Formation of “A-frame” dirhenium(I) hexacarbonyl complexes by trans-1,2-bis(diphenylphosphino)ethylene and bis(bidentate) ligands

Abstract

A series of A-frame dirhenium(I) hexacarbonyl complexes bridged by trans-1,2-bis(diphenylphosphino)-ethylene (dppene) and bis(bidentate) ligands (L) were synthesized: [Re2(μ-dppene)(CO)6(μ,η2:η2-L)] (L = 1,2-dithioooxalate, 1; tetrathiooxalate, 2; dithiooxamidate, 3 and oxamidate, 4). X-ray crystallographic analysis of 1–3 confirmed that the dppene ligand adopts a syn bridging conformation with nearly eclipsed P–Re bonds in these complexes. The angle between the phosphorus lone pairs of the diphosphine is adjusted to suit different Re⋯Re distances (5.6–6.4 Å) mainly by twisting the ethylene CC bond and enlarging the P–CC angles of the phosphine backbone. Complex 2 forms dimers in the solid state via intermolecular S⋯S interactions (3.39 Å). Proton and 31P NMR data indicate that these dimers persist in chloroform solution but not in DMSO. Natural bond orbital analysis revealed the S⋯S interactions to be between the orbital occupied by the lone pair electrons in each sulphur atom as a donor, and virtual orbitals consisting of S–C σ*, S–Re σ*, and S–C π* states on the acceptor sulphur atom. The binding energy of the dimer was explicitly computed to be 8.14 kcal/mol.