The trans coordination of the benzene ring of the indenyl-Rh(CO)(2) complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene (NBD) (''extra-indenyl effect''). The activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species, eta(1)-indenyl-Rh(CO)(2)(L(2)). in addition, the rate of exchange of the Cr(CO)(3) group of the complexes trans-[Cr(CO)(3)-indenyl-Rh(CO)(2)], 3, and trans-[Cr(CO)(3)-indenyl-Rh(COD)], 3a, and suitable accepters (hexamethylbenzene and cycloheptatriene) is markedly increased with respect to that measured for the same reaction in the monometallic complex eta-naphthalene-Cr(CO)(3) (''extra-naphthalene effect''). These mutual effects of the Cr(CO)(3) and RhL(2) units are transmitted through the 10 pi electron indenyl framework, and the results obtained are in agreement with the existence of an haptomeric ground-state equilibrium between the two isomers trans-[Cr(CO)(3)-mu-eta(6),eta(3)-indenyl-RhL(2)], I, and trans-[Cr(CO)(3)-mu,eta(4):eta(5)-indenyl-RhL(2)], II.
Heterobimetallic indenyl complexes. Kinetics and Mechanism of Substitution and Exchange Reactions of trans-[Cr(CO)3-indenyl-Rh(CO)2] with Olefins
CECCON, ALBERTO;GAMBARO, ALESSANDRO;SANTI, SAVERIO;
1996
Abstract
The trans coordination of the benzene ring of the indenyl-Rh(CO)(2) complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene (NBD) (''extra-indenyl effect''). The activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species, eta(1)-indenyl-Rh(CO)(2)(L(2)). in addition, the rate of exchange of the Cr(CO)(3) group of the complexes trans-[Cr(CO)(3)-indenyl-Rh(CO)(2)], 3, and trans-[Cr(CO)(3)-indenyl-Rh(COD)], 3a, and suitable accepters (hexamethylbenzene and cycloheptatriene) is markedly increased with respect to that measured for the same reaction in the monometallic complex eta-naphthalene-Cr(CO)(3) (''extra-naphthalene effect''). These mutual effects of the Cr(CO)(3) and RhL(2) units are transmitted through the 10 pi electron indenyl framework, and the results obtained are in agreement with the existence of an haptomeric ground-state equilibrium between the two isomers trans-[Cr(CO)(3)-mu-eta(6),eta(3)-indenyl-RhL(2)], I, and trans-[Cr(CO)(3)-mu,eta(4):eta(5)-indenyl-RhL(2)], II.
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