Selective photosynthesis of Z-olefins through crystalline metal-organic cage-initiated expeditious cascade reactions

The semi-hydrogenation of alkyne to form Z-olefins with high conversion and high selectivity is still a huge challenge in the chemical industry. Moreover, flammable and explosive hydrogen as the common hydrogen source of this reaction increases the cost and danger of industrial production. Herein, we connect the photocatalytic hydrogen evolution reaction and the semi-hydrogenation reaction of alkynes in series and successfully realize the high selective production of Z-alkenes using low-cost, safe, and green water as the proton source. Before the cascade reaction, a series of isomorphic metal-organic cage catalysts (CoxZn8-xL6, x = 0, 3, 4, 5, and 8) are designed and synthesized to improve the yield of the photocatalytic hydrogen production. Among them, Co5Zn3L6 shows the highest photocatalytic activity, with a H-2 generation rate of 8.81 mmol g(-1 )h(-1). Then, Co5Zn3L6 is further applied in the above tandem reaction to efficiently reduce alkynes to Z-alkenes under ambient conditions, which can reach high conversion of >98% and high selectivity of >99%, and maintain original catalytic activity after multiple cycles. This "one-pot" tandem reaction can achieve a highly selective and safe stepwise conversion from water into hydrogen into Z-olefins under mild reaction conditions.