p-Block metallocenes: The other side of the coin

Although transition metal metallocenes {such as ferrocene, [(C5H5)(2)Fe]} have been a cornerstone in the development of modern organometallic chemistry and continue to be a focus for chemical and structural studies, in comparison the chemistry of the main group metal counterparts has remained relatively undeveloped. The recent resurgence of interest in p-block (Groups 13-15) metallocenes in particular has given fresh insights into the structural preferences, bonding requirements and reactivity of these under-publicised species, which in many ways represent 'the other side of the coin'. The more varied (ionic and covalent) character of the metal-ligand bonds and the less restricted electronic requirements of p-block metals leads to greater structural diversity and radically different reactivity than is found for the transition metal relatives. This short review focuses on the remarkable range of p-block complexes that has so far been uncovered and attempts to unravel some of the electronic and structural trends in these species.