Bridged fac-tricarbonylrhenium(I)-biscarbene complexes: Synthesis, characterization, and molecular dynamics

Six new biscarbene complexes of the type fac-[(CO)₃Re ^IBr(L)], where L represents a chelating bis(N-heterocyclic carbene) ligand consisting of two alkylene-bridged (R′), N-substituted (R) imidazoline moieties (1,1′-diR-3,3′-R′-diimidazoline-2, 2′-diylidene), were synthesized. Spectroscopic methods and X-ray crystallography were employed to characterize the complexes in solution and the solid state. The observed dynamic behavior of the complexes in solution was examined in more detail by temperature-dependent ¹H NMR experiments and further analyzed by DFT calculations.