[((Cl)Im(Dipp))P=P(Dipp)][GaCl4]: a polarized, cationic diphosphene.

The reaction of the neutral diphosphanide [((Cl)Im(Dipp))P-P(Cl)(Dipp)] (6) ((Cl)Im(Dipp) = 4,5-dichloro-1,3-bis(Dipp)-imidazol-2-yl; Dipp = 2,6-di-iso-propylphenyl) with methyl triflate (MeOTf) leads to the formation of cationic diphosphane [((Cl)Im(Dipp))(Me)P-P(Cl)(Dipp)](+) (8+) in a stereoselective methylation. In contrast, reacting with the Lewis acid GaCl3 yields cationic diphosphene [((Cl)Im(Dipp))P=P(Dipp)](+) (7+), which is explained by a low P-Cl bond dissociation energy. The significantly polarized P=P double bond in 7+ allows for its utilization as an acceptor for nucleophiles - the reaction with Cl(-) regenerates diphosphanide and the reaction with PMe3 gives cation [((Cl)Im(Dipp))P-P(PMe3)(Dipp)] (9+).

Dioxomolybdenum(VI) complexes with pyrazole based aryloxide ligands: synthesis, characterization and application in epoxidation of olefins.

Synthesis, characterization, and epoxidation chemistry of four new dioxomolybdenum(VI) complexes [MoO(2)(L)(2)] (1-4) with aryloxide-pyrazole ligands L = L1-L4 is described. Catalysts 1-4 are air and moisture stable and easy to synthesize in only three steps in good yields. All four complexes are coordinated by the two bidentate ligands in an asymmetric fashion with one phenoxide and one pyrazole being trans to oxo atoms, respectively.