The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Visible-light photocatalysis is a rapidly developing and powerful strategy to initiate organic transformations as it closely adheres to the tenants of green and sustainable chemistry. Generally, most visible-light-induced photochemical reactions occur through single-electron transfer (SET) pathways. Recently, visible-light-induced energy transfer (EnT) reactions have received considerable attentions from the synthetic community as this strategy provides a distinct reaction pathway, and remarkable achievements have been made in this field. In this Minireview, we highlight the most recent advances in visible-light-induced EnT reactions.

No abstract

Separation technology is central to industries as diverse as petroleum, pharmaceuticals, mining, and life sciences. Metal-organic cages, a class of molecular containers formed via coordination-driven self-assembly, show great promise as separation agents. Precise control of the shape, size, and functionalization of cage cavities enables them to selectively bind and distinguish a wide scope of physicochemically similar substances in solution. Extensive research has thus been performed involving separations of high value targets with coordination cages, ranging from gases and liquids to compounds dissolved in solution. Enantiopure capsules also show great potential for the separation of chiral molecules. The use of crystalline cages as absorbents, or the incorporation of cages into polymer membranes, could increase the selectivity and efficiency of separation processes. This review covers recent progress in using metal-organic cages to achieve separations, with discussion of the many methods of using them in this context. Challenges and potential future developments are also discussed.Compared to metal-organic frameworks (MOFs), a class of solid, porous coordination-based materials that have been widely used for separation, [29][30][31][32] an advantage of coordination cages is their tailorable solubilities. 33,34 Cages in solution, in contrast to solid MOFs, can deform or de-ligate so as to encapsulate a guest much larger than the cage pores. Cages can also be incorporated into polymers, [35][36][37][38] as fillers, to prepare mixed-matrix membranes for performing separations. [39][40][41][42] The solubility of these capsules in different solvents enables them, in contrast to MOFs, to form homogeneous mixtures with polymer matrices, avoiding agglomeration or precipitation of fillers during membrane formation, which may lead to poor separation performance.This review summarizes recent advances in using metal-organic cages for separations, with emphasis on their multiple modes of use, ranging from cages in solution and in the solid, to polymer membranes and separation columns with cages incorporated. Cages in solution for extractionCoordination cages have been explored as liquid-phase extractants to extract target molecules from an immiscible liquid phase (liquid-liquid extraction) or a solid phase (solid-liquid extraction).These strategies require binding affinities that are strong enough to pull target molecules from the initial phase into another. Cages bring guests into solvents in which the guests are not normally soluble; the cages are thus useful liquid-phase extractants. Successful application of this extraction strategy requires cages that are stable in different solvents. The high stability of a host-guest complex after extraction can impede extractant recycling and cargo recovery, however stimuli-responsive guest release can be used to overcome these challenges. [43][44][45][46][47] Liquid-liquid extractionThe Nitschke group recently reported Fe II 4L4 tetrahedron 1 (Figure 1A), prepared from an azaphosp...

The rapidly growing area of iminium and enamine catalysis in enantioselective photochemistry is reviewed, with an emphasis on catalytic modes and reaction types.