Rare-Earth- and Uranium-Mesoionic Carbenes: A New Class of f-Block Carbene Complex Derived from an N-Heterocyclic Olefin.

ABSTRACT: Neutral mesoionic carbenes (MICs) have emerged as an important class of carbene, however they are found in the free form or ligated to only a few d-block ions. Unprecedented f-block MIC complexes [M(N'')₃ {CN(Me)C(Me)N(Me)CH}] (M=U, Y, La, Nd; N''=N(SiMe₃ )₂ ) are reported. These complexes were prepared by a formal 1,4-proton migration reaction when the metal triamides [M(N'')₃ ] were treated with the N-heterocyclic olefin H₂ C=C(NMeCH)₂ , which constitutes a new, general way to prepare MIC complexes. Quantum chemical calculations on the 5f³ uranium(III) complex suggest the presence of a U=C donor-acceptor bond, composed of a MIC?U ?-component and a U(5f)?MIC(2p) ?-back-bond, but for the d⁰ f⁰ Y and La and 4f³ Nd congeners only MIC?M ?-bonding is found. Considering the generally negligible ?-acidity of MICs, this is surprising and highlights that greater consideration should possibly be given to recognizing MICs as potential ?-acid ligands when coordinated to strongly reducing metals.

SUBMITTER: Seed JA 

PROVIDER: S-EPMC5601227 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature