A new carbbenzyloxymethylenetriparatolylphosphorane ylide (BTPY), {(p-tolyl) 3 PCHCOOCH 2 C 6 H 5 },was synthesized and characterized with elemental analysis as well as various spectroscopic techniques. The reactions of the title ylide with mercury(II) chloride, mercury(II) bromide and mercury(II) iodide in equimolar ratios using dry methanol as solvent have yielded [BTPY AE HgCl 2 ] 2 (1), [BTPY AE HgBr 2 ] 2 (2) and [BTPY AE HgI 2 ] 2 (3), respectively. Single crystal X-ray analysis of 2 reveals the presence of a centrosymmeteric dimeric structure containing the ylide and HgBr 2 . The analytical data, IR and 1 H, 13 C and 31 P NMR data for the latter compound are similar to those of 1 and 3, indicating similar structures. The theoretical studies indicated that, for all three compounds, the observed trans-like structure for compound 2, is more stable than the possible cis-like structure in each case.

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The reaction between secondary amines, benzoyl isothiocyanate, and dialkyl acetylenedicarboxylates (¼ dialkyl but-2-ynedioates) in the presence of silica gel (SiO 2 ) led to alkyl 2-(dialkylamino)-4-phenylthiazole-5-carboxylates in fairly high yields. The structures of the products were confirmed by their IR, 1 H-and 13 C-NMR, and mass spectra, and by a single-crystal X-ray structure determination.

The organophousphorus complexes of [(PPh 3) 2 Hg 2 Cl 4 ] (4), [(PPh 3) 2 Hg 2 Br 4 ] (5) and [(PPh 3) 2 Hg 2 I 4 ] (6) were resulted from nucleophilic substitution of triphenylphosphine ligand with trip -tolylphophine complexes (1-3). The crystal structures of two organophousphorus complexes of mercury(II) ions 4 and 6 have been determined by means of the X-ray diffraction. Both complexes were crystallized in the monoclinic space groups P2(1)/c, and have very similar bond lengths, angles pattern and same substituted triphenylphosphine ligand. Single crystal X-ray analysis of title structures reveal the presence of a centrosymmeteric dimeric structure containing the ligand and mercury halides.

¼ Cl, Br, and I) in equimolar ratios in MeOH as solvent leads to the binuclear products 1 -3 (Scheme 1). The bridgesplitting reaction of the binuclear complex [{HgI 2 (bbtppy)} 2 ] (3c) by DMSO yields the mononuclear complex [HgI 2 · (bbtppy) (DMSO)] (3d) (Scheme 2). This bridge-splitting reaction can also be a method for the synthesis of mononuclear products. C-Coordination of the ylide and O-coordination of DMSO are demonstrated by a single-crystal X-ray-analysis of the mononuclear complex 3d. Characterization of the obtained compounds was also performed by means of elemental analysis and IR and 1 H-, 31 P-, and 13 C-NMR spectroscopy. A theoretical study of some Hg II complexes with phosphonium ylides is also reported.Introduction. -The coordination chemistry of the phosphonium ylides (¼ phosphoranes) of the type R 3 P þ ÀCH 2 À , is well known [1 -4]. Resonance-stabilized phosphonium ylides, particularly, the keto ylides, are also successfully used as ligands in organometallic and coordination chemistry owing to their accessibility and stability towards air and moisture [5] [6]. Juxtaposition of the keto group and the carbanion in the phosphonium ylides allows for the resonance delocalization of the ylide electron density providing additional stabilization to the ylide species. This so-called astabilization provides ylides with the potential to act as an ambidentate ligand and thus bond to an Hg II center through either the C-atom (see B) or O-atom (see A 1 and A 2 ). Although many bonding modes are possible for keto ylides [7], coordination through the C-atom is more predominant and observed with soft metal ions, e.g., Pd II , Pt II , Ag I , Hg II , Au I , and Au III [8] [9 -12], whereas O-coordination dominates when the metals involved are hard, e.g., Ti IV , Zr IV , and Hf IV [13].