Spectroscopic Models for Proximal Nickel

An informative spectroscopic model for the CO-bound, reduced proximal Ni site is derived from the anionic tripodal ligand PhTt , or phenyl-tris(tert-butylthio- 

A dinickel(Il) system has been described that undergoes reversible reduction at the proximal nickel center to a Ni(ll)-Ni(l) state and further irreversible reduction to a Ni(ll)-Ni(0) state (Fig. 12.15) [112]. Both of the nickel atoms in the beginning complex exhibit square planar geometry, but the Ni(SR)2(PR3)2 center becomes tetrahedral upon reduction to the Ni(ll)-Ni(l) state, as evidenced by EPR spectroscopy. A related geometric change during the catalytic cycle of the ACS enzyme has been suggested. 

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