Reactivity of the unsaturated anion decacarbonyltetra-µ-hydrido-tri-rhenate(1–) toward phenols. Crystal and molecular structures of the tetraethylammonium salts of the triangular cluster anion [Re3(µ-H)3(µ-OC6F5)(CO)10]– and of the binuclear anion [Re2(µ-OC6H5)3(CO)6]–

Abstract

The reactions of [Re₃(µ-H)₄(CO)₁₀]^– with phenols have been investigated under different conditions. The acidity of phenols is sufficient to abstract one hydride of the Re(µ-H)₂ Re system leading to compounds [Re₃(µ-H)₃(µ-OC₆R₅)(CO)₁₀]^–(R = H or F) or, under a CO atmosphere, to neutral [Re₃(µ-H)₃(CO)₁₂]. The NEt₄⁺ salt of the pentafluorophenoxide derivative has been investigated by X-ray analysis. The crystals are monoclinic, space group P2₁/c, with a= 9.304(1), b= 19.357(3), c= 18.063(3)Å, β= 94.72(1)°, and Z= 4. The structure was solved and refined on the basis of 3 897 significant counter data, to a final R 0.028. The anion contains an isosceles triangle of Re atoms, with two longer hydride-bridged edges [3.215(1) and 3.243(1)Å] and one shorter edge [2.975(1)Å] doubly bridged by a hydride and the phenoxide ligand [Re–O 2.176(5)Å]. Reaction of [Re₃(µ-H)₄(CO)₁₀]^– with an excess of phenol at high temperature leads to cluster degradation, with formation of the binuclear anion [Re₂(µ-OC₆H₅)₃(CO)₆]^–. The NEt₄⁺ salt of the latter has been studied by single-crystal X-ray analysis: orthorhombic, space group Pc2₁n(non-standard setting of Pna2₁), with a= 9.568(1), b= 18.865(3), c= 18.948(3)Å, and Z= 4. The structure solution and refinements were based on 2 168 significant counter data, the final R value being 0.031. The anion contains two Re(CO)₃ units, joined through three phenoxide bridges. The mean Re–O bond length is 2.14 Å, and the non-bonding Re ⋯ Re contact is 3.154(1)Å. Pyrolysis in n-heptane of [Re₃(µ-H)₃(µ-OC₆H₅)(CO)₁₀]^– gives selectively [Re₃(µ-H)₃(µ₃-OC₆H₅)(CO)₉]^–, in a reaction that is readily reversed under CO at room temperature.