Stereochemical Approaches to Mechanisms of Hydrocarbon Reactions on Metal Catalysts

Abstract

This chapter focuses on stereochemical approaches to mechanisms of hydrocarbon reactions on metal catalysts. The chapter discusses the classic Horiuti–Polanyi mechanism of hydrogenation of olefins and describes competitive reactions for hydrogenation of cycloalkenes. Some basic facts are established from exchange with deuterium of numerous alkanes and polycycloalkanes especially on Pd catalysts. The interconversion of monoadsorbed and αβ-diadsorbed species can be very rapid especially on Pd and Rh before desorption of alkane. This interconversion is referred to as the “αβ process.” The αβ process propagates readily along a chain of carbon atoms, and, in acyclic paraffins with rapid rotation about C–C bonds, every H atom is readily replaced, as evidenced by the very large quantities of the perdeutero isomer in initial products from exchange of n-hexane on Pd films. The propagation of the exchange reaction is blocked if the chain of carbon atoms contains a quaternary center or a bridgehead.