Surninary Contrary to recent interpretations, it is demonstrated by 1S3W n.m.r. and by VIv e.s.r. spectroscopy that: (i) the a2 isomer of [(P04)2Wl,0,3]10-, and its a,OJ3-by absence of a W atom from one of the 3-fold W30,, groups which cap the ends of the latter complex, rather than by removal or substitution of one W atom from the 12 which are around the complex's 'belt'; and(ii) ~-[(Po4)~w180~]s-differs from its a isomer by a 60' rotation, about its 3-fold axis, of one of the 'cap' W3013 groups rather than by a 60° rotation of one PW, 'halfunit' relative to the other one.
Reduction of mixtures of copper(I1) and 3,5-di-tert-butyl-o-benzoquinone (DTBQ) at mole ratios of 1:2 in acetonitrile or dimethyl sulfoxide yields a copjw(1I)atecholato (DTBC)semiquinonato (DTBSQ) complex [Cu"(DTBC)(DTBSQ)-] and a CU"(DTBC)~" complex. These complexes, their oxidation products, and three mixed-ligand complexes [Cu"-(DTBC)(bpy), Cun(DTBC)(phen), and Cun(DTBC)(en)] have been characterized by cyclic voltammetry, optical spectroscopy, and ESR. The formation constants, Kf, for the Cu"(DTBC)(DTBSQ)-and CuI*(DTBC);-complexes have approximate values of 4 X lOI4 and 1.6 X 10" M-2, respectively. Formation of a stable copper(I1)semiquinonato complex as a redox intermediate provides another versatile 1 -electron pathway for the copper-catechol-quinone system, which may be pertinent to the redox chemistry of related systems in biology and to catalytic oxygen activation.Copper, which is an essential component of many oxidase and oxygenase enzymes,'-* appears to be required for lignin formation in plant^,^ and its complexes catalyse oxidative delignification processes. lo Electrochemical studies indicate 0020-1669/83/1322-2790$01.50/0 0 1983 American Chemical Society R e t r y No. Cun(DTBC)(DTBSQ)-, 86822-03-9; CU"(DTBC)~~, 86822-04-0; Cu"(DTBC)(bpy), 59368-85-3; Cu"(DTBC)(phen), 59368-86-4; Cu"(DTBC)(en), 74463-13-1; DTBQ, 3383-21-9; Cu, 7440-50-8.
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