Preparative studies of alkoxy derivatives of manganese carbonyl

Abstract

Oligomeric alkoxy derivatives of bromopentacarbonyl manganese (I) and bromotetracarbonylmanganese (^+) (I) were prepared by reaction with a base and a variety of alcohols. The nature of the products, their structural and bonding features are discussed in the context of alkoxide chemistry in general. Reactions of Mn(CO)(_5)Br with triethylamine and alcohols in hydrocarbon solvents at 55ºC were monitored by IR spectroscopy which indicated the formation of one major product, either a Mn(_3)(CO)(_g)(OR)(_3) or a Mn(_4)(CO)(_12)(OR)(_4) complex. Yields were non-reproducible and isolated solids were shown to be a mixture of products. Mass spectral data indicated oligomers of the type [Mn (CO) (_3) (OR) ] (_n), where n = 3 to 6, and dimers of formula [Mn(CO) (_4) (OR)] (_2). Reliable yields were obtained using sodium carbonate as the base and acetone as the solvent. The products are mixtures and mass spectral data shows a predominance of trimeric alkoxy derivatives, although products with n = 4 to 6 and dimers were also found. A monomer was obtained with triphenylcarbinol, Mn(CO)(_5)(OCPh(_3)).The results of the reactions of Mn(CO)(_4)(PPh(_3))Br with triethylamine and alcohols in hydrocarbon solvents are more difficult to interpret. Mixtures of products are obtained, dimeric alkoxy derivatives [Mn(CO)(_3)(PPh(_3)) OR](_2) predominating. However, non-alkoxy complexes appear to be the major products in a number of cases. A 1.2ppm shift in the d(_6)-acetone (^1)H NMR spectrum of the methoxy complex [Mn(CO) (_3) (OM(^6)e) ] (_n) was attributed to paramagnetic species of the type [Mn (OMe) (_2) ] (_n). These paramagnetic compounds may well be present in other product mixtures. Attempted purification techniques and methods of separation of the product mixtures are also discussed.