Oxidation states copper complexes

In a standard ATRP reaaion, a solution of the lower oxidation state copper complex is added to the reaction medium or formed in situ from a Cu salt and an N-containing ligand. This can present a problem if active catalyst complexes are formed because the readily oxidized activator complex can react with oxygen, present in the system as an impurity, and be quickly deactivated. However, this spontaneous oxidation could increase the efficiency of initiation from R-X since termination reaaions required to form the equivalent of the persistent radical could be avoided or reduced. ... 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

The reactions of copper(II) complexes to be considered are of two types (i) ligand substitution reactions and (ii) redox reactions, i.e. electron transfer involving a change in oxidation state, copper(I)/(II)/(III). 

Water does not attack copper but in moist atmo spheres it slowly forms a characteristic green surface layer (patina). The metal will not react with dilute sulphuric or hydrochloric acids, but with nitric acid oxides of nitrogen are formed. Copper compounds contain the element in the +1 and +2 oxidation states. Copper(l) compounds are mostly white (the oxide is red). Copper(II) salts are blue in solution. The metal dso forms a large number of coordination complexes. 

Arylations under metal-catalyzed conditions are generally suggested to proceed by transfer of one aryl group to the metal to create a high oxidation state ArM complex, followed by reductive elimination with the nucleophile, which has either coordinated before (Pd) or after (Cu) the step with At2lX (Scheme Id). Catalytic cycles involving Pd /Pd and CuVCu are often described, but the precise arylation mechanisms are stiU a matter of debate and are not covered here [37-43]. Copper-catalyzed reactions are often performed in dichloromethane (DCM) or 1,2-dichloroethane (DCE), using either a copper(l) or copper(II) source, whereas the Pd-catalyzed conditions vary more. 

When naming complex ions the number and type of ligands is written first, followed by the name of the central metal ion. If the complex as a whole has a positive charge, i.e. a cation, the name of the central metal is written unchanged and followed by the oxidation state of the metal in brackets, for example [Cu(N 113)4] becomes tetra-ammine copper(II). A similar procedure is followed for anions but the suffix -ate is added to the central metal ion some examples are ... 

Oxidation state is a frequently used (and indeed misused) concept which apportions charges and electrons within complex molecules and ions. We stress that oxidation state is a formal concept, rather than an accurate statement of the charge distributions within compounds. The oxidation state of a metal is defined as the formal charge which would be placed upon that metal in a purely ionic description. For example, the metals in the gas phase ions Mn + and Cu are assigned oxidation states of +3 and +1 respectively. These are usually denoted by placing the formal oxidation state in Roman numerals in parentheses after the element name the ions Mn- " and Cu+ are examples of manganese(iii) and copper(i). 

Derived from the German word meaning devil s copper, nickel is found predominantly in two isotopic forms, Ni (68% natural abundance) and Ni (26%). Ni exists in four oxidation states, 0, I, II, III, and IV. Ni(II), which is the most common oxidation state, has an ionic radius of —65 pm in the four-coordinate state and —80 pm in the octahedral low-spin state. The Ni(II) aqua cation exhibits a pAa of 9.9. It forms tight complexes with histidine (log Af = 15.9) and, among the first-row transition metals, is second only to Cu(II) in its ability to complex with acidic amino acids (log K( = 6-7 (7). Although Ni(II) is most common, the paramagnetic Ni(I) and Ni(III) states are also attainable. Ni(I), a (P metal, can exist only in the S = state, whereas Ni(lll), a cT ion, can be either S = or S =. ... 

Organometallic porphyrin complexes containing the late transition elements (from the nickel, copper, or zinc triads) are exceedingly few. In all of the known examples, either the porphyrin has been modified in some way or the metal is coordinated to fewer than four of the pyrrole nitrogens. For nickel, copper, and zinc the 4-2 oxidation state predominates, and the simple M"(Por) complexes are stable and resist oxidation or modification, thus on valence grounds alone it is easy to understand why there are few organometallic examples. The exceptions, which exist for nickel, palladium, and possibly zinc, are outlined below. Little evidence has been reported for stable organometallic porphyrin complexes of the other late transision elements. 

In view of this, it is not surprising that dithiocarbamato compounds with copper in the oxidation state + 3 are stable instead it must be regarded as unexpected that Cu(I) dithiocarbamato complexes exist. The latter complexes are not simply monomeric, but they are tetrameric metal cluster compounds. Obviously, the stability must be attributed to the metal-metal bond rather than to the stabilising effect of the ligand. 

In copper dithiocarbamato complexes the metal can have the oxidation states + 1, + 2 and +3. The complexes synthesized up to the present are summarised in Table 2. 

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