Formazanate Complexes of Hypervalent Group 14 Elements as Precursors to Electronically Stabilized Radicals

The stability of molecular radicals containing main‐group elements usually hinges on the presence of bulky substituents that shield the reactive radical center. We describe a family of Group 14 formazanate complexes whose chemical reduction allows access to radicals that are stabilized instead by ge...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2018-07, Vol.57 (31), p.9870-9874
Main Authors: Maar, Ryan R., Catingan, Sara D., Staroverov, Viktor N., Gilroy, Joe B.
Format: Article
Language:English
Subjects:
Anions
Chemical reduction
Electrons
formazanate ligands
Germanium
group 14 heterocycles
Ligands
main-group elements
Molecular chains
Organic chemistry
Radicals
redox chemistry
Silicon
Tin
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Summary:The stability of molecular radicals containing main‐group elements usually hinges on the presence of bulky substituents that shield the reactive radical center. We describe a family of Group 14 formazanate complexes whose chemical reduction allows access to radicals that are stabilized instead by geometric and electron‐delocalization effects, specifically by the square‐pyramidal coordination geometry adopted by the Group 14 atom (Si, Ge, Sn) within the framework of the heteroatom‐rich formazanate ligands. The reduction potentials of the Si, Ge, and Sn complexes as determined by cyclic voltammetry become more negative in that order. Examination of the solid‐state structures of these complexes suggested that their electron‐accepting ability decreases with increasing size of the Group 14 atom because a larger central atom increases the nonplanarity of the ligand‐based conjugated π‐electron system of the complex. The experimental findings were supported by density‐functional calculations on the parent complexes and the corresponding radical anions. Chemical reduction of formazanate complexes of hypervalent Group 14 elements results in stable radical anions containing Si and Ge. These radicals are stabilized not by bulky substituents but rather through electron delocalization over the formazanate ligand, which is enabled by an unusual square‐pyramidal coordination geometry of the Group 14 atom in the parent complexes.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201806097