F5MgBr. The rhodium analog of 7, mer-(PMe(3))(3)Rh(C6F5)(H)(Si(SEt)(3)) (9), was obtained similarly from C6F5Rh(PMe(3))(3), (8) and 1. Unlike the extremely easily hydrolyzable parent silane 1, compounds 5-7 are stable in H2O/THF and even in NaOH/H2O/THF solutions. This stabilization is attributed to the electron-donating capacity of the Ir centers, which efficiently reduces electrophilicity of the silicon. Reactivity of the rhodium complex 9 is strikingly different, cleanly producing in the presence of 5 equiv of H2O the ethylthio-complex mer-(PMe(3))(3)Rh(C6F5)(H)(SEt) (10). Compound 10 was identified spectroscopically and was synthesized independently from 8 and HSEt. A plausible scheme accounting for the generation of 10 under the hydrolysis conditions is presented. The observed difference in the reactivities of 5-7 and 9 is explained in terms of their different tendencies to reductively eliminate H-Si(SEt)(3).