Reactivity, variable temperature solution 1H NMR studies and MO calculations of dimolybdenum allenylidene complexes of the type [( η5-C 5H 5) 2Mo 2(CO) 4( μ, η2(4e)-CCCR1R2)

Abstract

The reactivity, towards nucleophiles and electrophiles, of dimolybdenum allenylidene complexes of the type [Cp 2Mo 2(CO) 4(μ,η 2(4e)-CCCR1R2)] (Cp= η 5-C 5H 5) has been investigated. The nucleophilic attacks occur at the C γ carbon atom, while electrophiles affec the C α atom. Variable temperature solution 1H NMR studies show a dynamic behavior of these complexes consisting of an equilibrium between two enantiomers with a symmetrical [Cp 2Mo 2(CO) 4(μ-σ,σ(2e)-CCCR1R2)] transition state. Extended Hückel MO calculations have been carried out on the model [Cp 2Mo 2(CO) 4(μ,η 2-CCCH 2]. 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.