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.