Relative rates of ligand substitution on nonacarbonyltris(μ-hydrido)(μ₃-methylidyne)triruthenium clusters. The crystal structure of (μ-H)₃Ru₃(μ₃-CPh)(CO)₇(AsPh₃)₂

Substitution on (μ-H)₃Ru₃(μ₃-CX)(CO)₉ (X=OMe, Me, Cl, Ph) by triphenylarsine proceeds sequentially to (μ-H)₃Ru₃(μ₃-CX)(CO)_9-n(AsPh₃)_n (n = 1, 2, 3). A single-crystal X-ray crystallographic study of (μ-H)₃Ru₃(μ₃-CPh)(CO)₇(AsPh₃)₂ has been performed. This complex crystallizes in the centrosymmetric monoclinic space group C2/c [No. 15] with a 36.746(19), b 12.743(6), c 22.802(11) Å, β 108.60(4)°, V 10119 ų and Z = 8. Data for 2θ 4.0-35.0° (Mo-K_α were collected on a Syntex P2₁ automated four-circle diffractometer and the structure was refined to R_f 7.2% for all 3208 reflections (R_f 5.4% for those 2523 reflections with |F_o| > 6σ(|F_o|)). The crystal structure establishes axial coordination for the triphenylarsine ligands on different metal atoms. The rate of CO dissociation from (μ-H)₃Ru₃(μ₃-CX)(CO)₉ is found to depend upon X in the order: X = OMe (36) ⇌ > Me (3.2) > Cl (2.3) > Ph (1) at 298 K. The labilizing effect of the methoxy substituent is attributed to stabilization of the transition state by π-donation to the Ru₃C core.