ansa-Vanadocene Complexes - Syntheses, Structures and Ligand Exchange Reactions

Abstract

Tetramethylethano-bridged vanadocene dichlorides (CH3)4C2(3-R-C5H3)2VCl2 with R = H, Me, t-Bu are obtained by reacting the corresponding ligand MgCl salts with vanadium(III) acetylacetonato compounds, followed by oxidation with PCl3 or AgCl. Smooth ligand exchange reactions of these ansa-vanadocene dichlorides afford acetylacetonato cations and binaphtholate complexes; from these, the dichlorides are regenerated by exposure to MgCl2 in THF solution. Separation of meso and rac isomers (as well as enantiomer separation) is achieved via corresponding binaphtholate complexes; conversion to the vanadium(III) diisonitrile cations (CH3)4C2(3-R-C5H3)2V(CNt-Bu)2+ allows an assessment of diastereoisomer ratios by 1H NMR. Lewis-acidic bistriflate derivatives of these ansa-vanadocene complexes are obtained from the dichlorides by reaction with silver triflate.