Mono-cation catalyst

The systems with individual cations 1.8%CuH-ZSM-5 and 1.4%CoH-ZSM-5 demonstrate a rather high catalytic activity in ethane oxidation, when pre-calcined at 500-550°C (Fig. 1, lines 1 and 2). However, the heating of these catalysts on air at 750°C for 2 h leads to drastic drop in catalytic activity in C2Hg complete oxidation (Fig. 1, lines 1 and 2 ). The modification of the parent sample 1.8%CuH-ZSM-5 by 1% of Co leads to a over-additive rise in the catalytic activity. At the same time, the thermostability of this Co/CuH-ZSM-5 bi-cationic sample increases very noticeably the calcination of the catalyst at 750°C for 2 h leads to some drop in activity, but this calcined sample still exceeds the most active mono-cationic sample CuH-ZSM-S/jqqO (Fig. 1, lines 3 and 3 ). 

Special multicomponent catalysts were necessary for N-aUcylation of sterically hindered anilines with alkoxy alcohols [9]. Doping Cu-chromite with Pd accelerated the hydrogenation of the imine intermediate this was found to be the rate-limiting step for all the catalysts. Alkali cations (Na and Ba ) increased the activity whereas acidic centers (e. g. Cr " " and Al ) favored hydrogenolysis of the ether bond. For N-alkylation with secondary alkoxy alcohols a Pt/Si02 catalyst doped with Sn + and Ca ions afforded the best performance. Yields of mono-alkylated anilines varied in the range 22-93 % depending on the steric hindrance in the reactants. 

Keto esters are obtained by the carbonylation of alkadienes via insertion of the aikene into an acylpalladium intermediate. The five-membered ring keto ester 22 is formed from l,5-hexadiene[24]. Carbonylation of 1,5-COD in alcohols affords the mono- and diesters 23 and 24[25], On the other hand, bicy-clo[3.3.1]-2-nonen-9-one (25) is formed in 40% yield in THF[26], 1,5-Diphenyl-3-oxopentane (26) and 1,5-diphenylpent-l-en-3-one (27) are obtained by the carbonylation of styrene. A cationic Pd-diphosphine complex is used as the catalyst[27]. 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

Both rhodium and osmium porphyrins are active for the cyclopropanation of alkenes. The higher activity of the rhodium porphyrin catalysts can possibly be attributed to a more reactive, cationic carbene intermediate, which so far has defied isolation. The neutral osmium carbene complexes are less active as catalysts but the mono- and bis-carbene complexes can be isolated as a result. 

Some chiral mono-, acyl- and di-thioureas have been used as ligand for the Rh-catalysed asymmetric hydroformylation of styrene. Although thiourea ligands form inactive systems with [Rh(COD)Cl]2 as the catalyst precursor, in standard conditions (40 °C, 40 bar CO -l- H2 1/1), the cationic Rh complex [Rh(COD)2]Bp4 combined with monothioureas as the ligand showed moderate to good activity (Scheme 29) [114]. 

With trisubstituted benzoquinones and use of the cationic oxazaborolidinium catalyst B, 2-[tra-(isopropyl)silyloxy]-l,3-butadiene reacts at the monosubstituted quinone double bond. The reactions exhibit high regioselectivity and more than 95% e.e. With 2-mono- and 2,3-disubstimted quinones, reaction occurs at the unsubstituted double bond. The regiochemistry is directed by coordination to the catalyst at the more basic carbonyl oxygen. 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

The active species generated when bis(arylimino)pyridine iron (5) and cobalt (6) halides are activated with MAO was, by analogy with metallocene catalysts, initially considered to be a highly reactive mono-methylated cobalt(II) or iron(II) cation of the form LM-Me+ bearing a weakly coordinating counter-anion such as [X-MAO]-(X = halide, Me). To examine this theory a number of spectroscopic investigations have been directed towards identifying the active species (vide infra). 

The bis-DIOP complex HRh[(+)-DIOP]2 has been used under mild conditions for catalytic asymmetric hydrogenation of several prochiral olefinic carboxylic acids (273-275). Optical yields for reduction of N-acetamidoacrylic acid (56% ee) and atropic acid (37% ee) are much lower than those obtained using the mono-DIOP catalysts (10, II, 225). The rates in the bis-DIOP systems, however, are much slower, and the hydrogenations are complicated by slow formation of the cationic complex Rh(DIOP)2+ (271, 273, 274) through reaction of the starting hydride with protons from the substrate under H2 the cationic dihydride is maintained [cf. Eq. (25)] ... 

Brunelle, Chapter 5, also demonstrated that bis-quaternary salts with appropriate spacing between the quaternary nitrogens are dramatically better than mono-quaternary salts as catalysts for transfer of divalent anions, such as the di-anion of bisphenol A. Thus the ion pair formed from the di-anion and a bis-quat appears to be more easily formed and transferred than the species formed from the di-anion and two mono-quaternary cations. 

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