Reactions of 1,2,5-Triphenylphosphole and its Oxide, Sulfide, and Selenide with some Transition Metal Halides

Reactions of 1,2,5-triphenylphosphole (TPP) and 1,2,5-triphenylphosphole oxide (TPPO), sulfide (TPPS), and selenide (TPPSe) with some transition metal halides have been studied in dry, oxygen-free organic solvents. The reactivity of these ligands is clearly a function of the oxidation states of the metal, with the order being M(II) < M(III) < M(IV) < M(V). For example the ligands do not react with the metal(II) halides (Mn, Fe, Ni), while rapid reactions occur with niobium(V) and tantalum(V). Iron(III) and copper(II) are both reduced by TPP. The complexes resulting from these studies are mostly simple adducts of the various metal halides, although other species such as phospholium salts [Formula: see text] and oxytrichloride adducts, MOX3•TPPO(M = Nb, Ta) are also described. In the phospholium salts, the phosphole ring is protonated at the phosphorus atom which is in direct contrast to pyrrole derivatives. The origin of the oxygen atom in the oxytrichloride complexes is discussed and compared with data on the analogous triphenylphosphine oxide systems, where cleavage of the P=O bond occurs.