Carbonylation polymerizations, palladium catalyzed

The most widely employed synthetic route to aramids is based on the polycondensation of dicarboxylic acids with diamines in the presence of condensing agents. Good reviews on the synthesis of aramids have recently appeared (1-3). Recently, promising alternative synthetic routes to aramids have been reported and are described herein. These include the polycondensation of N-silylated diamines with diacid chlorides, the addition-elimination reaction of dicarboxylic acids with diisocyanates, and the palladium-catalyzed carbonylation polymerization of aromatic dibromides, aromatic diamines and carbon monoxide. 

The insertion of CO into palladium carbon bonds is a common step in many palladium-catalyzed carbonylation reactions and polymerizations. This reaction takes place under moderate CO pressure (1-3 atm). From the range of compounds that can be carbonylated, it can be inferred that CO will insert into alkyl, aryl, and alkynic bonds (equation 13). One of the few types of Pd-C bonds inert to CO insertion is the Pd-acyl bond, thus only single carbonylations are normally observed. However, a few examples of double carbonylation have been reported. In the case of palladium-catalyzed formation of PhCOCONEt2 from Phi, CO, and NHEt2, reductive elimination from a bisacyl complex has been established as the mechanism, rather than CO insertion into a Pd-acyl bond. 

Arenediazonium tetrafluoroborates (ArN2Bp4 where Ar=X-C6H4 X=H, 2-Me, 3-Me, 4-Me, 4-MeO, 4-MeCO, 2-Ph, 2-CI, 3-CI, 4-CI, 4-Br, 4-1, 3-NO2 and 4-NO2), like iodoarenes are converted into aldehydes in good yield by palladium-catalyzed carbonylation in the presence of poly-methylhydrosiloxane (PMHS) at room temperature. The rather slow reaction rate is remarkably enhanced by replacing the polymeric silane with EtaSiH (Eq 1.37). ° ... 

The use of readily available and cheap formate salts is an economically attractive variant for performing palladium-catalyzed reductive carbonylations [22, 23]. For example, Cai and his associates developed a silica-supported phosphine palladium complex ( Si -P-Pd) for the formylation of aryl bromides and iodides with sodium formate (1 bar CO, 90-110 °C) [24]. The polymeric catalyst could be recovered afterwards and shown in simple model reactions comparable catalytic activity than homogeneous PdCl2(PPh3)2 (Table 3.3). 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

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