Co-catalyst system

During the reaction, the palladium catalyst is reduced. It is reoxidized by a co-catalyst system such as cupric chloride and oxygen. The products are acryhc acid in a carboxyUc acid-anhydride mixture or acryUc esters in an alcohoHc solvent. Reaction products also include significant amounts of 3-acryloxypropionic acid [24615-84-7] and alkyl 3-alkoxypropionates, which can be converted thermally to the corresponding acrylates (23,98). The overall reaction may be represented by ... 

In sharp contrast, Bartoli showed that the (salen) Co catalyst system could be applied to the kinetic resolution of terminal epoxides with unprotected tert-butyl carbamate as nucleophile with extraordinarily high selectivity factors (Scheme 7.40) [72]. Excellent yields and selectivities are also obtained with use of ethyl, Cbz,... 

Metallocenes are homogeneous catalysts that are often soluble in organic solvents. Therefore, polymerization can occur via a solution process with a non-polar diluent dissolving the propylene gas, the catalyst, and the co-catalyst system. They can also be adsorbed onto an inert substrate which acts as part of the fluidized bed for gas phase polymerization processes. 

If ligand dissociation is important, and if it is more extensive when L = PPh3 than when L = PR3, then the PPh3-Co catalysts system should be very sensitive to changes in ligand concentration. This was found to be the case (55), as shown in Fig. 6. 

Comparison of Catalytic Properties of Some Fe and Co Catalyst Systems... 

List of Components of Fe and Co Catalyst Systems MX + Ligand + Cocatalyst0... 

This class is made up of a number of catalyst-co-catalyst system. The first step is the ionisation of the catalyst and the second step is the reaction of proton with the olefins. 

A novel homogeneous process for the catalytic rearrangement of 3,4-epoxy-l-butene to 2,5-dihydrofuran has been successfully developed and scaled-up to production scale. A tri(n-alkyl)tin iodide and tetra-(n-alkyl)phosphonium iodide co-catalyst system was developed which met the many requirements for process operation. The production of a minor, non-volatile side product (oligomer) was the dominating factor in the design of catalysts. Liquid-liquid extraction provided the needed catalyst-oligomer separation process. 

The metallocene catalysts must be first activated by an aluminoxane co-catalyst, e.g., tetramethylaluminoxane (MAO) which is an oligomer, n being 10-15 (Fig. 9.5-2, right). Because a high excess of MAO is required for activation, a binary co-catalyst system was developed consisting of an organoborate and tri-isobutylaluminium (TiBA). Organoborate can be used in a stoichiometric ratio which reduces the costs and the residue of activator products in the polymer [5]. 

Finally, we reported a di-iron(III) catalyst 24 and the corresponding copolymerization activity [147]. This system was able to produce copolymer with CHO/C02 and demonstrated a TOF of 53 h 1, at 80°C, lObar and aCHO/Fe ratio of 10,000 1. The system did not yield copolymer with PO, but addition of one equivalent of [PPN]C1, per Fe centre, allowed the conversion of PO into cyclic propylene carbonate with TOFs around 10 h 1. Previously, some heterobimetallic iron tert-butoxide complexes ( (7-BuO)5FeLa] and [(f-BuO)4FeZn]) had been reported for the copolymerization of PO and C02 [153]. This catalyst was the first use of an iron complex for the homogeneous copolymerization of CHO and C02. Rieger and coworkers recently reported a mononuclear Fe system that showed similar behaviour towards PO [154] and some copolymer formation with CHO/C02 strongly dependent on the co-catalyst system [98]. 

The widely accepted mechanism for olefin hydroformylation using a HRh(PR3)2(CO) catalyst system was proposed over 30 years ago by Wilkinson et al [104]. The catalytic cycle comprises many of the fundamental reac-... 

The TBAF-catalyzed allylation of aldehydes with 10 proceeds efficiently in refluxing THF.92 In contrast, a Pd-TBAF co-catalyst system enables the allylation at room temperature (Equation (20)).93 This mild allylation is due to the formation of a bis-7r-allylpalladium complex as the actual allylating agent. 

The 7t-allylpalladium-TBAF co-catalyst system described in Equation (20) enables the allylation of aromatic imines as well as aldehydes at room temperature.93 Chiral 7t-allylpalladium complex 21 is an efficient asymmetric catalyst of the imine allylation (Equation (29)).93 126... 

Kennedy and milliman Alky laluminum-Co catalyst Systems 297... 

In 2001, Mdstern reported on the oxidative alkenylation of arenes with olefins using a RU/O2/CO catalyst system (Eq. 9.12) [26], but details of the reaction mechanism have not been elucidated. Very recently, Gunnoe reported ethylation and propylation of ben-... 

An active co-catalyst system was proposed (83). The system is composed of 2,4,6-tris(diethanolamino)-s-triazine and l,3,5-tris(3-dimethylamino i opyl) hexahydro-s-triazine. This catalyst was used to jx-epare rigid carbodiimide foams from TDI without external heating. 

For example, if the co-catalyst system Cu VCu is used for the regeneration of Pd from Pd formed during the course of the reaction, the simultaneously arising Cu has to be regenerated itself by another oxidant, for example oxygen. In this case water arises as a side product. In Scheme 1 this is shown in a simplified form. 

Low-temperature solution processes are state-of-the-art for the production of ethylene/propylene or ethylene/propylene/diene elastomers (EPDR or EPDM). A continuous stirred-tank reactor (CSTR) or a series of two or even more such reactors is used [2]. n-Hexane, n-heptane, or Ce, C7 fractions are the solvents. Catalyst, co-catalyst and other compounds are introduced with the solvent into the reactor. The monomers (ethylene, propylene) are injected as gases other olefins are introduced in liquid form. The polymerization process runs around 50 °C and at pressures up to 2 MPa. Downstream the catalyst/co-catalyst system is deactivated and their residues are dissolved in dilute acid or aqueous NaOH. The copolymer is stabilized with an antioxidant. Steam treatment removes the rest of the solvent and monomers, and agglomerates the product to crumbs. These crumbs are then dried and finished to bales or pellets. 

Rather interestingly, radical cations have also been identified in styrene polymerizations catalysed by more conventional Lewis acid/co-catalyst systems [BF3/0(C2Hs)2, AlCla/PhOH, BFs/PhOH] by employing 2,4,6-tri-t-butyl-nitrosobenzene as a trap. One wonders once again therefore if the mechanisms which are generally accepted to operate do indeed represent a total picture. 

It is known that allylation of aldehydes with allyltrimethylsilane occurs in the presence of a catalytic amount of TBAF under reflux in THF [333]. In contrast, a Pd-TBAF co-catalyst system effectively promotes the allylation even at room temperature (Scheme 10.131) [376]. A plausible reaction mechanism for this allylation involves the formation of bis-7r-allylpalladium complex 121, which can be observed in a stoichiometric reaction of Ti-allylpalladium chloride dimer, allyltrimethylsilane, and TBAF. 

As shown in Scheme 10.132 (Section 10.3.1.2), Yamamoto et al. have recently reported highly enantioselective allylation of aromatic and a, -unsaturated aldehydes with allyltrimethoxysilane using (P)-(p-Tol-)BINAP AgF as catalyst [377]. Shibasaki et al., on the other hand, have succeeded in asymmetric allylation of acetophenone with allyltrimethoxysilane by use of a p-Tol-BINAP CuCl-TBAT co-catalyst system (up to 61% ee) [378]. 

There is no single mechanism for Ziegler-Natta polymerization because of the variety of catalyst and co-catalyst systems as well as the different phases in which the reaction may take place. The process of stereoregular polymerization can be understood tfom the mechanism of initiation and propagation as the monomer is inserted at the polymerization site on the catalyst surface. The detailed mechanism for achieving stereospecificity is an active area of research (Corradini and Busico, 1989, Tait and Watkins, 1989), but some general principles may be learned tfom the simple Ziegler-Natta catalysts (Allcock and Lampe, 1981). 

They were able to extend the scope of the direct arylation to simple, completely unactivated arenes, such as benzenes by development of a palladium-pivalic acid co-catalyst system (Scheme 28) [48]. 

For hydroamination a co-catalyst system contains PhNMe2H[B(C6F5)4] and 1, which is made from Me2Zn. Hydrosilylation of terminal aUcenes employing t-butylzinciosilanes and lithium hiphenyl-2,2 -dioxide in the presence of CuCN proceeds nicely. ... 

Pd(Ph3P)4 catalyzes the carbonylation of benzyl and vinyl bromides under phase transfer conditions in the presence of hydroxide to form the corresponding carboxyhc acids. A wide variety of substitution is tolerated and the products are formed in moderate to excellent yield at room temperature and at normal pressure (1 atm CO). Extension of the reaction to the formation of esters from aryl, alkyl, and vinyl bromides has been described. These transformations usually require a co-catalyst system of Pd(Ph3P)4 and [(l,5-cyclohexadiene)RhCl]2 in the presence of either M(OR)4 (M=Ti, Zr) or M(OR)3 (M=B, Al) (eq 22). 

The C-H/olefin coupling of aryloxazolines proceeds with unusual product selectivity. In this case, alkylation products, i.e., formally dehydrogenation products, are obtained as a major product (Eq. 22) [11]. These types of dehydrogenation compounds are believed to be formed via a carbometalation pathway. The first example of this type of alkenylation of arenes with olefins using palladium(II) complexes via C-H bond cleavage was reported in 1967 [32]. Later, several efforts were made to perform this reaction in a catalytic manner [33]. In 2001,Milstein et al. [34] reported the oxidative alkenylation of arenes with olefins using a RU/O2/CO catalyst system (Eq. 23). Details of the reaction mechanism have not been elucidated. 

In a first batch of lactide ROPs an appropriate solvent and catalyst were determined, see Table3.3. The polydispersity of poly(lactic acid) synthesized in TCM compared to DCM was significantly lower. The addition of thiourea co-catalyst lead to an improved PDI in case of DCM, while no change was observed in TCM. However, when using poly(4-X-styrene)-OH as macroinitiator only the DBU/thiourea co-catalyst system was found to yield copolymer. Considering Fig. 3.12b, the lactide... 

---