Deciphering the influence of alkylene bridged and chelating mode on Pd-C and Pd-X (X=Cl, Br and I) bonding interaction within bis-(NHC)-palladium complexes Mouzong D’Ambassa Gaël 1* , Moto Ongagna Jean 1 , Adjieufack Abel Idrice 2 , Djendo Mazia Suzane Leonie 1 , Bikele Mama Désiré 2* 1 Department of Chemistry, Faculty of Science, University of Douala, Cameroon, 2 Physical and Theoretical Chemistry Laboratory, University of Yaoundé I, Cameroon, *corresponding author The research of catalytic systems able to activate and functionalize the C-H bonds at low cost have stimulated a particular interest from both a scientific and economic viewpoint. The conversion of methane into methanol catalyzed by Pd-bis(NHC) complexes is one of the advances in organometallic catalysis [1-3] . This reaction highlighted the reactive power of theses complexes. Although a great deal of work has been carried out on these complexes, some factors governing their reactivity have not yet been elucidated. This research work is devoted to examine the influence of alkylene bridged and chelating mode on the topological, electronic and bonding properties of a series of bis-(NHC)-palladium complexes. The optimized geometries of these complexes were performed using generic basis set (Lanl2DZ for halogen and palladium atoms and 6-31G(d)) in gas phase and DMSO. DFT approaches combine to QTAIM, NBO, CDA, EDA, and DFT-conceptual analysis were used to analyse Pd–C and Pd–X bonding interaction within bis-(NHC)-palladium complexes. Our data indicated that higher activation of Pd-C bonds has been found out for phenyl and nitro complexes. Most stable Pd…C interactions have been detected for abnormal mode with methylene bridge. Two preferential configurations have adopted by the metallacycles: a boat (methylene bridged) and chair (ethylene bridged) like configurations. In the whole, higher activation of Pd-C bonds has been found out for phenyl and nitro complexes. Most stable Pd…C interactions have been detected for abnormal mode with methylene bridge. The energy decomposition analysis (EDA) indicates that the better electrostatic character is obtained by hydrogen and phenyl complexes in both chelation modes. In both chelation modes, the hybridization around the metal cation for the Pd-C bond has been found to be almost sp 2 d for methylene-bridged palladium complexes (in both media). But, this hybridization becomes sp 3 contrary for ethylene bridge complexes. By the means of the energy decomposition analysis, Pd…C interactions have shown to be stronger for ethylene bridged abnormal complexes (in gas phase). By contrast, their Pd…X interactions are weaker. The donation/back-donation ratio (d/b) values of [bis(NHC)]… [PdX 2 ] interactions demonstrated that these are Fischer carbene. The ethylene bridged abnormal complexes have therefore been elected as palladium complexes with better catalytic activities. References 1. Munz D, Meyer D, Strassner T (2013). Organometallics 32:3469–3480; 2. Ingrosso G, Midollini N (2003). J Mol Catal A-Chem 204-205: 425–431. 3. T. Strassner, M. Muehlhofer, A. Zeller, E. Herdtweck, W. A. Herrmann; J. Org. Chem. 689 (2004) 1418–1424.
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