Electrochemistry and Infrared Spectroelectrochemistry of the Substituted Phosphine Complexes, XTa(CO)4(dppe) (X = I, Br) and XM(CO)2(dppe)2 (X = H, I, Br, Cl; M= Nb, Ta)

Christine A. Blaine, John E. Ellis, Kent R. Mann

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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.

Original languageEnglish (US)
Pages (from-to)1552-1561
Number of pages10
JournalInorganic Chemistry
Issue number6
StatePublished - Mar 1 1995


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