Reactivity of 2-chalcogenopyridines with palladium–phosphine complexes: isolation of different complexes depending on the nature of chalcogen atom and phosphine ligand

Abstract

Reactions of either Pd(0) phosphine complexes with dipyridyldichalcogenides or [PdCl₂(P^∩P)] (P^∩P = dppe, dppp) with pyridylchalcogenolate ions have been examined and a variety of Pd(II) complexes have been isolated and characterized. Oxidative addition of {SeC₅H₃(3-R)N}₂ (R = H or Me) to [Pd(P^∩P)₂] (P^∩P = dppe, dppp) gave either a mononuclear complex, [Pd{2-Se-C₅H₃(3-R)N}₂(P^∩P)] (for P^∩P/R: dppe/H or Me; dppp/H) or a cationic binuclear complex, [Pd₂{μ-SeC₅H₃(3-Me)N}₂(dppp)₂]²⁺ (4b) (R = Me) whereas reactions involving the tellurium analogue exclusively afforded trinuclear complexes, [Pd₃(μ-Te)₂(P^∩P)₃]Cl₂ (P^∩P = dppe (2) or dppp (6)). The latter was also obtained in the substitution reaction between [PdCl₂(P^∩P)] and NaTeC₅H₃(3-R)N. The substitution reactions between [PdCl₂(dppe)] and Pb{EC₅H₃(3-R)N}₂ yielded mononuclear complexes, [Pd{2-E-C₅H₃(3-R)N}₂(dppe)] (1a–1e) (E = S, Se or Te) while in the case of [PdCl₂(dppp)], the reactions resulted in the formation of mono-, bi- and tri- nuclear complexes depending on the nature of the chalcogen atom (E = S, Se or Te) and the substituent on the pyridyl ring (R = H or Me). Treatment of dipyridyl ditellurides, {TeC₅H₃(3-R)N}₂ (R = H or Me), with [Pd(PPh₃)₄] gave expected tellurolate complexes, [Pd{2-TeC₅H₃(3-R)N}₂(PPh₃)₂] (7a, 7b) which on prolonged standing in CDCl₃ solution gave green crystals of [PdCl{2-Te(Cl)₂C₅H₃(3-Me)N}(PPh₃)] (9). The molecular structures of {TeC₅H₃(3-Me)N}₂, [Pd₂{μ-TeC₅H₃(3-Me)N}₂(dppp)₂]Cl₂·3H₂O (5·3H₂O), [Pd₃(μ-Te)₂(dppp)₃]Cl₂·3CHCl₃ (6·3CHCl₃) and [PdCl{2-Te(Cl)₂C₅H₃(3-Me)N}(PPh₃)] (9) were established by single crystal X-ray diffraction analyses.