Complexes of Dioxygen

Dioxygen (molecular oxygen 1 adducts of metal complexes have been studied extensively because of their importance as oxygen carriers in biological systems (Sec. V-1) and as catalytic intermediates in oxidation reactions of organic 

As discussed in Sec. II-l, the bond order of the 0-0 linkage decreases as the number of electrons in the anribonding 2pir orbital increases in the following order  

The decrease in the bond order causes an increase in the 0-0 distance and a decrease in the piOj). In fact, there is a good linear relationship between the O-O bond order and the (Oj) of these simple dioxygen compounds. 

Dioxygen adducts of more complex molecules are generally classified into two groups complexes which exhibit v(02) in the 1200-1 lOOcm region are called superoxo because their frequencies are clo.se to that of KO , and complexes whose are in the 920-750 cm are called peroxo because their frequencies are close to that of Na202- As will be shown later, there are many compounds which exhibit (02) outside of these regions. Thus, ihis distinction of dioxygen adducts is not always clear-cut. 

Structurally, the dioxygen adducts are classified into three types  

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All successful myoglobin and hemoglobin model compounds provide steric bulk on the distal side of the porphyrin ring with a hydrophobic pocket for complexation of dioxygen as well as a bulky alkyl imidazole proximal ligand... 

A picnic-basket porphyrin is reminiscent of the lacunar cyclidenes mentioned earlier, in which an alkyl chain tied the ends of the cyclidene together and formed a pocket for the complexation of dioxygen. Cobalt complexes of the picnic-basket porphyrins 31 bind dioxygen reversibly at room temperature with high oxygen affinities (84). The oxygen affinity increases as the basket size decreases (as determined by the length... 

There are many reviews that cover various aspects of oxidation. These include ones on alkane activation,166 catalytic selective oxidation,167 metal complexes of dioxygen,168 metal-catalyzed oxidation,169 biomimetic oxidations,170 oxidation with peroxides,171 catalytic oxidations with peroxides,172 catalytic oxidations with oxygen,173 oxidations with dioxiranes,174 and oxidation of pollutants.175... 

AH of the commercial inorganic peroxo compounds except hydrogen peroxide are described herein, as are those commercial organic oxidation reactions that are beheved to proceed via inorganic peroxo intermediates. Ozonides and superoxides are also included, but not the dioxygen complexes of the transition metals. 

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

Porphyrinic co-complexes as novel multinuclear catalysts for the reduction of dioxygen directly to water 97ACR437. 

Chemistry of transition metal complexes supported by hydrotris(pyrazolyl) borates and chemistry of dioxygen complexes based on these ligands 99YGK619. 

The hexamethylbenzene complex could be similarly deprotonated [54, 57] but the red complex obtained is then stable and its x-ray crystal structure could be recorded [55], showing a dihedral angle of 32° between the cyclohexadienyl plane and the exocyclic double bond (Fig. 5). This complex can also be cleanly obtained by the reaction of dioxygen with the 19e wostructural complex Fe CpfCgMeg) as shown in the preceding section. 

The structure and reactivity of dioxygen complexes of the transition metals, M. H. Gubelmann and A. F. Williams, Struct. Bonding (Berlin), 1983,55,1-65 (529). 

Complexes III and IV have Fe-porphyrin prosthetic groups (hemes), complex IV also contains copper atoms which are involved in electron transport. Complexes I, III, and IV use the energy of electron transport to pump protons out of the matrix so as to maintain a pH gradient and an electrical potential difference across the inner membrane required for ATP synthesis (see below and Appendix 3). It is important to remember that all dehydrogenations of metabolic substrates remove two protons as well as two electrons and that a corresponding number of protons are consumed in the final reduction of dioxygen (Figures 5, 6). 

Complex IV consists of 13 peptides, two heme A groups (cytochrome a and a3> and two or three Cu atoms (Table 2). It spans the inner membrane and protrudes into the intermembrane space. Complex IV catalyzes the reduction of dioxygen by oxidized cytochrome c, and four protons derived from the matrix are consumed in the reaction. 

Activation of Dioxygen by Cobalt Group Metal Complexes Claudio Bianchini and Robert W. Zoellner... 

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

Simandi LI (2003) Advances in catalytic activation of dioxygen by metal complexes. Kluwer, Dordrecht... 

The oxidation of phenol, ortho/meta cresols and tyrosine with Oj over copper acetate-based catalysts at 298 K is shown in Table 3 [7]. In all the cases, the main product was the ortho hydroxylated diphenol product (and the corresponding orthoquinones). Again, the catalytic efficiency (turnover numbers) of the copper atoms are higher in the encapsulated state compared to that in the "neat" copper acetate. From a linear correlation observed [7] between the concentration of the copper acetate dimers in the molecular sieves (from ESR spectroscopic data) and the conversion of various phenols (Fig. 5), we had postulated [8] that dimeric copper atoms are the active sites in the activation of dioxygen in zeolite catalysts containing encapsulated copper acetate complexes. The high substratespecificity (for mono-... 

Bianchini C, Zoellner RW. 1997. Activation of dioxygen by cobalt group metal complexes. Advinorg Chem 44 263. 

Le Mest Y, L Her M. 1995. Electrochemical generation of a new type of dioxygen carrier complex. Reversible fixation of dioxygen by the highly electron-deficient two-electron oxidized derivative of a dicobalt face-to-face diporphyrin. J Chem Soc Chem Commun 1441. 

Vasudevan P, Santosh, Mann N, Tyagi S. 1990. Transition metal complexes of porphyrins and phthalocyanines as electiocatalysts for dioxygen reduction. Transition Metal Chemistry, 15, 81-90. 

Infra-red absorption bands have been reported for a wide range of dioxygen complexes (77). In general, the only band observed for type 11(G) complexes is in the range 800—900 cm , which has been assigned to the 0-0 stretch (164). This assignment has been confirmed for... 

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