Electron-transfer reactions of polynuclear

The Electron-Transfer Reactions of Polynuclear Organotransition Metal Complexes... 

Dyotropic Rearrangements and Related cr-o- Exchange Processes, 16, 33 Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Electron-Transfer Reactions of Mononuclear Organotransition Metal Complexes, 23, I Electron-Transfer Reactions of Polynuclear Organotransition Metal Complexes, 24, 87 Fast Exchange Reactions of Group 1, 11, and 111 Organometallic Compounds, 8, 167 Fischer-Tropsch Reaction, 17, 61 Fluorocarbon Derivatives of Metals, 1, 143... 

Table 6 Rate constants and activation parameters for electron-transfer reactions involving polynuclear complexes. The expression in the column headed Rate is defined so that for a reaction of stoicheiometry a At + bBj +. .. —> products, the rate is given by R = —(lla)d[Ai]ldt, etc. For other conventions, see Table 2a... 

Carbene Complexes Carbonyl Complexes ofthe Transition Metals Cyanide Complexes of the Transition Metals Dinuclear Organometallic Cluster Complexes Electron Transfer in Coordination Compounds Electron Transfer Reactions Theory Electronic Structure of Organometallic Compounds Luminescence Nucleic Acid-Metal Ion Interactions Photochemistry of Transition Metal Complexes Photochemistry of Transition Metal Complexes Theory Polynuclear Organometallic Cluster Complexes. 

More recently, it has become clear that many polynuclear compounds undergo electron-transfer reactions, and several reviews devoted wholly or partly to this subject have appeared 1-4). Studies of the redox properties of polymetallic species can provide information on the nature of the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO), on the possible cooperativity between metal sites, on the existence of mixed-valence compounds, and on the ways in which one-electron (or, more rarely, two-electron) changes affect structure and reactivity. 

The chemistry of non-peroxo polynuclear cobalt(III) ammines is reviewed with particular emphasis on Werner s major contributions. Modern work in this area has shown that Werner s conclusions regarding the structures of these compounds are substantially correct in spite of the relatively primitive techniques he had available. There is much current interest in polynuclear cobalt(III) complexes because of their relationship to oxygen carriers and intermediates in electron transfer reactions. Modern techniques such as spectroscopy and x-ray diffraction have been used to determine the electronic and molecular structures of these compounds. 

In spite of the many modern techniques available to the chemist, the known chemistry of polynuclear cobalt (III) complexes is essentially that deduced by Werner 60 years ago. Since his work, no new polynuclear cobalt complexes have been prepared and characterized and no new reactions uncovered. Modem work in this area is being aimed at attaining a better understanding of the electronic structures inherent in polynuclear ions, which would be of value in a variety of active fields. The chemistry of polynuclear complexes is important in such new areas as synthetic oxygen carriers, electron transfer reactions, and transition metal catalysis. The fact that these new investigations are solidly based on Werner s pioneer investigations testifies to the genius with which he opened up a new area of coordination chemistry, with only the simple chemical techniques available to him. His work in the area of polynuclear cobalt(III) ammine complexes should continue to serve as a model of solid research for some time to come. 

An alternative starting point in chemically reacting fossil fuels is to treat them as if they were graphite. As noted earlier, graphite and larger polynuclear aromatic hydrocarbons are far from inert with respect to electron-transfer reactions, and thus the use of chemistry known to work for graphite may be of possible use in the investigation of coal, petroleum, and their derivatives. In the next two sections, we will discuss aspects of reduction and oxidation of carbonaceous solids and thereby parallel the chapters in this book on the reduction and oxidation of polynuclear aromatic hydrocarbon molecules. 

A prime feature of many of these systems and others with both Fe and Mo, are reversible electron transfer redox reactions and these give a clue to the importance of such polynuclear species in Nature. The compounds are made quite readily from FeCl2, FeCla, [FeClJ1- 2, or [Fe(SR)4]12 as shown in Fig. 17-E-5. 

Topics which have formed the subjects of reviews this year include photosubstitution reactions of transition-metal complexes, redox photochemistry of mononuclear and polynuclear" complexes in solution, excited-state electron transfer processes, transition-metal complexes as mediators in photochemical and chemiluminescence reactions, lanthanide ion luminescence in coordination chemistry, inorganic photosensitive materials," and photocatalytic systems using light-sensitive co-ordination compounds. Reviews have also appeared on the photoreduction of water.Finally, various aspects of inorganic photochemistry have been reviewed in a single issue of the Journal of Chemical Education. 

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