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An Unsaturated Four-Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum-Molybdenum Quadruple Bond.

Research paper by Natalia N Curado, Mario M Carrasco, Jesus J Campos, Celia C Maya, Amor A Rodríguez, Eliseo E Ruiz, Santiago S Alvarez, Ernesto E Carmona

Indexed on: 05 Nov '16Published on: 05 Nov '16Published in: Chemistry - A European Journal



Abstract

We describe the synthesis, molecular, and electronic structure of the complex [Mo2Me2{µ-HC(NDipp)2}2] (2), that contains a dimetallic core with a MoMo quadruple bond and features uncommon four-coordinate geometry and fourteen-electron count at each Mo atom (Dipp = 2,6-iPr2C6H3). The coordination polyhedron approaches a square pyramid with one of the Mo atoms nearly co-planar with the basal square plane in which the coordination position trans with respect to the Mo-Me bond is empty. The other three sites contain two trans N atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms a Mo-Mo bond of length 2.080(1) Å, consistent with a quadruple bond. Compound 2 reacts with THF and PMe3 to yield the mono-adducts [Mo2Me(μ-Me){µ-HC(NDipp)2}2(L)] (3·THF and 3·PMe3, respectively) with one terminal and one bridging methyl groups. In contrast, 4-dimethylaminopyridine (dmap) forms the bis-adduct [Mo2Me2{µ-HC(NDipp)2}2(dmap)2] (4), with terminally coordinated methyl groups. Hydrogenolysis of complex 2 leads to the bis(hydride) [Mo2H2{µ-HC(NDipp)2}2(thf)2] (5·THF) with elimination of CH4. Computational, kinetic and mechanistic studies, that include the use of D2, and of complex 2 labelled with 13C (99%) at the Mo-CH3 sites, support the intermediacy of a methyl-hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl group to the MoMo core is also reported.