Syntheses of molybdenum(II) and molybdenum(IV) complexes bearing tethered homoallylic phosphines

Photolysis of [CpMo(CO)(3)Cl] in the presence of 2-(1-propenyl)phenyldiphen ylphosphane (PP, cis/trans mixture) yields the complex [CpMo(CO)Cl(PP)], 2, with an olefin ligand tethered to a phosphorus donor atom. A trans configu ration of the substituents at the olefinic unit is thermodynamically prefer red, so that the corresponding complex 2(t) can be isolated in isomerically pure form under certain conditions. However, the cis-olefin complex 2(e) h as been characterized in its mixture with 2(t), too. Treatment of 2(t) with HNMe2 leads to the intramolecular elimination of HCl under formation of th e compound [CpMo(CO)(CH2-CHCHC6H4PPh2)], 3, bearing a chelating pi -allyl/P Ph2 ligand. When a CH2Cl2 solution of 3 is photolyzed in the presence of N2 O, the CO ligand is replaced by two chloride ligands, i.e., the Mo center i s oxidized to the oxidation state +IV. The resulting complex [CpMoCl2(CH2-C HCHC6H4PPh2)], 4, is one of the rare examples, where a soft allyl ligand is bound to a metal center in a comparatively high oxidation state. However, probably due to the chelate effect, the Mo-allyl bond is remarkably stable. All compounds 2-4 have been investigated by means of single-crystal X-ray diffraction, and their crystal structures are discussed.