title: Enhanced π-Back-Donation as a Way to Higher Coordination Numbers in d10[M(NHC)n] Complexes: A DFT Study.
abstract: We aim to understand the electronic factors determining the stability and coordination number of d10transition-metal complexes bearing N-heterocyclic carbene (NHC) ligands, with a particular emphasis on higher coordinated species. In this DFT study on the formation and bonding of Group 9-12 d10[M(NHC)n] (n=1-4) complexes, we found that all metals form very stable [M(NHC)2] complexes, but further coordination depends on the specific interplay of 1) the interaction energy (ΔEint) between the [M(NHC)n-1] (n=2-4) fragment and the incoming NHC ligand, and 2) the strain energy (ΔEstrain) associated with bending of the linear NHC-M-NHC arrangement. The key observation is that ΔEstrain, which is an antagonist for higher coordination numbers, can significantly be lowered by M→NHC π*-back-donation. This leads to favorable thermodynamics for n=3-4 for highly electrophilic metals in our study, and thus presents a general design motif to achieve coordination numbers beyond two. The scope of our findings extends beyond the NHC model systems and has wider implications for the synthesis of d10[MLn] complexes and their catalytic activity.
authors: Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors: Jörn
authors: J
authors: Nitsch
authors: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.
authors: Lando P
authors: http://orcid.org/0000-0003-0052-0121
authors: LP
authors: Wolters
authors: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.
authors: Célia
authors: http://orcid.org/0000-0002-2973-5321
authors: C
authors: Fonseca Guerra
authors: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.|Institute for Molecules and Materials (IMM), Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
authors: F Matthias
authors: http://orcid.org/0000-0003-4655-7747
authors: FM
authors: Bickelhaupt
authors: Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors: Andreas
authors: http://orcid.org/0000-0002-6952-7391
authors: A
authors: Steffen
keywords: N-heterocyclic carbenes; density functional calculations; energy decomposition analysis; metal complexes; pi-back-bonding