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Investigation of Bridgehead Effects on Reduction Potential in Alkyl and Aryl Azadithiolate‐Bridged (µ‐SCH 2 XCH 2 S) [Fe(CO) 3 ] 2 Synthetic Analogues of [FeFe]‐H 2 ase Active Site
Author(s) -
Rana Atanu,
Kumar Das Pradip,
Mondal Biswajit,
Dey Subal,
Crouthers Danielle,
Dey Abhishek
Publication year - 2018
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201800335
Subject(s) - chemistry , substituent , aryl , alkyl , lone pair , density functional theory , amine gas treating , stereochemistry , medicinal chemistry , ring (chemistry) , crystallography , computational chemistry , molecule , organic chemistry
Factors affecting the Fe I Fe I /Fe I Fe 0 reduction potentials (E 0 ) in a series of propane and azadithiolate bridged (µ‐SRS)[Fe(CO) 3 ] 2 synthetic model complexes of diiron hydrogenases are investigated. The E 0 is found to vary from 60 to 390 mV depending on the nature of the substituent (Alkyl or Aryl) on the nitrogen atom at the bridgehead of the azadithiolate. The E 0 is found to shift to more negative values as the average C‐O stretching vibrations ν(CO) avg of the CO ligands decreases, i.e., with increasing backbonding from the iron centers. This trend is accompanied by a linear dependence of the E 0 on the σ Hammett parameter of the para substituents in a series of Arylamine bridged complexes and on the gas phase proton affinities (PA) of a series of Alkylamine bridged complexes. The unexpected dependence of E 0 on the substituents on the bridgehead nitrogen is addressed by computational chemistry. Density functional theory (DFT) calculations accurately reproduce the geometric structures and the correlations between E 0 , ν(CO) avg , σ and PA observed in the experimental data. It is concluded that while for Alkyl‐amine bridged complexes an interaction between the nitrogen lone pair with C–S σ* affects ca. 60 mV shift in the E 0 , the inductive and mesomeric effects of the substituents in the Aryl ring are responsible for ca. 300 mV shift in the E 0 of the Aryl‐amine bridged complexes.