Binuclear palladium macrocycles synthesized via the weak-link approach

The "weak-link approach" to metallomacrocycle synthesis has been employed to synthesize a series of Pd(II) macrocycles in high yield. Although this approach has been used to construct several Rh(I) complexes with a variety of ligands, the generality of this methodology with respect to transition metals has not been demonstrated. When added to [Pd(NCCH₃)₄[BF₄]₂, the phosphinoalkyl ether or thioether ligands produce "condensed intermediates", [(μ-(1,4-(PPh₂CH₂ CH₂X)₂-Y)₂Pd₂)] [BF₄]₄ (4, X = O, Y = 2,3,5,6- ((CH₃)₄C₆); 5, X = O, Y = C₆H₄; 6, X = S, Y = C₆H₄), containing strong P-Pd bonds and weaker O-Pd or S-pd bonds. The weak bonds of these intermediates can be quantitatively broken through simple ligand substitution reactions to generate the macrocyclic structures [(μ-(1,4-(PPh₂CH₂ CH₂X)₂-Y)₂(Z)₄Pd₂)] BF₄]_n (7, X = O, Y = 2,3,5,6-((CH₃)₄ C₆), Z = CH₃CN, n = 4; 8, X = O, Y = C₆H₄, Z = CH₃CH, n = 4; 9, X = O, Y = 2,3,5,6-((CH₃)₄C₆), Z = CN, n = 0; 10, X = O, Y = C₆H₄, Z = CN, n = 0; 11, X = S, Y = C₆H₄, Z = CN, n = 0), in quantitative yields. The extension of this approach to Pd(II) should provide new pathways for modifying the binding and catalytic capabilities of these complexes. Solid-state structures as determined by single-crystal X-ray diffraction studies are presented for compounds 6, 8, and 9.