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

Tetramethylethano-bridged vanadocene dichlorides (CH 3 ) 4 C 2 (3-R-C 5 H 3 ) 2 VCl 2 with R = H, Me, t -Bu are obtained by reacting the corresponding ligand MgCl salts with vanadium(III) acetylacetonato compounds, followed by oxidation with PCl 3 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 MgCl 2 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 (CH 3 ) 4 C 2 (3-R-C 5 H 3 ) 2 V(CN t -Bu) 2 + allows an assessment of diastereoisomer ratios by 1 H NMR. Lewis-acidic bistriflate derivatives of these ansa -vanadocene complexes are obtained from the dichlorides by reaction with silver triflate.