Catalysts for these reactions

Sbp5, and ZtlCl2, serve as catalysts for these reactions. 

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

Bis(diamino)alanes (R2N)2A1H were used for the hydroalumination of terminal and internal alkenes [18, 19]. TiCb and CpjTiCb are suitable catalysts for these reactions, whereas CpjZrCb exhibits low catalytic activity. The hydroaluminations are carried out in benzene or THF soluhon at elevated temperatures (60°C). Internal linear cis- and trans-alkenes are converted into n-alkylalanes via an isomerization process. Cycloalkenes give only moderate yields tri- and tetrasubstituted double bonds are inert. Hydroaluminahon of conjugated dienes like butadiene and 1,3-hexa-diene proceeds with only poor selechvity. The structure of the hydroaluminahon product of 1,5-hexadiene depends on the solvent used. While in benzene cyclization is observed, the reaction carried out in THF yields linear products (Scheme 2-10). 

CO3 species was formed and the X-ray structure solved. It is thought that the carbonate species forms on reaction with water, which was problematic in the selected strategy, as water was produced in the formation of the dialkyl carbonates. Other problems included compound solubility and the stability of the monoalkyl carbonate complex. Van Eldik and co-workers also carried out a detailed kinetic study of the hydration of carbon dioxide and the dehydration of bicarbonate both in the presence and absence of the zinc complex of 1,5,9-triazacyclododecane (12[ane]N3). The zinc hydroxo form is shown to catalyze the hydration reaction and only the aquo complex catalyzes the dehydration of bicarbonate. Kinetic data including second order rate constants were discussed in reference to other model systems and the enzyme carbonic anhy-drase.459 The zinc complex of the tetraamine 1,4,7,10-tetraazacyclododecane (cyclen) was also studied as a catalyst for these reactions in aqueous solution and comparison of activity suggests formation of a bidentate bicarbonate intermediate inhibits the catalytic activity. Van Eldik concludes that a unidentate bicarbonate intermediate is most likely to the active species in the enzyme carbonic anhydrase.460... 

Chloroprene (2-chloro-l,3-butadiene 105), which is a mass-produced, inexpensive industrial material, is an excellent precursor to a variety of terminal allenes 107 [97]. The palladium-catalyzed reaction of 105 with pronucleophiles 106 in the presence of an appropriate base gave the terminal allenes 107 in good yields (Scheme 3.53). The palladium species generated from Pd2(dba)3-CHC13 and DPEphos was a good catalyst for these reactions of chloroprene. In contrast, (Z)-l-Phenyl-2-chloro-l,3-buta-diene, which is isostructural with the bromo-substrate 101, was nearly inert under these conditions. There is no substituent at the vicinal ris-position to the chloride in 105, which allows oxidative addition of the C-Cl bond in 105 to the Pd(0) species. 

CH CH + CO + ROH CH2=CH-C00R Nickel carbonyl is the catalyst for these reactions. 

Application to both Type I and Type II intramolecular Diels-Alder cycloaddition has also met with appreciable success, the most efficient catalyst for these reactions being imidazolidinone 21 (Scheme 7) [51, 52]. The power of the inttamolecular Diels-Alder reaction to produce complex carbocyclic ring structures from achiral precursors has frequently been exploited in synthesis to prepare a number of natural products via biomimetic routes. It is likely that the ability to accelerate these reactions using iminium ion catalysis will see significant application in the future. 

Hydroamination of Allenes Different related amines can also be cyclized. The use of free amino groups led to long reaction times (several days), but sulfonamides, acetyl or BOc as protecting group led to fast conversion (in the latter case, problems of diastereoselectivity were observed). Optimization studies showed that, although cationic gold (I) complexes were not effective for these conversions, AuCI was a very good catalyst for these reactions. 

The described results indicate that there is not evident influence of a kind of nickel matrix on the dehydrosulfurization of thiols and sulfides. In order to obtain active catalysts for these reactions, the Ni-cation exchange procedure insted of the impregnation should be applied. 

This reaction has been used to prepare many a-methylene lactone derivatives.537 The above alkyne carbonylations were all catalyzed by phosphorus ligand-containing complexes. Some phosphorus-free catalysts for these reactions are also known, such as PdCl2 in presence of thiourea.538 This catalyst system also effects ring closure of 1,6-diynes (equation 131).539... 

Typical catalysts for these reactions are the so-called noble metals Pt and Pd, and transition metal oxides V205, Cr203, and CuO. Because the surface of the catalyst is rendered ineffective ("poisoned") by adsorption of lead, automobiles with catalytic converters must use unleaded gasoline. 

Although very dramatic rate enhancements have been observed with labile metal ions such as copper(n) and nickel(n), most studies have involved kinetically inert d6 cobalt(m) complexes. In general, copper(n) complexes have been found to be the most effective catalysts for these reactions. 

The past decade has seen extensive development of cross-coupling reactions of organozinc compounds and organic halides catalyzed by nickel or palladium catalysts. Although nickel-based catalysts are more reactive with respect to the organic halide partner, the number of failures with these catalysts and the greater selectivity realized with palladium-based catalysts have resulted in the almost exclusive use of the latter group of catalysts for these reactions. 

Nature makes use of this property by having imidazole groups attached to proteins in the form of the amino add histidine and using them as nucleophilic, basic and acidic catalytic groups in enzyme reactions (this will be discussed in Chapters 49 and 50). We use this property in the same way when we add a silyl group to an alcohol. Imidazole is a popular catalyst for these reactions. 

Nickel carbonyl is the catalyst for these reactions. In another Reppe process, acetylene is reacted with formaldehyde to yield butyndiol, which can be converted to butadiene for the manufacture of the synthetic rubber Buna the catalyst is nickel cyanide ... 

The sulfuric acid and the HI decomposition reactions in Sections II and III are both catalytic processes. A variety of oxides, activated charcoal, and platinum have been employed as the catalyst for these reactions. Ongoing research in this area is trying to identify the optimal catalyst support to minimize the overall cost and integration of the catalyst into the process systems. 

Certain halogenated compounds will condense with paraffinic, olefinic, or aromatic hydrocarbons. Catalysts for these reactions are of the Ftiedel-Crafts type. Thus, the condensation of alkyl halides with ethylene in the presence of aluminum chloride, zinc chloride, iron chloride, etc., furnishes higher alkyl halides. An example is the reaction of /-butyl chloride and ethylene to form l-chloro-3,3-dimethylbutane (75%). ... 

There are two primary sources of commercial production of H2 [other than by-product H2 from dehydrogenation, etc]. They are SR [Steam Reforming] and the partial oxidation of heavier hydrocarbons. SR uses a variety of hydrocarbon sources. Both approaches convert the carbon components to CO2, but a large portion of H2 is derived from added steam. The amount of CO2 generated depends [7] upon the hydrocarbon feedstock. Most of the current chemical approaches to H2 production also produce CO2 as a by-product however, SMR coproduces much less CO2 than partial oxidation. Therefore, it does not make sense to use H2 to remove CO2 when more CO2 is produced whenever one makes H2. There is a very small need for making CO/H2O or CH4 from CO2/H2, and we already have ample catalysts for these reactions. 

---