Olefin metatheses in metal coordination spheres:: a new approach to steric shielding in dirhenium sp carbon chain complexes of the formula (η5-C5Me5)-Re(NO)(PR3)(CCCCCCCC)(R3P)(ON)Re(η5-C5Me5)

Reaction of chiral racemic [(eta(5)-C5Me6)Re(NO)(NCCH3)(CO)]+BF4- and the olefin-containing phosphine Ph2P(CH2)(6)CH = CH2 (2-butanone, reflux) gives [(eta(5)-C5Me5)Re(NO)(PPh2(CH2)(6)CH = CH2)(CO)]+BF4- (95%), which is reduced (LiAlH4) to the phosphine methyl complex (eta(5)-C5Me5)Re(NO)(PPh2(CH2)(6)CH = CH2)(CH3) (92%).,Reactions with HBF4.OEt2/chloroben-zene, HCequivalent toCCequivalent toCSiMe(3), and t-BuOK give (eta(5)-C5Me5)Re(NO)(PPh2(CH2)(6)CH = CH2)(C equivalent to CC equivalent to CSiMe3) (two steps, 96%/81%). Desilylation (wet n-Bu4N+F-) yields a butadiynyl complex (88%), which is coupled (Cu(OAc)(2)/pyridine) to the mu-octatetraynediyl complex (eta(5)-C5Me5)-Re(NO)(PPh2(CH2)(6)CH=CH2)(C equivalent to CC equivalent to CC equivalent to CC equivalent to C)(H2C=CH(CH2)(6)PPh2)(ON)Re(eta(5)-C5Me5) (16, 63%), believed to be a mixture of diastereomers. The reaction of 16 and Grubbs' catalyst, Ru(=CHPh)(PCY3)(2)(Cl)(2), gives (eta(5)-C5Me5)Re(NO)(PPh2(CH2)(6)CH=CH)(Cequivalent to CC equivalent to CC equivalent to C)- ((CH2)(6)PPh2)(ON)Re(eta(5)-C5Me5) (17, 77-84%) as a mixture of isomers. However, the hydrogenation of 17 to the target molecule (eta(5)-C5Me5)Re(NO)(PPh2(CH2)(7))(Cequivalent toCCequivalent toCCequivalent toCCequivalent toC)((CH2)(7)PPh2)(ON)Re(eta(5) -C5Me5) (18), while sometimes successful, could not be scaled or effected in a reproducible manner.