Decisive role of non-rare earth metals in high-regioselectivity addition of μ3-carbido clusterfullerene

Endohedral clusterfullerenes featuring encapsulation of metal clusters which transfer electrons to the outer fullerene cages show intriguing chemical properties different from empty fullerenes. Despite the extensive studies on the chemical properties of empty fullerenes, especially C-60, chemical functionalization of endohedral clusterfullerenes has been less explored, and previous reports are primarily limited to the well-known metal nitride and carbide clusterfullerenes. Herein, we report the first chemical functionalization of an emerging endohedral clusterfullerene mu(3)-carbido clusterfullerene (abbreviated as mu(3)-CCF) bearing central mu(3)-C and Ti(IV) atoms forming a Ti=C double bond. A mu(3)-CCF Dy2TiC@/(h)-C-80 is synthesized, and its molecular structure is unambiguously determined by single-crystal X-ray diffraction for the first time. A photochemical cycloaddition reaction of Dy2TiC@/(h)-C-80 with 2-adamantane-2,3-[3H]-diazirine (abbreviated as AdN(2)) is then carried out and only one monoadduct Dy2TiC@/(h)-C-80-Ad is obtained, indicating its high regioselectivity. According to the X-ray single-crystal structure of Dy2TiC@/(h)-C-80-Ad, the Ad moiety selectively attacks the [6,6]-bond (conjunction of two fused hexagons), which is adjacent to the Ti4+ ion instead of the two Dy3+ ions, affording a [6,6]-open addition pattern. Theoretical calculations unveil that the Ti(IV) ion plays a decisive role in high regioselectivity, and the formation of [6,6]-open Dy2TiC@/(h)-C-80-Ad is thermodynamically preferred. Contrarily, a similar reaction of a Ti(III)-containing nitride clusterfullerene Y2TiN@C-80 with AdN(2) is predicted to generate a different type of adduct with the addition sites adjacent to the Y3+ ion instead of the Ti3+ ion. This reveals the peculiarity of the chemical property of mu(3)-CCF resulting from the existence of the non-rare earth metal Ti with a high oxidation state.

Automated summary

This study reports the first chemical functionalization of an emerging endohedral clusterfullerene mu(3)-CCF. The high regioselectivity of the reaction is determined by the presence of Ti(IV) ion. A similar reaction involving a Ti(III)-containing nitride clusterfullerene reveals the peculiarity of mu(3)-CCF's chemical property due to the non-rare earth metal Ti with a high oxidation state.