Stabilization of nickel complexes with Ni 0H-N bonding interactions using sterically demanding cyclic diphosphine ligands

Eric S. Wiedner, Jenny Y. Yang, Shentan Chen, Simone Raugei, William G. Dougherty, W. Scott Kassel, Monte L. Helm, R. Morris Bullock, M. Rakowski DuBois, Daniel L. DuBois

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57 Citations (Scopus)

Abstract

The series of complexes Ni(P tBu 2N R 2) 2, [Ni(P tBu 2N R 2) 2]BF 4, [HNi(P tBu 2N R 2) 2]BF 4, and [Co(P tBu 2N Ph 2) 2]BF 4(P tBu 2N R 2 = 1,5-dialkyl-3,7-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane; alkyl = phenyl, benzyl) have been synthesized and characterized. Spectroscopic, electrochemical, and X-ray diffraction studies indicate these complexes are stable as a result of the tetrahedral arrangement of the two diphosphine ligands. Electrochemical oxidation of [HNi(P tBu 2N Ph 2) 2]BF 4 results in rapid proton transfer from nickel at a rate faster than can be observed on the CV time scale. Double protonation of Ni(P tBu 2N Bn 2) 2forms the endo-endo, endo-exo, and exo-exo isomers of [Ni(P tBu 2N BnHN Bn) 2](BF 4) 2, which were found to be more stable toward loss of H 2 than previously observed for similar complexes. The presence of Ni 0HN hydrogen bonds at the endo protonation sites of [Ni(P tBu 2N BnHN Bn) 2](BF 4) 2 results in significant differences in the Ni(I/0) oxidation potentials of each of the isomers. The differences in E 1/2(I/0) values correspond to bond free energies of 7.4 and 3.7 kcal/mol for the first and second Ni 0HN hydrogen bonds of the endo-exo and endo-endo isomers, respectively. Computational studies give bond dissociation energies of the Ni 0HN bonds that are within 1-2 kcal/mol of the experimentally determined values.

Original languageEnglish
Pages (from-to)144-156
Number of pages13
JournalOrganometallics
Volume31
Issue number1
DOIs
Publication statusPublished - Jan 9 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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