Aromatic π-Systems More Curved Than C₆₀. The Complete Family of All Indenocorannulenes Synthesized by Iterative Microwave-Assisted Intramolecular Arylations

Abstract

Syntheses and X-ray crystal structures are reported for all seven members of the indenocorannulene family, comprising indenocorannulene, both isomers of diindenocorannulene, both isomers of triindenocorannulene, tetraindenocorannulene, and pentaindenocorannulene. With each additional indenoannulation, the pyramidalization of the trigonal carbon atoms at the hub of the corannulene increases. Five of the seven indenocorannulenes contain carbon atoms at the hub that are actually more pyramidalized than the carbon atoms of C(60). This work demonstrates, for the first time, that extended pi-systems with curvatures exceeding those of the most curved stable fullerenes and carbon nanotubes can be prepared by ordinary laboratory methods in solution, without recourse to high-temperature gas phase methods, such as flash vacuum pyrolysis. This proof of principle presages the days when scientists will be able to synthesize isomerically pure fullerenes and single-chirality nanotubes by well-understood, controlled chemical methods. Pentaindenocorannulene, itself, represents an attractive precursor to the C(5v) end-cap of an all-carbon, single-walled, "armchair" [5,5]nanotube.

Foregoing Rigidity to Achieve Greater Intimacy

“…Coordination slightly flattens the indenocorannulene surface compared to its free form with the bowl being less curved in 2 A (bowl depth is 1.008 vs. 1.047 in 2 B and 1.056 in free indenocorannulene), and that allows a closer packing of molecules along the stack in the former. For comparison, corannulene is significantly more affected by coordination, with its bowl depth being reduced to 0.754 in 1 compared to 0.870 in free C 20 H 10 . [12] The smaller bowl deformation in the indenocorannulene complex can be attributed to the shift of primary Hg-C interactions away from the corannulene core to the peripheral indeno group (Figure 5).…”

Rational Synthesis of Fullerenes

“…Here the palladium(0)-catalyzed direct arylation utilizing bromo and chloro derivatives has been found to be effective for the synthesis of small fullerene fragments [19]. The largest fullerene fragments obtained so far contain 50 carbon atoms and formally represent more than 83% of the C 60 fullerene surface (Figure 3) [20].…”

“…Although the largest synthesized C 50 bowl is more curved than C 60 [20], the rational synthesis of fullerene following this route still remains a challenge. This is mainly connected with difficulties to perform the Pd-catalyzed cyclization in a domino fashion.…”

Synthesis, Structures, and Physical Properties of Aromatic Molecular-Bowl Hydrocarbons

“…In contrast to the parent compound 98 [128], the substituted indenocorannulene [27] is slightly flattened, revealed by comparing their bowl depths and the POAV pyramidalization angles (Table 6). Each additional indenoannulation increases the bowl depth and the curvature.…”

“…This synthetic approach allows a variety of functional groups to be regioselectively introduced. Scott and coworkers improved the synthesis of indenocorannulene 98 by conducting Pd-catalyzed intramolecular arylation reaction of (2-chlorophenyl)-corannulene 29 under microwave-assisted conditions (Scheme 30) [128]. The efficient condition allows a simple formation of multi-indenocorannulenes.…”