CIS-DIENE AND TRANS-DIENE COORDINATION IN RUTHENIUM(II) ACETYLACETONATE COMPOUNDS

Reduction of Ru(acac)3 with zinc in ethanol in the presence of 1,3-dienes leads to the formation of Ru(eta-4-diene)(acac)2 complexes (diene = 2,3-dimethyl-1,3-butadiene, 2,4-hexadiene, 1,3-cyclohexadiene, 2,4-dimethyl-1,3-pentadiene). Except for the cyclohexadiene compound, these complexes involve unusual eta-4-trans-diene coordination in the ground state and may be observed in two isomeric forms. In the case of the 2,3-dimethyl-1,3-butadiene complex, small amounts of a third isomeric form may be observed, which appears to involve eta-4-cis-diene coordination. Single-crystal X-ray structural studies have been carried out for the 2,4-dimethyl-1,3-pentadiene and cyclohexadiene complexes. For the former, the space group is P2(1)/n with a = 10.614 (8) angstrom, b = 13.31 (1) angstrom, c = 12.93 (1) angstrom, beta = 90.81 (6)-degrees, and V = 1826.5 angstrom 3 for Z = 4, while, for the latter, the space group is Pbca, with a = 11.642 (4) angstrom, b = 16.162 (6) angstrom, c = 33.78 (1) angstrom, and V = 6356.0 angstrom 3 for Z = 16 (two independent molecules). The former (latter) structures were refined to discrepancy indices of R = 0.037 (0.051) and 0.035 (0.044) for 4015 (4200) reflections having I > 2-sigma(I) (2.5-sigma(I) for the latter).