Reaction of transition metal carbonyls with soluble polyselenides: synthesis and structure of [(C6H5)4P]2[Re2(Se4)2(CO)6]

The reaction of rhenium decacarbonyl with polyselenide anions in DMF solution has been investigated. Two equivalents of K2Se3 react with Re2(CO)10 in DMF solution at 100 °C, in the presence of excess [(C6H5)4P]Br, to produce [(C6H5)4P]2[Re2(Se4)2(CO)6]. This can be isolated as an analytically pure red crystalline solid in 25% yield. The compound has been characterized crystallographically; space group P21/n, Z = 2, a = 12.052(3) Å, b = 14.619(5) Å, c = 16.159(4) Å, β = 98.31(2)°, V = 2817(1) Å3, R = 0.0583, Rw = 0.0653. In addition to two well-separated tetraphenylphosphonium counterions, the compound consists of the [Re2(Se4)2(CO)6]2− dianion. This molecule is a rhenium dimer with each metal coordinated to three CO ligands and a Se42− chain. One end of the chelating tetraselenide chain is bridging both rhenium atoms, completing an octahedral coordination environment around each metal atom. The bridging distances are slightly asymmetric, leading to the suggestion that the bridging selenide has some dative character. Keywords: selenides, rhenium carbonyls, Zintl ions, p-block clusters.