Article
Regulation of the Rate of Dinucleation of a Monocopper(I) Complex Containing Bipyrimidine Rotary Units by Restricted Double Pyrimidine Rotation
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Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Inorg. Chem., Article ASAP
DOI: 10.1021/ic500074c
Publication Date (Web): March 5, 2014
Copyright © 2014 American Chemical Society
*E-mail: skume@hiroshima-u.ac.jp., *E-mail:nisihara@chem.s.u-tokyo.ac.jp.
Abstract
New copper(I) complexes with coordinated 2-(4′-methyl)pyrimidinyl moieties were fabricated, and the isomerism of their pyrimidine ring linkage was investigated. The ligands bis[2-(diphenylphosphino)phenyl] ether (DPEPhos) and 4,4′-dimethyl-2,2′-bipyrimidine (dmbpm) were used to synthesize a heteroleptic copper(I) complex, [CuI(DPEPhos)(dmbpm)]·BF4(1·BF4), and a dinuclear copper(I) complex, [(CuI)2(DPEPhos)2(μ-dmbmp)](BF4)2 [2·(BF4)2]. The X-ray crystallographic structures, UV–vis absorption spectra, and luminescence properties of the complexes were analyzed. The thermodynamic and kinetic aspects of the isomerism of1·BF4 were examined by variable-temperature NMR. Double pyrimidine ring rotation was found to be restricted sterically by the bulky DPEPhos ligands. This limited the number of the possible isomers: 1·BF4 showed only isomers with either one (io isomer) or both (oo isomer) of the two methyl groups positioned away from the copper center, while dinuclear 2·(BF4)2was only found as a symmetric (io–io) isomer, with each of the two methyl groups positioned toward different copper centers. The addition of [Cu(MeCN)2(DPEPhos)] (3·BF4) allowed both isomers of 1·BF4 to form 2·(BF4)2, although at different rates and via different pathways, which were analyzed using time-dependent UV–vis spectroscopy. The io isomer dinucleated more quickly than the oo isomer owing to it being able to form 2·(BF4)2 (i) without bond dissociation and (ii) without a sterically congested ii configuration around the copper center. In contrast, oo-1·BF4 required (i) recombination of the bipyrimidine coordination bonds or (ii) formation of a product with higher thermodynamic energy, unsymmetric (ii–oo) 2·(BF4)2. These findings are interpreted as demonstrating a novel kinetic property: a conversion rate determined by pyrimidine ring inversion.
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