Copper coordination complexes, models

In our ongoing efforts to develop oxidation catalysts that are functional in water as environmentally berrign solvent, we synthesized a water-soluble pentadentate salen ligand with polyethylene glycol side chairts (8). After coordination of copper(II) ions to the salen ligand, a dinuclear copper(II) complex is obtained that is soluble in water, methanol and mixtures of both solvents. The aerobic oxidation of 3,5-di-tert.-butylcatechol (DTBC) into 3,5-di-terr.-butylqitinone (DTBQ) was used as a model reaction to determine the catalytically active species and initial data on its catalytic activity in 80% methanol. 

In their pursuit of modeling Type I copper proteins, Kitajima et al. reported112 a rare, tetrahedrally coordinated complex (105), which displayed an EPR spectrum consistent with the presence of the unpaired electron in the dz2 orbital.1 They also isolated a square-pyramidal DMF adduct (complex (106)). They were successful in providing structural proof of a copper(II) complex (trigonal pyramidal) with C6F5S -coordinated complex (107), with CuN3S chromo-phore.113 The X-ray analysis (poor data set) of a closely similar complex with Ph3CS as the... 

Copper(II) complexes with phenoxo ligands have attracted great interest, in order to develop basic coordination chemistry for their possible use as models for tyrosinase activity (dimeric complexes) and fungal enzyme galactose oxidase (GO) (monomeric complexes). The latter enzyme catalyzes the two-electron oxidation of primary alcohols with dioxygen to yield aldehyde and... 

Krebs and co-workers synthesized a series of dinuclear copper(II) complexes as models for catechol oxidase 91 (365) (distorted SP Cu-Cu 2.902 A), (366) (distorted five-coordinate geometry Cu-Cu 3.002A), (367) (distorted SP Cu-Cu 2.995 A), (368) (distorted five-coordinate geometry Cu-Cu 2.938 A), and (369) (distorted SP Cu-Cu 2.874 A). These complexes were characterized by spectroscopic and electrochemical methods. From kinetic analysis, a catalytic order for catecholase activity (aerial oxidation of 3,5 -di - ter t-buty lcatec h o 1) was obtained.326... 

Using 1,4,8,11-tetraazacyclotetradecane, the structure of complex (800) (distorted trigonal planar Cu-Cu 6.739 A) was determined. Reactivity with 02 was investigated to demonstrate the formation of trans-l,2-peroxo species.585 As part of their work with copper(I) complexes with 02, the structure of a dicopper(I) complex ((801) distorted tetrahedral 7.04 A), supported by macrocyclic ligand environment, was reported by Comba and co-workers. Tolman and co-workers structurally characterized a three-coordinate copper(I)-phenoxide complex (802) (planar T-shaped) that models the reduced form of GO.587 The copper(I) analogue [Cu(L)][CF3-SO3]-0.43MeOI I (803) of a copper(II) complex (534) was also reported to demonstrate the role of ligand framework conformability in CV /Cu1 redox potentials.434 Wilson and co-workers... 

We were interested in the behaviour of polymeric catalysts in order to confirm that typical polymer effects may occur. Oxidative coupling of 2,6-disubstituted phenols, as developped by Hay (7), was chosen as a model reaction and the catalytic activities of coordination complexes of copper with several polymeric tertiary amines were compared with the activities of their low molecular weight analogs. The overall reaction scheme is presented in scheme 1. 

Copper-reconstituted cytochrome c ( cyt-c) has also been investigated with transient absorption methods (49). No evidence of ghotoinduced ejection of the fifth ligand is observed in either cyt-c or the model Cu-porphyrin 5-coordinate complexes (60-62). This is consistent with the likely transient state being a non-dissociative w w or d 2 2 charge-transfer state. 

Large numbers of five-coordinate copper(II) complexes in several stereochemistries are known. The spectra which have been most studied with a view to interpretation are those of the trigonal bipyramidal complexes, for which assignments have been proposed on the basis of molecular orbital, angular overlap, and crystal-field models. 

During the past 10-15 years a great deal of effort has been put into characterizing the biological role of copper using the combined or separate techniques of biology/biochemistry and of coordination chemistry (Section 53.4.8.1). 30,1186-1196 Parallel to this has been an equally extensive effort to prepare and characterize a wealth of coordination complexes of the copper(Il) ion in an attempt to model the physical and chemical behaviour of the biological copper system (Section 53.4.8.2).30,1180 1191 1203 These two approaches are outlined in the next two sections. 

An important condition for chiral matrices is that they need to form labile interactions with the substrate in order to facilitate both the recovery of the enantioselec-tively coordinated ligand and the recycling of the chiral matrix. Usually copper(II) complexes have been used[48]. Due to the problems involved in the modeling of Jahn-Teller distorted copper(II) complexes (see Chapter 11 for a detailed discussion on... 

Cuprous ion complexes with four ligands are normally tetrahedral, involving spi hybrid orbitals (electronic distribution A). However, the cuprous hydrogen complex II, which is of the form (Cu X3H), is isoelec-tronie with four coordinate complexes of cupric ion, of the form (Cu11 ), which are known to be planar and to use dsp2 orbitals (distribution B). It seemed possible, therefore, that because of its unusual electronic structure, complex II was also planar. Construction of scale (Fischer-Taylor-Hirschfelder) models indicates that this is probably not the case. A planar model of I can be constructed but not of II insufficient space exists to accommodate the hydrogen atoms between the copper ions in II. If, however, tetrahedral coordination is permitted about the copper ions, no... 

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