Single crystal to single crystal [2+2] photoreactions in chloride and sulphate salts of 4-amino-cinnamic acid via solid-solution formation: a structural and kinetic study

Abstract

A set of molecular salts with general formula [1H]nA·xH2O (1 = 4-amino-cinnamic acid, A(n-) = NO3(-), BF4(-), PF6(-), SO4(2-), x = 0, 1) was prepared and structurally characterized. [1H]Cl and [1H]2SO4·H2O(II) were found to undergo an SCSC stepwise [2+2] photodimerization, which was followed by X-ray diffraction; a kinetic analysis was performed on single crystals of both salts. In the case of [1H]Cl the photoreaction was also studied on polycrystalline materials.

Making crystals with a purpose; a journey in crystal engineering at the University of Bologna

“…With this in mind we have prepared and investigated the [2 + 2] photoreactivity in a series of molecular salts with the general formula [1H] n AÁxH 2 O (1 = 4-amino-cinnamic acid, A nÀ = NO 3 À , BF 4 À , PF 6 À , SO 4 2 À , x = 0, 1). Amongst all, only the chloride and sulfate salts were found to undergo SCSC [2 + 2] photodimerization to generate the corresponding -dimers containing crystals (d'Agostino et al, 2016). Moreover, the conversions were followed stepwise by single-crystal X-ray diffraction: in both cases, upon irradiation, the presence in the crystals of the cyclobutane ring was detected, and its percentage increased up to complete conversion, as shown in Fig.…”

Can Chain-Reaction Polymerization of Octadecyl Acrylate Occur in Crystal?

“…Among all crystalline-state photopolymerization systems, photoinitiated [2 + 2] − and [4 + 4] , cycloaddition reactions were mostly investigated in diene, diyne, heterocyclic derivatives, metal–organic framework, and phenanthrene-containing systems. The criteria for crystalline-state [2 + 2] cycloaddition was reported by Schmidt and co-workers. , They proposed that the center-to-center distance d between the nearest-neighbor double bonds is of the order of 4 Å through topochemical rules, and the experimental observed limit is 3.5 Å < d < 4.2 Å.…”

Exploiting the Hydrogen-Bonding Capacity of Organoboronic Acids to Direct Covalent Bond Formation in the Solid State: Templation and Catalysis of the [2 + 2] Photodimerization

“…Here, we reveal the hydrogen-bonding capacity of organoboronic acids to direct chemical reactivity − in the organic solid state (Scheme a). Specifically, we demonstrate 4-methoxy­phenyl­boronic acid ( 4-MeO-ba ) in the cocrystal ( 4-MeO-ba )·( bpe ) (where bpe = trans -1,2-bis­(4-pyridyl)­ethylene) to act as a bifunctional hydrogen-bond-donor template by assembling bpe by way of (B)­O–H···N hydrogen bonds in a discrete four-component supramolecular assembly to undergo an intermolecular [2 + 2] photodimerization.…”

“…Specifically, studies of cocrystals and related hydrates of boronic acids with bipyridines showed the components to assemble by way of (B)­O–H···N hydrogen bonds wherein the acids enforced the pyridines to stack into face-to-face geometries. The observations prompted us to explore the use of organoboronic acids to direct the [2 + 2] photodimerization in the solid state. − In the design, a boronic acid, in a syn–syn conformation (Scheme b), would support the formation of discrete four-component hydrogen-bonded molecular assemblies wherein face-to-face stacking of a pyridyl-functionalized alkene would conform to the geometry of Schmidt to undergo the photodimerization …”