Mechanisms for Acceleration of Halide Anation Reactions of Platinum(IV) Complexes. REOA versus Ligand Assistance and Platinu(II) Catalysis without Central Ion Exchange

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Abstract

Chloride anation of trans-Pt(CN)4ClOH2− has been studied with and without Pt(CN)42− present at 25.0 °C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)42− is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)4···OH22−, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)4···OH3−.

Reaction between PtCl5OH2− and chloride is accelerated by Pt(CN)42− and gives PtCl62− as the reaction product. The rate law is givenat 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)42− in this reaction is very similar to that of the assisting halide in the halide assisted anations. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl−] shows that formation of a bridged intermediate of the type Pt(II)Cl4ClPt(IV)(CN)4OH23− is formed in the initial reaction step, not five-coordinated PtCl53−.

Detaljer

Författare
Enheter & grupper
Externa organisationer
  • Lund University
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Oorganisk kemi

Nyckelord

  • Reaction Mechanism, Platinum(IV), Ligand substitution , REOA, Reductive elimination/Oxidative addition, Platinu(II) catalysis, Ligand assistance, Kinetics
Originalspråkengelska
Sidor (från-till)175-183
TidskriftInorganica Chimica Acta
Volym121
Utgåva nummer2
StatusPublished - 1986 nov 17
PublikationskategoriForskning
Peer review utfördJa