Incorporating Phosphaalkenes into Oligoacetylenes

Schäfer, Bernhard; Öberg, Elisabet; Kritikos, Mikael; Ott, Sascha

doi:10.1002/ange.200802253

Cited by 25 publications

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“…The introduction of heteroatoms into purely acetylenic scaffolds is even more in its infancy. We have recently reported the incorporation of phosphaalkenes into acetylenic frameworks to form acetylenic phosphaalkenes (A x PA, x = number of acetylene substituents), [34][35][36] an effort that has now also been extended into group 12 elements with the report of a disi- Abstract: Bis-TMS protected C,C-diacetylenic phosphaalkene (A 2 PA) 1 (Mes*P=CA C H T U N G T R E N N U N G (CCTMS) 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.…”

Section: Introductionmentioning

confidence: 99%

Acetylene‐Expanded Dendralene Segments with Exotopic Phosphaalkene Units

Geng

Ott

2011

Chemistry A European J

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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 π 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.

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Section: Introductionmentioning

confidence: 99%

Acetylene‐Expanded Dendralene Segments with Exotopic Phosphaalkene Units

Geng

Ott

2011

Chemistry A European J

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A Convenient Method for the Synthesis of α‐Ethynylphospholes and Modulation of Their π‐Conjugated Systems

2009

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Cascade Reactions Forming Highly Substituted, Conjugated Phospholes and 1,2‐Oxaphospholes

2012

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Dedicated to Professor Peter J. Garratt on the occasion of his 78th birthday Highly unsaturated hydrocarbons [1] based on aromatics, alkenes, acetylenes, and combinations thereof are organic semiconductors. As such, they are interesting both from a basic research viewpoint [2] and in terms of their applications in electronics and photonics devices. [3] The replacement of carbon centers of such compounds by heavier low-valent main group elements, phosphorus in particular, has become increasingly popular. Polyheteroaromatic structures based on the phosphole motif (I; Figure 1) have achieved a considerable degree of maturity and found application, for example, in organic light-emitting diodes (OLEDs); [4] phosphorus analogues of polyphenylvinylenes (II) [5] and oligoacetylenes (III) [6] have also been reported. In all examples depicted in Figure 1, phosphorus inclusion greatly alters the electronic properties of the compounds compared to all-carbon-based analogues, and also offers a number of options for postsynthetic manipulations, such as metal complexations or oxidations. [7] In contrast to the plethora of synthetic procedures that are available for the preparation of pure hydrocarbons, the synthetic arsenal for the construction of I-III is limited. Considering the reliability of the Wittig reactions for the conversion of aldehydes and ketones into alkenes, we were intrigued by the option to use the analogous phospha-Wittig-Horner (pWH) reaction [8][9][10] to prepare P-containing oligoacetylenes from appropriate acetylenic ketones. Whereas traditional phosphonium ylides react with diacetylenic ketones exclusively in a 1,2-addition, which makes Wittigtype reactions a reliable tool for the preparation of 1,1diethynylethenes, [11,12] herein we demonstrate that a pWH reagent 1 exhibits a completely different reactivity. The observed 3,4-addition initiates a cascade of reactions that ultimately leads to the formation of either penta-substituted bis-phospholes or 2,5-dihydro-1,2-oxaphospholes, depending on the substituent at the acetylene termini of the diethynylketone (Scheme 1).As with all Wittig-type reactions, the pWH reaction is also initiated under basic conditions, in this case, by the addition of lithium diisopropylamide (LDA). The Li salt of 1 [9] is added to 1,5-bis(TES)-penta-1,4-diyne-3-one (2 a, TES = SiEt 3 ), [13,14] resulting in a red solution from which a bright red product 3 can be isolated in 57 % yield after silica gel chromatography. Mass spectrometric analysis of the product indicates that no simple pWH reaction occurred, as the observed molecular weight (m/z = 1159.15577, corresponding to C 43 H 60 O 9 P 2 Si 3 W + Ag) suggests that both P units of the pWH reagent are still present in the product and that 1 has reacted with two equivalents of ketone 2 a. Consistently, the 31 P NMR spectrum features two phosphorus centers (d( III P) = 167.4 ppm, d( V P) = 6.8 ppm), which couple to each other with J P-P = 63 Hz. A high degree of unsaturation can be expected from the presence of 11 quaternary c...

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Incorporating Phosphaalkenes into Oligoacetylenes

Cited by 25 publications

References 30 publications

Acetylene‐Expanded Dendralene Segments with Exotopic Phosphaalkene Units

Acetylene‐Expanded Dendralene Segments with Exotopic Phosphaalkene Units

A Convenient Method for the Synthesis of α‐Ethynylphospholes and Modulation of Their π‐Conjugated Systems

Cascade Reactions Forming Highly Substituted, Conjugated Phospholes and 1,2‐Oxaphospholes

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