Sonogashira reactions on dimolybdenum paddlewheel complexes at the ligand periphery

Dimolybdenum paddlewheel complexes (Mo2PWCs) are well-known and appreciated for their fascinating photophysical and electrochemical properties. These complexes can be linked together via an organic linker to form so-called “dimers of dimers”, which have been investigated in the literature to improve our understanding of through-bond electronic communication between two redox-active metal cores. Additionally, due to their desirable properties, Mo2PWCs are seen as potential candidates for synthons towards molecular assemblies such as molecular wires and molecular diodes. However, molecular diodes require an element of asymmetry, which cannot be introduced through traditional self-assembly methodologies due to the formation of undesirable side products, which cannot be separated. To work around this limitation, reactivity at the ligand periphery is proposed as a new, highly selective way of linking two Mo2PWCs together. In this project, a series of Mo2PWCs bearing an iodo- or terminal alkyne functionality at the periphery of their ligands have been prepared. These Mo2PWCs are able to undergo the Sonogashira reaction on their ligands to expand their functionality and to link together two Mo2PWCs towards the synthesis of a symmetric Mo2 dimer of dimers. The synthesis of asymmetric dimers of dimers was attempted using two Mo2PWCs bearing different ancillary ligands. The product was observed but could not be isolated due to ligand scrambling taking place between the two starting materials while in solution. This work therefore proves that performing reactions at the ligand periphery is a plausible way of introducing asymmetry to Mo2-based molecular assemblies, so long as synthetic limitations unrelated to the reactions themselves are addressed. Finding a way around these limitations will be the subject of future work.