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

Reactions of [Ir 2 (CO) 3 (dppm) 2 ] ( 1; dppm = Ph 2 PCH 2 PPh 2 ) with CH 3 I and CH 3 OCH 2 I give the oxidative-addition products [Ir 2 (R)(I)(CO)(μ-CO)(dppm) 2 ] (R = CH 3 ( 3 ), CH 2 OCH 3 ( 4 )). The X-ray structure determination of 4 ·CH 2 Cl 2 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 CH 3 I but reacts with CH 3 OCH 2 I to give [RhIr(CH 2 OCH 3 )(I)(CO)(μ-CO)(dppm) 2 ] ( 5 ). Reaction of 3 or 5 with methyl triflate results in iodide abstraction to yield the known compound [Ir 2 (CH 3 )(CO)(μ-CO)(dppm) 2 ][CF 3 SO 3 ] and [RhIr(CH 2 OCH 3 )(CO)(μ-CO)(dppm) 2 ][CF 3 SO 3 ] ( 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 [Ir 2 (H) 2 (CO) 2 (μ-COCH 3 )(dppm) 2 ][CF 3 SO 3 ] ( 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-CH 2 )(μ-I)(dppm) 2 ][CF 3 SO 3 ] (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 CH 2 I 2 and ICH 2 CN yield [MIr(CO) 2 (μ-I)(μ-CO)(Ph 2 PCHPPh 2 )(dppm)] (M = Ir ( 10 ), Rh ( 11 )) together with CH 3 I and CH 3 CN, 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 [Ir 2 (CO) 2 (μ-Br)(μ-CO)(Ph 2 PCHPPh 2 )(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 Ph 2 PC(H)PPh 2 ligand, as expected for sp 2 hybridization and partial multiple-bond character in the P−C bonds.