Heterocyclic-2-thione derivatives of metals incorporating cyclopalladated azobenzenes of variable nuclearity and N,S-bridged 1D polymer of [bis(pyridine-2-thiolato)mercury(ii)]

Abstract

In this investigation, the reactivity of azobenzene-based cyclopalladated precursors with a series of heterocyclic-2-thiones is described. Reactions of the precursor, [Pd₂(μ-Cl)₂ -(κ²:C,N-deazb)₂], with pyridine-2-thione (pytH), or pyrimidine-2-thione (pymtH), yielded the red-brown dinuclear compounds [Pd₂(μ-N,S-pyt)₂(κ²:C,N-deazb)₂] (1) and [Pd₂(μ-N,S-pymt)₂(κ²:C,N-deazb)₂] (2) (deazbH = 4,4′-diethoxyazobenzene). A similar reaction of [Pd₂(μ-Cl)₂(κ²:C,N-p-mazb)₂] with N-phenyl-imidazolidine–2-thione (imdtH–NPh) yielded a trinuclear compound, [Pd₃(μ-N,S-imdt-NPh)₄(κ²:C,N-pmazb)₂] (4) (pmazb = p-methoxyazobenzene). A direct reaction of PdCl₂ with azobenzene (azbH) and N-methyl-imidazolidine–2-thione (imdtH–NMe) afforded a mononuclear compound, [Pd(κ¹S-imdtH-NMe)Cl(κ²:C,N-azb)] (3). In the compounds 1, 2 and 4, the thio-ligands, pyt⁻, pymt⁻ and imdt–NPh⁻ are coordinating as anions with N,S-bridging (1, 2, 4) and in compound 3, imdtH–NMe is coordinating as a neutral ligand through the S-donor atom only. Compounds 1–4 are luminescent in the visible region. A reaction of HgCl₂ with azobenzene (azbH), and pyridine–2-thione in DMF, did not yield the cyclometallated compound, [Hg₂(μ-N,S-pyt)₂(κ²:C,N-azb)₂]; rather, it afforded two coordinate compounds, [Hg(κ¹S-pyt)₂] (5), with polymerisation occurring via weak N⋯Hg bonds.