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

Abstract

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-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (M = Os ( 5 ), Ru ( 6 ); dppm = μ-Ph 2 PCH 2 PPh 2 ) to produce the corresponding substituted olefin (through loss of N 2 and subsequent coupling of the diazoalkane-generated alkylidene fragment and the methylene unit), the known tetracarbonyl species [RhM(CO) 4 (dppm) 2 ][CF 3 SO 3 ] (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 (η 2 -CH 2 -CHR)(dppm) 2 ][CF 3 SO 3 ] ( 7; R = CO 2 Et) is observed, which decomposes with release of the olefin upon warming. The methylene-bridged tetracarbonyl species [RhM(CO) 4 (μ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (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 N 2 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-η 1:η 1 -N 2 C(COH)CO 2 Et)(dppm) 2 ][CF 3 SO 3 ] (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-η 1:η 1 -N 2 C(CO 2 Et) 2 )(dppm) 2 ][CF 3 SO 3 ] (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 (η 1 -Ν 2 CHSiMe 3 )(dppm) 2 ][CF 3 SO 3 ]] ( 12 ), in which the TMSDM ligand binds terminally on Os opposite the Rh−Os bond.