STRUCTURAL CHARACTERIZATION OF U(1)-ETA(2)-CIS-1,2-BIS(DIPHENYLPHOSPHINO)ETHENE)]

The structure of [Ru3(CO)10(mu1-eta2-c-dpp)] (c-dpp = cis-1,2-bis(clip henylphosphino)ethene) has been determined by X-rav crystallography. T he crystals are monoclinic, space group P2(1)/n, with cell dimensions: a = 10.4590(17), b = 24.197(6). c = 14.500(4) angstrom, beta = 100.00 3 (22)-degrees and Z = 4. This structure was refined to give R = 0.031 and R(w) = 0.028 using 5052 reflections with I > 2sigma(I) in the ran ge of 2 less-than-or-equal-to 20 less-than-or-equal-to 50-degrees (Mo Kalpha). The structure suggested previously to contain a 1.2-bridging c-dpp ligand is now found to contain the ligand in a 1,1-chelating geo metry, which is also maintained in solution as indicated by the large downfield P-31 coordination shift. This five-membered chelate ring is not perpendicular as observed for a similar ring in [Ru3(CO)10(mu3-eta 2-bipy)] (bipy = 2,2'-bipyridine) but nearly coplanar with the RU3 pla ne. The synthesis and the structures of [M3(CO)10(L-L)] and [M2(CO)6(L -L)] (M = Fe, Ru or Os; L-L = chelating c-dpp or bridging 1,2-bis(dime thylarsino)tetrafluorocyclobutene) are compared and a general reaction mechanism from [M3(CO)12] to [M3(CO)10(L-L)] and [M3(CO)6(L-L)] is pr oposed.