Probing the binding sites and coordination limits of buckybowls in a solvent-free environment: Experimental and theoretical assessment

This work overviews the coordination properties of fullerene fragments or buckybowls, a new class of open geodesic polyaromatic hydrocarbons that map onto the surface of fullerenes but lack their full closure. In contrast to fullerenes, the bowl-shaped polyarenes have both the convex and concave unsaturated carbon surfaces open and available for coordination, which makes them unique and interesting π-ligands for metal binding reactions. Variable synthetic methods based on solution and solid-state reactions have been developed to access transition metal complexes of buckybowls and to reveal their coordination properties. These studies have been mainly focused on the smallest fragments of the C60-fullerene, corannulene (C20H10) and sumanene (C21H12). In order to utilize directional metal–π-arene interactions effectively and to differentiate π-bonding sites of buckybowls, we have introduced a micro-scale gas-phase deposition method. We have proven this technique to be very effective for the preparation of metal complexes of buckybowls in a single crystalline form. Plus, it allowed us to expand the coordination studies to larger bowls, including dibenzo[a,g]corannulene (C28H14), monoindenocorannulene (C26H12), and the C3-symmetric hemifullerene (C30H12). Specifically, several dimetal core complexes of varied electrophilicity have been used in the gas-phase coordination reactions to identify the preferential binding sites and to test the coordination limits of π-bowls in a solvent-free environment. The coordination preferences of several buckybowls having different surface area and bowl depth, as well as different curvature and strain are compared and discussed here based on the results of X-ray diffraction and DFT calculation studies.