A solid-state [2 + 2] photodimerization involving coordination of Ag(I) ions to 2-pyridyl groups

Photoreactive Ag(I) complexes of p-toluenesulfonate ions with the unsymmetrical alkene trans-1-(4-acetoxyphenyl)-2-(2-pyridyl)ethylene 1 is reported. The crystal [Ag(p-tol)(1)₂]•(H₂O) (p-tol = p-toluenesulfonate) undergoes a [2 + 2] photocycloaddition reaction in quantitative yield to afford the head-to-tail (ht) photoproduct rctt-1,3-bis(2-pyridyl)-2,4-bis(4-acetoxyphenyl)cyclobutane 2 regioselectively. The aromatic rings of the olefin participate in face-to-face π–π interactions and adopt an anti-conformation to position the carbon–carbon double bonds (C = C) in a suitable orientation to undergo photoreaction between neighboring complexes.