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)(C⋮CC⋮CC⋮CC⋮C)(R3P)(ON)Re(η5-C5Me5)

Reaction of chiral racemic [(η 5 -C 5 Me 5 )Re(NO)(NCCH 3 )(CO)] + BF 4 - and the olefin-containing phosphine Ph 2 P(CH 2 ) 6 CH CH 2 (2-butanone, reflux) gives [(η 5 -C 5 Me 5 )Re(NO)(PPh 2 (CH 2 ) 6 CH CH 2 )(CO)] + BF 4 - (95%), which is reduced (LiAlH 4 ) to the phosphine methyl complex (η 5 -C 5 Me 5 )Re(NO)(PPh 2 (CH 2 ) 6 CH CH 2 )(CH 3 ) (92%). Reactions with HBF 4 ·OEt 2 /chlorobenzene, HC⋮CC⋮CSiMe 3, and t- BuOK give (η 5 -C 5 Me 5 )Re(NO)(PPh 2 (CH 2 ) 6 CH CH 2 )(C⋮CC⋮CSiMe 3 ) (two steps, 96%/81%). Desilylation (wet n -Bu 4 N + F - ) yields a butadiynyl complex (88%), which is coupled (Cu(OAc) 2 /pyridine) to the μ-octatetraynediyl complex (η 5 -C 5 Me 5 )Re(NO)(PPh 2 (CH 2 ) 6 CH CH 2 )(C⋮CC⋮CC⋮CC⋮C)(H 2 C CH(CH 2 ) 6 PPh 2 )(ON)Re(η 5 -C 5 Me 5 ) ( 16, 63%), believed to be a mixture of diastereomers. The reaction of 16 and Grubbs' catalyst, Ru( CHPh)(PCy 3 ) 2 (Cl) 2, gives ( 17, 77−84%) as a mixture of isomers. However, the hydrogenation of 17 to the target molecule ( 18 ), while sometimes successful, could not be scaled or effected in a reproducible manner.