Characterization of Rh(I) complexes bearing N-2-nitrobenzenesulfonyl substituted, N-heterocyclic carbenes

Synthesis and structural characterization of novel Rh(I) complexes bearing 1,2,4-triazol-3-ylidene or imidazol-2-ylidene substituted with an N-2-nitrobenzenesulfonyl (N-nosyl) group are described. The complexes were characterized by infrared (IR), NMR, and single-crystal X-ray diffraction analyses. The Tolman electronic parameter (TEP) values of both of the 1,2,4-triazol-3-ylidene (2064 cm−1) and imidazol-2-ylidene (2059 cm−1), as determined from the average carbonyl (CO) stretching frequencies for the corresponding RhCl(NHC)(CO)2 (NHC = N-heterocyclic carbene) complexes, were higher than that of RhCl(IMes)(CO)2 (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (2050 cm−1). As the TEP values of the NHCs increased, the 13C NMR signal of the carbenic carbon in the corresponding RhCl(NHC)(cod) (cod = 1,5-cyclooctadiene) and RhCl(NHC)(CO)2 complexes shifted downfield. Moreover, the crystallographic analysis of the RhCl(NHC)(cod) complexes revealed that one of the Sdouble bond; length as m-dashO bonds in the sulfonyl group could be conjugated with the NHC frameworks, while the remaining Sdouble bond; length as m-dashO bond conjugated with the 2-nitrophenyl groups of the N-nosyl substituent.