Propyne catalysts

Moulijn et al. (33) studied the reactions of some linear alkynes over a W08-Si02 catalyst in a fixed-bed flow reactor. Besides metathesis, cyclotrimerization to benzene derivatives occurred. Thus, propyne yielded, in addition to metathesis products, a mixture of trimethylbenzenes. From this an indication of the mechanism of the metathesis of alkynes can be obtained. 

Because of the almost complete absence of the 1,2,3-isomer in the product mixture when propyne, 1-butyne, or 1-pentyne were passed over the W08-Si02 catalyst, it was concluded that cyclotrimerization over this catalyst does not occur via a cyclobutadiene complex (39). 

Carbonylation of methanol to acetic acid is fully discussed in Chapter 9. Another carbonylation process using a phosphine ligand to control the course of the reaction is a highly atom efficient route to the widely used monomer methyl methacrylate (Scheme 4.19). In this process the catalyst is based on palladium acetate and the phosphine ligand, bisphenyl(6-methyl-2-pyridyl) phosphine. This catalyst is remarkably (>99.5%) selective for the 2-carbonylation of propyne under the relatively mild conditions of <100 °C and 60 bar pressure. 

The regiochemistry of Al-H addition to unsymmetrically substituted alkynes can be significantly altered by the presence of a catalyst. This was first shown by Eisch and Foxton in the nickel-catalyzed hydroalumination of several disubstituted acetylenes [26, 32]. For example, the product of the uncatalyzed reaction of 1-phenyl-propyne (75) with BujAlH was exclusively ds-[3-methylstyrene (76). Quenching the intermediate organoaluminum compounds with DjO revealed a regioselectivity of 82 18. In the nickel-catalyzed reaction, cis-P-methylstyrene was also the major product (66%), but it was accompanied by 22% of n-propylbenzene (78) and 6% of (E,E)-2,3-dimethyl-l,4-diphenyl-l,3-butadiene (77). The selectivity of Al-H addition was again studied by deuterolytic workup a ratio of 76a 76b = 56 44 was found in this case. Hydroalumination of other unsymmetrical alkynes also showed a decrease in the regioselectivity in the presence of a nickel catalyst (Scheme 2-22). 

Only one publication describes the use of a zeolite as catalyst in the hydroamina-tion ofalkynes. MeNH2 reacts with 1-propyne over a Zn(ll) ion-exchanged Y zeolite (ZnY) at room temperature and atmospheric pressure to give a mixture of N-iso-propylidenemethylamine and N-n-propylidenemethylamine (Eq. 4.58) [238]. 

With terminal alkynes, the direction of the reaction depends on the nature of the substituent, the type of amine and the catalyst. Thus, dialkylamines can react with propyne to give 4-dialkylamino-4-methyl-2-pentynes traced from the Hy regioselec-hve formation of 2-dialkylaminopropene, i.e. the Markovnikov hydroaminahon product (Scheme 4-11) [256]. 

Diphenylacetylene and 1-phenyl-1-propyne were hydrogenated to the corresponding 1,2-disubstituted alkenes in aqueous organic biphasic media using [ RuCl2(wtppms)2 2] and an excess of wtppms (80 °C, 1 bar H2, TOFs up to 25 h-1). The stereoselectivity of the reaction depended heavily on the pH of the catalyst-containing aqueous phase (Fig. 38.1) and, under acidic conditions, Z-al-kenes could be obtained with a selectivity close to 100% [71]. 

Z)-Methyl styrene was easily obtained by hydrogenation of 1-phenyl-1-propyne using Lindlar s catalyst (5% palladium on calcium carbonate, poisoned with lead) in //-hexane under an atmospheric pressure of hydrogen. The mixture, containing 90% of (Z)-methyl styrene and 10% of the overreduced alkane, was used without further purification. 

Comparison of the different types of cobalt catalysts shows that the in situ system [Eq.(2)] is most accessible while the Rep-, R(ind)-, and bori-ninato ligands having electron-withdrawing substitutents are the most active. The difference between the 14e" and the 12e core complexes makes itself apparent in the chemoselectivity of the reaction. Catalysts containing a 14-electron core favor pyridine formation, whereas those containing a 12-electron core (i.e., the rj -allylcobalt systems) favor the formation of benzene derivatives by cyclotrimerization of the alkynes. For example, in the reaction of propyne and propionitrile at 140°C in the presence of a 12-electron system (5), a 2 1 ratio of benzene to pyridine product is formed, whereas a catalyst containing the cpCo moiety (a 14-electron system) leads (under identical conditions) to the predominant formation of pyridine derivatives (84HCA1616). 

Fig. 2. Propyne conversion and reaction temperature for various [rj -cpCoL] complexes as catalysts.

Copper(I) acetylide is used in a diagnostic test for CH unit to prepare pure copper powder in purification of acetylene and as a catalyst in the synthesis of acrylonitrile and 2-propyn-l-ol. 

As described in the previous section, the ruthenium-catalyzed propargylic alkylation of propargylic alcohols with acetone afforded the corresponding alkylated products in high yields with complete selectivity [27]. When an optically active 1 -phenyl-2 -propyn-1 -ol was treated with acetone at room temperature in the presence of la as catalyst, only a racemic alkylated product was obtained [27]. This result... 

The catalytic propargylic alkylation was investigated in the presence of thiolate-bridged diruthenium complexes as catalysts generated in situ from reactions of [Cp RuCl(p2-Cl)]2 with optically active thiols prepared from the corresponding optically active alcohols [27]. Typical results for the reaction of 1-phenyl-2-propyn-l-ol with acetone in the presence of a variety of catalysts are shovm in Scheme 7.19. 

In this paper we will report on using a series of modifiers to enhance selectivity during 1-phenyl-1-propyne over a Pd/alumina catalyst. The modifiers, trans-cinnamaldehyde, trans-cinnamonitrile, 3-phenylpropionitrile, and 3-phenylpropylamine, were chosen to have a functionality that potentially could adsorb more strongly than an alkene and to be unreactive under the reaction conditions. 

The reaction of 1-phenyl-l-propyne (IPP) was then studied after modilying the catalyst with trans-cinnamaldehyde (TCA), trans-cinnamonitrile (TCN), 3-phenylpropionitrile (3PPN), and 3-phenylpropylamine (3PPA). The first-order rate constant calculated for the loss of 1-phenyl-l-propyne in each of the systems is reported in Table 1. All the modifiers were unreactive under the conditions used. 

Silylformylation of 1-alkynes is not affected by the presence of small amounts (2 to 3 molar equiv.) of water or methanol in the reaction mixture. The corresponding products are formed in yields similar to the reaction without these additives.This information implies that the silylformylation of alkyne is not affected by the presence of a protic functional group, such as hydroxy and amino groups in alkyne. In fact, 2-propyn-l-ol 54 smoothly gives 55, in which the hydroxy group remains intact (Equation (15)). (Z)-Selectivity in 55 is drastically improved by the reaction in the absence of EtsN or by use of Rh2(pfb)4 as the catalyst. The Rh complex is known to work as an active catalyst for alcoholysis of hydrosilane." " In particular, since Rh2(pfb)4 shows high activity for alcoholysis of EtsSiH in the absence of it is quite notable that the product derived from silane alcoholysis is not detected at... 

Reactions of alkynes with xenon difluoride have not been widely investigated. Propyne reacts more slowly with xenon difluoride in the absence of a catalyst than propene, to form a complex product mixture with 33% 2,2-difluoropropene.26 Diphenylethyne treated with xenon difluoride in the presence of hydrogen fluoride forms 1,2-diphenyltctrafluoroethane in 50% yield, comparable yields of 1,2-dialkyltetrafluorocthanes are observed on treatment of 1,2-dialkyl-propenes with xenon difluoride in dichloromethane at room temperature.58... 

In 1975, it was discovered that WCk, which is a typical metathesis catalyst, is capable to catalyze the polymerization of phenylacetyl-ene. Subsequently, various substituted acetylenes have been polymerized by this type of catalyst. In 1983, poly(l-(trimethylsilyl)-l-propyne)) was synthesized in the presence of Tads and NbCls (35). The alkyne polymerization has many similarities with ROMP. 

The epimeric diketones 281 have been synthesized by condensing 2,3-0-isopropylidene-D-glyceraldehyde with propyne via a Grignard reaction, followed by oxidation of the O-acetylated epimers to the diketones using a ruthenium catalyst and iodosylbenzene as the oxidant.498... 

The chemical properties and uses of propargyl alcohol has three potentially reactive sites (1) a primary hydroxyl group (i.e., CH2OH), (2) a triple bond (-C=C-), and (3) an acetylenic hydrogen (-C=CH) that makes the alcohol an extremely versatile chemical intermediate. The hydroxyl group can be esterified with acid chlorides, anhydrides, or carboxylic acids, and it reacts with aldehydes or vinyl ethers in the presence of an acid catalyst to form acetals. At low temperatures, oxidation with chromic acid gives propynal or propynoic acid ... 

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