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Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene‐1,2‐dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units
Author(s) -
Dicks James P.,
Zubair Muhammad,
Davies E. Stephen,
Garner C. David,
Schulzke Carola,
Wilson Claire,
McMaster Jonathan
Publication year - 2015
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.201500138
Subject(s) - chemistry , redox , delocalized electron , cyclopentadienyl complex , cobalt , electron paramagnetic resonance , electron transfer , crystallography , ligand (biochemistry) , trifluoroacetic acid , cyclobutadiene , photochemistry , medicinal chemistry , stereochemistry , catalysis , inorganic chemistry , organic chemistry , biochemistry , physics , receptor , nuclear magnetic resonance , molecule
The compounds [(η 5 ‐C 5 H 5 )Co{SC(H)CRS}] [R = phenyl ( 1 ), pyridin‐3‐yl ( 2 ) or pyrazin‐2‐yl ( 3 )] have been synthesized and characterized by elemental analysis, 1 H NMR, mass spectrometry and X‐ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH 2 Cl 2 solution each compound undergoes a reversible one‐electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5:1 excess of trifluoroacetic acid the one‐electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [ 1 ] y , [ 2 ] y and [ 3 ] y ( y = 0 or –1) and the monoprotonated forms [ 2 H] z and [ 3 H] z ( z = +1 or 0), and this has provided insight into the nature of the redox‐active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene‐1,2‐dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring‐opened form of the molybdenum cofactor of oxygen‐atom‐transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle.