Reactions of the Binuclear Complexes [MIr(CO)3(Ph2PCH2PPh2)2] (M = Rh, Ir) with Alkyl Halides: Dramatic Reactivity Differences as a Function of Metal Combination and Alkyl Halide

Abstract

Reactions of [Ir2(CO)3(dppm)2] (1; dppm = Ph2PCH2PPh2) with CH3I and CH3OCH2I give the oxidative-addition products [Ir2(R)(I)(CO)(μ-CO)(dppm)2] (R = CH3 (3), CH2OCH3 (4)). The X-ray structure determination of 4·CH2Cl2 shows that the alkyl group is the sole terminal ligand on one metal while the iodo and a carbonyl are terminally bound to the adjacent metal. The mixed-metal analogue [RhIr(CO)3(dppm)2] (2) does not react with CH3I but reacts with CH3OCH2I to give [RhIr(CH2OCH3)(I)(CO)(μ-CO)(dppm)2] (5). Reaction of 3 or 5 with methyl triflate results in iodide abstraction to yield the known compound [Ir2(CH3)(CO)(μ-CO)(dppm)2][CF3SO3] and [RhIr(CH2OCH3)(CO)(μ-CO)(dppm)2][CF3SO3] (8), respectively. In the mixed-metal compound iodide removal results in migration of the methoxymethyl group from Rh to Ir. Iodide abstraction from 4 results in a double C−H bond activation to yield the methoxycarbyne-bridged [Ir2(H)2(CO)2(μ-COCH3)(dppm)2][CF3SO3] (6). In the reactions of 4 and 5 with methyl triflate some methoxide abstraction also occurs, yielding the methylene-bridged products [MIr(CO)2(μ-CH2)(μ-I)(dppm)2][CF3SO3] (M = Ir (7), Rh (9)) as minor products in between 15 and 30% yield. The reactions of [MIr(CO)3(dppm)2] (M = Ir (1), Rh (2)) with CH2I2 and ICH2CN yield [MIr(CO)2(μ-I)(μ-CO)(Ph2PCHPPh2)(dppm)] (M = Ir (10), Rh (11)) together with CH3I and CH3CN, respectively, by hydrogen abstraction from one of the dppm ligands and iodine atom coordination at the metals. Reactions of 1 with allyl bromide and benzyl bromide yield the bromo analogue [Ir2(CO)2(μ-Br)(μ-CO)(Ph2PCHPPh2)(dppm)2] (12). The X-ray structure of 10·THF has been determined and shows a planar Ir−P−C(H)−P−Ir moiety, short P−C bonds (1.72(2) Å), and a 122(1)° angle at carbon of the Ph2PC(H)PPh2 ligand, as expected for sp2 hybridization and partial multiple-bond character in the P−C bonds.