Coordinated ligand reactions transfer

The rate also varies with butadiene concentration. However, the order of the rate dependence on butadiene concentration is temperature-de-pendent, i.e., a fractional order (0.34) at 30°C and first-order at 50°C (Tables II and III). Cramer s (4, 7) explanation for this temperature effect on the kinetics is that, at 50°C, the insertion reaction to form 4 from 3, although still slow, is no longer rate-determining. Rather, the rate-determining step is the conversion of the hexyl species in 4 into 1,4-hexadiene or the release of hexadiene from the catalyst complex. This interaction involves a hydride transfer from the hexyl ligand to a coordinated butadiene. This transfer should be fast, as indicated by some earlier studies of Rh-catalyzed olefin isomerization reactions (8). The slow release of the hexadiene is therefore attributed to the low concentration of butadiene. Thus, Scheme 2 can be expanded to include complex 6, as shown in Scheme 3. The rate of release of hexadiene depends on the concentra-... 

B35. G. Wilkinson, R. D. Gillard and J. A. McCleverty (eds) Comprehensive Coordination Chemistry, Vol. 1. Theory and Background, Pergamon, Oxford, 1987. Chapter 7.1, M. L. Tobe (Substitution) Chapter 7.2, T. J. Meyer and H. Taube (Electron Transfer) Chap. 7.4 D. St. C. Black (Reactions of Coordinated Ligands). 

A cis-coordinating ligand is apparently required to bind and activate MeOH so that a methoxy group is transferred to the polyketone chain and a hydride remains on palladium. Two mechanisms are possible for this reaction (i) nucleophilic attack by the oxygen at the acyl carbonyl with concerted formation of Pd-H (ii) formation of a Pd(acyl) (methoxy) complex and H, followed by reductive elimination and subsequent proton attack on a Pd center. No experimental evidence favoring either mechanism in ethene/CO copolymerisation has been provided so far. 

These states lie on the reaction coordinate of proton transfer to a hydride ligand of cluster [W3S4(PH3)6H3]+ according to eq. (10.23). 

Reaction 4 shows that the ruthenium center with three coordinated carbonyls can transfer one such ligand to the piperidine (presumably coordinated). The mechanism suggested for the acetate complex includes exactly analogous steps (Reactions 6 and 7). The kinetics for the hydride-catalyzed system, however, are quite different and show a first-order dependence in Ru and a more complex dependence on CO (Figure 4). Further, no autocatalysis is evident. 

The most widely studied and most exploited of inorganic ECL reactions, however, is that of tris(2,2 -bipyridine) ruthenium(II), [(bpy)3Ru]2+. The emissive excited state is a metal-to-ligand charge transfer state of triplet spin multiplicity the emission yield is approximately 10% and oxygen does not significantly quench the luminescence [22], The complex can exhibit ECL following sequential oxidation at the metal center and reduction of the coordinated 2,2 -... 

In the Feaq3 +/Craq2 + reaction, the inverse dependence on [H + ] has provided strong evidence for OH-bridged transition state for electron transfer. Similarly useful information has been obtained in a large number of cases involving acid-base equilibria of coordinated ligands. 

Some intermolecular reactions involving the coordinated ligands (e.g., hydrogen or proton transfer) may be fast enough to compete with the excited state decay. However, except for a few cases [e.g., Ru(bpy)2(CN)2 34 and Ru(bpy)2 (bpy-4,4 -(COOH)2 )2 + 35)] reactions of this kind have not yet been well documented for transition metal complexes, although they are very common for organic molecules19, 36,37. ... 

Historically, the development of ET theory has been based on inorganic systems, in which the (metal-ion) redox centers are surrounded by coordinated ligands [52]. In those cases in which no new metal-ligand bonds are formed or bond breakage is observed, the interaction between the redox centers is weak (usually Hda < 200 cm-1), and such reactions are conventionally designated as outer-sphere (OS) electron transfer [52, 53]. 

Identify reaction steps in Fig. 8.2 that illustrate the concepts of (a) the trans effect, (b) nucleophilic attack on a coordinated ligand, (c) insertion of alkene into an M-H bond, and (d) intramolecular electron transfer. 

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