The dizinc bond as a ligand: A computational study of elongated dizinc bonds

Abstract

Following the synthesis of [Zn(η-CMe)] (in short [ZnCp ]) many complexes of the directly bonded Zn-Zn unit were prepared and characterized, leading to the recognition of an isolobal analogy between the Zn-Zn bond and the molecule of dihydrogen. Prompted by these results, we have investigated η-Zn-coordination of [ZnCp] and [ZnPh] (Cp = CH, Ph = CH) to several selected transition metal fragments and report herein the results of a QTAIM study of complexes [(ZnR)Fe(CO)], [(η-ZnR)M(CO)] and [(η-ZnR)Pd(PR′)] (for R = Cp, Ph; M = Cr, Mo, W; and R′ = F, H, Me). A decrease of ρ, ∇ρ and delocalization indexes δ(Zn,Zn), relative to corresponding values in the parent molecules of [ZnCp] and [ZnPh], accompanied dizinc coordination. In most cases the computed δ(Zn,Zn) parameters were indicative of significant electron density sharing between the two Zn atoms. Nevertheless, the interaction with [Fe(CO)] resulted in oxidative cleavage of the coordinated Zn-Zn bond, due to high π backdonation to the σ∗ Zn MO as deduced from the δ(M,O) index. The Zn-Zn bond critical points identified in our study are discussed. The computed Zn-Zn contacts concentrate in the range 2.44–2.58 Å, and we propose that this interval corresponds to elongated dizinc bonds.