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, [(mu-(1,4(PPh2CH2CH2X2)-Y2Pd2)][BF4](4) (4, X = O, Y = 2,3,5,6-((CH3)(4)C-6); 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 [(mu-(1,4-(PPh2CH2CH2X)(2)-Y)(2)(Z)(4)Pd-2)][BF4](n) (7, X = O, Y = 2,3,5,6-((CH3)(4)C-6), Z = CH3CN, n = 4; 8, X = O, Y = C6H4, Z = CH3CN, n = 4; 9, X = O, Y = 2,3,5,6-((CH3)(4)C-6), Z = CN, n = 0; 10, X = O, Y = C6H4, Z = CN, n X = S, Y = C6H4, Z = CN, n = O), 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.