Synthesis, Characterization, and Crystal Structure of (μ-H)₂Ru₃(μ₃-≡²-CHC(0)0CH3)(C0)9, a Stabilized Intermediate in the Reductive Elimination of Hydrocarbons from Trimetallic Clusters

Pyrolysis of(m-h)3ru3(/43-CC0₂CH₃)(C0)9 at 70 °C produces(jl4-h)2ru3(ju3-7²-CHC(0)0CH₃)(C0)9 (56% yield), characterized by spectroscopic methods and by X-ray crystallography. The complex (tt-H)₂Ru₃-0u₃-i7²-CHC(O)OCH₃)(CO)₉ crystallizes in the centrosymmetric triclinic space group PI (No. 2) with a = 11.357 (3) A, h =12.427 (3) A, c = 14.886 (4) A, a = 73.989 (21)°, 13 = 69.581 (20)°, y = 88.081 (20)°, V = 1885.4 (9) A³⁴, and Z = 4. Diffraction data (Mo Ka, 26 = 5-50°) were collected with a Syntex P2_: automated four-circle diffractometer, and the structure was refined to R_F= 3.2% for all 6682 data (Rp - 2.3% for those 5586 data with F₀ > 6o-(|F₀|)). There are two crystallographically independent (but chemically equivalent) molecules in the asymmetric unit. Each molecule consists of a triangular array of ruthenium atoms. The a-carbon atom of the jLi₃-77²-CHC(0)0CH₃ ligand bridges ruthenium atoms Ru(l) and Ru(3) with Ru-C = 2.135 (4)-2.154 (4) A, while the carbonyl oxygen of this ester group is coordinated to the third ruthenium atom, Ru(2) (Ru-O = 2.134 (3)-2.145 (3) A). Each ruthenium atom is linked to three terminal carbonyl ligands, while the Ru(l)-Ru(3) and Ru(2)-Ru(3) bonds are bridged by hydride ligands. Variable-temperature '1-1 and¹³C NMR spectra of (ti-H)₂Ru₃(M3V-CHC(0)0CH₃)(C0)₉ indicate that two hydride migration processes occur on the NMR time scale. Conversion of 0i-H)₃Ru₃(M3-CCO₂CH₃)(CO)₉ to (≡-H)₂ru3(m3-t²-CHC(0)0CH₃)(C0)9 involves reductive elimination of a single C-H bond and stabilization of the resulting unsaturated Ru atom by coordination of the acyl; complete elimination of methyl acetate is achieved by treatment of(≡-H)2RU3(≡3-≡7²-CHC(0)0CH₃)(C0)9 with CO.