Application in Homogeneous Catalysis

The pre.sent account follows a Journey in this arena from solution calorimetric studies dealing with nucleophilic carbene ligands in an organometallic system to the use of these thermodynamic data in predicting the feasibility of exchange reactions to applications in homogeneous catalysis. 

Abstract Allenylidene complexes have gained considerable significance in the context of transition-metal carbene chemistry due to their potential applications in organic synthesis. The aim of this chapter is to draw together a general presentation of the most efficient synthetic routes, the main structural features and reactivity patterns, as well as current applications in homogeneous catalysis, of aU-carbon-substituted allenylidenes and related cumulenylidene complexes containing an odd number of carbon atoms. 

Lanthanide-based catalysts, despite finding a lot of application in homogeneous catalysis, can be rather problematic due to the lability of some ligand types and the versatility of their coordination chemistry in the -1-3 oxidation state this makes the controlled synthesis of single-site Ln complexes a quite ambitious goal [92]. McLain and coworkers first demonstrated the high potential of a homoleptic yttrium complex Y(OCH2CH2NMe2)3 as ROP catalyst for the preparation of PLA from rac-lactide and that it promotes a rapid and controlled polymerization... 

Platinum alkene complexes have been known since 1830 when Zeise s salt was discovered. Alkene complexes of platinum(II) are kinetically more stable than their palladium counterparts, but this feature makes them less attractive for applications in homogeneous catalysis. A number of reviews have been written on alkene complexes.620-623... 

The pentamethyl cyclopentadiene lanthanide complexes containing hydrocarbyl substituents have been studied extensively for their applications in homogeneous catalysis and C-H activation. The well-known catalyst of the Ziegler-Nutta type Cp2LnMe(Et20) is typical of the large number of compounds [155] that have been studied. Solvent-free electrophilic alkyl derivatives serve as precursors of the majority of the compounds which have been studied. 

In recent years the synthesis of chiral and achiral tripodal phosphines and their application in homogeneous catalysis has been studied in more detail [2]. Enantiomerically pure tripodal ligands were synthesized from the corresponding trichloro compounds and chiral, cyclic lithio-phosphanes, e.g. 17, (Scheme 6) [21,22], Using a rhodium(I) complex of ligand 18, an enantiomeric excess of 89 % was obtained in the asymmetric hydrogenation reaction of methyl acetami-docinnamate (19). 

Although the reaction is successful with many representatives of the purine family, it relies on the protonation of the N -nitrogen atom [81] meaning that substituents at N and N cannot be chosen at will, thus limiting the scope for steric, electronic and chiral diversification of a purine derived carbene ligand for application in homogenous catalysis. Furthermore, the NH functionality may have adverse effects in catalytic reactions and the yields of C-bound complexes are generally low. 

Gold(l) complexes of alkenes and alkynes appear to play an important role as intermediates of the gold(l)-catalyzed addition of water, alcohols, carboxylic acids, or amines to these substrates. The elfect of this 7r-complexation (22) is superior to the performance of mercury(ll) in this type of reactions. " In a similar way, gold(III) salts have found applications in homogeneous catalysis. ... 

Epoxide isomerization through C-O bond cleavage promoted by Rh(I) and Ir(I) complexes and its application in homogeneous catalysis have been also reported [105]. 

For a review on water-soluble phosphine complexes and their application in homogeneous catalysis, see N. Pinault and D. W. Bruce, Coord. Chem. Rev. 241, 1 (2003). 

Complexes of the [SnCl3] anion and. to a lesser extent, the [GeCl3] anion have found extensive application in homogeneous catalysis.1 All the Group VIII metals have been reported to form... 

A related area of research involves the paramagnetic -polyphospholyl complexes of the transition metals [rj -(C R P5 )2]M (n = 0-3), also referred to as phosphamet-allocenes. Although the subject has been previously reviewed, several new trends have emerged, in particular, some promising applications in homogeneous catalysis. ... 

The phosphine metal complexes now finding application in homogeneous catalysis are those of the tertiary organic phosphines. They were discovered around the middle of the last century and their ability to combine with heavy metal salts noted almost immediately, but the application of their metal complexes to homogeneous catalysis came only after the lapse of about 100 years. 

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