Palladium-based systems

Amidocarbonylation converts aldehydes into amido-substituted amino acids, which have many important industrial applications ranging from pharmaceuticals to detergents and metal-chelating agents.588 Two catalyst systems have been developed, a cobalt-based system and, more recently a palladium-based system. In the cobalt system, alkenes can be used as the starting material, thus conducting alkene-hydroformylation, formation of hemi-amidal and carbonylation in one pot as... 

An example of a non-palladium-based system was reported by Madec et al. They made use of Ni(PPh3)2Gl2 for the coupling of vinylcarbamates and alkynylmagnesium reagents in benzene at higher temperatures (70 °G), and obtained good yields of product. ... 

The versatility and stability of (NHC)-palladium-based systems in crosscoupling reaction has allowed their utilization in elegant multistep one-pot processes. 

To date, only one other palladium-based system has shown good selectivity in the hydrogenation of alkynes to Z-alkenes, however, only poor selectivity was obtained in the case of arylalkynes [193,194],... 

A recent patent has described the carbonylation of methanol to give acetic acid using a palladium-based system (119). The system requires alkyl halide promoters and electron-rich nitrogen ligands (e.g., 2,2 -bipyridine) and operates in the ranges 125-250°C and 20-210 atm. There is insufficient information available to allow discussion of pathways involved. 

In contrast, there are a few studies with palladium-based systems. The catalytic precursors are usually prepared by activating neutral [PdX(t -allyl)(L )] with silver salts of weakly coordinating anions or with NaBARF. The reactions are often carried out at room temperature in dichloromethane or THF. A selection of catalytic results is given in Table 8.1. 

Before starting the discussion on these palladium-based systems, we must note that many patents in this field also mention the use of other metals, especially rhodium and/or ruthenium, in place of palladium. However, under the same conditions, these last two metals appear to give always worst results with respect to palladium and they appear to have been included only for patenting purposes. Often their use is limited to one example and relevant data are not reported on Chemical Abstracts. Thus we will not discuss them here. A discussion of the catalytic systems specifically optimised with these metals is given in appropriate paragraphs. 

DMT.l Palladium-based Systems, All vertical modes only, for comparison purposes, are shown in Table 30.1. 

Palladium-based systems—all vertical mode only... 

Hennis AD, PoUey ID, Long GS, Sen A et al. (2(X)1) Novel, efficient, palladium-based system for the polymerization of noibomene derivatives scope and mechanism. OiganometaUics 20 2802-2812... 

Osborn and coworkers [108-110] reported that CuCl in combination with OSO4 or Pr4NRu04 (TPAP) catalyzes the aerobic oxidation of alcohols. The scope is rather limited, however, and the system would not appear to have any advantages over the earlier described ruthenium- and palladium-based systems. Similarly an Mo02(a-cac)2-Cu(N03)2 system[lll] resulted in rather low activities and selectivities for the oxidation of primary activated and secondary alcohols. 

The most widely used homogeneous palladium catalyst is palladium carboxylate. Table 6 lists the palladium-based catalyst systems developed for NBR hydrogenation [75-87]. They are regarded as homogeneous cata-... 

JOVANOVIC, G., Sacrittichai, P., Toppinen, S., Microreactors systems for dechlorination of p-chlorophenol on palladium based metal support catalyst theory and experiment, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, 11-14 March 2002, pp. 314-325, AIChE Pub. No. 164, New Orleans (2002). 

Tarasevich MR, Zhutaeva GV, Bogdanovskaya VA, Radina MV, Ehrenburg MR, Chalykh AE. 2007. Oxygen kinetics and mechanism at electrocatalysts on the base of palladium-iron system. Electrochim Acta 52 5108-5118. 

Mikami et al X developed a palladium-based catalyst system 22, capable of forming quaternary centers via a carbonyl-ene reaction. This is one of the few recent examples of a carbonyl-ene reaction that uses a ketone rather than an aldehyde and affords 84% yields in the case of the five-membered ring (23, n = 1) to near quantitative yields for the six-membered ring (23, n = 2), with 96% ee or better in both cases (Equation (12)). This catalyst system also shows selectivity when other ene partners are used, giving synl anti ratios equal to or better than the titanium systems and affords linear products with complete ( )-selectivity. 

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