Conproportionation

The diarsine and arsine/phosphine analogues of dppm have been used to prepare bridged diplatinum(I) complexes, in both cases with terminal chloro ligands.116,117 Both complexes react with carbon monoxide to produce carbonyl-bridged species. The mixed thio/phosphine ligand Ph2PCH2SMe (PS) also forms a diplatinum(I) complex by conproportionation of its dichloroplat-inum(II) complex with [Pt(dba)2].118 This dimer reacts with carbon monoxide to produce an unsupported dimer [PtCl(PS)(CO)]2 with the thioether arm of the Ph2PCH2SMe unbound. 

This reaction is endothermic by 12 kJ mol-1. The formal monoamine conproportionation reaction 38... 

We now consider heteroaromatic diamines with the condition that an amino group is not a to a heterocyclic nitrogen. The only thermochemical data we can find are for 2,8-diamino acridine for which the solid-phase enthalpy is 127 7 kJmol-1. In the absence of significant substituent and solid state effects, thermoneutrality is expected for the conproportionation reaction 40 that produces diaminoarenes from monoamine derivatives. 

This is an example of conproportionation. The net results were CdSe deposits that required thermal treatments to obtain optimal photoactivity due to the presence of elemental Se [129]. The initial solution to this problem was to search for a Se precursor in a lower oxidation state, such as selenosulfite, SeSOs [132]. The nominal oxidation state of Se in this species is zero, as it is formed by the reaction of elemental Se with sulfite ... 

Use of selenosulfite in combination with EDTA complexed Cd, eliminated the elemental Se contamination, and improved the photoresponse of the as-formed deposits [132]. A second method for avoiding conproportionation, also suggested by Skyllas-Kazacos, was to use a cyanide solution to dissolve elemental Se (or Te) and high concentrations of CdCU [127]. Again, the Se was felt to be in the zero oxidation state. 

The solution to the conproportionation problem was adoption of the program shown in Fig. 20, where the Te atomic layers were deposited using the two steps described in the last section initial deposition of several atomic layers worth of Te at a potential sufficiently positive that no Te ... 

The conproportionation reaction of aromatic aldehydes or aldehydes lacking a-hydrogens under alkaline conditions, yielding an alcohol and an acid. 

Although the values of T igp are relatively large in water and in methanol, a finite amount of Cu(I) exists in any Cu(II) solution that is in contact with metallic copper. In fact, the molecularity associated with dictates that the fraction of copper in solution in the form of Cu(I) increases as the total concentration of solvated copper ion decreases. Thus, at micromolar levels in water, for example, the two oxidation states can be maintained in essentially equal amounts. In acetonitrile, the equilibrium for reaction 5 lies far to the left so that solvated Cu(I) is readily generated by placing copper metal in contact with a Cu(II) solution (conproportionation). As a consequence, the Cu(I) salt, [Cu(CH3CN)4]C104, is easily prepared [18] and is temporally stable. 

A key precursor to multidentate arsines is o-bromophenyldichloroarsine, which may be similarly obtained if the diazotization is conducted in glacial acetic acid and the source of arsenic is AsCl (equation 34).107,10 Conproportionation of PhAsCl, and PhAsO gives Ph2AsCl (contaminated with PhAsCl2 and PhjAs).106... 

The mechanism will vary in precise detail according to the metal. In the case of ruthenium complexes, it is quite common to observe a conproportionation and the formation of a ruthenium(iv) intermediate. In other cases, the unavailability of the metal oxidation states precludes reaction. For example, cobalt(m) complexes of cyclam cannot be oxidised to imine species because although a cobalt(ii)/cobalt(m) couple is possible, the cobalt(n) oxidation state is not accessible under oxidative conditions. In the case of metal ions which can undergo two oxidation state changes, alternative mechanisms which do not involve radical species have been suggested. 

The synthesis of fluotrimazole starts from m-xylene. Peroxide catalyzed perchlorination converts this to m-trichloromethyl-benzo-trichloride. m-Trichloromethyl-benzotrifluoride is then obtained by selective chlorine/fluorine exchange. This key product is also readily accessible on a technical scale by conproportionation of the two corresponding m-trihalomethyl-benzotrihalogenides. Friedel-Crafts reaction with benzene leads to trifluoromethyl-tritylchloride, which reacts smoothly with 1,2,4-triazole in polar solvents to give fluotrimazole. 

Osakada, K. Hamada, M. Yamamoto, T. Inter-molecular alkynyl ligand transfer in Pd(II) and platinum(II) complexes with CCC02R and CCPh ligands. Relative stability of the alkynyl complexes and conproportionation of dialky-nyl and diiodo complexes of these metals. Organometallics 2000, 19, 458—468. 

In contrast Shilov and his group propose a very different mechanism (Scheme 20), which involves a bridging dinitrogen and four vanadium atoms, each acting as a one-electron reductant (contrasting to Schrau-zer s proposal that vanadium acts as a two-electron reductant). The hydrazine may then be reduced to ammonia. On theoretical grounds Shilov considers that dA metal ions would make the best dinitrogen reducers in these binuclear systems (44), and there is ample evidence to support the formulation of vanadium(II) dinuclear species in aqueous solution. However, Shilov postulates and finds vanadium(III) products, which Schrauzer ascribed to a conproportionation (289) as shown in Eq. (78). 

Scheme 1.11 The preparation of structure 10 from a mixture of ligand subcomponents (top) and through the covalent conproportionation of subcomponents from preformed structures 11 and 12 (bottom).

Complex VII (137) seems quite clearly to be of the average valency type (Fig. la, curves 3,3). Again, there is a near infrared electronic absorption band, but it is narrower than that expected for an intervalence band and is not subject to solvent shifts. The conproportionation constant is large (Kcoa > 1013) and the valences are delocalized at least on the infrared time scale (kex > 1013 sec ). 

The detection of [PhIO(salen)Mn-0-Mn(salen)OIPh]2+ in the ESMS experiments was the first direct observation of the conproportionation of Mnm and Mnv-oxo species as the mechanism for parking the catalytically active complex in a more persistent form, the mechanism postulated earlier by Kochi et al. [102]. The microscopic reverse process, the disproportionation of the p-oxo bridged dinuclear complex, would lead to the release of [0=Mnv(salen)]+. This... 

The second set of experiments involved conproportionation reactions with controlled acidity. A ten-fold excess of the mild oxidant IF5 was added to a solution of I2 in basic HF and the acidity was gradually increased by quantitative stepwise additions of SbF5. The same general features emerged as for the first set of experiments. IF5 and I2 co-existed in basic HF. Increase in acidity led to equilibrium formation firstly of It and IJ, then of IJ and It and, in strongly acidic HF, It was the only species present other than excess IF5. 

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