Regioselective Bis-functionalization of Endohedral Dimetallofullerene, La₂@C₈₀: Extremal La–La Distance

Abstract

Bis-functionalization of endohedral metallofullerene La(2)@C(80) by carbene addition is reported herein. Adducts were characterized using spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for bisadduct La(2)@C(80)(CClPh)Ad (3, Ad = adamantylidene) revealed that both carbene additions occur at the 6,6-bond junction on the C(80) cage with ring cleavages and that La atoms are positioned collinearly with spiro carbons. It is noteworthy that the La-La distance in 3 is highly elongated by carbene bis-functionalization compared to the distance in pristine La(2)@C(80) and reported functionalized derivatives. The metal positions were confirmed through density functional calculations.

Crystallographic Evidence for Direct Metal–Metal Bonding in a Stable Open‐Shell La2@Ih‐C80 Derivative

“…[29] Inside the cage,t he two La atoms can move freely, resulting in up to 17 disordered sites with occupancies varying from 0.02 to 0.22, whereas the distances between the two La atoms range from 3.779 t o3 .676 . Notably,t he mean LaÀLa distance (3.71 ; with an average deviation from the mean of 0.04 ) is comparable to the calculated La À La covalent bond length (3.723 ) in the La 2 @I h -C 80 À anion, [32] thus presenting clear experimental evidence of direct metalmetal bonding inside 2.I na ddition, this LaÀLa distance is much shorter (by 0.04-0.449 ) than the values in pristine La 2 @I h -C 80 and any other La 2 @I h -C 80 derivatives [33][34][35][36][37][38][39][40][41] ( Table 2), which further confirms the formation of the metal-metal bond.…”

“…[30] Moreover,n od imerization occurs in the crystalline state.I nc ontrast, the monoadduct formed by benzylation of C 60 is ad imer in its crystal form. Notably,t he mean LaÀLa distance (3.71 ; with an average deviation from the mean of 0.04 ) is comparable to the calculated La À La covalent bond length (3.723 ) in the La 2 @I h -C 80 À anion, [32] thus presenting clear experimental evidence of direct metalmetal bonding inside 2.I na ddition, this LaÀLa distance is much shorter (by 0.04-0.449 ) than the values in pristine La 2 @I h -C 80 and any other La 2 @I h -C 80 derivatives [33][34][35][36][37][38][39][40][41] ( Table 2), which further confirms the formation of the metal-metal bond. Notably,t he mean LaÀLa distance (3.71 ; with an average deviation from the mean of 0.04 ) is comparable to the calculated La À La covalent bond length (3.723 ) in the La 2 @I h -C 80 À anion, [32] thus presenting clear experimental evidence of direct metalmetal bonding inside 2.I na ddition, this LaÀLa distance is much shorter (by 0.04-0.449 ) than the values in pristine La 2 @I h -C 80 and any other La 2 @I h -C 80 derivatives [33][34][35][36][37][38][39][40][41] ( Table 2), which further confirms the formation of the metal-metal bond.…”

Adamantylidene Addition to M3N@Ih‐C80 (M=Sc, Lu) and Sc3N@D5h‐C80: Synthesis and Crystallographic Characterization of the [5,6]‐Open and [6,6]‐Open Adducts

“…In related works, crystallographic characterization of Ad bis-adducts of La 2 @I h -C 80 and La 2 @D 2 -C 72 also revealed that the second Ad additions occurreda ts ites near the encaged La atoms. [30,31] Figure 9p resentst he optimizeds tructures with their relative energies of five selected isomerso fL u 3 N@I h -C 80 (Ad) 2 .T he Ad bis-adduct with the second addition at [6,6]-(34-55) site (designated as the [6,6]-(34-55) bis-adduct),w hich matches the X-ray structureo f5b,i se nergetically the most stable among the five candidates. The [6,6]-(36-57) and [6,6]- (35)(36) bis-adducts, in which the second addition site is near one of the encaged Lu atoms,a re 1.36 and 3.76 kcal mol À1 ,r espectively,h igher in energy than the [6,6]-(34-55) bis-adduct.…”

Structural and electronic properties of endohedral metallofullerenes

“…This is because that one metal is trapped inside the cavity provided by the broken cage bond, and the other metal has to be fixed in the other end of the cage because of strong electrostatic repulsions. Very recently, we designed a stepwise procedure to functionalize La 2 @C 80 in a regioselective manner 36. The isolated bis‐adduct was concisely characterized with various techniques, including single crystal XRD (Figure 9d).…”