Mesityl oxo molybdenum and tungsten compounds. II. Unexpected formation of monomesityl molybdenum(V,VI) compounds

The synthesis of known MoO(2)Mes(2) from MoO2Cl2 and MgMes(2) (1:1) in THF is accompanied by the formation of monomesityl molybdenum compounds. From ligand exchange and reduction arise [MesMoOCl(3)](-) (3a) and [MesMoO(3)](-) (3c). 3a and 3b crystallize in form of [(MesMoO(3))(2)[Mg2Cl2(THF)(5)](2)][MesMoOCl(3)](2)(THF)(2), which has been characterized by X-ray structural analysis. In 3 two MesMoO(3) units are linked in a ring-like manner via magnesium ions, The anion 3a, which possesses a distorted trigonal-bipyramidal arrangement, was also isolated as [Mg(THF)(6)][MesMoOCl(3)](2) which was investigated by X-ray analysis, The reaction of MoO2Cl2 with MgMes(2) in a 1:0,5 ratio generates thr compounds [Mg(THF)(4)(MoO3Cl)(2)] and MoOCl3(THF)(2). Reaction pathways which may lead to these compounds are discussed.