Synthesis, characterization, and structural studies of mercury(II) complexes of new bidentate phosphorus ylide

The reaction of Ph2PCH2CH2PPh2 (dppe) with BrCH2C(O)C6H4NO2 (1:1.05 molar ratio) in acetone produces a mixture of the new monophosphonium salt [Ph2PCH2CH2PPh2CH2C(O)C6H4NO2]Br (1) and the diphosphonium salt [NO2C6H4C(O)CH2PPh2CH2CH2PPh2CH2C(O)C6H4NO2]Br2 (2). Compound 2 was insoluble in acetone and thus easily separated from the solution of 1. Further, by reacting both the mono- and diphosphonium salts with the appropriate bases the bidentate phosphorus ylides, [Ph2PCH2CH2PPh2CHC(O)C6H4NO2] (3) and [NO2C6H4C(O)CHPPh2CH2CH2PPh2CHC(O)C6H4NO2] (4) were obtained. The reaction of ligand 3 with mercury(II) halides in dry methanol leads to the formation of the P,P-coordinated monomeric complexes {HgX2(Ph2PCH2CH2PPh2CHC(O)C6H4NO2)2} [X = Cl (5), Br (6), I (7)]. The structure of complex 7 being unequivocally determined by single crystal X-ray diffraction techniques. Characterization of these species was also performed by elemental analysis, IR spectroscopy and 1H, 31P, and 13C NMR techniques. These analyses being consistent with a 2:1 stoichiometry ylide/Hg(II) for compounds 5 through 7. Results obtained from theoretical studies are also consistent with a product in which two ylides are coordinated to the Hg(II) center through their phosphine groups, being this product the most stable among all the possible products.