From sterically crowded molecular machines to luminescent tetracenes: symmetry breaking in organic and organometallic chemistry
Dr. Michael McGlinchey
School of Chemistry & Chemical Biology
University College Dublin
Friday, October 17, 2014
C2-361 (Reading Room)
Abstract: Molecular rearrangements in organic or organometallic chemistry are frequently hidden processes whose existence is revealed, and their energetics elucidated, only when the symmetry is broken, often in a subtle way so as to perturb the system very minimally. In the course of our studies of the dynamics of potential molecular gearwheels, such as ferrocenyl-pentanaphthylbenzene, (C6Et6)Cr(CO)3 or [C7Ph7]+, the attempted synthesis of 9-fluorenyl-pentaphenylbenzene led instead to a series of fluorenylidene-allene dimers, and ultimately to tetracenes. This entire 10-step mechanism was elucidated by X-ray crystallography. Subsequently, allenes or alkynes containing silyl or dibenzosuberenylidene moieties yielded novel, unexpected rearrangement products. One of these gave rise to a molecule of formula C60H36 that can be mapped directly onto the fullerene skeleton; another serendipitously provided the first experimental verification of the initial step of the Pauson-Khand process for the formation of cyclopentenones. Propargyl-allenes, formed by dimerization of allenes, react with metal carbonyls or with silver nitrate leading to novel polycyclic systems. Finally, we describe how the combination of a haptotropic shift of a metal carbonyl moiety and a molecular paddlewheel was used to provide the first successful demonstration of an organometallic molecular brake.