AN IN-SITU FOURIER-TRANSFORM INFRARED STUDY OF CO2 ELECTROREDUCTION CATALYZED BY NI(0)-4,4'-DIMETHYL 2,2'-BIPYRIDINE AND NI(0)-1,10-PHENANTHROLINE COMPLEXES

The electrochemical reduction of CO2 by electrogenerated LNi(0) and (L (.-))Ni(0) (L = 4,4'-dimethyl-2,2'-bipyridine, 1,10-phenanthroline) co mplexes has been studied using in-situ Fourier transform IR spectrosco py. Electrogenerated [L(2)NI] reacts slowly with CO2 to produce [Ni(L) (CO)(2)]; no intermediates could be detected in this reaction. However , the dicarbonyls with both L = Phen and L = 4,4'-dimethyl-2,2'-bipyri dine (Me(2)Bipy) react with trace water to give [Ni-2(mu-H)(CO)(6)](-) , providing a route that is operative at relatively high potentials. A t more negative potentials (below -1.6 V vs. the saturated calomel ele ctrode (SCE)), where a catalytic current due to CO2 reduction is seen, spectroscopic evidence for the transient formation of [Ni(Me(2)Bipy(. -))(CO)(2)] has been found. It appears that [Ni(Me(2)Bipy(.-))(CO)(2)] reacts sufficiently fast that its steady state concentration in the t hin layer is very low. In contrast, [Ni(Phen(.-))(CO)(2)] is more stab le. For both complexes, electrogenerated CO, which cannot escape from the thin layer, attacks the radical dicarbonyl species to form [NI(CO) (4)], which is then ultimately reduced to nickel carbonyl cluster anio ns. [Ni(Phen)(CO)(2)] also reacts to produce a metalloformate species, not observed with the Me(2)Bipy analogue. The OC-Ni-CO angle was calc ulated for each of the four [Ni(L)(CO)(2)] and [Ni(L(.-))(CO)(2)] spec ies and was found to be 104 degrees +/- 2 degrees, in agreement with t he expected tetrahedral geometry of a Ni(0) complex.