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

• Novel Rh(I) N-2-nitrobenzenesulfonyl substituted NHC complexes were synthesized.
• Electronic properties were evaluated by spectroscopic and crystallographic analyses.
• They exhibited stronger π-accepting and poorer σ-donating abilities compared to IMes.
• One of the SO bonds in sulfonyl group conjugated with the NHC frameworks.

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 SO bonds in the sulfonyl group could be conjugated with the NHC frameworks, while the remaining SO bond conjugated with the 2-nitrophenyl groups of the N-nosyl substituent.

Two novel Rh(I) complexes bearing N-2-nitrobenzenesulfonyl substituted N-heterocyclic carbenes (NHCs) were synthesized. The NHC-metal complexes were characterized by IR, NMR, and single-crystal X-ray diffraction analyses.Figure optionsDownload as PowerPoint slide