TY - JOUR

T1 - 1,4-Disilacyclohexa-2,5-diene

T2 - A molecular building block that allows for remarkably strong neutral cyclic cross-hyperconjugation

AU - Tibbelin, Julius

AU - Wallner, Andreas

AU - Emanuelsson, Rikard

AU - Heijkenskjöld, Filip

AU - Rosenberg, Martin

AU - Yamazaki, Kaoru

AU - Nauroozi, Djawed

AU - Karlsson, Leif

AU - Feifel, Raimond

AU - Pettersson, Roland

AU - Baumgartner, Judith

AU - Ott, Sascha

AU - Ottosson, Henrik

PY - 2014

Y1 - 2014

N2 - 2,3,5,6-Tetraethyl-1,4-disilacyclohexa-2,5-dienes with either four chloro (1a), methyl (1b), or trimethylsilyl (TMS) (1c) substituents at the two silicon atoms were examined in an effort to design rigid compounds with strong neutral cross-hyperconjugation between π- and σ-bonded molecular segments arranged into a cycle. Remarkable variations in the lowest electronic excitation energies, lowest ionization energies, and the first oxidation potentials were observed upon change of substituents, as determined by gas phase ultraviolet (UV) absorption spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and cyclic voltammetry. A particularly strong neutral cyclic cross-hyperconjugation was observed in 1c. Its lowest electron binding energy (7.1 eV) is distinctly different from that of 1b (8.5 eV). Molecular orbital analysis reveals a stronger interaction between filled π(C[double bond, length as m-dash]C) and π(SiR2) group orbitals in 1c than in 1a and 1b. The energy shift in the highest occupied molecular orbital is also reflected in the first oxidation potentials as observed in the cyclic voltammograms of the respective compounds (1.47, 0.88, and 0.46 V for 1a, 1b and 1c, respectively). Furthermore, 1,4-disilacyclohexadiene 1c absorbs strongly at 273 nm (4.55 eV), whereas 1a and 1b have no symmetry allowed excitations above 215 nm (below 5.77 eV). Thus, suitably substituted 1,4-disilacyclohexa-2,5-dienes could represent novel building blocks for the design of larger cross-hyperconjugated molecules as alternatives to traditional purely cross-π-conjugated analogues, and could allow for design of molecules with properties that are not accessible to those that are exclusively π-conjugated.

AB - 2,3,5,6-Tetraethyl-1,4-disilacyclohexa-2,5-dienes with either four chloro (1a), methyl (1b), or trimethylsilyl (TMS) (1c) substituents at the two silicon atoms were examined in an effort to design rigid compounds with strong neutral cross-hyperconjugation between π- and σ-bonded molecular segments arranged into a cycle. Remarkable variations in the lowest electronic excitation energies, lowest ionization energies, and the first oxidation potentials were observed upon change of substituents, as determined by gas phase ultraviolet (UV) absorption spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and cyclic voltammetry. A particularly strong neutral cyclic cross-hyperconjugation was observed in 1c. Its lowest electron binding energy (7.1 eV) is distinctly different from that of 1b (8.5 eV). Molecular orbital analysis reveals a stronger interaction between filled π(C[double bond, length as m-dash]C) and π(SiR2) group orbitals in 1c than in 1a and 1b. The energy shift in the highest occupied molecular orbital is also reflected in the first oxidation potentials as observed in the cyclic voltammograms of the respective compounds (1.47, 0.88, and 0.46 V for 1a, 1b and 1c, respectively). Furthermore, 1,4-disilacyclohexadiene 1c absorbs strongly at 273 nm (4.55 eV), whereas 1a and 1b have no symmetry allowed excitations above 215 nm (below 5.77 eV). Thus, suitably substituted 1,4-disilacyclohexa-2,5-dienes could represent novel building blocks for the design of larger cross-hyperconjugated molecules as alternatives to traditional purely cross-π-conjugated analogues, and could allow for design of molecules with properties that are not accessible to those that are exclusively π-conjugated.

U2 - 10.1039/C3SC52389F

DO - 10.1039/C3SC52389F

M3 - Journal article

VL - 5

SP - 360

EP - 371

JO - Chemical Science

JF - Chemical Science

SN - 2041-6520

IS - 1

ER -