Synthesis, Structural Characterization, and Photochemical [2+2] Cycloaddition of a Coordination Polymer: Multiweek Inorganic-Organic Chemistry Experiments

The [2 + 2] photocycloaddition reaction of olefins is an effective, atom-economical approach to produce cyclobutane compounds in organic synthetic chemistry, and they usually exhibit high regioselectivity and stereoselectivity. Here we devised a solid-state [2 + 2] photocycloaddition experiment that introduces senior undergraduate students with the principles of coordination chemistry, organic chemistry, structural chemistry, and supramolecular chemistry, which have been widely used in material chemistry, catalysis, nanotechnology, and other fields. The experiment employs coordination interactions that act as templates to directing the [2 + 2] photocycloaddition reaction. A photoreactive coordination polymer [Zn(oba)(4-npy)](2)(4-npy)(0.25) (1, 4-npy = (E)-4-(2-(naphthalen-1-yl)vinyl)pyridine, H(2)oba = 4,4 '-oxidibenzoic acid) is solvothermally prepared and undergoes a [2 + 2] photocycloaddition reaction, affording the new compound [Zn-2(oba)(2)(HT-pncb)](4-npy)(0.25) (1a, HT-pncb = rctt-1,3-bis(4-pyridyl)-2,4-bis(1-naphthyl)cyclobutane; HT = head-to-tail) upon UV light illumination. The experiments will strengthen the students' experimental skills while the diverse characterization experiments will allow them to experience the contribution of each method and their complementarity in monitoring the structural changes that occur upon photoreaction. This comprehensive project will help students broaden the research horizon, cultivate research skills, follow strict scientific procedures, and promote rigorous thinking in a laboratory course.