title: Carbones as Ligands in Novel Main-Group Compounds E[C(NHC)2]2(E=Be, B+, C2+, N3+, Mg, Al+, Si2+, P3+): A Theoretical Study.
abstract: Quantum chemical calculations of the main-group compounds E[C(NHCMe)2]2(E=Be, B+, C2+, N3+, Mg, Al+, Si2+, P3+) have been carried out using density functional theory at the BP86/def2-TZVPP and BP86-D3(BJ)/def2-TZVPP levels of theory. The geometry optimization at BP86/def2-TZVPP gives equilibrium structures with two-coordinated species E and bending angles C-E-C between 152.5° (E=Be) and 110.5° (E=Al). Inclusion of dispersion forces at BP86-D3(BJ)/def2-TZVPP yields a three-coordinated beryllium compound Be[C(NHCMe)2]2as the only energy minimum form. Three-coordinated isomers are found besides the two-coordinated energy minima for the boron and carbon cations B[C(NHCMe)2]2+and C[C(NHCMe)2]22+. The three-coordinated form of the boron compound is energetically lower lying than the two-coordinated form, while the opposite trend is calculated for the carbon species. The theoretically predicted bond dissociation energies suggest that all compounds are viable species for experimental studies. The X-ray structure of the benzoannelated homologue of P[C(NHCMe)2]23+that was recently reported by Dordevic et al. agrees quite well with the calculated geometry of the molecule. A detailed bonding analysis using charge and energy decomposition methods shows that the two-coordinated neutral compounds Be[C(NHCMe)2]2and Mg[C(NHCMe)2]2possess strongly positively charged atoms Be and Mg. The carbodicarbene groups C(NHCMe)2serve as acceptor ligands in the compounds and may be sketched with dative bonds (NHCMe)2C←E→C(NHCMe)2(E=Be, Mg). Dative bonds in which the carbones C(NHCMe)2are donor ligands are suggested for the cations (NHCMe)2C→E←C(NHCMe)2(E=B+, Al+). The dications and trications possess electron-sharing bonds in which the bonding situation is best described with the formula [(NHCMe)2C]+-E-[C(NHCMe)2]+(E=C, Si, N+, P+).
authors.affiliation: Fachbereich Chemie der, Philipps-Universität, Hans-Meerwein-Strasse 4, 35032, Marburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Hermann
authors.affiliation: Fachbereich Chemie der, Philipps-Universität, Hans-Meerwein-Strasse 4, 35032, Marburg, Germany.|Donostia International Physics Center (DIPC), P.K. 1072, 20080, Donostia, Euskadi, Spain.
authors.forename: Gernot
authors.initials: G
authors.lastname: Frenking
keywords: bonding analysis; carbodicarbene; carbones; dative bonding; electron-shared bonding; main-group complexes; quantum chemical calculations