Homo‐ and methano[60]fullerenes with chiral attached moieties – ¹H and ¹³C NMR chemical shift assignments and diastereotopicity effects

Abstract

(1)H and (13)C NMR chemical shift predictions of homo- and methano[60]fullerenes containing chiral centers in attached fragment were made using the two-dimensional NMR technique (HH COSY, (1)H-(13)C HSQC and HMBC) and the quantum chemistry GIAO calculation method in the PBE/3ζ approach. The influence of a chiral substituent on the (13)C chemical shifts of diastereotopic fullerene carbons was estimated by comparing the calculated and experimental (13)C NMR spectra. The resonances of the fullerene carbons in α-, β- and δ-positions relative to the position of the substituent exhibit the greatest diastereotopic splitting.

Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

“…The experimental evidences for the ring currents were NMR high‐frequency proton chemical shifts in C 60 H 2 , as well as in some fullerene systems we described earlier . The ring currents also affect 13 C NMR high‐frequency and low‐frequency chemical shifts in fullerene derivatives, as it was observed in recent works.…”

“…Using the GIAO‐PBE/3z method, we have performed earlier full 13 C NMR assignments for the C S spiro‐cycloalkylidenehomo‐ and C 2V methanofullerenes, C 1 chiral spiro‐cycloadducts, and those with sulphur atoms in attached fragments, аs well as for C 2V N ‐substituted aziridinofullerenes . An accuracy of the method was assessed on the basis of calculations of 1 H and 13 C NMR CSs for simple organic compounds and a series of fullerene derivatives, whose structure was unequivocally determined with the NMR INADEQUATE technique …”

Synthesis and NMR Spectral Studies of the 7-C60-Adduct of N,N-(Tetrachlorophthaloyl) Dehydroabietylamine

“…The signals at δ C 44.61, 84.80, 77.66 ppm were assigned to C-7 and the sp 3 -hybridized bridgehead carbon atom C-21, 22 on the cyclopropyl moiety due to the long-range cross peaks of δ C 44.61 ppm/H-6 α , 6 β , 14, 11, δ C 84.80 ppm/H-6 α , 6 β and δ C 77.66 ppm/H-6 α . This pattern is unambiguously diagnostic for C 1 symmetric structure with 6,6-junction [ 14 , 15 ].…”

Carbene Additions to Fullerenes

“…They employed Pd(OAc) 2 in the reaction of ethereal diazomethane with C 60 at 0 °C and isolated the methanofullerene in 15% yield. Tuktarov and co-workers developed three-component catalytic systems Pd(acac) 2 –PPh 3 –Et 3 Al to improve the efficiencies of cycloadditions. − The formation ratio of the adducts depends on the substituents of the diazo compounds they used and the reaction conditions. When diazoesters or diazoketones were used for the three-component Pd(acac) 2 –4PPh 3 –4Et 3 Al catalytic reactions, [6,6] closed methanofullerenes were obtained exclusively in 30–60% yields.…”