A-FRAME VS OPEN-BOOK GEOMETRIES IN BINUCLEAR COMPLEXES BRIDGED BY DIPHOSPHINES AND MERCAPTOTHIAZOLINATE LIGANDS - UNUSUAL EXAMPLES INVOLVING A BRIDGING BIS(DIPHENYLPHOSPHINO)ETHANE GROUP

Reaction of the tetracarbonyl species [M(CO)2(mu-mtz)]2 (M = Rh, Ir; m tz = 2-mercaptothiazolinate) with 1 equivalent of the diphosphines (Ph 2P(CH2)nPPh2; n = 1 (dppm), 2 (dppe)) yields the compounds [M2(CO)2(mu -L)(mu-mtz)2] (M = Rh, L = dppm (1), dppe (3); M = Ir, L = dppm (2)), which readily undergo oxidative addition of iodine to give [M2I2(CO)2( mu-L)(mu-mtz)2] (M = Rh, L = dppm (4), dppe (6); M = Ir, L = dppm (5)) . When 2 equivalents of dppm are used, the A-frame compounds [M2(CO)2( eta1-Mtz)(mu-mtz)(dppm)2] (M = Rh (7), Ir (8)) are afforded. In soluti on the dangling mtz group of 7 undergoes exchange with both the free m tz anion and the bridging mtz ligand. Compounds 7 and 8 are also produ ced by treatment of trans-[MCl(CO)(dppm)]2 (M = Rh, Ir) with 2 equival ents of the mtz anion. Reaction of these dppm-bridged dichloro species with 1 equivalent of the mtz anion yields [M2Cl(CO)2(mu-mtz)(dppm)2] (M = Rh (9a), Ir (10)). Compound 9a undergoes reversible Cl- dissociat ion to give [Rh2(CO)2(mu-mtz)(dppm)2][Cl] (9b), which is also the stab le form in the solid. Reaction of 9 with CO gives the carbonyl-bridged species [Rh2(CO)2(mu-CO)(mu-mtz)(dppm)2][Cl]. The structures of 6 and 9b have been determined by X-ray crystallography. Compound 6 crystall izes in the triclinic space group P1BAR with one-half equivalent of TH F per asymmetric unit in a cell having a = 9.856(3) angstrom, b = 14.0 78(6) angstrom, c = 16.245(5) angstrom, alpha = 103.66(3)degrees, beta = 93.21(3)degrees, gamma = 92.91(3)degrees, V = 2182(1) angstrom3, an d Z = 2, and has refined to R = 0.045 and R(w) = 0.057 on the basis of 433 parameters varied. Compound 9b crystallizes with one equivalent o f CH2Cl2 in the monoclinic space group P2(1)/n with a = 11.400(1) angs trom, b = 21.944(2) angstrom, c = 22.134(1) angstrom, beta = 92.494(7) degrees, V = 5532(1) angstrom3, and Z = 4, and has refined to R(w) = 0 .062 and R(w) = 0.082 on the basis of 613 parameters varied.