Abstract
The reactivities of the heterobinuclear complexes, [MM′(CO)4(dppm)2][X] (MM′ = RhOs, RhRu, IrRu; dppm = µ-Ph2PCH2PPh2; X = BF4, CF3SO3) with diazomethane are reported. The RhOs species reacts to give three products of methylene-group incorporation, depending on the temperature; at 80 °C the methylene bridged product, [RhOs(CO)4(µ-CH2)(dppm)2][X], is formed exclusively, at ambient temperature only [RhOs(η1-C3H5)(CH3)(CO)3(dppm)2][X], having the allyl group bound to Rh and the methyl group bound to Os, is obtained, while at intermediate temperatures [RhOs(η1:η1-C4H8)(CO)3(dppm)2][X], having the butanediyl fragment chelating on Os, is generated. Based on labeling studies a mechanism is proposed rationalizing formation of the different products. Under the same range of conditions the Rh/Ru and Ir/Ru species yield only the methylene bridged products, [MM′(CO)4(µ-CH2)(dppm)2][X] (MM′ = RhRu, IrRu). A rationalization for the different reactivities observed and a description of the roles of the different metals in coupling of the methylene groups are presented. Attempts to model key intermediates in the methylene coupling sequence promoted by the Rh/Os complexes, through coupling of methylene groups with ethylene or alkynes, are described. Key words: heterobinuclear, rhodium/osmium, rhodium/ruthenium, iridium/ruthenium, methylene coupling, FischerTropsch, alkyne insertions, bimetallic cooperativity.
Publisher
Canadian Science Publishing
Subject
Organic Chemistry,General Chemistry,Catalysis
Cited by
41 articles.
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