Treatment of HgCl2 with 2-LiC6H4PPh2 gives [Hg(2-C6H4PPh2)(2)] (1), whose phosphorus atoms take up oxygen, sulfur, and borane to give the compounds [Hg{2-C6H4P(X)Ph-2}(2)] [ X = 0 (3), S (4), and BH3 (5)], respectively. Compound 1 functions as a bidentate ligand of wide, variable bite angle that can span either cis or trans coordination sites in a planar complex. Representative complexes include [HgX2.1] [X = Cl (6a), Br (6b)], cis-[PtX2.1] [X = Cl (cis-7), Me (9), Ph (10)], and trans-[MX2.1] [X = Cl, M = Pt (trans-7), Pd (8), Ni (11); X = NCS, M = Ni (13)] in which the central metal ions are in either tetrahedral (6a,b) or planar (7-11, 13) coordination. The trans disposition of I in complexes trans-7, 8, and 11 imposes close metal-mercury contacts [2.8339(7), 2.8797(8), and 2.756(8) A, respectively] that are suggestive of a donor-acceptor interaction, M --> Hg. Prolonged heating of 1 with [PtCl2(cod)] gives the binuclear cyclometalated complex [(eta(2)-2-C6H4PPh2)Pt(mu-2-C6H4PPh2)(2)HgCl] (14) from which the salt [(eta(2)-2-C6H4PPh2)Pt 2-C6H4PPh2)(2)Hg]PF6 (15) is derived by treatment with AgPF6. In 14 and 15, the mu-C6H4PPh2 groups adopt a head-to-tail arrangement, and the Pt-Hg separation in 14, 3.1335(5) Angstrom, is in the range expected for a weak metallophilic interaction. A similar arrangement of bridging groups is found in [Cl((Bu3P)-Bu-0)Pd(mu-2-C6H4PPh2)(2)HgCl] (16), which is formed by heating 1 with [PdCl2((PBu3)-Bu-n)(2)]. Reaction of 1 with [Pd(dba)(2)] [dba = dibenzylideneacetone] at room temperature gives [Pd(1)(2)] (19) which, in air, forms a trigonal planar palladium(0) complex 20 containing bidentate 1 and the monodentate phosphine-phosphine oxide ligand [Hg(2-C6H4PPh2){2-C6H4P(O)Ph-2}](.) On heating, 19 eliminates Pd and Hg, and the C-C coupled product 2-Ph(2)PC(6)H(4)C(6)H(4)Pph(2)-2 (18) is formed by reductive elimination. In contrast, 1 reacts with platinum(O) complexes to give a bis(aryl)platinum(II) species formulated as [Pt(eta(1)-C-2-C6H4PPh2)(eta(2) -2-C6H4PPh2)(eta(1)-P-1)]. Crystal data are as follows. Compound 3: monoclinic, P2(1)/n, with a = 11.331(3) Angstrom, b = 9.381(2) Angstrom, c = 14,516 Angstrom, beta = 98.30(2)degrees, and Z = 2. Compound 6b.2CH(2)Cl(2): triclinic, P (1) over bar, with a = 12.720(3) Angstrom, b = 13.154(3) Angstrom, c = 12.724(2) Angstrom, alpha = 92.01(2)degrees, beta = 109.19(2)degrees, gamma = 90.82(2)degrees, and Z = 2. Compound trans-7.2CH(2)Cl(2): orthorhombic, Pbca, with a = 19.805(3) Angstrom, b = 8.532(4) Angstrom, c = 23.076(2) Angstrom, and Z = 4. Compound 11.2CH(2)Cl(2): orthorhombic, Pbca, with a = 19.455(3) Angstrom, b = 8.496(5) Angstrom, c = 22.858(3) Angstrom, and Z = 4. Compound 14: monoclinic, P2(1)/c, with a = 13.150(3) Angstrom, b = 12.912(6) Angstrom, c = 26.724(2) Angstrom, beta = 94.09(1)degrees, and Z = 4. Compound 20.C6H5CH3.0. 5CH(2)Cl(2): triclinic, P (1) over bar, with a = 13.199(1) Angstrom, b = 15.273(2) Angstrom, c = 17.850(1) Angstrom, alpha = 93.830(7), beta = 93.664(6), gamma = 104.378(7)degrees, and Z = 2.