NMR EVIDENCE FOR FORMATION OF NEW ALCOHOL RHENIUM COMPLEXES AS INTERMEDIATES IN IONIC HYDROGENATIONS OF CARBONYL GROUPS WITH SYSTEMS COMPOSED OF REH2(NO)(CO)(PR3)(2) (R = PR-I, CH3, OPRI) AND CF3COOH
Vi. Bakhmutov et al., NMR EVIDENCE FOR FORMATION OF NEW ALCOHOL RHENIUM COMPLEXES AS INTERMEDIATES IN IONIC HYDROGENATIONS OF CARBONYL GROUPS WITH SYSTEMS COMPOSED OF REH2(NO)(CO)(PR3)(2) (R = PR-I, CH3, OPRI) AND CF3COOH, Inorganica Chimica Acta, 278(1), 1998, pp. 122-126
Low-temperature hydrogenations of benzaldehyde and acetone by systems
ReH2(CO)(NO)(PR3)(2)/CF3COOH in CD2Cl2 with R = Pr-i (1a), CH3 (1b) an
d OPri (1c) result in formation of the new unstable alcohol complexes
[ReH(CO) (NO)(PR3)(2)(ROH) ](+)[CF3COO](-) (R* = C6H5CH2, (CH3)(2)CH)
characterized by the low-temperature NMR spectra. Heating the reactio
n solutions above 210-240 K leads to alcohol elimination to form monoh
ydrides ReH(CO)(NO)(PR3)(2)(CF3COO). Hydrogenation rates decrease in t
he order 1b > 1c > 1a and C6H5CH=O > (CH3)(2)C=O. Hydrogenation proces
ses remain effective under H-2 (or D-2) atmosphere and in the presence
of an excess of CF3COOH when the dihydrides exist as dihydrogen compo
unds [ReH(H-2)(CO)(NO)(PR3)(2)](+)[CF3COO](-). Relative acidity of the
dihydrogen complexes decreases in the order OPri > Pr-i > CH3. The hy
drogenation with dihydrogen complexes is discussed in terms of an ioni
c mechanism. (C) 1998 Elsevier Science S.A. All rights reserved.