UNEXPECTED REACTIVITY OF FUNCTIONALIZED LEWIS BASE STABILIZED SILANEDIYL TRANSITION-METAL COMPLEXES TOWARD ORGANOLITHIUM NUCLEOPHILES

(Organosilanediyl)chromium(0) pentacarbonyl complexes, [2-(Me(2)NCH(2) )C6H4]RSi=Cr(CO)(5) (R = Me, Ph, t-Bu, Ph-C=C-, Me(3)Si-C=C-), are obt ained in good yield through the coupling reactions of (arylhydrogenosi lanediyl)chromium(0) pentacarbonyl complex [2-(Me(2)NCH(2))C6H4]HSi=Cr (CO)(5), with the corresponding organolithium nucleophiles. Unexpected ly, the chloro- and bromosilanediyl complexes [2-(Me(2)NCH(2))C6H4]XSi =Cr(CO)(5) (X = Cl, Pr) are unreactive, but the fluorosilanediyl compl ex is even, more reactive than, the hydrogenosilanediyl complex with m ethyllithium. Possible geometries of the intermediate resulting in fro ntside attach of the nucleophile upon a zwitterionic silicon species a re discussed.