REACTIONS OF THE CYANOMETHYL COMPLEX (ETA-5-C5H5)RE(NO)(PPH3)(CH2CN) AND YLIDE COMPLEX [(ETA-5-C5H5)RE(NO)(PPH3)(CH2P(PARA-TOL)3)]+PF6- WITH NORMAL-BULI/TMEDA - GENERATION, STEREOSPECIFIC ALKYLATION, AND BASICITY OF TRANSITION-METAL-SUBSTITUTED CARBANIONS AND YLIDES

Reaction of the cyanomethyl complex (η5-C5H6)Re(NO)(PPh3)(CH2CN) (2) with n-BuLi/TMEDA (THF, -78 °C) and then CH3OSO2CF3 stereospecifically gives (SR,RS)-(η5-C5H5)Re(NO)(PPh3)(CH(CH3)CN) ((SR,RS)-4, 75%). Reaction of PPN+CN- and the ethylidene complex sc-[(η5-C5H5)Re(NO)(PPh3)(═CHCH3)]+PF6- (sc-8) gives the opposite diastereomer, (SS,RR)-4 (91%). The former reaction proceeds, as assayed by31P NMR spectroscopy and deuterium labeling, via the initial formation (ca. 2:1) of carbanions Li+[(η5-C5H5)Re(NO)(PPh3)(CHCN)]- (5) and (η5-C5H4Li)Re(NO)(PPh3)(CH2CN) (6); 6 isomerizes to 5 thermally (-78 °C, 2.5 h) or upon addition of CH3OSO2CF3. Complex 5 is the first observable transition-metal-substituted carbanion (IR (cm-1):νCN 1980;νNo 1597) and is also stereospecifically alkylated by n-C4H9I. Equilibration reactions show the Cα acidity of 2 (THF) to be less than that of CH3CN and comparable to that of CH3CH2CN. Reactions of (SR,RS)/(SS,RR)-4 and n-BuLi/TMEDA give only cyclopentadienyl ligand lithiation. Reactions of the ylide complex [(η5-C5H5)Re(NO)(PPh3)(CH2P(p-tol)3)]+PF6- with n-BuLi/TMEDA (THF, -24 °C) and then CH3OSO2CF3 (-78 °C) stereospecifically give (SS,RR)-(η5-C5H5)Re(NO)(PPh3)(CH(CH3)P(p-tol)3)]+PF6- ((SS,RR)-16, 83%). This transformation proceeds, as assayed by31P NMR spectroscopy, via the ylide (η5-C5H5)Re(NO)(PPh3)(CH═P(p-tol)3). An authentic sample of (SS,RR)-16 is prepared from sc-8 and P(p-tol)3 (90%). © 1990, American Chemical Society. All rights reserved.