Synthesis, Structure, and Ligand Dynamics of Triosmium Imidoyl Clusters and Their Isocyanide Derivatives

The synthesis of [formula omitted] (10), the coproduct [formula omitted] (9) and the related imidoyl cluster (μ-H)(μ-η²-CH₃CH₂CNCH₂-CH₂CH₃)Os₃(CO)₁₀ (11) are reported. Thermolysis of 9 at 98 °C yields 10 quantitatively, and both 10 and 11 are decarbonylated thermally or photochemically to yield μ₃-imidoyl clusters [formula omitted] (2) and (μ-H)(μ₃η²-CH₃CH₂CNCH₂CH₂CH₃)Os₃(CO)₉ (3), respectively. The reactions of 2 and 3 with RNC (R = CH₃, C(CH₃)₃) are reported, and in both cases initial adducts [formula omitted] and (μ-H)(μ-η²CH₃CH₂CNCH₂CH₂CH₃)Os₃(CO)₉(CNR) (R = CH₃, 14; R = C(CH₃)₃, 15) are isolated in high yield. Thermolysis of 12–15 at 128 °C yields the μ³-imidoyl complexes [formula omitted] and (μ-H)(μ₃-η²-CH₃CH₂CNCH₂CH₂CH₃)Os₃(CO)₈(CNR) (R = CH₃, 18; R = C(CH₃)₃, 19). Variable temperature ¹H- and ¹³C-NMR and ¹H- and ¹³C-EXSY experiments are reported for 2, 10, and 16–19 which reveal, in detail, the multistage nature of the ligand exchange processes. In solution, complexes 12–19 exist as a large number of positional isomers which do not interconvert in the case of 12–15 but which are interconverted by the motion of the μ₃-imidoyl ligand and axial-radial exchange in 16–19. Solid-state structures for 2, 9, 12, 13, and 16 are reported. Compound 2 crystallizes in the monoclinic space group P2₁/m with unit cell parameters a = 7.681(1) Å, b = 14.801(2) Å, c = 8.157(2) Å, β = 106.06(1)°, V = 891(1) ų, and Z = 2. Least-squares refinement of 2179 reflections gave a final agreement factor of R = 0.044 (R_w = 0.043). Compound 9 crystallizes in the triclinic space group P2₁ with unit cell parameters a = 9.294(3) Å, b = 15.758(5) Å, c = 7.406(2) Å, α = 81.10(2)°, β = 76.47(2)°, γ = 74.88(2)°, V = 992(1) ų, and Z = 2. Least-squares refinement of 2677 reflections gave a final agreement factor of R = 0.037 (R_w = 0.044). Compound 12 crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 8.987(2) Å, b = 16.067(2) Å, c = 14.436(3) Å, β = 93.06(1)°, V = 2081(1) ų, and Z = 4. Least-squares refinement of 2579 reflections gave a final agreement factor of R = 0.051 (R_w = 0.057). Compound 13 crystallizes in the monoclinic space group P2₁/c with unit cell parameters a = 9.216(1) Å, b = 19.372(5) Å, c = 15.176(3) Å, β = 116.38(2)°, V = 2427(2) ų, and Z = 4. Least-squares refinement of 4673 reflections gave a final agreement factor of R = 0.044 (R_w = 0.053). Compound 16 crystallizes in the triclinic space group P2₁/c with unit cell parameters a = 8.574(4) Å, b = 15.660(6) Å, c = 8.437(2) Å, β = 80.69(4)°, β = 67.12(4)°, γ = 74.09(4)°, V = 1002(1) ų, and Z = 2. Least-squares refinement of 3738 reflections gave a final agreement factor of R = 0.058 (R_w = 0.061).