Convenient syntheses of zero valent 2,2′-bipyridine and related complexes of transition metals

The neutral tris-2,2′-bipyridine(bipy) and 1,10-phenanthroline(phen)compounds Mbipy₃ and Mphen₃ can be made conveniently in high yield by sodium amalgam reduction of the chlorides of Ti, Zr, Hf, V, Nb, Ta, Cr or better, for Mo, W and Re, the respective adducts MoCl₄L, WCl₄L and ReCl₄(THF) in tetrahydrofuran containing the ligands. The Cr and Mo compounds can also be obtained from the dimeric acetates M₂(CO₂Me)₄. For vanadium, similar compounds have been obtained from 2,2′-dipyridylamine, 2,2′-dipyridyldisulfide and di-t-butyldiimine. Reduction of VCl₃ in THF containing one equivalent of 2,2′-bipyridine under CO gives the carbonyl V(CO)₄bipy. Interaction of Vbipy₃ with NO and CH₃I give respectively, V(NO)bipy₃ and [V(CH₃)I(bipy)].