Synthesis and characterization of half-sandwich N-heterocyclic carbene complexes of cobalt and rhodium
Abstract
A series of novel half-sandwich M(I) and M(III) complexes (M = Co, Rh) bearing the N-heterocyclic carbene ligand 1,3-dimesitylimidazol-2-ylidene (IMes) have been prepared and characterized. Thus, (η5-C5R5)M(IMes)(C2H4) (M = Co, Rh; R = H, Me) were obtained from the corresponding bis(ethene) complexes (η5-C5R5)M(C2H4)2, except for CpRh(IMes)(C2H4) which was prepared via the novel 16-electron Rh(I) compound Rh(IMes)(C2H4)2Cl. The carbonyl compounds (η5-C5R5)Co(IMes)(CO) (R = H, Me) were synthesized by thermal CO substitution of (η5-C5R5)Co(CO)2. A diamagnetic, apparently 16-electron Co(III) compound [CpCo(IMes)I]+[I3−] was obtained from CpCo(IMes)(CO) and I2. Finally, Co(III) and Rh(III) complexes CpCo(IMes)Me2 and Cp*Rh(IMes)Me2 were prepared by methylation of [CpCo(IMes)I]+[I3−], and ligand exchange at Cp*Rh(Me2SO)Me2, respectively. The molecular structures of CpCo(IMes)(CO), CpRh(IMes)(C2H4), Cp*Rh(IMes)(C2H4), and Cp*Rh(IMes)Me2 were determined by single crystal X-ray diffraction. Steric and electronic factors imposed by the strongly donating and sterically demanding IMes ligand are discussed on the basis of X-ray crystallographic, NMR, and IR spectroscopic analyses. Very poor correlations are found between values for 1JRh–C(carbene) and dRh–C(carbene) data for Rh(I) N,N-heterocyclic carbene complexes including literature data and this work.