Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

Abstract

Copper(I) bromide complexes (2a and 2b) of NHC–phenolimine ligand precursors {3‐[(1R,2R)‐2‐{[1‐(3,5‐di‐tert‐butyl‐2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1a) and 3‐[(1R,2R)‐2‐{[1‐(2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1b), respectively} have been prepared. Complexes 2a and 2b exhibit copper coordination only through the carbene carbon atom (C) and do not spontaneously eliminate HBr to give additional phenoxyimine (NO) bonds, which is attributed to intramolecular hydrogen bonding. Crystallisation of 2a and 2b gives 2a′ and 2b′, respectively, that contain (C) copper(I) bromide and (NO)2 copper(II) coordination. Complex 2b′ also exhibits intermolecular CuIBr interactions giving a Cu2Br2 bridge that links two molecules of 2b′ resulting in an ellipse motif. Reduction of the ligand precursor imine group of 1a allows synthesis of silver(I) and copper(I) NHC–phenolamine complexes 6 and 7, respectively, that also retain the phenol hydrogen atom. Attempts to selectively prepare 2a′ gave a copper(II) complex 9 that exhibits an (NO)2CuII structure with pendant imidazolium salt groups. Reaction between the silver(I) bromide derivative of 1a and CuCl2·2H2O gives a complex derived from a Cu6(O)(OH)4Cl3 core and two (NO) and one (CNO) ligands, respectively. The use of 2a and 7 as precatalysts for 1,4‐conjugate addition to enones and aziridination of alkenes was studied, showing that, whilst both catalysts are active, enantioselectivities are low, which is attributed to the lack of Cu‐(NO) coordination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Molecular Recognition of Trans-Chiral Schiff Base Metal Complexes for Induced CD

“…As for biomolecules such as proteins, however, CD spectra are used for monitoring folding or unfolding of peptide chains after binding small molecules of metal complexes [25]. This different phenomenon is not classified into the induced CD mentioned in this article.…”

Simple and versatile selective synthesis of neutral and cationic copper(i) N-heterocyclic carbene complexes using an electrochemical procedure

“…1). [24][25][26][27] The route avoids the requirement of inert conditions, with the only side-product being water. Imidazolium chloride/bromide salts are used to prepare neutral complexes, though there are many ligand precursors for which this route is not suited, particularly those containing less bulky nitrogen substituents.…”

“…1 Copper(I)-NHCs prepared using imidazolium salts with Cu 2 O. [24][25][26][27] of 1-methylimidazole and tert-butyl 2-chloroacetate. The ligand precursors were fully characterised using NMR spectroscopy and mass spectrometry.…”

Preparation of Diamine‐β‐diketiminato Copper(II) Complexes and Their Application in the Reverse Atom‐Transfer Radical Polymerization of Styrene

“…The [CuCl2]anion is precedented in over 100 other salts, of which we found fourteen containing a Cu II cation in the Cambridge Structural Database. These cations are mostly 5-coordinate complexes, [30][31][32][33][34][35][36][37][38][39][40][41] but there are also two examples of 4-coordinate complexes like the cation of compound 2 in the structures of the chloro-(2,6-bis((1,3-di-tert-butylimidazolin-2-imino)methyl)pyridine)copper(II) and [Cu(Ph3AsO)4] 2+ salts. [42][43] The relevant geometric parameters of the cations in the two structures are reported and compared in Table 1.…”