SPECTROSCOPIC AND VOLTAMMETRIC STUDY OF THE DECEPTIVELY SIMPLE SOLUTION CHEMISTRY OF THE [CR(CO)(2)(PH(2)PCH(2)CH(2)PPH(2))(2)](+ 0) SYSTEM/

IR, ESR, and P-31 NMR spectroscopy, electrospray mass spectrometry, st eady-state microelectrode voltammetry, and rotating-disk voltammetry h ave been used to characterize the solution chemistry of the deceptivel y simple Cr(CO)(2)(dpe)(2) (dpe = Ph(2)PCH(2)CH(2)PPh(2)) system in be nzene, toluene, chloroform, dichloromethane, acetone, and acetonitrile . These techniques show that while the expected cis-Cr(CO)(2)(dpe)(2) (cis(0)) and trans-Cr(CO)(2)(dpe)(2) (trans(0)) compounds are present, trans-[Cr(CO)(2)(dpe)(2)](+) (trans(+)) also is involved in the solut ion chemistry of the Cr(CO)(2)(dpe)(2) system and that complex and rap id reactions may occur between these three compounds. The 17-electron cation trans(+), formed in the presence of oxygen, is the key compound in these reactions. Electrospray mass spectrometry and ESR spectrosco py confirm that trans(+) is present in solutions of Cr(CO)(2)(dpe)(2). The formation of paramagnetic transf modifies the apparent isomeric d istribution of the cis(0) and trans(0) isomers determined by NMR metho ds because of line-broadening and relaxation effects. There is also an unfortunate coincidence of IR absorptions between the two carbonyl ba nds of cis(0) and the single bands of both trans(0) and trans(+); ther efore, interpretation of data obtained from IR spectroscopy is also di fficult in this system. However, steady-state microelectrode and rotat ing-disk voltammetric techniques generally are able to resolve the iso merization equilibrium reaction trans(0) reversible arrow cis(0) from the redox reactions involving formation of the transf cation. Equilibr ium constant calculations for the reaction trans(0) reversible arrow c is(0) demonstrate that while cis(0) is slightly favored in nonpolar so lvents such as benzene and toluene, it is moderately favored in more p olar solvents. Equilibrium constants for cis(+) reversible arrow trans (+) and trans(0) + cis(+) reversible arrow cis(0) + trans(+) reactions also are calculated from the voltammetric data and their solvent depe ndences are considered.