Regioselective Mono‐ and Dialkylation of [6,6]‐open C₆₀(CF₂): Synthetic and Kinetic Aspects

Abstract

Alkylation of homofullerene [6,6]-C 60 (CF 2 ) 2À dianion with the set of alkyl halides, RX, was established to demonstrate an effect of RX nature on the conversion, product composition, and regioselectivity. The respective C 60 (CF 2 )RH, C 60 (CF 2 )R 2 and C 60 (CF 2 )R'R'' compounds were obtained in the reaction with sterically unhindered RX, isolated by HPLC and unequivocally characterized. The kinetic studies evidenced S N 2 mechanism for both alkylation steps, yielding mono-and dialkylated C 60 (CF 2 ), respectively, and indicated the negative charge localization at the bridgehead carbon atoms as well as a steric hindrance of the CF 2 moiety likely to be a key factors for the S N 2 reaction mechanism and observed regioselectivity. The significant difference in the rate constants of the first and the second steps is attributed to the different activation barriers predicted by DFT calculations which makes possible to develop synthetic methods for the regioselective preparation of monoalkylated C 60 (CF 2 ) RH and heterodialkylated C 60 (CF 2 )R'R'' derivatives.[a] V.

Para‐C60(CF2)(CF3)R: a family of chiral electron accepting compounds accessible through a facile one‐pot synthesis

“…The distance between the bridgehead carbon atoms in para ‐C 60 (CF 2 )(CF 3 )Me is 2.40(1) Å. This is an intermediate value between the ones for cis ‐2‐C 60 (CF 2 ) 2 [1.726(5) and 1.979(5) Å] [21] and 1,9‐C 60 (CF 2 )R 2 [2.65–2.66] Å [5,6] . Each molecule is surrounded by seven neighboring molecules with the shortest intermolecular C⋅⋅⋅C distances (3.00–3.35 Å), providing effective intermolecular π‐π interactions required for effective charge transport.…”

“…However, poor solubility of C 60 (CF 2 ) hinders solution‐based processing of the compound. Hence a method of regioselective C 60 (CF 2 ) 2− dianion alkylation was recently investigated in detail both from materials science [5] and reaction kinetics [6] perspectives. The resulting bridgehead 1,9‐C 60 (CF 2 )R 2 derivatives generally feature increased solubilities and better film morphologies, while the performance of the thin‐film device can be tuned by careful selection of the alkyl groups [5] .…”