Cyclopalladation of telluro ether ligands: synthesis, reactivity and structural characterization

Abstract

Treatment of [PdCl₂(PhCN)₂] with diaryl telluride in 1 : 2 molar ratio gave mononuclear palladium complexes, trans-[PdCl₂(TeR₂)₂] (1) (R = Mes (1a) (Mes = 2,4,6-trimethylphenyl), Ph (1b), o-tol (1c) (o-tol = ortho-tolyl)). Reaction of [PdCl₂(TeMes₂)₂] with one equivalent of [PdCl₂(PhCN)₂] or Na₂PdCl₄ with TeRR′ afforded chloro-bridged binuclear complexes, [Pd₂(μ-Cl)₂Cl₂(TeRR′)₂] (2) (R/R′ = Mes/Mes (2a); Mes/Ph (2b); Ph/Ph (2c)). A toluene–methanol solution of trans-[PdCl₂(TeMes₂)₂] on refluxing for 30 minutes yielded a binuclear cyclopalladated complex, [Pd₂(μ-Cl)₂{CH₂C₆H₂(4,6-Me₂)TeMes)}₂] (3). When the refluxing was prolonged, a mononuclear complex cis-[PdCl₂{MesTeCH₂C₆H₂(4,6-Me₂)TeMes}] (4) was isolated. Treatment of palladium acetate with TeMes₂ afforded an acetato-bridged analogue of 3, [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeMes}₂] (5a) together with a very minor component, a tetranuclear complex, [Pd(μ-OAc)(μ-TeMes)]₄ (6). This reaction with unsymmetrical tellurides, MesTeR, also gave cyclopalladated complexes [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeR}₂] (R = o-tol (5b) and Ph (5c)) in which 2-methyl of the mesityl group of the telluride was exclusively metallated. The complex trans-[PdCl₂(TeMes₂)₂] on refluxing in xylene gave palladium telluride, Pd₇Te₃. These complexes were characterized by elemental analyses, IR and NMR (¹H, ¹³C and ¹²⁵Te) spectroscopy. The molecular structures of trans-[PdCl₂(TeMes₂)₂] (1a), [Pd₂(μ-Cl)₂Cl₂(TeMes₂)₂]·2acetone (2a·2acetone), cis-[PdCl₂{MesTeCH₂C₆H₂(4,6-Me₂)TeMes}] (4), [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)TeMes)}₂]·toluene (5a·toluene), [Pd₂(μ-OAc)₂{CH₂C₆H₂(4,6-Me₂)Tetol-o}₂] (5b) and [Pd(μ-OAc)(μ-TeMes)]₄ (6) were established by single crystal X-ray diffraction analyses. The mononuclear complex 1a was isolated in two polymorphic forms each with the trans configuration.