REACTIVITY, VARIABLE-TEMPERATURE SOLUTION H-1-NMR STUDIES AND MO CALCULATIONS OF DIMOLYBDENUM ALLENYLIDENE COMPLEXES OF THE TYPE A(5)-C5H5)(2)MO-2(CO)(4)(MU,ETA(2)(4E)-C=C=CR1R2)]
Jf. Capon et al., REACTIVITY, VARIABLE-TEMPERATURE SOLUTION H-1-NMR STUDIES AND MO CALCULATIONS OF DIMOLYBDENUM ALLENYLIDENE COMPLEXES OF THE TYPE A(5)-C5H5)(2)MO-2(CO)(4)(MU,ETA(2)(4E)-C=C=CR1R2)], Inorganica Chimica Acta, 250(1-2), 1996, pp. 119-127
The reactivity, towards nucleophiles and electrophiles, of dimolybdenu
m 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 betw
een two enantiomers with a symmetrical [Cp(2)Mo(2)(CO)(4)(mu-sigma,sig
ma(2e)-C=C=CR1R2)] transition state. Extended Huckel MO calculations h
ave 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 th
at the electrophilic attacks are under charge control, while the nucle
ophilic attacks are rather under orbital control.