Synthesis and reactivity of silylated tetrathiafulvalenes

Abstract

Novel organosilylated tetrathiafulvalenes (TTFs) possessing Si-H or Si-Si bonds have been synthesised. The crystal structures of several derivatives have been determined by X-ray diffraction, including that of dimeric (Si2Me4)(TTF)2 (11) incorporating a diatomic SiMe2-SiMe2 linker. Cyclic voltammetry measurements in all cases show two oxidation waves. DFT calculations were performed to rationalize the absence of an electronic communication between the two TTF moieties of 11 through the disilanyl spacer. The reactivity of the Si-H bond has been exploited to prepare the dinuclear complex [{Ru(CO)4}2{mu-(Me2Si)4TTF}] (14), starting from Ru3(CO)12 and TTF(SiMe2H)4 (1). Treatment of 14 with 2 equiv. of PPh3 or dppm results in selective substitution of a CO ligand trans to a SiMe2 group to afford mer-[{Ru(PPh3)(CO)3}2{mu-(Me2Si)4TTF}] (13) and mer-[{Ru(CO)3}2(eta1-dppm){mu-(Me2Si)4TTF}] (16). Attempts to transform the Si-H bonds of some TTF(SiMe2H)n (n = 1, 2) into Si-O functions using stoichiometric amounts of water in the presence of tris(dibenzylideneacetone)dipalladium(0) were unsuccessful. Quantitative cleavage of the C(TTF)-Si bond was observed instead of formation of TTF-based-siloxanes. Essays of catalytic bis-silylation of phenylacetylene with 11 and TTF(SiMe2-SiMe3) (9) in the presence of Pd(OAc)2/1,1,3,3-tetramethylbutylisocyanide failed. Again, cleavage of the C(TTF)-Si bond was noticed.

Heteroatom Bridged Tetrathiafulvalenes

“…Mono-and disilicon bridges bis(TTFs) 4 and 5 ( Figure 6), prepared by lithiation of TTF precursors followed by quenching of the monolithiated TTF with dichloro-dimethylsilane and dichloro-tetramethyldisilane, respectively, have been reported by Fourmigué et al (4a-b) [36] and Guyon et al (5). [37] Single crystal X-ray structures have been determined for compounds 4a and 5. The TTF units are almost perpendicular to each other in 4a, with a dihedral angle of 77°between the two mean planes, while in 5 they are anti-parallel, the dihedral angle amounting at 180°( Figure 7).…”

“…European Journal of Inorganic Chemistry molecular distance between the two TTF in 4a is 4.19 Å, much larger than the sum of the van der Waals radii of two sulfur atoms. [38,39] While compounds 4a-c show sequential oxidation of the TTF units in radical cation and then dication, [36] the mono-electronic processes being separated by about 100 mV, in the disilicon bridged compound 5 the oxidation of the redox active units arise concomitantly, [37] indicating negligible electron communication between TTFs. In order to explain the difference in the electrochemical behavior of compounds 4a and 5, DFT calculations have been performed.…”

6,6-Dimethyl-2H,5H,6H,7H-1,3-dithiolo[4,5-f][1,5,3]dithiasilepin-2-one

“…For silicon-containing tetrathiafulvalene (TTF) derivatives as ligands, see: Guyon et al (2005), and as precursors for the construction of polymetallic arrays, see: Hameau et al (2008). For their use in the preparation of conducting charge-transfer complexes and radical-cation salts, see: Biaso et al (2007).…”

Bis(tetrathiafulvalenes) with aromatic bridges: electron delocalization in the oxidized species through EPR and theoretical studies

“…Diethyl ether was distilled over sodium and benzophenone and toluene was distilled over sodium. Nuclear magnetic resonance spectra were recorded on a Bruker Avance DRX 500 spectrometer operating at 500.04 MHz for 1 H and 125.75 MHz for 13 C. Chemical shifts are expressed in parts per million (ppm) downfield from external TMS. The following abbreviations are used: s, singlet; d, doublet; t, triplet.…”

“…4 For the bis(TTF) systems, likely able to give rise to mono-and biradical species, spin delocalization and magnetic properties directly depend upon the nature of the bridge between the two TTF moieties. 5 Dimeric TTF systems reported so far in the literature, in which the TTF units are closely connected, include those containing direct linking of TTF units, 6 ethylene bridge as in [(EDT-TTF-CH 2 ) 2 ] (EDT = ethylenedithio), 7 1,1-ethenediyl bridge, 8 acetylene bridge, 9 heteroatom based linkers as in the extensive series formulated as X(TTF) 2 , with X = S or Se, 10 Te, 11 PPh, SiMe 2 or Hg, 12 Me 2 Si-SiMe 2 , 13 and SbMe, 14 or two heteroatomic bridges as in the more rigid derivatives of X 2 (TTF) 2 type, with X = S, 15 Te, 16 PPh, 17 SiMe 2 and GeMe 2 18 (Chart 1). Intramolecular electronic communication between the TTF units has been evidenced in many of these systems, especially by cyclic voltammetry, where splitting of the oxidation waves was observed.…”