STEREOSELECTIVE SYNTHESIS OF CIS AND TRANS ISOMERS OF [(MO(CO)(3)CL)(2)(MU-ETA(5)ETA(5)-(C5H3(SIME(2)))(2))]

Reaction of (1,3,5-C(6)H(3)Me(3))Mo(CO)(3) (1) and (C5H4(SiMe(2)))(2) in THF (THF = tetrahydrofuran) at room temperature gives the bimetallic complex cis-[{Mo(CO)(3)H}(2){mu-eta(5):eta(5)-(C5H3(SiMe(2)))(2)}] (cis-3), where the two molybdenum atoms are situated in cis positions with respect to the [eta(5):eta(5)-(C5H3(SiMe(2)))(2)](2-) ligand. In contrast, reaction of 1 with the potassium salt of the [(C5H3(SiMe(2)))(2)](2-) anion gives the bimetallic complex trans-K-2[{Mo(CO)(3)}(2){mu-eta(5):eta(5)-(C5H3(SiMe(2)))(2)}] (trans-2), where the two molybdenum atoms are situated in trans positions with respect to the [eta(5):eta(5)-(C5H3(SiMe(2)))(2)](2-) ligand. trans-a can be transformed into trans-[{Mo(CO)(3)H}(2){mu-eta(5):eta(5)-(C5H3(SiMe(2)))(2)}] (trans-3) by reaction with acetic acid. The hydride complexes cis-3 and trans-3 react with CCl4 to give cis- and trans-[{Mo(CO)(3)Cl}(2){mu-eta(5):eta(5)(C5H3(SiMe(2)))(2)}] (4), respectively. The solid-state structures of cis-4 and trans-4 have been determined by single-crystal X-ray analysis. cis-4 crystallizes in the orthorombic space group Pnma with Z = 2 in an unit cell of dimensions a 11.435(3) Angstrom, b = 18.881(3) Angstrom, and c = 23.535(4) Angstrom. trans-4 crystallizes in the monoclinic space group C2/c with Z = 4 in an unit cell of dimensions a = 17.168(5) Angstrom, b = 10.195(1) Angstrom, c = 16.329(4) Angstrom, and beta = 119.37(1)degrees. The structures have been solved from diffractometer data by a combination of heavy atom, direct methods, and Fourier synthesis and refined by full-matrix least squares on the basis of 2348 observed reflections to R = 0.075 and R(w) = 0.11, for cis-4, and on the basis of 2597 observed reflections to R = 0.033 and R(w) = 0.057, for trans-4.