Issue 20, 2022

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

Abstract

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[triple bond, length as m-dash]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[triple bond, length as m-dash]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(κ2-OAc)(EtOH)(μ-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[triple bond, length as m-dash]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[triple bond, length as m-dash]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[triple bond, length as m-dash]N)}(PPh3)]2 being dependant upon the nature of the arene-substituent, while addition of excess PPh3 affords mononuclear [Hg{SC6H3XN(C[triple bond, length as m-dash]N)}(PPh3)2]. With dppm, binuclear [Hg{SC6H3XN(C[triple bond, length as m-dash]N)}(κ1-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[triple bond, length as m-dash]N)}(κ11-diphosphine)]n result in which ocap binds in a simple chelate fashion. Somewhat unexpectedly, with dppp, binuclear complexes [Hg2{SC6H3XN(C[triple bond, length as m-dash]N)}2(μ,κ11-dppp)] result in which two diphosphines bridge the Hg2 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.

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

Supplementary files

Article information

Article type
Paper
Submitted
08 Feb 2022
Accepted
21 Apr 2022
First published
25 Apr 2022
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2022,51, 7889-7898

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

S. A. Al-Jibori, A. A. Irzoqi, A. S. M. Al-Janabi, A. I. A. Al-Nassiry, S. Basak-Modi, S. Ghosh, C. Wagner and G. Hogarth, Dalton Trans., 2022, 51, 7889 DOI: 10.1039/D2DT00391K

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