Phosphine Addition and Substitution Reactions on Unusually Reactive Triosmium Clusters: (μ-H)(μ₃-η²-C=NCH₂CH₂CH₂)Os₃(CO)₉ and (μ-H)(μ₃-η²-CH₃CH₂C=NCH₂CH₂CH₃)Os₃(CO)₉

The reactions of (μ-H)(μ₃-η²-C=NCH₂CH₂CH₂)Os₃(CO)₉ (1), (μ-H)(μ₃-η²-CH₃CH₂C=NCH₂CH₂CH₃)-Os₃(CO)₉ (2), (μ-H)(μ-η²-C=NCH₂CH₂CH₂)Os₃(CO)₁₀ (3), and (μ-H)(μ-η²-CH₃CH₂C=NCH₂CH₂CH₃)-Os₃(CO)₁₀ (4) with trialkylphosphines at 25–100 °C have been studied. At room temperature 1 gives a phosphine addition product (μ-H)(μ-η²-C=NCH₂CH₂CH₂)Os₃(CO)₉P(C₆H_s)₃ (5) where the phosphine has added to the metal atom formerly π-bound to the C=N bond of the μ₃-imidoyl ligand; 5 exists as two isomers in solution. Compound 5 rearranges to the isomeric 6a and 6b at 100 °C in which the phosphine is at one of the two metal atoms bridged by the hydride and the imidoyl ligand. At 100 °C 3 substitutes phosphine for carbonyl to also give 6a and 6b, which on further thermolysis at 125 °C decarbonylate to give (μ-H)(μ₃-η²-C=NCH₂CH₂CH₂)Os₃(CO)₈P(C₆H₆)₃ (7). In contrast, reaction of 2 with triphenylphosphine at room temperature gives (μ-H)(μ-η²-CH₃CH₂C=NCH₂CH₂CH₃)Os₃(CO)₉P(C₆H₆)₃) (8), which exists as a mixture of five of six possible positional isomers with respect to location of the phosphine, hydride, and imidoyl ligands in solution. The reaction of 4 with triphenylphosphine at 100 °C gives this same mixture of isomers. Decarbonylation of 8 proceeds at 125 °C to give (μ-H)(μ₃-η²-CH₃CH₂C=NCH₂CH₂CH₃)Os₃-(CO)₈P(C₆H₅)₃) (9) and the dihydrido orthometalation product (μ-H)₂(μ-η²-CH₃CH₂C=HCH₂CH₂CH₃)-Os₃(CO)₈(μ-η²-(C₆H₅)₂P(o-C₆H₄)) (10). Reaction of 2 with trimethylphosphine or trimethyl phosphite gives the addition products (μ-H)(μ-η²-CH₃CH₂C=NCH₂CH₂CH₃)Os₃(CO)₉PR₃ (R = CH₃, 11; R = OCH₃, 12), which are structurally analogous to 5 in solution. The origin of the structural differences between the addition products obtained from the reaction of 1 and 2 with P(C₆H₅)₃ and from 2 with the different phosphorous ligands is discussed in terms of steric interactions between the imidoyl ligand and the phosphorous ligand. All compounds reported were characterized by ¹H NMR, infrared spectroscopy, and elemental analysis. In addition, solid-state structures for 5, 6a, 8a, and 9 were determined. Compound 5 crystallizes in the triclinic space group P1 (No. 2) with unit cell parameters a = 10.762 (2) Å, b = 17.442 (2) Å, c = 8.595 (2) Å, α = 97.38 (1)°, ß = 94.04 (1)°, γ = 97.44 (1)°, V = 1580 (1) ų, and Z = 2. Subsequent least-squares refinement of 5058 reflections gave a final agreement factor of R = 0.032 (R_w = 0.041). Compound 6a crystallizes in the monoclinic space group P2₁/c (No. 14) with unit cell parameters a = 9.307 (2) Å, b = 15.601 (3) Å, c = 21.773 (4) Å, β = 97.59 (2)°, V = 3134 (2) ų, and Z = 4. Least-squares refinement of 4316 reflections gave a final agreement factor of R = 0.029 (R_w = 0.036). Compound 8a crystallizes in the triclinic space group P1 (No. 2) with unit cell parameters a = 12.684 (3) Å, b = 16.254 (3) Å, c = 9.561 (2) Å, α = 99.53 (1)°, β = 96.69 (2)°, γ = 112.57 (2) Å, V = 1760 (1) ų, and Z = 2. Least-squares refinement of 4236 reflections gave a final agreement factor of R = 0.031 (R_w = 0.038). Compound 9 crystallizes in the orthorhombic space group P2₁2₁2₁ (No. 19) with unit cell parameters a = 9.626 (1) Å, b = 15.342 (2) Å, c = 22.849 (3) Å, V = 3374 (1) ų, and Z = 4. Least-squares refinement of 2841 reflections gave a final agreement factor of R = 0.031 (R_w = 0.027).