Reactions of the electron-rich triply bonded dirhenium(II) complexes Re2X4(μ-dppm)2 (X=Cl, Br) with dioxygen. Part II. The synthesis and structural characterization of the complexes ReOCl3(dppmO) (dppmO=Ph2PCH2P(O)Ph2) and Re2(μ-O)Cl6(μ-dppm)2