[V2Cl3(thf)6]2[Zn2Cl6]: Reagent for a Highly Selective Pinacol-Coupling Reaction

There has been a continuous interest in the pinacol-coupling reaction, which connects two carbonyl groups to create a vicinal diol. A large number of low-valent metals, their salts, or complexes are known for this reaction, namely, Li, Mg, Al, Si, Ti, V, Cr, Fe, Zn, Sn, Ce, Sm, Yb, Hg, etc. Into this field, the well characterized vanadium reagent, [V 2 Cl 3 (thf) 6 ] 2 [Zn 2 Cl 6 ](1), [90823-11-3], was introduced by Pedersen and his coworkers in 1989. [ 2 , 3 ] Now, this reagent has become one of the most effective reagents for the pinacol-coupling reaction, owing to its high ability of controlling three types of selectivity, namely: 'homo vs hetero', 'syn vs anti', and 'intramolecular vs intermolecular'. The deep green reagent (1) is typically prepared from VCl 3 (thf) 3 and Zn dust in dichloromethane at room temperature. [ 2 . 3 ] Due to the air sensitivity of VCl 3 (thf) 3 , a one-pot procedure starting from VCl 3 has also been reported.