Molybdenum(II) complexes with α-diimines. Catalytic activity in organic and ionic liquid solvents

The new [MoX(η³-C₃H₅)(CO)₂(α-diimine)] complexes with: (i) X = Br or triflate and α-diimine = 1,10-phenanthroline (phen) and dipyridophenazine (dppz); and (ii) X = Br and α-diimine = phen and dppz, with several substituents, are synthesized and characterized. The structures of [MoBr(η³-C₃H₅)(CO)₂(Cl-phen)] and [Mo(CF₃SO₃)(η³-C₃H₅)(CO)₂(dppz)] are determined by using single-crystal X-ray diffraction. These and three complexes of 2,2'-bipyridyl (bpy), and its two derivatives with Me and tBu substituents, are tested in the homogeneous catalytic epoxidation of several olefins in dichloromethane, exhibiting, in general, a good selectivity towards the respective epoxide and relatively low TOFs. For the first time, the oxidation of cis-cyclooctene with some of these catalysts is also conducted in a variety of room-temperature ionic liquids (RTILs). In the presence of [MoBr(η³-C₃H₅)(CO)₂(phen)], the conversions, in general, increase, compared with the reactions in organic solvents. Interestingly, different chemoselectivity is found when [C₆mim][Ntf₂] and [C₂mim][FAP] are used with diol (24-26 %). On the other hand, [MoBr(η³-C₃H₅)(CO)₂(L)] (L = Me-phen or dppz) exhibits much lower conversions in the RTILs tested than in common organic solvents. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)