Catalysts Al-based

Di Cosimo et al. investigated the structural requirements and reaction pathways in condensation reactions of alcohols, using Mg/Al mixed oxides obtained by decomposition in N2 at 673 K for 4 h of LDH precursors with a wide range of composition [53], and found that the mechanistic pathway of the condensation reactions is affected not only by the catalyst acid-base properties but also by the chemical nature of the alcohols as well as steric factors. 

Although early catalysts were based on cobalt, nowadays, rhodium catalysts are preferred because they require lower pressure and afford higher chemo- and regioselectivity [1,2]. In recent years, extensive research into the production of only linear aldehydes has provided impressive results. The application of phosphines with a wide bite angle in the rhodium catalyzed hydroformylation of terminal alkenes enable the regioselectivity to be almost totally controlled [3]. Branched selective hydroformylation, al- 

Noble Metal Catalysts. Rh-based catalysts have been investigated on different supports, resulting in different H2 and CO yields. Gasoline and naphtha POX over a supported Rh catalyst were reported by Fujitani et al. For y-alumina supported Rh catalyst, maximum yields of 96% of both H2 and CO were reported with 0.2 wt% Rh loading at 700°C, an air equivalence ratio of 0.41, and a liquid hourly space velocity (LHSV) of 2 h A 0.05 wt% Rh supported on zirconia yielded 98% H2 and 85% CO at 725°C, an 

Reduction of cocatalyst-cost by the application of catalyst systems that require less Al-based cocatalyst (this goes along with reduction of residual Al in the product). 

As noted, for example by van der Wiele and van den Berg,4 the interaction between the molecule to be oxidized and the catalyst is based on the electron-donating and -accepting properties and can be described in terms of the acid-base properties. Activity and selectivity are thus expected to depend on the relative acidity and basicity. Thus Boreskov et al.80 observed a clear correlation between the acidity of a V205/Ti02 catalyst modified with different alkali metals and the selectivity for 0-xylene oxidation. The most acidic site was assumed to be responsible for the destructive oxidation. Thus the selectivity increased with the basicity, i.e., with the atomic number of the alkali metal. 

The oxidative radical ring opening of cyclopropanols 191 mediated by Mn(pic)3 was developed by Narasaka and coworkers. Their efforts culminated recently in the development of a silver-catalyzed method (see Part 3, Sect. 6.2). Kulinkovich et al. based a manganese-catalyzed process on it. Manganese abietate 192 (1—1.5 mol%) was used as the catalyst and oxygen as the terminal oxidant (Fig. 54) [289]. 

In a pair of papers last year, Scott Nelson of the University of Pittsburgh expanded the range of the ketene aldol . In the first paper (J. Am. Chem. Soc. 2004,126, 14), he employed a chiral Al-based catalyst 3. This catalyst mediated additions such as propionyl bromide 1 to 2 to give 4 in 98 2 syn/anti ratio and 95% . 

In a detailed study Maiwald et al. used the Nd allyl complex Nd(rj3- 3115)3 for the polymerization of BD in toluene. A linear relationship between - ln(l - x) and polymerization time was obtained. An intercept at 10 to 12 min was attributed to an induction period [291]. Similar results were obtained for a variety of catalyst mixtures based on Nd allyl compounds [293]. 

The Meerwein-Ponndorf-Verley (MPV) reduction [236] of carbonyl moieties to produce the corresponding alcohols is usually conducted under the influence of stoichiometric or excessive amounts of Al-based catalysts, in particular Al(0 Pr)3  

The alkene metathesis reaction arose serendipitously from the exploration of transition-metal-catalysed alkene polymerisation. Due to the complexity of the polymeric products, the metathetic nature of the reaction seems to have been overlooked in early reports. However, in 1964, Banks and Bailey reported on what was described as the olefin disproportionation of acyclic alkenes where exchange was evident due to the monomeric nature of the products [8]. The reaction was actually a combination of isomerisation and metathesis, leading to complex mixtures, but by 1966 Calderon and co-workers had reported on the preparation of a homogeneous W/Al-based catalyst system that effected extraordinarily rapid alkylidene 

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