Cyclic Alkyl(amino) Carbene Stabilized Complexes with Low Coordinate Metals of Enduring Nature

• DOI: 10.1021/acs.accounts.5b00381
• Publication Date: 2016-02-29T14:18:42Z
• Authors: Sudipta Roy; Kartik Chandra Mo...; Herbert W. Roesky
• Keywords: Models, Molecular; Coordination Complexes; Electron Spin Resonance Spectroscopy; Methane; 01 natural sciences; 0104 chemical sciences

N-Heterocyclic carbenes (NHCs) are known to stabilize some metal atoms in different oxidation states mostly by their strong σ-donation. After the successful syntheses of cyclic alkyl(amino) (cAACs), they have been proven be much more effective stabilizing electron rich species. In cAAC, one σ-withdrawing and π-donating nitrogen NHC is replaced a σ-donating quaternary carbon atom leading lower lying LUMO. This makes acceptance π-back-donation from element bound carbene cAAC energetically advantageous. Further evidence suggests that can use lone pair electrons present on adjacent controlled way depending accumulation density metal. It has found utilized as excellent ligand for stabilization complex with three coordinate center [(cAAC)2M(I)-Cl; M = Fe, Co, Cr]. Complex (cAAC)2M(II)Cl2 [M Cr] was prepared reacting anhydrous M(II)Cl2 two equiv followed treatment KC8 (reducing agent) obtain (cAAC)2M(I)-Cl. The corresponding cation (cAAC)2M(+) isolated when (cAAC)2M(I)-Cl reacted sodium-tetraarylborate (lithium) toluene or fluorobenzene. CV Fe] it reversibly undergo reduction. cations Co Fe were reduced Na(Hg) KC8, respectively. (cAAC)2Co(I)Cl directly (cAAC)2Co(0) KC8. Analogous (cAAC·)2Zn(II) (cAAC)2Mn complexes reduction (cAAC)MCl2 Zn, Mn] presence cAAC. square planar (cAAC)2NiCl2 LiN(iPr2) (KC8) (cAAC)2Ni(0). (cAAC)2Pd(0) (cAAC)2Pt(0) substituting all four triphenylphosphines (Ph3P)4M(0) Pd, Pt] cAACs. Cation Cu, Au] sodium/potassium neutral analogue [(cAAC)2Cu, (cAAC)2Au]. Two Zn/Mn/Cu/Au stabilized ligands possessing radical atoms, while analogous Co/Fe/Ni/Pd/Pt contain metals zero state. ground electronic structure (cAAC)2M thoroughly studied theoretical calculations. this Account, we summarize our developments low two, one, most significantly utilizing cAACs ligands.