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

Addition of 2-aminobenzothiazole (abt) and substituted derivatives to Hg(OAc) leads to the high yield formation of -cyano-aminothiophenolate (ocap) complexes [Hg{SCHXN(CN)}] (X = H, Me, Cl, Br, NO) resulting from dehydrogenation and C-S bond cleavage. The reaction appears to be unique to Hg(OAc) and with HgCl the product [HgCl(abt)] contains an intact abt ligand, but reacts with acetate to afford the ocap complex [Hg{SCHN(CN)}]. Binding of abt to Hg(II) has previously been probed in molecular structures of [Hg(sac)(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) was carried out at low temperatures the intermediate [Hg(κ-OAc)(EtOH)(μ-HNCNSCH)] was isolated resulting from a single ligand deprotonation thus allowing a mechanism for ring-opening to be proposed. Reactions of [Hg{SCHXN(C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 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 PPh two different binding modes are seen in complexes [Hg{SCHXN(CN)}(PPh)] being dependant upon the nature of the arene-substituent, while addition of excess PPh affords mononuclear [Hg{SCHXN(CN)}(PPh)]. With dppm, binuclear [Hg{SCHXN(CN)}(κ-dppm)] result in which the diphosphine binds in a monodentate fashion. With the more flexible diphosphines, dppe and dppb, coordination polymers [Hg{SCHXN(CN)}(κ,κ-diphosphine)] result in which ocap binds in a simple chelate fashion. Somewhat unexpectedly, with dppp, binuclear complexes [Hg{SCHXN(CN)}(μ,κ,κ-dppp)] result in which two diphosphines bridge the Hg 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 -cyano-aminothiophenolate complexes, being shown to be a highly versatile ligand that can adopt a number of different coordination modes.