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)

Abstract

Reaction of chiral racemic [(η5-C5Me5)Re(NO)(NCCH3)(CO)]+BF4- and the olefin-containing phosphine Ph2P(CH2)6CHCH2 (2-butanone, reflux) gives [(η5-C5Me5)Re(NO)(PPh2(CH2)6CHCH2)(CO)]+BF4- (95%), which is reduced (LiAlH4) to the phosphine methyl complex (η5-C5Me5)Re(NO)(PPh2(CH2)6CHCH2)(CH3) (92%). Reactions with HBF4·OEt2/chlorobenzene, HC⋮CC⋮CSiMe3, and t-BuOK give (η5-C5Me5)Re(NO)(PPh2(CH2)6CHCH2)(C⋮CC⋮CSiMe3) (two steps, 96%/81%). Desilylation (wet n-Bu4N+F-) yields a butadiynyl complex (88%), which is coupled (Cu(OAc)2/pyridine) to the μ-octatetraynediyl complex (η5-C5Me5)Re(NO)(PPh2(CH2)6CHCH2)(C⋮CC⋮CC⋮CC⋮C)(H2CCH(CH2)6PPh2)(ON)Re(η5-C5Me5) (16, 63%), believed to be a mixture of diastereomers. The reaction of 16 and Grubbs' catalyst, Ru(CHPh)(PCy3)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.