REACTIVITY, VARIABLE TEMPERATURE SOLUTION H-1 NMR STUDIES AND MO CALCULATIONS OF DIMOLYBDENUM ALLENYLIDENE COMPLEXES OF THE TYPE [(ETA(5)-C5H5)(2)MO-2(CO)(4)(MU,ETA(2)(4E)-C=C=CR1R2)]

摘要

The reactivity, towards nucleophiles and electrophiles, of dimolybdenum allenylidene complexes of the type [Cp(2)Mo(2)(CO)(4)(mu,eta(2)(4e)-C=C=CR1R2)] (Cp = eta(5)-C5H5) has been investigated. The nucleophilic attacks occur at the C-gamma carbon atom, while electrophiles affect the C-alpha atom. Variable temperature solution H-1 NMR studies show a dynamic behavior of these complexes consisting of an equilibrium between two enantiomers with a symmetrical [Cp(2)Mo(2)(CO)(4)(mu-sigma,sigma(2e)-C=C=CR1R2)] transition state. Extended Huckel MO calculations have been carried out on the model [Cp(2)Mo(2)(CO)(4)(mu,eta(2)-C=C=CH2)]. The calculated charges of the allenylidene carbon atoms suggest that the electrophilic attacks are under charge control, while the nucleophilic attacks are rather under orbital control. [References: 23]