Dept. of Biochemistry & Organic Chemistry
Henrik Ottosson
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Assoc. Prof. Henrik Ottosson Uppsala University Department of Biochemistry and Organic Chemistry Box 576 S-751 23 Uppsala, Sweden
Phone: +46 (0)18 471 3809 FAX: +46 (0)18 471 3818 E-mail: Henrik.Ottosson@biorg.uu.se
Visiting address: BMC, Husargatan 3
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Themes for research
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Conjugation and aromaticity Molecular electronics Low-coordinated Group 14 compounds Qualitative MO- and VB-theory |
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Key publications
The First Isolable 2-Silenolate
Zwitterionic Silenes: Interesting Goals for Synthesis?
Fulvenes, Fulvalenes, and Azulene: Are They Aromatic Chameleons?
Z/E-Photoisomerizations of Olefins with 4n- or (4n + 2)-Electron Substituents: Zigzag Variations in Olefin Properties along the T1 State Energy Surfaces
Heavy Group 14 (1,n+2)-Dimetallabicyclo[n.n.n]alkanes and (1,n+2)-Dimetalla[n.n.n]propellanes: Are They All Realistic Synthetic Targets?
Research projects
Selective chemistry with the Si=C bond: Experimental proofs for the formation of the first transient Si=C double bonded compound, a silene, was obtained through pyrolysis of a silacyclobutane by Gusel’nikov and Flowers 40 years ago. The first isolable silene was synthesized in 1981 by A. G. Brook, and since then the field of Si=C bonded compounds has gradually grown. However, these species have so far not obtained any widespread applications in organic synthesis, presumably because of their very low stability, unless substituted by very bulky groups, as well as their rather unselective reactivity. We now focus on silenes influenced by reversed Si=C bond polarity, i.e. a partial negative charge at Si and partial positive charge at C, as these tend to react more selectively with dienes in [4+2] cycloadditions than silenes with a natural Si=C bond polarity. They are also less moisture sensitive. The reverse Si=C bond polarization is effected through pi-electron donor substituents at the C atom. We predominatly work with the fundamental structure and reactivity aspects of reverse polarized silenes and silenolates, and collaborate with the group of Dr. Patrick Steel, Univ. of Durham (UK), on synthetic methodology and further applications.
Applications of triplet state aromaticty: Some 35 years ago Baird showed, based on perturbation MO-theory, that annulenes which are antiaromatic in their electronic ground are aromatic in their lowest triplet excited state, and vice versa for annulenes that are aromatic in their ground state. We have used this concept to deduce that fulvenes, fulvenes and azulenes act as aromatic chameleons as they can adapt to the aromaticity requirements of different electronic states. As a result of their ability to adapt their electronic structures to several electronic states, their polarities in these states will be opposite. E.g. in the singlet ground state pentafulvene is influenced by a resonance structure with a negatively charged five-membered ring, but in the triplet state a resonance structure with a positively charged triplet state aromatic ring is instead important. We reason that this concept can be used to tailor substituted fulvenes, fulvalenes and azulenes with very predictable properties (e.g. band gaps) to function in molecular materials.
The concept of triplet state aromaticity can also be used to rationalize the profiles of triplet state energy surfaces for Z/E-isomerizations of substituted olefins. A gain in aromaticity or loss in antiaromaticity when the C=C bond is twisted in the T1 state will lead to an energy gain, whereas the opposite will be the case if aromaticity is lost upon C=C bond twist. Even though a very fundamental finding it could be useful for the improved design of optical switches that are based on Z/E-isomerizations of olefins.
Rigid Si, Ge, and Sn-based wires for molecular electronics: Presently, the majority of molecular electronics components rely on pi-conjugation for charge transport in one way or the other. Sigma-conjugation has several advantages that motivate development of components based on this type of conjugation as well. Linear polysilanes and polystannanes are well-known sigma-conjugated polymers, but it has been shown that charge carriers often are localized to rather short segments of such chains, a result of the fact that these polymers are conformationally very flexible so that charge carriers are trapped at structural inhomogenities. We now seek alternative more rigid sigma-conjugated molecules that would be better suited to carry charge.
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