ja0472533_si_001.cif (85.25 kB)
A Homoleptic Molybdenum(IV) Enolate Complex: Synthesis, Molecular and Electronic Structure, and NCN Group Transfer To Form a Terminal Cyanoimide of Molybdenum(VI)
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posted on 2004-09-15, 00:00 authored by Han Sen Soo, Joshua S. Figueroa, Christopher C. CumminsA monomeric molybdenum(IV) tetrakis enolate complex Mo(OC[Ad]Mes)4, 1, where Ad =
2-adamantylidene and Mes = 2,4,6-Me3C6H2, has been synthesized and characterized structurally by X-ray
diffraction, chemically through NCN group-transfer reactivity, and computationally to investigate the origins
of the observed structure that is intermediate between tetrahedral and square planar. No prior examples
of Mo(OR)4 have been structurally characterized despite having been the subject of both experimental and
theoretical interest. Complex 1 has a singlet ground state and thus a metal-based lone pair of electrons.
The latter has been visualized with the aid of the electron localization function (ELF) and appears as a
two-bladed propeller with D2d symmetry. Complex 1 makes a simple 1:1 adduct with t-BuNC that is trigonal
bipyramidal with an axial isocyanide as demonstrated by X-ray crystallography. This trigonal bipyramidal
1:1 adduct has a triplet ground state and provides a model for the way in which 1 interacts with NCN group
donor dbabhCN prior to NCN group transfer to form the terminal cyanoimide complex 1-NCN. The calculated
Mo−N bond dissociation enthalpy for 1-NCN is 104 kcal mol-1, 30 kcal mol-1 greater than that for the
corresponding dissociation of NCN from cyanophosphiniminato NCNPMe3.