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

Tellers, David M; Bergman, Robert G
May 2001
Canadian Journal of Chemistry;May2001, Vol. 79 Issue 5/6, p525
Academic Journal
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.


Related Articles


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics