Phosphazene vs.diazaphospholene PN-bond cleavage in spirocyclic cyclodiphosphazenes

Abstract

Thermolysis of 2-azido-1,3,2-diazaphospholenes offers access to novel and rare spirocyclic cyclodiphosphazenes. The spectroscopic data and X-ray structure of one representative of the 2-azido-1,3,2-diazaphospholenes reveals an ionic bonding situation explaining sufficiently its rather high thermal stability. The cyclodiphosphazenes were characterised by NMR, mass spectrometry, and X-ray diffractometry. The results of ESI-FT-ICR studies demonstrate the potential of these compounds to undergo reductive elimination at a phosphazene unit via [1,4]-cycloreversion of a lambda5-diazaphospholene ring, as well as symmetrical cleavage of the P2N2-unit. The unexpected inclusion of benzene in the crystal of one of the cyclodiphosphazenes was interpreted in terms of molecular recognition. Chemical reaction studies comprise the proof of double N-protonation at a phosphazene ring, and hydrolytic degradation via selective cleavage of a phosphazene P-N bond.

Recent Developments in the Chemistry of N-Heterocyclic Phosphines

“…1,3,2-Diazaphospholes, NHP, and 1,3,2-diazaphospholenium cations were also reported to react with a -diimines or a -diketones via [1 + 4] cycloaddition to give appropriate spirocyclic phosphorane derivatives [27,37,38,72,80] . Thermolysis of P-azido-NHPs was reported to proceed via cleavage of dinitrogen to produce rather stable cyclodiphosphazenes which were further found to be capable of undergoing mono-or diprotonation at the imino-nitrogen atoms [83] . ESI-FT-ICR mass spectrometry reveals that the cations upon collision induced activation undergo interesting fragmentation processes leading to cleavage of either four-or five-membered rings that are presumably best described as [2 + 2] or [1 + 4] retro-cycloadditions.…”

Synthesis of Unique Phosphazane Macrocycles via Steric Activation of C–N Bonds

“…Hence, in all the above cases, larger macrocycles are anticipated as the sole product obtained (Scheme , method A). While species containing NH bridges within the P 2 N 2 ring have been previously described, they are rare and require the presence of tetracoordinate phosphorus atoms. − Unfortunately, attempts to synthesize species of the type [(μ-N t Bu)­(μ-NH)­(PNH 2 ) 2 ] or [(μ-N t Bu)­(μ-NH)­(PCl) 2 ] were unsuccessful.…”

Crystal structure of 2-azido-1,3-bis(2,6-diisopropylphenyl)-1,3,2-diazaphospholidine

“…A search of the Cambridge Structural Database (Groom et al, 2016) indicated that no other 2-azido-1,3,2-(diarylamino)phospholidine derivatives have been structurally characterized. Some structurally similar compounds were identified, however, namely 2-azido-1,3-bis(2,6-diisopropyllphenyl)-1,3,2-diazaphospholene (CSD refcode CILBAC; Gediga et al, 2014) and its corresponding 2,6-dimethylphenyl derivative (GOFHAL; Burck et al, 2008). Acyclic derivatives featuring bis(diisopropylamino) (PIJZAJ; Englert et al, 1993) and bis(dicylohexylamino) (ZABCEK; Cowley et al, 1995) ligands are known, and also 1-azido-N,N 0 -bis(2,4,6-tri-tert-butylphenyl)phosphinediamine (YABVUV; Nieger et al, 2016).…”