Synthesis, structure, and ligand dynamics of triosmium imidoyl clusters and their isocyanide derivatives

Article abstract of DOI:10.1021/om00030a047

The synthesis of (μ-H)(μ-η²-C=NCH₂CH₂CH ₂)Os₃(CO)₁₀ (10), the coproduct (μ-H)(μ-η¹-NCH₂CH₂CH ₂CH₂)Os₃(CO)₁₀ (9) and the related imidoyl cluster (μ-H)(μ-η²-CH₃CH₂C=NCH ₂CH₂CH₃)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 (μ-H)(μ₃-η²-C=NCH₂CH ₂CH₂)Os₃(CO)₉ (2) and (μ-H)(μ₃-η²-CH₃CH ₂C=NCH₂CH₂CH₃)Os ₃(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 (μ-H)(μ-η²-C=NCH₂CH₂CH ₂)Os₃(CO)₉(CNR) (R = CH₃, 12; R = C(CH₃)₃, 13) and (μ-H)(μ-η²-CH₃CH₂C=NCH ₂CH₂CH₃)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 (μ-H)(μ₃-η²-C=NCH₂CH ₂CH)₂Os₃(CO)₈(CNR) (R = CH₃, 16; R = C(CH₃)₃, 17) and (μ-H)(μ₃-η²-CH₃CH ₂C=NCH₂CH₂CH₃)Os ₃(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) A?, b = 14.801(2) A?, c = 8.157(2) A?, β = 106.06(1)°, V = 891(1) A?³, 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) A?, b = 15.758(5) A?, c = 7.406(2) A?, α = 81.10(2)°, β = 76.47(2)°, γ = 74.88(2)°, V = 992(1) A?³, 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) A?, b = 16.067(2) A?, c = 14.436(3) A?, β = 93.06(1)°, V = 2081(1) A?³, 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) A?, b = 19.372(5) A?, c = 15.176(3) A?, β = 116.38(2)°, V = 2427(2) A?³, 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) A?, b = 15.660(6) A?, c = 8.437(2) A?, α = 80.69(4)°, β = 67.12(4)°, γ = 74.09(4)°, V = 1002(1) A?³, and Z = 2. Least-squares refinement of 3738 reflections gave a final agreement factor of R = 0.058 (R_w = 0.061).