Synthesis and characterization of a new family of unsaturated triangular rhenium cluster anions of formula [Re3(µ-H)4(CO)9L]–(L = neutral two-electron donor ligand). X-Ray crystal and molecular structures of the tetraethylammonium salts of the anions with L = triphenylphosphine and pyridine

Abstract

The unsaturated triangular cluster anion [Re₃(µ-H)₄(CO)₁₀]^– can undergo selective substitution of one of the axial carbonyl ligands of the Re(CO)₄ vertex by neutral two-electron donor ligands L, giving unsaturated [Re₃(µ-H)₄(CO)₉L]^– derivatives. The anions with L = NCMe, PPh₃, and pyridine (py) have been synthesized either by thermal activation or, more effectively, by carbonyl elimination using Me₃NO·2H₂O. X-Ray single-crystal analyses of the PPh₃ and py derivatives, as [NEt₄]⁺ salts, have been performed. Both species crystallize in the monoclinic system, space group P2₁/n, with a= 11.448(2), b= 25.311(6), c= 13.596(3)Å, β= 94.00(2)°, and Z= 4 for the PPh₃ derivative, and a= 11.087(1), b= 15.951(2), c= 17.598(4)Å, β= 104.84(2)°, and Z= 4 for the py derivative. The geometries of the two anions are similar to that of the parent anion, with the PPh₃ or the py ligand co-ordinated in an axial position with respect to the Re₃ triangle, which presents a short Re–Re bond (close to 2.80 Å) doubly bridged by hydrides. The McCN derivative is the most reactive member of this new family, containing two active centres: the labile nitrile and the unsaturated moiety. Its reaction with methanol, leading to the anion [Re₃(µ-H)₃(CO)₉(µ₃-OMe)]^–, exemplifies the possibility of new reaction paths involving both the active sites of this molecule.