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/

Citation
Am. Bond et al., 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/, Organometallics, 13(9), 1994, pp. 3434-3441
Citations number
15
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry Inorganic & Nuclear","Chemistry Inorganic & Nuclear
Journal title
ISSN journal
0276-7333
Volume
13
Issue
9
Year of publication
1994
Pages
3434 - 3441
Database
ISI
SICI code
0276-7333(1994)13:9<3434:SAVSOT>2.0.ZU;2-N
Abstract
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.