Reactivity of cyclopalladated complexes. Part 5. Insertion reactions of diphenylacetylene, 1-phenylprop-1-yne, and hexafluorobut-2-yne with cyclopalladated compounds. Crystal and molecular structure of chloro{3–4-η-4-[(2-dimethylaminomethyl)phenyl]-1,4-dimethyl-2,3-diphenylbuta-1,3-dienyl-C1N}palladium(II) and bromo{3–4-η-4-[(2-dimethylaminomethyl)phenyl]-2,4-dimethyl-1,3-diphenylbuta-1,3-dienyl-C1N}-palladium(II)

Abstract

Reactions between disubstituted alkynes RC₂R′(R = R′= Ph and R = Me, R′= Ph) and [{Pd(dmba)X}₂](dmba =NN-dimethylbenzylamine, X = Cl or Br) afford bis-insertion products [Pd{(RCCR′)₂C₆H₄CH₂NMe₂}X] in high yield. With MeC₂Ph two isomers have been isolated, (1b_α) and (1b_β). In order to establish their molecular structures, a single-crystal X-ray diffraction study has been made on the chloro-derivative of (1b_β) and the bromo-derivative of (1b_α). Crystals of (1b_α; X = Br) are monoclinic, space group P2₁/c, Z= 4, with a= 15.362(13), b= 12.368(5), c= 14.886(11)Å, and β= 94.86(13)°. The structure has been refined to R 0.078 (R′ 0.105) for 2 529 independent reflections; the two acetylenes inserted into the Pd–C bond have a head-to-tail arrangement, the Pd being σ-bonded to a carbon bearing a phenyl group. Crystals of (1b_β; X = Cl) are monoclinic, space group P2₁, Z= 2, with a= 8.227(6), b= 16.059(33), c= 8.923(9)Å, and β= 99.30(12)°. The structure has been refined to R 0.074 (R′ 0.065) for 2 077 independent reflections. The molecule shows a tail-to-tail arrangement for the two inserted acetylenes, the carbon σ-bonded to the palladium bearing a methyl group. The corresponding reaction with the 8-methylquinoline palladated dimer affords a benzenoid trimer via a bis-insertion analogue which was isolated for R = R′= Ph. Hexafluorobut-2-yne (hfb) reacts with the above palladated dimers and those formed from benzo[h]quinoline and NN-dimethyl-1-naphthylamine to give novel halide-bridged binuclear complexes with seven-membered rings. They are formed by formal insertion of one hfb unit into the Pd–C σ bond. With the naphthylamine dimer only an organic compound was isolated. The novel dimeric complexes easily afford monomeric derivatives by bridge-splitting reactions with pyridine or PPh₃.