Synthesis and electrochemical properties of 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles and tricyanoacrylates

Abstract

The reaction of phenylacetylenes 4a-h with copper(1) acetate (5) and TCNE (tetracyanoethylene) in THFIacetonitrile gave 4-phenyl-l-buten-3-yne-l,1,2-tricarbonitriles 6a-h. 4i did not react to give 6i. The phenylacetylenes 4b-i were prepared by a two-step synthesis starting from the corresponding phenyl halides lb-i. The tricyanoacrylates 8 were synthesized from the corresponding cyanoacetates ?, TCNE and catalytic amounts of pyridine in THE -Cyclovoltammetric investigations showed that the butenynes 6 and the tricyanoacrylates 8 are strong electron acceptors which can be easily reduced. The radical anions 6'-are unstable in acetonitrile and react irreversibly with 6 to give oligomeric anions 6;-. Only 4-(2,4,6-trimethoxyphenyl)-1 -buten-3-yne-1,1,2-tricarbonitrile (6h) is reduced to a radical anion 6h'-which associates with 6h in a reversible follow-up process to form a dimeric anion 6h;-. By contrast, the tricyanoacrylates 8 can be reversibly reduced to their respective radical anions and dianions.In the last three decades various theories of organic ferromagnets were proposed [']. Compounds with unpaired electrons like stable organic radicals or radical ions are always required. In recent years organic materials with ferromagnetic properties at low temperatures could be synthesized. These materials are ionic charge-transfer complexes (CT complexes) prepared from strong electron donors (D) and strong electron acceptors (A); Miller et a1.t21 synthesized an organometallic CT complex decamethylferrocene (D) and TCNE (tetracyanoethylene) (A) with a Curie temperature T, = 4.8 K. Wudl et al.L3] published in 1991 the first purely organic ferromagnet, a CT complex containing tetrakis(dimethy1amino)ethene (D) and f~l1erene-C~~ (A) with T, = 16.1 K.In our approach to ferromagnetic CT complexes we investigated the synthesis of new organic donors and acceptors as well as their electrochemical behaviour which gave information about redox potentials and stabilities of the corresponding radical ions.In this paper we describe the synthesis and the electrochemical properties of 4-phenyl-1 -buten-3-yne-1,1,2-tricarbonitriles 6 with functional groups at the phenyl ring and tricyanoacrylates 8. These compounds derive from TCNE by replacement of a cyano group by a phenylacetylene or an ester moiety. They are still unknown, except 6a which is described by Ukhin et al.t4] and by Hopf et al.L5], and methyl tricyanoacrylate which has been published by Hall et al.r61. We investigated butenynes 6 and tricyanoacrylates 8 because we expected them to be strong electron acceptors which possibly could form stable radical anions. Synthesis of Phenylacetylenes 4 and Butenynes 6The catalytic condensation of phenyl halides with protected acetylenes gives, after removal of the protecting group, the corresponding phenylacetylene~[~-~]. We found that these reactions are suitable for the preparation of phenylacetylenes 4b-i. The protected acetylenes used were 2-methyl-3-butyn-2-01 (Scheme 1) and 2-propyn-1-01 (Scheme 2). During the condensations under...

Donor‐Substituted Cyanoethynylethenes: π‐Conjugation and Band‐Gap Tuning in Strong Charge‐Transfer Chromophores

“…Synthesis of donor-substituted CEEs: In contrast to the high reactivity of CEE 8, the DMA donor-substituted tricyanoethynylethene 19, prepared according to Dulog et al [11] by reacting TNCE with the copper(i) acetylide formed from N,N-dimethyl-4-ethynylaniline (Scheme 1), features high stability. Solutions of 19 are bright blue, and the shiny metallic solid can be sublimed undecomposed at 100 8C/0.1 mbar.…”

“…Dulog et al reported the synthesis of several aryl-substituted tricyanomonoethynylethenes [11] from TCNE and copper(i) arylacetylides, prepared from the corresponding acetylenes with CuOAc. The yield of this nucleophilic additionelimination reaction increased with increasing electron-donating character of the aryl ring.…”

“…[11] CEEs combine the scaffolding capacity of TEEs with the electron-accepting properties of TCNE, thereby providing a versatile class of modular building blocks for the construction of novel conjugated p-systems. In addition, introduction of electron donors should result in the formation of strong intramolecular charge-transfer (CT) chromophores.…”

Conjugation and optoelectronic properties of acetylenic scaffolds and charge-transfer chromophores

“…The first class of potent electron acceptors, which we developed, are the cyanoethynylethenes (CEEs), of which only two derivatives had been reported previously [71,72]. CEEs are hybrid derivatives combining the synthetic versatility of TEEs for the construction of π-conjugated scaffolds with the [73]; all potentials in this review are measured under these conditions using cyclic voltammetry (CV) or rotating disc voltammetry (RDV)] (Fig.…”

Advanced opto-electronics materials by fullerene and acetylene scaffolding

“…However, it does not contain vectors for functionalization and incorporation into larger molecular frameworks. This led us to develop a class of TEE-TCNE hybrids, the CEEs of which only two derivatives had been previously reported [46,47].…”