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Issue 8, 1980
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Mechanistic studies of some oxidative-addition reactions: free-radical pathways in the Pt0–RX, Pt0–PhBr, and PtII–R′SO2X reactions (R = alkyl, R′= aryl, X = halide) and in the related rhodium(I) or iridium(I) systems

Abstract

Spin-trapping studies, using R′NO (R′= But or C6HMe4-2,3,5,6), have been carried out on: (i) various Pt0–alkyl halide (RX) systems, e.g.[P(PR″3)n](R″= Et or Ph, n= 3 or 4)–Mel; (ii) a number of PtII–sulphonyl or acyl halide reactions, e.g. cis-[PtMe2(PtMe2Ph)2]–p-MeC6H4SO2X; and (iii) several RhI– or IrI–alkyl halide additions. In most cases the appropriate nitroxyl spin adduct R(R′)N·O or R′(p-MeC6H4SO2)N·O [but not R-(R‴CO)N·O] is observed by e.s.r. spectroscopy. In conjunction with appropriate control experiments, this leads to the unequivocal conclusion that free radicals are implicated in systems (i)(X = Cl, Br, or l) and (ii)(X = Cl or Br). By means of the nitrone PhCH[double bond, length half m-dash]N(O) But, a platinum(I) complex has been trapped during the course of the [Pt(C2H4)(PPh3)2]–Etl reaction; its formulation as [Pt{CH(Ph)N·O(But)}l(PPh3)2] is based on e.s.r. data. Trityl chloride adds to [Pt(PPh3)3][but not so rapidly to a rhodium(I) or iridium(I) substrate] to give Ph3Ċ and [PtCl2(PMe2Ph)2]; Ph2CHBr and [Pt(PPh3)3] give (Ph2CH)2 as the principal organic product. Galvinoxyl inhibits the addition of p-MeC6H4SO2Cl to [PtMe2(PMe2Ph)2]. Azobis(isobutyronitrile) under photolysis catalyses the oxidative addition of PhBr to [Pt(PPh3)3]. Whereas the addition of Mel to [Pt(PPh3)3] in benzene leads exclusively to the 1 : 1 adduct, in tetrahydrofuran by far the major product is [Ptl2(PPh3)2]. It is concluded that reactive halides RX add to a platinum(0) substrate via a geminate radical pair [PtILn(X)]+ R˙, whereas with less reactive halides, or in the sulphonyl halide–PtII addition, a radical-chain mechanism is operative.

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Article type: Paper
DOI: 10.1039/DT9800001448
Citation: J. Chem. Soc., Dalton Trans., 1980, 1448-1456
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    Mechanistic studies of some oxidative-addition reactions: free-radical pathways in the Pt0–RX, Pt0–PhBr, and PtII–R′SO2X reactions (R = alkyl, R′= aryl, X = halide) and in the related rhodium(I) or iridium(I) systems

    T. L. Hall, M. F. Lappert and P. W. Lednor, J. Chem. Soc., Dalton Trans., 1980, 1448
    DOI: 10.1039/DT9800001448

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