Historical and Mechanistic Aspects

First attempts for decarbonylation of aldehydes were conducted with transition-metal complexes in stoichiometric or near-stoichiometric reactions. Later on, also active catalysts and milder reaction protocols could be identified. The reaction proceeds best with electrophilic aldehydes and nucleophilic metal centers [5]. 

Hydrcformylation Fundamentals, Processes, and Applications in Organic Synthes, First Edition. 

An excess of PPhg may inhibit the decarbonylation (but see also below) [5]. This effect has been rationalized by assuming equilibrium between two rhodium(lll) complexes hosting two or three phosphine ligands. Only the former representing a 16e complex is the active decarbonylation catalyst. 

Chiral aldehydes can be decarbonylated under full retention of the configuration, but occasionally partial racemization may take place [10]. In general, decarbonylation with stoichiometric rhodium-arylphosphine complexes can be achieved at ambient temperature, but usually the catalytic version requires more severe conditions. Goldman et al. [11] discovered that trialkylphosphines form significantly more active catalysts, as exemplified with the binuclear complex [Rh(PMe3)(CO)Cl]2. The complex operates even at room temperature. A similar effect was also noted with iridium-phosphine catalysts [12]. 

Prince and Raspin [18] reported that decarbonylation of aldehydes with ruthenium complexes proceeded more slowly compared to that with rhodium. Moreover, the main product was the olefin and not the alkane. Evolving hydrogen may reduce the starting aldehyde depending of the substrate used. For instance, the decarbonylation of w-butanal with a binuclear PPhj-modified Ru complex gave propylene in 80% yield. In strong contrast, when an excess of butanal was employed, butanol was formed in excess. 

---

This chapter will first address each reaction, including their historical and mechanistic aspects, and then will discuss how CuAAC and TEC have added to the polymer chemist s repertoire of techniques for the functionalization of polymer chains. The second half of the chapter will be organized by polymer architecture. A lengthy discussion aimed at convincing the reader of the suitability of these reactions to be applied to polymeric systems will be forgone since the scope of the systems to which these reactions have been successfully applied speaks for itself However, throughout this chapter there are several architectures that serve as proof of the efficacy of TEC and CuAAC because of the particularly high demands of the reactions required to synthesize these example systems. The three showcase systems (Sections 6.11.2, 6.11.6, and 6.11.7) discussed are the attachment of a moiety to the end or backbone of a polymer chain (polymer chain ends can be... 

The historical and mechanistic aspects and the synthetic applications of the reaction have been the subject of a number of comprehensive review articles by Barton himself, as well as his pupils. ... 

---