Synthesis, Structure, Thermal Behavior and cis/trans Isomerization of 2,2′-(EMe3)2 (E = C, Si, Ge, Sn) Substituted Azobenzenes

Abstract

The synthesis of a series of 2,2′-bis(trimethyltetrel) azobenzenes is reported, evaluating the different synthetic approaches that different group 14 element substituents individually require. The synthetic access to the carbon substituted congener is very different from the heavier tetrels, in that the key step is the formation of the N=N bond in azobenzene, rather than the azobenzene-C bond. Sn could be introduced with a cross-coupling route, whereas the Si and Ge congeners were prepared by a stannylation-lithiation-electrophilic quenching sequence. Iodo-lithium exchange was also a possible route to obtain the dilithiated species, which can be attributed to the chelating effect of the nitrogen atoms. However, the organo-lead species could not be obtained via these routes. The resulting structures were fully characterized (NMR, FTIR, HRMS and XRD). Furthermore, their thermal properties (TGA and DSC) and their photoswitching behavior in solution (UV-VIS & NMR experiments) were investigated and compared for the different tetrels (C, Si, Ge, Sn).

Experimental and Theoretical Studies of a Spirostannole and Formation of a Pentaorganostannate

“…The tin–lithium exchange reaction is an efficient and very mild method to generate organolithium compounds that cannot be synthesised by traditional halogen–lithium exchange reactions or only proceed with little conversion [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Because of this, it is of interest to compare the often-used linear organotin reagents with the cyclic stannoles concerning their reactivity with MeLi.…”

Synthesis and crystal structure of (E)-1,2-bis[2-(methylsulfanyl)phenyl]diazene

“…Azobenzenes are common motifs in dyes because of their high thermal and photochemical stability (Yesodha et al, 2004;Lagrasta et al, 1997). We recently presented methods to substitute azobenzenes in the ortho, meta and para-positions with trimethyltin as a novel functionalization method, giving rise to a dual tin-lithium exchange (Strü ben et al, 2014(Strü ben et al, , 2015Hoffmann et al, 2019). In particular, we described the effect on the diortho-substitution on azobenzenes with trimethyl-tetrels and the resulting effects on the switching properties (Hoffmann et al, 2019).…”

“…We recently presented methods to substitute azobenzenes in the ortho, meta and para-positions with trimethyltin as a novel functionalization method, giving rise to a dual tin-lithium exchange (Strü ben et al, 2014(Strü ben et al, , 2015Hoffmann et al, 2019). In particular, we described the effect on the diortho-substitution on azobenzenes with trimethyl-tetrels and the resulting effects on the switching properties (Hoffmann et al, 2019). In this context, we present here a novel diortho-substituted azobenzene, (C 7 H 7 NS) 2 , (I), bearing two methylsulfide groups.…”

“…A search of the Cambridge Structural Database (CSD version 5.4.0; update August 2019; Groom et al, 2016) revealed no azobenzene-based structures that contain methyl thioethers. However, some general ortho-substituted azobenzenes have been deposited (Yamamura et al, 2008;Kano et al, 2001;Hoffmann et al, 2019). Additionally, some diortho-substituted thioazoxybenzenes were reported previously (Szczygelska-Tao et al, 1999;Kertmen et al, 2013).…”

“…The synthesis of 2,2 0 -bis(trimethylstannyl)azobenzene was recently described (Hoffmann et al, 2019). For further details of a similar transmetallation of a stannylated azobenzene, see: Strü ben et al (2015).…”