Catalyzed hydrogenation of solid alkynes: an example of supramolecular enhanced catalytic hydrogenation reaction

An unusual catalyzed hydrogenation reaction of solid pheylalkynyl derivatives in the absence of a solvent is studied. The unique solid state catalytic reaction of a pheylalkynyl substrate precoated on a supported metallic catalyst is being explained in terms of supramolecular chemistry. The formation of molecular aggregates of the alkyne substrate in a close proximity to the transition metal enables a fast catalytic process in the solid phase. Catalytic sites are created via molecular recognition and self-assembly mechanisms. The accessibility of the metallic catalyst to the molecular stacks of the substrate enables a fast catalytic reaction in the absence of a solvent. The kinetics of the hydrogenation reaction is interpreted and explained via self-assembled stacks that are constructed as a result of the well-known pi-pi interaction between pheylalkynyl molecules. XRD and TGA characteristics of the supported substrate also indicate the formation of substrate-catalyst sites, which have different characteristics from the pure substrate. The dependence of the hydrogenation kinetics on the type of catalyst support, size of the molecular stack, and catalyst concentration is studied. (C) 2000 Elsevier Science B.V. All rights reserved.