Coordination and Activation of Diazoalkanes in the Presence of Rh/Ru and Rh/Os Metal Combinations

• Published in: Organometallics 2008-07, Vol.27 (13), p.3070-3081
• Main Authors: Samant, Rahul G, Graham, Todd W, Rowsell, Bryan D, McDonald, Robert, Cowie, Martin
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om700756q

The substituted diazoalkanesethyl diazoacetate (EDA), diethyl diazomalonate (DEDM), and trimethylsilyl diazomethane (TMSDM)react readily with the methylene-bridged tricarbonyl species [RhM(CO)3(μ-CH2)(dppm)2][CF3SO3] (M = Os (5), Ru (6); dppm = μ-Ph2PCH2PPh2) to produce the corresponding substituted olefin (through loss of N2 and subsequent coupling of the diazoalkane-generated alkylidene fragment and the methylene unit), the known tetracarbonyl species [RhM(CO)4(dppm)2][CF3SO3] (M = Os (1), Ru (2)), and uncharacterized decomposition products. In the reaction of 5 with EDA at −20 °C the intermediate olefin adduct, [RhOs(CO)3(η2-CH2-CHR)(dppm)2][CF3SO3] (7; R = CO2Et) is observed, which decomposes with release of the olefin upon warming. The methylene-bridged tetracarbonyl species [RhM(CO)4(μ-CH2)(dppm)2][CF3SO3] (M = Os(3), Ru (4)) also react with these diazoalkanes to yield the same products, only at a much slower rate. Attempts to generate the alkylidene-bridged products, analogous to 3 and 4, by reaction of 1 or 2 with EDA, DEDM, and TMSDM accompanied by loss of N2 instead gave complexes containing the diazoalkane unit. In the reaction with EDA condensation of this unit with a carbonyl ligand occurs accompanied by migration of the diazoalkane hydrogen to the carbonyl oxygen, yielding [RhM(CO)3(μ-η1:η1-N2C(COH)CO2Et)(dppm)2][CF3SO3] (M = Os (8), Ru (9)). The new diazoalkane-like group bridges the metals via the terminal nitrogen, while also binding to the group 8 metal via the enol carbon that originated from a carbonyl group. In the related reaction involving DEDM, substitution of a carbonyl yields [RhM(CO)3(μ-η1:η1-N2C(CO2Et)2)(dppm)2][CF3SO3] (M = Os (10), Ru (11)), in which the intact diazoalkane ligand again bridges via the terminal nitrogen. However, in this case one of the ester carbonyls binds to the group 8 metal, replacing the carbonyl group that was displaced. Although the RhRu compound 2 does not react with TMSDM, the analogous RhOs compound (1) does react, yielding [RhOs(CO)3(η1-Ν2CHSiMe3)(dppm)2][CF3SO3]] (12), in which the TMSDM ligand binds terminally on Os opposite the Rh−Os bond.