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Acetylene-Expanded Dendralene Segments with Exotopic Phosphaalkene Units
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
2011 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 43, 12153-12162 p.Article in journal (Refereed) Published
Abstract [en]

Bis-TMS protected C, C-diacetylenic phosphaalkene (A(2)PA) 1 (Mes*P=C(C CTMS)(2); Mes*=2,4,6-tBu(3)Ph) has been used as a building block for the construction of butadiyne-expanded dendralene fragments in which phosphaalkenes feature as exotopic double bonds. Treatment of 1 with CuCl gives rise to a Cu(I) acetylide that is selectively formed at the acetylene trans to the Mes* group. The cis-TMS-acetylene engages in similar chemistry, albeit at higher temperatures and longer reaction times. The differentiation between the two acetylene termini of 1 allows for the controlled synthesis of the title compounds by a variety of different Cu- and Pd-catalyzed oxidative acetylene homo- and heterocoupling protocols. Crystallographic characterization of A(2)PA 1 and dimeric Mes*P=C(C CR(1))C(4)(R(2)C C)C=PMes* (3b, R(1)=R(2)=Ph; 6, R(1)=R(2)=TMS), and 10 (R(1)=R(2)=C CPh) verifies that the stereochemistry across the P=C bond is conserved during the coupling reactions, whereas spectroscopic evidence reveals cis/trans isomerization in an iodo-substituted A(2)PA intermediate 4 (Mes*P=C(C CTMS)(C CI). UV/Vis spectroscopic and electrochemical studies reveal that efficient pi conjugation operates through the entire acetylenic phosphaalkene framework, even in the cross-conjugated dimeric structures. The P centers contribute considerably to the frontier molecular orbitals of the compounds, thereby leading to smaller HOMO-LUMO gaps than in all-carbon-based congeners. Phenyl- and/or ethynylphenyl substituents at the A(2)PA framework influence the HOMO and LUMO to a varying degree depending on their relationship to the Mes* group, thus enabling a fine-tuning of the frontier molecular orbitals of the compounds.

Place, publisher, year, edition, pages
2011. Vol. 17, no 43, 12153-12162 p.
Keyword [en]
carbon-rich compounds, conjugation, dendralenes, oxidative acetylene coupling, phosphaalkenes
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-166122DOI: 10.1002/chem.201101358ISI: 000297316100031OAI: oai:DiVA.org:uu-166122DiVA: diva2:476200
Available from: 2012-01-11 Created: 2012-01-10 Last updated: 2017-12-08Bibliographically approved

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Geng, Xue-LiOtt, Sascha

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