Drawbacks Arising from the High Steric Congestion in the Synthesis of New Dendritic Polyalkylaromatic Polyradicals

Abstract

The synthesis of the highly strained tris(R,R-bis(pentachlorophenyl)-2,4,5,6-tetrachlorotolyl)methane (8), which is the precursor of the first generation of the polyradical series III, has been achieved by exhaustive chlorination of compound 11. Stepwise divergent synthesis, by successive FriedelCrafts reactions, of the precursors of dendritic series II and III was not possible since the limit generation was reached in the earlier synthetic steps due to high steric congestion. Several polyradical mixtures derived from 8 have also been prepared, being stable under ambient conditions. The formation, electrochemistry, and magnetic properties of these polyradical species are discussed. The steric hindrance of highly chlorinated hydrocarbon 8 prevents the formation of tetraradical 15.

Valence Tautomerism: New Challenges for Electroactive Ligands

“…This allows the corresponding anions and cations to be obtained, either chemically or electrochemically, both in solution and in solid state, which also show considerable stabilities in accordance with the steric shielding of their central carbon atoms. Such persistence as well as the particular structural and conformational characteristics of radicals of this family, has enabled them to be functionalized in order to build pure organic open-shell dendrimers with high-spin ground states [70] and pure-organic mixedvalence molecular wires exhibiting intramolecular electrontransfer phenomena. [71] More recently, Veciana et al have described the use of perchlorotriphenylmethyl radicals, properly functionalized with carboxylic groups, to obtain complexes combining paramagnetic metal ions and pure organic radicals as ligating sites.…”

Magneto-structural defects on a congested nanoscopic polyradical dendrimer

“…However, the numerous experimental problems found along the synthesis of the pentadecaradical and its hydrocarbon precursor, seems to indicate we are reaching the limit generation for this series [7]. Recently we have faced the preparation and characterization of polyradical compounds belonging to series II [8]. Here we present the preparation and magnetic characterization of tetraradical 1, which belongs to the first generation of series II.…”

Sulfur monochloride in organic synthesis

“…Although the yields are moderate, it is worth noting that, respectively, 13 and 30 chlorine atoms are introduced at a time into a molecule. 8,9 Scheme 2…”