Linkage isomerization reactions

When the value for AV is negative, an increase in pressure will increase the rate of reaction. This has been observed for the linkage isomerization reaction (see Chapter 20)... 

By making a plot of In k versus P, it is possible to determine the volume of activation, AVT For the linkage isomerization reaction shown in Eq. (20.81), the volume of activation is -6.7 0.4cm3 mol-1. Therefore, it can be concluded that the mechanism shown in Eq. (20.81) is not correct. In fact, the negative volume of activation indicates that in the transition state the N02- does not become detached... 

In recent years, the photoinduced linkage isomerization reactions of bound nitrosyl appearing in different complexes have been... 

N-, 0-, and S-heterocyclic ligands also form [Os(NH3)5 t)2-(C,C)-L ]2+ complexes [L = 2,6-lutidine, 2,6-lutidinium, pyridinium, N-methylpyridinium, and lV-methyl-4-picolinium (85, 167), NJV -dimethylimidazolium (90), pyrrole (90, 179), IV-methylpyrrole (90, 179), thiophene (90,179), furan (90,179), and 1,3-dimethyluracil (72, 73)]. On oxidation to Os(III), arene ligands are rapidly lost from the coordination sphere, or in the case of the substituted arene ligands with good a donors, rapid linkage isomerization reactions occur (Section V,D). 

Given the facile linkage isomerization reactions for a large number of 7)2-bound ligands coordinated to [Os(NH3)5]2+, it is astonishing that... 

Scheme 14. Kinetics and thermodynamics of the linkage isomerization reactions of [Os(NH3)s(NR2Ph)]3+/2 +...

The strains due to the platinated macrocycle and the double helix are necessary to induce the linkage isomerization reaction. The DNA duplex containing the central sequence G AG CTC (G indicating the platinated guanine residue) in which the half-life of the intrastrand cross-link G AG is about 2 h, is taken as reference. The cleavage of the phosphodiester backbone at the level of the macrocycle decreases the rate of the rearrangement by at least a factor of ten. Over a period of 48 h, no rearrangement was detected when the 1,3-intrastrand cross-link is at the 3 - or 5 -end of the platinated strand in the duplex. 

In many transition metal complexes, geometrical and linkage isomerization reactions involve ligand substitution processes. One example of a photoin-duced linkage isomerization reaction, namely, the isomerization from an S-to an O-bonded sulfinato complex, Co(en)2(S02CH2CH2NH2)2+, has been studied as a function of pressure. The O-bonded product undergoes a thermal back reaction to the S-bonded complex and this system, shown in... 

Even though metal ions such as Ru(II), Ru(III) and Pt(II) are usually fairly inert to substitution with the type of nitrogen ligands found on nucleic acids, the close juxtaposition of intrabase, intrastrand and interstrand sites may facilitate metal ion movement so as to modulate mutagenic or anticancer effects. l ro clear examples of this have now been studied with ruthenium ammine complexes which point out the effects of both pH and electrochemical environments on these linkage isomerization reactions. 

Cobaltjpcntaamminenitrilotriacetato-eleclron transfer with hexaaquairon, 369 Cobalt, pentaammincnitrito-isomerization, 465 linkage isomerization reactions, 465 Cobalt, pentaamminenitro-dichloride... 

Linkage isomerization reactions, 465 Linked redox centres, 493 Liquid-liquid extraction, 538-549 Lowry, Thomas Martin, 16 Luteocobalt—see Cobalt, hexaammine-Luteocobaltic chloride —see Cobalt, hexaammine-, chloride... 

In general, the Ru(II) coordination site Is Identical to that of Ru(III) since both are normally substitution-inert and have fairly high affinities for most types of nitrogen ligands (12-14.16.25). However, this Is not always the case and the reduction of 4-(Ado)(HH3)5Ru(III) results In a rapid linkage Isomerization reaction (k 1.5 sec ) with the Ru(II) Ion presumably coordinating at the N(l) position (19,26). Similarly, reduction of 7-(l,3 4Ie2Xan)(NH3)5Ru(III)... 

Figure 32 Proposed mechanism for photoinduced linkage isomerization reactions of toluene solution of (TPP)Mn(ONO) (8). Reproduced with permission from Ref. (8). Copyright 2010 American Chemicai Society.

A number of linkage isomerism reactions have been studied for complexes of (HjNjjRu ". These exploit the fact that Ru(II) favors the softer donor atom and tt-acceptor systems, while Ru(III) favors harder donor atoms and does not participate in n bonding. Thus, one isomer of Ru(II) is prepared, then oxidized to Ru(III) by chemical or electrochemical methods and the isomerism is observed. The Ru(III) isomer can be reduced... 

Isomerization, A detailed investigation has been reported of catalysed and uncatalysed cis-trans and linkage isomerization reactions of [PdL2(tet)2] (L = a phosphine, tet = 5-methyl or 5-trifluoromethyl tetrazolate). This leads to the postulation of general mechanisms, involving five-co-ordinate transition states, that... 

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