Photochemical preparation of the cis isomers of dichlorobis(tri-n-alkyl-phosphine)palladium(II)(alkyl = Et, Prn, or Bun); the crystal-structure analysis of the overcrowded n-propyl homologue

Abstract

Ultraviolet irradiation of the trans forms of the title compounds in nitromethane gives up to 70% of the labile cis isomers, which can be isolated in crystalline form. Irradiation of a 1 : 1 mixture of trans-[Pd(PEt₃)₂Cl₂] and trans-[Pd(PPrⁿ₃)₂Cl₂] gives almost entirely a 1 : 1 mixture of the corresponding cis isomers and only a few percent of cis-[Pd(PEt₃)(PPrⁿ₃) Cl₂], indicating a predominantly intramolecular mechanism. Crystals of cis-[Pd(PPrⁿ₃)₂Cl₂] are monoclinic, with space group P2₁/m, a= 9.729(1), b= 13.816(3), c= 9.614(1)Å, β= 100.77(1)°, and Z= 2. The structure has been refined to R= 0.029 for 1 873 reflections collected by a four-circle diffractometer. The cis-planar structure reveals considerable overcrowding [P–Pd–P 105.75(6)°, one Pd–P–C 121.1°(mean)]. The Pd–P distances are short (mean 2.322 Å) and the Pd–Cl distances long (mean 2.407 Å), attributable to the trans effect.