A novel chiral ligand system L containing one pyridyl and two imidazolyl donor functions has been synthesized and investigated with respect to its Cu(I) and Cu(II) coordination chemistry. Reaction with [Cu(MeCN)4]PF6 and [Cu(MeCN)4]OTf led to the dimeric complexes [LCu]2X2 (1, X = PF6; 2, X = OTf) with the ligands L in different configurations (R,S). The ligand matrix formed in these complexes can also host a Cu(II) ion instead of two Cu(I) ions so that mixed crystals of [L2Cu]X2 and [LCu]2X2 can be produced. The pure compounds [L2Cu]X2 (3, X = PF6; 4, X = OTf) can be obtained by treatment of 1 and 2 with O2 in acetonitrile, respectively. From the corresponding solution 3 crystallizes with the two L molecules in different configurations, while 4 crystallizes with the ligands in (S,S) or (R,R) configurations, respectively. Crystals containing the analogous diastereomers of 3 were obtained, besides those isolated previously, when this compound was synthesized by reaction of 1 with AgPF6. On treating 2 with O2 as the oxidant in acetonitrile, besides formation of 4, additional evidence for oxygenation of L to L(ox), where one of the original phenyl units corresponds to a phenolate function, was found: The dinuclear complex [L(ox)Cu(OH)(OTf)CuL](OTf) (5) was isolated as the final product of O2 activation and conversion, which resembles the one of tyrosinase. In acetonitrile 5 reacts further to give 4 and [L(ox)2Cu2](OTf)2 (6), and hence, product mixtures are obtained. In CH2Cl2 decomposition can be avoided, and hence, changing the solvent from acetonitrile to CH2Cl2 leads to selective formation of 5.
New tripodal ligand L2 featuring three different pyridyl/imidazolyl-based N-donor units at a bridgehead C atom, from which one of the imidazolyl units is separated by a phenylene linker, was synthesized and investigated with regards to copper(I) complexation. The resulting complex [(L2)Cu]OTf (2(OTf)), the known complex [(L1)Cu]OTf (1(OTf); L1 differs from L2 in that it lacks the phenylene spacer) and [(L3)Cu]OTf (3(OTf)), prepared from a known chiral, tripodal, N-donor ligand featuring pyridyl, pyrazolyl, and imidazolyl donors, were tested as catalysts for the oxidation of sodium 2,4-di-tert-butylphenolate (NaDTBP) with O2. Indeed, they mediated NaDTBP oxidation to give mainly the corresponding catecholate and quinone (Q). None of the complexes 1(OTf), 2(OTf), and 3(OTf) is superior to the others, as yields were comparable and, if the presence of protons is guaranteed by concomitant addition of the phenol DTBP, the oxidation can also be performed catalytically. For all complexes stoichiometric oxidations under certain conditions (concentrated solutions, high NaDTBP content) were found to also generate products typical for metal-mediated intradiol cleavage of the catecholate with O2. As shown representatively for 1(OTf) this dioxygenation sets in at a later stage of the reaction. Initially a copper species responsible for the monooxygenation must form from 1(OTf)/NaDTBP/O2, and only thereafter is the copper species responsible for dioxygenation formed and consumes Q as substrate. Hence, under these circumstances complexes 1(OTf)-3(OTf) show both monooxygenase and catechol dioxygenase activity.
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A catalytic aldol condensation in the presence of lithium perchlorate and tertiary amines is described giving pure products in high yields. The aldol condensation can be performed even in the presence of hydrated lithium perchlorate. a,b-Unsaturated carbonyl compounds, diarylylidene or dialkylidene carbonyl compounds, are very important precursors in the perfume industry, 1 for bioactive pyrimidines, 2 as agrochemicals, and as liquid crystal polymers. 3 Moreover, a,b-unsaturated carbonyl compounds are important structural elements in the curcumin family of natural products which exhibit certain anti-cancer properties. 4 They were used in the indium-catalyzed synthesis of substituted vinylcyclopropanones 5 or the goldcatalyzed alkylation of indoles. 6 Many of these substances are widely used as ligands in palladium-catalyzed coupling processes, 7 moreover, some of these ligands are extremely expensive. 8Recently, several methods appeared describing the synthesis of arylidene-or alkylideneketones. Several metal salts were employed as reagents in these reactions, 9 however, often higher temperatures and long reaction times are necessary for complete conversion and hence formation of byproducts increased. In addition, most of these reactions were accompanied by low chemoselectivity, also self-condensations were observed rather than cross-aldol condensations, which caused problems in their purification.During our ongoing studies of aldol processes in the presence of LiClO 4 10 we developed a very mild, easy, and catalytic process for the synthesis of arylidene and alkylidene carbonyl compounds, which we describe herein.
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