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{SC 6 H 3 XN(CN)}] n (X = H, Me, Cl, Br, NO 2 ) resulting from dehydrogenation and C-S bond cleavage. The reaction appears to be unique to Hg(OAc) 2 and with HgCl 2 the product [HgCl 2 (abt)] n contains an intact abt ligand, but reacts with acetate to afford the ocap complex [Hg{SC 6 H 4 N(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(κ 2 -OAc)(EtOH)(μ-HNCNSC 6 H 4 )] 2 was isolated resulting from a single ligand deprotonation thus allowing a mechanism for ring-opening to be proposed. Reactions of [Hg{SC 6 H 3 XN(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 PPh 3 two different binding modes are seen in complexes [Hg{SC 6 H 3 XN(CN)}(PPh 3 )] 2 being dependant upon the nature of the arene-substituent, while addition of excess PPh 3 affords mononuclear [Hg{SC 6 H 3 XN(CN)}(PPh 3 ) 2 ]. With dppm, binuclear [Hg{SC 6 H 3 XN(CN)}(κ 1 -dppm)] 2 result in which the diphosphine binds in a monodentate fashion. With the more flexible diphosphines, dppe and dppb, coordination polymers [Hg{SC 6 H 3 XN(CN)}(κ 1 ,κ 1 -diphosphine)] n result in which ocap binds in a simple chelate fashion. Somewhat unexpectedly, with dppp, binuclear complexes [Hg 2 {SC 6 H 3 XN(CN)} 2 (μ,κ 1 ,κ 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.