Synthesis and structure of ruthenium(II)-diene complexes

The reaction of Ru(acac)(3) in ethanol in the presence of dienes (diene = 2,5-dimethyl-2,4-hexadiene, isoprene, 1,2,4,5-tetramethyl-1,4-cyclohexadiene) with zinc as reducing agent affords Ru(acac)(2)(diene) complexes. For the acyclic diene ligands, the Ru(acac), unit exhibits a preference for the trans-diene coordination. The structures for the 2,5-dimethyl-1,3-hexadiene and 1,2,4,5-tetramethyl-1,4-cyclohexadiene derivatives have been determined crystallographically. The Ru(acac)(2)(hexadiene) complex crystallizes in the monoclinic space group P2(1)/n with a = 10.658(2) Angstrom, b = 12.075(3) Angstrom, c = 15.332(3) Angstrom and beta = 108.07(5)degrees for Z = 4. The cyclohexadiene complex crystallizes in a triclinic space group P (1) over bar, with a = 8.495(4) Angstrom, b = 8.456(4) Angstrom, c = 14.364(6) Angstrom, and alpha = 78.88(2)degrees, beta = 82.60(2)degrees, gamma = 78.04(2)degrees for Z = 2. The solid-state structure for the dimethylhexadiene complex revealed an eta(4)-trans-diene coordination, while for the cyclic diene it revealed isolated olefin interactions.