The kinetic isotope effects (KIEs), k H /k D , have been determined for reaction of CH 3 I/CD 3 I with several organoplatinum(II) complexes [PtR 2 (NN)], in which the bidentate NN ligand is bpy=2,2 0 -bipyridine, t Bu 2 bpy=4,4 0 -bis(tert-butyl)-2,2 0 -bipyridine, phen=1,10-phenanthroline, or Me 2 phen=2,9-dimethyl-1,10-phenanthroline, at different temperatures and in solvents having different polarities. The values obtained for the secondary R-deuterium KIEs are close to 1 and are dependent on the solvent; values of up to 7-10% larger are obtained for the reactions in the polar solvent acetone as compared to those obtained in the nonpolar solvent benzene. The data also indicate that the steric crowding around the squareplanar coordination sphere of the platinum(II) complexes with the ligand Me 2 phen results in higher KIEs. The reactions involving dimethylplatinum(II) complexes, [PtMe 2 (NN)], were fast, and a 1:1 molar ratio (of complex and reagent) technique was successfully used to measure the rate constants accurately by conventional UV-visible spectroscopy. It is shown that there are significant advantages to measuring the reaction rates under second-order condition, as compared to the usual pseudo-first-order method.

The mechanism of oxidative addition of ethyl iodide to [PtMe 2 (2,2 0 -bipyridine)], 1, has been investigated by product analysis and by study of secondary deuterium kinetic isotope effects (KIEs), using the reagents C 2 H 5 I, C 2 D 5 I, CH 3 CD 2 I, and CD 3 CH 2 I. The reactions in acetone and benzene give [PtIMe 2 Et(bipy)], mostly as the product of trans oxidative addition, but with some of the isomeric product of cis oxidative addition and some [PtIMe 3 (bipy)], resulting from methyl group transfer. The reaction in benzene is light-sensitive, giving additional major products [PtI 2 Me 2 (bipy)] and [PtIMe 2 -(OOEt)(bipy)], as well as several minor products indicative of a photochemically initiated free-radical reaction. No H/D exchange within the ethyl group was observed in any of the products. The dark reactions in acetone and benzene follow second-order kinetics, with large negative values of the entropy of activation, indicating the S N 2 mechanism of oxidative addition of ethyl iodide to 1. However, for reaction with C 2 H 5 I vs C 2 D 5 I, values of the KIE k H /k D range from 1.32 to 1.72 in acetone and from 1.44 to 1.90 in benzene solution, and studies with CH 3 CD 2 I and CD 3 CH 2 I show that Rand β-deuterium KIEs make about equal contributions to the overall KIE. These are the first reports of isotope effects on the rate of oxidative addition reactions of ethyl halides, and the high values of the secondary deuterium KIE were unexpected for the S N 2 mechanism. Possible reasons for these observations are discussed. Scheme 2. a Free-Radical Chain Mechanism of Oxidative Addition with Possible Formation of Alkylperoxo Complexes of Platinum(IV) a R = i-Pr.

Secondary α-deuterium (α-D) kinetic isotope effects (KIEs) have been determined for the reactions of the (diimine)diarylplatinum(II) complexes [Pt(p-MeC6H4)2(NN)] (NN = bipyridine (bpy), 1a; NN = 4,4‘-dimethyl-2,2‘-bipyridine (Me2bpy), 1b; NN = 4,4‘-di-tert-butyl-2,2‘-bipyridine ( t Bu2bpy), 1c) with MeI in acetone solvent at different temperatures. Consistent with an SN2-type mechanism, very small normal secondary deuterium isotope effects (k H/k D) values of 1.00−1.11 are obtained for the reactions studied. The trends in KIEs and activation parameter values are discussed in terms of recent experimental and theoretical investigations. The platinum(IV) products have been fully characterized using 1H and 13C NMR spectroscopy.

A new tetramethylplatinum(IV) complex [PtMe 4 (dppf)] [2; dppf = 1,1Ј-bis(diphenylphosphanyl)ferrocene], as the first platinum(IV) complex to contain a chelating dppf ligand, was prepared by the reaction of the known dimeric tetramethylplatinum(IV) complex cis,cis-[Me 4 Pt(µ-SMe 2 ) 2 PtMe 4 ] (1) with the biphosphane ligand dppf (2 equiv.) at room temperature by replacement of the SMe 2 ligands with the P ligating atoms of dppf. The single-crystal X-ray structure of complex 2 revealed that the dppf chelating ligand is arranged close to the "synperiplanar-eclipsed" conformation, with a Cp(centroid)···Fe···Cp(centroid) twist angle of 17.6°and a dppf bite angle, P1-Pt1-P2, of 95.77(3)°. This is in contrast to the usually preferred "synclinal-staggered" conformation, in which the Cp(centroid)···Fe···Cp(centroid) twist angle is close to 36°as found in Pt II complexes with chelating dppf ligands,

In various pharmaceutical and food industries, sulfite is utilized for the inhibition of nonenzymatic and enzymatic browning. Also, in brewing industries, it acts as an antioxidizing and antibacterial agent. Several toxic and adverse reactions, including vitamin deficiency, hypersensitivity, and allergic diseases, have been attributed to sulfite ingestion that may cause dysbiotic oral and gut microbiota events. Thus, the content of sulfite in foods must be controlled and monitored, and it is essential to find a specific, reproducible, and sensitive method to detect sulfite. Some analytical solutions are being tested to quantify sulfite. However, due to their advantage over traditional techniques, electroanalytical techniques are attracting much attention because they are simple, fast, affordable, and sensitive to implement. In addition, by the electrode modification, the morphology and size can be controlled, resulting in the miniaturization to be used in portable electrochemical devices. Therefore, the present review addressed some articles on the electrooxidation of sulfite from real samples using various electrochemical sensors.