These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Mechanistic insights into catalytic h(2) oxidation by ni complexes containing a diphosphine ligand with a positioned amine base.
    Author: Yang JY, Bullock RM, Shaw WJ, Twamley B, Fraze K, DuBois MR, DuBois DL.
    Journal: J Am Chem Soc; 2009 Apr 29; 131(16):5935-45. PubMed ID: 19341269.
    Abstract:
    The mixed-ligand complex [Ni(dppp)(P(Ph)(2)N(Bz)(2))](BF(4))(2), 3, (where P(Ph)(2)N(Bz)(2) is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane and dppp is 1,3-bis(diphenylphosphino)propane) has been synthesized. Treatment of this complex with H(2) and triethylamine results in the formation of the Ni(0) complex, Ni(dppp)(P(Ph)(2)N(Bz)(2)), 4, whose structure has been determined by a single-crystal X-ray diffraction study. Heterolytic cleavage of H(2) by 3 at room temperature forms [HNi(dppp)(P(Ph)(2)N(Bz)(mu-H)N(Bz))](BF(4))(2), 5a, in which one proton interacts with two nitrogen atoms of the cyclic diphosphine ligand and a hydride ligand is bound to nickel. Two intermediates are observed for this reaction using low-temperature NMR spectroscopy. One species is a dihydride, [(H)(2)Ni(dppp)(P(Ph)(2)N(Bz)(2))](BF(4))(2), 5b, and the other is [Ni(dppp)(P(Ph)(2)N(Bz)(2)H(2))](BF(4))(2), 5c, in which both protons are bound to the N atoms in an endo geometry with respect to nickel. These two species interconvert via a rapid and reversible intramolecular proton exchange between nickel and the nitrogen atoms of the diphosphine ligand. Complex 3 is a catalyst for the electrochemical oxidation of H(2) in the presence of base, and new insights into the mechanism derived from low-temperature NMR and thermodynamic studies are presented. A comparison of the rate and thermodynamics of H(2) addition for this complex to related catalysts studied previously indicates that for Ni(II) complexes containing two diphosphine ligands, the activation of H(2) is favored by the presence of two positioned pendant bases.
    [Abstract] [Full Text] [Related] [New Search]