6130-92-3

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Two phosphorus-containing hydrazines, namely morpholin-4- ylphosphoramidic acid diethyl ester (1a) and (2,2,6,6-tetramethylpiperidin-1- yl)phosphoramidic acid diethyl ester (2a), have been synthesized. The corresponding hydrazyl radicals (1b and 2b) have been obtained, by in situ oxidation, and their properties have been investigated by EPR spectroscopy. The 1b radical shows spectra strongly dependent on temperature due to the inversion of the morpholin ring and to rotation about the N-N bond. Since, in the investigated temperature range, both motions take place in the EPR time scale, a kinetic study of these process could be made by analyzing the spectral lineshape variations. The 2b radical is highly persistent and shows a strong temperature and solvent dependence of the phosphorus splitting. The latter property was usefully exploited to study the guest host interaction of this radical with cyclodextrins. A method is also proposed for the determination of affinity constants for cyclodextrins of nonparamagnetic compounds.

The syntheses, direct spectroscopic observation, and kinetics of thermal decomposition of the persistent 1,1-diazenes, N-(2,2,6,6-tetramethylpiperidyl)nitrene (4) and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (5) are reported.The electronic absorption spectrum of 4 at -78 deg C reveals a structured absorption for the n,?* transition: λmax = 543 nm, λ0,0 = 620 nm, and εmax = 18 +/- 3 in Et2O; λmax = 541 nm and λ0,0 = 610 in CH2Cl2; λmax = 526 nm and λ0,0 = 592 nm in i-PrOH.The electronic absorption spectrum of 1,1-diazene 5 at -78 deg C reveals a structured absorption band for the n,?* transition: λmax = 497 nm and λ0,0 = 572 nm and εmax = 20 +/- 3 in CH2Cl2; λmax = 487 nm and λ0,0 = 552 nm in i-PrOH.The infrared spectrum of 4 shows a strong absorption at 1595 cm-1 (R214N=14N stretch) and provides evidence that 1,1-diazene 4 has considerable N=N double-bond character in the ground state.The infrared spectrum of 5 shows a strong absorption at 1638 cm-1 (R214N=14N stretch).The unimolecular rate of thermal decomposition of 4 is sensitive to solvent, the rate increasing with decreasing solvent polarity (krel = 1.0, 1.7, 4.8 in THF, Et2O, and hexane, respectively).The activation parameters for the unimolecular fragmentation of 1,1-diazene 4 are as follows: log A = 11.6 +/- 0.5 and Ea = 16.9 +/- 0.7 kcal mol-1 in hexane; log A = 13.7 +/- 0.3 and Ea = 20.0 +/- 0.4 kcal mol-1 in Et2O; log A = 13.6 +/- 0.3 and Ea = 20.1 +/- 0.4 kcal mol-1 in THF.The activation parameters for the bimolecular dimerization of 4 are log A = 3.8 +/- 0.7 and Ea = 6.4 +/- 0.9 kcal mol-1 in CDCl3.The unimolecular rate of thermal decomposition of 5 is sensitive to solvent, the rate increasing with decreasing solvent polarity, krel = 1.0, 2.4, and 5.1 for THF, Et2O, and hexane, respectively.The activation parameters for the unimolecular fragmentation of 1,1-diazene 5 are as follows: log A = 10.9 +/- 0.3 and Ea = 16.8 +/- 0.5 kcal mol -1 in hexane; log A = 12.4 +/- 0.4 and Ea = 19.0 +/- 0.6 kcal mol-1 in Et2O; log A = 12.1 +/- 0.3 and Ea = 19.1 +/- 0.4 kcal mol-1 in THF.At -41.1 deg C the bimolecular rate constant for the dimerization of 5 is 8.5 * 10-5 L/(mol s), 90 times slower than that found for 4.The change from a six-membered to five-membered ring 1,1-diazene causes a shift to higher energy for the n,?* transition and a shift to increased wavenumber (cm-1) for the N=N stretching frequency, not unlike that of the isoelectronic ketones, tetramethylcyclohexanone and tetramethylcyclopentanone.Similar Ea values for the unimolecular thermal fragmentation of 4 and 5 may indicate the strain energy difference between 4 and 5 is also small.An approximate value of 30.5 kcal mol-1 for the heat of formation of the 1,1-diazene 5 is estimated, indicating the 1,1-diazene 5 has a higher heat of formation than...

Restricted rotation about the N-N bond in unhindered, non-conjugated hydrazones (e.g.Me2N-N=CH2) has been detected by 13C n.m.r. below -150 degC.The results indicate that the N=C plane is coplanar with the dynamically averaged plane of the sp3 nitrogen, in contrast with hindered hydrazones (containing the 2,2,6,6-tetramethylpipridinyl ring, TMP) where the N=C moiety adopts a perpendicular conformation.Effects due to the slowing of ring reversal were not observed in hydrazones containing the TMP ring, but were detected in other hindered derivatives such as TMP-NH2 and TMP-NO.A most interesting feature becomes apparent in two hydrazones with the 2,6-cis-dimethylpiperidinyl (DMP) ring, DMP-N=CH2 and DMP-N=CHPh.In the same molecule the N=C moiety is coplanar with the averaged sp3 nitrogen plane when the methyls are axial, but perpendicular when the methyls are equatorial.