Synthesis and characterization of palladium(II)-η3-allyl–ylide complexes. X-Ray crystal structure of [PdCl(η3-2-MeC3H4){Ph3PC(H)COMe}]

Abstract

The complexes [PdCl(η³-2-XC₃H₄){Ph₃PC(H)COR}][R = Me, X = H (1) or Me(2); R = Ph, X = H (3) or Me (4)] have been obtained in high yields by treatment of the dimers [{PdCl(η³-2-XC₃H₄)}₂] with the keto-stabilized ylides Ph₃PC(H)COMe [ampp, (acetylmethylene)triphenylphosphorane] and Ph₃PC(H)COPh [bmpp, (benzoylmethylene)triphenylphosphorane] in CH₂Cl₂ solution. They have been characterized by analytical data, i.r., low-temperature ¹H and ³¹P-{¹H} n.m.r., and for complex (2) also by ¹³C n.m.r. spectroscopy. Spectroscopic evidence indicates that complexes (1)–(4) in solution at low temperature are present as two diastereoisomeric forms arising from co-ordination on the metal centre of the asymmetric ylidic carbon atom and of the η³-allyl ligand. In CH₂Cl₂ solution at room temperature the complexes are in equilibrium with their reagents. Reaction with PPh₃ and [AsPh₄]Cl gives [ PdCl(η³-2-XC₃H₄)(PPh₃)] and [AsPh₄][PdCl₂-(η³-2-XC₃H₄)], respectively, and the free ylide. The X-ray crystal structure of complex (2) was determined showing that, in the solid state, only one diastereoisomer is present. The crystals are monoclinic, space group P2₁/n with a= 9.668(3), b= 14.879(4), c= 16.226(3)Å, β= 99.85(2)°, and Z= 4. Final full-matrix least-squares refinement, based on 3 063 reflections, converged to R= 0.031. The keto-stabilized ylide ligand is C bonded to the metal with a Pd–C distance of 2.193(3)Å.