SYNTHESIS AND REACTIONS OF DIRHENIUM ALKENYLIDENE AND ALKYLIDYNE COMPLEXES

Reaction of Cp(CO)(2)Re=Re(CO)(2)Cp* with the enyne HC=CC(CH3)=CH2 ga ve 2)Re{mu-eta(1),eta(3)-CH=CC(CH3)=CH2CO}Re(CO)Cp (1), in which an alpha,beta-unsaturated carbonyl unit bridges the Re-Re bond. Thermal rearrangement of 1 led to the isopropenyl-substituted mu-alkenylidene complex Cp(CO)(2)Remu-C=CHC(CH3)=CH2Re(CO)(2)Cp* (2). Protonation o f the conjugated mu-alkenylidene complex 2 occurred exclusively at the remote delta-carbon to produce the cationic mu-alkylidyne dirhenium c omplex {Cp(CO)(2)Remu-CCH=C(CH3)(2)Re(CO)(2)Cp*}(BF4) (3). Nucleoph ilic addition to 3 occurred selectively at the gamma-carbon to give ad dition products including Cp(CO)(2)Remu-C=CHC(CH3)(2)CH(CO(2)Et)(2) Re(CO)(2)Cp (6) and Cp*(CO)(2)Remu-C=CHC(CH3)(3)Re(CO)(2)Cp* (7). mu-Alkenylidene complex 3 underwent an unusually facile ene reaction w ith dimethyl acetylenedicarboxylate (DMAD) to produce -C=CHC(=CH2)CH2C (CO(2)Me)=CH(CO(2)Me)Re(CO)(2)Cp (8).