Kiyoshi Fujisawa

'Radical-controlled' oxidative polymerization of m-cresol catalyzed by μ-η2 :η2-peroxo dicopper(II) complex

Abstract Described is an oxidative polymerization of m-cresol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane)copper complex, from which a μ-η2:η2-peroxo dicopper(II) complex is formed under dioxygen and reacts with m-cresol to give ‘controlled’ phenoxy radical–copper(I) complex exclusively without formation of ‘free’ phenoxy radical. The present catalyst showed the highest activity in the metal complex catalysts reported for the polymerization of m-cresol with dioxygen. The resulting polymer consisted of oxyphenylene units and showed high molecular weight and high thermal stability. The high selectivity toward Cue5f8O linkage would be due to the coupling from the phenoxy radical species controlled by this catalyst.

Radical-controlled' oxidative polymerization of o-cresol catalyzed by μ-η2 :η2-peroxo dicopper(II) complex

Abstract Described is an oxidative polymerization of o -cresol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane)copper complex, from which a μ -η 2 xa0:xa0η 2 -peroxo dicopper(II) complex is formed under dioxygen. This complex reacts with o -cresol to give ‘controlled’ phenoxy radical-copper(I) complex exclusively without formation of ‘free’ phenoxy radicals. The resulting polymer was composed mainly of 2-methyl-1,4-phenylene oxide unit and showed high thermal stability. The polymerization catalyzed by ( N , N , N ′, N ′-tetramethylethylenediamine)copper complex, a typical catalyst for 2,6-dimethylphenol polymerization, gave the polymer containing larger amounts of o -linkage structures and quinone moieties.

Transition metal peroxo complexes relevant to metalloproteins

A series of dioxygen complexes of copper, iron, and manganese have been synthesized using bulky tripodal nitrogen ligands, hydrotris(3,5-dialkyl- 1-pyrazolyl)borate, as models for the active sites in the metalloproteins. A binuclear copper peroxo complex having p-q2:

Square planar nickel compounds with bulky thiols

coordination mode serves as an accurate model of the active site of oxy-hemocyanin. The reactivities of the complex and related peroxo copper complexes suggested a new radical type reaction mechanism for tyrosinase catalysis. Dioxygen complexes of iron are designed to provide structural and mechanical information for a non-heme oxygen carrier and monooxygenase, hemerythrin and tyrosine hydroxylase. A mononuclear dioxygen complex of manganese represents the first artificial example of hydrogen bond between the peroxide and proton in the ligand and binuclear manganese complexes do the models for the active intermediates of dioxygen evolution sites for PSII.

Model Studies on Nonheme Monooxygenases

Abstract Details of the syntheses and the results of X-ray structural analyses of square planar Ni compounds with aliphatic thiolato-sulfur ligands, [Ni(dpmep)2] (1) and [Ni(tpttd)] (2), where Hdmep and H2tpttd are the abbreviations for 2-(2,2-diphenyl-2-mercaptoethyl) pyridine and 2,2′,11,11′-tetraphenyl-1,5,8,12-tetrahiadodecane, respectively, are presented. Each of the thialato-sulfur atoms of these compounds is sterically protected by two benzene rings at the α carbon position to suppress dimerization upon synthesis. 1 · 1.5CH2Cl2 · MeCN crystallizes monoclinic P21/n with a = 18.362(3), b = 16.894(4), c = 13.273(4) A , β = 104.59(2)°, V = 3984(3) A 3 and Z = 4.2 · 1.5 MeCn crystallizes triclinic P 1 with a = 15.091(6), b = 15.661(3), c = 14.085(7) A , α = 96.00(2), β = 90.89(4), γ = 99.70(2)°, V = 3261(4) A and Z = 4. The Niue5f8S and Niue5f8N bond lenghts of 1 were compared with those of the nickel center in the A-cluster of carbon monoxide dehydrogenase.

Highly Regioselective Oxidative Polymerization of 4-Phenoxyphenol to Poly(1,4-phenylene oxide) Catalyzed by Tyrosinase Model Complexes

Occurrence of a wide variety of nonheme iron monooxygenases is known as described in . The best characterized example among this class of proteins is methane monooxygenase [1-3] of which the active site consists of a paired iron centers [4]. Because of its remarkable catalytic activity, effective for aerobic oxidation of methane to methanol, the structure/catalytic mechanism of methane monooxygenase (MMO) has attracted the attention of many chemists, and the X-ray structural analysis of the resting state [5] of its hydroxylase component (MMOH) as well as the spectroscopic identification of some reaction intermediates have been recently accomplished [6-8]. The active site structure of MMOH determined by X-ray crystallography is illustrated in Fig. 1. Two iron(II) ions are triply bridged with two carboxylate groups and a hydroxide. One of the carboxylate ligands originates from the acetate contained in the buffer solution used for the crystallization. A dioxygen carrying protein for some marine worms, hemerythrin, is known to contain a similar dinuclear iron site [9-12]. The precise coordination structure of the active site and the dioxygen binding fashion in this protein have been the subject of numerous investigations, which have been reviewed extensively [9-12]. It is noteworthy that hemerythrin binds dioxygen as schematically illustrated below in eq. (1), resulting in the formation of a stable asymmetric hydroperoxo adduct, whereas usually iron hydroperoxo species are supposed to be extremely unstable and reactive.