Ligand substitution reactions coordinated ligands

Ligand substitution reactions (see Ligand Substitution) are at the heart of many catalytic transformations, since creation of vacant coordination sites oftentimes requires liberation of one or more ligands from the coordination sphere of the metal. Important and/or industrially relevant processes using organoruthenium catalysts include the... 

The ligand substitution reaction of CH2CI2 in Cp(NO)(Ph3P)Re(ClCH2Cl) " by thiophene and 2,5-dimethylthiophene yields the (S) coordinated complex of type... 

Ligand substitution reactions at low-valent four-, five- and six-coordinate transition metal centres. J. A. S. Howell and P. M, Burkinshaw, Chem. Rev., 1983, 83, 557-599 (468). 

The results presented in Section IV.D.l show that the net loss of the dioxorhenium(VII) species, and the ultimate formation of the phosphate R3PO, must occur in two stages because the rate of reaction (17) shows a direct first-order phosphine dependence. That said, the chemical mechanism is still open to discussion does the first step entail abstraction of an oxo oxygen or addition to it If the former, the cycle is completed by PR3 coordination to a four-coordinate rhenium intermediate if the latter, the addition step is then followed by yet another ligand substitution reaction. The alternatives are presented in Schemes 1 and 2. 

Langford and Gray proposed in 1965 (13) a mechanistic classification for ligand substitution reactions, which is now generally accepted and summarized here for convenience. In their classification they divided ligand substitution reactions into three categories of stoichiometric mechanisms associative (A) where an intermediate of increased coordination number can be detected, dissociative (D) where an intermediate of reduced coordination number can be detected, and interchange (I) where there is no kinetically detectable intermediate [Eqs. (2)-(4)]. In Eqs. (2)-(4), MX -i and... 

The traras-effect has been defined as the effect of a coordinated group on the rate of substitution reactions of ligands trans to itself See Basolo, E. Pearson, R. G. Prog. Inorg. Chem. 1962, 4, 381. 

The coordinative modification is carried out using complexes in the oxidation state 2 +, not 3 +, for facilitating the ligand substitution reactions leading to the binding (192,196). The reason is that the... 

Photocalorimetry offers a convenient alternative to other methods of AH determination and, in some instances, may be the only practical method. The ligand substitution reactions of robust Werner-type complexes are a case in point. Conventional thermochemical measurements are complicated by the slowness of the substitution process and/or by competing reactions. Some of these same complexes, however, undergo clean photosubstitutions with high quantum yields and thus are excellent candidates for photocalorimetry. Examples include [Cr(NH3)6]3+, [Cr(CN)6]3-and [Co(CN)6]3-.192 Photocalorimetric measurements of AH have also been obtained for isomerization and redox reactions of coordination compounds.193194... 

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