Catalytic Proton Coupled Electron Transfer from Metal Hydrides to Titanocene Amides, Hydrazides and Imides: Determination of Thermodynamic Parameters Relevant to Nitrogen Fixation

Iraklis Pappas, Paul J. Chirik

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

The hydrogenolysis of titanium-nitrogen bonds in a series of bis(cyclopentadienyl) titanium amides, hydrazides and imides by proton coupled electron transfer (PCET) is described. Twelve different N-H bond dissociation free energies (BDFEs) among the various nitrogen-containing ligands were measured or calculated, and effects of metal oxidation state and N-ligand substituent were determined. Two metal hydride complexes, (η5-C5Me5)(py-Ph)Rh-H (py-Ph = 2-pyridylphenyl, [Rh]-H) and (η5-C5R5)(CO)3Cr-H ([Cr]R-H, R= H, Me) were evaluated for formal H atom transfer reactivity and were selected due to their relatively weak M-H bond strengths yet ability to activate and cleave molecular hydrogen. Despite comparable M-H BDFEs, disparate reactivity between the two compounds was observed and was traced to the vastly different acidities of the M-H bonds and overall redox potentials of the molecules. With [Rh]-H, catalytic syntheses of ammonia, silylamine and N,N-dimethylhydrazine have been accomplished from the corresponding titanium(IV) complex using H2 as the stoichiometric H atom source. The data presented in this study provides the thermochemical foundation for the synthesis of NH3 by proton coupled electron transfer at a well-defined transition metal center.

Original languageEnglish (US)
Pages (from-to)13379-13389
Number of pages11
JournalJournal of the American Chemical Society
Volume138
Issue number40
DOIs
StatePublished - Oct 12 2016

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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