Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X = Cl or Br; dppm = Ph2PCH2PPh2) with tertiary phosphine and phosphite ligands. The isolation and characterization of the 1:1 adducts Re2X4(dppm)2(PR3) and Re2Cl4(dppm)2[P(OR)3] and the crystal structure of [Re2Cl3(dppm)2(NCEt)2]PF6