TY - JOUR
T1 - Mechanistic insights into catalytic H 2 oxidation by Ni complexes containing a diphosphine ligand with a positioned amine base
AU - Yang, Jenny Y.
AU - Bullock, R. Morris
AU - Shaw, Wendy J.
AU - Twamley, Brendan
AU - Fraze, Kendra
AU - DuBois, M. Rakowski
AU - DuBois, Daniel L.
PY - 2009/4/29
Y1 - 2009/4/29
N2 - The mixed-ligand complex [Ni(dppp)(P ph 2N Bz 2)](BF 4) 2, 3, (where P ph 2N 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° complex, Ni(dppp)(P ph 2N 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 2N Bz(μ-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) 2Ni(dppp)(P ph 2N Bz 2)](BF 4) 2, 5b, and the other is [Ni(dppp)(P ph 2N Bz 2H 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" complexes containing two diphosphine ligands, the activation of H 2 is favored by the presence of two positioned pendant bases.
AB - The mixed-ligand complex [Ni(dppp)(P ph 2N Bz 2)](BF 4) 2, 3, (where P ph 2N 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° complex, Ni(dppp)(P ph 2N 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 2N Bz(μ-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) 2Ni(dppp)(P ph 2N Bz 2)](BF 4) 2, 5b, and the other is [Ni(dppp)(P ph 2N Bz 2H 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" complexes containing two diphosphine ligands, the activation of H 2 is favored by the presence of two positioned pendant bases.
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U2 - 10.1021/ja900483x
DO - 10.1021/ja900483x
M3 - Article
C2 - 19341269
AN - SCOPUS:69949169617
VL - 131
SP - 5935
EP - 5945
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 16
ER -