Triosmium clusters derived from benzylamine and benzyl alcohol: formation of a µ3-o-phenylene complex in the conversion of benzyl alcohol into benzene

Abstract

Benzylamine reacts (125 °C) with [Os₃(CO)₁₂] to give mainly the µ-carbamoyl complex [Os₃(CO)₁₀H{µ-OCN-(CH₂Ph)H}] together with small amounts of [Os₃(CO)₁₀H{µ-N(CH₂Ph)H}] which may also be obtained by decarbonylation of the first product. The complex [Os₃(CO)₁₀(C₈H₁₄)₂] gives (60–70 °C) the same products, but with the benzylamido-complex predominating. It is probable, but not established, that these derivatives are involved in the [Os₃(CO)₁₂]-catalysed carbonylation of benzylamine to (PhCH₂NH)₂CO. The analogue of only one of these, [Os₃(CO)₁₀H(µ-OCH₂Ph)], is formed from benzyl alcohol, and thermolysis of nonane solutions of this derivative at 146 °C in sealed glass tubes gives C₆H₆, PhCHO, [Os₃(CO)₁₂], and [Os₄(CO)₁₂H₄] only; related products are obtained from the 4-methyl-substituted analogue, while [Os₃(CO)₁₀H(µ-OCMePhH)] gives only PhCOMe as an organic product. A possible scheme for these degradations is discussed in terms of the intermediates [Os₃(CO)₉H₂(µ-OCH₂C₆H₄)] and [Os₃(CO)₉H₂(µ₃-C₆H₄) which have been isolated from reaction solutions flushed with N₂. The complex [Os₃(CO)₉H₂(µ₃-C₆H₃Me-4)] is formed from both isomers [Os₃(CO)₁₀H(OCH₂C₆H₄Me-2 or -4)]. Interconversions and structures (based on spectroscopic evidence) of the above complexes are described.