Synthesis and structure of tetranuclear orthometallated Pd(ii) complexes derived from bis-iminophosphoranes

Abstract

The reaction of Pd(OAc)₂ with bis-iminophosphoranes Ph₃PNCH₂CH₂CH₂NPPh₃ (1a), [C₆H₄(C(O)NPPh₃)₂-1,3] (1b) and [C₆H₄(C(O)NPPh₃)₂-1,2] (1c), gives the orthopalladated tetranuclear complexes [{Pd(µ-Cl){C₆H₄(PPh₂NCH₂-κ-C,N)-2}}₂CH₂]₂ (2a) [{Pd(µ-OAc){C₆H₄(PPh₂NC(O)-κ-C,N)-2}}₂C₆H₄-1′,3′]₂ (2b) and [{Pd(µ-OAc){C₆H₄(PPh₂NC(O)-κ-C,N)-2}}₂C₆H₄-1′,2′]₂ (2c). The reaction takes place in CH₂Cl₂ for 1a, but must be performed in glacial acetic acid for 1b and 1c. The process implies in all cases the activation of a C–H bond on a Ph ring of the phosphonium group, with concomitant formation of endo complexes. This is the expected behaviour for 1a, but for 1b and 1c reverses the exo orientation observed in other ketostabilized iminophosphoranes. The influence of the solvent in the orientation of the reaction is discussed. The dinuclear acetylacetonate complexes [{Pd(acac-O,O′){C₆H₄(PPh₂NCH₂-κ-C,N)-2}}₂CH₂] (3a), [{Pd(acac-O,O′){C₆H₄(PPh₂NC(O)-κ-C,N)-2}}₂C₆H₄-1′,3′] (3b) and [{Pd(acac-O,O′){C₆H₄(PPh₂NC(O)-κ-C,N)-2}}₂C₆H₄–1′,2′] (3c) have been obtained from the halide-bridging tetranuclear derivatives. The X-ray crystal structure of [3c·4CHCl₃] is also reported.