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Slow proton transfer to coordinated carboxylates: studies on [Ni(O2CR){PhP(CH2CH2PPh2)2}](+) (R = Et or Ph)

Lookup NU author(s): Ahmed Alwaaly, Professor Richard Henderson


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The reactions between [Ni(O2CR)(triphos)](+) (R = Et or Ph, triphos = PhP(CH2CH2PPh2)(2)) and mixtures of lutH(+) and lut (lut = 2,6-dimethylpyridine) have been studied in MeCN at 25.0 degrees C using stopped-flow spectrophotometry. The kinetics and spectroscopic changes indicate an equilibrium reaction, presumably involving protonation of an oxygen site (the only sites on the complex containing lone pairs of electrons). Proton transfer is slow and comparison of the kinetic data shows that the rates are insensitive to the R substituent. Using the kinetic data, the pK(a)s of [Ni(HO2CR)(triphos)](2+) (pK(a) = 14.5) have been calculated showing that when coordinated to the {Ni(triphos)}(2+) site, RCO2H is about 8 pK(a) units more acidic than the free acid. Comparison of the kinetic results on the reactions of [Ni(O2CR)(triphos)](+) with mixtures of lutH(+) and lut and those of the analogous [Ni(S2CR)(triphos)](+) show that protonation at oxygen is at least 7.6 x 10(3) times faster than to sulfur, and the coordinated carboxylic acid is ca. 8 pK(a) units less acidic than the corresponding coordinated carboxydithioic acid.

Publication metadata

Author(s): Alwaaly A, Henderson RA

Publication type: Article

Publication status: Published

Journal: Journal of Coordination Chemistry

Year: 2015

Volume: 68

Issue: 17-18

Pages: 3069-3078

Print publication date: 17/06/2015

Online publication date: 14/05/2015

Acceptance date: 21/04/2015

ISSN (print): 0095-8972

ISSN (electronic): 1029-0389

Publisher: Taylor & Francis


DOI: 10.1080/00958972.2015.1047773


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