Reversible Redox Chemistry of Anionic Imidazole-2-thione-Fused 1,4-Dihydro-1,4-diphosphinines

Abstract

Anionic 1,4-dihydro-1,4-diphosphinines were synthesized from tricyclic 1,4-diphosphinines and isolated as blue powdery salts M[ 2a – 2c ]. Reaction of solutions of these monoanions with iodomethane led to P -methylated compounds 3a – 3c . An oxidation/reduction cycle was examined, starting from solutions of K[ 2a ] via P–P coupled product 4a and back to K[ 2a ], and the recyclability and redox chemistry of this cycle were confirmed by experimental and simulated cyclic voltammetry analysis, which is proposed as a potential 2-electron cathode for rechargeable cells. TD-DFT studies were used to examine species that might be involved in the process.

P-Centred redox reactions of a 1,4-dihydro-1,4-phosphasiline

“…S28†), obtained from X-ray diffraction studies, shows the two rings in an antarafacial conformation at the P–P bond. This is in contrast to the twisted conformations occurring in the structures of related tricyclic 1,4-diphosphinine derivatives V and VI , 2,4 most possibly reflecting the steric effects of the additional alkyl chains at the Si-bound N centres.…”

“…The peak separations between the two processes is 3.17 V for 5b (compared to 2.81 V for V ). 4 The deviations in the peak separations for both the P,P-system and P,Si-system are similar (0.28 V for the P,P-system; 0.36 V for the P,Si-system). This signifies that the extent to which the peak potentials shift in the anion-dimer redox process is similar regardless of the heteroatomic system.…”

“…1, R = SiMe 3 ) reported previously by us, along with a detailed mechanistic study of voltammetry that was supported by digital simulation. 4 All evidence points to a very similar mechanism being operative for the K[ 4b ]/ 5b interconversion. An EC/EEC sequence, i.e.…”

“…Based on our previous studies on redox reactions of anionic 1,4-dihydro-1,4-diphosphinines III and IV , 2,4 we treated a freshly prepared Et 2 O solution of K[ 4b ] with an Et 2 O solution of I 2 dropwise at −80 °C. The formation of a pale greenish-yellow solution was observed containing product 5b having a P–P bond (Scheme 4).…”

“…The chemical reversibility of the redox processes relating III to V (and IV to VI ) was also confirmed by voltammetry, and is phosphorus-centred, in stark contrast to known λ 3 - to λ 5 -phosphinine conversions. 4 The synthesis and isolation of sila-aromatic compounds such as silabenzenes 5 and -naphthalenes 6 was finally enabled by the use of bulky Si-substituents through the suppression of oligomerization, whereas earlier attempts failed due to the weaker π-bonding within sila-aromatics. 7 In the same vein, disila-aromatic systems remained inaccessible until bulky substituents such as Si– i Pr[CH(SiMe 3 ) 2 ] 2 , 7 Bbt (Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl) 8 or Tbb (Tbb = 2,6-bis[bis(tri-methylsilyl)methyl]-4-[tris(methyl)-methyl]phenyl) 9 were used.…”