title: N-heterocyclic carbenes bearing two, one and no nitrogen atoms at the ylidene carbon: insight from theoretical calculations.
abstract: Electronic structure, thermodynamic stability and ligand properties in LRh(CO)2Cl complexes of a series of N-heterocyclic carbenes (NHCs) were studied at the DFT level. The systems under study are: imidazolin-2-ylidene (1), imidazolidin-2-ylidene (2), cyclic(alkyl)(amino)carbene (CAAC, 3), pyrazolin-3-ylidene (4), pyridin-2-ylidene (5), and pyridin-4-ylidene (6). The main structural feature influencing the properties of these species is the number of nitrogen atoms at the ylidene carbon. A decrease of the number of nitrogen atoms on the one hand leads to an increase in donor ability and ligand-to-metal bond strength, but lowers the stability of the NHC on the other hand. The number of nitrogen atoms can be taken as a key parameter for the classification of carbenes into 2N-NHC, 1N-NHC and r-NHC (r = remote).
authors.affiliation: Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow, 119991, Russian Federation.
authors.forename: Aleksandr A
authors.initials: AA
authors.lastname: Tukov
authors.forename: Adrien T
authors.initials: AT
authors.lastname: Normand
authors.forename: Mikhail S
authors.initials: MS
authors.lastname: Nechaev
mesh_terms: D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008024:Ligands; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D006571:Heterocyclic Compounds; D008024:Ligands; D009942:Organometallic Compounds; C030011:carbene; D002244:Carbon; D012238:Rhodium; D009584:Nitrogen; D008697:Methane