ReH5(Cyttp) (Cyttp = PhP(CH2CH2CH2PCy2)2) reacts with RO2CC=CCO2R in excess in benzene solution at room temperature to yield ReH3(RO2CCH=CHCO2R)(Cyttp) (R = Me, 1a; R = Et, 1b). Similarly conducted reactions of ReH5(ttp) (ttp = PhP(CH2CH2CH2PPh2)2) with RO2CC=CCO2R afford Re(eta-2-(C,O)-C(CO2R)=CHCO2R)(RO2CCH=CHCO2R)(ttp) (R = Me, 2a; R = Et, 2b). Crystal data for 2a.MeOH: P2(1)/n, a = 10.988 (2) angstrom, b = 20.648 (2) angstrom, c = 20.494 (2) angstrom, beta = 92.61 (1)-degrees; V = 4645 angstrom3; Z = 4, R = 0.040, R(W) = 0.042 for 6243 reflections with F(o)2 > 3-sigma(F(o)2).