SYNTHESIS AND REACTIVITY OF BRIDGING BIS(ALKYL) AND BIS(ALKYLIDENE) COMPLEXES DERIVED FROM THE CHIRAL RHENIUM FRAGMENT [(ETA-5-C5H5)RE(NO)(PPH3)]+
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abstract
Reactions of Li+ [(5-C5H5) Re(NO)(PPh3)]- and TfO(CH2nOTf(0.5 equiv.; a, n = 3; b, n = 4; c, n = 5; d, n = 8) give the bridging bis(alkyl) complexes (5-C5H5)Re(NO)(PPh3(CH2)n(PPh3) (NO)Re (5-C5H5) (7a-d, 80-89%) as 50-75:50-25 mixtures of configurational diastercomers (meso, dl). Reactions of 7 and Ph3C+PF6- (2 equiv.) give the bridging bis(alkylidene) complexes [(5-C5H5) Re(NO)(PPh3(=CH(CH2)n-2HC=)(PPh3)(NO)Re(5-C5H5)]2+2PF6-(3a-d, 76-93%). When heated in chlorobenzene, 3c and 3d rearrange (kobs = 3.9 10-5 s-1, 3c, 72C; 6.3 10-5 s-1, 3d, 66C) to the bridging bis(alkene) complexes [(5-C5H5)Re(NO)(PPh3(H2CCH(CH2) n-4HCCH2)-(PPh3)(NO)Re(5-C5H5)]2+2PF6- (5c,d2+ 2PF6-, 90-97%). No cycloalkene complexes derived from ReCHR/ReCHR coupling are detected. Complexes 5c2+ 2BF4- and 5d2+ 2BF4- are independently prepared by reactions of (5-C5H5)Re(NO)(PPh3)(CH3), HBF4OEt2and ,-dienes in chlorobenzene. 1992.
