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.