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

A series of dipeptide substituted 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, and the dipeptide consists of the non-natural amino acid, 3-(4-aminophenyl)propionic acid (NNA), coupled to amino acid/esters = glutamic acid, alanine, lysine, and aspartic acid). Each of these complexes is an active electrocatalyst for H2 production. The effects of the outer-coordination sphere on the catalytic activity for the production of H2 were investigated; specifically, the impact of sterics, the ability of the side chain or backbone to protonate and the pKa values of the amino acid side chains were studied by varying the amino acids in the dipeptide. The catalytic rates of the different dipeptide substituted nickel complexes varied by over an order of magnitude. The amino acid derivatives display the fastest rates, while esterification of the terminal carboxylic acids and side chains resulted in a ...

Authors:   Avijita Jain; Matthew L. Reback; Mary Lou Lindstrom; Colleen E. Thogerson; Monte L. Helm; Aaron M. Appel; Wendy J. Shaw
Journal:   Inorganic Chemistry
Year:   2012
DOI:   10.1021/ic300149x
Publication date:   04-Jun-2012
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