The stepwise hydrogenation of a nitrile on an osmium cluster: X-ray crystal structures of [Os3(µ-H)(µ-NHCH2CF3)(CO)10], [Os3(µ-H)2(µ3-NCH2CF3)(CO)9], and [Os3H(µ-H)3(µ3-NCH2CF3)(CO)8]

Abstract

The hydrogenation of [Os₃(µ-H)(µ-NCHCF₃)(CO)₁₀](1) and [Os₃(µ-H)(µ-η²-NHCCF₃)(CO)₁₀](2) which are, respectively, the major and minor products of the reaction of CF₃CN with [Os₃H₂(CO)₁₀] has been studied. Molecular hydrogen (49 atm, 140 °C, 16 h) reacts with (1) to give complexes [Os₃(µ-H)(µ-NHCH₂CF₃)(CO)₁₀](3), [Os₃(µ-H)₂(µ₃-NCH₂CF₃)(CO)₉](4), and [Os₃H(µ-H)₃(µ₃-NCH₂CF₃)(CO)₈](5), in comparable yields (25–30%). The reaction of hydrogen (23 atm, 120 °C, 16 h) with (2) gives (3) in ca. 80% yield together with at least two other unidentified complexes in low (<5%) yields. X-Ray diffraction studies of (3), (4), and (5) are reported. Crystals of (3) are monoclinic, space group C2/c, with a= 19.983(3), b= 15.562(3), c= 14.089(3)Å, β= 118.80(3)°, and Z= 8. 2 248 Reflections with l 3σ(I)[3 ⩽θ⩽ 25°] refined to R= 0.042 and R′= 0.043. Complex (4) crystallises in space group P2₁/c, with a= 9.383(2), b= 12.388(2), c= 16.171(3)Å, β= 97.79(2)°, and Z= 4. 3091 Unique data [I 3σ(I), 3 ⩽θ < 25°] refined to R= 0.051 and R′= 0.053. Complex (5) is monoclinic, space group C2/c, with a= 17.387(3), b= 8.137(2), c= 26.142(3)Å, β= 99.15(4)°, and Z= 8. 1 944 Reflections with I 3σ(l)[3 ⩽θ⩽ 25°] refined to R= 0.046 and R′= 0.046. A partial model for the hydrogenation of a nitrile on a cluster, based on the isolation of the complexes (1)–(5), is presented and discussed.