Investigating the Role of the Outer-Coordination Sphere in [Ni(PPh2NPh-R2)2]2+ Hydrogenase Mimics

Journal Article · Mon Jun 18 00:00:00 EDT 2012 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic300149x· OSTI ID:1047369

Jain, Avijita; Reback, Matthew L; Lindstrom, Mary L; Thogerson, Colleen E; Helm, Monte L; Appel, Aaron M; Shaw, Wendy J

A series of dipeptide nickel complexes with the general formula, [Ni(PPh2NNNA-amino acid/ester2)2](BF4)2, have been synthesized and characterized (P2N2= 1,5-diaza-3,7-diphosphacyclooctane, amino acid/esters = glutamic acid, alanine, lysine, and aspartic acid). Each of these complexes is an efficient electrocatalyst for H2 production. The contribution of the outer-coordination sphere, specifically the impact of sterics, the ability to protonate and the pKa of amino acid side chain on the hydrogen production activity of these complexes, was investigated. The rates of all of the catalysts ranged over an order of magnitude. The amino acid containing complexes display 2-3 times higher rates of hydrogen production than the corresponding ester complexes, suggesting the significance of protonated species (side chains/backbone of amino acids) in the outer-coordination sphere. The largest had the fastest rates suggesting that catalytic activity is not hindered by sterics. However, the shapes of catalytic waves are indicative of hindered electron transfer and may suggest a competing mechanism for catalysis than that observed for the unsubstituted parent complex. These studies demonstrate the significant contribution that the outer-coordination sphere can have in tuning the catalytic activity of small molecule hydrogenase mimics.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1047369
• Report Number(s): PNNL-SA-85188; INOCAJ; KC0302010; TRN: US201216%%228
• Journal Information: Inorganic Chemistry, Vol. 51, Issue 12; ISSN 0020-1669
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AMINO ACIDS
CATALYSIS
CATALYSTS
COMPLEXES
ELECTROCATALYSTS
ELECTRON TRANSFER
ESTERS
GLUTAMIC ACID
HYDROGEN PRODUCTION
HYDROGENASES
LYSINE
MOLECULES
NICKEL COMPLEXES
PRODUCTION
SPHERES
TUNING
catalysis
bioinspired
amino acid catalysts