Oxalate-bridged dirhenium(I) hexacarbonyl complexes: synthesis, reactions, and crystal structures

The complex [{Re(CO)5}2(μ,η1:η1-C2O4)] 1 undergoes thermal decarbonylation to give [Re2(CO)6(C2O4)]n, which reacts with triphenylphosphine and trans-1,2-bis(diphenylphosphino)ethylene (dppene) to give anti-[Re2(PPh3)2(CO)6(μ,η2:η2-C2O4)] 2 and [Re2(μ-dppene)(CO)6(μ,η2:η2-C2O4)] 4, respectively. Complex 2 is oxidized on prolonged exposure to air (1 week) to form anti-[Re2(OPPh3)2(CO)6(μ,η2:η2-C2O4)] 3. In the presence of excess dppene, the complex [Re2(μ-dppene)2(CO)6(μ,η1:η1-C2O4)] 5 is also formed alongside 4. With the chelating diphosphine 1,3-bis(diphenylphosphino)propane (dppp), the complex [(η2-dppp)Re(CO)3(μ,η1:η1-C2O4)Re(CO)3(η2-dppp)] 6 is formed. The structures of 3 and 4 have been determined by X-ray crystallography. The dppene ligand in complex 4 adopts an unusual “syn” conformation wherein the two phosphorus lone pairs of electrons are eclipsed, thus forming an “A-frame” type of bridge.