The chelating ligand, 1,1’-bis(diphenylphosphino)cobaltocene (dppc) is used as an electrochemically tunable ligand for altering electrophilicity of the carbonyl carbon in metal carbonyl complexes. The Re carbonyl complexes [Re(CO)(4-n)(CH3CN)(n)dppc](2+/+), n = 0 (cis), 1 (fac), 2 (cis,cis), and [fac-Re(CO)(3)(NCO)dppc](+/0) were prepared and characterized in both stales of charge indicated. Single crystal X-ray crystallography was performed for both states of charge of [Re(CO)(4)dppc](2+/+ with the oxidized and reduced forms crystallizing in the monoclinic space groups C2/c and P2?1/c, respectively; The most pronounced structural difference between the two forms is the Cp(centroid)-Co distance, which is 0.09 Angstrom longer for the reduced form. Cyclic voltammetry shows that E(1/2) for the Co(III)/Co(II) couple is 200-400 mV more positive for coordinated dppc than for the free ligand. For each CO substituted, E(1/2) becomes similar to 100 or 200 mV more negative for substitution by CH3CN or NCO-, respectively. Solution IR spectroscopy shows that v(CO) for the oxidized form of each species is typically similar to 15 cm(-1) higher than for the reduced form, but the dumber and relative intensities of the carbonyl absorptions are the same. In every redox pair the oxidized species has higher reactivity with respect to nucleophilic attack at the carbonyl carbon. In CH3CN at 25.0 degrees C, [fac-Re(CO)(3)- (CH3CN)dppc](+2) reacts with amine N-oxides (CH3)(3)NO, N-methylmorpholine N-oxide, and (CH3)(2)(C6H5)NO similar to 200 times faster than [fac-Re(CO)(3)(CH3CN)dppc](+) to form [cis,cis-Re(CO)(2)(CH3CN)(2)dppc](+2/+), while [cis-Re(CO)(4)dppc](+2) reacts with N-3(-) 5400 times faster than [cis-Re(CO)(4)dppc](+) to form [fac-Re(CO)(3)(NCO)dppc](+/0), with Delta Delta H double dagger = 3-4 kcal/mol in both cases. The ionic strength and dielectric strength dependence of the reactivity of [Re(CO)(4)dppc](+2/+) toward N-3(-) were assayed to investigate electrostatic contributions to the attenuation of reactivity of [Re(CO)(4)dppc](+2/+) toward N-3(-) caused by reduction of the dppc ligand.