Oxygen reversibility

In 1963 Vaska 164) discovered that the iridium complex Ir(PPh3)2C (CO) takes up molecular oxygen reversibly with 1 1 stoichiometry. This complex has since been shown to reversibly sorb (1 1) ethylene (755), carbon dioxide (765), F2C=CF2 and F3C—C=C—CF3 (767), as well as various other ligands (765). Ibers md La Placa (769)... 

Compounds affecting the ability of Hb to bind oxygen reversibly... 

Several low-spin mono- and dicobalt (II) complexes of simple amines in solutions were reported to bind molecular oxygen reversibly (7). The best known example of the binuclear peroxy complexes is [(H3N)5-Co-02-Co(NH3)5]5+ (8). In aqueous solutions no definitive evidence for mono-... 

The earliest known dioxygen complex contained [(NH3)10Co2O2]4+, first described by Werner and Myelius in 1893.94 A surge of interest in dioxygen complexes arose after the Co11 chelate of bis(salicylaldehyde)ethylenediimine was shown to take up oxygen reversibly by Tsumaki in 1938.95 It is only recently, however, that the existence of mononuclear superoxo complexes has been established and structural studies performed upon them. A vast array of Co chelates based on Schiff bases such as (4) and (5) have been synthesized. 

Oxidative phenolic coupling.1 This cobalt complex and the related salcomine (2, 160, 3, 245 6, 507), both of which bind oxygen reversibly (102 2Co), catalyze the oxygenation of the phenol 1 to give carpanone 2 in 90-94% yield. Related complexes ol l c(ll) and Mn(II) are less effective. PdCl2 effects this reaction in 46% yield (4, 17(1) singlet oxygen is less efficient (29% yield). 

A number of transition metals are now known147-156 to form stable dioxygen complexes, and many of these reactions are reversible. In the case of cobalt, numerous complexes have been shown to combine oxygen reversibly.157 158 Since cobalt compounds are also the most common catalysts for autoxidations, cobalt-oxygen complexes have often been implicated in chain initiation of liquid phase autoxidations. However, there is no unequivocal evidence for chain initiation of autoxidations via an oxygen activation mechanism. Theories are based on kinetic evidence alone, and many authors have failed to appreciate that conventional procedures for purifying substrate do not remove the last traces of alkyl hydroperoxides from many hydrocarbons. It is usually these trace amounts of alkyl hydroperoxide that are responsible for chain initiation during catalytic reaction with metal complexes. 

Copolymers (XVI) which have oxime moiety give complexes of Fe(II), Co(II) and Ni(II), and they adsorb and desorb molecular oxygen reversibly (157). 

It is the oxygen-carrier protein found in marine invertebrates it binds oxygen reversibly in a manner similar to Hb and Mb. Several oligomers are known, but a diiron subunit is common to all of them. 

Zinc oxide loses oxygen reversibly at high temperatures and assumes a yellow colour and an enhanced electronic conductivity. The charge carriers are electrons and the conductivity is described as -type (n=negative). It is not certain how the excess metal is accommodated, but it was originally suggested that the excess zinc is present in interstitial positions as two Zii+ ions or one Zn atom. The energy requirement would be more reasonable if the interstitial entity was assumed to be a Zn + ion and the excess electrons considered to be trapped in its nei bourhood, i.e. distributed over a number of... 

NO forms 1 1 low-spin complexes with Mn(TPP) and Mn(TPP)X (TPP = tetraphenylporphyrin, X = Cl, OAc, or CN)." and Mn(TPP)py takes up oxygen to form Mn(TPP)02, rather than Mn(TPP)(py)02. The authors suggest that this finding explains the fact that manganese(ii) haemoglobin does not bind oxygen reversibly, as the adjacent imidazole of the protein bonds to the metal and drives the... 

The cobalt porphyrins deserve special interest because of their biological relevance to vitamin Bi2 chemistry, their capacity to bind oxygen reversibly and their catalytic activities in various redox reactions of the axial ligands. Both the latter aspects will be included in the following descriptions. 

Preparation.1 This maroon-colored chelate is prepared from N,N -disalicylalethylenediamine and cobalt (II) chloride. It can bind oxygen reversibly (102 2Co) both in the solid state and in various solvents.2 Van Dort and Geursen3 used it as a homogeneous catalyst for the oxidation of phenols by molecular oxygen. In methanol solution the main products from phenols with a free para position are the p-benzoquinones (yields 15-80%). In chloroform solution radical-complex products are sometimes the main products. 

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