Phase-Transfer Catalysis in Organometallic Chemistry

Abstract

This chapter discusses stoichiometric organic reactions, catalytic organic reactions, and organometallic synthesis. One of the major developments in organic chemistry during the past 15 years has been the application of phase-transfer catalysis to synthesis. As a basis for discussing the concept of the liquid–liquid phase-transfer process, nucleophilic substitution reactions of halides with quaternary ammonium halides functioning as catalysts are considered in the chapter. The first experiments that were carried out in the author's laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes to anilines by triiron dodecacarbonyl. The reaction of halides with iron pentacarbonyl, base, and tetrabutylammonium bromide as the catalyst has been reported to give ketones and variable amounts of hydrocarbons. One of the most important metal carbonyl anions, as far as catalytic processes are concerned, is the cobalt tetracarbonyl anion, Co(CO) 4 − . The chapter describes crown ether-catalyzed generation of the Co(CO) 4 − ion in ether or hydrocarbon solvents. The carbonylation of halides to carboxylic acids, catalyzed by Co 2 (CO) 8 , is a transformation of genuine synthetic utility. Even certain phase-transfer catalysts can be carbonylated to carboxylic acids by acetylcobalt tetracarbonyl. Alcohols can be dehydrogenated to carbonyl compounds by exposure to a catalytic amount of a rhodium complex under phase-transfer conditions. The formation of dihalocarbene is one of the most useful phase-transfer processes developed in organic chemistry. Chromium tricarbonyl complexes of arylacetic esters can be alkylated by the use of phase-transfer catalysis or sodium hydride in N,N-dimethylformamide.