CATIONIC VINYLIDENE-BRIDGED COMPLEXES AND THEIR REACTIONS WITH ALKYNES TO YIELD EITHER ALKYNE-BRIDGED AND VINYLIDENE-BRIDGED OR BIS(VINYLIDENE) PRODUCTS - FACILE INTERCONVERSION BETWEEN TERMINAL AND BRIDGING VINYLIDENE BONDING MODES

Reaction of the cationic A-frame complex [Ir-2(CO)(2)(mu-I)(dppm)(2))] [SO3CF3] (2) (dppm = Ph2PCH(2)PPh(2)) with either acetylene or phenyla cetylene at -78 degrees C yields the respective species [Ir-2(CO)(HCCR )(mu-I)(mu-CO)(dppm)(2)][SO3CF3] (R = H, Ph), in which the alkyne is t erminally bound to one metal. At ambient temperature these alkyne addu cts slowly rearrange to the vinylidene-bridged species [Ir-2(CO)(2)(mu -I)(mu-CC(H)R)(dppm)(2)][SO3CF3]. An analogous allene adduct is obtain ed in the reaction of 2 with allene. Reaction of the neutral, vinylide ne-bridged complexes [Ir2I2(CO)(2)(mu-CC(H)R)(dppm)(2)] (R = H, Ph) wi th methyl triflate yields the same cationic vinylidene-bridged species through loss of CH3I. Protonation of this neutral vinylidene-bridged species (R = H) at -40 degrees C yields an ethylidyne-bridged product which rearranges to a vinylidene- and hydride-bridged product at ambie nt temperature. Reaction of [Ir-2(Co)(2)(mu-I)(mu-CC(H)Ph)(dppm)(2)][S O3CF3] with either acetylene or phenylacetylene yields alkyne- and phe nylvinylidene-bridged products Ir2I(CO)(2)(mu-CC(H)Ph)(mu-HCCR)(dppm)( 2)][SO3CF3] (R = H, Ph), and the X-ray structure of a derivative, [Ir2 I2(CO)(2)(mu-CC(H)Ph)(mu-HCCH)(dppm)2] (15), has been carried out. The reaction of [Ir-2(CO)(2)(mu-I)(mu-CCH2)(dppm)(2)][SO3CF3] with phenyl acetylene yields an unusual bis(vinylidene) product, [Ir2I(CO)2(CCH2)( CC(H)Ph)(dppm)(2)][SO3CF3] (19), in which each vinylidene is terminall y bound to a different metal. Reaction of 19 with either I- or CO conv erts the terminal vinylidenes to bridging groups yielding [Ir2I(L)(CO) (2)(mu-CCH2)(mu-CC(H)Ph)(dppm)(2)](n+) (L = I, n = 0; L = CO, n = 1). The structure of the diiodo species (20b) has been determined by X-ray techniques. Compound 15, as the CH2Cl2 solvate, crystallizes in the m onoclinic space group P2(1)/c with a = 15.799(3) Angstrom, b = 18.029( 2) Angstrom, c = 21.126(5) Angstrom, beta = 99.48(2)degrees, V = 5935( 4) Angstrom(3) (T = -65 degrees C), and Z = 4. On the basis of 7406 un ique observations and 441 parameters varied, the structure refined to R = 0.034 and R(w) = 0.040. This complex has a bridging phenylvinylide ne and a bridging acetylene group with the iodo ligands bound cis to t he alkyne bridge. Compound 20b crystallizes in the tetragonal space gr oup I4(1)/a with a = 30.407(5) Angstrom, c = 13.065(6) Angstrom, V = 1 2079(6) Angstrom(3), and Z = 8 (T = 22 degrees C). On the basis of 373 0 unique observations and 305 parameters varied, the structure refined to R = 0.045 and R(w) = 0.050. In this product both the vinylidene an d the phenylvinylidene groups are bridging, with the iodo ligands havi ng an anti arrangement on adjacent metals.