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EPR Studies on Branched High‐Spin Arylnitrenes
Author(s) -
Chapyshev Sergei V.,
Korchagin Denis V.,
Budyka Mikhail F.,
Gavrishova Tatia.,
Neuhaus Patrik,
Sander Wolfram
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201200200
Subject(s) - nitrene , electron paramagnetic resonance , chemistry , photodissociation , resonance (particle physics) , relaxation (psychology) , line (geometry) , spectral line , analytical chemistry (journal) , radical , nuclear magnetic resonance , crystallography , molecular physics , atomic physics , photochemistry , physics , geometry , psychology , social psychology , mathematics , organic chemistry , astronomy , catalysis , biochemistry , chromatography
The UV ( λ >305 nm) photolysis of triazide 3 in 2‐methyl‐tetrahydrofuran glass at 7 K selectively produces triplet mononitrene 4 ( g =2.003, D T =0.92 cm −1 , E T =0 cm −1 ), quintet dinitrene 6 ( g =2.003, D Q =0.204 cm −1 , E Q =0.035 cm −1 ), and septet trinitrene 8 ( g =2.003, D S =−0.0904 cm −1 , E S =−0.0102 cm −1 ). After 45 min of irradiation, the major products are dinitrene 6 and trinitrene 8 in a ratio of ∼1:2, respectively. These nitrenes are formed as mixtures of rotational isomers each of which has slightly different magnetic parameters D and E . The best agreement between the line‐shape spectral simulations and the experimental electron paramagnetic resonance (EPR) spectrum is obtained with the line‐broadening parameters Γ ( E Q )=180 MHz for dinitrene 6 and Γ ( E S )=330 MHz for trinitrene 8 . According to these line‐broadening parameters, the variations of the angles Θ in rotational isomers of 6 and 8 are expected to be about ±1 and ±3°, respectively. Theoretical estimations of the magnetic parameters obtained from PBE/DZ(COSMO)//UB3LYP/6‐311+G(d,p) calculations overestimate the E and D values by 1 and 8 %, respectively. Despite the large distances between the nitrene units and the extended π systems, the zero field splitting (zfs) parameters D are found to be close to those in quintet dinitrenes and septet trinitrenes, where the nitrene centers are attached to the same aryl ring. The large D values of branched septet nitrenes are due to strong negative one‐center spin–spin interactions in combination with weak positive two‐center spin–spin interactions, as predicted by theoretical considerations.