Reactions of Os3(CO)12 with carboxylic acids in a microwave reactor; synthesis of Os2(benzoate)2(CO)6, a dinuclear osmium(I) compound with aromatic carboxylate ligands

Microwave heating is used to synthesize compounds of the type Os2(μ-O2CR)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 Os3(CO)12 for less than 15 min in acetic or propionic acid, respectively. This method may also be used to prepare the new compound Os2(μ-O2CH)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 Os3(CO)12 and excess benzoic acid in 1,2-dichlorobenzene gives another new complex Os2(μ-O2CC6H5)2(CO)6 (4). X-ray crystallographic analyses of 3 and 4 reveal molecular structures similar to that of 1 with approximate C2v symmetry. When the molar ratio of benzoic acid to Os3(CO)12 is 1:1, then the major product is the trinuclear cluster Os3(μ-H)(μ-O2CC6H5)(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 Os3(CO)12 instead of through a multi-step procedure.

Microwave heating is used to rapidly synthesize the osmium carbonyl complexes Os3(μ-H)(μ-benzoate)(CO)10 and Os2(μ-O2CR)2(CO)6, with R = H, Me, Et, and Ph, from Os3(CO)12 in a single step.Figure optionsDownload as PowerPoint slideHighlights
► Faster, simpler, and higher-yield syntheses of diosmium complexes by microwave heating.
► Two new compounds synthesized and structurally characterized: Os2(formate)2(CO)6 and Os2(benzoate)2(CO)6.
► First example of a diosmium(I) carbonyl compound with aromatic carboxylate ligands.
► First example of a direct, single-step reaction of Os3(CO)12 with an aromatic carboxylic acid.