Russian Journal of General Chemistry, Vol. 71, No. 11, 2001, pp. 1819 1820. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 11, 2001,
pp. 1924 1925.
Original Russian Text Copyright
2001 by Kolodyazhnyi, Andrushko.
LETTERS
TO THE EDITOR
Phosphorus Nitrogen Diad Prototropic Tautomerism
of Phosphonous Bis(1-methylbenzylamides)
O. I. Kolodyazhnyi and N. V. Andrushko
Institute of Bioorganic and Petroleum Chemistry, National Academy of Sciences of Ukraine, Kiev, Ukraine
Received November 4, 2000
In the previous paper we reported that phosphorous
tris(alkylamides) exist as PH-iminophosphoranes [1].
Proceeding with these studies, we found that phospho-
nous bis[(S)-1-methylbenzylamides] Ia Id also exist
in a tautomeric equilibrium with aminoiminophos-
phoranes IIa IId. Considering the important theoret-
ical value of the diad prototropic equilibria, we have
studied the tautomerism of compounds Ia Id.
shift of phosphine form
PH-iminophosphorane form
(ppm), chemical shift of
P
1
(ppm), JPH (Hz), ratio
P
of tautomeric forms PIII/PIV]: Ia, Ph, CDCl3, 60.04,
13.63, 534, 37 : 63; Ib, 4-Me2NC6H4, CDCl3, 61.39,
14.67, 526, 47 : 53; Ic, 4-FC6H4, CDCl3, 60.11, 12.15,
538, 62 : 38; Id, t-Bu, C6D6, 88.65, 7.27, 596, 95 : 5.
The ratio of the signals characterizing the ratio
of tautomeric forms depends on the nature of substit-
uents and solvent. Electron-donating substituents in
the p-position of the benzene ring 4-RC6H4P(NHR )2,
R = Me2N > H > F, decrease the acidity of the PH
H
N R
B
RPCl2 + H2NR
R P
N R
H
Ia Id
form and shift the prototropic equilibrium I
II to
the right. The ratio of tautomeric forms of Ia depends
on the solvent as follows: 37 : 63 (CDCl3), 40 : 60
(CD2Cl2), 42 : 58 (C6D6), and 56 : 44 (diethyl ether).
That is, the content of the PH form increases in the
series of solvents chloroform > methylene chloride >
benzene > ether.
H
P
R
H
R
S
N R
N R
N R
N R
S8
P
Evidently, the position of the equilibrium of the
diad phosphorus nitrogen prototropism depends on
the relative acidity of the PH and NH forms, shifting
to the side of the form with the less mobile proton.
H
H
IIa IId
IIIa IIIc
B = H2NR or Et3N; R = Alk, Ar; R = (S)-CH(Me)Ph.
Compounds I were prepared by the reactions of
alkyl- and aryldichlorophosphines with (S)-1-methyl-
benzylamine. The structure of compounds I and the
position of the tautomeric equilibrium were studied
by NMR spectroscopy. In the 31P NMR spectra of
Ia Ic we observed a downfield triplet with 3JPH 18 Hz
(PNH coupling) belonging to the phosphine form
and a doublet of doublets with a very large coup-
ling constant 1JPH 555 Hz, belonging to the PH-imino-
phosphorane form. In the 31P {1H} spectra it trans-
forms into a singlet, which confirms the existence of
Compounds Ia Ic add sulfur to form the corre-
sponding phosphine sulfides IIIa IIIc, which con-
firms their structure.
Phenylphosphonothioic bis(1-methylbenzyl-
amide) IIIa. A solution of chlorophosphine (0.1 mol)
in 10 ml of ether was added dropwise with stirring
to a solution of ( )-(S)-methylbenzylamine (0.2 mol)
and triethylamine (0.2 mol) in 25 ml of ether, cooled
to 70 C. The mixture was warmed up to room tem-
perature and stirred for 2 h. Triethylamine hydrochlo-
ride was filtered off, and the solvent was evaporated.
The residue was phenylphosphonous bis(1-methyl-
benzylamide) Ia, a viscous oil, yield 95%. Com-
pound Ia was dissolved in benzene, mixed with equi-
molar amount of finely ground sulfur, and left over-
1
the PH bond. The H NMR spectra contain a doublet
1
with the same constant JPH.
The tautomerism of Ia Id is characterized by the
following data [compound no., R, solvent, chemical
1070-3632/01/7111-1819$25.00 2001 MAIK Nauka/Interperiodica
Kolodyazhnyi, O. I.
