Doubly activated supramolecular reaction: transesterification of acyclic oligoether esters with metal alkoxides

Reactivity and Product Selectivity of Fluoroalkyl Carbonates in Substitution Reactions with Primary Alcohols and Amines

The present study reports a systematic investigation of the substitution reactions of a series of symmetric and unsymmetric fluoroalkyl carbonates with primary alcohols or amines. The reactivity of the haloalkyl carbonate depends mainly on the electrophilicity and steric crowdedness of the carbonyl group and the leaving ability of the haloalkyl alcohols. Diethyl carbonate as a reference substrate showed no reaction with the alcohol or amine. However, bis(2,2,2-trifluoroethyl) carbonate [(F₃-EtO)₂CO] having electron-withdrawing trifluoroethyl groups enabled substitution reactions, with relatively higher reactivities to those for diphenyl carbonate [(PhO)₂CO]. Furthermore, (F₆-iPrO)₂CO, bearing two sets of hexafluoroisopropyl groups, showed dramatic acceleration of the reactions, in which the observed reactivities were similar to those for bis(perfluorophenyl) carbonate [(F₅-PhO)₂CO]. The electrophilicity of the carbonyl group and the leaving ability of the alcohols in the series of haloalkyl carbonates were found to be correlated with the wavenumbers of their carbonyl groups in IR spectra and pK_a for the eliminated alcohols, respectively. Since the eliminated fluoroalkyl alcohols exhibit weak affinity with the organic products and have lower boiling points owing to a characteristic property of the fluoroalkyl group, they could be readily removed from the product by simple evaporation below 100 °C with or without reduced pressure.

Can Cyclen Bind Alkali Metal Azides? A DFT Study as a Precursor to Synthesis

Can cyclen (1,4,7,10-tetraazacyclododecane) bind alkali metal azides? This question is addressed by studying the geometric and electronic structures of the alkali metal azide-cyclen [M(cyclen)N3] complexes using density functional theory (DFT). The effects of adding a second cyclen ring to form the sandwich alkali metal azide-cyclen [M(cyclen)2N3] complexes are also investigated. N3(-) is found to bind to a M(+) (cyclen) template to give both end-on and side-on structures. In the end-on structures, the terminal nitrogen atom of the azide group (N1) bonds to the metal as well as to a hydrogen atom of the cyclen ring through a hydrogen bond in an end-on configuration to the cyclen ring. In the side-on structures, the N3 unit is bonded (in a side-on configuration to the cyclen ring) to the metal through the terminal nitrogen atom of the azide group (N1), and through the other terminal nitrogen atom (N3) of the azide group by a hydrogen bond to a hydrogen atom of the cyclen ring. For all the alkali metals, the N3-side-on structure is lowest in energy. Addition of a second cyclen unit to [M(cyclen)N3] to form the sandwich compounds [M(cyclen)2N3] causes the bond strength between the metal and the N3 unit to decrease. It is hoped that this computational study will be a precursor to the synthesis and experimental study of these new macrocyclic compounds; structural parameters and infrared spectra were computed, which will assist future experimental work.

Control of reaction pathways in the photochemical reaction of a quinone with tetramethylethylene by metal binding

The present study reports a novel supramolecular photochemical reaction that focuses on the direct electronic interactions between a host reaction substrate and guest metal salts. The reaction pathways in the photochemical reactions of quinone derivatives bearing a methoxy group and a long oligoether sidearm QEn (n = 0 and 3) with tetramethylethylene (TME) are changed upon noncovalent complexations of the host reactant with alkali and alkaline earth metal ions and a transition metal salt. The photochemical reaction of QEn with TME provides a mixture of [2 + 2] cycloadducts 1aEn and 1bEn, hydroquinone H2QEn, and monoallyl ether adducts of hydroquinones 2aEn and 2bEn. The photochemical reaction proceeds by the photoinduced electron transfer mechanism, where photoirradiation brings about formation of a radical ion pair [QEn˙(-), TME˙(+)] as the primary intermediate. We found that the yields and selectivity of these photoproducts are changed upon electronic interactions of QEn˙(-) with the metal salts. The photochemical reaction in the absence of metal salts provides H2QEn as its major product, whereas QE3, having the long sidearm, dominantly produces 2aE3 at the expense of 1aE3, 1bE3, and H2QE3 when it forms a size-favorable host-guest complex with divalent Ca(2+). In contrast, QEn selectively provides oxetanes 1aEn and 1bEn in the presence of Pd(OAc)2, which can form complexes with the quinone through metal-olefin and coordination interactions in the ground and photoexcited states of the quinone.