Catalysis unsaturated organic compounds

Hydrogenation reactions are reactions in w hich hydrogen is added to some compound, particularly unsaturated organic compounds. A large number of reactions of this type are of commercial importance, and almost all of them are catalyzed by either a soHd catalyst (heterogeneous catalysis) or some catalyst in solution (homogeneous catalysis). One of the simplest reactions of this type is the hydrogenation of ethylene to produce ethane. 

Ligand-metal bifunctional catalysis provides an efficient method for the hydrogenation of various unsaturated organic compounds. Shvo-type [83-85] Ru-H/OH and Noyori-type [3-7] Ru-H/NH catalysts have demonstrated bifimctionality with excellent chemo- and enantioselectivities in transfer hydrogenations and hydrogenations of alkenes, aldehydes, ketones, and imines. Based on the isoelectronic analogy of H-Ru-CO and H-Re-NO units, it was anticipated that rhenium nitrosyl-based bifunctional complexes could exhibit catalytic activities comparable to the ruthenium carbonyl ones (Scheme 29) [86]. 

The conditions influence the direction of the reactions between the nucleophile and unsaturated carbonyl compounds as well. For example, the reaction of hydrazides of some organic acids with chalcone in the presence of acetic acid involves the carbonyl group of the unsaturated ketone, while basic catalysis (piperidine) promotes /3-addition [45]. An analogous influence of the acidity on the direction is observed in reactions with binucleophiles [46]. Numerous similar examples are given in the appropriate chapters of this book. 

This is an important area with many available methods. We shall look first at organic catalysis and then change to catalysis by metal complexes. The same type of intermediate 117 used for conjugate addition is clearly also suitable for Diels-Alder reactions with the same proviso it must be more reactive then the a,(5-unsaturated carbonyl compound as that too can do Diels-Alder reactions. And of course the first formed product 118 must hydrolyse rapidly to release the catalyst 102. 

Metal-catalyzed reactions have been of major importance in synthetic organic chemistry. Over the past decade, enantio- and diastereoselective metal-mediated domino catalysis has emerged as an effective tool to construct really highly complex molecules in one-pot processes [2, 4b,d]. Among them, enantioseletcive metal-catalyzed conjugate additions (in particular, Cu-catalyzed 1,4-addition to a,P-unsaturated carbonyl compounds) have been useful components of domino reactions [4d, 5]. The generated metal enolates 2 after the additions of nucleophiles readily react with a variety of electrophiles (Scheme 11.1). Enantioselectivity of 3 depends on the first addition of nucleophiles to the P-position of the unsaturated carbonyl compounds 1. 

Beletskaya, I. R Ananikov, V. R Khemchyan, L. L. In Synthesis of Phosphorus Compounds via Metal-Catalyzed Addition ofP-HBond to Unsaturated Organic Molecules, Peruzzini, M. G. L., Ed. Catalysis by Metal Complexes 2011 Vol. 37, pp 213-264. 

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