Polynuclear transition metal complexes dinuclear

The present review deals with the anchoring/grafting of transition metal complexes (mononuclear, dinuclear, or polynuclear) on inorganic supports except zeolites, which are covered in Section A.2.3. Catalysts with anchored complexes which are the analogs of homogeneous catalysts are described in Section A.2.2.1.4. 

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. 

Transition metal complexes can be classified into mononuclear and dinuclear (or polynuclear) complexes. Depending on the effective atomic number of the metal and the kind of ligands, the complexes can be mononuclear like Fe(CO)s or dinuclear like Co2(CO)g. The characteristic feature of dinuclear metal complexes is that they have a metal-metal bond in their structure. The metal-metal bond is cleaved oxidatively by the reaction with some covalent molecules to form a-bonded complexes. This reaction is regarded as a one-electron oxidation. This is another way of forming o-bonded complexes and is useful for organic synthesis. 

There is much current interest in the synthesis and reactivity of transition metal complexes containing P atoms or aggregates. In particular, (/i-t -P2) dinuclear and cyclo (t/ -Ps) mononuclear complexes have received special attention, on account of their ability to act as complex ligands in the formation of polynuclear complexes. Whereas reported syntheses of these... 

Precatalytic Reactions and Xpre. The catalyst precursor must transform under reaction conditions into intermediates to obtain an active system. This transformation may involve, in a small number of cases, only a single elementary step, for example, the dissociation of a ligand from a transition-metal complex. However, a series of elementary reaction steps are usually required to convert the catalyst precursor. Useful examples include (1) the degradation of a polynuclear precursor to mononuclear intermediates, (2) the modification of a precursor with a ligand L which is used to control selectivity, and (3) the transformation of finely divided metal. The characteristic time scale for the precatalytic reaction will be denoted tpre, and the instantaneous reaction rate will be denoted Ppre- Precatalytic phenomena and the associated induction periods have been directly monitored in a number of in situ spectroscopic studies using a variety of mononuclear, dinuclear, polynuclear, and metallic precursors (11). 

An interesting feature of hydrido transition metal-PF3 complexes is that apart from a few dinuclear systems (Section VI) only mononuclear systems are so far known and there is as yet no corresponding chemistry analogous to that of polynuclear carbonyl hydrido compounds. The trifluorophosphine metal hydrido compounds are usually highly acidic and can readily form metallate ions such as [M(PF3)m]x and [MH(PF3) r. 

The hexaaza [ISJaneNe forms complexes with transition metal ions and with certain alkali and alkaline earth and lanthanide ions. For the higher aza macrocycles with seven or more donor atoms, dinuclear complexes become possible. A systematic investigation of both the structural and thermodynamic aspects of copper complexes formed with the larger polyaza macrocycles from heptaaza to dodecaaza has been published. All of the macrocycles were found to form hydroxo species as well as polynuclear complexes. A number of structures have been determined for the higher polyaza macrocycles, both in complexed and noncomplexed forms, and structures range from highly boat shaped to nearly planar. ... 

Future applications of the AOM will include the analysis of the optical spectra and magnetic properties of transition metal ions located in polynuclear systems. Calculations on infinite structures (chains) have already been reported [110], and a parametrization scheme for the evaluation of orbital-exchange parameters in magnetically coupled dinuclear complexes was presented recently [111]. Another interesting aspect concerns the dynamic extension of the AOM which allows, for example, Jahn-Teller energies to be calculated [112, 113]. Finally, it should be... 

Eliminations from Os(CO)4RR occur by dinuclear mechanisms only if either R or R is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO)4H2, the vacant site is created by dissociation of CO. With Os(CO)4-(H)CH the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO)4(H)C2H and various polynuclear ethyl osmium derivatives show that (3-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 

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