Transition metal complexes, Cu+

At present, the correlation contains one transition metal complex, Cu(Hfacac)2. The results on this complex are very interesting and somewhat unusual for a transition metal system in that enthalpies have been obtained in a poorly solvating solvent with nonionic donors (52), instead of the t5 ical stability constant study on a metal cation in some highly polar solvent. Data from this latter type of investigation have many practical uses, but are impossible to interpret and understand. The transition metal ion complex we have studied can be incorporated into the E and C scheme using the same base parameters that are used to correlate the enthalpies of formation of all the other Lewis acid-base adducts in the scheme. 

In ATRP, the range of polymerizable monomers have been extended to vinyl acetate, dienes and vinyl chloride.Also, new metals (Mo, Os, Ti) and new ligands were successfully introduced. ATRP was successfully carried out in miniemulsion and microemulsion as well as in CO2 or in ionic liquids. New initiating systems were developed for ATRP, such as ARGET and ICAR. They start from oxidatively stable transition metal complexes (Cu") and are activated in the presence of reducing agents. Reduced amount of catalyst and its... 

Intermolecular alkynyl ligand transfer of transition metal complexes is more common than the aryl and alkyl ligand transfer. Alkynyl compounds of Cu(I) and Hg(II) transport the ligand to other transition metals, giving various alkynyl transition metal complexes. [Cu(C=CR)] [171], isolated or generated in situ from the reaction of alkyne, Cul, and base, was employed in preparation of a number of alkynyl complexes of group 5-10 transition metals. The alkynyl hgand transfer is depicted schematically in Eq. 5.46 [172-175]. 

The preparation of a series of transition metal complexes (Co. Ni. Pd. Pt, Ir. Au. Cu. Ag) with ambident anion (70) and phosphines as ligands has been reported recently (885). According to the infrared and NMR spectra the thiazoline-2-thione anion is bounded through the exocyclic sulfur atom to the metal. The copper and silver complexes have been found to be dimeric. 

Clusters can be formed by reacting transition-metal complexes with group-IB derivatives. The reaction of Ir(COXPPh3)2CI with Cu phenylacetylide gives rise to two cluster products ... 

Metal-Catalyzed. Cyclopropanation. Carbene addition reactions can be catalyzed by several transition metal complexes. Most of the synthetic work has been done using copper or rhodium complexes and we focus on these. The copper-catalyzed decomposition of diazo compounds is a useful reaction for formation of substituted cyclopropanes.188 The reaction has been carried out with several copper salts,189 and both Cu(I) and Cu(II) triflate are useful.190 Several Cu(II)salen complexes, such as the (V-f-butyl derivative, which is called Cu(TBS)2, have become popular catalysts.191... 

A variety of transition metal complexes including organometallics was subjected to an ac electrolysis in a simple undivided electrochemical cell, containing only two current-carrying platinum electrodes. The compounds (A) are reduced and oxidized at the same electrode. If the excitation energy of these compounds is smaller than the potential difference of the reduced (A ) and oxidized (A ) forms, back electron transfer may regenerate the complexes in an electronically excited state (A+ + A A + A). Under favorable conditions an electrochemiluminescence (eel) is then observed (A A + hv). A weak eel appeared upon electrolysis o t]jie following complexes Ir(III)-(2-phenylpyridine-C, N ) [Cu(I)(pyridine)i],... 

Compounds of transition metals (Mn, Cu, Fe, Co, Ce) are well known as catalysts for the oxidation of hydrocarbons and aldehydes (see Chapter 10). They accelerate oxidation by destroying hydroperoxides and initiating the formation of free radicals. Salts and complexes containing transition metals in a lower-valence state react rapidly with peroxyl radicals and so when these compounds are added to a hydrocarbon prior to its oxidation an induction period arises [48]. Chain termination occurs stoichiometrically (f 1) and stops when the metal passes to a higher-valence state due to oxidation. On the addition of an initiator or hydroperoxide, the induction period disappears. 

In order to make a formal separation between two- and three-center aspects of coordinative bonding, we shall first consider various aspects of simple two-center dative M—L coordination within the framework of normal-valent transition-metal complexes. Aspects of hypervalent cu-bonding to form higher-coordinate complexes (the more common experimental species) will subsequently be considered in Section 4.5.3. 

As a result of the strong tendency toward 3c/4e hypervalent bonding, each M—L coordinative bond of a normal-valent ML transition-metal complex will be susceptible to successive cu-additions by other coordinative ligands L cf. (3.212a) ... 

However, we have shown how the 18-electron rule is commonly satisfied in the absence of any significant p-orbital participation, on the basis of hypervalent 3c/4e cu-bonding interactions wholly within the framework of normal-valent sd" hybridization. Results of NBO and Mulliken analyses of high-level wavefunctions for transition-metal complexes commonly exhibit only paltry occupation of the outer p orbitals (comparable in this respect to the weak contributions of d-type polarization functions in main-group bonding). 

In many other reactions of zirconacydes catalyzed by transition metal complexes containing Cu, Ni, Pd, etc., a-bond metathesis (transmetallation) must undoubtedly be involved, but such products have not generally been identified. Partly for this reason, they are not discussed here. Readers are referred to the chapter by T. Takahashi. 

Extremely high selectivities are frequently interpreted as "ion fixation", which suggests an irreversible phenomenon. This is the case for exchanges of Cs, Rb and K in illite clay minerals (95-96) as well as for Cu(NHj) exchange in fluorhectorite (66). However, reversibility was verified from the Hess law for adsorption of Cs, Rb and K on the high affinity sites in illite (91) and modified montmorillonites (101) as well as for the exchange of transition metal complexes (29, 75). 

The direct conversion of alcohols and amines into carbamate esters by oxidative carbonylation is also an attractive process from an industrial point of view, since carbamates are useful intermediates for the production of polyurethanes. Many efforts have, therefore, been devoted to the development of efficient catalysts able to operate under relatively mild conditions. The reaction, when applied to amino alcohols, allows a convenient synthesis of cyclic urethanes. Several transition metal complexes, based on Pd [218— 239], Cu [240-242], Au [243,244], Os [245], Rh [237,238,246,247], Co [248], Mn [249], Ru [224,250-252], Pt [238] are able to promote the process. The formation of ureas, oxamates, or oxamides as byproducts can in some cases lower the selectivity towards carbamates. 

Transition metal complexes encapsulated in the cavities of zeolites and meso-porous materials exhibit enhanced catalytic activity, compared to their neat analogs. " We had earlier found that Cu(II)-acetate exhibited enhanced regiose-lective orf/zo-hydroxylation of phenols using atmospheric oxygen as the oxidant on encapsulation in molecular sieves Y, MCM-22 or VPI-5. Rao et al. had also found a similar enhancement for encapsulation in Al-MCM-48. 

Natural inorganic ligands of heavy metals in subsurface water, which are present in a concentration of about 1 millimolar, include nitrite, sulfate, chloride, carbonate, and bicarbonate. These potential ligands generally are efficient only under special conditions. For example, in an alkaline environment, carbonate and bicarbonate can be significant complexors of transition metals like Cu or the uranyl ion, and cadmium may be complexed with Cl" or SO to form... 

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