Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-N′-arylformamidines

Article abstract of DOI:10.1002/hc.21283

Cyclic zwitterionic phosphoranides 2a,b were found to be intermediate products in the reaction of N,N-dimethyl-N′-(aryl)formamidines with PBr₃. The structure of phosphoranide 2a was determined by means of the X-ray and quantum chemistry investigations. Mechanism of its formation was proposed based on Density functional theory (DFT) calculations. Reactions of 2 with amines and selenium yielded either C-phosphorylated formamidines or benzazaphospholes. The first example of intramolecular heterocyclization of a pentavalent phosphorus derivative 15b into 3Cyrillic capital letter en-1,3-benzazaphosphole has been demonstrated.

Full text of DOI:10.1002/hc.21283

Heteroatom Chemistry
Volume 27, Number 1, 2016
Zwitterionic Phosphoranides as Intermediates
in the Reaction of Phosphorus Tribromide with
N,N-Dimethyl-Nꢀ-arylformamidines
Anatoliy P. Marchenko, Georgyi N. Koidan, Anastasia N. Hurieva,
Alexander B. Rozhenko, and Aleksandr N. Kostyuk
Institute of Organic Chemistry, Kyiv 02094, Ukraine
Received 15 April 2015; revised 10 July 2015; accepted 21 July 2015
reaction of PBr3 with Pr4N+Br− and later was
ABSTRACT: Cyclic zwitterionic phosphoranides
characterized by the X-ray diffraction study [1].
2a,b were found to be intermediate products in
Since then several other phosphoranides fea-
the reaction of N,N-dimethyl-Nꢀ-(aryl)formamidines
turing halogens have been reported, such
with PBr3. The structure of phosphoranide 2a was
as tetrafluorophosphoranide [2, 3], tetraonio-
determined by means of the X-ray and quantum
substituted phosphoranide [4], chlorophospho-
chemistry investigations. Mechanism of its forma-
ranides [5–7], and bromophosphoranides [8, 9].
tion was proposed based on Density functional the-
Recently, it has been shown that carbene lig-
ory (DFT) calculations. Reactions of 2 with amines
ands are also very effective in stabilizing phos-
and selenium yielded either C-phosphorylated for-
phoranides.
Thus,
reacting
imidazolylidene
mamidines or benzazaphospholes. The first exam-
ple of intramolecular heterocyclization of a pen-
tavalent phosphorus derivative 15b into 3Н-1,3-
with PCl3 in hexane afforded phosphoranide B
(R = Cl) almost in quantitative yield [6]. Another
rare example is cationic phosphoranide C [5].
ꢁC
benzazaphosphole has been demonstrated.
2015
Wiley Periodicals, Inc. Heteroatom Chem. 27:12–
22, 2016; View this article online at wileyonlineli-
brary.com. DOI 10.1002/hc.21283
X
P
X
Dipp
Dipp
R
R
X
X
N+
N+
Dipp
N+
X
X
Cl
Cl
N
P
P-
P-
Cl
N
N
Cl
Cl
Dipp
Dipp
N
-
Dipp
TfO
A
B
C
D
INTRODUCTION
Other stable phosphoranides D were prepared by
Phosphoranides A are hypervalent anionic phos-
phorus (III) compounds formally with the 10
electron valence shell and distorted pseudotrigonal
bipyramidal arrangement at phosphorus. The more
electronegative are ligands forming a phospho-
ranide, the higher is its stability. The first isolated
placing on an organic scaffold in the peri positions,
for example naphthalen-1,8-diyl, a donor group like
R2N or R2P dimensionally close to the P(III) group
[10–14]. The sole review devoted to phosphoranides
was published by Dillon in 1994 [15], and some as-
pects were discussed by Macdonald et al. [16].
Previously, we reported on the phosphorylation
of N,N-dimethyl-Nꢀ-(p-tolyl)formamidine by PBr3 in
pyridine with an excess of triethylamine taken in mo-
lar ratio of 1:1:1.4 [17]. An intermediate in the reac-
tion, postulated as C-dibromophosphine, was char-
acterized by 31P Nuclear magnetic resonance (NMR)
phosphoranide Pr4N+PBr4 was prepared by the
−
Correspondence to: Aleksandr N. Kostyuk; e-mail: a.kostyuk
@yahoo.com.
Supporting Information is available in the online issue at
www.wileyonlinelibrary.com.
ꢁC
2015 Wiley Periodicals, Inc.
12

Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-Nꢀ-arylformamidines 13
SCHEME 1 Synthesis of compounds 2a,b.
FIGURE 2 2a–c and other known dibromophosphoranides
2d–f.
mamidines and triethylamine remains unreacted.
Although the reaction proceeded readily and com-
pletely, it was difficult to isolate 2a,b due to the
presence of triethylamine hydrobromide. As a way
to circumvent the problem, using an excess of for-
mamidines 1a,b as a base was proposed. The reac-
tion of 3 equiv of formamidines 1a,b with phospho-
rus tribromide proceeded three times slower, but the
quantitative precipitation of hydrobromide of 1 al-
lowed isolating compounds 2a,b (Scheme 1).
The structure of compound 2a was ascertained
by X-Ray single crystal study (Fig. 1). Thus, along
with structure D, 2a represents the rare example
of the cyclic zwitterionic phosphoranide. The main
features of 2a are the P-Br distances (2.6945(16)
˚
˚
and 2.5792(15) A vs. 2.23 A in PBr3 [19]), and a
widened Br1-P-Br2 bond angle (161.1°). These agree
well with the values previously found for other phos-
phoranides (Fig. 2, Table 1).
FIGURE 1 ORTEP presentation of structure 2a. Main ge-
ometry parameters (bond lengths in A, bond angles in
degrees): P3-Br1 2.6945(16), P3-Br2 2.5792(15), P3-N1
1.645(4), P3-C2 1.850(5), C1-N1 1.487(6), C1-N2 1.515(6),
C2-N2 1.329(6), C2-N4 1.309(6), C1-N3 1.393(6), N1-P3-C2
88.3(2), Br1-P3-Br2 161.12(6), N1-P3-Br2 97.52(16), C2-P3-
Br1 85.38(16), C2-P3-Br2 83.20(16).
˚
TABLE 1 Structural Features of Known Dibromophospho-
ranides
Item
l(P-Br1)
l(P-Br2)
ࢬBr1PBr2
ࢬXPX
2d
2e
2f
2.527
2.496
2.327
2.620
2.496
2.957
170.0
171.4
176.6
99.4 (BrPBr)
101.4 (CPC)
100.8 (PPC)
spectroscopy and chemical transformations leading
to derivatives of C-phosphorylated formamidines.
Meanwhile, its quite unusual 31P NMR chemical
shift (56.8 parts per million (ppm)) and inability,
unlike the similar monochlorophosphines, to cyclize
into 3H-1,3-benzazaphosphole upon treatment with
triethylamine raised doubts concerning its constitu-
tion [18].
To investigate the structure and electron distri-
bution in 2a in more detail, we have carried out
quantum chemical calculations at the RIJCOSX-
TPPSh/TZVP [20, 21] (further referred as DFT) and
RI-MP2/TZVP [22] (further referred as MP2) levels of
approximation for 2a as well as for the model struc-
ture 2c (Fig. 2). The equilibrium structures (Fig. 3)
and calculated structural parameters (Table 2) agree
well with the experiment: for 2a, PBr1 bond is pre-
dicted to be longer than PBr2.
Formally, structures 2 might also be considered
as the donor–acceptor adducts of the cyclic phosphe-
nium dication with two bromide anions coordinated
on the vacant p-orbital of phosphorus. It is stabi-
lized via interaction with the neighboring nitrogen
RESULTS AND DISCUSSION
To elucidate the structure of the phosphorylation
products, we decided to isolate them. We have found
that 1 equiv of phosphorus tribromide reacts with 2
equiv of formamidine 1 and 1 equiv of triethylamine
affording products 2 with 31P chemical shift very
close to the δP value, previously postulated for the
C-dibromophosphine. Any excess of the for-
Heteroatom Chemistry DOI 10.1002/hc

14 Marchenko et al.
FIGURE 3 Equilibrium (RI-MP2/TZVP) structures of 2a (left) and 2c (right). See Table 2 for the selected geometry parameters.
TABLE 2 Selected Geometry Parameters for Equilibrium Structures 2a,c Calculated at the MP2 and DFT (in Italic) Levels of
Approximation
˚
Bond Lengths (A)
Bond angles (deg)
Item
P-Br1
P-Br2
P-C2
P-N1
C1–N1
C1–N2
C2–N2
Br1PBr2
CPN
2a
2.647
2.726
2.568
2.627
2.615
2.581
2.678
2.666
1.855
1.862
1.849
1.861
1.695
1.705
1.698
1.698
1.461
1.467
1.442
1.446
1.494
1.536
1.493
1.512
1.333
1.333
1.326
1.329
160.0
160.1
159.6
160.3
87.2
87.9
87.6
87.7
2c
SCHEME 2 Mesomeric structures of 2.
(mesomeric structures 2C and 2D in Scheme 2), and
tions of mesomeric forms 2A(2Aꢀ) and 2C. A signifi-
cant delocalization of positive charge on N2 and N4
is also supported by the calculated positive values
of total charges on these atoms (+0.082 and +0.03,
respectively), derived from Mayer population anal-
ysis [23]. Finally, the significantly elongated C1–N2
bond (1.515 A, calc. 1.494 A) indicates its partially co-
ordinative character and some contribution of Lewis
structures 2E(2Eꢀ).
The large Br-P-Br bond angle (160.0°), predicted
for 2a, agrees well with the experimental value
(Br(2)-P(3)-Br(1) 161.1°) and with the formal rep-
resentation of 2a as phosphenium dication with two
the P(3)–N(1) bond is shortened in solid state to
˚
1.645 A (the gas phase calculations at the MP2 level
of theory provide slightly longer distances 1.695 and
˚
1.698 A for 2a and 2c, respectively). In contrast, the
˚
corresponding P(3)–C(2) bond (1.850 A) is slightly
˚
˚
longer than the typical P–C single bond (approxi-
˚
˚
mately 1.8 A). The C2–N2 bond is shortened (1.329 A)
(the corresponding calculated values are 1.333 and
˚
1.326 A, respectively). The dimethylamino group is
coplanar with the heterocyclic ring and participates
in delocalization of positive charge (N(4)–C(2) 1.309
˚
˚
A (calc. 1.316 and 1.322 A). This indicates contribu-
Heteroatom Chemistry DOI 10.1002/hc

Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-Nꢀ-arylformamidines 15
SCHEME 3 Mechanistic proposal for the formation of 2a.
into account (+3.7 kcal/mol). In addition, this stage
can be driven by forming an insoluble hydrobromide
of 1a. As we have shown recently [25], carbenes of
type 5a easily isomerize to the corresponding C-P
derivative 6a (ꢀE = –11.2 and –8.3 kcal/mol for the
gas phase and for the solution in dichloromethane,
respectively). The inherent activation energy derived
from the relaxed energy surface scan in the gas phase
is very low (approximately 3.0 kcal/mol) and the cor-
responding transition state structure cannot even be
located. Finally, 6a reacts with the second formami-
dine molecule forming the cyclic adduct 2a (ꢀE =
–12.6 and –14.7 kcal/mol for the gas phase and for the
solution in dichloromethane, respectively). The com-
plete energy balance for reaction 3ꢀ1a + PBr3→2a
+ 1a*HBr + ꢀE is only slightly negative in vacuum
FIGURE 4 Jmol plot of the equilibrium structure of 4a (DFT,
COSMO, dichloromethane).
(ꢀE = –1.6 kcal/mol), but is significantly more fa-
vored in dichloromethane (ꢀE = –18.7 kcal/mol).
Our attempts to extend the reaction on other bro-
bromide anions interacting with the formally va-
cant p-orbital at phosphorus (structures 2C, 2D). The
small CPBr angles (C(2)-P(3)-Br(1) 85.4 and C(2)-
P(3)-Br(2) 83.2°) are also noteworthy. The bromine
atoms are bent over the C-P bonds, interacting to
some extent with C2 (Lewis structure 2F).
mophosphines (Me2NPBr2, PhPBr2, Ph2PBr) failed.
They did not react with 1.
For further investigation, phosphoranides 2a,b
were used without any purification. It was found
that 2a,b readily reacted with dimethylamine and se-
lenium (Scheme 4). The composition and structure
of the reaction products depend on the amount of
dimethylamine and order of mixing the reactants.
According to 31P NMR data, adding an excess of
dimethylamine (n > 4 equiv) to the reaction mix-
ture and in 30 min selenium led to C-phosphorylated
formamidines 7a,b and then to compounds 8a,b.
The latter were separated chromatographically in
76–78% yields. NMR spectra of 7 and 8 are con-
sistent with the literature data [18]. The addition of
only 1 equiv of dimethylamine led to the formation of
3Н-1,3-benzazaphospholes 9a,b, which after oxida-
tion with selenium were separated chromatographi-
cally as the corresponding selones 10a,b. By simul-
taneous addition of selenium and dimethylamine to
the reaction mixture, the formed products also de-
pend on the amount of dimethylamine (Scheme 4).
Adding a large excess of dimethylamine (> 4 equiv)
A possible mechanism of formation of 2a
is proposed in Scheme 3. As the first step, an
intermediate adduct of formamidine 1a with PBr3
3a is formed. Geometry optimization for 3a with tak-
ing into account solvent effects results in the struc-
ture 4a as shown in Fig. 4. The equilibrium geome-
try represents the phosphoranide structure with one
˚
P–Br bond significantly elongated (2.912 A) com-
˚
pared to the two other ones (2.239 and 2.413 A);
in this case, the reaction energy is negative (ꢀE =
–5.5 kcal/mol in dichloromethane). Therefore, the
structure 4a exists in the solution as the bromide
of N-phosphanoformamidinium salts [24]. Depro-
tonation of 4a provides a substituted diaminocar-
bene 5a; the HBr elimination is overall unfavorable
(ꢀE = +17.0 kcal/mol), while the reaction energy
is significantly less positive by taking solvent effects
Heteroatom Chemistry DOI 10.1002/hc

16 Marchenko et al.
SCHEME 4 Reactions of 2 with dimethylamine and selenium by stepwise and simultaneous adding.
FIGURE 5 ORTEP presentation of structure of 12b (cocrystallized acetonitrile molecule is omitted). Main geometry parameters
˚
(bond lengths in A, bond angles in degrees): P1-C1 1.851(5), P1-N2 1.638(4), P1-Se2 2.0736(14), P1-N3 1.620(4), C1-N1
1.326(5), C2-N2 1.464(5), N1-C2 1.512(5), C1P1N2 89.64(19), Se2P1N3 114.39(16), N1C2N2 103.3(3).
resulted in the formation of compounds 11a,b,
whereas using 1 equiv of dimethylamine yielded di-
azaphospholidinium salts 12a,b.
This structural flexibility also becomes appar-
ent in the chemical properties of 12a,b. Upon heat-
ing at 100°С for 5 h in acetonitrile, compounds
12a,b eliminated formamidine 1a,b and quanti-
tatively rearranged into 3Н-1,3-benzazaphospholes
10a,b (Scheme 6). The reaction of 12b with t-Bu3P in
methylene chloride proceeded readily at 40°С form-
ing thermally unstable phosphorus (III) derivative:
1,4,2-(λ3)diazaphospholane 13b. In the 31Р NMR
spectrum of the reaction mixture, the signals of
t-Bu3PSe and two diastereoisomers of 13b (δр 78.0
and δр 75.6 with the integral ratio 2:3) were found.
Compound 13b was stable below 0°С and eas-
ily added selenium affording 12b with the same
isomeric ratio. At 10°С, compound 13b decom-
posed into formamidine hydrobromide 1b and benz
azaphosphole 9b, which was isolated in the form
of selenide 10b. Although in the both men-
tioned cases the cleavage of the cyclic P-N bond
Compounds 11 and 12 are crystalline solids
and stable on air. Their structures were confirmed
by NMR spectroscopy, mass spectrometry, and
single crystal X-Ray diffraction for 12b (Fig. 5).
The molecular structure of 12b demonstrates two
˚
elongated bonds: P1–C1 (1.851(5) A) and N1–C2
˚
(1.512(5) A). Similarly to the corresponding weak-
ened bond in 2a (Scheme 2), the latter is practi-
cally the coordinative bond and reflects contribu-
tion of mesomeric structure 12C (Scheme 5). A
consequence of the C–N bond lability is the sol-
vent dependence of the ratio of diastereomers. In
the 31Р NMR spectra of 12a (12b), the integral
intensity ratio of corresponding signals changes
from 14:1 (6:1) in chloroform to 4:1 (2.1:1) in
acetonitrile.
Heteroatom Chemistry DOI 10.1002/hc

Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-Nꢀ-arylformamidines 17
SCHEME 5 Lewis structures of 12.
SCHEME 6 Reactions of 12a,b with cleavage and retention of the cyclic P–N bond.
(Scheme 8). This is the first example of electrophilic
cyclizations for pentavalent phosphorus derivatives:
the formation of 3Н-1,3-benzazaphospholes was pre-
viously reported only for trivalent C-phosphorylated
N-arylformamidines [18].
SCHEME 7 Synthesis of bromobenzazaphospholes 14a,b.
CONCLUSIONS
We have studied the reaction of N,N-dimethylamino-
Nꢀ-arylformamidines with phosphorus tribromide
and found that it results in the unique structural
type cyclic zwitterionic phosphoranides 2, which
are highly reactive species and can easily be trans-
formed into C-phosphorylated formamidines or ben-
zazaphospholes. In addition, the new type of hete-
rocyclization reaction has been found: amidinium
derivative of phosphorus (V) undergoes the cycliza-
tion into 3Н-1,3-benzazaphosphole.
occurred, the reactions of 12a,b with Me2NH
and PhNH2 proceeded with retention of the P-N
bond affording compounds 11a,b, hydrobromides
of tris(dimetylamino)methane, and 1а.
Upon heating in benzene, compounds 2 were
transformed into bromobenzazaphospholes 14 and
hydrobromides of 1 (Scheme 7). Compounds 14a,b
are bright red crystals, structure of which was con-
firmed by 1H, 13C, and 31P NMR spectroscopy,
chemical transformations into the known benzaza-
phospholes 10a,b, as well as X-Ray analysis for hy-
drobromide 14b, which formed as result of partial
hydrolysis of 14b during the growth of single crystal
(Fig. 6).
Previously, we have shown that trivalent
C-phosphorylated formamidines 7 cyclized into ben-
zazaphospholes 9 in the presence of acids [9].
Now, we found that salt 15b bearing a pen-
tavalent phosphorus substituent is transformed
into 3Н-1,3-benzazaphosphole 10b upon melting
(mp 151–152°С) or boiling its acetonitrile solution
EXPERIMENTAL
All procedures with air- and moisture-sensitive com-
pounds were performed under atmosphere of dry ar-
gon in flame-dried glassware. Solvents were purified
and dried by standard methods. Melting points were
determined with an electrothermal capillary melt-
1
ing point apparatus and given uncorrected. H and
13C NMR spectra were recorded on a Bruker Avance
DRX 500 (500.13 and 125.75 MHz, respectively). 31
P
NMR spectra were recorded on a Varian VXR-300
Heteroatom Chemistry DOI 10.1002/hc

18 Marchenko et al.
FIGURE 6 ORTEP representation of structure of hydrobromide of 14b. The bromide anion indicates no short contacts with
˚
the cationic moiety and is omitted for clarity. Main geometry parameters (bond lengths in A, bond angles in degrees): P3-C1
1.817(2), P3-C7 1.863(3), P3-Br2 2.3722(7), N1-C7 1.338(3), N2-C7 1.305(3), Br2P3C7 87.48(8), C1P3Br2 95.34(8) C1P3C7
87.16(1).
SCHEME 8 Cyclization of P(V) salt 15b into benzazaphosphole 10b.
(121.42 MHz) spectrometer. Chemical shifts (δ) are
reported in ppm relative to internal TMS (for 1H and
13C) and external 85% H3PO4 (for 31P). Chromatog-
raphy was performed on silica gel Gerudan SI60.
Elemental analyses were performed by the Micro-
analytical laboratory of the Institute of the Organic
Chemistry National Academy of Sciences, Ukraine.
gorithm [28, 29] was used with the accurate grid
parameters (Grid5, GridX6). For all optimized ge-
ometries, the vibrational analyses were carried out
numerically checking for an absence of imaginary
frequencies. Then, the structures were reoptimized
at the RI-MP2/TZVP [22] level of theory. The struc-
tures were presented graphically using the JMol pro-
gram [30].
X-Ray Investigations. Crystal data for 2a, 12b,
and 14b and details of the experiment are given in
the Supporting Information. CCDC-886698, CCDC-
886697, and CCDC-886696 contain the supplemen-
tary crystallographic data for these compounds.
These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of 2. To a solution of PBr3 (10 mmol)
in CH2Cl2 (40 mL), a solution of formamidine 1a,b
(30 mmol) in CH2Cl2 (30 mL) was added at –50°C
with stirring. The reaction mixture was allowed to
warm to 20°C, and the stirring was continued for 5 h.
The precipitated hydrobromide of formamidine 1a,b
was filtered off and washed with CH2Cl2 (2 × 20 mL).
The filtrate was evaporated, the residue was washed
with ether (2 × 20 mL), dried in vacuo, and dissolved
in THF (30 mL). The solution was filtered, the filtrate
was evaporated, and the residue was recrystallized
from CH3CN (18°C) to give yellowish crystals. Yield:
2a 2.91 g (56%), mp 139–140°C; 2b 2.99 g (53%), mp
143–145°C.
Quantum Chemical Calculations. All structures
were optimized using the ORCA program packet [26]
without any symmetry restriction. First, geometry
optimization was carried out using the TPSSh hy-
brid meta-GGA DFT method [20,21]. The TZVP basis
sets were used (the TZV basis sets of triple-zeta qual-
ity [27] plus one p-function set for hydrogen or one
d-function set for all other atoms). For the higher
efficiency of calculations, the parallel RIJCOSX al-
Phosphoranide 2a. 31P NMR (CDCl3): δ (ppm)
1
56.8; H NMR (500 MHz, CDCl3) δ 7.78 (d, J = 7.5
Heteroatom Chemistry DOI 10.1002/hc

Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-Nꢀ-arylformamidines 19
Hz, 1H, CH), 7.40–7.46 (m, 6H, CH), 7.29 (t, J = 8.0
Hz, 2H, CH), 7.16 (t, J = 7.0 Hz, 1H, CH), 6.41 (d,
J = 5.0 Hz, 1H, CH), 3.45 (s, 3H, NCH3), 2.55 (s, 3H,
NCH3), 2.34 (br s, 6H, NCH3); 13C NMR (CDCl3): δ
171.5 (d, J = 32 Hz, C3), 138.6 (d, J = 18 Hz, C),
137.1 (C), 130.2 (CH), 129.8 (CH), 129.7 (CH), 129.4
(CH), 128.5 (CH), 127.0 (CH), 126.4 (CH), 123.9 (d, J
= 6 Hz, CH), 106.0 (d, J = 15 Hz, C5H), 45.4 (NCH3),
45.2 (NCH3), 42.4 (NCH3). Anal. calcd % (Found)
for C18H23Br2N4P: C 44.47 (44.12), H 4.77 (4.47), N
11.52 (11.23), P 6.37 (6.01).
1,1-Bis(dimethylamino)-N,N-dimethyl-Nꢀ-(4-
methylphenyl)phosphinecarboximidamide Selenide
8b. Yield 76%, Rf 0.4–0.6 (CH2Cl2); mp 85–86°C.
1H NMR (500 MHz, CDCl3) δ 7.33 (d, 2H, J = 7.5
Hz), 6.68 (d, 2H, J = 8.0 Hz), 2.86 (s, 6H), 2.81 (d,
12H, J = 11.0 Hz), 2.29 (s, 3H) [18b].
Synthesis of 10. To a solution of PBr3 (0.01
mol) in CH2Cl2 (34 mL) at –50 °C, a solution of for-
mamidine 1a (1b) (0.02 mol) and Et3N (0.03 mol) in
CH2Cl2 (34 mL) was added with stirring. The temper-
ature of the reaction mixture was raised to 20°C for
5 min, kept for 1 h, and then cooled to –20°C, and a
solution of Me2NH (0.01 mol) in CH2Cl2 (5 mL) was
added. The reaction mixture was allowed to warm to
15°C and after 1 h, 31P NMR of the reaction mixture
confirmed the formation of benzaazphospholes 9 (δp
61 for both 9a and 9b) [18]. Selenium (0.87 g, 0.011
mol) was added and the reaction mixture was stirred
for 1 h; excess of selenium was filtered off. The fil-
trate was evaporated, and the residue was extracted
with benzene (3 × 10 mL). Benzene was evaporated
under reduced pressure and then formamidine 1a
(1b) (bp 75–80°C/0.05 Torr) was distilled off. The
residue was chromatographed on silica gel (eluent
CH2Cl2). For 10a,b, Rf 0.05–0.25 (CH2Cl2).
Phosphoranide 2b. 31P NMR (CDCl3): δ (ppm)
67.7; 1H NMR (500 MHz, CDCl3) δ 7.66 (dd, J1 = 8.0
Hz, J2 = 2.0 Hz, 1H, CH), 7.36 (d, J = 7.6 Hz, 2H, CH),
7.25–7.30 (m, 3H, CH), 7.12 (d, J = 8.4 Hz, 2H, CH),
6.33 (d, J = 5.2 Hz, 1H, CH), 3.47 (s, 3H, NCH3), 2.57
(s, 3H, NCH3), 2.20–2.40 (br s, 6H, NCH3), 2.38 (s,
3H, Ar-CH3), 2.28 (s, 3H, Ar-CH3); 13C NMR (CDCl3):
δ 171.8 (d, J = 36 Hz), 140.6, 136.5, 135.8 (d, J = 14
Hz), 134.0 (d, J = 1.25 Hz), 130.3 (d, J = 13 Hz),
130.0, 126.8, 124.1 (d, J = 6 Hz), 106.2 (d, J = 15
Hz), 45.3 (d, J = 22 Hz), 42.2, 21.3, 21.1. Anal. calcd
% (Found) for C20H27Br2N4P: C 46.71 (46.52), H 5.29
(5.01), N 10.89 (11.02), P 6.02 (6.38).
Synthesis of 8. To a solution of PBr3 (0.01 mol)
in CH2Cl2 (35 mL) at –50°C, a mixture of formami-
dine 1a (1b) (0.02 mol) and triethylamine (0.03 mol)
in CH2Cl2 (35 mL) was added with stirring. The tem-
perature of the reaction mixture was raised to 20°C
in 5 min and kept for 1 h. The reaction mixture was
cooled to 10°C and dimethylamine (0.08 mol) was
added. The reaction mixture was allowed to warm
to 20°C and stirred for 20 min. Finely ground sele-
nium was added and stirred for 10 min. The reaction
mixture was evaporated to dryness. The residue was
extracted with diethyl ether (3 × 25 mL), and the
ether was evaporated. From the solid residue, excess
formamidine 1a,b was distilled off (bp 100°C/0.05
Torr). The remained solid residue was recrystallized
from pentane, and the target product precipitated at
–10°C was collected by filtration to afford approxi-
mately 70% yield. The mother liquor was evaporated
and the residue was chromatographed using CH2Cl2
as an eluent to give additional 6–8% of the target
product.
N,N,Nꢀ,Nꢀ-Tetramethyl-3H-1,3-
benzazaphosphole-2,3-diamine
3-selenide
10a.
Yield 1.95 g (65%), mp 101–102°C. 31P NMR
1
(CDCl3): δ (ppm) 55.5; H NMR (500 MHz, CDCl3)
δ 7.30 (m, 2H, CH), 7.05 (m, 1H, CH), 6.96 (m, 1H,
CH), 3.32 (s, 3H, NCH3), 3.17 (s, 3H, NCH3), 2.71
(d, J = 12.4 Hz, 6H, NCH3); 13C NMR (CDCl3): δ
164.3 (d, J = 70 Hz, C2), 154.4 (d, J = 30 Hz, C5),
134.3 (CH), 127.5 (d, J = 14 Hz, CH), 123.4 (d, J =
12 Hz, CH), 121.4 (d, J = 116 Hz, C4), 120.2 (d, J =
6 Hz, CH), 38.9 (NCH3), 36.6 (d, J = 5 Hz, NCH3);
MS (APCI, 70 eV): m/z (%) = 301 (100) [M + H]+.
Anal. calcd % (Found) for C11H16N3PSe (300.20): C
44.01(44.12), H 5.37(5.42), N 14. 00 (13.89), P 10.32
(10.45).
N,N,Nꢀ,Nꢀ-Tetramethyl-4-methyl-3H-1,3-
benzazaphosphole-2,3-diamine
3-selenide
10b.
Yield 1.92 g (62%), mp 108–109°C. 31P NMR
1
(CDCl3): δ (ppm) 55.8; H NMR (500 MHz, CDCl3)
δ 7.09 (m, 2H, CH), 6.94 (m, 1H, CH), 3.29 (s, 3H,
NCH3), 3.14 (s, 3H, NCH3), 2.69 (d, J = 12.4 Hz,
6H, NCH3), 2.22 (s, 3H, CH3); 13C NMR (CDCl3): δ
163.9 (d, J = 71 Hz, C2), 152.0 (d, J = 29 Hz, C5),
135.1 (CH), 133.0 (d, J = 11 Hz, C), 127.8 (d, J =
14 Hz, CH), 126.3 (d, J = 116 Hz, C4), 119.9 (d, J =
6 Hz, CH), 38.8 (NCH3), 36.6 (d, J = 5 Hz, NCH3),
20.8 (CH3); MS (APCI, 70eV): m/z (%) = 315 (100)
1,1-Bis(dimethylamino)-N,N-dimethyl-Nꢀ-
phenylphosphinecarboximidamide
Selenide
8a.
Yield 78%, Rf 0.4–0.5 (CH2Cl2), mp 72–73°C (hex-
1
ane); H NMR (500 MHz, CDCl3) δ 7.22 (t, 2H, J =
7.5 Hz), 6.89 (t, 1H, J = 7.5 Hz), 6.76 (d, 2H, J = 7.50
Hz), 2.87 (s, 6H), 2.77 (d, 12H, J = 12.0 Hz) [18b].
Heteroatom Chemistry DOI 10.1002/hc

20 Marchenko et al.
[M + H]+. Anal. calcd % (Found) for C12H18N3PSe
(314.23): C 45.87 (45.64), H 5.77 (5.48), N 13.37
(13.01), P 9.86 (9.53).
NCH3), 2.89 (d, J = 11.6 Hz, 6H, NCH3); 13C NMR
(CDCl3): δ 152.8 (d, J = 158 Hz), 148.8 (d, J = 18
Hz), 139.6, 129.2, 128.7, 122.5, 121.3, 121.2, 118.7
(d, J = 6 Hz), 41.7 (d, J = 5 Hz), 36.8 (d, J = 5 Hz);
MS (APCI, 70 eV): m/z (%) = 394 (100) [M + H]+.
Anal. calcd % (Found) for C17H23N4PSe (393.33): C
51.91(51.99), H 5.89 (5.76), N 14.24 (14.01), P 7.87
(7.75).
Synthesis of 10 from 12. A solution of 12a (12b)
(0.5 mmol) in acetonitrile (3 mL) was heated in
a sealed tube for 5 h at 100°C. The precipitated
formamidine hydrobromide 1a (1b) was filtered
and the filtrate evaporated. The residue was chro-
matographed on silica gel (eluent CH2Cl2). Yield:
10a (96%), mp 101–102°C; 10b (92%), mp 108–
109°C.
1-Dimethylamino-1-(4-methylphenylamino)-
N,N-dimethyl-Nꢀ-4-methylphenylphosphine-
carboximidamide Selenide 11b. Yield 2.94
g
(68%), mp 152–153ºC. 31P NMR (CDCl3): δ (ppm)
41.8. 1H NMR (500 MHz, CDCl3) δ 7.79 (s, 1H,
NH), 7.11 (d, J = 7.5 Hz, 2H, CH), 7.07 (d, J = 7.5
Hz, 2H, CH), 6.90 (d, J = 7.5 Hz, 2H, CH), 6.82 (d,
J = 7.5 Hz, 2H, CH), 2.95 (s, 6H, NCH3), 2.91 (d, J
= 11 Hz, 6H, NCH3), 2.35 (s, 3H, ArCH3), 2.30 (s,
3H, ArCH3); 13C NMR (CDCl3): δ 152.9 (d, J = 159
Hz), 146.2 (d, J = 19 Hz), 137.0, 131.8, 130.6, 129.7,
129.2, 121.0, 118.6 (d. J = 6 Hz), 41.7 (d, J = 5 Hz),
36.8 (d, J = 5Hz), 20.9, 20.8. MS (APCI, 70 eV): m/z
(%) = 422 (100) [M + H]+. Anal. calcd % (Found)
for C19H27N4PSe (421.39): C 54.16(53.96), H 6.46,
(6.44), N 13.30 (13.02), P 7.35 (7.65).
Synthesis of 10b from 13b. To a solution of 12b
(0.5 mmol) in CH2Cl2 (5 mL) cooled to –50°C, a solu-
tion of tri-tert-butylphosphine (0.5 mmol) in CH2Cl2
(1 mL) was added. The reaction mixture was allowed
to warm to 10°C, kept 1.5 h and then selenium (0.5
mmol) was added. After 1 h, the solvent was evapo-
rated and the residue was chromatographed on silica
gel (eluent CH2Cl2). t-Bu3PSe Rf 0.3–0.5 (CH2Cl2),
yield 0.13 g (93%), mp 161–162°C. Compound 10b
Rf 0.05–0.1 (CH2Cl2), yield 0.13 g (83%), mp 108–
109°C.
Synthesis of 10 from 14. To a solution of 0.3
mmol of 14a (14b) in benzene (2 mL), dimethy-
lamine (0.05 g, 1.1. mmol) was added at 0°C with
stirring. The reaction mixture was stirred for 15 min
at 20°C, and then selenium (0.4 g, 0.5 mmol) was
added. After 2 h, the excess selenium was filtered
and the filtrate evaporated. The residue was chro-
matographed on silica gel (eluent CH2Cl2). Yield:
10a 0.08 g (86%), 10b 0.08 g (83%).
Reaction of 12a with Aniline. To a solution of
12a (1 g, 1.9 mmol) in CH2Cl2 (5 mL), aniline
(0.19 g, 2 mmol) was added and the reaction mix-
ture was heated in a sealed tube for 3 h at 80°C.
The precipitate formamidine hydrobromide 1a (0.4
g, 95%) was filtered off and the filtrate evaporated.
The residue was crystallized from acetonitrile at
−18°C. Yield 11a 0.69 g (93%).
Synthesis of 11. To a solution of PBr3 (0.01
mol) in CH2Cl2 (34 mL) at –50°C, a solution of for-
mamidine1a (1b) (0.02 mol) and Et3N (0.03 mol) in
CH2Cl2 (34 mL) was added. The temperature of the
reaction mixture was raised to 20°C for 5 min, kept
for 1 h, cooled to –20°C, and successively added sele-
nium (0.015 mol) and the solution of Me2NH (> 0.04
mol) in CH2Cl2 (5 mL). The reaction mixture was
heated to 20°C and stirring was continued for 1 h,
and then evaporated to dryness. The residue was ex-
tracted with diethyl ether (3 × 20 mL), the ether was
evaporated under vacuum, and the product was pu-
rified by crystallization at –10°C from diethyl ether.
Reaction of 12 with Dimethylamine. To a solu-
tion of 12a (12b) (5 mmol) in CH2Cl2 (15 mL), a so-
lution of dimethylamine (0.5 g, 11 mmol) in CH2Cl2
(4 mL) was added with stirring at 0°C. Stirring was
continued for 15 h at 15°C. The solvent was evapo-
rated to constant weight; the residue was extracted
with diethyl ether (6 × 25 mL). The ether extract was
evaporated, and the product 11a (11b) was crystal-
lized from acetonitrile at –18°C. Yield: 11a 1.82 g
(93%), 11b 1.8 g (90%). Insoluble in diethyl ether,
hexamethyltriaminomethane hydrobromide (1.16 g,
5 mmol) was suspended in ether (15 mL) and treated
with lithium dimetylamide (0.29 g, 5.6 mmol). The
mixture was stirred for 2 h at 15°C, and the solvent
was evaporated at 12 Torr. The residue was distilled
to give hexamethyltriaminomethane (0.45 g, 61%).
Bp 30–31°C/12 Torr.
1-Dimethylamino-1-phenylamino-N,N-dimethyl-
Nꢀ-phenylphosphine-carboximidamide Selenide 11a.
Yield 2.74 g (70%), mp 123–125ºC.31P NMR (CDCl3):
δ (ppm) 41.7; 1H NMR (500 MHz, CDCl3) δ 7.86
(s, 1H, NH), 7.20–7.27 (m, 4H, CH), 6.92–6.98 (m,
4H, CH), 6.88 (d, J = 7.6 Hz, 2H, CH), 2.92 (s, 6H,
Synthesis of 12a,b. To a solution of PBr3 (0.01
mol) in CH2Cl2 (34 mL), a solution of formamidine
Heteroatom Chemistry DOI 10.1002/hc

Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-Nꢀ-arylformamidines 21
1a (1b) (0.02 mol) and Et3N (0.03 mol) in CH2Cl2
(34 mL) was added at –50°C with stirring. The tem-
perature of the reaction mixture was raised to 20°C
for 5 min, kept for 1 h, cooled to –20°C, and succes-
sively added selenium (0.015 mol) and a solution of
Me2NH (0.02 mol) in CH2Cl2 (5 mL). The reaction
mixture was warmed to 15–20°C and kept stirring
for 1 h, and then evaporated to dryness. The residue
was washed with dry diethyl ether (30 mL), dried,
and washed with brine (NaBr) (20 mL). A solid por-
tion was filtered, dried, and dissolved in CH2Cl2 (20
mL), and an insoluble part was filtered off. The fil-
trate was evaporated in vacuum; the target product
was purified by crystallization from CH3CN.
Synthesis of 14. A solution of 2a,b (0.4 mmol)
in benzene (1 mL) was heated in a sealed tube for 1 h
(for 14a) or 1.5 h (for 14b) at 100°C. The precipitated
hydrobromide of 1a,b was filtered off, and the filtrate
was evaporated to give the target compound 14.
(3-Bromo-3H-benzo[1,3]azaphosphol-2-
yl)dimethylamine 14a. Red crystals, yield 0.09
1
g (90%), mp 71–75°C. 31P NMR (C6D6): δ 28.2; H
NMR (500 MHz, C6D6) δ 7.35–7.41 (m, 2H, CH),
7.03 (t, J = 7.5 Hz,1H, CH), 6.77 (m, 1H, CH), 2.74
(br. s, 3H, NCH3), 2.58 (br. s, 3H, NCH3); 13C NMR
(C6D6): δ 175.6 (d, J = 35.0 Hz, P-C-N), 161.9 (C),
133.4 (CH), 130.2 (d, J = 20.0 Hz, C), 130.1 (d, J =
28.0 Hz, CH), 122.0 (d, J = 5.0 Hz, CH), 119.6 (CH),
41.2 (br. s, NCH3), 37.8 (br. s, NCH3). Anal. calcd %
(Found) for C9H10BrN2P (257.07): C 42.05(41.75),
H 3.92(3.75), N 10.90 (10.64), P 12.05 (12.24).
(2,5-Bis-dimethylamino-1,4-diphenyl-2-
selenoxo-2λ5-[1,4,2]
diazaphospholidin-3-ylidene)-
dimethylamonium Bromide 12a. Yield 3.59
g
(80%), mp 193–194ºC (decomp.). 31P NMR (CDCl3):
1
δ (ppm) 45.1 (max), 49.4 (min); 14:1. H NMR (500
(3-Bromo-5-methyl-3H-benzo[1,3]azaphosphol-
MHz, CDCl3) δ 8.67 (d, J = 7.0 Hz, 1H, CH); 7.90 (s,
1H, C CH), 7.79 (d, J = 7.1 Hz, 2H, CH), 7.20–7.42
(m, 5H, CH), 7.11 (t, J = 7.5 Hz, 1H, CH), 7.06 (s, 1H,
2-yl)dimethyl-amine 14b. Red crystals, yield 0.08
1
g (80%), mp 93–95ºC. 31P NMR (C6D6): δ 33.0; H
NMR (500 MHz, C6D6) δ 7.32 (d, J = 8.0 Hz, 1H,
CH), 7.06 (m, 1H, CH), 6.90 (d, J = 8.0 Hz, 1H,
CH), 2.78 (br. s, 3H, NCH3), 2.62 (br. s, 3H, NCH3),
1.96 (s, 3H, CH3); 13C NMR (C6D6): δ 174.7 (d, J
= 35.0 Hz, P-C-N), 160.2 (C), 134.3 (CH), 131.2 (d,
J = 5.0 Hz, C), 130.4 (d, J = 28.0 Hz, CH), 129.8 (d,
J = 13.0 Hz, C), 119.6 (CH), 41.1 (br. s, NCH3), 37.8
(br. s, NCH3), 20.3 (CH3). Anal. calcd % (Found)
for C10H12BrN2P (271.10): C 44.31(43.96), H 4.46
(4.26), N 10.33(10.11), P 11.43 (11.83).
3
CH), 3.46 (s, 3H, NCH3), 2.89 (d, JP-H = 12.1 Hz,
6H, NCH3), 2.75 (s, H, NCH3), 2.11 (s, 6H, NCH3).
13C NMR (CDCl3): δ 158.0 (d, J = 57 Hz), 136.8 (d,
J = 5 Hz), 136.7, 130.3, 129.6, 129.4, 129.0, 128.5,
126.4, 126.0, 124.7, 96.5 (d, J = 5 Hz), 44.6, 41.6,
38.3 (d, J = 6 Hz). MS (APCI, 70 eV): m/z (%) = 450
(100) [M + H]+ (minus Br). Anal. calcd % (Found)
for C20H29BrN5PSe (529.32): C 45.38(45.18), H 5.52
(5.33), N 13.23(13.45), P 5.85 (6.02).
Synthesis of 15b. To a solution of 8b (0.01
mmol, 3.8 g) in CH2Cl2 (15 mL) at –20°C, a 10% solu-
tion of HCl in ether (5 mL) was added and stirred for
10 min at this temperature. The solvent was evapo-
rated, and the residue was washed with ether (2 ×
20 mL) and dried in vacuo (0.05 Torr) till constant
weight. Yield 3.6 g (92%), mp 151–152ºC. 31P NMR
(2,5-Bis-dimethylamino-1,4-di(4-methylphenyl)-
2-selenoxo-2λ5-[1,4,2]diaza-phospholidin-3-ylidene)-
dimethylamonium Bromide 12b. Yield 3.79
g
(79.5%), mp 188–190ºC (decomp.). 31P NMR
1
(CDCl3): δ (ppm) 45.4 (max), 49.5 (min); 5.4:1. H
NMR (500 MHz, CDCl3) δ 9.43 (s, 1H, N-CH), 8.38
(d, J = 7.5 Hz, 1H, CH), 7.64 (d, J = 8.0 Hz, 2H,
CH), 7.24 (d, J = 7.5 Hz, 1H, CH), 7.13 (d, J = 7.5
Hz, 1H, CH), 7.07 (d, J = 7.5 Hz, 2H, CH), 6.96 (d,
J = 6.5 Hz, 1H, CH), 3.49 (s, 3H, NCH3), 2.91 (d, J =
12.5 Hz, 6H, NCH3), 2.78 (s, 3H, NCH3), 2.53 (s, 3H,
NCH3), 2.30 (s, 3H, ArCH3), 2.23 (s, 3H, ArCH3),
2.13 (s, 6H, NCH3). 13C NMR (CDCl3): δ 158.0 (d, J
= 111 Hz), 140.1, 136.4, 134.1, 133.7 (d, J = 4 Hz),
131.0, 130.1, 129.1, 128.5, 125.9, 124.9, 96.5 (d, J
= 8 Hz), 44.3 (d, J = 2.5 Hz), 41.7 (d, J = 5 Hz),
38.2 (d, J = 6.0 Hz), 34.6, 21.2, 20.1. MS (APCI,
70 eV): m/z (%) = 478 (100) [M + H]+. Calcd.for
C22H33N5PSe 477 (minus Br). Anal. calcd % (Found)
for C22H33BrN5PSe (557.38): C 47.41(47.22), H 5.97
(5.86), N 12.56 (12.45), P 5.56 (5.64).
1
(CDCl3): δ 64.5; H NMR (500 MHz, CDCl3) δ 11.80
(br. s, 1H, NH), 7.40 (d, J = 8.1 Hz, 2H, CH), 7.17 (d,
J = 8.1 Hz, 2H, CH), 3.55 (br. s, 3H, NCH3), 2.95 (br.
s, 3H, NCH3), 2.92 (d, J = 11.4 Hz, 12H, NCH3), 2.31
(s, 3H, CH3); 13C NMR (CDCl3): δ 161.7 (d, J = 110.7
Hz, P–C=N), 137.3 (C), 134.9 (C), 129.7 (CH), 123.6
(CH), 45.4 (br. s, NCH3), 42.8 (br. s, NCH3), 38.0
(d, J = 4.0 Hz, P(NCH3)2), 20.8 (CH3). Anal. calcd %
(Found) for C14H26ClN4PSe (395.77): C 42.49(42.52),
H 6.62(6.37), N 14.16 (13.98), P 7.83 (7.57).
Synthesis of 10b from 15b. A solution of 15b
(0.68 g, 1.7 mmol) in acetonitrile (5 mL) was heated
in a sealed ampoule with stirring for 2 h at 100°C.
Heteroatom Chemistry DOI 10.1002/hc

22 Marchenko et al.
[11] Kilian, P.; Knight, F. R.; Woollins, J. D. Chemistry
2011, 17, 2302–2328.
[12] Wawrzyniak, P.; Fuller, A. L.; Slawin, A. M. Z.; Kilian,
P. Inorg Chem 2009, 48, 2500–2506.
[13] Carre´, F. H.; Chuit, C.; Corriu, R. J. P.; Douglas, W.
E.; Guy, D. M. H.; Reye´, C. Eur J Inorg Chem 2000,
2000, 647–653.
The solvent was evaporated, and the residue was ex-
tracted with benzene (3 × 5 mL). The solvent was
evaporated and the residue was chromatographed
on silica gel using CH2Cl2 as an eluent. Compound
10b Rf 0.05–0.1 (CH2Cl2), yield 0.32 g (60%).
[14] Chuit, C.; Reye´, C. Eur J Inorg Chem 1998, 1998,
1847–1857.
[15] Dillon, K. B. Chem Rev 1994, 94, 1441–1456.
[16] Ellis, B. D.; Macdonald, C. L. B. Coord Chem Rev
2007, 251, 936–973.
[17] Tolmachev, A. A.; Merkulov, A. S.; Oshovskii, G. V.
Chem Heterocycl Compd 1997, 33, 877–878.
[18] (a) Marchenko, A.; Koidan, H.; Hurieva, A.;
Merkulov, A.; Pinchuk, A.; Yurchenko, A.; Rozhenko,
A. B.; Jones, P. G.; Tho¨nnessen, H.; Kostyuk, A.
Tetrahedron 2011, 67, 7748–7758 (b) Marchenko, A.;
Koidan, H.; Hurieva, A.; Merkulov, A.; Pinchuk, A.;
Yurchenko, A.; Kostyuk, A. Tetrahedron 2010, 66,
3668–3677.
ACKNOWLEDGMENTS
The financial support from the Alexander von Hum-
boldt foundation (Germany) for A.B. Rozhenko for
technical equipment of the theoretical chemistry lab-
oratory is gratefully acknowledged. The authors also
thank the Institute of Cybernetic, NAS of Ukraine,
and the SKIT team for providing an access for A.B.R.
to the SKIT computer cluster.
REFERENCES
[19] Kuchitsu, K.; Shibata, T.; Yokozeki, A.; Matsumura,
C. Inorg Chem 1971, 10, 2584–2587.
[20] Tao, J.; Perdew, J.; Staroverov, V.; Scuseria, G. Phys
Rev Lett 2003, 91, 146401.
[1] Sheldrick, W. S.; Schmidpeter, A.; Zwaschka, F.; Dil-
lon, K. B.; Platt, A. W. G.; Waddington, T. C. J Chem
Soc, Dalton Trans 1981, 413.
[2] Christe, K. O.; Dixon, D. A.; Mercier, H. P. A.;
Sanders, J. C. P.; Schrobilgen, G. J.; Wilson, W. W. J
Am Chem Soc 1994, 116, 2850–2858.
[3] Shyshkov, O. A. Ph.D. Thesis; University of Bremen,
2006; 177 p.
[4] Karsch, H. H.; Witt, E.; Hahn, F. E. Angew Chem, Int
Ed 1996, 35, 2242–2244.
[5] Schwedtmann, K.; Holthausen, M. H.; Feldmann, K.-
O.; Weigand, J. J. Angew Chem, Int Ed 2013, 52,
14204–14208.
[21] Staroverov, V. N.; Scuseria, G. E.; Tao, J.; Perdew, J.
P. J Chem Phys 2003, 119, 12129.
[22] Weigend, F.; Ha¨ser, M.; Patzelt, H.; Ahlrichs, R. Chem
Phys Lett 1998, 294, 143–152.
[23] Mayer, I. Int
151–154.
J
Quantum Chem 1984, 26,
[24] Marchenko, A.; Koidan, G.; Hurieva, A.; Savateev, A.;
Rozhenko, A. B.; Sotiropoulos, J.-M.; Shishkina, S.
V.; Shishkin, O. V.; Kostyuk, A. Eur J Inorg Chem
2014, 2014, 1192–1203.
[6] Wang, Y.; Xie, Y.; Abraham, M. Y.; Gilliard, R. J.;
Wei, P.; Schaefer, H. F.; Schleyer, P.v.R.; Robinson,
G. H. Organometallics 2010, 29, 4778–4780.
[7] Dillon, K. B.; Platt, A. W. G.; Schmidpeter, A.;
Zwaschka, F.; Sheldrick, W. S. Z Anorg Allg Chem
1982, 488, 7–26.
[25] Marchenko, A.; Koidan, G.; Hurieva, A.; Kurpiieva,
O.; Vlasenko, Y.; Rozhenko, A. B.; Kostyuk, A. Eur J
Inorg Chem 2014, 2014, 3259–3270.
[26] Neese, F. Wiley Interdiscip Rev Comput Mol Sci
2012, 2, 73–78.
[27] Schäfer, A.; Huber, C.; Ahlrichs, R. J Chem Phys 1994,
[8] Mu¨ller, G.; Matheus, H.-J.; Winkler, M. Z Naturforsch
2001, 56b, 1155–1162.
[9] Mu¨ller, G.; Brand, J.; Jetter, S. E. Z Naturforsch 2001,
56b, 1163–1171.
[10] Surgenor, B. A.; Bu¨hl, M.; Slawin, A. M. Z.; Woollins,
J. D.; Kilian, P. Angew Chem, Int Ed 2012, 51, 10150–
10153.
100, 5829–5835.
[28] Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U.
Chem Phys 2009, 356, 98–109.
[29] Izsa´k, R.; Neese, F.
144105.
[30] Jmol: an open-source Java viewer for chemical struc-
tures in 3D. Available at http://www.jmol.org/.
J Chem Phys 2011, 135,
Heteroatom Chemistry DOI 10.1002/hc