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

Abstract

Following the synthesis of [Zn 2 (η 2 -C 5 Me 5 ) 2 ] (in short [Zn 2 Cp ∗ 2 ]) 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 2 -Zn 2 -coordination of [Zn 2 Cp 2 ] and [Zn 2 Ph 2 ] (Cp = C 5 H 5 , Ph = C 6 H 5 ) to several selected transition metal fragments and report herein the results of a QTAIM study of complexes [(ZnR) 2 Fe(CO) 4 ], [(η 2 -Zn 2 R 2 )M(CO) 5 ] and [(η 2 -Zn 2 R 2 )Pd(PR′ 3 ) 2 ] (for R = Cp, Ph; M = Cr, Mo, W; and R′ = F, H, Me). A decrease of ρ BCP , ∇ 2 ρ BCP and delocalization indexes δ(Zn,Zn), relative to corresponding values in the parent molecules of [Zn 2 Cp 2 ] and [Zn 2 Ph 2 ], 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) 4 ] resulted in oxidative cleavage of the coordinated Zn-Zn bond, due to high π backdonation to the σ∗ Zn 2 MO as deduced from the δ(M,O CO ) 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.