Photoreaction of adsorbed dIIodomethane: Halide effects of a series of neutral palladium(II) coordination cages

A series of Pd₆L₄-type neutral coordination cages, [Pd₆X₁₂L₄] (X^- = Cl^- and Br^-), are constructed via self-assembly of (COD)PdCl₂ and K₂PdBr₄ with C₃-symmetric N,N′,N′′-tris(2-pyridinylmethyl)-1,3,5-benzenetricarboxamide (L), respectively. The iodide analogue [Pd₆I₁₂L₄] is smoothly synthesized from [Pd₆Br₁₂L₄] in the presence of CH₂I₂ under mild conditions. The replacement of bromide to iodide in the nanocage system represents a landmark achievement in synthetic-methodology development. The CH₂I₂ molecules are adsorbed in the order [Pd₆I₁₂L₄] > [Pd₆Br₁₂L₄] > [Pd₆Cl₁₂L₄] and in the "like-attracts-like" pattern, presumably owing to the van der Waals force. Irradiation of [Pd₆I₁₂L₄]·3.5CH₂I₂ with 1-methylcyclohexene in chloroform at 350 nm preferentially affords the cyclopropanation product.