Which component of the quadruple bond breaks first upon protonation of the octachlorodimetallate anions [MM′Cl8]4−, M,M′ = Mo, W? A theoretical study of reactivity, mechanism and bonding

The protonation of the quadruple metal–metal bond in homo- and heteronuclear octachlorodimetallate complex anions, [Mo2Cl8]4−, [MoWCl8]4− and [W2Cl8]4−, are studied using Density Functional Theory methods. The activation energies and exothermicities for the reaction [MM′Cl8]4− + H+ → [MM′(μ-H)(μ-Cl)2Cl6]3− (MM′ = Mo, W) are calculated and the relative reactivities of the three different cores, Mo24+, W24+ and MoW4+, are discussed. The reaction mechanism is investigated. It is found that a π component of the quadruple metal–metal bond is broken to form the bridged hydride three center bonds in the [Mo2(μ-H)Cl8]3−, [MoW(μ-H)Cl8]3− and [W2(μ-H)Cl8]3− anions.

Graphical abstractThe protonation of the quadruple metal–metal bond in homo- and heteronuclear octachlorodimetallate complex anions, [Mo2Cl8]4−, [MoWCl8]4− and [W2Cl8]4−, are studied using Density Functional Theory methods. The activation energies and exothermicities for the reaction [MM′Cl8]4− + H+ → [MM′(μ-H)(μ-Cl)2Cl6]3− (MM′ = Mo, W) are calculated and the relative reactivities of the three different cores, Mo24+, W24+ and MoW4+, are discussed. The reaction mechanism is investigated. It is found that a π component of the quadruple metal–metal bond is broken to form the bridged hydride three center bonds in the [Mo2(μ-H)Cl8]3−, [MoW(μ-H)Cl8]3− and [W2(μ-H)Cl8]3− anions.Figure optionsDownload full-size imageDownload as PowerPoint slide