Ultra-low catalyst loading as a concept in economical and sustainable modern chemistry:: The contribution of ferrocenylpolyphosphane Ligands

The challenge of sustainability in modern chemistry will be met with new technologies and processes provided significant progress is made in several key research areas, such as the expansion of chemistry from renewable feedstock, the design of environmentally benign chemicals and solvents, the minimization of depletive resources, and the development of high - performance catalysis. In this prospect, ligand chemistry is a pivotal science that links modern-organic, -inorganic, -organometallic, and -coordination chemistry through a vast number of valuable applications, precisely associated to catalysis. We review in this article our recent work on catalysis promoted by original ferrocenyl tetra-, tri-, and diphosphane ligands. New concepts, taking advantages of this family of branched multidentate ligands, have led to progress in homogeneous catalysis. The search for catalyst longevity and ultra-low catalyst loadings (high turnover numbers), on the basis of multidentarity effects and robustness of the ferroceryl backbone were focused on high-value palladium-catalyzed C-C cross-couplings, such as Heck, Suzuki, and Sonogashira reactions. Low catalyst loading was also explored for C-N cross-coupling in the allylic animation of achiral substrates. The advantages of this newly born family of ligands in the class of multidentate compounds are discussed in light of the valuable information gathered up to now on their reactivity, structure, and mechanistic behavior. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)