SYNTHESIS AND PROPERTIES OF BRIDGING SILOXYL LIGANDS IN DIRHENIUM CARBONYL-COMPLEXES

Reaction of the complex Re2(CO)8[mu-C(H)C(H)Bu(n)](mu-H) with HSi(OMe)3 in a refluxing heptane solution yielded the new compound Re2(CO)8[mu-eta2-Si(OMe)3](mu-H) (1) in 51% yield. Compound 1 was converted to a PMe2Ph derivative Re2(CO)7(PMe2Ph)[mu-eta2-Si(OMe)3](mu-H) (2) in 25% yield by treatment with Me3NO in the presence of PMe2Ph. Compounds 1 and 2 were characterized crystallographically, and each was found to contain an eta2-Si(OMe)3 ligand bridging the two rhenium atoms. In compound 2 the phosphine ligand is coordinated to the rhenium atom that contains the coordinated oxygen atom. Both compounds exhibit a dynamical activity at elevated temperatures in which the OMe groups of the Si(OMe)3 ligand are averaged. The activation barrier in 2 is slightly higher than that in 1. Compound 2 reacts with H2O at 25-degrees-C to yield the adduct Re2(CO)7(PMe2Ph)[Si(OMe)3](H2O)(mu-H) (3) in 76%. A structural analysis of 3 showed that the Si-OMe bridge was opened by a cleavage of the Re-O bond and the addition of H2O to that site. One of the hydrogen atoms of the H2O ligand is hydrogen bonded to one of the OMe groups of the Si(OMe)3 ligand. Compound 3 readily loses H2O and is converted back to 2. Crystal data: for 1, space group = Pl, a = 9.766(2) angstrom, b = 12.344(4) angstrom, c = 8.741(2) angstrom, alpha = 109.52(2)-degrees, beta = 110.97(2)-degrees, gamma = 79.54(2)-degrees, Z = 2, 2103 reflections, R = 0.039; for 2, space group = P2(1)/c, a = 14.579(1) angstrom, b = 7.832(2) angstrom, c = 22.357(3)angstrom, beta = 101.88(1)-degrees, Z = 4, 2327 reflections, R = 0.035; for 3, space group = P2(1), a = 10.347(2) angstrom, b = 12.482(3) angstrom, c = 11.026(2) angstrom, beta = 109.53(1)-degrees, Z = 2, 1822 reflections, R = 0.021.