| The compound [RhIr(CO)2(mu-CCPh)(dppm)2][X] (X = BF4, 2a; X = O3SCF3, 2b; dppm = Ph2pCH2PPh2) is an "A-frame" species in which the bridging phenylacetylide group is sigma-bound to iridium and pi-bound to rhodium. Reaction of compound 2 with hydride yields [RhIr(H)(CO)2(mu-CCPh)(dppm)2] (6), which rearranges to give the phenylvinylidene complex [RhIr(CO)2(mu-CCHPh)(dppm) 2] (7). Phosphines, olefins, and alkynes bind terminally to iridium, yielding compounds of the type [RhIr(CO)2(L)-(mu-CCPh)(dppm) 2][O3SCF3] (L = PR3, olefin, alkyne). Addition of terminal alkynes or dihydrogen results in oxidative addition at the iridium centre, yielding [RhIr(X)(CO)2-(mu-H)(mu-CCR)(dppm) 2][O3SCF3] (X = CCPh, H; R = Ph, Me). Addition of allyl bromide also results in oxidative addition, followed by rearrangement to the allylvinylidene complex [RhIrBr(CO)(mu-C=C(Ph)CH2CH=CH 2)(mu-CO)(dppm)2][X] (X = BF4, 28a; X = O3SCF3, 28b), in which the olefinic moiety of the bridging vinylidene ligand is coordinated to rhodium.; Addition of allyl bromide to 2 in the presence of a silver salt results in the formation of the pi-allyl complex [RhIr(eta 3-CH2CHCH2)(CO)2(mu-CCPh)(dppm) 2][X]2 (X = BF4, 36a; X = O 3SCF3, 36b). Addition of halide causes rearrangement to the allylvinylidene complex, while other nucleophiles attack the central carbon of the allyl, forming the iridacyclobutane complexes [RhIr(CH 2CHRCH2)(CO)2(mu-CCPh)(dppm)2][X] (R = PMe3, [X] = [BF4]2, 37; R = H, [X] = [O3SCF3], 38; R = CN, [X] = [O3SCF3], 39).; Treatment of 2 with an excess of carbon disulphide leads to the formation of a number of species, including (RhIr(CO)(eta 1:eta3-CC(Ph)SCSCS2)(mu-CO)(dppm 2)][BF4] (40) and [RhIr(CO)(SCSCS2)(mu-CCPh)(mu-CO)(dppm) 2][BF4] (41). In both these complexes, two molecules of carbon disulphide have condensed in a "head-to-tail" fashion; in 40, the resulting C2S4 fragment has also coupled with the alkynyl ligand to form a thiovinylidene ligand. Addition of butyl isothiocyanate to 2 results in the formation of [RhIr(CCPh)(CO) 2(mu-SCNnBu)(dppm)2][BF4] ( 43), which rearranges to the oxidative addition product [RhIr(CCPh)(CN nBu)(CO)(mu-S)(mug-CO)(dppm)2][BF4] ( 44).; The two isomeric compounds [Ir2(CO)2(mu-eta 1: eta1-MeO2CC≡CCO 2Me) (dppm)2] (46) and [Ir2(CO) 2(mu-eta2: eta2-MeO2CC≡CCO 2Me) (dppm)2] (47) differ primarily in the orientation of the alkyne ligand. The air-sensitive 46 reacts readily with a number of reagents at the external face of one iridium centre. The stable 47 reacts only with HBF4 to give the vinyl-bridged species [Ir2(CO)2(eta1: eta2-MeO 2CC=CHCO2Me)(dppm)2][BF4] (53 ). Several vinyl species of the type [Ir2(CO)n(eta 1-RC=CHR')(dppm)2][BF4] (R, R' = CO2Me, CO2Et, Ph; n = 3, 4) were also prepared. |
