Reactions of aryl isocyanates with hydridotriosmium carbonyl cluster compounds

Article abstract of DOI:10.1021/ic50218a055

The reactions of aryl isocyanates with the cluster complexes H₂Os₃(CO)₉L [I, L = CO; II, L = P(CH₃)₂C₆H₅] are described. The major products of the reaction of I with aryl isocyanates are complexes containing N-arylformamido ligands formed by the transfer of one hydride ligand to the carbon atom of the isocyanate molecule. An X-ray crystallographic analysis of the product (μ-H)(μ-p-CH₃C₆H₄NCHO)Os ₃(CO)₁₀ (III) was performed: space group P1, a = 7.925 (2) A?, b = 11.705 (3) A?, c = 13.928 (4) A?, α= 66.71 (2)°, β = 80.17 (2)°, γ = 79.18 (2)°, Z = 2, _ρcalcd = 2.83 g/cm³. For 3902 reflections, R = 0.052 and R_w = 0.062. III contains an N-p-tolylformamido ligand which is coordinated by its nitrogen and oxygen atoms across one edge of a triangular cluster of three osmium atoms. Reaction of III with dimethylphenylphosphine readily gives the monosubstitution product (μ-H)(μ-p-CH₃C₆H₄NCHO)Os ₃(CO)₉[P(CH₃)₂C₆H ₅] (V). An X-ray crystallographic analysis of V was performed: space group P1, a = 10.690 (1) A?, b = 13.034 (2) A?, c = 13.200 (4) A?, α = 109.78 (2)°, β = 93.05 (2)°, γ = 110.25 (2)°, Z = 2, _ρcalcd = 2.28 g/cm³. For 3985 reflections, R = 0.047 and R_w = 0.061. V is similar to III except that it contains a dimethylphenylphosphine ligand coordinated in an equatorial position on the osmium atom coordinated to the oxygen atom of the bridging N-p-tolylformamido ligand. The major product of the reaction of II with p-tolyl isocyanate was an isomer of V which was characterized by spectroscopic and X-ray crystallographic methods as (μ-H)(μ-p-CH₃C₆H₄NHCO)Os ₃(CO)₉[P(CH₃)₂C₆H ₅] (VI): space group P2₁/c, a = 12.210 (2) A?, b = 14.337 (4) A?, c = 17.739 (4) A?, β = 104.49 (2)°. For reflections, R_w = 0.034 and R_w = 0.032. VI contains an N-hydrido-N-p-tolylcarboxamido ligand which is coordinated by its carbon and oxygen atoms across an edge of a triangular cluster of osmium atoms. This product was evidently formed by transfer of a hydrogen atom from the cluster to the nitrogen atom of the isocyanate. A minor product (μ-H)(μ-N-p-CH₃C₆H₄NHCO)Os ₃(CO)₁₀ (VII), which is similar to VI, was also isolated from the reaction of I with p-tolyl isocyanate. It was shown that III and VII cannot be interconverted under the reaction conditions. They are, thus, presumed to be formed by independent competing reactions. The changes in hydrogen transfer obtained when a carbonyl ligand is replaced with a dimethylphenylphosphine ligand are discussed.