TY - JOUR
T1 - Investigating the role of the outer-coordination sphere in [Ni(P Ph 2N Ph-R 2) 2] 2+ hydrogenase mimics
AU - Jain, Avijita
AU - Reback, Matthew L.
AU - Lindstrom, Mary Lou
AU - Thogerson, Colleen E.
AU - Helm, Monte L.
AU - Appel, Aaron M.
AU - Shaw, Wendy J.
PY - 2012/6/18
Y1 - 2012/6/18
N2 - A series of dipeptide substituted nickel complexes with the general formula, [Ni(P Ph 2N NNA-amino acid/ester 2) 2](BF 4) 2, have been synthesized and characterized (P 2N 2 = 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 H 2 production. The effects of the outer-coordination sphere on the catalytic activity for the production of H 2 were investigated; specifically, the impact of sterics, the ability of the side chain or backbone to protonate and the pK a 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 decrease in the catalytic rate by 50-70%, implicating a significant role of protonated sites in the outer-coordination sphere on catalytic activity. For both the amino acid and ester derivatives, the complexes with the largest substituents display the fastest rates, indicating that catalytic activity is not hindered by steric bulk. These studies demonstrate the significant contribution that the outer-coordination sphere can have in tuning the catalytic activity of small molecule hydrogenase mimics.
AB - A series of dipeptide substituted nickel complexes with the general formula, [Ni(P Ph 2N NNA-amino acid/ester 2) 2](BF 4) 2, have been synthesized and characterized (P 2N 2 = 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 H 2 production. The effects of the outer-coordination sphere on the catalytic activity for the production of H 2 were investigated; specifically, the impact of sterics, the ability of the side chain or backbone to protonate and the pK a 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 decrease in the catalytic rate by 50-70%, implicating a significant role of protonated sites in the outer-coordination sphere on catalytic activity. For both the amino acid and ester derivatives, the complexes with the largest substituents display the fastest rates, indicating that catalytic activity is not hindered by steric bulk. These studies demonstrate the significant contribution that the outer-coordination sphere can have in tuning the catalytic activity of small molecule hydrogenase mimics.
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U2 - 10.1021/ic300149x
DO - 10.1021/ic300149x
M3 - Article
C2 - 22662880
AN - SCOPUS:84862542166
VL - 51
SP - 6592
EP - 6602
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 12
ER -