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

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.