Diverse reactivity of alkynes with the binuclear methyl and incipient methyl complexes [RhIr(CH3)(CO)(3)(Ph(2)PCH(2)PPh(2))(2)][CF3SO3] and [Ir2H(CO)(3)(mu-CH2)(Ph(2)PCH(2)PPh(2))(2)][CF3SO3]

The binuclear diiridium complex, [Ir2H(CO)(3)(mu-CH2)(dppm)(2)][CF3SO3] (2), reacts with acetylene and phenylacetylene to give the alkyne- and vinylidene-bridged complexes, [Ir-2(CH3)(CO)(3)(mu-HC=CR)(dppm)(2)][CF3SO3] and [Ir-2(CH3)(CO)(3)(mu-C=C(H)R)(dppm)(2)][CF3SO3] (R = H, Ph), respectively, in each case, At -78 degrees C in the acetylene reaction an intermediate acetylide-hydride, [Ir-2(H)(CH3)(CO)(3)(mu-C=CH)(dppm)(2))[CF3SO3], is observed, which transforms into the vinylidene product at higher temperature. The reaction of the related mixed-metal species [RhIr(CH3)(CO)(3)(dppm)(2)][CF3SO3] (1) with acetylene at -78 degrees C gives an acetylene-bridged intermediate analogous to that observed in the diiridium system, but warming to ambient temperature results in dissociation of the rhodium end of one of the diphosphines, which undergoes nucleophilic attack at the Ph end of the alkyne to yield [RhIr-(CH3)(mu-eta(1):eta(2):eta(1)-HC=C(H)PPh(2)CH(2)PPh(2))(dppm)][CF3SO3]. The reaction of 1 with phenylacetylene at -78 degrees C yields a methyl-hydrido-phenylacetylide intermediate analogous to that observed in diiridium-acetylene chemistry; however, upon warming reductive elimination of methane occurs to give the phenylacetylide-bridged species [RhIr(CO)(3)(mu-C=CPh)-(dppm)(2)][CF3SO3], which reacts with excess phenylacetylene to give the diacetylide-hydride product [RhIr(C=CPh)(CO)(2)(mu-H) (mu-C=CPh)(dppm)(2)][CF3SO3]. Monitoring of the reaction at various temperatures by multinuclear NMR allows the characterization of the observed intermediates, Both compounds 1 and 2 react with dimethyl acetylenedicarboxylate (DMAD) to give the respective products [MIr(C(R)=C(CH3)R)(Co)(3)(dppm)(2)][CF3SO3] (M = Rh, Ir; R = CO(2)Me) resulting from alkyne insertion into the metal-methyl bond. Also observed in the diiridium chemistry is the alkyne-bridged product [Ir-2(CH3)(CO)(3)(mu-DMAD)(dppm)(2)][CF3-SO3]. The structure of [RhIr(C=CPh)(CO)(2)(mu-H)(mu-C=CPh)(dppm)(2)][Cf3SO3] was determined by X-ray crystallography, This compound crystallizes with 2 equiv of CH2Cl2 in the monoclinic space group P2(1)/c in a cell having a = 17.821(3) Angstrom, b = 24.780(5) Angstrom, c = 17.892(3) Angstrom, beta = 117.56(1)degrees, V = 7004(2) Angstrom(3), and Z = 4. On the basis of 8365 unique observations the structure has been refined to R = 0.064 and R(w) = 0.083. Both acetylides are sigma-bound to Ir in a mutually trans orientation, with one also engaging in a weak pi-interaction with Ph, The hydride ligand bridges both metals on the face opposite the bridging acetylide group.