Experimental and theoretical investigation of intramolecular transformations of silicon-containing (haloalkyl)phosphorylated ureas and acylamides

Article abstract of DOI:10.1134/S1070363206030078

Silicon-containing chloromethylphosphorylated ureas undergo transformation involving evolution of chlorotrimethylsilane and formation of 1,3,4-oxazaphospholes. Their analogs, silicon-containing phosphorylated acylamides, transform in another way, viz. by

Full text of DOI:10.1134/S1070363206030078

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 3, pp. 376 380.
Original Russian Text M.A. Pudovik, G.A. Chmutova, L.K. Kibardina, S.A. Terent’eva, R.Kh. Bagautdinova, N.A. Khailova, R.M. Kamalov,
A.N. Pudovik, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 3, pp. 396 400.
Pleiades Publishing, Inc., 2006.
Dedicated to the 90th Anniversary of Corresponding Member
of the Russian Academy of Sciences A.N. Pudovik
Experimental and Theoretical Investigation
of Intramolecular Transformations of Silicon-containing
(Haloalkyl)phosphorylated Ureas and Acylamides
M. A. Pudovik, G. A. Chmutova, L. K. Kibardina, S. A. Terent’eva,
R. Kh. Bagautdinova, N. A. Khailova, R. M. Kamalov, and A. N. Pudovik
Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center,
Russian Academy of Sciences, ul. Arbuzova 8, Kazan, Tatarstan, 420088 Russia
Received December 20, 2004
Abstract Silicon-containing chloromethylphosphorylated ureas undergo transformation involving evolution
of chlorotrimethylsilane and formation of 1,3,4-oxazaphospholes. Their analogs, silicon-containing phos-
phorylated acylamides, transform in another way, viz. by -cleavage to form the corresponding siloxyphos-
phonates. Quantum-chemical investigation of thermodynamic characteristics of these processes was carried
out.
DOI: 10.1134/S1070363206030078
We previously showed that phenyl (chloromethyl)-
phosphonoisocyanatidate (I) easily takes up dialkyl-
amines to give chloromethylphosphorylated ureas II.
In the presence of equimolar amount of a base (pri-
mary, secondary, or tertiary amine), the latter undergo
cyclization leading to 1,3,4-oxazaphospholes III. The
role of the base is to form initially an H-complex
including the amine molecule and the proton of the
secondary amido group, which is accompanied by
weakening or cleavage of the N H bond. The sub-
sequent nucleophilic attack of the carbonyl oxygen
atom on the chloromethyl carbon atom leads to separa-
tion of amine hydrochloride and formation of oxaza-
phosphole III [1].
NEt3
H
N
O
O
N
PhO P
PhOPNCO + Et2NH Et N
PhOP
C NEt2
O
3
C NEt2
O
Et3N HCl
Cl CH2
II
CH2Cl
I
III
We suggested an that analogous synthetic result can
be obtained by cyclization of silicon-containing phos-
phorylated ureas. This approach seemed preferred,
since it excluded the necessity of using solvents and
amines and involved no filtration and solvent removal
stages. To verify this suggestion, we studied the
reaction of isocyanate I with diethyl(trimethylsilyl)-
amine.
SiMe3
N
O
I + Me3SiNEt2
C NEt2
PhO P
III
Me3SiCl
Cl CH2
IV
O
376

EXPERIMENTAL AND THEORETICAL INVESTIGATION
377
Actually, heating of equimolar amounts of iso-
cyanate I and silylamine is accompanied by evolution
of chlorotrimethylsilane and formation of 1,3,4-oxaza-
phosphole III. Its physicochemical characteristic are
identical to those of the previously obtained sample.
The reaction involves initial addition of silylamine by
the isocyanato group with intermediate formation of
phosphorylated silicon-containing urea IV. The sub-
sequent nucleophilic substitution by the halomethyl
carbon atom results in formation of final product III
and evolution of chlorotrimethylsilane.
synthetic approach to substituted oxazaphospholes can
be extended to obtain silicon-containing (haloalkyl)-
phosphorylated acylamides. We planned to synthesize
the latter via reaction of (halomethyl)phosphonochlo-
ridates Va Vc with N,O-bis(trimethylsilyl)acetamide
(VI). The subsequent cyclization of acylamidophos-
phonate VIII by the mentioned scheme was expected
to give C-alkyl-substituted phosphole IX. But it
occurred that the reaction involve liberation of aceto-
nitrile along with chlorotrimethylsilane and yields
trimethylsilyl (halomethyl)phosphonates XIa and
XIb.
It was reasonable to suggest that the developed
SiMe3
O
O
2
N
O
C Me
PhO P
Cl CH2
VIII
N
RO P
Me3SiHlg
Me3SiCl
MeCN(SiMe3)2
O
C Me
O
O
VI
HlgCH2
RO
IX
PCl +
OSiMe3
O
O
P
HlgCH2
MeC=NSiMe3
N
HlgCH2
RO
1
^
POSiMe3
C Me
VII
MeCN
RO
XIa XIc
V, X, XI, Hlg = Cl, R = Ph (a), Et (c); Hlg = Br, R = Ph (b).
Me3SiHlg
Me3SiO
Xa Xc
It follows from published data that disilylated acyl-
amides VI undergo reversible 1,3-N O trimethylsilyl
migration and thus can exist in the amide and imide
forms. Bis(trimethylsilyl)acetamide (VI), according
to spectral data, exists mainly in imide form VII [2].
The obtained experimental data show that phosphono-
chloridates Va, Vb react with the imide form of silyla-
ted acetamide VII, and the process takes pathway 1.
Pathway 2 suggests phosphorylation of amide form
VI to form intermediate VIII that undergoes 1,3-
substituent in phosphonochloridates on the synthetic
result of their reaction with silylacetamide VI, we
prepared ethyl (bromoethyl)- and ethyl (bromopropyl)-
phosphonochloridates (XIVa, XIVb). The reactions
of dibromoethane or dibromopropane with tris(tri-
methylsilyl) phosphite produce (bromoalkyl)phos-
phonates XIIa, XIIb. Their chlorination with phos-
phorus pentachloride allowed us to prepare phos-
phonic dichlorides XIIIa, XIIIb whose partial esteri-
fication gives target phosphonochloridates XIVa,
XIVb. It was found that the reaction of phosphonates
XIVa, XIVb with silylacetamide VI provides the
same synthetic result, i.e. it yields trimethylsilyl
(bromoalkyl)phosphonates XV.
N
O trimethylsilyl migration yielding intermediate
XI; finally, the latter decomposes to give product XI.
To assess the effect of the length of the haloalkyl
O
O
O
2PCl5
EtOH, B
B HCl
Br(CH2)nBr + P(OSiMe3)3
Br(CH2)nP(OSiMe3)2
Br(CH2)nPCl2
Br(CH2)nP Cl
Me3SiBr
2POCl3,
2Me3SiCl
OEt
XIIa, XIIb
XIIIa, XIIIb
XIVa, XIVb
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 3 2006

378
PUDOVIK et al.
O
XIVa, XIVb + VI
Br(CH2)nP OSiMe3,
Me3SiCl,
MeCN
OEt
XVa, XVb
XII XV, n = 2 (a), 3 (b).
Note that silicon-containing phosphorylated ureas
by different pathways, we perfomed quantum-che-
mical calculations of structures XVIa XVIc, XVIIa
XVIIc, XVIII, XIX, and XXa XXc that model the
structures of phosphorylated ureas, acylamides, and
possible reaction products.
and amides, while only slightly differing in structure
(diethylamino instead of methyl group), transform by
different pathways to give linear or cyclic products.
To find out why compounds IV and VIII transform
O
MeP
N
1
+ Me3SiCl
R
SiMe3
O
XVIII
O
Me
N
XVIIa XVIIc
P
C R
O
O
ClCH2
2
MePOSiMe3 + RCN
XVIa XVIc
XXa XXc
CH2Cl
XIX
XVI, XVII, XX, R = NMe2 (a), Me (b), Ph (c).
Table 1. Energetic characteristics of compounds studieda
The calculations were carried out by the semi-
empirical PM3 method using the MOPAC 6 program
package [3], and by the density functional method
(DFT/PBE/3z) using the PRIRODA program [4].
DFT method, 3z basis
Comp.
no.
H0f,
kcalmol
1
E0, au
G298, au
As follows from the calculation results listed in
Tables 1 and 2, the processes that take place in prac-
tice are thermodynamically favorable. Therewith, with
dimethylamino derivative XVIa, -decomposition
(pathway 2) is thermodynamically unfavorable and
does not take place. With methyl derivative XVIb,
both pathways are thermodynamically favorable, and
the energy gap between pathways 1 and 2 is not large.
The reason that -decomposition is the only pathway
to be realized is probably explained by specific fea-
tures of reaction mechanisms, that is by kinetic factors.
A qualitatively analogous picture would be observed
at R=Ph (compound XVIc). Such structural factors as
the highest negative charge on oxygen, the highest
located HOMO, the weakest (longest) C Cl bond, and
the strongest N Si bond in compound XVIa com-
pared to its analogs XVIb and XVIc (Table 3) argue
in favor of the intramolecular cyclization of dimethyl-
amino derivative XVIa into XVIIa, that evidently
XVIa
XVIb
XVIc
XVIIa
XVIIb
XVIIc
XVIII
XIX
XXa
XXb
XXc
XXIa
XXIb
XXIc
187.7
181.8
144.1
106.8
99.7
63.8
87.4
203.8
23.0
23.3
1745.298823
1572.270776
1763.780334
876.322270
703.294807
894.806456
868.982914
1439.687305
305.602517
132.591641
324.100669
1745.302642
1572.270008
1763.786152
1745.353284
1572.318654
1764.832403
876.364350
703.328888
894.845689
869.015525
1439.731474
305.635833
132.615700
324.131106
1745.359137
1572.319580
1764.840506
58.5
189.2
182.6
148.5
a
0
( H ) Enthalpy of formation of the molecule in the standard
f
state; (E ) total energy including zero-point energy; and
0
(G ) Gibbs energy.
298
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 3 2006

EXPERIMENTAL AND THEORETICAL INVESTIGATION
379
Table 2. Energetic characteristics of cyclization, -decomposition, and rearrangement by the results of PM3a and DFTb
calculations
Cyclization
-Decomposition
Rearrangement
Parameter
XVIa
XVIIa
XVIb
XVIIb
XVIc
XVIIc
XVIa
XXa
XVIb
XXb
XVIc
XXc
XVIa
XXIa
XVIb
XXIb
XVIc
XXIc
Hf0
E0
G298
6.4
4.0
16.7
5.3
4.5
16.2
7.1
5.7
18.1
7.0
5.6
1.0
1.3
5.3
18.3
1.5
4.8
19.1
1.5
2.4
3.7
0.9
0.4
1.0
4.4
3.6
5.1
a
0
0
0
b
H
=
H (prod.)
H (reag.).
E
=
E (prod.)
E (reag.),
G
=
G
(prod.)
G
(reag.).
f
f
f
0
0
0
298
298
298
involves nucleophilic attack of the carbonyl oxygen
on the chloromethyl carbon. All tables list data for
the most stable conformers of the compounds under
study. The possibility of the reversible N O trime-
thylsilyl migration in compounds XVIa, XVIb to
form imido derivatives XXIa, XXIb should also be
mentioned.
Table 3. Principal geometric and electronic characteristics
of compounds XVIa XVIc by the results of DFT calcula-
tions
Comp.
no.
qO
HOMO, au lC Cl
,
lN Si,
XVIa
XVIb
XVIc
0.2573
0.2409
0.2318
0.2148
0.2247
0.2252
1.810
1.800
1.807
1.826
1.851
1.849
SiMe3
O
P
O
P
Me
Me
N
N
C R
O
C R
ClCH2
ClCH2
OSiMe3
methyl)phosphonic dichloride with phenol for several
XVIa XVIc
XXIa XXIc
hours gave 70% of compound Vb, bp 106 C (0.09
mm Hg). 31P NMR spectrum:
26.1 ppm. Found,
P
XVI, XXI, R = NMe2 (a), Me (b), Ph (c).
%: P 11.17. C7H7BrClO2P. Calculated, %: P 11.50.
Phenyl trimethylsilyl (chloromethyl)phospho-
nate (XIa). A mixture of 2.25 g of (chloromethyl)-
phosphonate Va and 2.05 of bis(trimethylsilyl)acet-
amide (VI) was kept for 2 h at 100 C. Fractionation
of the resulting mixture gave 2.0 g (73%) of com-
pound XIa, bp 75 C (0.02 mm Hg), n2D0 1.5249 [6].
As seen from Table 2, the calculation methods used
show that rearrangement is always thermodynamically
favorable, but with the dimethylamino- and phenyl
derivatives it is much more preferred than with the
methyl derivative.
31P NMR spectrum:
5.15 ppm. Found, %: P 9.60.
EXPERIMENTAL
P
C10H16BrO3PSi. Calculated, %: P 9.91.
1
The H NMR spectra were registered on a Bruker
Phenyl trimethylsilyl (bromomethyl)phospho-
nate (XIb). A mixture of 4.05 g of chlorophos-
phonate Vb and 3.0 g of silylacetamide VI was heated
for 1 h at 140 C. Fractionation of the resulting mix-
ture gave 2.8 g (58%) of compound XIb, bp 116 C
(0.08 mm Hg), n2D0 1.5040. 31P NMR spectrum:
7.09 ppm. Found, %: P 9.60. C10H16BrO3PSi. CalP-
culated, %: P 9.91.
WM-250 (250.13 MHz) spectrometer against residual
proton signals of deuterated solvents (chloroform-d
and acetone-d6). The 31P NMR spectra were obtained
on a Bruker MSL-400 (161.97 MHz) spectrometer
against external 85% phosphoric acid.
2-(Diethylamino)-4-phenoxy-4,5-dihydro-
1,3,4 -oxazaphosphole-2,4-dione (III). A mixture
5
of 2.3 g of phosphonoisocyanatidate I and 1.45 g of
diethyl(trimethylsilyl)amine was kept for 2 h at 120 C.
Fractionation of the reaction mixture gave 1.6 g (60%)
of compound III, bp 219 220 C (0.02 mm Hg), nD20
Ethyl trimethylsilyl (chloromethyl)phos-
phonate (XIc) was prepared analogously from 3.54 g
of chlorophosphonate Vc and 4.06 g of silylacetamide
VI. Yield 2.6 g (56%), bp 59 C (0.06 mm Hg), nD20
1.4319. 31P NMR spectrum: P 10.22 ppm. Found, %:
P 12.96; Si 11.71. C6H16ClO3PSi. Calculated, %:
P 13.44; Si 12.14.
1.5383 [5]. 31P NMR spectrum:
51.50 ppm.
P
Phenyl (bromomethyl)phosphonochloridate
(Vb). Heating of equimolar amounts of (bromo-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 3 2006

380
PUDOVIK et al.
Bis(trimethylsilyl) (2-bromoethyl)phosphonate
Ethyl trimethylsilyl (2-bromoethyl)phosphonate
(XVa). A mixture of 7.0 g of chloride XIVa and 6.0 g
of silylacetamide VI was kept for 20 h at 20 C.
Fractionation gave 4.2 g (49%) of compound XIIIa,
(XIIa). A mixture of 45 g of tris(trimetylsilyl) phos-
phite and 61 g of dibromoethane was kept for 2 h at
160 C. Fractionation of the resulting mixture gave
30 g (59%) of compound XIIa, bp 78 79 C (0.08 mm
bp 85 C (0.1 mm Hg), n2D0 1.4413. 1H NMR spectrum,
Hg), n2D0 1.4437. 31P NMR spectrum:
7.28 ppm.
, ppm: 0.18 (Me3Si). 31P NMR spectrum,
Found, %: P 9.39; Si 16.96. C8H22BrO3PPSi2. Calcu-
lated, %: P 9.30; Si 16.81.
P
17.26 ppm. Found, %: P 10.89; Si 9.63. C7H18BrO3
SiP. Calculated.%: P 10.72; Si 9.68.
Bis(trimethylsilyl) (3-bromopropyl)phospho-
nate (XIIb). A mixture of 15 g of tris(trimetylsilyl)
phosphite and 40 g of dibromopropane was heated for
2 h at 170 C. Bromotrimethylsilane and dibromo-
propane were distilled off, and the residue was frac-
tionated in a vacuum to give 9.5 g (55%) of com-
pound XIIb, bp 115 C (0.1 mm Hg), n2D0 1.4508. 31P
Ethyl trimethylsilyl (3-bromopropyl)phospho-
nate (XVb). A solution of 5.0 g of phosphonochlo-
ridate XIV in 30 ml of anhydrous diethyl ether was
mixed with a solution of 4 g of silylacetamide VI in
20 ml of diethyl ether. The resulting mixture was kept
for 2 days at 20 C. Fractionation gave 3.4 g (57%) of
NMR spectrum:
11.58 ppm. Found, %: P 8.22; Si
compound XVb, bp 92 C (0.06 mm Hg), n2D0 1.4500.
15.76. C8H24BrO3PPSi2. Calculated, %: P 8.93; Si
15.76.
1H NMR spectrum, , ppm: 0.17 (Me3Si). 31P NMR
spectrum:
21.13 ppm. Found, %: C 31.44; H 6.22;
P
P 10.19. C8H20BrO3PSi. Calculated, %: C 31.68;
H 6.60; P 10.23.
(2-Bromoethyl)phosphonic dichloride (XIIIa). A
mixture of 24.5 g of phosphonate XIIa, 0.3 g of
copper monochloride, and 41.7 g of phosphorus pen-
tachloride was kept for 1 h at 100 C. Fractionation of
the reaction mixture gave 15.4 g (68%) of compound
XIIIa, bp 108 110 C (10 mm Hg) [7]. 31P NMR
spectrum: P 44.21 ppm. Found, %: P 13.39. C2H4Br
Cl2OP. Calculated, %: P 13.72.
ACKNOWLEDGMENTS
The work was financially supported by the Russian
Foundation for Basic Research (project no. 03-03-
33064).
(3-Bromopropyl)phosphonic dichloride (XIIIb).
Phosphonate XIIb, 18 g, was heated to 150 C, and
22.5 g of phosphorus pentachloride was added in
portions. The resulting mixture was kept for 2 h at
20 C and fractionated to give 10.5 g (87%) of com-
pound XIIIb, bp 153 156 C (20 mm Hg) [8]. 31P
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48.81 ppm.
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 3 2006