Synthesis and structure of complexes of phosphorus pentachloride with 4-dimethylaminopyridine and n-methylimidazole

Article abstract of DOI:10.1002/hc.20392

Complexes of phosphorus pentachloride with 4-dimethylaminopyridine and N-methylimidazole were synthesized. The molecular structure of the phosphorus pentachloride complex with N-methylimidazole was determined by single-crystal X-ray diffraction. In the cationic part of the complex, the phosphorus atom possesses four P - Cl bonds within the range 2.109-2.148 A and two cis-P-N bonds (1.811 and 1.832 A) with N-methylimidazole and exhibits slightly distorted octahedral coordination with angles at phosphorus atom in the range 87.57°-91.50°. The relative stability of the cis and trans conformations of the complex was studied by DFT calculations. The chemical properties and reactivity of the compounds obtained are determined; their utility as condensing agents in the synthesis of amides from acids and amines was shown.

Full text of DOI:10.1002/hc.20392

Heteroatom Chemistry
Volume 19, Number 2, 2008
Synthesis and Structure
of Complexes of Phosphorus Pentachloride
with 4-Dimethylaminopyridine and
n-Methylimidazole
Sergey E. Pipko, Ludmila V. Bezgubenko, Anatoliy D. Sinitsa,
Eduard B. Rusanov, Evgeniy G. Kapustin, Mark I. Povolotskii,
and Volodymyr V. Shvadchak
Institute of Organic Chemistry, National Academy of Sciences of Ukraine,
Murmanskaya 5, 02094, Kyiv-94, Ukraine
Received 19 October 2006; revised 17 June 2007
INTRODUCTION
ABSTRACT: Complexes of phosphorus pen-
tachloride with 4-dimethylaminopyridine and
N-methylimidazole were synthesized. The molecular
structure of the phosphorus pentachloride com-
plex with N-methylimidazole was determined by
single-crystal X-ray diffraction. In the cationic part
of the complex, the phosphorus atom possesses
The ability of phosphorus halides to form complexes
with amines was discovered a long-time ago. For the
first time, the formation of complexes in the mix-
tures of triethylamine and phosphorus halides was
postulated by W. R. Trost in 1954 [1]. Complexes
of PCl3and PBr3with triethylamine [2–4], PCl5 and
PF5 with pyridine [5–8], PCl3, PBr3, and PBr5 with
N,N-dimethylaminopyridine (DMAP) [9,10] were
obtained later.
Interest in complexes of this type has origi-
nally arisen due to consideration of their possible
role as transition state models for nucleophilic sub-
stitution reactions at phosphorus. Later, the cat-
alytic properties of pyridine and other nitrogen-
containing bases in phosphorylation reactions were
discovered. The effect was explained by the for-
mation of complexes as active electrophilic species
[11–13].
˚
four P Cl bonds within the range 2.109–2.148 A
˚
and two cis-P–N bonds (1.811 and 1.832 A) with
N-methylimidazole and exhibits slightly distorted
octahedral coordination with angles at phosphorus
atom in the range 87.57◦–91.50◦. The relative stability
of the cis and trans conformations of the complex
was studied by DFT calculations. The chemical
properties and reactivity of the compounds obtained
are determined; their utility as condensing agents in
the synthesis of amides from acids and amines was
ꢀ
C
shown. 2008 Wiley Periodicals, Inc. Heteroatom Chem
19:171–177, 2008; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20392
However, all complexes obtained up to now were
extremely easily hydrolyzable compounds. This cre-
ated difficulties in their study and practical use. We
have synthesized some new representatives of these
complexes, which have unusual stability and chem-
ical reactivity.
Correspondence to: Ludmila V. Bezgubenko; e-mail:
Bezgubenko@ukr.net.
c
ꢀ
2008 Wiley Periodicals, Inc.
171

172 Pipko et al.
RESULTS AND DISCUSSION
Two N-methylimidazole ligands N1N2C1–C4 and
N3N4C5–C8 are planar (mean deviation of atoms
from least-squares planes of heterocycles do not ex-
Crystalline complexes 4a,b of 1:2 composition, ac-
cording to their elemental analysis, are formed
by the interaction of PCl5 1 and DMAP 2 or N-
methylimidazole 3 in chloroform.
˚
ceed 0.014 and 0.007 A, respectively), and the dihe-
dral angle between planes is 59.6◦.
A series of short CH···Cl contacts of the hydro-
gen atoms of N-methylimidazole with the chloride
˚
anion within the range of 2.65–2.85 A have been
found in crystals. Six of seven H···Cl contacts have
“chelate”-like nature that may stabilize strongly the
crystal topology of the cis-isomer. This supposition
was studied by DFT calculations of conformations A
(cis) and B (trans). Calculated conformations of 4b
with the [Cl]− anion are given in Fig. 3.
DFT calculations of the systems under study
were carried out using the B3LYP and B3PW91
schemes incorporated in the Gaussian 98W program
suite [14]. A standard basis set 6-31+G (2d,2p) was
used throughout.
Values of the total energy of the conformers and
ions are listed in Table 1. Calculations of 4b with-
out the [Cl]− anion show that conformation B is
more stable by 6.45 kcal/mol at the B3LYP and by
the 6.40 kcal/mol at the B3PW91 level. At the same
time, calculations of 4b with the [Cl]− anion demon-
strate specific interactions between the anion and
the hydrogen of the heterocyclic moieties making
conformation A more stable by 15.80 kcal/mol at the
B3LYP and by 15.90 kcal/mol at the B3PW91 level
of the theory.
In the NMR 31P spectrum of complex 4a, a sig-
nal of six-coordinated phosphorus at −195 ppm split
into a quintet with a coupling constant 3 JPH = 18 Hz
1
is observed. In the NMR H spectrum, the corre-
sponding splitting of the resonance of the α-protons
of the pyridine ring is detected. This fact confirms
the coordination of two molecules of the ligand with
formation of a complex of six-coordinated phospho-
rus. The same situation is observed in the spectra of
complex 4b.
The molecular structure of compound 4b was
determined by single-crystal X-ray diffraction. The
perspective view of molecule 4b is given in Fig. 1. A
fragment of molecular packing is presented in Fig. 2.
In the cationic part of the complex, the phos-
phorus atom possesses four P Cl bonds within the
The calculation of the [Cl]− shows specific inter-
actions between the hydrogen atom at the C2 atom
of the imidazole ring and the anion. The C H bond
lengths are listed in Table 2. The B3PW91 method
shows greater changes in C H bond lengths.
˚
range 2.109–2.148 A and two cis-P N bonds (1.811
˚
and 1.832 A) with N-methylimidazole and exhibits
˚
slightly distorted octahedral coordination with an-
The distance between Cl–H(C5) is 2.216 A
gles at phosphorus atom in the range 87.57◦–91.50◦.
˚
(B3LYP) and 2.176 A (B3PW91) in conformation A.
˚
The distance between Cl–H(C5) is 2.096 A (B3LYP)
˚
and 2.037 A (B3PW91) in conformation B. These
changes in C H bond length and such small distance
between hydrogen atom and [Cl]− anion demon-
strate the effect of H-bond formation.
Interactions between the [Cl]− anion and the
cation lead to redistribution of electron density in
4b. Electron density distribution was analyzed at the
natural bond orbital framework [15] using the NBO
3.1 program [16]. The values of “natural charges”
on atoms (further charges) in the species under dis-
cussion are presented in Table 3. The interaction of
the cationic fragment with the [Cl]− anion decreases
the moiety charge by 0.132 e (B3LYP) and 0.146 e
(B3PW91) in conformation A and by 0.173 e (B3LYP)
and 0.159 e (B3PW91) in conformation B.
Different directions of electron density redistri-
bution with changing conformation from A to B
FIGURE 1 A perspective view of molecule 4b.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Structure of Complexes of Phosphorus Pentachloride with 4-Dimethylaminopyridine and n-Methylimidazole 173
FIGURE 2 Molecular packing of 4b.
were found for cation and neutral molecule. The
charge on the phosphorus atom increases when the
conformation changes from A to B in the cation op-
posite to the neutral molecule. Although charges on
Npyr decrease when the conformation of the cation
changes from A to B, the changes are opposite in the
neutral molecule.
The energy of the donor–acceptor interaction
between a p-type orbital of a lone pair of [Cl]−
anion and the antibonding orbital of the H C5
bond is 17.74 kcal/mol (B3LYP) and 20.07 kcal/mol
(B3PW91) in conformation A and 24.87 kcal/mol
(B3LYP) and 33.14 kcal/mol (B3PW91) in confor-
mation B. These values correlate with changes in
distance between [Cl]− anion and H atom.
These data are in support of a strong stabiliza-
tion of the cis-isomer crystal topology by interac-
tions between the [Cl]− anion and H-atoms of the
cationic part.
The complexes 4a,b are incomparably more sta-
ble to hydrolysis than the starting phosphorus pen-
tachloride and all known complexes of phosphorus
halides. In DMSO solution with 3% of water by vol-
ume, the hydrolysis of compound 4a proceeds to an
extent of 75% during 12 h, and for compound 4b
to an extent of 50% during 10 days. The suspension
of complexes 4a,b in ethanol 5 is stable at ambient
temperature. The alcoholysis with formation of di-
ethylphosphate 6 starts only when heated to boiling
point.
FIGURE 3 Calculated conformations of 4b with the Cl−
anion.
Heteroatom Chemistry DOI 10.1002/hc

174 Pipko et al.
TABLE 1 Total Energies (in hartree) of 4b
Conformation A
Conformation B
Method
Cation
Neutral
Cation
Neutral
B3LYP
B3PW91
−2713.1022662
−2713.1125376
−3173.5160436
−3173.4908691
−2712.6538131
−2712.6640084
−3173.0106928
−3172.9853555
TABLE 2 The Bond Lengths (in angstroms) in the Cation
of 4b and in the Neutral Molecule Obtained at B3LYP and
B3PW91 Levels
Conformation A
Conformation B
Method
Cation
Neutral
Cation
Neutral
In chloroform solution at ambient temper-
ature, complexes 4a,b do not react with di-
isobutylamine 7. The reaction proceeds only
B3LYP
B3PW91
1.074
1.075
1.097, 1.073
1.103, 1.073
1.074
1.075
1.111, 1.074
1.123, 1.075
after boiling the reaction mixture for
1 h.
Tetrakis(diisobutylamino)phosphonium chloride 8
is the product of the reaction.
carbodiimides or carbonyldiimidazole, where the re-
action must be conducted in two steps: at the first
stage, an activated derivative of the acid is produced,
at the second stage the amine is added and the acyla-
tion is carried out. The condensation with the help of
complex 4a allows us to avoid the intermediate stage
and to carry out the synthesis simply by heating all
three components together.
The optimal conditions of the reaction, and area
of its application are under study.
The unusual stability of the complexes 4a,b al-
lows to use them as new condensation reagents in
organic synthesis, for example, in obtaining amides
from carboxylic acids and amines. Test reactions of
derivatives of benzoic 9 and phenoxyacetic 12 acids
with p-phenetidin 10 in the presence of complex 4a
give the corresponding amides 11,13 in good yields.
EXPERIMENTAL
General Remarks
All reactions were performed under an inert atmo-
sphere of Ar in predried glassware. The solvents were
dried by distillation over the following drying agents
and were transferred under Ar: chloroform (P4O10),
acetonitrile (P4O10), ethanol (Na). Residual of water
in 4-dimethylaminopyridine and N-methylimidazole
was removed by azeotropic distillation with CCl4. 1H
and 31P NMR spectra were recorded on CDCl3 and
DMSO-d6 solutions on a Varian VXR-300 spectrom-
eter operating at 299.95 and 121.42 MHz, respec-
tively. Chemical shifts (δ) are given in ppm relative
to TMS and 85% H3PO4. Melting points were deter-
mined in closed tubes and were uncorrected. Ele-
mentary analyses were performed at the Micronaly-
sis Services of the Institute of Organic Chemistry of
National Academy of Sciences of Ukraine.
Tetrachlorobis(4-dimethylaminopyridine)phos-
phorus(V) Chloride (4a). A solution of 4-
dimethylaminopyridine 2 (5 g, 40.9 mmol) in
The method is more useful for preparative use
than condensation with standard reagents such as
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Structure of Complexes of Phosphorus Pentachloride with 4-Dimethylaminopyridine and n-Methylimidazole 175
TABLE 3 The Values of the Natural Charges (q, e) on the Atoms for the 4b Species
Cationic Fragment
Cationic Fragment with Cl−
B3LYP B3PW91
B3LYP
B3PW91
Atom
A
B
A
B
A
B
A
B
q(P)
Cl
1.207
−0.256
−0.256
−0.210
−0.210
−0.614
−0.614
−0.358
−0.358
−0.048
−0.048
1.240
−0.249
−0.249
−0.249
−0.249
−0.612
−0.612
−0.358
−0.358
−0.033
−0.033
1.213
−0.255
−0.255
−0.211
−0.211
−0.615
−0.615
−0.354
−0.354
−0.056
−0.056
1.234
−0.246
−0.246
−0.246
−0.246
−0.615
−0.615
−0.354
−0.354
−0.040
−0.040
1.254
−0.229
−0.298
−0.242
−0.268
−0.622
−0.647
−0.368
−0.354
−0.032
−0.060
−0.868
1.234
−0.224
−0.225
−0.303
−0.303
−0.630
−0.585
−0.367
−0.371
−0.021
−0.032
−0.827
1.248
−0.228
−0.293
−0.238
−0.263
−0.624
−0.650
−0.365
−0.352
−0.040
−0.068
−0.854
1.239
−0.216
−0.296
−0.216
−0.296
−0.637
−0.592
−0.363
−0.367
−0.030
−0.039
−0.841
Clꢁ
q(Npyr
)
q(Npy
C5
)
Cl
3
−3
˚
chloroform (10 mL) was added to a suspension of
PCl51 (1.7 g, 8.19 mmol) in chloroform (20 mL) with
intensive stirring. The solid phase was dissolved
quickly, then the product was precipitated. After
2 h, the precipitate was filtered and washed with
chloroform. Complex 4a was obtained as white
crystals (4.7 g, 99%) (solvate with one molecule of
chloroform); mp = 155◦C–160◦C. Elemental analysis
Calcd for C15H21Cl8N4P (571.955): C 31.50, H 3.70,
Cl 49.59, N 9.80, P 5.42; Found C 31.24, H 3.74, Cl
49.45, N 9.81, P 4.19. NMR (DMSO-d6): 1H, δ (ppm)
= 3.27s (12H, N-CH3), 6.96d (4H, CH (β-aromatic)
(JHH = 7 Hz)), 8.28s (1H, CHCl3), 9.30dd (4H, CH
(α-romatic), (JPH = 17 Hz), (JHH = 7 Hz)). 31P, δ
(ppm) = −196 quintet, 3 JPH = 17 Hz.
V = 1726.0 (7) A , Z = 4, dc = 1.597 g cm , µ = 9.915
mm−1, F(000) = 836. To avoid the decomposition
of the yellowish crystal of compound 4b with
size ca. 0.40 × 0.45 × 0.45 mm, it was placed in a
glass capillary. All crystallographic measurements
were performed at room temperature on a CAD4
Enraf–Nonius diffractometer operating in the ω –
2θ scan mode (the scanning ratio was ω/2θ = 1.2).
Intensity data were collected within range 4.6
≤ θ ≤ 64.9◦ using Cu Kα radiation (λ = 1.54178
˚
A). Intensities of 3182 reflections (2931 unique
reflections, R = 0.058) were measured. Data were
int
corrected for Lorenz and polarization effects. The
azimuthal absorption correction by PSI-scan (Tmin
0.0156, Tmax 0.0704) was applied. The structure was
solved by direct methods and refined by full-matrix
least-squares technique in the anisotropic approxi-
mation for non-hydrogen atoms using SHELXS97
and SHELXL97 programs. In the refinement, 2931
reflections (1973 reflections with I ≥ 2σ(I)) were
used. All hydrogen atoms were placed at calculated
position as “riding” model with Uiso = 1.2Uiso of
supporting carbon atoms. During the structure
refinement, the atoms of the methylene chloride
solvent molecule were observed close to inversion
center, but could not be modeled satisfactorily.
The SQUEEZE routine in PLATON was used to
modify the HKL file and the solvent equated to a
half molecule of methylene chloride per molecule of
complex. Convergence was obtained at R = 0.0567
and Rw(F2) = 0.1429, GOF = 0.984 (166 parameters;
observed/variable ratio 11.9; the largest and minimal
peaks in the final difference map 0.55 and −0.51
cis-Tetrachlorobis(1-methylimidazole)phosphorus(V)
Chloride (4b). Compound 4b was prepared as de-
scribed for 4a. Complex 4b was obtained as white
crystals, yield 97.8%; mp = 131.5◦C–137◦C (dec.).
Elemental analysis Calcd for C8H12Cl5N4P (372.448):
C 25.80, H 3.25, Cl 47.59, N 15.04, P 8.32; Found
C 25.51, H 3.21, Cl 50.91, N 12.97, P 7.29. NMR
(DMSO-d6): 1H, δ (ppm) = 3.86s (3H, N CH3), 7.56m
(2H, CH (4-aromatic),JPH = 5 Hz), 7.78m (2H, CH (5-
aromatic),JPH = 6 Hz), 9.80d (2H, CH (2-aromatic),
JPH = 4 Hz). 31P, δ (ppm) = −231 pseudo-heptet,
3 JPH = 5.8 Hz. Yellowish crystals suitable for X-ray
analysis were obtained by growing in methylene
chloride/chloroform (1:1).
X-ray Structure Determination of 4b. Crystal
1
2
Data: C8.50H13Cl6N4P (4b· CH2Cl2), M 414.90, mon-
3
2
2
2
˚
oclinic, space group P21/c (N 14), a = 7.056(2),
eA , weighting scheme ω = 1/[σ (Fo ) + (0.0943)P ],
where C = (Fo + 2Fc )/3). Full crystallographic
b= 19.139(3), c= 13.186(3) A, β = 104.24(2)◦,
2
2
˚
Heteroatom Chemistry DOI 10.1002/hc

176 Pipko et al.
parameters have been deposited at the Cambridge
Crystallographic Data Centre (CCDC). Any request
to the CCDC for these materials should quote the
full literature citation and reference number CCDC
624161. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033; or deposit@ccdc.cam.ac.uk).
(4ꢁ-Ethoxy)-4-methylbenzanilide 11. A mixture
of 4-methylbenzoic 9 acid (0.384 g, 2.82 mmol), p-
phenetidin 10 (0.322 g, 2.35 mmol), 4a (1.344 g, 2.35
mmol), and diisopropylethylamine (1.52 g, 11.75
mmol) in acetonitrile (2 mL) was heated in a boiling
water bath for 1 h. A solution of 1 g K2CO3 in wa-
ter (20 mL) was added to the reaction mixture. The
mixture was stirred for 0.5 h. The precipitate was fil-
tered off and was washed with a mixture of water and
1
acetonitrile (1:1) (0.43 g, 71%). NMR (CDCl3): H, δ
(ppm) = 1.41t (3H, O CH2 CH3, (JHH = 7 Hz)), 2.42s
(3H, Ar CH3), 4.03 q (2H, O CH2 CH3, (JHH = 7
Hz)), 6.88d (2H, CH (3ꢁ-aromatic), (JHH = 8.5 Hz)),
7.27d (2H, CH (2ꢁ-aromatic), (JHH = 8.5 Hz)), 7.52d
(2H, CH(3-aromatic), (JHH = 8.5 Hz)), 7.76d (2H,
CH(2-aromatic), (JHH = 8.5 Hz)), 7.71s (1H, NH).
General Procedure for Reaction of Complexes
4a,b with Ethanol
Compound 4a (or 4b) (1.59 mmol) was added to
dry ethanol 5 (108.5 mmol). The reaction mixture
was stirred at ambient temperature for 1 h, com-
pound 4a (or 4b) was not dissolved. According to
the 31P NMR spectrum, there was no phosphorus
compound in the reaction mixture at this point.
The mixture was stirred at 60◦C for 4.5 h until 4a
(or 4b) was completely dissolved. The yield of di-
ethylphosphate 6 was more than 95% according to
the 31P NMR spectrum. The identity of the prod-
uct was established by spectral comparison to di-
ethylphosphate, which was obtained by the hydrol-
ysis of diethylchlorophosphate. NMR (CDCl3): 1H, δ
(ppm) = 4.12 quintet (4H, OCH2, (JHH = JHP = 7 Hz)),
1.35t (6H, CH3), (JHH = 7 Hz)). 31P, δ (ppm) = −1m,
2 JPH = 12 Hz.
(4ꢁ-Ethoxy)-2-methylphenoxyacetanilide
13.
Compound 13 was prepared as described for 11.
0.54 g, 73%. NMR (CDCl3): 1H, δ (ppm) = 1.41t (3H,
O CH2 CH3, (JHH = 6.85 Hz)), 2.36s (3H, Ar CH3),
4.02q (2H, O CH2 CH3, (JHH = 6.85 Hz)), 4.61s (2H,
CH2 CO ), 6.85d (1H, CH(6-aromatic), (JHH = 8.1
Hz)), 6.88d (2H, CH(3ꢁ-aromatic), (JHH = 8.72 Hz)),
6.97m (1H, CH(3-aromatic), (JHH = 7.3 Hz)), 7.2m
(2H, CH(4,5-aromatic), (JHH = 7.3 Hz)), 7.48d (2H,
CH(2ꢁ-aromatic), (JHH = 8.72 Hz)), 8.23s (1H, NH).
REFERENCES
[1] Trost, W. R. Can J Chem 1954, 32, 356–361.
[2] Holmes, R. R.; Bertaut, E. F. J Am Chem Soc 1958,
80, 2980–2983.
[3] Holmes, R. R. J Phys Chem 1960, 64, 1295–1299.
[4] Holmes, R. R. J Am Chem Soc 1960, 82, 5285–5288.
[5] Beattie, I. R.; Webster M. J Chem Soc 1961, 1730–
1733.
[6] Dillon, K. B.; Reeve, R. N.; Waddington, T. C. J Chem
Soc, Dalton Trans 1977, 1410–1416.
[7] Dillon, K. B.; Reeve, R. N.; Waddington, T. C. J Chem
Soc, Dalton Trans 1977, 2382–2388.
[8] Il’in, E. G.; Shcherbakova, M. N.; Buslaev, Yu. A.
Doklad Akad Nauk SSSR 1976, 231, 107–109.
[9] Weiss, R.; Engel, St. Synthesis 1991, 1077–1079.
[10] Weiss, R.; Engel, St. Angew Chem, Int Ed Engl 1992,
104, 239–240.
[11] Corfield, J. R.; Oram, R. K.; Smith, D. J. H.; Trippett,
S. J Chem Soc, Perkin Trans I 1972, 713–716.
[12] Zarytova, V. F.; Ivanova, E. M.; Knorre, D. G.;
Vorbru¨ggen, H. Doklad Akad Nauk SSSR 1980, 255,
1128–1131.
[13] Ivonin, S. P.; Tolmachev, A. A.; Pinchuk, A. M.
In International Symposium Devoted to the 100th
Anniversary of Academician, Kirsanov, A. V. (Ed);
Institute of Organic Chemistry of the National
Academy of Sciences of Ukraine: Kyiv, Ukraine, 2002;
p. 40.
General Procedure for Reaction of Complexes
4a,b with Diisobutylamine
Compound 4a (or4b) (0.965 g, 1.69 mmol) was
added to a solution of diisobutylamine 7 (1.635 g,
12.7 mmol) in chloroform (5 mL). The reaction mix-
ture was stirred at ambient temperature for 0.5 h,
compound 4a (or 4b) was not dissolved. Accord-
ing to the 31P NMR spectrum, there was no phos-
phorus compound in the reaction mixture at this
point. Then the mixture was heated to the boil-
ing point, but no signal of phosphorus was de-
tected after 1 h of boiling the reaction mixture.
Compound 4a (or 4b) was dissolved completely
only after 6 h of boiling the reaction mixture.
The yield of tetrakis(diisobutylamino)phosphonium
chloride 8 was more than 95% according to
the 31P NMR spectrum. The identity of the
product was established by spectral comparison
to tetrakis(diisobutylamino)phosphonium chloride,
which was obtained by the reaction of PCl5 with di-
isobutylamine. 31P NMR (CHCl3), δ (ppm) = 58.5 m,
3 JPH = 12 Hz.
[14] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria,
G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski,
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Structure of Complexes of Phosphorus Pentachloride with 4-Dimethylaminopyridine and n-Methylimidazole 177
V. G.; Montgomery, J. A.; Stratmann, R. E.; Burant,
J. C.; Dapprich, S.; Millan, J. M.; Daniels, A. D.;
Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.;
Pomelli, C.; Adamo, C.; Clifford, S.; Ocherski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith,
T. A.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M. Revision. A.7.
Gaussian; Inc.: Pittsburgh, PA, 1998.
[15] (a) Weinhold, F.; Landis, C. Valency and Bonding;
Cambridge University Press: Cambridge, UK, 2005;
p. 749; (b) Reed, A. E.; Curtiss, L. A.; Weinhold, F.
Chem Rev 1988, 88, 899–926.
[16] Glendening, E. D.; Reed, A. E.; Carpenter, J. E.;
Weinhold, F. NBO version 3.1, the link 607 of the
program Gaussian 98.
Heteroatom Chemistry DOI 10.1002/hc