C-1-INSERTION REACTIONS AT CYCLODIMERIC (ETA(2)-ACETALDEHYDE) ZIRCONOCENE COMPLEXES

Carbonylation of dimethylzirconocene, followed by treatment with zirco nocene dihydride, benzyl chloride and then methyllithium, gave the (et a(2)-acetaldehyde)zirconocene dimer (9) as a mixture of trans- and cis -isomers isolated in a 1.5:1 ratio under kinetic control and in a 1:1. 7 ratio under thermodynamic control, respectively. Complexes trans-9/c is-9 were treated with carbon monoxide to give the trans-10/cis-10 mon oinsertion products, and with isonitriles RNC (R = CH(2)SiMe(3) (a), C Me(3) (b)) to give the mono- and bis-insertion products trans- and cis -ll(a, b) and 12(a, b), respectively. Complex 12a was characterized by X-ray diffraction. In all cases the trans/cis stereochemical informat ion was predominantly retained in the products, which indicates that d imetallic pathways are favoured in these insertion reactions of the me tallatricyclic (eta(2)-aldehyde)metallocene dimers.