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[Ni(Et2PCH2NMeCH2PEt2)2]2+ as a functional model for hydrogenases
Calvin J Curtis1, Alex Miedaner, Rebecca Ciancanelli
1National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, USA.
Inorganic Chemistry
|January 7, 2003
Summary
This study details nickel-phosphine complexes with unique hydride and proton acceptor sites. These complexes act as electrocatalysts for hydrogen oxidation and exhibit rapid proton exchange, crucial for understanding catalytic mechanisms.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Electrochemistry
Background:
- Nickel complexes with phosphine ligands are vital in catalysis.
- Understanding hydride and proton interactions in metal complexes is key for developing new catalytic systems.
- The ligand Et(2)PCH(2)N(Me)CH(2)PEt(2) (PNP) offers unique coordination properties.
Purpose of the Study:
- To synthesize and characterize nickel complexes with the PNP ligand.
- To investigate the catalytic activity of these complexes in hydrogen oxidation.
- To elucidate the mechanisms of hydride and proton transfer and exchange.
Main Methods:
- Synthesis of nickel-PNP complexes.
- Electrochemical studies including cyclic voltammetry.
- Spectroscopic analysis and thermodynamic calculations.
- Proton exchange studies in solution.
Main Results:
- Formation of [Ni(PNP)(2)](BF(4))(2) with hydride and proton acceptor sites.
- Identification of [HNi(PNP)(PNHP)](BF(4))(2) and [HNi(PNP)(2)](PF(6)) with distinct pK(a) values.
- Demonstration of rapid intramolecular and intermolecular hydride/proton exchange.
- Calculation of Ni-H bond dissociation free energies.
- Evidence for proton migration from Ni to the PNP ligand's nitrogen atom.
Conclusions:
- Nickel-PNP complexes are effective electrocatalysts for hydrogen oxidation.
- The bridging nitrogen atom in the PNP ligand plays a critical role in proton exchange reactions.
- Ligand structure and coordination geometry significantly influence hydride acceptor abilities.