Research Synopsis

A wide-ranging program of research has been initiated in the Pigge Group that impacts upon the broadly defined areas of organic/organometallic synthesis and supramolecular chemistry.

The continuing development of organometallic chemistry in the context of organic synthesis is resulting in more efficient approaches to synthetic targets, particularly those of significance in medicinal and/or materials chemistry. Moreover, organometallic-based synthetic routes often produce organic products that are virtually inaccessible via traditional methods. In this regard, we are investigating the organic chemistry of stable and readily available arene ruthenium complexes with the aim of developing concise and stereocontrolled approaches to complex ring systems. In particular, we have targeted heterocyclic materials that are structurally related to biologically active natural products. n⁶-Arene ruthenium complexes are ideally suited to serve as versatile synthetic intermediates as coordination of the metal dramatically alters the reactivity of the aromatic ring while also acting as a stereocontrol element. For example, these organometallic complexes are susceptible to reaction with nucleophiles, and this property has been successfully exploited in the stereocontrolled construction of various fused- and spirocyclic aza-heterocycles.

The field of supramolecular chemistry has experienced enormous growth over the past 35 years and now occupies a prominent position within the research community. As methods for detecting and quantifying supramolecular associations developed, so, too, did the cognitive realization that virtually every non-covalent intermolecular interaction is mediated by discrete and energetically significant supramolecular attractions. Part of the allure of supramolecular chemistry is the significant role it plays in seemingly disparate fields ranging from biological chemistry to materials science. Thus, research in this area occurs across many disciplines encompassing all the traditional chemistry divisions. Derivatives of 1,3,5-tribenzoylbenzene (1) are readily available via regioselective amine-catalyzed cyclotrimerization of aryl ethynyl ketones. The semi-rigid polyaromatic framework inherent to 1 impart upon these materials many desirable characteristics commonly found in supramolecular chemistry building blocks. In addition, simple triaroylbenzenes have shown a propensity to form crystalline inclusion complexes with small molecule guests, and certain derivatives exhibit polymorphism. Thus, these readily available materials serve as useful probes of various solid-state phenomena. The triaroylbenzene framework is amenable to further synthetic elaboration and so general programs of research have been initiated with the aim of utilizing the unique features of triaroylbenzenes in the design and synthesis of numerous functional supramolecular systems, including metal-organic coordination polymers, crystalline inclusion complexes, dendritic materials, catalysts, and cyclophane-derived molecular receptors. For example, an efficient modular synthetic strategy for constructing crown ether-like macrocycles (crownophanes) such as 2 has been developed. The number of ethylene oxy units in 2 can be easily varied, thereby resulting in crownophanes that display different selectivity for the binding of alkali metal and ammonium cations. A variation on this theme is illustrated in 3, a triaroylbenzene derivative with three crown ether substituents along the periphery. Compound 3 and its congeners are easily constructed and should be capable of binding multiple small metal cations or, through cooperative intramolecular interactions, larger metal and organic cations.