Comparison of [Ni(PPh2NPh2)2(CH3CN)]2+ and [Pd(PPh2NPh2)2]2+ as electrocatalysts for H2 production

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Abstract

The complexes [Ni(PPh2NPh2)2(CH3CN)]2+ and [Pd(PPh2NPh2)2]2+, where PPh2NPh2 is 1,5-diphenyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane, are compared as electro-catalysts for H2 production under identical experimental conditions. With [(DMF)H]+ as the acid in acetonitrile solution, [Pd(PPh2NPh2)2]2+ afforded a turnover frequency (TOF) of 230 s-1 for formation of H2 under dry conditions and a TOF of 640 s-1 when H2O was added. These rates are similar to the TOFs of 590 s-1 (dry) and 720 s-1 (wet) that were previously measured for [Ni(PPh2NPh2)2(CH3CN)]2+ using [(DMF)H]+. The [Ni-(PPh2NPh2)2(CH3CN)]2+ and [Pd(PPh2NPh2)2]2+ complexes both exhibited large current enhancements when treated with trifluoroacetic acid (TFA). At a TFA concentration of 1.8 M, TOF values of 5670 and 2060 s-1 were measured for [Ni(PP 2NP 2)2(CH3CN)]2+ and [Pd(PPh 2NP 2)2]2+, respectively. The fast rates observed using TFA are, in part, attributed to homoconjugation of TFA in acetonitrile solutions, which decreases the effective pKae of the acid. In support of this hypothesis, dramatically lower rates of H2 production were observed using p-anisidinium, which has a pKaMe value comparable to that of TFA but does not homoconjugate significantly in acetonitrile solutions. (Figure Presented)

Original languageEnglish
Pages (from-to)4617-4620
Number of pages4
JournalOrganometallics
Volume33
Issue number18
DOIs
Publication statusPublished - Sep 22 2014

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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