Olefin metatheses in metal coordination spheres: a new approach to steric shielding in dirhenium sp carbon chain complexes of the formula (eta(5)-C5Me5)-Re(NO)(PR3)(C CC CC CC C)(R3P)(ON)Re(eta(5)-C5Me5)
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Reaction of chiral racemic [(5-C5Me5)Re(NO)(NCCH3)(CO)] +BF4- and the olefin-containing phosphine Ph2P(CH2)6CH=CH2 (2-butanone, reflux) gives [(5-C5Me5)Re(NO)(PPh2(CH2 )6CH=CH2)(CO)]+BF4- (95%), which is reduced (LiAlH4) to the phosphine methyl complex (5-C6Me5)Re(NO)(PPh2(CH2 )6CH=CH2)(CH3) (92%). Reactions with HBF4OEt2/chlorobenzene, HCCCCSiMe3, and t-BuOK give (5-C5Me5)Re(NO)(PPh2(CH2 )6CH=CH2)(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 -octatetraynediyl complex (5-C5Me5)Re(NO)(PPh2(CH2 )6CH=CH2)(CCCCCCCC)(H 2C=CH(CH2)6PPh2)(ON)Re(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 (5-C5Me5)Re(NO)(PPh2(CH2 )6CH=CH)(CCCCCCCC)((C H2)6PPh2)(ON)Re(5-C5 Me5) (17, 77-84%) as a mixture of isomers. However, the hydrogenation of 17 to the target molecule (5-C5Me5)Re(NO)PPh2(CH 2)7)(CCCCCCC C)((CH2)7PPh2)(ON)Re(5-C 5Me5) (18), while sometimes successful, could not be scaled or effected in a reproducible manner.
