title: Tautomerization and Dimerization of 6,13-Disubstituted Derivatives of Pentacene.
abstract: Two new 6,13-disubstituted pentacene derivatives, 1 c and 1 d, with alkyl and triisopropylsilylethynyl substitution have been synthesized and characterized experimentally and computationally. The alkyl substituted 1 c and 1 d represent the first 6-alkyl-substituted pentacene derivative where the fully aromatic species dominates over the corresponding tautomer. Indeed, no tautomerization product is found for either 1 c or 1 d upon heating or in the presence of catalytic amounts of acid. On the other hand, an unexpected dimer (3 c) is formed from 1 c. A plausible mechanism for this new dimerization process of the 6-methyl-substituted pentacene derivative 1 c is proposed, which involves first a bimolecular hydrogen atom transfer followed by an intramolecular [4+2] Diels-Alder cycloaddition. In the case of 6-butyl substitution, neither tautomerization nor dimerization is observed. Computations support the proposed 1 c dehydrodimerization pathway, explain why 1 d does not dimerize, and show the importance of the nature of the group at C-13 in controlling the relative stability of 6-alkyl-substituted pentacene tautomers.
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA, 90095, USA.
authors: Marc
authors: http://orcid.org/0000-0001-9458-1114
authors: M
authors: Garcia-Borràs
authors: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany.
authors: Akihito
authors: A
authors: Konishi
authors: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany.
authors: Andreas
authors: A
authors: Waterloo
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA, 90095, USA.
authors: Yong
authors: Y
authors: Liang
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA, 90095, USA.
authors: Yang
authors: Y
authors: Cao
authors: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany.
authors: Constantin
authors: C
authors: Hetzer
authors: Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
authors: Dan
authors: http://orcid.org/0000-0001-8392-1208
authors: D
authors: Lehnherr
authors: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany.
authors: Frank
authors: F
authors: Hampel
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA, 90095, USA.
authors: Kendall N
authors: http://orcid.org/0000-0002-8387-5261
authors: KN
authors: Houk
authors: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany.|Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
authors: Rik R
authors: http://orcid.org/0000-0002-7645-4784
authors: RR
authors: Tykwinski
keywords: 6,13-disubstituted pentacenes; dehydrodimerization; density functional calculations; polycycles; tautomerism