The electrochemistry and spectroelectrochemistry of the substituted group V carbonyl complexes XTa(CO)4− (dppe) (X = I, Br) and XM(CO)2(dppe)2 (X = I, Br, Cl, H; dppe = 1,2 bis(diphenylphosphino)ethane; M = Nb, Ta) have been investigated. The XTa(CO)4(dppe) tetracarbonyl species exhibit irreversible oxidations at Ea = +868 mV (X− = Br−) and Ea = +1276 (X− = I−) mV. Spectroelectrochemical oxidation of these complexes at Eapp = +1000 mV indicates that CO is evolved with decomposition to non-carbonyl containing products. The reduction chemistry of ITa(CO)4(dppe) showed an irreversible cathodic process at Ec = −1541 mV in TBA+-PF6−/THF with two coupled oxidation processes (at Ea = −530 mV and Ea = +100 mV). Spectroelectrochemical reduction of ITa(CO)4(dppe) generates Ta(CO)4(dppe)−; oxidation of the anion produces ITa(CO)4(dppe) at the first coupled process and HTa(CO)4(dppe) at the second, respectively. The more highly substituted XM(CO)2-(dppe)2 compounds each exhibit a one-electron reversible oxidative process in CH2Cl2/TBA+PF6− (E° ca. −270 to +110 mV) that generate stable (electrochemical time scale) 17-electron species, (XM(CO)2(dppe)2+) that were also characterized by IR spectroelectrochemical techniques. EPR spectra observed for these radical cations exhibit ten line signals at g = 2.04 (X− = Cl−) and g = 2.05 (X− = H−) with characteristic coupling to 93Nb (I = 9/2) (A = 115 G for X− = Cl−; A = 113 G for X− = H−). Attempts to isolate salts of the XM(CO)2(dppe)2+ species were unsuccessful.