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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
Author(s) -
Simonovic Stevan,
Whitwood Adrian C.,
Clegg William,
Harrington Ross W.,
Hursthouse Michael B.,
Male Louise,
Douthwaite Richard E.
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200801152
Subject(s) - chemistry , copper , bromide , medicinal chemistry , intramolecular force , ligand (biochemistry) , carbene , hydrogen bond , polymer chemistry , stereochemistry , molecule , inorganic chemistry , organic chemistry , catalysis , biochemistry , receptor
Copper(I) bromide complexes ( 2a and 2b ) of NHC–phenolimine ligand precursors {3‐[(1 R ,2 R )‐2‐{[1‐(3,5‐di‐ tert ‐butyl‐2‐hydroxyphenyl)meth‐( E )‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3 H ‐imidazol‐1‐ium bromide ( 1a ) and 3‐[(1 R ,2 R )‐2‐{[1‐(2‐hydroxyphenyl)meth‐( E )‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3 H ‐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 Cu I Br interactions giving a Cu 2 Br 2 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 ) 2 Cu II structure with pendant imidazolium salt groups. Reaction between the silver(I) bromide derivative of 1a and CuCl 2 · 2H 2 O gives a complex derived from a Cu 6 (O)(OH) 4 Cl 3 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)