Rhodium(I) and Silver(I) Complexes of 4, 5‐Dicyano‐1, 3‐dimesityl‐ and 4, 5‐Dicyano‐1, 3‐dineopentylimidazol‐2‐ylidene

Abstract

AbstractThe new N‐heterocyclic carbene (NHC) precursors 4, ‐dicyano‐1, ‐dimesityl‐ (9) and 4, 5‐dicyano‐1, 3‐dineopentyl‐2‐(pentafluorophenyl)imidazoline (14) were synthesized. The structure of 9 could be determined by X‐ray crystallography. With the 2‐pentafluorophenyl‐substituted imidazolines 9 and 14, the [AgCl(NHC)], [RhCl(COD)(NHC)], and [RhCl(CO)2(NHC)] complexes [NHC = 4, 5‐dicyano‐1, 3‐dimesitylimidazol‐2‐ylidene (3) and 4, 5‐dicyano‐1, 3‐dineopentylimidazol‐2‐ylidene (4)] were obtained. Crystal structures of [AgCl(3)] (15), [RhCl(COD)(3)] (17), [RhCl(COD)(4)] (18), and [RhCl(CO)2(3)] (19) were solved and with the crystal data of 19, the percent buried volume ( %Vbur) of 31.8(±0.1) % was determined for NHC 3. Infrared spectra of the imidazolines 9 and 14 and of the complexes 15–20 were recorded and the CO stretching frequencies of complexes 19 and 20 were used to determine the Tolman electronic parameters of the newly obtained NHCs 3 (TEP: 2060 cm–1) and 4 (TEP: 2061 cm–1), thus proving that 1, 3‐substitution of maleonitrile‐NHCs does not have a significant effect for the high π‐acceptor strength of these carbenes.