"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(µ-mtz)]2 (M = Rh, Ir; mtz = 2-mercaptothiazolinate) with 1 equivalent of the diphosphines (Ph2P(CH2)nPPh2; n = 1 (dppm), 2 (dppe)) yields the compounds [M2(CO)2(µ-L)(µ-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(µ-L)(µ-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(η1-mtz)(µ-mtz)(dppm)2] (M = Rh (7), Ir (8)) are afforded. In solution the dangling mtz group of 7 undergoes exchange with both the free mtz anion and the bridging mtz ligand. Compounds 7 and 8 are also produced by treatment of trans-[MCl(CO)(dppm)]2 (M = Rh, Ir) with 2 equivalents of the mtz anion. Reaction of these dppm-bridged dichloro species with 1 equivalent of the mtz anion yields [M2Cl(CO)2(µ-mtz)(dppm)2] (M = Rh (9a), Ir (10)). Compound 9a undergoes reversible Cl− dissociation to give [Rh2(CO)2(µ-mtz)(dppm)2][Cl] (9b), which is also the stable form in the solid. Reaction of 9 with CO gives the carbonyl-bridged species [Rh2(CO)2(µ-CO)(µ-mtz)(dppm)2][Cl]. The structures of 6 and 9b have been determined by X-ray crystallography. Compound 6 crystallizes in the triclinic space group [Formula: see text] with one-half equivalent of THF per asymmetric unit in a cell having a = 9.856(3) Å, b = 14.078(6) Å, c = 16.245(5) Å, α = 103.66(3)°, β = 93.21(3)°, γ = 92.91(3)°, V = 2182(1) Å3, and Z = 2, and has refined to R = 0.045 and Rw = 0.057 on the basis of 433 parameters varied. Compound 9b crystallizes with one equivalent of CH2Cl2 in the monoclinic space group P21/n with a = 11.400(1) Å, b = 21.944(2) Å, c = 22.134(1) Å, β = 92.494(7)°, V = 5532(1) Å3, and Z = 4, and has refined to R = 0.062 and Rw = 0.082 on the basis of 613 parameters varied.