Synthesis and characterization of propylene and butylene bridged fac-tricarbonylrhenium(i) biscarbene complexes

Nine new complexes of the type fac-[(CO) ₃ReBr(L)], where L represents a chelating bis-NHC ligand consisting of two alkylene (propylene and butylene) bridged (R′) N-substituted (R) imidazoline moieties (1,1′-di-R-3,3′-R′-diimidazolin-2,2′-diylidene), were synthesized. Spectroscopic methods, elemental analysis, mass spectrometry and X-ray crystallography were employed to characterize the complexes both in solution and in solid state. The complexes were compared to the analogous complexes with smaller bridge lengths in order to reveal differences and similarities. Depending on the bridge length and the ligand size in some cases dinuclear complexes were obtained as small scale side products.