Synthesis and reactivity of [Pd2L2R2(µ-OH)2]-type complexes (L = PEt3 or PPh3; R = Me, PhCH2 or Ph). Crystal structure of [Pd2(PPh3)2Ph2(µ-OH)(µ-NHC6H4OMe-p)]

Abstract

The metathesis of Cl^– by OH^– in [Pd₂(PEt₃)₂R₂(µ-Cl)₂] gave the binuclear hydroxo complexes [Pd₂(PEt₃)₂R₂(µ-OH)₂] (R = Me or PhCH₂) which in CDCl₃ solution exist as 1∶1 mixtures of syn and anti isomers. They reacted with 3,5-dimethylpyrazole (Hdmpz) in 1∶2 molar ratio to yield the corresponding azolate complexes anti-[Pd₂(PEt₃)₂R₂(µ-dmpz)₂] and with oxalic acid (H₂ox), in 1∶1 molar ratio, to afford the corresponding oxalate complexes anti-[Pd₂(PEt₃)₂R₂(µ-ox)]. The cleavage of the OH bridges of the di-µ-hydroxo complexes yields the mononuclear [Pd(PEt₃)₂R(OH)] which in solution are present as 1∶1 mixtures of cis and trans isomers. Binuclear µ-hydroxo-µ-amido palladium complexes [Pd₂L₂R₂(µ-OH)(µ-NHR″)₂] (R = Me, L = PEt₃; R = Ph, L = PPh₃; R″ = Ph, C₆H₄Me-p, C₆H₄OMe-p, C₆H₄Cl-p or C₆H₄NO₂-p) have been prepared by reaction of [Pd₂L₂R₂(µ-OH)₂] with the corresponding aromatic amine R″NH₂. The NMR data indicate that the isolated complexes are the anti isomers. The crystal structure of complex [Pd₂(PPh₃)₂Ph₂(µ-OH)(µ-NHC₆H₄OMe-p)] has been established; the Pd₂ON ring is severely bent.