Silver and Rhodium Complexes of Stable, Monomeric Imidazolidin‐2‐ylidenes: Synthesis, Reactivity and Decomposition Pathway

Silver( I ) complexes of the freely stable carbenes 1,3‐bis(2,4,6‐trimethylphenyl)imidazolidin‐2‐ylidene ( 3 ) and 1,3‐bis(2,6‐diisopropylphenyl)imidazolidin‐2‐ylidene ( 4 ) were prepared from the imidazolinium chlorides 1 and 2 , respectively, and silver oxide. These two air‐stable and light‐sensitive carbene complexes [AgCl( 3 )] ( 5 ) and [AgCl( 4 )] ( 6 ) were characterized by NMR spectroscopy, and the molecular structure of 6 was confirmed by X‐ray diffraction. The imidazolidin‐2‐thiones 7 and 8 were obtained by reaction of the silver carbene complexes 5 and 6 , respectively, with elemental sulfur at ambient temperature. Spectroscopic evidence for the formation of the rhodium( I ) complex [(cod)Rh(Cl)( 10 )] ( 11 ) with the sterically demanding 1,3‐di‐ tert ‐butyl‐imidazolidin‐2‐ylidene ligand 10 obtained in situ from 1,3‐di‐ tert ‐butyl‐imidazolinium tetrafluoroborate 9 is presented. Because of the steric demand of the carbene ligand 10 , complex 11 decomposed rapidly in solutions of chlorinated or polar solvents.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)