Dialkyl and Trialkyl Heterobinuclear Complexes of Rhodium and Iridium:  Models for Adjacent-Metal Involvement in Bimetallic Catalysts

The heterobinuclear dialkyl complexes [RhIr(R) 2 (μ-CO)(dppm) 2 ] (dppm = μ-Ph 2 PCH 2 PPh 2; R = CH 3 ( 2 ), CH 2 Ph ( 3 )) have been prepared. Both A-frame-like compounds have one alkyl group terminally bound to each metal and a bridging carbonyl ligand. Some subsequent reactivity studies of 2 are reported. Reaction of 2 with CO yields [RhIr(CO) 3 (dppm) 2 ] and acetone. If this reaction is monitored at low temperature by NMR spectroscopy, the dicarbonyl species [RhIr(CH 3 ) 2 (CO) 2 (dppm) 2 ] ( 4 ) is first observed, followed by [RhIr(CH 3 ) 2 (CO) 3 (dppm) 2 ] ( 5 ). In both products, both methyl groups are bound to Ir. Warming to ambient temperature under CO yields acetone and [RhIr(CO) 3 (dppm) 2 ]. Crossover experiments suggest that acetone arises primarily from an intramolecular process. We propose that migratory insertion of a CO and a methyl group occurs on Ir; presumably reductive elimination also occurs from this metal. Compound 2 reacts with H 2 at −78 °C to yield [RhIrH(CH 3 ) 2 (μ-H)(μ-CO)(dppm) 2 ] ( 6 ), in which one methyl group is bound to Rh while the other, together with a hydride ligand, is terminally bound to Ir. This latter species reacts with CO at 0 °C to yield [RhIrH(C(O)CH 3 )(CH 3 )(μ-H)(μ-CO)(dppm) 2 ] ( 7 ), in which migratory insertion involving CO and the Rh-bound methyl group has yielded a Rh-bound acetyl group. At ambient temperature, under an atmosphere of CO, [RhIr(CO) 3 (dppm) 2 ] is formed, together with acetaldehyde and methane. Crossover experiments support a predominantly intramolecular process for acetaldehyde formation but are equivocal on the formation of methane. Compound 2 oxidatively adds CH 3 I or n - C 4 H 9 I, yielding [RhIr(CH 3 ) 2 (R)(μ-I)(μ-CO)(dppm) 2 ] (R = CH 3, n - C 4 H 9 ), in which the added alkyl group in each case is bound to Ir. The n - butyl product reacts with CO to yield [RhIr( n - C 4 H 9 )(CH 3 ) 2 (μ-CO) 2 (dppm) 2 ][I], in which the n - butyl group has migrated to Rh. A similar product, [RhIr(CH 3 ) 3 (μ-CO) 2 (dppm) 2 ][CF 3 SO 3 ], is obtained in the reaction of 2 with methyl triflate in the presence of CO.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.