Reactivity, variable temperature solution 1H NMR studies and MO calculations of dimolybdenum allenylidene complexes of the type [(η5-C5H5)2Mo2(CO)4(μ,η2(4e)-CCCR1R2)]

The reactivity, towards nucleophiles and electrophiles, of dimolybdenum allenylidene complexes of the type [Cp2Mo2(CO)4(μ,η2(4e)-CCCR1R2)] (Cp=η5-C5H5) has been investigated. The nucleophilic attacks occur at the Cγ carbon atom, while electrophiles affec the Cα atom. Variable temperature solution 1H NMR studies show a dynamic behavior of these complexes consisting of an equilibrium between two enantiomers with a symmetrical [Cp2Mo2(CO)4(μ-σ,σ(2e)-CCCR1R2)] transition state. Extended Huckel MO calculations have been carried out on the model [Cp2Mo2(CO)4(μ,η2-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.