W. Simanko et al., Rh(acac)(CO)(PR3) and Rh(oxinate)(CO) (PR3) complexes-substitution chemistry and structural aspects, J ORGMET CH, 602(1-2), 2000, pp. 59-64
The substitution of CO in Rh(acac)(CO)(2) by the phosphorus ligands P(OPh)(
3), P(NC4H4), and PPh2(NC4H4) has been studied kinetically by stopped-flow
spectrophotometry as a function of temperature. With P(OPh)(3) and P(NC4H4)
(3), both CO ligands are replaced in a stepwise fashion via the intermediat
e Rh(acac)(CO)(PR3). However, the disubstituted complexes Rh(acac)(PR3)(2)
are thermodynamically unstable. Judged from the activation parameters, the
individual steps are associative processes. In the case of PPh2(NC4H4) only
the monosubstituted complex is formed. The differences in the substitution
rates as well as the stability of the various products are largely dominat
ed by electronic (e.g. basicity) effects. X-ray structures of some of the m
ono-substituted complexes are given. In addition, also the reaction of Rh(o
xinate)(CO)(2) with P(OPh)(3) has been studied kinetically showing that oxi
nate has a labilizing effect relative to acetylacetonate (C) 2000 Elsevier
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