Synthesis, structure and reactivity with phosphines of Hg(II) ortho-cyano-aminothiophenolate complexes formed via C-S bond cleavage and dehydrogenation of 2-aminobenzothiazoles

Addition of 2-aminobenzothiazole (abt) and substituted derivatives to Hg(OAc)(2) leads to the high yield formation of ortho-cyano-aminothiophenolate (ocap) complexes [Hg{SC6H3XN(C N)}](n) (X = H, Me, Cl, Br, NO2) resulting from dehydrogenation and C-S bond cleavage. The reaction appears to be unique to Hg(OAc)(2) and with HgCl2 the product [HgCl2(abt)](n) contains an intact abt ligand, but reacts with acetate to afford the ocap complex [Hg{SC6H4N(C N)}](n). Binding of abt to Hg(II) has previously been probed in molecular structures of [Hg(sac)(2)(abt)L] (L = MeOH, DMSO) and these have been reexamined to understand the perturbation of abt upon coordination. When the reaction of abt and Hg(OAc)(2) was carried out at low temperatures the intermediate [Hg(kappa(2)-OAc)(EtOH)(mu-HNCNSC6H4)](2) was isolated resulting from a single ligand deprotonation thus allowing a mechanism for ring-opening to be proposed. Reactions of [Hg{SC6H3XN(C N)}](n) with mono- and bidentate phosphines have been studied, affording a series of complexes in which the ocap ligands adopt four different binding modes in the solid state, as shown by a number of crystallographic studies. In all, the ligand chelates to a single mercury centre but spans to the second via either: (i) a simple S,N-chelate, (ii) coordination through nitrogen of the C N group, (iii) the sulfur acting as a thiolate-bridge, (iv) both thiolate bridging and cyanide coordination. With PPh3 two different binding modes are seen in complexes [Hg{SC6H3XN(C N)}(PPh3)](2) being dependant upon the nature of the arene-substituent, while addition of excess PPh3 affords mononuclear [Hg{SC6H3XN(C N)}(PPh3)(2)]. With dppm, binuclear [Hg{SC6H3XN(C N)}(kappa(1)-dppm)](2) result in which the diphosphine binds in a monodentate fashion. With the more flexible diphosphines, dppe and dppb, coordination polymers [Hg{SC6H3XN(C N)}(kappa(1),kappa(1)-diphosphine)](n) result in which ocap binds in a simple chelate fashion. Somewhat unexpectedly, with dppp, binuclear complexes [Hg-2{SC6H3XN(C N)}(2)(mu,kappa(1),kappa(1)-dppp)] result in which two diphosphines bridge the Hg-2 centre, while with dppf mononuclear chelates are proposed to result. Thus, the simple and high-yielding ring-opening of 2-aminobenzothiazole and substituted derivatives by mercuric acetate provides ready access to a range of novel ortho-cyano-aminothiophenolate complexes, being shown to be a highly versatile ligand that can adopt a number of different coordination modes.