SYNTHESIS AND REACTIVITY OF BRIDGING BIS(ALKYL) AND BIS(ALKYLIDENE) COMPLEXES DERIVED FROM THE CHIRAL RHENIUM FRAGMENT [(ETA-5-C5H5)RE(NO)(PPH3)]+

Reactions of Li+[(eta5-C5H5)Re(NO)(PPh3)]- and TfO(CH2)nOTf (0.5 equiv.; a, n = 3; b, n = 4; c, n = 5; d, n = 8) give the bridging bis(alkyl) complexes (eta5-C5H5)Re(NO)(PPh3)(CH2)n(PPh3)(NO)Re (eta5-C5H5) (7a-d, 80-89%) as 50-75:50-25 mixtures of configurational diastereomers (meso, dl). Reactions of 7 and Ph3C+PF6- (2 equiv.) give the bridging bis(alkylidene) complexes [(eta5-C5H5) Re(NO)(PPh3)(=CH(CH2)n-2HC=)(PPh3)(NO)Re(eta5-C5H5)]2+2PF6- (3a-d, 76-93%). When heated in chlorobenzene, 3c and 3d rearrange (k(obs) = 3.9 X 10(-5) s-1, 3c, 72-degrees-C; 6.3 x 10(-5) s-1, 3d, 66-degrees-C) to the bridging bis(alkene) complexes [(eta5-C5H5)Re(NO)(PPh3)(H2C=CH(CH2)n-4HC=CH2)-(PPh3)(NO)Re(eta5-C5H5)]2+2PF6-(5c,d2+ 2PF6-, 90-97%). No cycloalkene complexes derived from Re=CHR/Re=CHR coupling are detected. Complexes 5C2+ 2BF4- and 5d2+ 2BF4- are independently prepared by reactions of (eta5-C5H5)Re(NO)(PPh3)(CH3), HBF4.OEt2, and alpha,omega-dienes in chlorobenzene.