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 gave Cp*(CO)(2)Re{mu-eta(1),eta(3)-CH=C[C(CH3)=CH2]CO}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)Re[mu-C=CHC(CH3)=CH2]Re(CO)(2)Cp* (2). Protonation of the conjugated mu-alkenylidene complex 2 occurred exclusively at the remote delta-carbon to produce the cationic mu-alkylidyne dirhenium complex {Cp*(CO)(2)Re[mu-CCH=C(CH3)(2)]Re(CO)(2)Cp*}(BF4) (3). Nucleophilic addition to 3 occurred selectively at the gamma-carbon to give addition products including Cp*(CO)(2)Re[mu-C=CHC(CH3)(2)CH(CO(2)Et)(2)] Re(CO)(2)Cp* (6) and Cp*(CO)(2)Re[mu-C=CHC(CH3)(3)]Re(CO)(2)Cp* (7). mu-Alkenylidene complex 3 underwent an unusually facile ene reaction with dimethyl acetylenedicarboxylate (DMAD) to produce Cp*(CO)(2)Re[mu-C=CHC(=CH2)CH2C(CO(2)Me)=CH(CO(2)Me)]Re(CO)(2)Cp* (8).