Poly-hetero-ω-functionalized Alkanethiolate-Stabilized Gold Cluster Compounds

Abstract

This paper describes two synthetic approaches, simultaneous and stepwise exchange, to poly-hetero-ω-functionalized monolayer-protected cluster compounds (MPC's), as well their spectroscopic and electrochemical characterization. Poly-hetero-ω-functionalization of MPC's provides a framework within which to study intra- and intermolecular cluster chemistry and to design multistep, mutually supporting catalytic and electron donor/acceptor reactions on cluster surfaces. Factors affecting the extent of exchange (measured by NMR) include the steric bulk of the ω-functional group as well as the chain lengths of the protecting and incoming ligands. Poly-hetero-ω-functionalized clusters can incorporate mixed redox functions as illustrated by microelectrode voltammetry of a poly-ferrocene/anthraquinone mixed cluster. The cluster voltammetric waves lie at potentials consistent with those observed in dilute solutions of the unbound electroactive thiols, within the uncertainty of the Ag quasi-reference electrode potential. Diffusion coefficients and hydrodynamic radii suggest that the outer parts of the cluster chains may be free-draining. This research demonstrates that 3D-SAMs with mixed ω-functionalized alkanethiolate ligands (both redox and nonredox active) can be synthesized and characterized and provides the groundwork for synthesis of “nanofactory” cluster compounds designed to exhibit mutually supporting, multistep chemical and redox catalytic reactions, and for an enhanced capacity to study functional group reactivities at organized monolayer interfaces.