TITLE

Mechanistic study of ligand substitution processes in TpIr(III) complexes

AUTHOR(S)
Tellers, David M; Bergman, Robert G
PUB. DATE
May 2001
SOURCE
Canadian Journal of Chemistry;May2001, Vol. 79 Issue 5/6, p525
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The synthesis of the cationic hydridotris(pyrazolyl)borate iridium(III) complex [Tp(PMe[sub 3] )IrMe(ClCH[sub 2] Cl)][BAr[sub f] ] (2-CH[sub 2] Cl[sub 2] ) is reported. Spectroscopic characterization of 2-CH[sub 2] Cl[sub 2] in CH[sub 2] Cl[sub 2] solution indicates that exchange of bound CH[sub 2] Cl[sub 2] with free CH[sub 2] Cl[sub 2] is slow on the NMR time scale. Under 50 atm (1 atm = 101.325 kPa) of N[sub 2] , the CH[sub 2] Cl[sub 2] in 2-CH[sub 2] Cl[sub 2] is displaced by N[sub 2] to yield [Tp(PMe[sub 3] )IrMe(N[sub 2] )][BAr[sub f] ] (2-N[sub 2] ). The stronger nucleophile CH[sub 3] CN reacts rapidly with 2-CH[sub 2] Cl[sub 2] to produce [Tp(PMe[sub 3] )IrMe(NCCH[sub 3] )][BAr[sub f] ] (4). A kinetic study was performed on CH[sub 2] Cl[sub 2] substitution in 2-CH[sub 2] Cl[sub 2] by CD[sub 3] CN. The data are most consistent with dissociative loss of CH[sub 2] Cl[sub 2] to generate the unsaturated species ([Tp(PMe[sub 3] )IrMe][BAr[sub f] ]) which then reacts with CD[sub 3] CN to generate [Tp(PMe[sub 3] )IrMe(NCCD[sub 3] )][BAr[sub f] ]. Further evidence for a dissociative mechanism was obtained by comparison of ligand substitution rates for the Tp complexes with the analogous Tp[sup Me2] complexes (Tp[sup Me2] = hydridotris(3,5-dimethylpyrazolyl)borate). The relevance of these substitution experiments to C—H activation by cationic iridium(III) complexes is discussed.Key words: iridium, hydridotris(pyrazolyl)borate, methylene chloride and dinitrogen complexes, dissociative substitution.On a réalisé la synthèse du complexe cationique hydridotris(pyrazolyl)borate d'iridium(III) ([Tp(PMe[sub 3] )IrMe(ClCH[sub 2] Cl)][BAr[sub f] ]) (2-CH[sub 2] Cl[sub 2] ). Une caractérisation spectroscopique du 2-CH[sub 2] Cl[sub 2] en solution dans le CH[sub 2] Cl[sub 2] indique que l'échange des CH[sub 2] Cl[sub 2] liés et libres est lente sur l'échelle de temps de la RMN. Sous 50 atm (1 atm = 101.325 kPa) de N[sub 2] , le CH[sub 2] Cl[sub 2] du 2-CH[sub 2] Cl[sub 2] est déplacé par le N[sub 2] pour conduire à la formation de [Tp(PMe[sub 3] )IrMe(N[sub 2] ])[BAr[sub f] ] (2-N[sub 2] ). Le CH[sub 3] CN, un nucléophile plus puissant, réagit rapidement avec le 2-CH[sub 2] Cl[sub 2] pour conduire à la formation de [Tp(PMe[sub 3] )IrMe(NCCH[sub 3] )][BAr[sub f] ] (4). On a réalisé une étude cinétique sur la vitesse de remplacement du CH[sub 2] Cl[sub 2] de 2-CH[sub 2] Cl[sub 2] par du CD[sub 3] CN. Les données sont plutôt en accord avec une perte dissociative du CH[sub 2] Cl[sub 2] générant l'espèce insaturée [Tp(PMe[sub 3] )IrMe][BAr[sub f] ] qui réagit alors du CH[sub 3] CN pour générer le [Tp(PMe[sub 3] )IrMe(NCCD[sub 3] )][BAr[sub f] ]. On a obtenu d'autres données favorisant un mécanisme dissociatif en comparant les vitesses de substitution des complexes Tp avec celles des complexes analogues Tp[sup Me2] (Tp[sup Me2] = hydridotris(3,5-diméthylpyrazolyl)borate). On discute de la pertinence de ces expériences de substitution sur l'activation des liaisons C—H par les complexes cationiques de l'iridium(III).Mots clés : iridium, hydridotris(pyrazolyl)borate, complexes avec le chlorure de méthylène et le diazote, substitution dissociative.
ACCESSION #
10580663

 

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