Leela Jain

Bio: Leela Jain is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Platinum & Carbene. The author has an hindex of 4, co-authored 5 publications receiving 277 citations. Previous affiliations of Leela Jain include Indian Institutes of Technology.

The organic-chemistry of platinum(iv)

Abstract: Publisher Summary This discusses the salient discoveries made recently in the organic chemistry of platinum(IV). Investigations on monoorganoplatinum(IV) compounds are scanty, probably because of the absence of straightforward preparative methods and also because of their poor solubilities in organic solvents. Bromination of platinum(II) complexes having amine, tertiary phosphine, or arsine ligands containing at least one olefinic group often yields metallated platinum(IV) complexes. The first diorganoplatinum(IV) compound, [PtMe 2 I 2 ] n , was isolated by treating [PtCl 6 ] 2– with methylmagnesium iodide in diethyl ether. The isomers containing a water molecule trans to a methyl group are labile and crystallize from the solution as [PtMe 2 (X)(gly)] 2 (X = Br) species. The reaction of alkyl iodides with cis-[Pt(tol) 2 ,(py) 2 ] is accompanied by the displacement of a tolyl group and the formation of diorganoplatinum(IV) complexes. The reaction of methyl iodide with mercapto-bridged dinuclear platinum(II) complexes, [Pt(μ-SMe)R(PMe 2 Ph)] 2 (R=Me, Ph), involves dinuclear platinum(IV) intermediates, which ultimately yield mononuclear platinum(II) or (IV) complexes, depending on the nature of R. Nitrous oxide was the only gaseous product formed during the reaction. Pyrolysis of dimethylplatinum(IV) compounds yields methyl halide or ethane, depending on the configuration of the complex. Halides, pseudohalides, and related compounds are among the best known organoplatinum(IV) derivatives. Trimethylplatinum halides and pseudohalides are tetrameric in the solid state as well as in solution. Oxidative addition of chlorine to platinum(II) carbene complexes affords the corresponding platinum(IV) compounds when the carbene ligand contains only alkyl groups.

The Organic Chemistry of Platinum(IV)

Abstract: Publisher Summary This discusses the salient discoveries made recently in the organic chemistry of platinum(IV). Investigations on monoorganoplatinum(IV) compounds are scanty, probably because of the absence of straightforward preparative methods and also because of their poor solubilities in organic solvents. Bromination of platinum(II) complexes having amine, tertiary phosphine, or arsine ligands containing at least one olefinic group often yields metallated platinum(IV) complexes. The first diorganoplatinum(IV) compound, [PtMe 2 I 2 ] n , was isolated by treating [PtCl 6 ] 2– with methylmagnesium iodide in diethyl ether. The isomers containing a water molecule trans to a methyl group are labile and crystallize from the solution as [PtMe 2 (X)(gly)] 2 (X = Br) species. The reaction of alkyl iodides with cis-[Pt(tol) 2 ,(py) 2 ] is accompanied by the displacement of a tolyl group and the formation of diorganoplatinum(IV) complexes. The reaction of methyl iodide with mercapto-bridged dinuclear platinum(II) complexes, [Pt(μ-SMe)R(PMe 2 Ph)] 2 (R=Me, Ph), involves dinuclear platinum(IV) intermediates, which ultimately yield mononuclear platinum(II) or (IV) complexes, depending on the nature of R. Nitrous oxide was the only gaseous product formed during the reaction. Pyrolysis of dimethylplatinum(IV) compounds yields methyl halide or ethane, depending on the configuration of the complex. Halides, pseudohalides, and related compounds are among the best known organoplatinum(IV) derivatives. Trimethylplatinum halides and pseudohalides are tetrameric in the solid state as well as in solution. Oxidative addition of chlorine to platinum(II) carbene complexes affords the corresponding platinum(IV) compounds when the carbene ligand contains only alkyl groups.

“Turning Over” Definitions in Catalytic Cycles

Abstract: “Indeed, the catalytic activity, for a valid comparison, must be referred to the number of exposed surface atoms of a specified kind. Thus a convenient way to express catalytic activity is by means of a turnover number equal to the number of reactant molecules converted per minute per catalytic site for given reaction conditions.” With these words of Boudart the first definition of what later was called the Turnover Frequency (TOF) entered into the realm of heterogeneous chemistry. It was a term borrowed from enzymatic kinetics, and slowly passed to homogeneous catalysis. Nowadays it is a ubiquitous term, focusing strictly on the catalytic center, as distinct from the classical term “rate of reaction”, which emphasizes the generation of products or the consumption of reactants. Despite its utility and common use, the TOF concept is still not well-defined and leads to confusion. IUPAC’s gold book, the most authoritative source of chemical terminology, has a very concise definition of the turnover frequency: “Commonly called the turnover number, N, and defined, as in enzyme catalysis, as molecules reacting per active site in unit time.” This description of the TOF has two main problems. The first is the difficulty of providing a one-to-one correspondence between name and function, since (as appeared in Boudart’s paragraph) the terms “turnover frequency” (TOF) and “turnover number” (TON) seem to have one and the same meaning. However, in typical catalytic jargon, both expressions have very different connotations. Sometimes also the terms “turnover rate” and “catalytic constant” (kcat) are used interchangeably in the literature with the same meaning. To make matters worse, the TOF is occasionally considered a rate-constant, since the rate of reaction (r = TOF × [Cat]) depends on the catalysts concentration. However, the TOF itself can depend on the concentration of reactants and products even at saturation, and in this sense it is closer to a rate than to a kinetic constant. In spite of this, from a strict terminological stance the TOF is a frequency, with units of time−1. All this debate evidently resembles the biblical story of the Tower of Babel and the confusion of languages. The second problem of IUPAC’s and Boudart’s definitions is a recurring expression of the TOF as a function of the number of reactants consumed, or even of the products generated. In most cases it is indeed an accurate way to derive the TOF, but for instance in bimolecular reactions this is not the case. Moreover, and from a philosophical perspective, when expressing the TOF as a function of produced or consumed molecules, the focus of the measure goes back to those molecules instead of emphasizing the role of the catalyst (see Scheme 1).