Chemical reduction of highly-twisted 9,10,11,20,21,22-hexaphenyltetrabenzo[a,c,l,n]pentacene (C74H46, 1) was investigated using Li and Cs metals as the reducing agents. The Cs-induced reduction of 1 in the presence of 18-crown-6 ether enabled the isolation of a solvent-separated ion pair (SSIP) with a “naked” monoanion. Upon reduction with Li metal, a double reductive dehydrogenative annulation of 1 was observed to afford a new C74H422– dianion. The latter was shown to undergo a further reduction to C74H424– without additional core transformation. All products were characterized by single-crystal X-ray diffraction and spectroscopic methods. Subsequent in-depth theoretical analysis of one vs. two and four electron uptake by 1 provided insights into how the changes of geometry, aromaticity and charge facilitated the core transformation of twistacene observed upon two-fold reduction. These experimental and theoretical results pave the way to understanding of the reduction-induced core transformations of highly twisted and strained π-systems.
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Doubly‐Reduced Pentacene in Different Coordination Environments: X‐ray Crystallographic and Theoretical Insights into Structural and Electronic Changes
Chemical reduction of pentacene (C22H14,
- NSF-PAR ID:
- 10362869
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 28
- Issue:
- 9
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Chemical reduction of a benzo‐fused double [7]helicene (
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Abstract Chemical reduction of a benzo‐fused double [7]helicene (
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tert ‐butyl‐3a2‐azapentabenzo[bc ,ef ,hi ,kl ,no ]corannulene (1 a ) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na+(18‐crown‐6)(THF)2}3{Na+(18‐crown‐6)(THF)}(1 a 2−)2], revealed the presence of a naked dianion. In contrast, controlled reaction of1 a with Cs allowed the isolation of singly and doubly reduced forms of1 a , both forming π‐complexes with cesium ions in the solid state. In [{Cs+(18‐crown‐6)}(1 a −)]⋅THF, asymmetric binding of the Cs+ion to the concave surface of1 a −is observed, whereas in [{Cs+(18‐crown‐6)}2(1 a 2−)], two Cs+ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.
