2,3-Dialkynyl-1,4-diazabuta-1,3-dienes as Novel π-Systems: Synthesis, Structure, and Electronic Properties

Abstract

The introduction of alkynyl groups into the 2,3‐positions of the 1,4‐diazabuta‐1,3‐diene (DAD) backbone succeeds along two complementary synthetic routes either by condensing triisopropylsilyl‐terminated dialkynyl‐1,2‐diones with primary aromatic amines or by a palladium‐mediated alkynylation of bis(imidoyl chlorides). X‐ray crystallographic analyses of two dialkynyl DAD derivatives reveals their planar (E‐s‐trans‐E) conformations in the solid state. However, the central CC bond of both DAD backbones investigated has a length of 1.491(2) Å, and is therefore too long to indicate efficient delocalization across the DAD core. The UV/Vis spectra of dialkynyl DADs demonstrate that their absorptions in comparison to those of non‐alkynyl DADs are bathochromically shifted by more than 40 nm, thereby demonstrating the suitability of the title compounds for developing NIR chromophores. The electron absorption properties of differentially N,N′‐disubstituted dialkynyl DADs gave no indication for a push‐pull effect across the DAD skeleton and suggest the ynimine moiety as the active chromophore of dialkynyl DADs. The electrochemical properties of the title compounds were determined by cyclo‐ and steady state voltammetry and show that introducing alkynyl groups leads to more easily reducible DAD systems. Again, the perception of dialkynyl DADs as covalently linked, but electronically decoupled ynimine units is corroborated by the redox potential of a differentially N,N′‐disubstituted dialkynyl DAD. Similar conclusions were drawn from semiempirical MO (PM3) calculations of dialkynyl DADs.

Oligomeric and Polymeric Systems with a Cross-conjugated π-Framework

“…16 Compounds based on 2,3-diethynyl-1,3-butadienes 11-13 are much less common, with or without pendent substitution. [17][18][19][20] Hybrids such as 14 have been reported, 21 as have heteroatom derivatives such as the vicinal diimine derivatives 15 and 16 22 and the dicyano substituted 17. 19 The formation of a 2,3-diethynyl-1,3-butadiene via the Pdcatalyzed dimerization of a cumulene was explored by Suzuki et al, giving a potentially interesting building block 18 for cross-conjugated oligomers and polymers via desilylation and elaboration (Scheme 4).…”

The Modular Approach to Acetylenic Phthalocyanines and Phthalocyanine Analogues

“…With the acetylenic diones 5 in hand, their synthetic potential for the construction of various N ‐heterocycles34 and the vicinal diimines 7 31,35,36 was readily explored. In the context of the preparation of acetylenic phthalocyanine analogues, we were particularly interested in the conversion of 5 into the 3,4‐dimethylene‐hexa‐1,5‐diynes 6 .…”

“…Key compounds in this design are the hexa‐1,5‐diyne‐3,4‐diones 5 29 (Figure 3). These vicinal diones not only provide the basis for the synthesis of related building blocks such as the dialkynylbuta‐1,3‐dienes 6 30 and the vicinal diimines 7 ,31 but also function as suitable starting materials for the preparation of azamacrocycles with phthalocyanine cores.…”

A diaryl-terminated hexa-1,5-diyne-3,4-dione

“…The second question concerns the effective conjugation path of the hexa-1,5-diyne-3,4-dione framework. We have speculated that, similar to the related 2,3-dialkynyl-1,4diazabutadienes (Faust, Go È belt, Weber et al, 1999), a valid description of dialkynyldiones is that of two interconnected but largely electronically independent bis(ynone) units, rather than that of a species fully delocalized along the hexadiynedione core. The present solid-state study is the ®rst on this class of compounds and was undertaken to shed some light on these matters.…”

“…The title compound, (I), is a newly synthesized member of the diacetylenic 1,2-diones, a class of compounds ®rst introduced in 1996 (Faust & Weber, 1996;Faust et al, 1997). The two typifying interconnected ynone moieties of this molecular structure give rise to a rich chemistry which we have explored to form, inter alia, metal-chelating diazabutadienes (Faust, Go È belt & Weber, 1999;Faust, Go È belt, Weber et al, 1999), alkyne-substituted nitrogen-heterocyclic carbenes (Faust & Go È belt, 2000) and acetylenic phthalocyanines (Faust, 2001). Despite these successful developments, two questions remain about the electronic aspects of these compounds.…”