Metallodendritic catalysis for redox and carbon-carbon bond formation reactions:: A step towards green chemistry

Metallodendritic catalysts combine the advantages of homogeneous and heterogeneous catalysts: they are soluble and perfectly well defined on the molecular level, and yet they can be recovered by precipitation, ultra-filtration or ultra- centrifugation (as biomolecules) and recycled several times. In this article, we summarize our recent work in this field with examples operating under ambient conditions in metathesis, Pd-catalyzed Sonogashira coupling, redox catalysis of nitrate and nitrite cathodic reduction to ammonia and various oxidation reactions by H2O2 catalyzed by polyoxometallates. The dendritic effects on the catalytic efficiencies are scrutinized, i.e., the comparison of the metallodentritic catalysts with their monomeric models and among the dendrimer generations. It is concluded that metallostars or low-generation metallodendrimers usually are optimized catalysts in terms of efficiency and recovery/re-use. 1 Introduction 2 Dendritic Ruthenium-Benzylidene Catalysts that form Dendrimer-Cored Stars with Norbornene by ROMP 3 Copper-Free, Recoverable Dendritic Catalysts for the Sonogashira Reaction 4Water-Soluble Star-Shaped Organometallic Redox Catalyst for the Cathodic Reduction of Nitrate and Nitrite to Ammonia in Water 5 Highly Efficient Recoverable Dendritic Polyoxo-metallate Catalysts for the Epoxidation of Olefins with H2O2 in Biphasic Medium under Ambient Conditions 6 Concluding Remarks and Outlook.