Click reactions of 2H-azaphosphirene chromium and molybdenum complexes and a surprisingly facile access to a 2H-1,4,2-diazaphosphole derivative

Article abstract of DOI:10.1016/j.poly.2011.04.014

Ring expansion reactions of 2H-azaphosphirene chromium and molybdenum complexes 1a,b with dimethyl cyanamide, triflic acid, and, subsequently at ambient temperature, with triethylamine gave a mixture of the respective 2H-1,4,2-diazaphosphole complex 2a,b

Full text of DOI:10.1016/j.poly.2011.04.014

Polyhedron 30 (2011) 1799–1805
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Click reactions of 2H-azaphosphirene chromium and molybdenum complexes
and a surprisingly facile access to a 2H-1,4,2-diazaphosphole derivative
Holger Helten a, Gregor Schnakenburg b, Rainer Streubel b,
⇑
a School of Chemistry, University of Bristol, Cantock’s Close, Bristol, BS8 1TS, UK
b Institut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Ring expansion reactions of 2H-azaphosphirene chromium and molybdenum complexes 1a,b with
dimethyl cyanamide, triflic acid, and, subsequently at ambient temperature, with triethylamine gave a
mixture of the respective 2H-1,4,2-diazaphosphole complex 2a,b and the non-ligated heterocycle 3. If
the deprotonation with NEt3 was carried out at low temperature, the selective formation of complexes
2a,b was observed, which were isolated in excellent yields and fully characterized (including single-crys-
tal X-ray crystallography). Experimental and computational results revealed that the P, Cr and P, Mo
bonds of 2H-1,4,2-diazaphosphole complexes are significantly weakened upon N-protonation of the het-
erocyclic ligand. When mixtures of 1a,b, TfOH, and Me2NCN were warmed to ambient temperature, the
primarily formed N-protonated of 2H-1,4,2-diazaphosphole complexes 4a,b could be observed by 31P
NMR spectroscopy. The latter underwent decomplexation to give the N-protonated free ligand 5, which
could be isolated and characterized by multinuclear NMR experiments. The neutral non-ligated hetero-
cycle 3 was isolated from a one-pot reaction of 1b with TfOH and Me2NCN by adding NEt3 to a solution of
intermediately formed 5.
Received 1 January 2011
Accepted 6 April 2011
Available online 19 April 2011
Dedicated to Prof. F. Mathey on the occasion
of his 70th birthday
Keywords:
Azaphosphirene
Click reaction
Chromium
Molybdenum
Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction
achieved via formal insertion of a nitrile into the P–N bond of I
using trifluoromethane sulfonic acid (CF3SO3H; hereafter referred
The construction of N-heterocycles such as triazoles using click
reactions [1–5] based on facile and reliable synthetic protocols,
has received considerable interest during the last decade, as it
can be applied to various fields of research [6–8]. Nonetheless,
this chemistry has yet to be extended to heavier main group ele-
ment heterocycles. A promising approach to gain access to new
and novel phosphorus heterocycles [9,10] is the ring expansion
of small, strained heterocycles [11–16] by selective activation of
an endocyclic bond. In particular, the insertion of easily available
to as triflic acid or TfOH) and, subsequently, a nitrogen base such
as triethylamine was used for deprotonation [18–20].
We recently demonstrated that the new concept can also be
applied to the atom efficient synthesis of 2,3-dihydro-1,3-aza-
phosphete, 3H-1,3-azaphosphole, and 1,3,5-oxazaphosphol-3-ene
complexes via insertion of an isonitrile, an alkyne [21], or carbonyl
derivatives [22], respectively. Furthermore, we showed that it can
easily be extended to oxaphosphirane [23,24] and azaphosphiridine
[25] complex chemistry, thus establishing the click chemistry con-
cept to the field of strained phosphorus heterocycles; separation via
column chromatography is necessary, sometimes. Mechanistic
studies revealed that the heteroatom (N or O) of the respective
three-membered ring system is protonated in the first reaction step
[18,21,23–27], which leads to ring opening in the cases of 2H-aza-
phosphirene [18,21] and oxaphosphirane complexes [23,24,26,27].
In the case of azaphosphiridine complexes the protonated ring does
not open up spontaneously, but the P–N bond is activated towards
the attack of electron-rich nitriles [25].
diatomic
p-systems such as nitriles, alkynes, alkenes, or carbonyl
derivatives into endocyclic P,N bonds is a current challenge of
special interest. A recent report demonstrated that exocyclic PIII–
N bonds of cyclodiphosphazanes are even more reactive than
endocyclic bonds [17].
Recently, we developed a novel and facile methodology for the
ring expansion of three-membered P-heterocyclic ligands in the
coordination sphere of tungsten. For example, ring expansion of
2H-azaphosphirene complexes (I) [15,16] leading to 2H-1,4,2-
diazaphosphole complexes (II: a = b = RCN; Scheme 1) was
Herein, we report the extension of the new concept to reactions
of 2H-azaphosphirene chromium and molybdenum complexes,
which gives access – not only to 2H-1,4,2-diaza-phosphole chro-
mium and molybdenum complexes – but also to the free (N-pro-
tonated or neutral) ligands in a one-pot reaction.
⇑
Corresponding author. Tel.: +49 228 735345; fax: +49 228 739616.
E-mail addresses: jahns-streubel@t-online.de, r.streubel@uni-bonn.de (R. Streu-
bel).
0277-5387/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.014

1800
H. Helten et al. / Polyhedron 30 (2011) 1799–1805
NMR (121.5 MHz, C6D6): d = 146.3 (s); IR (KBr): nu(tilde) = 2959
(w, CH3/CH), 2931 (w, CH3/CH), 2901 (w, CH3/CH), 2855 (w, CH3/
CH), 2059 (m, sh, CO), 1981 (m, sh, CO), 1927 (s, CO), 1917 (s,
CO), 1606 (m, CN), 1538 cmÀ1 (w, CN); UV–Vis (n-pentane): kmax
(abs.) = 202 (sh, 0.901), 209 (sh, 1.012), 225 (1.217), 234 (sh,
1.156), 253 (sh, 0.951), 286 (0.458), 351 (0.102), 390 (0.082),
439 nm (sh, 0.049); MS (FAB+, 52Cr): m/z (%): 443.1 ([MÀ4CO]+,
76), 415.1 ([MÀ5CO]+, 100), 400.1 ([MÀ5COÀCH3]+, 46), 364.2
([M+HÀW(CO)5]+, 63); MS (EI, 52Cr): m/z (%): 555.1 ([M]+, 48),
540.1 ([MÀCH3]+, 29), 527.1 ([MÀCO]+, 11), 443.1 ([MÀ4CO]+,
52), 415.1 ([MÀ5CO]+, 100), 400.1 ([MÀ5COÀCH3]+, 67), 363.1
([MÀCr(CO)5]+, 36), 290.1 ([MÀCr(CO)5ÀSiMe3]+, 31), 73.0
([SiMe3]+, 48); elemental analysis (%) Anal. Calc. for
C22H30CrN3O5PSi2: C, 47.56; H, 5.44; N, 7.56. Found: C, 47.09; H,
5.66; N, 7.36%.
[W]
R
a
[W]
R
a
[W]
R
[W]
R
P
P
R'
R'
P
P
R''
R'
R''
E
b
E
N
b
N
R'
III
IV
I
II
Scheme 1. 2H-Azaphosphirene complexes (I), five-membered phosphorus hetero-
cyclic complexes II derived from I, oxaphosphirane and/or azaphosphiridine
complexes III, and five-membered phosphorus heterocycles IV derived from III
(a = b: p-system; [W] = W(CO)5; III, IV: E = O, NMe).
2. Experimental
2.1. General procedures
2.3. Synthesis of [2-bis(trimethylsilyl)methyl-5-dimethylamino-3-
phenyl-2H-1,4,2-diazaphosphole-jP]pentacarbonylmolybdenum(0)
(2b)
All manipulations were carried out in an atmosphere of purified
and dried argon using standard Schlenk techniques. Solvents were
dried over sodium wire or CaH2 (CH2Cl2) and distilled under argon.
2H-Azaphosphirene complexes 1a,b [28] were prepared according
to the method described in the literature. Dimethyl cyanamide was
purchased from Acros and distilled from CaH2. Melting points were
determined using a Büchi apparatus type S; the values are not cor-
rected. Elemental analyses were performed by using an Elementar
VarioEL instrument. UV–Vis absorption spectra were recorded on a
Shimadzu UV-1650 PC spectrometer (k = 190–1100 nm) from
n-pentane solution at ambient temperature and IR spectra were re-
corded as KBr pellets using a Thermo Nicolet 380 FT-IR spectrom-
To a stirred solution of 273 mg (0.52 mmol) of 2H-azaphosphi-
rene complex 1b in 7 mL of CH2Cl2 were added consecutively 45
(0.55 mmol) of dimethyl cyanamide and 46 L (0.52 mmol) of
TfOH at À30 °C while the initially yellow colored solution turned
deep red. After 2 min 74 L (0.53 mmol) of NEt3 was added while
l
L
l
l
the reaction mixture turned light orange. Then, all volatiles were
removed in vacuo (ꢀ10À2 mbar), and the product was purified by
column chromatography on silica (À30 °C, 2 Â 6 cm, petroleum
ether/Et2O: 100/1). Evaporation of the solvents of the first fraction
(ꢀ10À2 mbar) yielded 2b.
eter. NMR data were recorded on
a Bruker Avance 300
spectrometer at 30 °C using C6D6 or CD2Cl2 as solvent and internal
standard; coupling constants J are reported in Hz, chemical shifts
in ppm relative to tetramethylsilane (1H: 300.13, 13C: 75.5, 29Si:
2b: Yellow solid; yield: 274 mg (0.46 mmol, 89%); m.p.: 104 °C
(decomp.); 1H NMR (300.13 MHz, C6D6): d = À0.18 (ssat
,
,
|2JSiH| = 6.2 Hz, |1JCH| = 119.5 Hz, 9H; Si(CH3)3), 0.51 (ssat
59.6 MHz), nitromethane (15N: 30.4 MHz), and 85% H3PO4 31P:
(
|2JSiH| = 6.4 Hz, |1JCH| = 119.8 Hz, 9H; Si(CH3)3), 0.91 (d,
|2JPH| = 2.4 Hz, 1H; CH(SiMe3)2), 2.82 (s, 3H; NCH3), 2.98 (s, 3H;
NCH3), 7.16 (mc, 3H; meta + para-Hphenyl), 8.17 (mc, 2H; ortho-Hphe-
nyl); 13C{1H} NMR (75.5 MHz, C6D6): d = 3.1 (dsat, |3JPC| = 1.6 Hz,
|1JSiC| = 52.0 Hz; Si(CH3)3), 3.9 (dsat, |3JPC| = 2.6 Hz, |1JSiC| = 52.9 Hz;
Si(CH3)3), 21.4 (d, |1JPC| = 11.6 Hz; CH(SiMe3)2), 37.7 (s; NCH3),
37.7 (s; NCH3), 128.9 (s; meta-Cphenyl), 131.3 (d, |3JPC| = 2.6 Hz;
121.5 MHz). Mass spectra were recorded on a Kratos Concept 1H
(FAB+, mNBA) spectrometer or a MAT 95 XL Finnigan spectrometer
(EI, 70 eV); selected data are given.
2.2. Synthesis of [2-bis(trimethylsilyl)methyl-5-dimethylamino-3-
phenyl-2H-1,4,2-diazaphosphole-jP]pentacarbonylchromium(0) (2a)
ortho-Cphenyl), 133.1 (d, |2JPC| = 20.4 Hz; ipso-Cphenyl), 133.2 (s;
2+3
To a stirred solution of 250 mg (0.51 mmol) of 2H-azaphosphi-
rene complex 1a in 7 mL of CH2Cl2 were added consecutively 45
(0.55 mmol) of dimethyl cyanamide and 46 L (0.52 mmol) of
TfOH at À30 °C while the initially yellow colored solution turned
deep red. After 1 min 74 L (0.53 mmol) of NEt3 was added while
para-Cphenyl), 164.7 (d,
|
J | = 0.7 Hz; PNC), 201.3 (d,
PC
1+4
lL
|
J
PC
| = 29.7 Hz; PCN), 206.5 (d, |2JPC| = 8.4 Hz; COcis), 211.1 (d,
l
|2JPC| = 23.0 Hz; COtrans); 29Si{1H} NMR (59.6 MHz, C6D6): d = 2.2
(dsat
|2JPSi| = 11.8 Hz, |1JSiC| = 52.0 Hz), 2.3 (dsat |2JPSi| = 1.3 Hz,
,
,
l
|1JSiC| = 53.0 Hz); 31P NMR (121.5 MHz, C6D6): d = 122.7 (s); IR
(KBr): nu(tilde) = 2957 (w, CH3/CH), 2930 (w, CH3/CH), 2901 (w,
CH3/CH), 2855 (w, CH3/CH), 2070 (m, sh, CO), 1988 (m, sh, CO),
1952 (s, CO), 1929 (s, CO), 1919 (s, CO), 1604 (m, CN), 1538 cmÀ1
(w, CN); UV–Vis (n-pentane): kmax (abs.) = 208 (sh, 0.758), 228
(1.013), 234 (1.016), 250 (sh, 0.828), 286 (0.306), 348 (0.080),
396 nm (0.058); MS (FAB+, 98Mo): m/z (%): 602.0 ([M+H]+, 3),
545.1 ([MÀ2CO]+, 21), 447.0 ([M+HÀ5COÀCH3]+, 16), 364.2
([M+HÀW(CO)5]+, 100); MS (EI, 98Mo): m/z (%): 601.1 ([M]+, 4),
the reaction mixture turned light red. Then, all volatiles were re-
moved in vacuo (ꢀ10À2 mbar), and the product was purified by col-
umn chromatography on silica (À30 °C, 2 Â 6 cm, petroleum ether/
Et2O: 100/1). Evaporation of the solvents of the first fraction
(ꢀ10À2 mbar) yielded 2a.
2a: Orange solid; yield: 242 mg (0.44 mmol, 85%); m.p.: 110 °C;
1H NMR (300.13 MHz, C6D6): d = À0.19 (ssat
,
|2JSiH| = 6.5 Hz,
|2JSiH| = 6.5 Hz,
|1JCH| = 119.6 Hz, 9H; Si(CH3)3), 0.50 (ssat
,
|1JCH| = 119.7 Hz, 9H; Si(CH3)3), 1.02 (d, |2JPH| = 2.7 Hz, 1H;
CH(SiMe3)2), 2.80 (s, 3H; NCH3), 2.95 (s, 3H; NCH3), 7.16 (mc, 3H;
meta + para-Hphenyl), 8.15 (mc, 2H; ortho-Hphenyl); 13C{1H} NMR
573.1
([MÀCO]+,
11),
545.1
([MÀ2CO]+,
21),
447.0
([MÀ3COÀMe2NCN]+, 37), 363.2 ([MÀMo(CO)5]+, 94), 290.1
([MÀMo(CO)5ÀSiMe3]+, 84), 190.0 ([Me3SiPC(H)SiMe3]+, 22), 73.0
([SiMe3]+, 100); elemental analysis (%) Anal. Calc. for C22H30Mo-
N3O5PSi2: C, 44.07; H, 5.04; N, 7.01. Found: C, 44.20; H, 5.06; N,
6.85%.
(75.5 MHz, C6D6): d = 3.2 (dsat
,
|3JPC| = 1.9 Hz, |1JSiC| = 52.0 Hz;
Si(CH3)3), 4.1 (dsat, |3JPC| = 2.3 Hz, |1JSiC| = 53.0 Hz; Si(CH3)3), 22.5
(d, |1JPC| = 9.7 Hz; CH(SiMe3)2), 37.6 (s; NCH3), 37.7 (s; NCH3),
128.7 (s; meta-Cphenyl), 131.6 (d, |3JPC| = 1.6 Hz; ortho-Cphenyl),
133.1 (s; para-Cphenyl), 133.2 (d, |2JPC| = 20.7 Hz; ipso-Cphenyl),
2.4. Synthesis of 2-bis(trimethylsilyl)methyl-5-dimethylamino-3-
phenyl-2H-1,4,2-diazaphosphole (3)
1+4
163.7 (s; PNC), 200.5 (d,
|
J
| = 31.7 Hz; PCN), 217.4 (d,
PC
|2JPC| = 12.6 Hz; COcis), 222.0 (d, |2JPC| = 6.8 Hz; COtrans); 29Si{1H}
NMR (59.6 MHz, C6D6): d = 1.4 (dsat
|2JPSi| = 11.0 Hz,
|1JSiC| = 52.2 Hz), 2.3 (dsat |2JPSi| = 3.3 Hz, |1JSiC| = 53.0 Hz); 31P
,
To a stirred solution of 100 mg (0.19 mmol) of 2H-azaphosphi-
rene complex 1b in 4 mL of CH2Cl2 were added consecutively 16 lL
,

H. Helten et al. / Polyhedron 30 (2011) 1799–1805
1801
(0.20 mmol) of dimethyl cyanamide and 17
l
L (0.19 mmol) of
of TfOH at À60 °C while the initially yellow colored solution turned
deep red. The protonated intermediate 4a was identified by 31P
TfOH at À60 °C while the initially yellow colored solution turned
deep red. After 6 min the cooling bath was removed, and the reac-
tion mixture turned brownish while warming to room tempera-
ture. After 7 h the reaction mixture was cooled to À30 °C and
NMR
|
spectroscopy
J
| = 22.9 Hz, |2JPH| = 8.9 Hz).
PH
(121.5 MHz,
CH2Cl2):
d = 157.7
(d,
2+5
32
l
L (0.40 mmol, 2 equiv.) of pyridine was added. Subsequently,
2.7. X-ray crystallography
n-pentane was added while rigorous stirring and the formation
of a brownish precipitate was observed. After filtering off the pre-
cipitate, all volatiles were removed in vacuo (ꢀ10À2 mbar). Then
the crude product was dissolved in 17 mL of n-pentane and filtered
over a small amount of silanized silica gel at À50 °C. Evaporation of
the solvent (ꢀ10À2 mbar) gave 3.
Suitable single crystals of 2a,b were obtained from concentrated
n-pentane solutions upon decreasing the temperature from ambi-
ent temperature to +4 °C. Data were collected on a Nonius Kap-
paCCD diffractometer equipped with a low-temperature device
(Cryostream, Oxford Cryosystems) at 123 K using graphite mono-
3: Yellow oil; yield: 14.7 mg (0.04 mmol, 21%); 1H NMR
chromated Mo Ka radiation (k = 0.71073 Å). The structures were
(300.13 MHz, C6D6): d = 0.26 (s, 18H; Si(CH3)3), 0.75 (dsat
,
solved by Patterson methods (SHELXS-97) [29] and refined by full-
matrix least squares on F2 (SHELXL-97) [29]. All non-hydrogens were
refined anisotropically. The hydrogen atoms were localized by dif-
ference electron density determination and refined isotropically
using the riding model on the bound atoms. Absorption corrections
were carried out semi-empirically from equivalents (minimum/
maximum transmissions = 0.86208/0.89804 (2a) and 0.87878/
0.89913 (2b).
|2JPH| = 0.8 Hz, |2JSiH| = 8.8 Hz, 1H; CH(SiMe3)2), 3.11 (s, 6H;
N(CH3)2), 7.16 (mc, 3H; meta + para-Hphenyl), 8.01 (mc, 2H; ortho-
Hphenyl); 13C{1H} NMR (75.5 MHz, C6D6): d = 2.0 (brsat
,
|1JSiC| = 51 Hz; Si(CH3)3), 18.6 (dsat, |1JPC| = 56.9 Hz, |1JSiC| = 39.0 Hz;
CH(SiMe3)2), 38.2 (s; N(CH3)2), 128.5 (d, |3JPC| = 8.1 Hz; ortho-Cphe-
nyl), 129.1 (s; meta-Cphenyl), 131.4 (d, |5JPC| = 2.3 Hz; para-Cphenyl),
135.8 (d, |2JPC| = 15.8 Hz; ipso-Cphenyl), 167.4 (d, |2+3JPC| = 1.1 Hz;
PNC), 210.6 (d, |1+4JPC| = 52.4 Hz; PCN); 31P NMR (121.5 MHz,
C6D6): d = 95.4 (s).
2.7.1. Crystal structure data for complex 2a (C22H30CrN3O5PSi2)
Crystal
a = 9.2995(3), b = 12.7072(8), c = 11.6982(6) Å, b = 92.008(3),
V = 1381.53(12) Å3, Z = 2, calc = 1.336 mg mÀ3, 2hmax = 58°, col-
lected (independent) reflections = 11154 (6490), Rint = 0.0402,
= 0.594 mmÀ1
316 refined parameters, restraint, R1 (for
I > 2
size
0.52 Â 0.18 Â 0.18 mm,
monoclinic,
P21,
2.5. Synthesis of 2-bis(trimethylsilyl)-methyl-5-dimethylamino-3-
phenyl-2H-1,4,2-diazaphosphol-1-ium trifluoromethanesulfonate (5)
q
To a stirred solution of 100 mg (0.19 mmol) of 2H-azaphosphi-
rene complex 1b in 4 mL of CH2Cl2 were added consecutively 16
l
,
8
lL
r(I)) = 0.0346, wR2 (for all data) = 0.0621, S = 0.961, maxi-
(0.20 mmol) of dimethyl cyanamide and 17 L (0.19 mmol) of
l
mum/minimum residual electron density = 0.447/À0.379 e ÅÀ3
.
TfOH at À60 °C while the initially yellow colored solution turned
deep red. After 6 min the cooling bath was removed, and the reac-
tion mixture turned brownish while warming to room tempera-
ture. The protonated intermediate 4b was identified by 31P NMR
spectroscopy (121.5 MHz, CH2Cl2): d = 130.6 (d, |2+5JPH| = 22.9 Hz,
|2JPH| = 6.4 Hz). After 7 h n-pentane was added under rigorous stir-
ring and the formation of a light green precipitate was observed,
which was filtered, washed with n-pentane, and dried in vacuo
(ꢀ10À2 mbar) to give 5.
2.7.2. Crystal structure data for complex 2b (C22H30MoN3O5PSi2)
Crystal
a = 9.3471(5), b = 12.7344(11), c = 11.8746(9) Å, b = 93.523(4),
V = 1410.76(18) Å3, Z = 2, calc = 1.411 mg mÀ3, 2hmax = 58°, col-
lected (independent) reflections = 10766 (6251), Rint = 0.0465,
= 0.641 mmÀ1
317 refined parameters, restraint, R1 (for
I > 2
size
0.60 Â 0.08 Â 0.08 mm,
monoclinic,
P21,
q
l
,
1
r
(I)) = 0.0380, wR2 (for all data) = 0.0676, S = 0.713, maxi-
mum/minimum residual electron density = 0.434/À0.438 e ÅÀ3
.
5: Light green solid; yield: 85 mg (0.17 mmol, 88%); 1H NMR
(300.13 MHz,
CD2Cl2):
d = 0.01
(ssat
,
|2JSiH| = 6.5 Hz,
|4JPH| = 0.7 Hz,
2.8. Computational methods
|1JCH| = 120.7 Hz, 9H; Si(CH3)3), 0.27 (dsat
,
|1JCH| = 118.3 Hz, 9H; Si(CH3)3), 0.93 (d, |2JPH| = 4.0 Hz, 1H;
DFT calculations were carried out with the TURBOMOLE V5.9.1 pro-
gram package [30]. Optimizations [31] were done with the local
Slater-Dirac exchange [32,33] and the correlation energy density
functional (No.V) by Vosko, Wilk, and Nusair (VWN (V)) [34] to-
gether with Becke’s gradient corrected exchange functional B88
[35] in combination with the gradient corrected correlation func-
tional by Perdew (P86) [36] within the RI (Resolution of the Iden-
tity) approximation [37–39] (hereafter referred to as RI-BP86). The
split valence shell basis set SV(P) [40] was used for all atoms, and
the inner shell electrons of molybdenum and tungsten were substi-
tuted by the scalar-relativistic effective core potential ECP-28-
MWB or ECP-60-MWB [41], respectively. The influence of the polar
solvent was taken into account by employing the COSMO approach
5+6
CH(SiMe3)2), 3.49 (d,
|
J | = 2.6 Hz, 3H; NCH3), 3.67 (d,
PH
5+6
|
J | = 1.7 Hz, 3H; NCH3), 7.62 (mc, 2H; meta-Hphenyl), 7.75 (mc,
PH
1H; para-Hphenyl), 7.95 (mc, 2H; ortho-Hphenyl), 9.78 (d,
2+5
|
J
| = 28.3 Hz, h1/2 = 9.1 Hz, 1H; NH); 13C{1H} NMR (75.5 MHz,
PH
CD2Cl2): d = 1.3 (dsat, |3JPC| = 7.8 Hz, |1JSiC| = 52.4 Hz; Si(CH3)3), 1.9
(dsat
|3JPC| = 3.2 Hz, |1JSiC| = 52.5 Hz; Si(CH3)3), 21.1 (d,
,
|1JPC| = 63.7 Hz; CH(SiMe3)2), 39.6 (d, |4+5JPC| = 1.3 Hz; NCH3), 41.1
(d, |4+5JPC| = 1.9 Hz; NCH3), 120.7 (q, |1JFC| = 319.7 Hz; CF3), 129.8
(d, |3JPC| = 10.3 Hz; ortho-Cphenyl), 129.9 (s; meta-Cphenyl), 132.6 (d,
|2JPC| = 17.8 Hz; ipso-Cphenyl), 135.7 (d, |5JPC| = 1.6 Hz; para-Cphenyl),
165.9 (d, |2+3JPC| = 0.4 Hz; PNC), 211.8 (d, |1+4JPC| = 40.4 Hz; PCN);
15N NMR (30.418 MHz, CD2Cl2): d = À277 (NMe2), À276
(|1+4JPN| = 28 Hz, |1JNH| = 91 Hz; N1H); 29Si{1H} NMR (59.6 MHz,
CD2Cl2): d = 5.3 (d, |2JPSi| = 3.5 Hz), 5.8 (d, |2JPSi| = 17.4 Hz); 31P
NMR (121.5 MHz, CD2Cl2): d = 100.7 (d, |2JPH| = 28.0 Hz).
[42] with e = 8.93. For cavity construction the atomic radii of Bond
[43], obtained from crystallographic data, were used; the atomic
radius of tungsten was set to 2.2230 Å. The stationary points were
characterized by numerical vibrational frequencies calculations
[44–46]. Single point calculations were carried out with the same
density functional combination but with the valence-triple-f basis
set TZVP [47], ECP-28-MWB for molybdenum, and ECP-60-MWB
for tungsten. The COSMO approach was employed with the same
parameters as used for optimizations. Zero point corrections and
thermal corrections to free energies were adopted from frequen-
cies calculations on the optimization level.
2.6. Reaction of [2-bis(trimethylsilyl)methyl-3-phenyl-2H-
azaphosphirene-jP]pentacarbon-ylchromium(0) (1a) with dimethyl
cyanamide and trifluoromethanesulfonic acid
To a stirred solution of 97 mg (0.20 mmol) of 2H-azaphosphi-
rene complex 1a in 4 mL of CH2Cl2 were added consecutively
16 lL (0.20 mmol) of dimethyl cyanamide and 17 lL (0.19 mmol)

1802
H. Helten et al. / Polyhedron 30 (2011) 1799–1805
1) TfOH
–30 °C -> r.t.
2) NEt3
(OC)5M
Ph
CH(SiMe3)2
CH(SiMe3)2
P
P
Ph
N
N
+
– [Et3NH][OTf]
N
N
i)
NMe2
NMe2
(OC)5M
Ph
CH(SiMe3)2
+ Me2NCN
3
2a,b
P
CH2Cl2
N
exo
1) TfOH
–30 °C
2) NEt3
(OC)5M
CH(SiMe3)2
1a,b
ii)
2
P
3
N1
Ph
N4
5
– [Et3NH][OTf]
1a, 2a: M = Cr
1b, 2b: M = Mo
NMe2
2a,b
Scheme 2. Synthesis of 2H-1,4,2-diazaphosphole complexes 2a,b.
3. Results and discussion
With the aim of preparing the 2H-1,4,2-diazaphosphole com-
plexes 2a,b, a CH2Cl2 solution of 2H-azaphosphirene complex 1a
or 1b [28], respectively, and dimethyl cyanamide was treated with
triflic acid and, subsequently, with triethylamine (Scheme 2).
When the acid was added either at ambient temperature or at
À30 °C and the reaction mixture was then warmed to room tem-
perature (i), after the addition of NEt3 31P{1H} NMR spectroscopic
monitoring revealed the resonance of the free 2H-1,4,2-diaza-
phosphole ligand 3 (d = 95.4) besides that of the desired product
2a,b. During the addition of TfOH initially intensely red colored
solutions were formed, but upon warming up, the solutions turned
greenish brown, which also served as a visual indication for the on-
set of decomplexation.
By careful control of the reaction conditions the decomplex-
ation could completely be prevented. When the addition of TfOH
was carried out at about À30 °C and deprotonation with NEt3
was performed within few minutes, 2H-1,4,2-diazaphosphole
complexes 2a,b were the only reaction products observed by
31P{1H} NMR spectroscopy (ii, Scheme 2). Complexes 2a,b were
purified by low-temperature column chromatography and ob-
tained in excellent yields (85% and 89%, respectively). They were
characterized by multinuclear NMR experiments, mass spectrome-
try, IR and UV–Vis spectroscopy, and single-crystal X-ray diffrac-
tion studies (Fig. 1).
The NMR spectroscopic data of 2a,b are best compared to those
of their pentacarbonyl tungsten analogue 2c, which we reported
recently [18,48]. The 31P{1H} resonance of 2b appears about
21 ppm downfield from that of 2c, and complex 2a resonates fur-
ther 24 ppm at lower field (Table 1), which is a common trend
for tungsten, molybdenum, and chromium complexes of a given
class of ligands [49,50]. The 13C{1H} NMR data for the heterocyclic
ligand of 2a–c are almost unaffected by variation of the metal. As
anticipated, the carbonyl carbon resonances show a stronger
dependance on variation of the transition metal: the d values con-
tinuously increase within the series M = W < Mo < Cr for both the
cis- and the trans-CO carbon centers. In 2a the trans-CO carbon
has a smaller phosphorus–carbon coupling constant magnitude
than the cis-CO groups, which is also a common feature of penta-
carbonyl phosphane chromium complexes [49,50].
C18
M
C1
C2
P
N1
C3
N2
N3
SI2
SI1
Fig. 1. Molecular structure of complex 2a (M = Cr) in the crystal (50% probability
level, hydrogen atoms are omitted for clarity). Selected bond lengths [Å] and angles
in [°]: Cr–C18 1.870(2), Cr–P 2.4208(6), P–C3 1.828(2), P–N2 1.682(2), P–C1
1.887(2), C1–N1 1.292(3), C2–N2 1.311(2), C2–N3 1.337(3), N2–P–C1 90.35(10), P–
C1–N1 109.18(18), C1–N1–C2 110.16(18), N1–C2–N2 120.8(2), C2–N2–P
108.93(18), N2–C2–N3 122.1(2). For isotypic complex 2b (M = Mo): Mo–C18
2.003(4), Mo–P 2.5487(10), P–C3 1.830(4), P–N2 1.673(3), P–C1 1.877(4), C1–N1
1.293(5), C2–N2 1.315(5), C2–N3 1.341(6), N2–P–C1 90.91(17), P–C1–N1 109.2(3),
C1–N1–C2 110.0(3), N1–C2–N2 120.8(4), C2–N2–P 108.7(3), N2–C2–N3 123.0(4).
Table 1
Comparison of selected NMR spectroscopic data for chromium, molybdenum, and
tungsten complexes 2a–c, ligand 3, and N-protonated ligand 5.
2aa
2ba
2ca,b
3a
5c
dP
146.3
22.5
9.7
200.5
31.7
163.7
0.8
217.4
12.6
222.0
6.8
122.7
21.4
11.6
201.3
29.7
164.7
0.7
206.5
8.4
211.1
23.0
101.8
22.0
5.8
200.3
25.5
165.0
–
198.6
6.5
199.6
22.3
95.4
18.6
56.9
210.6
52.4
167.4
1.1
–
100.7
21.1
63.7
211.8
40.4
165.9
0.4
–
–
–
–
dC(Cexo
)
|1JPC|/Hz
dC(C3)
1+4
|
J
|/Hz
PC
dC(C5)
The IR spectra of 2a,b showed the characteristic C„O stretch
vibration bands for M(CO)5 complexes with slightly perturbed
C4v symmetry. They both show a single, well-separated band at
2059 (2a) or 2070 cmÀ1 (2b), respectively, assigned to an A1 vibra-
2+3
|
J
PC
|/Hz
dC(COcis
)
|2JPC|/Hz
dC(COtrans
|2JPC|/Hz
–
–
–
)
tion. Another band with low intensity appears at 1980–1990 cmÀ1
,
assigned to a normal mode of local B1 symmetry. In the range of
1900–1950 cmÀ1 two or three very intense and partially overlap-
ping bands appear, which are attributable to vibrations of local
a
b
c
In C6D6.
From Ref. [18].
In CD2Cl2.

H. Helten et al. / Polyhedron 30 (2011) 1799–1805
1803
A1 and E symmetry. Two bands assigned to C–N stretch vibrations
were observed at around 1605 and 1540 cmÀ1
In the UV–Vis spectra both complexes 2a,b show two
obviously, it occurred from protonated, intermediately formed
2H-1,4,2-diazaphosphole complexes.
.
p–
p⁄
To investigate the influence of the triflate anion on the decom-
plexation reaction in the absence of any Brønsted acid, complex 2b
was reacted in methylene chloride with [nBu4N][OTf]. Also here,
the resonance of the liberated ligand 3 was detected, but the
decomplexation was significantly slower than in the presence of
the acid; after 24 h the reaction mixture still contained 81% of
unreacted 2b and approximately 19% of 3.
In order to get more insight into the effects of protonation of
2H-1,4,2-diazaphosphole complexes, the isodesmic reactions (A)
and (B) were calculated using DFT methods (Table 2). These model
reactions provide information on the change in the metal–phos-
phorus bond strengths induced by N-protonation of 2H-1,4,2-
diazaphosphole complexes as they describe the transfer of a penta-
carbonyl metal fragment from a cationic to a neutral ligand system
[51]. Here, the cationic complexes in reactions (A) were used as
models for N1-protonated complexes; reactions (B) were calcu-
lated to estimate the effect of (hypothetical) N4-protonation. The
main result is that all reactions are thermodynamically favored,
which points to a weakening of the metal–phosphorus bonds upon
protonation.
By taking advantage of this effect, 2H-1,4,2-diazaphosphole 3
was synthesized in a one-pot reaction from complex 1b and
Me2NCN via treatment with triflic acid in methylene chloride.
When pyridine was added after several hours, heterocycle 3 was
obtained as the only phosphorus-containing product (Scheme 3).
By 31P NMR spectroscopic monitoring of reactions of 1a,b with
TfOH and dimethyl cyanamide evidence was obtained for the for-
mation of N1-protonated 2H-1,4,2-diazaphosphole complexes 4a
(d = 157.7, |2+5JPH| = 22.9 Hz) and 4b (d = 130.6, |2+5JPH| = 22.9 Hz)
in the primary reaction step (Scheme 3 and Fig. 2). Their reso-
nances are slightly downfield from those of the respective neutral
complexes 2a,b (4a: d = 157.7; 4b: d = 130.6) and show large phos-
phorus–proton couplings about 23 Hz in magnitude as observed
also for N1-protonated complexes cf. [18,19,22]. During the reac-
tions of both complexes these signals decreased in favor of a reso-
nance at d = 100.7 (|2JPH| = 28.0 Hz). Adding of cold n-pentane
yielded a light green precipitate, which, after workup, was identi-
fied as the 2H-1,4,2-diazaphospholium 5 by multinuclear NMR
and diverse shift-correlated 2D NMR experiments (Table 1).
The 31P resonance of the neutral ligand 3 appears 27.3 ppm up-
field from complex 2b (Table 1), but only slightly upfield from that
of its tungsten complex (2c: d = 101.8 [18]). The 13C NMR chemical
shifts of the 2H-1,4,2-diazaphosphole ring carbons are almost
absorption bands at similar wavelengths (286 and ca. 350 nm for
both complexes). Furthermore, they show a low-energy absorp-
tion, which is, on the basis of recently published results on related
systems [19], assigned to a metal-diazaphosphole-ligand charge
transfer (MLCT) process. It is noteworthy that this band is in the
case of the chromium complex 2a at significantly longer wave-
length. As a result also its optical end absorption appears at longer
wavelength (kmax = 439 nm; konset = 554 nm; cf. 2b: kmax = 396 nm;
konset = 508 nm, 2c: kmax = 407 nm; konset = 505 nm).
Complexes 2a,b (and also 2c) crystallize in the monoclinic
space group P21 and are isotypic; apart from their pentacarbonyl
metal fragments they exhibit almost identical bond lengths and
angles. The 2H-1,4,2-diazaphosphole rings are essentially planar
(mean deviations from least-squares planes: 0.033 Å (2a) and
0.027 (2b)) and, to a large extent, coplanar arranged with the
adjacent phenyl ring (twist angles: 7.6 (2a) and 8.6 (2b)). The
dimethylamino nitrogen atoms are almost perfectly trigonal pla-
nar coordinated (R< 360.0° (2a) and 359.9° (2b)) and the planes
of the NMe2 groups do not deviate significantly from the regres-
sion plane of the respective diazaphosphole ring (twist angles:
6.4° (2a) and 5.1° (2b)).
Insight into metal–phosphorus bond strengths of 2H-1,4,2-
diazaphosphole complexes was obtained from FAB-(positive
mode) and EI-mass spectra. While in the case of the chromium
complex 2a m/z 415 assigned to [2a-5CO]Å+ represented the base
peak of the FAB spectrum, the signal of protonated heterocycle
[3 + H]+ (m/z 364) was the base peak of the spectrum of molybde-
num complex 2b. Similar results were obtained also for 2H-1,4,2-
diazaphosphole tungsten complexes (e.g. 2c), but for complex 2b
this signal clearly dominated the spectrum while the abundance
of the molecular ion ([2b + H]+: m/z 602) was only 3%; for 2a the
molecular cation was not even detected by FAB-MS. Under EI con-
ditions, also loss of SiMe3 and methyl groups as well as ring frag-
mentations were observed for 2a,b. Furthermore, the radical
cationic heterocycle [3]Å+ was detected (m/z 363), in the spectrum
of complex 2a as the base peak.
From these results it can be concluded that the Cr,P and Mo,P
bonds of 2a,b are more labile than the W,P bond of 2c, and, more
important, the metal–phosphorus bonds become significantly
weakened through protonation of the heterocyclic ligand. This
may serve as an explanation why fast decomplexation was ob-
served in reactions of 1a,b with Me2NCN and TfOH (Scheme 2, i);
Table 2
Calculated thermochemical data for isodesmic W(CO)5 exchange reactions (RI-BP86/TZVP/ECP-28-MWB(Mo)/ECP-60-MWB(W), COSMO
(e
= 8.93)//RIBP86/SV(P)/ ECP-28-
MWB(Mo)/ECP-60-MWB(W), COSMO (
e
= 8.93); all values in kJ molÀ1).
Me
Me
N
(OC)5M
Me
Me
N
(OC)5M
Me
Me
N
P
P
P
P
P
P
H
Me
Me
Me
N
H
+
+
A)
B)
+
+
N
N
N
N
N
Me
Me
Me
Me
Me
Me
N
(OC)5M
Me
Me
N
(OC)5M
Me
Me
N
P
P
Me
N
N
N
N
Me
Me
Me
Me
H
H
A
B
M
Cr
Mo
W
DRE0
DRH298
À36.4
À34.4
À35.7
DRG298
À37.9
À35.3
À37.3
DRE0
DRH298
À33.0
À31.2
À32.7
DRG298
À35.6
À32.2
À34.4
À37.4
À35.0
À36.3
À34.0
À32.0
À33.4

1804
H. Helten et al. / Polyhedron 30 (2011) 1799–1805
(OC)5M
CH(SiMe3)2
H
CH(SiMe3)2
(OC)5M
Ph
TfOH
CH2Cl2, –60 °C -> r.t.
P
Ph
P
N
+ Me2NCN
TfO
N
N
NMe2
1a,b
4a,b
CH(SiMe3)2
CH(SiMe3)2
P
P
Ph
pyridine
H
Ph
N
N
TfO
– "M(CO)5"
– [PyH][OTf]
N
N
NMe2
NMe2
3
5
1a, 4a: M = Cr
1b, 4b: M = Mo
Scheme 3. Consecutive reaction of 2H-azaphosphirene complexes 1a,b with dimethyl cyanamide, TfOH, and pyridine.
Fig. 2. 31P{1H} NMR spectra recorded during the reaction of 1b with Me2NCN and TfOH (Scheme 3). Expansions of the resonances from proton-coupled 31P NMR spectra show
signal splitting due to 31P, 1H coupling.
unaffected by decomplexation. On the other hand, all phosphorus–
carbon coupling constant magnitudes are significantly increased,
except for |2+3JPC| of C5 where the effect is negligible. Noteworthy
is that the NMe2 moiety shows only one 1H and 13C resonance
for both methyl groups, thus pointing to a fast rotation about the
exocyclic C5,N bond in solution. This is in marked contrast to com-
plexes 2a–c. Interestingly, 3 also shows only one resonance corre-
sponding to the trimethylsilyl groups in 1H and 13C{1H} NMR
spectra. According to calculations on DFT niveau [52,53] this is
due to a fast inversion of the pyramidal phosphorus center in 3
CH(SiMe3)2
P2
δN = –276, |1+4J PN | = 28 Hz,
|1J PH | = 91 Hz
TfO
3
N1
Ph
H
N4
5
NMe2
δN = –277
5
Fig. 3. Assignment of the 15N NMR spectroscopic data for N1-protonated 2H-1,4,2-
diazaphosphole 5 (CD2Cl2).
(
R<(PR3) 306.2°) [54]; the activation barrier was predicted to be
only
D
G– = 54.9 kJ molÀ1
.
Comparison of the NMR data for 5 and its neutral congener 3 re-
veals that the 31P NMR chemical shift is slightly increased (by
5.3 ppm), while the 13C{1H} NMR data are almost unaffected by
protonation. The constitution of 5 was further supported by 1H,
15N HMQC NMR experiments; the assignment of the 15N NMR data
is shown in Fig. 3. The data for 5 are comparable to those that were
found for its tungsten complex (also protonated at N1;
d(N1) = À264, |1+4JPN| = 15 Hz; d(NMe2) = À269) cf. [18]. Also here,
the protonated nitrogen atom showed a long-range correlation
with the CH proton of the bis(trimethylsilyl)methyl group.
Unlike 3, the protonated heterocycle 5 shows two sets of reso-
nances corresponding to the SiMe3 groups in 1H, 13C{1H}, and
29Si{1H} NMR spectra; the barrier of inversion about phosphorus
is in 5 significantly higher (
D
G– = 75.5 kJ molÀ1
;
R<(PR3) 305.2°)
[52]. Presumably, the perturbation of the cyclic 6
p
-electron system
in the planar transition structure by the dimethylamino-nitrogen
lone pair is more pronounced for the cationic system 5 than for 3
(see Supporting Information). Furthermore, in the spectra of 5
two sets of 1H and 13C resonances were detected for the NMe2 sub-
stituent. This observation is easily understood, since rotation about

H. Helten et al. / Polyhedron 30 (2011) 1799–1805
[14] N.H. Tran Huy, L. Ricard, F. Mathey, Organometallics 26 (2007) 3614.
1805
the exocyclic C5,N bond should be restricted through formation of a
[15] R. Streubel, Coord. Chem. Rev. 227 (2002) 175.
[16] R. Streubel, Top. Curr. Chem. 223 (2003) 92.
more pronounced
p interaction between the dimethylamino-nitro-
gen and C5 due to protonation at N1.
[17] P. Chandrasekaran, J.T. Mague, M.S. Balakrishna, Tetrahedron Lett. 48 (2007)
5227.
[18] H. Helten, M. Engeser, D. Gudat, R. Schilling, G. Schnakenburg, M. Nieger, R.
Streubel, Chem. Eur. J. 15 (2009) 2602.
4. Conclusions
[19] H. Helten, J. Daniels, M. Nieger, R. Streubel, New J. Chem. 34 (2010) 1593.
[20] H. Helten, G. Schnakenburg, J. Daniels, A.J. Arduengo III, R. Streubel,
Organometallics 30 (2011) 84.
[21] H. Helten, G. von Frantzius, G. Schnakenburg, J. Daniels, R. Streubel, Eur. J.
Inorg. Chem. (2009) 2062.
[22] R. Streubel, J. Marinas Pérez, H. Helten, J. Daniels, M. Nieger, Dalton Trans. 39
(2010) 11445.
[23] H. Helten, J. Marinas Pérez, J. Daniels, R. Streubel, Organometallics 28 (2009)
1221.
[24] J. Marinas Pérez, H. Helten, G. Schnakenburg, R. Streubel, Chem. Asian J. 2011,
doi:10.1002/asia.201000861.
[25] S. Fankel, H. Helten, G. von Frantzius, G. Schnakenburg, J. Daniels, V. Chu, C.
Müller, R. Streubel, Dalton Trans. 39 (2010) 3472.
[26] J. Marinas Pérez, H. Helten, B. Donnadieu, C.A. Reed, R. Streubel, Angew. Chem.
122 (2010) 2670;
J. Marinas Pérez, H. Helten, B. Donnadieu, C.A. Reed, R. Streubel, Angew. Chem.,
Int. Ed. 49 (2010) 2615.
[27] J. Marinas Pérez, C. Albrecht, H. Helten, G. Schnakenburg, R. Streubel, Chem.
Commun. 46 (2010) 7244.
[28] R. Streubel, F. Ruthe, P.G. Jones, Eur. J. Inorg. Chem. (1998) 571.
[29] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[30] R. Ahlrichs, M. Bär, M. Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 162 (1989)
165.
It was shown that the newly established protocol for the ring
expansion of three-membered P-heterocycle complexes using tri-
flic acid and NEt3 can successfully be applied to the synthesis of
2H-1,4,2-diazaphosphole chromium and molybdenum complexes
via highly selective reactions; complexes 2a,b were isolated in
excellent yields. Additionally, depending on the specific reaction
conditions, this provides facile access to non-ligated 2H-1,4,2-
diazaphosphole ligands (N-protonated or neutral) in a one-pot
reaction from the same precursors. This opens up options to apply
these newly accessible heterocycles to further modification/func-
tionalization and/or to use them in coordination chemistry. Cur-
rent investigations aim at broadening the application of this click
protocol by using other three-membered phosphorus heterocycles
and p-substrates.
Acknowledgements
[31] M.V. Arnim, R. Ahlrichs, J. Chem. Phys. 111 (1999) 9183.
[32] P.A.M. Dirac, Proc. R. Soc. (London) A 123 (1929) 714.
[33] J.C. Slater, Phys. Rev. 81 (1951) 385.
[34] S.H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 58 (1980) 1200.
[35] A.D. Becke, Phys. Rev. A 38 (1988) 3098.
[36] J.P. Perdew, Phys. Rev. B 33 (1986) 8822.
[37] K. Eichkorn, O. Treutler, H. Öhm, M. Häser, R. Ahlrichs, Chem. Phys. Lett. 240
(1995) 283.
Financial support by the Deutsche Forschungsgemeinschaft, the
SFB 624 ‘‘Template’’, the Fonds der Chemischen Industrie (Kekulé
grant for H. Helten) and the cost action CM0802 ‘‘PhoSciNet’’ is
gratefully acknowledged. We also thank the John von Neumann
Institute for Computing (Jülich) (HBN12) for computing time.
[38] K. Eichkorn, O. Treutler, H. Öhm, M. Häser, R. Ahlrichs, Chem. Phys. Lett. 242
(1995) 652.
Appendix A. Supplementary data
[39] K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theo. Chem. Acc. 97 (1997)
119.
[40] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 97 (1992) 2571.
[41] D. Andrae, U. Häußermann, M. Dolg, H. Stoll, H. Preuß, Theor. Chim. Acta 77
(1990) 123.
CCDC 804573 and 804574 contains the supplementary crystal-
lographic data for 2a,b. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2011.04.014.
[42] A. Klamt, G. Schüürmann, J. Chem. Soc., Perkin Trans. 2 (1993) 799.
[43] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[44] P. Deglmann, F. Furche, R. Ahlrichs, Chem. Phys. Lett. 362 (2002) 511.
[45] P. Deglmann, F. Furche, J. Chem. Phys. 117 (2002) 9535.
[46] P. Deglmann, K. May, F. Furche, R. Ahlrichs, Chem. Phys. Lett. 384 (2004) 103.
[47] A. Schäfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 100 (1994) 5829.
[48] H. Helten, C. Neumann, A. Espinosa, P.G. Jones, M. Nieger, R. Streubel, Eur. J.
Inorg. Chem. (2007) 4669.
[49] H. Wilkens, A. Ostrowski, J. Jeske, F. Ruthe, P.G. Jones, R. Streubel,
Organometallics 18 (1999) 5627.
References
[50] R. Streubel, H. Wilkens, P.G. Jones, Chem. Eur. J. 6 (2000) 3997.
[51] Note that the values do not provide information on absolute magnitudes of the
metal–phosphorus bond strengths.
[1] H.C. Kolb, M.G. Finn, K.B. Sharpless, Angew. Chem. 113 (2001) 2056;
H.C. Kolb, M.G. Finn, K.B. Sharpless, Angew. Chem., Int. Ed. 40 (2001) 2004.
[2] V.V. Rostovtsev, L.G. Green, V.V. Fokin, K.B. Sharpless, Angew. Chem. 114
(2002) 2708;
[52] The inversion barriers for 3 and 5 were calculated using RI-BP86/TZVP/ECP-28-
MWB(Mo)/ECP-60-MWB(W),
MWB(Mo)/ECP-60-MWB(W), COSMO (
barriers for model phosphole and other possible mono-, di-, and
COSMO
(e = 8.93)//RIBP86/SV(P)/ECP-28-
V.V. Rostovtsev, L.G. Green, V.V. Fokin, K.B. Sharpless, Angew. Chem., Int. Ed. 41
(2002) 2596.
e
= 8.93). We also calculated inversion
a
[3] P. Wu, A.K. Feldman, A.K. Nugent, C.J. Hawker, A. Scheel, B. Voit, J. Pyun, J.M.J.
Fréchet, K.B. Sharpless, V.V. Fokin, Angew. Chem. 116 (2004) 4018;
P. Wu, A.K. Feldman, A.K. Nugent, C.J. Hawker, A. Scheel, B. Voit, J. Pyun, J.M.J.
Fréchet, K.B. Sharpless, V.V. Fokin, Angew. Chem., Int. Ed. 43 (2004) 3928.
[4] E.J. Yoo, M. Ahlquist, S.H. Kim, I. Bae, V.V. Fokin, K.B. Sharpless, S. Chang,
Angew. Chem. 119 (2007) 1760;
E.J. Yoo, M. Ahlquist, S.H. Kim, I. Bae, V.V. Fokin, K.B. Sharpless, S. Chang,
Angew. Chem., Int. Ed. 46 (2007) 1730.
[5] J.E. Hein, J.C. Tripp, L.B. Krasnova, K.B. Sharpless, V.V. Fokin, Angew. Chem. 121
(2009) 8162;
J.E. Hein, J.C. Tripp, L.B. Krasnova, K.B. Sharpless, V.V. Fokin, Angew. Chem., Int.
Ed. 48 (2009) 8018.
[6] S. Cronin, P.H. Chandrasekar, J. Antimicrob. Chemother. 65 (2010) 410.
[7] J.M. Holub, K. Kirshenbaum, Chem. Soc. Rev. 39 (2010) 1325.
[8] Special issue: Click Chemistry in Polymer Science: Macromol. Rapid Commun.
29 (2008) 943.
[9] F. Mathey (Ed.), P–C heterocycles: Phosphorus–Carbon Heterocyclic
Chemistry: The Rise of a New Domain, Pergamon, Oxford, 2001.
[10] M. Regitz, O.J. Scherer (Eds.), P–N heterocycles: A. Schmidpeter, K. Karaghiosoff
in Multiple Bonds in Low Coordination Phosphorus Chemistry, Thieme,
Stuttgart, 1990, pp. 258–286.
[11] A. Marinetti, F. Mathey, Tetrahedron Lett. 28 (1987) 5021.
[12] N.H. Tran Huy, F. Mathey, Tetrahedron Lett. 29 (1988) 3077.
[13] U. Heim, H. Pritzkow, U. Fleischer, H. Grützmacher, M. Sanchez, R. Réau, G.
Bertrand, Chem. Eur. J. 2 (1996) 68.
triazaphosphole isomers with
(see Supporting Information).
a r
3,k3-phosphorus center for comparison
[53] (a) For calculations on the aromaticity of phospholes and related heterocycles
see: L. Nyulászi, T. Veszprémi, J. Réffy, B. Burkhardt, M. Regitz, J. Am. Chem.
Soc. 114 (1992) 9080;
(b) L. Nyulászi, J. Phys. Chem. 99 (1995) 586;
(c) L. Nyulászi, J. Phys. Chem. 100 (1996) 6194;
(d) L. Nyulászi, Inorg. Chem. 35 (1996) 4690;
(e) M.N. Glukhovtsev, A. Dransfeld, P.V.R. Schleyer, J. Phys. Chem. 100 (1996)
13447.
[54] (a) For triphosphole derivatives with a planar environment at P see: F.G.N.
Cloke, P.B. Hitchcock, P. Hunnable, J.F. Nixon, L. Nyulászi, E. Niecke, V. Thelen,
Angew. Chem. 110 (1998) 1139;
(b) F.G.N. Cloke, P.B. Hitchcock, P. Hunnable, J.F. Nixon, L. Nyulászi, E. Niecke,
V. Thelen, Angew. Chem., Int. Ed. 37 (1998) 1083;
(c) F.E. Hahn, L. Wittenbecher, D. Le Van, R. Fröhlich, B. Wibbeling, Angew.
Chem. 112 (2000) 2293;
(d) F.E. Hahn, L. Wittenbecher, D. Le Van, R. Fröhlich, B. Wibbeling, Angew.
Chem., Int. Ed. 39 (2000) 2307;
(e) R. Streubel, U. Schiemann, P.G. Jones, J. Grunenberg, H.-M. Schiebel, D.
Gudat, Angew. Chem. 113 (2001) 2531;
(f) R. Streubel, U. Schiemann, P.G. Jones, J. Grunenberg, H.-M. Schiebel, D.
Gudat, Angew. Chem., Int. Ed. 40 (2001) 2471.