Template-stereocontrolled [2 + 2] photoreactions directed by surface recognition on hydrophilic functionalized carbon materials

Supramolecular assistance either in solution or in the solid state to the regioselective synthesis of single photodimers from [2 + 2] photoreactions surface-directed by multivalent H-bonding exo-templates based on hydrophilic carbon nanomaterials is shown.

A novel example of double reactivity by either photochemical [2+2] or thermal additions of an ionic organic supramolecular assembly

An example of double reactivity in the solid state was achieved from an ionic array directed by charge-assisted hydrogen bonds.

Study of temperature and ligand flexibility effects on coordination polymer formation from cyclobutanetetracarboxylic acid

Three novel coordination polymers (CPs) from rctt-H4Cbtc and 4,4’-bpe with Zn and Ni metal nodes have been synthesized. The CP derivates of Zn are an unusual example for the preparation of metastable phases involving temperature dependent and concomitant transformation.

Oxygen-initiated stereoselective thermal isomerisation of a cyclobutane derivative in the solid state

Solid-state [2+2] photochemical cycloaddition reactions have been extensively studied after the classical work of Schmidt in the 1960s. Of these, trans-1,2-bis(4'-pyridyl)ethylene (bpe) is one of the well-studied alkenes to synthesize tetrakis(4-pyridyl)cyclobutane (tpcb). However, almost all the solid-state [2+2] cycloaddition reactions of bpe yielded, almost exclusively, one of the four possible isomers, namely, the rctt-tpcb (r=regio c=cis and t=trans). Here we describe a stereoselective synthesis of the tetrahedrally disposed rtct-tpcb by the solid-state thermal isomerization of the rctt-isomer in atmospheric air. We propose that this isomerization occurs through a topochemical unimolecular mechanism by a radical chain pathway, initiated by molecular oxygen. This is supported by the nature of products formed in air and nitrogen, detection of a radical in ESR spectral studies, ESI-MS crossover experiments, VT PXRD studies along with QM, MD and docking calculations. The formation of a unique isomer by thermal isomerization may be a general phenomenon to quantitatively synthesize other useful stereoisomers from the existing isomers of cyclobutane derivatives.

Metal-organic frameworks containing a tetrapyridylcyclobutane ligand derived from isomerization reaction

The rctt isomer of tetrapyridylcyclobutane prepared from the solid-state [2 + 2] cycloaddition reaction of [bpeH(2)] x 2 CF(3)CO(2) [bpe = 1,2-bis(4-pyridyl)ethene] undergoes isomerization reaction to the rtct isomer in 100% yield, and this tetrahedral tetrapyridyl ligand forms two metal-organic frameworks having ptt and pts topology.