Synthesis of Aryl-Terminated Polyenaldehydes and Polyenetriethoxysilanes for Preparation of Self-Assembled Monolayers on Silicon Surfaces

Abstract

The synthesis of a,w-terminally functionalized polyenes with arenes or hetarenes at one end and either an aldehyde or a triethoxysilyl function at the other end, capable of reacting with H-terminated or oxidized silicon surfaces, is described. Analogous to known Wittig reactions, polyenedialdehydes 1 and 3, the latter derived from 1 and phosphonium chloride 2 in a twofold Wittig olefination, were converted with phosphonium bromides 4 to give the (all-E)-arylpolyenaldehydes 5 and 6. A terminal alkyl chain was introduced in dialdehydes 1a and 3a by reaction with P,P-didecyldibenzophospholium bromide 8, resulting in polyenals 9. Wittig olefination of 5c and 9a with phosphonium chloride 2 afforded the (2-thienyl)tridecahexaenal 7 and the docosahexaenal 10. With respect to monolayer formation on oxidized Si(100) surfaces, (9-anthryl)-and (2-thienyl)-w-functionalized polyenetriethoxysilanes 16 and 17 were prepared in a reaction sequence involving the introduction of a terminal triple bond with [3-(trimethylsilyl)prop-2-ynyl]triphenylphosphonium bromide (11), desilylation of the resulting arylpolyeninetrimethylsilanes 12, 13 with Bu 4 NF×3H 2 O, and subsequent hydrosilylation of the arylpolyenines 14, 15 using triethoxysilane under dichlorocyclooctadienylplatinum(II) catalysis.In donor-acceptor-substituted conjugated polyenes and oligothiophenes a quantitative energy transfer from the photoexcited donor, for example anthracene, to the acceptor, for example tetraphenyl porphyrin, could be proved by fluorescence spectroscopy. 2-6 Replacement of the porphyrin in these supermolecules by stronger electron acceptors such as fullerene, pyridines or pyridinium moieties, respectively, enables an uni-directed intramolecular electron transfer from the photoexcited anthracene donor to the respective acceptor. 7-9 In contrast to the energy transfer mentioned above, the electron transfer in these conjugated p-systems can already be interrupted by a methylene group as saturated spacer. This offers the possibility of incorporating, for example, photochemically switchable organic molecules 10 in donor-acceptor substituted conjugated p-systems in order to realize suitable components for electronic devices on a molecular level. Any application of the described isolated molecules as components in "molecular electronics , however, requires the formation of supramolecular structures, for example well-ordered monomolecular layers and bonding of the molecular building blocks to existing information systems (e.g., microelectronic silicon components). Anthracene-polyene pyridinium compounds have been investigated first with respect to such kind of ordering of single molecules. 11,12 As amphiphiles these compounds are able to form ordered monolayers on the water/air surface which are transferable onto solid supports (e.g. glass) by the Langmuir-Blodgett technique. The labile bonding of these functionalized monolayers to the solid support is a crucial disadvantage for possible applications of LB films in "molecular electronics . We have therefore ...

Bidirectional Hiyama–Denmark Cross‐Coupling Reactions of Bissilyldeca‐1,3,5,7,9‐pentaenes for the Synthesis of Symmetrical and Non‐Symmetrical Carotenoids

“…In order to explore the sequential Hiyama–Denmark cross‐coupling of a non‐symmetrical 1,10‐bissilyldeca‐1,3,5,7,9‐pentaene with modulated reactivity, the silanol group of pentaenylbissilane 6 was selectively activated by treatment with KOTMS. Then, addition of [Pd(dba) 2 ] and trienyl iodide 1 afforded, at ambient temperature, octaenylsilane 23 with good efficiency (59 % yield, Scheme ) . Thus, the reactivity of the non‐symmetrical 1,10‐bissilyldeca‐1,3,5,7,9‐pentaene follows the same trends described for the shorter unsubstituted 1,4‐bissilylbutadienes, and the observed selectivity can be diverted to the preparation of non‐symmetrical carotenoids.…”

Synthesis of Symmetrical and Nonsymmetrical Polyenes by Iterative and Bidirectional Palladium‐Catalyzed Cross‐Coupling Reactions

“…Thus, octaenylsilane 220 [84] could be isolated in 59 % yield from the selective monocoupling of 193 with trienyliodide 211 at the silanol terminus [26] . Further coupling of octaenylsilane 220 with either trienyliodide 211 , its terminal Z isomer 224 or the dihydro derivative 223 following activation with TBAF and using Pd 2 dba 3 ⋅CHCl 3 as catalyst afforded, in 90 %, 60 % and 78 % yields, respectively, β,β‐carotene 213 , the highly unstable isomer 9‐ cis ‐β,β‐carotene 225 , [85] and 7,8‐dihydro‐β,β‐carotene 226 .…”

Total Synthesis of Oxazolomycins

“…However, this transformation proceeded with poor regioselectivity to afford a 2:1 mixture of 73 and its 6‐iodo isomer. We then examined the hydrostannylation and hydrosilylation of the TBS ether of 75 under various conditions. However, these methods also did not exhibit high regioselectivity, although the yields were satisfying in all cases.…”