Reactions of Os_3(CO)_(12) with carboxylic acids in a microwave reactor; Synthesis of Os_2(benzoate)_2(CO) _6, a dinuclear osmium(I) compound with aromatic carboxylate ligands

摘要

Microwave heating is used to synthesize compounds of the type Os _2(μ-O_2CR)_2(CO)_6, including the first example with aromatic carboxylate ligands. The one-step preparation of these complexes is straightforward and does not require an air-free reaction environment. The compounds for which R = Me (1) or Et (2) are produced in higher yield than previously reported by the microwave irradiation of Os _3(CO)_(12) for less than 15 min in acetic or propionic acid, respectively. This method may also be used to prepare the new compound Os _2(μ-O_2CH)_2(CO)_6 (3) by reaction with formic acid, but a higher yield is obtained when 1,2-dichlorobenzene is used as a co-solvent. Irradiating a mixture of Os_3(CO)_(12) and excess benzoic acid in 1,2-dichlorobenzene gives another new complex Os _2(μ-O_2CC_6H_5)_2(CO) _6 (4). X-ray crystallographic analyses of 3 and 4 reveal molecular structures similar to that of 1 with approximate C_(2v) symmetry. When the molar ratio of benzoic acid to Os_3(CO)_(12) is 1:1, then the major product is the trinuclear cluster Os_3(μ-H)(μ-O _2CC_6H_5)(CO)_(10) (5) instead of a dinuclear compound. This represents the first instance in which a cluster of this type has been produced directly from Os_3(CO)_(12) instead of through a multi-step procedure.