Synthesis and characterization of nickel dithiocarbamate complexes bearingferrocenyl subunits

Syntheses of a unique molecule, nickel(II) dithiocarbamate bearing two ferr ocenyl groups (3), and its oxidized product, nickel(IV) dithiocarbamate bea ring three ferrocenyl groups (4(+)), are reported. Spectroelectrochemical i nvestigations have shown that the complex 4(+) undergoes a three-electron o xidation process, according to two quasireversible steps ([Ni-IV(Fe-II)(3)] (+) reversible arrow [Ni-IV(Fe-II)(2)Fe-III](2+)+e(-), [Ni-IV(Fe-II),Fe-III ](2+) reversible arrow [Ni-IV(Fe-III)(3)](4+)+2e(-)), whose redox potential s are separated by Delta E= 250 mV. The value Delta E is related to the com proportionation equilibrium ( [Ni-IV(Fe-II)3](+)+[Ni-IV(FeIII)(2)Fe-II](3+) reversible arrow [(NiFeIII)-Fe-IV(Fe-II)(2)](2+)) and results fi-om the co mbination of a statistical contribution and a term which reflects the elect rostatic repulsive interaction between the metal centers. In spite of the c hemical equivalence of the three ferrocenyl groups, the mixed-valence state [Ni-IV Fe-III(Fe-II)(2)](2+) (4(2+)) substantially persists in solution. M odel studies with ethylene-bridged bis(ferrocenylimine) (6) have revealed t hat the electrostatic term is much lower in the absence of the nickel(IV) c enter. Preliminary force-field simulations on 4(+) have shown that enhanced electrostatic repulsion caused by the oxidation of the ferrocenyl subunits affects the conformation of the molecule, which results in a significant d imensional increment. Stereochemical features of the molecules are related to the electrostatic interaction and Delta G(0) associated with the comprop ortionation process is affected by such strong deformation that a decrease in electrostatic repulsion results.