A NEW TYPE OF FERROCENOPHANE, 1ST EXAMPLE WITH DIMERIC STRUCTURE

The reaction of the ferrocene-1,1'-diselenol in the presence of NEt3, or the corresponding dilithium salt, with the tert-butylzirconocene dichloride led to the dimeric [3,3']ferrocenophane [Fe(C5H4Se)2Zr (C5H4tBu)2]2 (1), as opposed to the result published previously (B. Gautheron et G. Tainturier, J. Organomet. Chem., 262 (1984) C30. However, the H-1 NMR spectra of 1 recorded at different temperatures correspond well with those of a [3]ferrocenophane exhibiting a dynamic inversion of the ''ane'' bridge. The X-ray structure only allowed the choice between the two possible arrangements. Surprisingly, monomeric species were effectively isolated from the reaction when zirconocene dichloride and tert-butylhafnocene dichloride were used. The dependence of the dimeric structure on the nature of the elements present must be rationalized.