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This critical review deals with the applications of nanocatalysts in Suzuki coupling reactions, a field that has attracted immense interest in the chemical, materials and industrial communities. We intend to present a broad overview of nanocatalysts for Suzuki coupling reactions with an emphasis on their performance, stability and reusability. We begin the review with a discussion on the importance of Suzuki cross-coupling reactions, and we then discuss fundamental aspects of nanocatalysis, such as the effects of catalyst size and shape. Next, we turn to the core focus of this review: the synthesis, advantages and disadvantages of nanocatalysts for Suzuki coupling reactions. We begin with various nanocatalysts that are based on conventional supports, such as high surface silica, carbon nanotubes, polymers, metal oxides and double hydroxides. Thereafter, we reviewed nanocatalysts based on non-conventional supports, such as dendrimers, cyclodextrin and magnetic nanomaterials. Finally, we discuss nanocatalyst systems that are based on non-conventional media, i.e., fluorous media and ionic liquids, for use in Suzuki reactions. At the end of this review, we summarise the significance of nanocatalysts, their impacts on conventional catalysis and perspectives for further developments of Suzuki cross-coupling reactions (131 references).

We have shown that fibrous nanosilica (KCC-1) can serve as a suitable support for the synthesis of highly dispersed ruthenium (Ru) nanoparticles. The resulting KCC-1/Ru catalyst displayed superior activity for the hydrogenolysis of propane and ethane at atmospheric pressure and at low temperature. The high catalytic activity was due to the formation of Ru-nanoparticles with an active size range (1−4 nm) and the presence of hexagonal-shaped particles with several corners and sharp edges possessing reactive atoms with lowest coordination numbers. The catalyst was stable with an excellent lifetime and no sign of deactivation, even after eight days. This enhanced stability may be due to the fibrous nature of KCC-1 which restricts Ostwald ripening of Ru nanoparticles.

Since the discovery of the Ullmann reaction over a century ago, in 1901, [1] the transition-metal-catalyzed cross-coupling reaction has played an important role in the synthesis of CÀC bonds. [2] In 1981, Suzuki discovered a novel Pd-catalyzed crosscoupling reaction of aryl boronic acids and aryl halides, [3] which has been applied widely [4][5][6][7][8][9][10][11] and for which he received the 2010 Nobel prize in chemistry. This reaction has become an extremely powerful process for the synthesis of biaryls, which have a diverse spectrum of applications, ranging from pharmaceuticals to materials science. [12][13][14][15] Recently, the use of nanocatalysts has increased rapidly and has resulted in the development of several active and efficient nano-catalysts for various protocols. [16][17][18][19][20] These systems have several advantages over conventional catalysts, such as superior activity and improved stability. Combining metal nanoparticles with a support of choice provides a large field for the discovery of new, highly active nanocatalysts for important and challenging reactions, which also offer the additional advantage of recyclability. The preparation of Pd nanoparticles is usually based on the reduction of a metal salt in the presence of a reducing agent and a stabilizer. Many substrates, such as polymers, [21] dendrimers, [22] ionic liquids, [23] ordered mesoporous silica, [24] and carbon nanotubes, [25] have been used as stabilizers and supports for Pd nanoparticles. We recently reviewed these nano-catalysts for Suzuki coupling reactions [26] and observed that an extensive range of nano-catalyst systems was developed for this process in a short period of time. Although most of these nanocatalyst systems are active and usable, two main challenges still remain unresolved: 1) stable nano-catalysts that avoid activity loss from particle-size growth during the reaction caused by Ostwald ripening and 2) active nano-catalysts that use challenging, but economical chloroarenes as substrates.In a continuation of our search for green and sustainable nano-catalytic protocols, [27][28][29][30][31][32][33][34] we herein report novel Pd-nanocatalysts supported on our recently discovered high-surfacearea silica exhibiting a unique fibrous morphology (KCC-1). [27,28] We discovered that the high surface area of KCC-1 is attributable to fibers and not pores, which dramatically increases its accessibility.[27] We believe that this unique property will be very useful for the design of silica-supported catalysts, for which the accessibility of active sites can be increased significantly. After demonstrating the validity of this concept for the hydro-metathesis of olefins by using a KCC-1/TaH catalyst system, [28] we designed highly disperse Pd-nanoparticles supported on fibers of KCC-1 to examine the advantages of fibrous KCC-1 as a catalyst support in Suzuki coupling reactions.The first step in accomplishing this catalyst design was the functionalization of KCC-1 with amino groups, which could then act as pseudo chelators...

We observed that support morphology has dramatic effects on the performance of nitridated silica as a base. By simply replacing conventional silica supports (such as SBA-15 and MCM-41) with fibrous nanosilica (KCC-1), we observed multifold enhancement in the catalytic activity of the nitridated solid base for Knoevenagel condensations and transesterification reactions. This enhancement of the activity can be explained by amine accessibility, which is excellent in KCC-1 due to its open and flexible fibrous structure, that facilitates penetration and interaction with basic amine sites.