Synthesis, Electronic Structures, and Electrochemistry of 3‐Triarylphosphoraniminato‐1,3,5‐trithia‐2,4,6,8‐tetrazocines: Detection of Trithiatetrazocinyl Radical Anions

Abstract

Reaction of the bicyclic sulfur‐nitrogen heterocycles RC6H4CN5S3 (R=4‐CH3O, 4‐CH3, 4‐H, 4‐Cl, 4‐CF3, 3‐CF3) with PR’3 (R′=C6H5 or 4‐CH3OC6H4) produces 3‐phosphoraniminato‐7‐aryl‐1,3,5‐trithia‐2,4,6,8‐tetrazocines RC6H4CN4S3NPR’3. In all cases, only the endo‐isomers were isolated and characterized by 1H, 31P, and 19F NMR as well as UV spectroscopy and X‐ray crystallography. RB3LYP/6‐311+G(d,p)// RB3LYP/6‐31G(d,p) computations were undertaken to help explain the atom‐exact syntheses via intermediates previously detected spectroscopically. Three reasonable intermediates have been computed as stationary points with energies consistent with the observed reaction path. Cyclic and square‐wave voltammetry studies of RC6H4CN4S3NPR’3, using a glassy carbon working electrode in CH2Cl2 with 0.4 M [nBu4N][PF6], reveal two IRR reduction processes at RT in all cases at approximately −1.9 and −2.2 V, respectively, and one IRR oxidation process at approximately +1.0 V (versus Fc+/0). [RC6H4CN4S3NPR’3]−. radical anions (R’=4‐CH3OC6H4, R=4‐CH3O, 4‐H, 4‐CF3) were detected at −50 °C in CH2Cl2 by using in situ electrolysis and simultaneous electron paramagnetic resonance spectroscopy: [4‐RC6H4CN4S3NP(4‐CH3OC6H4)3]−., estimated a(31P)=0.078 mT, a(14N1)=0.031 mT, a(14N2,3)=0.256 mT, a(14N4,5)=0.341 mT. The signals decay rapidly, but after the electrolysis is ended, a persistent EPR signal is always obtained with EPR parameters that match known 4‐aryl‐1,2,3,5‐dithiadiazolyls, that is, a(N)=0.51 mT and g=2.0105, which are consistent with the production of [4‐CF3‐C6H4CN2S2]..