Catalyst systems derived from

The cycloaddition reaction between ethyl glyoxylate 4a and Danishefsky s diene 2a has been investigated by Ghosh et al. applying catalyst systems derived from Cu(OTf)2 and ligands (S)-Ph-BOX (S)-21a, (S)-t-Bu-BOX (S)-21b, and the confer-... 

Implementation of the C5, C5 -hydroxy lation protocol as described in Scheme 7.19 above (71/72 to 73/74) provided further efficiencies. The C5,C5 -chlorination proceeded uneventfully, but the chloro to alkoxy interchange was difficult and required optimization of the reaction conditions. The catalyst system derived from Pd2dba3 and the X-phos(t-Bu) ligand proved to be effective in the coupling with KOH to provide the desired bisphenol. The resulting product was highly unstable and decomposed under a one-pot alkylation protocol. Isolation of the bisphenol under carefully controlled conditions followed by immediate benzylation (BnBr, NaH, DMF) furnished key intermediate 79 in 70 % yield. 

Major differences were noted between the systems derived from Fe(CO)c and M(CO) (M = Cr, Mo, and W) with respect to the effect of the base concentration on the reaction rate. Thus in the case of the catalyst system derived from Fe(CO)5 tripling the amount of KOH while keeping constant the amounts of the other reactants had no significant effect on the rate of H2 production (11). However, in the case of the catalyst system derived from W(CO)g the rate of production increased as the amount of base was increased regardless of whether the base was KOH, sodium formate, or triethylamine (12). This increase may be interpreted as a first order dependence on base concentration provided some solution non-ideality is assumed at high base concentrations. Similar observations were made for the base dependence of H2 production in catalyst systems derived from the other metal hexacarbonyls Cr(CO) and Mo(CO) (12). Thus the water gas shift catalyst system derived from Fe(CO)5 has an apparent zero order base dependence whereas the water gas shift catalyst systems derived from M(CO)g (M - Cr, Mo, and W) have an approximate first order base dependence. Any serious mechanistic proposals must accommodate these observations. 

Major differences were also noted between the catalyst systems derived from Fe(CO) and those derived from M(CO) (M = Cr, Mo, and W) with respect to the effect of CO pressure on the reaction rate. In the system derived from Fe(CO)5 the rate of H- production in the early stages of the reaction was independent of the CO loading pressure in the range 10 to 40 atmospheres... 

The activation energies of these water gas shift catalyst systems were determined by rate measurements as a function of temperature. Thus on the basis of rate measurements at the five temperatures 180, 160, 150, 140, and 130°C the activation energy of the catalyst system derived from Fe(C0)5 was estimated at... 

Table I. Comparison of Catalyst Systems Derived from Fe(CO),. and M(C0)6 (M = Cr, Mo, W).

The rate of production using the catalyst system derived from Fe(CO)5 is thus seen to have a first order dependence on Fe(CO)j concentration and to be independent of CO pressure in accord with the experimental observations outlined above. Furthermore, the formate buffer system generated by reaction of CO with the base by equation 2 keeps the OH concentration essentially independent of the amount of base introduced into the system. Therefore the rate of H production using the catalyst system derived from Fe(CO), although having a first order dependence on OH concentration, is essentially independent of the base concentration. 

Asymmetric induction has also been achieved in the cyclization of aliphatic alcohol substrates where the catalyst derived from a spirocyclic ligand differentiates enantiotopic alcohols and alkenes (Equation (114)).416 The catalyst system derived from Pd(TFA)2 and (—)-sparteine has recently been reported for a similar cyclization process (Equation (115)).417 In contrast to the previous cases, molecular oxygen was used as the stoichiometric oxidant, thereby eliminating the reliance on other co-oxidants such as GuCl or/>-benzoquinone. Additional aerobic Wacker-type cyclizations have also been reported employing a Pd(n) system supported by A-heterocyclic carbene (NHC) ligands.401,418... 

In this and subsequent studies [41 14], Takeuchi and coworkers described the scope and selectivity of catalysts derived from [fr(COD)Cl]2 and achiral phosphorus ligands. Many of the trends that they uncovered have also been observed with more recently developed catalyst systems derived from chiral phosphoramidite ligands (Table 1). 

The first report of the copolymerization of an epoxide, namely, ethylene oxide and C02 is contained in a patent by Stevens [6]. However, this process, when carried out in the presence of polyhydric phenols, provided polymers which were viscous liquids or waxes possessing copious polyether linkages with only a few incorporated C02 units. The earliest metal-catalyzed copolymerization of epoxides and C02 was reported in 1969 by Inoue and coworkers, who employed a heterogeneous catalyst system derived from a 1 1 mixture of diethylzinc and H20 [7, 8], Subsequently, Kuran and coworkers investigated a group of related catalysts prepared from diethylzinc and di- and triprotic sources such as pyrogallol, with a slight improvement over Inoue s system for the production of polypropylene carbonate) from PO and C02 [9],... 

The few selected examples shown in Scheme 19 impressively demonstrate the efficiency of the catalyst system derived from 69 and a (halo-gen-free ) Pd source. Interestingly, the reactions employing the Pfaltz catalyst proceed in most cases without concomitant double bond migration. 

The reactivity of co-arylolefins over homogeneous catalyst systems derived from molybdenum and tungsten is affected by the length of the chain between aromatic ring and double-bond, by substituents at the double bond, and by substituents on the aromatic ring. ... 

Catalyst systems derived from Ln N(SiMe3)2 3 and chelating diamines (e.g., 25a, Fig. 17) are also active in the cyclization of aminoalkynes with quite remarkable activity and functional group tolerance (31) [141],... 

The present results demonstrate that the catalyst system derived from the compounds (I) operates quite satisfactorily at temperatures of at least 30°C and... 

Chiral zirconocene complexes have also been studied as catalysts for the hydrogenation of nonfunctionalized olefins115. Using homogeneous Ziegler Natta-type catalyst systems derived from [ethylenebis(4,5.6,7-tetrahydro-l-indenyl)]zirconium complexes and methyl aluminoxane [A1(CH3)0] , 2-phenyl-l-butene was hydrogenated in 36% optical yield (20 bar H2, benzene, 25 °C). Under the same conditions, the reaction of styrene with D2 gave optically active 1,2-dideuteroethylbenzene with 65% ee. 

The effect of substitution at the internal carbon of the allene was examined next, driven in part by the potential use of this process in the synthesis of targets bearing an angular substituent. In the presence of a catalyst system derived from 5 mol% RhCKPPhjlj and 5 mol% AgOTf in toluene at 110 °C, allene-vinylcyclopropane provides 61 in 44% yield (Eq. 66). In contrast to the cycloaddition of 54, cycloaddition of 60 produces 61 as a single diastereomer. 

A catalyst system derived from titanocene complex and methyl-aluminoxane (see Chap. 5) has been used to polymerize propylene and, depending on polymerization conditions, produce a block copolymer of crystalline and amorphous, elastomeric polypropylene [440] ... 

The ease of isomerization and the product distribution are greatly influenced by the catalyst employed, (290) becoming the major product by use of the catalyst system derived from bis(cyclo-octa-l,5-diene)nickel(0) and tetracyanoethylene. The origins of the peri- and regio-selectivities have been explained in terms of a MO treatment extended-Huckel calculations reveal that among the strained C—C bonds the C-2—C-5 and structurally equivalent bonds have MO shapes suitable for edge-on... 

In the meantime, further improvements on the catalyst system derived from the Wilkinson catalyst and the use of other Rh sources led to an increase in reactivity and selectivity toward the branched products and the conservation of the double-bond geometry, when linear allylic substrates were used [165b, 188]. 

Molecules containing both primary and secondary amines were subjected to reaction with chlorobenzene. The catalyst system derived from 28c provided the primary amine arylation products exclusively in excellent yields. 

The catalyst system derived from the biarylphosphine 62 and [Pd2(dba)3] enjoyed a broad scope of aryl bromides, chlorides, and triflates for the N-arylation of indole (Scheme 13.85) [131]. 

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