An Unsaturated Four‐Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum–Molybdenum Quadruple Bond. Issue 1 (7th December 2016)

• Record Type: Journal Article
• Authors: Curado, Natalia; Carrasco, Mario; Campos, Jesús; Maya, Celia; Rodríguez, Amor; Ruiz, Eliseo; Álvarez, Santiago; Carmona, Ernesto
• Is Part Of: Chemistry. Volume 23:Issue 1(2017)
• Page Start: 194
• Page End: 205
• Publication Date: 2016-12-07
• Subjects: agostic interactions -- alkyl complexes -- dimolybdenum -- kinetics -- theoretical calculations; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201604618
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: We describe the synthesis and the molecular and electronic structures of the complex [Mo2 Me2 {μ‐HC(NDipp)2 }2 ] (2 ; Dipp=2, 6‐ i Pr2 C6 H3 ), which contains a dimetallic core with an Mo–Mo quadruple bond and features uncommon four‐coordinate geometry and has a fourteen‐electron count for each molybdenum atom. The coordination polyhedron approaches a square pyramid, with one of the molybdenum atoms nearly co‐planar with the basal square plane, in which the trans coordination position with respect to the Mo−Me bond is vacant. The other three sites are occupied by two trans nitrogen atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms an Mo–Mo bond of length 2.080(1) Å, consistent with a quadruple bond. Compound2 reacts with tetrahydrofuran (THF) and trimethylphosphine to yield the mono‐adducts [Mo2 Me(μ‐Me){μ‐HC(NDipp)2 }2 (L)] (3⋅THF and3⋅PMe3, respectively) with one terminal and one bridging methyl group. In contrast, 4‐dimethylaminopyridine (dmap) forms the bis‐adduct [Mo2 Me2 {μ‐HC(NDipp)2 }2 (dmap)2 ] (4 ), with terminally coordinated methyl groups. Hydrogenolysis of complex2 leads to the bis(hydride) [Mo2 H2 {μ‐HC(NDipp)2 }2 (thf)2 ] (5⋅THF ) with elimination of CH4 . Computational, kinetic, and mechanistic studies, which included the use of D2 and of complex2 labelled with 13 C (99 %) at the Mo–CH3 sites, supported the intermediacy of a methyl‐hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl groups to the Mo≣Mo core is also reported. Abstract : The fab four : Low‐coordinate unsaturated dimethyl complexes of a quadruply bonded dimolybdenum bis(amidinate) fragment featuring terminal and bridging methyl coordination have been prepared and structurally characterised (see graphic).