Combining hydrogen bonding and metal coordination for controlling topochemical [2+2] cycloaddition from multi-component assemblies

The crystal engineering of hydrogen bonded metal assemblies based on stilbene-type compounds is exploited in order to drive [2 + 2] cycloaddition in the solid state. Harmonisation of hydrogen bonding and metal coordination is shown as an alternative supramolecular approach for the rational design of novel supramolecular photoreactive networks. This approach was extended to prepare five compounds based on Mn/trans-1,2'-(4-pyridyl)ethylene (4,4'-bpe). The structure-templating features of such arrangements are discussed in terms of their encoded self-complementary stereochemical information (persistence of O-H center dot center dot center dot N hydrogen bonds and the presence of multiple short contacts between double bonds of the 4,4'-bpe molecules). In this work, the tolerance of this approach to diverse structural factors such as number of hydrogen bonding sites on the metal centre, nature of the counterion and coordinating solvent is shown. All the arrays 1-5 are photoreactive in the solid state upon UV-irradiation leading to the regioselective synthesis of rctt-tetrakis(4-pyridyl) cyclobutane isomer (rctt-4,4'-tpcb) in high to moderate yield. An unprecedented example of supramolecular isomers (2 and 4) with similar solid sate reactivity is also reported. In addition, the compound 5 exhibits unexpected formation of the rctt-4,4'-tpcb isomer in the solid state, then a structural change induced by the desolvation of the material.