Reactions of the rhenium cyanomethyl complex (.eta.5-C5H5)Re(NO)(PPh3)(CH2CN) and ylide complex [(.eta.5-C5H5)Re(NO)(PPh3)(CH2P(p-tol)3))]+PF6- with n-BuLi/TMEDA: generation, stereospecific alkylation, and basicity of transition-metal-substituted carbanions and ylides