Studies on Three-Coordinate [Co{N(SiMe₃)₂}₂L] Complexes, L = N-Heterocyclic Carbene

Abstract

A series of three-coordinate N-heterocyclic carbene bis­(trimethylsilyl)­amide complexes of cobalt, [Co­{N­(SiMe3)2}2(NHC)] (NHC = N,N′-diarylimidazolin-2-ylidene, aryl = 2,6-diisopropylphenyl, SIPr (1), aryl = mesityl, SIMes (2); κ1-N,N′-diphosphanylimidazol-2-ylidene, PCP (5); κ1-N-phosphanyl-N′-2,6-diisopropylphenylimidazol-2-ylidene, PC (6); cyclic alkyl amino carbene :C­(Cy)­CH2CMe2N-2,6-Pri 2C6H3, cAACCy (7)) were prepared by the reaction of [Co­{N­(SiMe3)2}2] with the corresponding NHCs. The complexes exhibited interesting transamination reactivity in reactions with bulky 2,6-diisopropylaniline (NH2(DiPP)), where adjustment of the stoichiometry and reaction conditions resulted in the substitution of one or two N­(SiMe3)2 ligands by the anilido ligand NH­(DiPP), giving [Co­{N­(SiMe3)2}­{NH­(DiPP)}­(NHC)] (NHC = N,N′-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene, IPr (8)) and [Co­{NH­(DiPP)}2(NHC)] (NHC = SIPr (9); IPr (10); PCP (11)). X-ray crystallography revealed trigonal-planar coordination geometry at Co for all of the new complexes and long Co–CNHC bond lengths; in the cases of 5, 8, 9, 10, and 11, intramolecular Co···H and/or H···P interactions may provide further stabilization of specific conformations. Magnetic and electron paramagnetic resonance studies showed that the three-coordinate Co­(II) centers in 1–7 behave as S = 3/2 spins with strong anisotropy arising from the low symmetry of the coordination site (C 2v ). The anisotropy results in large values of the zero-field splitting parameter D.

Transition Metal Compounds of Pyridine‐Amide‐Functionalized Carbene Ligands: Synthesis, Structure, and Electrocatalytic Properties in Proton Reduction

“…The Co–C (1.92 Å) and Co–N (1.92–1.99 Å) bonds are slightly longer than the corresponding distances in the nickel compounds. The Co–C bond lengths are similar to those in reported Co‐carbene complexes . Hydrogen bond interactions are present between the water molecules, the chloride anions and the carbonyl oxygen atoms in [Co( L1 ) 2 ]Cl.…”

Iron and Cobalt Metallotropism in Remote‐Substituted NHC Ligands: Metalation to Abnormal NHC Complexes or NHC Ring Opening

“…[12] All CoÀNd istances (Co1 À N3, Co1 À N4, Co2 À N5) fall into the narrow range characteristic of aminide ligands,with atypical CoÀC NHC bond distance (1.951 (1) ). [13] Thus,aplausible description of the ligand system in 4a emerging from the metrical data is an aminidefunctionalized mesoionic aNHC,leading to consider Co1 and Co2 as Co II and Co I ,r espectively.A lternative resonance formulations can be found in the Supporting Information, Scheme S3.2. Interestingly, 4a is the only dinuclear complex with two Co{N(SiMe 3 ) 2 }moieties and nonbridging N(SiMe 3 ) 2 In contrast to 1a/1b, complexes 5a and 5b were obtained from the reaction of the tautomeric mixture IA tBu ÐAC tBu with [M{N(SiMe 3 ) 2 } 2 ] 2 (M = Co,F e) in toluene at room temperature for 3d or heating at 90 8 8Cf or 1h (Scheme 3 and Figures 5a nd 6).…”

Transition metal (Rh and Fe) complexes and main-group (Se and B) adducts with N,N′-diphosphanyl NHC ligands: a study of stereoelectronic properties

“…Related dinuclear rhodium complexes with bridging arylimidazolide-N 3 ,C 2 ligands containing a central six-membered ring have been recently reported. 10 Since PC NHC chelation was observed here with PC NHC P-RhCl and previously with Pd(II) and Cr(III) centres, 8a,9 but not with Cr(II) or Co(II), 9,11 we wondered whether the κC NHC coordination mode is more common with 3d metals. Thus, reaction of PC NHC P with [Fe 4 Cl 8 (THF) 6 ] in THF inside a glovebox (Scheme 1) afforded colourless, paramagnetic, air-sensitive crystals after crystallisation by addition of pentane.…”