Two Regioisomers of Endohedral Pyrrolidinodimetallofullerenes M₂@I_h‐C₈₀(CH₂)₂NTrt (M=La, Ce; Trt=trityl): Control of Metal Atom Positions by Addition Positions

Abstract

The two regioisomers of endohedral pyrrolidinodimetallofullerenes M(2)@I(h)-C(80)(CH(2))(2)NTrt (M = La, Ce; Trt = trityl) were synthesized, isolated, and characterized. X-ray crystallographic analyses of [6,6]-La(2)@I(h)-C(80)(CH(2))(2)NTrt and [6,6]-Ce(2)@I(h)-C(80)(CH(2))(2)NTrt revealed that the encapsulated metal atoms are located at the slantwise positions on the mirror plane that parallels the pyrrolidine ring. Paramagnetic NMR analyses of [6,6]- and [5,6]-Ce(2)@I(h)-C(80)(CH(2))(2)NTrt were also carried out to clarify the metal positions. As for the [6,6]-adduct, the metal positions obtained by paramagnetic NMR analysis agree well with the X-ray structure. In contrast, paramagnetic NMR analysis of the [5,6]-adduct showed that the two Ce atoms are collinear with the pyrrolidine ring. We also compared the observed paramagnetic effects of the pyrrolidinodimetallofullerenes with those of other cerium-encapsulating fullerene derivatives such as bis-silylated Ce(2)@I(h)-C(80) and a carbene adduct of Ce(2)@I(h)-C(80). We found that the metal positions can be explained by the electrostatic potential maps of the corresponding [6,6]- and [5,6]-adducts of [I(h)-C(80)(CH(2))(2)NTrt](6-). These findings clearly show that metal positions inside fullerene cages can be controlled by means of the addition positions of the addends. In addition, the radical anions of the pyrrolidinodimetallofullerenes were prepared by bulk controlled-potential electrolysis and characterized by X-band EPR spectral study.

Synthesis and Photoinduced Electron‐Transfer Reactions in a La2@Ih‐C80–Phenoxazine Conjugate

“…The electrochemical features of 4 , 5 , and the corresponding references in the form of cyclic (CV) and differential pulse voltammetry (DPV) are illustrated in Figures S10 and S11 in the Supporting Information, respectively, and are summarized in Table . Importantly, subtle differences characterize the redox potentials of the [6,6]‐ and [5,6]‐La 2 @C 80 (CH 2 ) 2 NTrt isomers . In this context, the redox potentials of 5 more closely resemble those of [5,6]‐La 2 @C 80 (CH 2 ) 2 NTrt, which further supports our conclusion that a [5,6]‐addition pattern is present in 5 .…”

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.…”

In-depth understanding of π-electron systems: New vistas in fullerene endohedrals

“…Similarly, the 1,3-dipolar cycloaddition of Ce 2 @I h -C 80 afforded [6,6]-closed and [5,6]-closed cycloadducts of Ce 2 @I h -C 80 (CH 2 ) 2 NTrt [34]. The structures of [6,6]-La 2 @I h -C 80 (CH 2 ) 2 NTrt and [6,6]-Ce 2 @I h -C 80 (CH 2 ) 2 NTrt were elucidated unambiguously using X-ray crystallography.…”