1887

n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Oksidatiewe addisie van jodometaan aan Rh(I)-neokupferraatkomplekse as model vir ’n unieke toepassing van Tolman se beginsels - oorspronklike navorsing

Volume 38 Number 1
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173

Abstract

Oksidatiewe addisie is van groot belang in katalitiese prosesse. Die Monsantoproses vir die produksie van asynsuur is een van die bekendste voorbeelde hiervan. In ’n poging om onsekerhede betreffende die meganisme van oksidatiewe addisie op te klaar, is ons groep geïnteresseerd in die manipulering van die reaktiwiteit van die Rh(I)-senter van die [Rh(LL′)(CO)(PR3)] tipe komplekse waar LL′ enkelgelaaide bidentate ligande en PR3 verskillende monodentate fosfienligande verteenwoordig. Hierdie fosfienligande varieer wat hulle elektroniese en steriese eienskappe betref en het soos die ander ligandvariasies ’n beduidende effek op die reaktiwiteit van die metaalsenter.
By die neokupferraatsisteem verloop oksidatiewe addisie met jodometaan via twee kompeterende paaie. Die k1-pad impliseer ’n nukleofiele aanval op CH3I wat tot ’n 16-elektron, vyfgekoördineerde intermediêr lei, waarvan die mate van ioonskeiding oplosmiddelafhanklik is. Die oplosmiddelondersteunde k2-pad kan as ’n uitsonderlike oksidatiewe addisie kataliseverskynsel beskou word. Deur die effek van variërende steriese en elektroniese eienskappe van die fosfienligande op die oksidatiewe addisie van die neokupferraatsisteem te bestudeer, kon ’n steries-elektroniese model, ontwikkel deur Tolman, toegepas word op die oksidatiewe addisiereaksies om die totale effek van die fosforligand in ’n bepaalde sisteem te evalueer. ’n Poging is aangewend om die fosfieneienskappe te kwantifiseer. Dit kan tot groter begrip rakende die samestelling en ontwerp van kataliste lei.

Die volgende afkortings word in die teks gebruik: opoH = 2-oksopiridien-1-olaatanioon; quinH = 2-karboksikinolien; oxH = oksien (8-hidroksikinolien); dmavkH = dimetielaminovinielketoon; fctfaH = ferrosenoïeltrifluoroasetoon; kupfH = kupferron (N-feniel-N-nitrosohidroksielamien); neokupfH = neokupferron (N-naftiel-N-nitrosohidroksielamien); cy = sikloheksiel

Oxidative addition of iodomethane to Rh(I) neocupferrate complexes as model for a unique application of Tolman’s principles: Oxidative addition is of great importance in catalytic processes. The Monsanto process for the production of acetic acid is one of the best examples thereof. In an effort to clear uncertainties concerning the mechanism of oxidative addition, our group is interested in the manipulation of the reactivity of the Rh(I) centre of the [Rh(LL′)(CO)(PR3)] type of complexes, where LL′ represents monocharged bidentate ligands, and PR3 different monodentate phosphine ligands. These phosphine ligands vary
with regard to their electronic as well as their steric properties and have, as with other ligand variations, a marked effect on the reactivity of the metal centre. Oxidative addition of iodomethane in the neocupferrate system proceed via two competitive pathways. The k1-path implies a nucleophilic attack on CH3I, leading to a 16-electron, five-coordinate intermediate of which the degree of ion separation is solvent dependent. The solvent supported k2-pathway can be regarded as an exceptional oxidative
addition catalytic phenomenon. By studying the effect of varying steric and electronic properties of the phosphine ligands on the oxidative addition of the neocupferrate system, a steric-electronic model, developed by Tolman, could be applied to the oxidative addition reactions in order to evaluate the total effect of the phosphorous ligand in a particular system. An effort was made to quantify the phosphine properties. This can possibly lead to greater understanding concerning the composition and design of catalysts.

The following abbreviations was used in the text: opoH = 2-oxopyridine-1-olate anion; quinH = 2-carboxyquinoline; oxH = oxine (8-hydroxyquinoline); dmavkH = dimethylaminovinyl ketone; fctfaH = ferrocenoyltrifluoroacetone; cupfH = cupferron (N-phenyl-N-nitrosohydroxylamine); neocupfH = neocupferron (N-naphtyl-N-nitrosohidroxylamine); cy = cyclohexyl



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2020-04-22
2020-07-05

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