Synthesis and Characterization of a Triphenyl‐Substituted Radical and an Unprecedented Formation of a Carbene‐Functionalized Quinodimethane

Abstract

The trichlorosilylcarbene monoradical (Cy-cAAC ·)SiCl3 (1) was directly converted to (Cy-cAAC ·)SiPh3 (2) by substitution of the three chlorine atoms with phenyl groups without affecting the radical center adjacent to the silicon atom. In addition to the structure determination, compound 2 was studied by EPR spectroscopy and DFT calculations. The three hyperfine lines in the EPR spectrum of 2 are due to the coupling with (14)N nucleus. Functionalized 1,4-quinodimethane Me2-cAAC=C6H4=CPh2 (7) was isolated, whereas carbon analogue of radical 2 was targeted. Cyclic voltammogram of 7 indicated that a stable radical-anion 7 ·-, as well as a radical-cation 7 ·+, can be prepared. Theoretical calculations showed that one-electron ionization energy and electron affinity of 7 are 5.1 and 0.7 eV mol(-1), respectively.

Isolable Anionic, Neutral and Cationic Radicals from Reactions ofN,N′‐Dimesityldiamidocarbene and Lewis Acids

“…The formation of 9 stands in contrast to the neutral quinoidal‐derivative derived from the reaction of a cyclic alkyl amino carbene (CAAC) with trityl cation . Presumably the stronger pi‐accepting ability of DAC leads to loss of H .…”

NHCs in Main Group Chemistry

“…Formation of the stable quinodimethane 478 in the reaction of Me2 CAAC with tritylium salts was reported by Roesky and co-workers (Scheme 80). 525 Synthesis and investigation of the stable bis(cumulene)-p-quinoid system 479, obtained by reduction of the respective bis(2-acetylenylimidazoulium) salt, has been reported recently by Boere, Clyburne, Masuda, and colleagues. 526 Synthetic approaches to the related openshell systems and systems with radicaloid character are discussed in the following section.…”

“…The reaction of the trichlorosilylcarbene radical 654b with phenyllithium furnishes the red carbon-centered radical 656 via chloride substitution in 90% yield (Scheme ). The tetra-coordinate silicon nucleus adopts a distorted tetrahedral geometry similar to that observed in the precursor. The triphenylsilylcarbene radical 656 exhibits three hyperfine lines, in contrast to the 15 for 654 , in the X-band EPR spectrum at g = 2.0019, due to the coupling with one 14 N nucleus.…”

Stable cyclic (alkyl)(amino)carbene (cAAC) radicals with main group substituents

“…The trichlorosilylcarbene radical ( 45a ) was directly converted to ( cy cAAC˙)SiPh 3 ( 46 ; Fig. 12) in 90% yield by substitution of the three chlorine atoms with phenyl groups using PhLi without affecting the radical center adjacent to the silicon atom 32. The X-band EPR spectrum of 46 exhibits three hyperfine lines due to coupling with one nitrogen nucleus ( a ( 14 N) = 5.4 G).…”