Organic Sponge Supported Nanometer Gold And Bifunctional Photocatalyst:Highly Efficient Catalyst For Cross-dehydrogenative Coupling

Bulk gold,being the most stable among all metals,was for many years considered as an inert catalyst.However,gold particles with size on the scale of nanometers(gold nanoparticles,Au NPs)have been recognized as surprisingly active and extraordinary effective green catalysts,generating a highly popular research topic in the frontier between homogeneous and heterogeneous catalysis.In this regard,several types of gold(0),such as gold nanoparticles(Au NPs),gold nanopores(Au NPore)and gold nanoclusters(Aun(L)m),have been well developed as catalysts for various organic transformations.Despite these elegant pioneering studies,conventional filtration or centrifugation is still required for the recycle of these kinds of gold catalysts as they are generally nano-size solid particles.The extra separation process greatly limited their reusability and practical application in industry.The recovery and reuse of catalysts is a very important and eternal subject in green chemical synthesis,water is the greenest and cheapest reaction medium,therefore,the development of green,highly efficient and reusable catalyst in water is highly anticipated.Recently we have found that a hydrophobic polydimethylsiloxane(PDMS)sponge material can be successfully applied to the immobilization of organic photocatalyst and has achieved excellent results.In addition to its convenient separation and purification due to its sponge-type,it is more interesting that this hydrophobic porous sponge material supported catalyst has the distinct highly effective catalytic activity in the water.Taking into consideration of the remarkable catalytic activity of gold nanoparticles together with the hydrophobicity of PDMS sponge,which should be beneficial for organic reactions in water,we reasoned that the PDMS sponge supported gold nanoparticles should be a promising heterogeneous catalyst for efficient organic transformations in water.With our continual interests on PDMS sponge supported catalysts and nanometal catalysts,in this paper,we demonstrate for the first time that a hydrophobic PDMS sponge supported nanometer gold can act as a highly efficient recyclable catalyst for cross-dehydrogenative coupling(CDC)of tertiary amines with various nucleophiles in water.We have found out that PDMS sponge nano-gold can provide much better catalytic activity than free nano gold in water.Therefore,it should be believed that this porous hydrophobic PDMS sponge material will be a promising carrier for the development of highly efficient recyclable catalysts in water.In addition,PDMS sponge has high light transmittance.After covalent bond modification,PDMS sponge successfully connects rose and proline to PDMS sponge using glutamic acid as Linker to prepare hydrophobic bifunctional catalyst.Intramolecular cross-dehydrogenative coupling of N-phenyltetrahydroisoquinoline derivatives was carried out using a bifunctional sponge as catalyst.Moreover,the asymmetric CDC reaction was further achieved by using the proline on the bifunctional sponge catalyst,which broadened the application value of sponge as catalyst carrier.In conclusion,PDMS sponge was modified by surface modification technology,and a simple and efficient organic sponge catalyst carrier was successfully developed by combining the modified sponge with nanogold or small molecule catalyst.PDMS organic sponge as a catalyst carrier has the following advantages: strong stability,easy recovery,multiple times of reuse,high reactivity,easy to put a large number of experiments.The results show that PDMS sponge is a promising heterogeneous catalyst for both gold nanoparticles and small molecular catalysts.