Olefin Trifluoroacetato Derivatives of Copper(I) and Their Olefin/CO Exchange Reactions

Compounds of the general formula Cu(CF3COO)(olefin) (olefin = cyclooctene (coe), 1,5-cyclooctadiene (cod), diethylfumarate (defu), methylcinnamate (meci)) have been prepared, and the molecular structures have been solved by X-ray diffraction for olefin = coe, defu, meci. The complexes feature a dimeric [Cu2(μ-CF3COO)2(olefin)2] core with bridging trifluoroacetates and a η2-bonded olefin. In the case of the defu and meci complexes, [Cu2(μ-CF3COO)2(olefin)2] dimeric units are linked by the oxygen atom of a carbonyl group of the ester to give polymeric chains. The compound [Cu2(μ-CF3COO)2(meci)2]n is the first structurally characterized example of a metal-bonded methylcinnamate. By recrystallization of [Cu2(CF3COO)2(cod)2], a derivative featuring a cod/Cu molar ratio of 0.5 has been isolated and structurally characterized as [Cu2(μ-CF3COO)2(μ-cod)]n, which represents the first example of a polymeric metal complex containing a bridging cod ligand. The carbonylation reaction of [Cu(CF3COO)(olefin)]2 (olefin = coe, cod, defu; 2Cu(CF3COO)(olefin) + 2CO ⇄ [Cu(CF3COO)(CO)]2 + 2(olefin)) has been studied gas volumetrically, and the equilibrium constants are 12.6 ± 2.4 M-1 (298.3 K, cod), (6.3 ± 3.2) × 102 M-1 (293.2 K, coe), and (1.1 ± 0.7) × 107 M-1 (293.2 K, defu). The enthalpy changes, obtained from variable-temperature experiments, are −46 ± 4 (olefin = cod), −71 ± 17 (coe), and −112 ± 20 kJ mol-1 (defu). These data for copper(I) are compared with those obtained for the 3d3 V(II) and 5d10 Au(I) systems VCp2(CO) and AuCl(CO).