Protonation of Unsaturated Hydrocarbon Ligands: Regioselectivity, Stereoselectivity, and Product Specificity

Article abstract of DOI:10.1002/anie.199609461

Understanding the mechanisms of pro-tonation of hydrocarbon ligands is fundamental to a wide range of chemistry including organic synthesis, organo-metallic chemistry, and even bioinor-ganic chemistry. Protonation at carbon or metal sites is often slow, with the result that in species containing both types of sites, initial protonation can be at either the metal or the carbon. This has fundamental consequences on the reactivity of hydrocarbon ligands, which are highlighted in this article. In particular, many reactions are apparently the result of a regioselective protonation on the basis of structural analysis of the isolated products. In fact, these products are often formed by an indirect route involving kinetically controlled protona-tion at the wrong site followed by rearrangement to form the thermodynamically controlled, apparently regioselec-tive, product. Other aspects of the pro-tonation mcchanisms of complexes containing hydrocarbon ligands are discussed, with an emphasis on the manner in which competitive protonation at metal or ligand can be exploited to select which hydrocarbon is produced and to control the stereochemistry of the hydrocarbon.