KINETICS OF ISOTOPE-EXCHANGE AND MECHANISMS OF CATALYTIC ACTIVATION OF DIHYDROGEN BY METAL-COMPLEXES IN SOLUTIONS

Strict kinetic equations of isotope exchange of diatomic molecules wer e used for the first time far studying the mechanism of the catalytic activation of dihydrogen in homogeneous metal-complex systems. Theoret ical bases and formal apparatus of the exchange kinetics are presented ; types of exchange are classified, and approaches to the determinatio n of their contributions from experimental data are analyzed. The kine tics of exchange of deuterium-labeled dihydrogen in homogeneous pallad ium phosphine complex-CF3COOH/H2O-H-2 systems was studied. It is shown that in these systems, the homoexchange of dihydrogen is absent, and two types of heteroexchange are observed, whose relative contributions vary within wide limits depending on the composition of the systems. Possible mechanisms of the catalytic activation of dihydrogen in the s tudied systems were analyzed on the basis of the isotope-kinetic data obtained. Taking into account the spectroscopic information on the sta te of the palladium complexes, we concluded that the observed regulari ties of exchange can be interpreted in terms of a mechanism including consecutive stages of heterolysis of dihydrogen on the Pd(II) phosphin e complex and acid-type dissociation of the Pd-H bond in the palladium monohydride complex formed. It is shown that the rates of these two s tages are unambiguously related to the isotope-kinetic parameters of t he dihydrogen exchange.