¹³C and ¹⁵N NMR shieldings of 1,2,4‐diazaphospholes in the solid state and in solution

Abstract

The solid state13C and15N CPMAS NMR spectra of 3,5-di-tert-butyl-1,2,4-diazaphosphole4and 3,5-diphenyl-1,2,4-diazaphosphole5have been recorded. The X-ray structure of the first compound was already known (it is a cyclic dimer with localized N–H protons) while the structure of the second cannot be determined due to the difficulty to grow suitable single crystals. NMR results pointed out that4is a “classical” compound while5is probably a tetramer showing Intermolecular Solid-State Proton Transfer (ISSPT). GIAO/ab initio calculations have been carried out to estimate the absolute1H,13C and15N shieldings. The agreement with the experimental chemical shifts is good enough to assign the signals of carbons C-3 and C-5.

Synthesis and Characterization of η5-1,2,4-Diazaphospholide Complexes of Ruthenium

“…The 31 P{ 1 H} NMR resonance (C 6 D 6 , 23 °C) is observed at −61.89 ppm, which is drastically shifted upfield relative to the corresponding signals of the free heterocyclic ligand H[3,5- t Bu 2 dp] ( 31 P δ +65.4 ppm) and the potassium salt 1 ( 31 P δ +50.65 ppm). , The observed significant upfield shift resonance upon ligation of the anion to transition metals in the 31 P{ 1 H} NMR spectrum is generally diagnostic for the π-bonding of metals to a phosphorus atom. , The 13 C{ 1 H} NMR spectrum (C 6 D 6 , 23 °C) displays resonances at δ 31.75 (s), 34.823 (d, 2 J CP = 30.0 Hz, C CH 3 ), and 148.280 (d, 1 J CP = 273.0 Hz, P C N) for the 1,2,4-diazaphospholide ligand of complex 3 . At δ 31.75, however, the coupling constant ( 3 J CP (Me)) is too small to be observed (the 3 J CP (Me) coupling constant (26.8 Hz) is observed for 1 ). , Surprisingly, a coupled resonance at δ 89.06 (d, J CP = 26.0 Hz) for the carbon atoms of the pentamethylcyclopentadienyl ring is observed in complex 3 , presumably due to the closer distance between the interacting nuclei. The resonance at δ −58.55 in the 31 P{ 1 H} NMR spectrum (C 6 D 6 , 23 °C) strongly supports the π-bonding of ruthenium to the 1,2,4-diazaphospholide in complex 4 (vs 31 P δ +67.19 ppm for 2 )…”

1,3‐Dipolarophile Character of an Extremely Bulky Phosphaalkyne Mes*C≡P (Mes* = 2,4,6‐tBu3C6H2) Leading to the Formation of 1,2,4‐Diazaphospholes with Unique Hydrogen Bonding Properties

“…Actually, the total energy of theoretically optimized structures for model compounds 8x , 9x , and 9xx suggested facile conversion from 8 to 9 as well as the migratory aptitude of the silyl group (Figure 3). 15–17 In the 13 C NMR spectroscopic data of 9 , the H‐substituted carbon atom C(sp 2 )‐3 has a slightly smaller 1 J PC constant ( 1 J PC = 53.7 Hz, C H) than the C‐5 ( 1 J PC = 59.7 Hz, C Mes*), which might represent a 5‐substituted 1 H ‐1,2,4‐diazaphosphole 18–20. The exclusive formation of 9 without a 1,2,3‐diazaphosphole isomer indicates that regioselective [2+3] cycloaddition of 1 with the CN 2 moiety proceeds under kinetic control by the bulky Mes* group21 followed by subsequent silyl group migration13,14,16 to gain higher aromatic stabilization.…”