Increasing the Curvature of a Bowl-Shaped Polyarene by Fullerene-like η2-Complexation of a Transition Metal at the Interior of the Convex Surface

Abstract

The first transition metal complex of monoindenocorannulene, [{Rh2(O2CCF3)4}2·(C26H12)] (1), has been synthesized by gas-phase deposition and has been structurally characterized by X-ray crystallography. In the solid state, it forms a 2D organometallic network based on intermolecular Rh−C interactions and rare tetra-bridged coordination of a π-bowl. In addition to η2-rim binding, one Rh(II) center interacts exclusively with interior carbon atoms on the convex surface, exhibiting an η2-coordination type previously observed only in closed, all-carbon buckyballs. The latter unique coordination of Rh(II) accentuates the pyramidalization of the C atoms of monoindenocorannulene. Thus, in contrast to all other reported Rh(II) complexes with buckybowls, metal complexation leads to a curvature increase of the C26H12 core in 1. DFT calculations (PBE0) reveal the preferred coordination sites of C26H12 to be the rim of the corannulene core, followed by the interior spoke and then the rim CC bonds of the indeno site. This calculated trend is nicely followed by the average Rh−C bond distances in the solid-state structure of 1: 2.567 (rim) < 2.687 (spoke) < 2.715 Å (indeno site). The nature of Rh(II)−π interactions was quantitatively evaluated in terms of ligand-to-metal and metal-to-ligand contributions, showing the consistently greater role of the former in all computed complexes.