Filling the void: controlled donor–acceptor interaction facilitates the formation of an M–M single bond in the zero oxidation state of M (M = Zn, Cd, Hg). Issue 4 (18th December 2019)

• Record Type: Journal Article
• Authors: Saha, Ranajit; Pan, Sudip; Chattaraj, Pratim K.; Merino, Gabriel
• Is Part Of: Dalton transactions. Volume 49:Issue 4(2019)
• Page Start: 1056
• Page End: 1064
• Publication Date: 2019-12-18
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt04213j
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : We present viable M2 (NHB Me )2 (M = Zn, Cd, Hg; NHB Me = (HCN Me )2 B) complexes where the controlled donor-acceptor interaction leads to M 0 –M 0 single bond. Abstract : The intriguing question of whether it is possible to form a genuine M 0 –M 0 single bond for the M2 species (M = Zn, Cd, Hg) is addressed here. So far, all the bonds reported in the literature are exclusively M I –M I . Herein, we present viable M2 (NHB Me )2 (M = Zn, Cd, Hg; NHB Me = (HCN Me )2 B) complexes in which the controlled donor–acceptor interaction leads to an M 0 –M 0 single bond. In these complexes, M2 in the 1 ∑g ground state with the ( n σg + ) 2 ( n σu + ) 2 ( n = 7, 10 and 14 for M = Zn, Cd and Hg, respectively) valence electron configuration forms donor–acceptor bonding with singlet 2NHB Me ligands where a combined effect of dominant (+, −) σ-backdonation from the antibonding ( n σu + ) 2 orbital of M2 to the 2NHB Me ligands and a somewhat weaker (+, +) σ-donation from the 2NHB Me ligands to the bonding ( n + 1)σg + orbital leads to the unorthodox bonding situation of forming an M–M single bond in the zero oxidation state by eventually nullifying one effect by another. This is an unprecedented situation in the sense that the NHB Me ligand acts as a strong σ-acceptor and a weaker σ-donor. A comparison with the experimentally reported M2 (Ph Dipp )2 complexes reveals the uniqueness of the NHB Me ligand in exhibiting such a bonding scenario. The M2 (NHB Me )2 complex is thermochemically viable with respect to possible dissociation channels at room temperature, except for metal extrusion processes, M2 (NHB Me )2 → M + M(NHB Me )2 and M2 (NHB Me )2 → M2 + (NHB Me )2 . Although the latter two processes are exergonic, they are kinetically protected by a high free energy barrier of 26.5–39.5 kcal mol −1 . The experimental characterization of M2 (Ph Dipp )2 despite similar exergonic channels reveals such kinetic stability to be enough for the viability of the M2 (NHB Me )2 complexes. Furthermore, the ligand exchange reaction considering M2 (Ph Me )2 as the starting material also turned out to be feasible. Therefore, the M2 (NHB Me )2 complexes are the first cases that feature a neutral M2 moiety with a single M 0 –M 0 covalent bond, where M is a Group 12 metal.