Bidentate phosphinophenol ligands. Preparation and electrochemistry of the Re(III) complexes of 2-(diphenylphosphinomethyl)-4-methylphenol (P1OH) and 2-diphenylphosphinophenol (P2OH). Crystal and molecular structure of mer-Re[P1O]3

The reaction of 2-(diphenylphosphinomethyl)-4-methylphenol (P1OH) and 2-diphenylphosphinophenol (P2OH) on ReCl3(MeCN)(PPh3)2 in a 3:1 ratio leads to the formation of the homoleptic Re(III) complexes Re(P1O)3 (1) and Re(P2O)3 (2) in high yield. 1 is reasonably stable in air in the solid state and in solution, which is not the case for 2. Orange–red crystals of 1 contain distorted octahedral Re entities in which the metal is coordinated to three bidentate phosphinophenolato ligands in the mer configuration. Cyclic voltammetry of 1 and 2 shows two well defined monoelectronic quasi-reversible redox waves, one reductive attributed to the Re(III)/Re(II) couple and one oxidative due to the Re(III)/Re(IV) one. A second oxidative wave, attributed to the Re(IV)/Re(V) couple, is reversible only for 1, indicating the lower stability of 2 toward oxidation. In agreement with this, 2 gives, in air, the Re(V)-oxo species ReO(OP2O)(P2O)2 (3) quantitatively, whose structure is confirmed by X-ray diffraction.