Triazaphospholes versus triazoles: An investigation of the differences between click -derived chelating phosphorus- and nitrogen-containing heterocycles

Article abstract of DOI:10.1021/om4010077

A new class of pyridyl-functionalized triazaphospholes bearing either ^tBu or SiMe₃ substituents at the 5-position of the N ₃PC heterocycle have been prepared via the click reaction starting from 2-(azidomethyl)pyridine and the corresponding phosphaalkynes. In order to investigate the electronic structure and donor-acceptor properties of such novel chelating and low-coordinate phosphorus heterocycles, calculations at the DFT level have been carried out. Moreover, cyclic voltammetry measurements were performed and the results were compared with those for the structurally related triazole-based systems, demonstrating a significant influence of the phosphorus atom as well as the substitution pattern on the electronic properties of the novel compounds. The P,N hybrid ligands form Re(I) complexes of the type [(N^amN)Re(CO)₃Br] via coordination of the nitrogen atom N² to the metal center rather than via the phosphorus atom, as verified crystallographically.

Full text of DOI:10.1021/om4010077

Article
pubs.acs.org/Organometallics
Triazaphospholes versus Triazoles: An Investigation of the
Differences between “Click”-Derived Chelating Phosphorus- and
Nitrogen-Containing Heterocycles
Julian A. W. Sklorz, Santina Hoof, Michael G. Sommer, Fritz Weißer, Manuela Weber, Jelena Wiecko,
Biprajit Sarkar, and Christian Muller*
̈
Institut fur Chemie und Biochemie, Anorganische Chemie, Freie Universitat Berlin, Fabeckstraße 34/36, Berlin 14195, Germany
S
* Supporting Information
t
ABSTRACT: A new class of pyridyl-functionalized triazaphospholes bearing either Bu or
SiMe3 substituents at the 5-position of the N3PC heterocycle have been prepared via the
“click” reaction starting from 2-(azidomethyl)pyridine and the corresponding phosphaal-
kynes. In order to investigate the electronic structure and donor−acceptor properties of such
novel chelating and low-coordinate phosphorus heterocycles, calculations at the DFT level
have been carried out. Moreover, cyclic voltammetry measurements were performed and the
results were compared with those for the structurally related triazole-based systems,
demonstrating a significant influence of the phosphorus atom as well as the substitution
pattern on the electronic properties of the novel compounds. The P,N hybrid ligands form
Re(I) complexes of the type [(N∧mN)Re(CO)3Br] via coordination of the nitrogen atom N2
to the metal center rather than via the phosphorus atom, as verified crystallographically.
modular 1,3-dipolar cycloaddition reaction, starting from azides
and phosphaalkynes, as shown by Regitz et al.3 As a matter of
fact, the copper-catalyzed azide−alkyne cycloaddition reaction
(CuAAC, “click reaction”), introduced independently by
Sharpless and Medal in 2002,4 has found widespread
application in various research areas, such as homogeneous
catalysis, molecular materials, dendrimers, and supramolecular
chemistry, due to a facile and atom-economical assembly of
target molecules. This powerful tool can indeed be used for
straightforward and simple access to functionalized ligands.5
Interestingly, when phosphaalkynes were used instead of
terminal alkynes, only one regioisomer was formed thermally
and selectively without the need for a copper catalyst, because
INTRODUCTION
■
Low-coordinate phosphorus compounds have recently regained
noticeable interest, as the very peculiar electronic and steric
properties of such λ3σ2 species differ significantly from those of
classical trivalent λ3σ3-phosphanes. These characteristics can be
transferred to more applied research fields, such as homoge-
neous catalysis and material science.1 Using a modular synthetic
route, we have recently demonstrated the access to various
donor-functionalized 2,4,6-triarylphosphinines, including phos-
phorus derivatives of 2,2′-bipyridine (A; Figure 1). By making
the PC bond is already polarized. According to Nyulas
́
zi and
Regitz, 3H-1,2,3,4-triazaphosphole has a conjugated π system
with a high degree of aromaticity, just like the corresponding
triazoles containing only nitrogen.6 In contrast to phosphinines,
however, they are expected to possess a higher π density at the
Figure 1. Pyridyl-functionalized phosphinine (A) and general
schematic structures of a 3H-1,2,3,4-triazaphosphole derivative (B)
and pyridyl-functionalized triazaphosphole (C).
phosphorus atom due to a N−CP ↔ N+C−P−
̅
conjugation, particularly evident in 1,3-azaphospholes, which
possess only the σ3N atom with π-donor properties.7
Interestingly, while the analogous donor-functionalized tri-
azoles have been intensely investigated in coordination
chemistry over the past decade,8 the synthesis and coordination
chemistry of donor-functionalized, chelating 3H-1,2,3,4-triaza-
phosphole derivatives is practically unknown.9,10 On the other
hand, the “click” reaction between donor-functionalized azides
use of the chelate effect, we could demonstrate that this neutral
P,N hybrid ligand easily forms coordination compounds with
transition-metal centers in both low as well as medium to high
oxidation states.2
Inspired by these findings, we started a program to
investigate the access to other classes of pyridyl-functionalized,
low-coordinate phosphorus compounds. We anticipated that
derivatives of 3H-1,2,3,4-triazaphospholes (B) are suitable
candidates, as they can generally be prepared selectively in a
Received: October 15, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and phosphaalkynes would provide access to polydentate
ligands, in which the stereoelectronic properties can be tuned
according to the additional phosphorus heteroatom and the
nature of the substituents. In this way, a whole new set of
phosphorus derivatives of triazoles would be readily available,
making detailed studies on the influence of the additional
heteroatom on the properties of triazole derivatives possible for
the first time. Surprisingly, only one example of such a species
has so far been characterized crystallographically, where a
tripodal tris(triazaphosphole) acts as a tridentate ligand with P
coordination toward a Pt(0) center, as reported by Jones et al.11
Stimulated by these findings, we envisaged the access and
detailed investigation of novel 2-pyridylmethyl-functionalized
1,2,3,4-triazaphospholes of type C (Figure 1). Due to the
presence of both σ2-phosphorus and σ2-nitrogen atoms within
one heterocycle, such ambidentate ligands contain two different
potential coordination sites (D, E; Figure 2). Consequently, we
Scheme 1. Synthesis of 2-Pyridylmethyl-Functionalized
Triazaphospholes (1, 2) and 2-Pyridylmethyl-Functionalized
Triazoles (3, 4)
phosphorus species with rather low π density at the phosphorus
atom.15 The SiMe3 group has indeed a rather large influence on
the chemical shift, as the P resonance in the 31P{1H} NMR
spectrum of compound 2 was observed at δ (ppm) 216.5
1
(CD2Cl2). The H NMR spectra of both 1 and 2 show a
doublet at δ (ppm) 5.8 (1) and 5.9 (2), due to coupling of the
methylene protons with the phosphorus atom (3JH−P = 1.4, 6.1
Hz). The proton H1 (Figure 3) is shifted the most downfield
and is detected at δ (ppm) 8.54 (1) and 8.53 (2). As an
example, Figure 3 shows the 1H NMR spectrum of
triazaphosphole 2, recorded in CD2Cl2.
Figure 2. Possible coordination modes of chelating triazaphospholes
(D, E) and 2-pyridylmethyl-functionalized triazole (F).
were interested in investigating the coordination chemistry of
these systems and the influence of additional substituents at the
PC moiety on the stereoelectronic properties of the ligands.
Since these compounds have not been reported in the literature
so far, we set out to synthesize the structurally related,
phosphorus-lacking triazole derivatives of type F as well (Figure
2). It should be noted here that a detailed comparison between
these heterocycles, having an otherwise identical substitution
pattern, has not been reported before.
RESULTS AND DISCUSSION
■
t
Since Bu-CP is accessible in a straightforward way, we
Figure 3. 1H NMR spectrum of 2 recorded in CD2Cl2 and assignment
of the respective protons. Inset: enlargement of the low-field region.
decided to start our investigations with this well-known
t
compound. Moreover, the Bu group does obviously not
prevent a possible η1(P) coordination of the corresponding
triazaphosphole to a transition-metal center.10 In order to
modify the electronic properties while retaining similar steric
properties of the heterocycle, we chose to introduce a SiMe3
group at the 5-position as well. It is known that silyl groups
attached directly to a π-electron system show relatively strong
electron-withdrawing effects due to an inverse hyperconjuga-
tion. On the other hand, the “click” reaction between an azide
and the required trimethylsilylphosphaethyne has not been
shown before. 2-(Azidomethyl)pyridine,12 tBu−CP,13 and
TMS−CP14 were thus prepared according to standard
literature procedures. Subsequently, the “click reaction”
between equimolar amounts of the azide and tert-butylphos-
phaethyne was carried out at room temperature in toluene
without any problem. Interestingly, it turned out that also the
reaction of trimethylsilylphosphaethyne with 2-(azidomethyl)-
pyridine proceeded straightforwardly, leading for the first time
to a TMS-substituted triazaphosphole derivative. The novel
compounds 1 and 2 were respectively obtained in 93% and 94%
yields as colorless solids (Scheme 1a).
For comparison reasons, the nitrogen-containing triazoles 3
and 4 were obtained according to a modified literature
procedure (tBu). Recently, Zhu et al.16 and Crowley et al.17
have demonstrated that analogous systems with different
substituents at the 5-position of the triazole mojety are easily
accessible. Compounds 3 and 4 were thus obtained as colorless
solids in 72 and 67% yields, respectively (Scheme 1b).
In order to get insight into the electronic structure of the
novel triazaphospholes, we first performed calculations at the
t
DFT level (B3LYP) on compound 1 (R = Bu), and the
frontier orbitals are depicted in Figure 4.
Similar to the situation in λ3σ2-phosphinines, the LUMO of
the low-coordinate phosphorus heterocycle shows a large
coefficient of π symmetry at the phosphorus atom, indicating
the π-accepting properties of such systems. The π-donor
properties of triazaphospholes are obvious from the HOMO.7
Moreover, a rather large coefficient of σ symmetry is present at
the nitrogen atoms N1 and N2 of the heterocycle in the
HOMO-1. Normally, nitrogen atom N1 in triazoles coordinates
preferentially to a transition-metal center. However, in
Compound 1 shows a downfield shift in the 31P{1H} NMR
spectrum at δ (ppm) 173.1 (CD2Cl2), which is typical for λ3σ2-
B
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 4. Frontier orbitals of the 2-pyridylmethyl-functionalized 3H-
1,2,3,4-triazaphosphole derivative 1.
chelating ligands, such as in 1 and 2, this nitrogen atom might
not be suitable for σ coordination due to the chelating effect
(vide infra).8h Very similar large coefficients of σ symmetry at
both the phosphorus atom and the nitrogen atom N2 are
further present in the energetically low-lying HOMO-4. If σ
coordination to a transition-metal center occurs, the energetic
difference between coordinating via the pyridyl nitrogen and
the nitrogen N2 or via the pyridyl nitrogen and the phosphorus
atom is thus expected to be very small and both coordination
modes might consequently be possible.
In order to investigate the electronic structure of compounds
1−4 experimentally, their electrochemical properties were
further examined by means of cyclic voltammetry (CH2Cl2,
THF, 0.1 M Bu4NPF6, v = 100 mV s−1) using ferrocene (Fc) as
the internal standard (Figure 5).
Figure 5. Electrochemical investigation of compounds 1−4: (a)
oxidation (measured in CH2Cl2); (b) reduction (measured in THF).
possibility to investigate the electronic properties of 1−4 by
means of IR spectroscopy of the resulting coordination
compounds. Crowley et al. have shown that Re(I) complexes
of type F (Figure 2, R = C6H5, 4-NO2-C6H5, 4-MeOC6H5, Bn)
can easily be prepared.17 In those coordination compounds, the
triazole moiety coordinates indeed via the N2 atom to the
[Re(CO)3Br] fragment, which is the least nucleophilic part.8h
This coordination mode can thus be attributed purely to the
chelating effect. Taking the frontier orbitals of the 3H-1,2,3,4-
triazaphosphole derivative 1 into account (Figure 4), we were
thus wondering whether coordination compound D or E would
be realized in combination with Re(I) (Figure 2).
We first paid attention to the coordination chemistry of the
triazaphospholes. Compounds 1 and 2 were reacted with
equimolar amounts of [Re(CO)5Br] in dichloromethane at T =
80 °C, and the reaction was monitored by means of 31P{1H}
NMR spectroscopy. After 8 h the conversions were complete
and the reaction products showed a resonance in the 31P{1H}
NMR at δ (ppm) 191.3 (R = tBu, 5) and at δ (ppm) 231.1 (R =
SiMe3, 6), respectively. From the chemical shift difference
(coordination compound ligand) of Δδ = 18.2 ppm and Δδ =
14.7 ppm, however, it is not conclusive whether the
triazaphosphole moiety coordinates via the phosphorus lone
pair or via the nitrogen lone pair to the metal center, since σ-
coordinated phosphinines show a similar chemical shift
difference upon coordination to a metal center. We therefore
attempted a crystallographic characterization, and crystals of
both products, suitable for X-ray crystal structure analysis, were
obtained either by slow cooling of a saturated solution of 5 in
dichloromethane or by slow diffusion of diethyl ether into a
solution of 6 in dichloromethane. Compound 5 crystallized in
the space group P21/n, and the molecular structure in the
In DCM, compounds 1 and 3 undergo irreversible oxidation
ox
ox
processes at Ep = +1.438 V (1) and Ep = +1.451 V (3) vs
Fc/Fc+. While 1 is slightly easier to oxidize than the
corresponding triazole 3, the SiMe3-substituted compounds 2
and 4 cannot be oxidized within the solvent window of DCM.
This finding is in line with the electron-withdrawing properties
of the SiMe3 group, directly bound to the π system of the
aromatic heterocycles. In THF, compounds 1−4 further
red
undergo irreversible reduction processes (Ep = −2.957 V
(1), Epred = −2.691 V (3), Ered = −2.911 V (2), Ered = −2.636 V
(4) vs Fc/Fc+). Obviously, the phosphorus-containing hetero-
cycles 1 and 2 are more difficult to reduce in comparison to the
triazoles 3 and 4. This can be attributed to the fact that
exchanging a C−H unit in a triazole by a phosphorus atom
leads, as expected, to a more electron-rich heterocycle and a
LUMO located higher in energy. Complementary to the
aforementioned observations, the presence of a SiMe3 group
(compounds 2 and 4) leads to lower reduction potentials in
comparison to the tBu-substituted analogues due to its electron-
withdrawing character, which lowers the energy of the LUMO.
As the phosphinine-based P,N ligand A (Figure 1) undergoes
a facile reaction with Re(CO)5Br with formation of the
complex [(A)Re(CO)3Br)], we decided to explore the
coordination chemistry of 1−4 also toward Re(I).1d At the
same time, the [Re(CO)3Br] metal fragment offers the
C
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
crystal, along with selected bond lengths and angles, is depicted
in Figure 6, showing the expected facial geometry of the
[L2Re(CO)3Br] complex.
and complex 8 turned out to be a useful resonance to monitor
the course of the reaction. Crystals of 7 (space group P1) and 8
(space group Pca21) suitable for X-ray diffraction were obtained
either by slow cooling of a saturated solution of 7 in hot
dichloromethane or by slow diffusion of diethyl ether into a
dichloromethane solution of 8. The molecular structures, along
with selected bond lengths and angles, are depicted in Figures 8
and 9, respectively.
Figure 6. Molecular structure of 5 in the crystal. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
lengths (Å) and angles (deg): P(1)−C(1), 1.731(7); C(1)−N(3),
1.363(8); N(3)−N(2), 1.302(6); N(2)−N(1), 1.341(7); N(1)−P(1),
1.699(5); N(1)−C(2), 1.481(7); C(2)−C(3), 1.515(8); N(2)−Re(1),
2.163(5); N(4)−Re(1), 2.205(5); Re(1)−Br(1), 2.6258(7); N(1)−
P(1)−C(1), 86.2(3); N(2)−Re(1)−N(4), 83.31(18).
Figure 8. Molecular structure of 7 in the crystal. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
lengths (Å) and angles (deg): C(2)−C(1), 1.366(7); C(1)−N(1),
1.352(6); N(1)−N(2): 1.321(5); N(2)−N(3), 1.337(5); N(3)−C(3),
1.460(6); C(3)−C(4), 1.512(7); C(4)−N(4), 1.351(5); N(2)−Re(1),
2.175(3); N(4)−Re(1), 2.218(3); Re(1)−Br(1), 2.6278(6); N(3)−
C(2)−C(1), 105.4(4); N(2)−Re(1)−N(4), 82.78(13).
The molecular structure of complex 6 (space group P21/c) is
depicted in Figure 7 and shows a facial geometry comparable to
that observed for compound 5.
Figure 7. Molecular structure of 6 in the crystal. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
lengths (Å) and angles (deg): P(1)−C(1), 1.730(8); C(1)−N(3),
1.348(10); N(3)−N(2), 1.306(8); N(2)−N(1), 1.336(7); N(1)−
P(1), 1.702(6); N(1)−C(2), 1.481(8); C(2)−C(3), 1.509(9); N(2)−
Re(1), 2.163(5); N(4)−Re(1), 2.192(5); Re(1)−Br(1), 2.6248(8);
C(1)−Si(1), 1.892(8); N(1)−P(1)−C(1), 86.7(3); N(2)−Re(1)−
N(4), 83.7(2).
Figure 9. Molecular structure of 8 in the crystal. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
lengths (Å) and angles (deg): C(2)−C(1), 1.43(3); C(1)−N(3),
1.42(2); N(3)−N(2), 1.32(2); N(2)−N(1), 1.36(2); N(1)−C(2),
1.34(3); N(1)−C(3), 1.51(3); C(3)−C(4), 1.44(3); C(4)−N(4),
1.37(2); N(2)−Re(1), 2.163(16); N(4)−Re(1), 2.233(18); Re(1)−
Br(1), 2.598(3); N(3)−C(2)−C(1), 107.0(17); N(2)−Re(1)−N(4),
82.5(6).
From the crystallographic characterization it is obvious that
both chelating ligands 1 and 2 coordinate to the Re(I) center
via the nitrogen atom N(2) of the triazaphosphole moiety,
rather than via the phosphorus atom. Interestingly, the
coordination of the least nucleophilic nitrogen atom N(2) to
a metal center has not been observed for triazaphospholes
before and is apparently enforced by the chelating effect.
In order to compare the stereoelectronic properties of the
triazaphospholes 1 and 2, Re(I) complexes containing the
chelating triazoles were prepared accordingly. Since a
phosphorus probe is absent, reactions of 3 and 4 with
equimolar amounts of [Re(CO)5Br] in dichloromethane at T
Similar to the case for compounds 5 and 6, the graphical
representations of 7 and 8 reveal the facial geometry of the
complexes [(3)Re(CO)3Br] and [(4)Re(CO)3Br] with the
nitrogen atoms N(2) of the triazole units coordinated to the
Re(I) centers. Apparently, exchanging the phosphorus atom in
5 and 6 by an isolectronic C−H group in 7 and 8 has only a
marginal effect on the bite angle N(4)−Re(I)−N(2), as values
of 83.31 (5), 83.67 (6), 82.78 (7), and 82.48° (8) were found.
Scheme 2 summarizes the reaction of ligands 1−4 with
[Re(CO)5Br], leading to the corresponding Re(I) complexes
5−8, in which coordination exclusively via the least nucleophilic
nitrogen atom N2 occurs.
1
= 85 °C were monitored by means of H NMR spectroscopy
and were found to be complete within 24 h. Especially the
As mentioned above, the carbonyl complexes provide the
possibility to obtain information on the electronic properties of
signal of the SiMe3 group in the 1H NMR spectrum of ligand 4
D
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Synthesis of Re(I) Complexes 5−8
the ligands. We therefore investigated Re(I) complexes 5−8
also by means of infrared spectroscopy (Table 1). As already
Table 1. Infrared Data for Coordination Compounds 5−8
compound
ν1
̃
(CO) (cm−1
)
ν2
̃
(CO) (cm−1
)
ν1
̃
(CO) (cm−1
)
[(1)Re(CO3)Br] (5)
[(2)Re(CO3)Br] (6)
[(3)Re(CO3)Br] (7)
[(4)Re(CO3)Br] (8)
2023
2021
2032
2026
1919
n.d.
1885
1879
1891
1898
1952
1949
Figure 10. Electrochemical investigation of compounds 5−8: (a)
oxidation (CH2Cl2); (b) reduction (THF).
anticipated from the cyclic voltammetry measurements, a clear
difference between the triazaphosphole-based complexes 5 and
6 and the triazole-based coordination compounds 7 and 8 can
CONCLUSION
̃
indeed be noticed. The ν(CO) stretching frequencies of 7 and
■
8 are slightly shifted to higher wavenumbers in comparison to
their phosphorus-containing analogues 5 and 6. This indicates
that the presence of a phosphorus atom leads to a ligand
system, which is more electron rich. An electron-withdrawing
Using the modular synthetic procedure for the preparation of
3H-1,2,3,4-triazaphosphole derivatives, we have demonstrated
access to a new class of chelating P,N hybrid ligands based on
low-coordinate phosphorus compounds. The pyridyl-function-
alized triazaphospholes bearing either tBu or SiMe3 substituents
at the 5-position of the N3PC heterocycle could easily prepared
by a noncatalyzed “click” reaction, starting from 2-
(pyridylmethyl)azide and the corresponding phosphaalkyne.
These compounds were compared in detail with the analogous
triazole-based chelates. Calculations at the DFT level have been
performed in order to investigate the electronic structure and
donor−acceptor properties of such low-coordinate phosphorus
heterocycles. Cyclic voltammetry measurements on the
triazaphospholes have been carried out, and the results were
compared with those for the analogous triazole-based systems,
demonstrating a significant influence of the phosphorus atom as
well as the different substituents on the electronic properties of
the heterocycles. The chelating triazaphospholes form Re(I)
complexes of the type [(N∧mN)Re(CO)3Br] by coordination of
the nitrogen atom N2 to the metal center rather than via the
phosphorus atom, as verified crystallographically. It should be
mentioned here that the extra phosphorus atom now provides
the possibility to prepare heterobimetallic complexes by
additional coordination of the phosphorus atom to a second
metal fragment. Moreover, the modular “click” reaction of
azides with phosphaalkynes can be used to prepare also fully
conjugated chelating ligands. Taking their special stereo-
electronic properties into account, the corresponding Re(I)
complexes could thus find application as novel and alternative
bipyridine-based systems, which have been used as photo-
catalysts for the reduction of CO2 or as triplet emitters in
OLEDs. Experiments to investigate such coordination com-
̃
influence of the SiMe3 group on the ν(CO) stretching
frequencies, as observed by the electrochemical investigations,
can, however, not be found in the IR spectra.
In addition, coordination compounds 5−8 were further
investigated by means of cyclic voltammetry (CH2Cl2, THF,
0.1 M Bu4NPF6, v = 100 mV s−1) using ferrocene (Fc) as the
internal standard (Figure 10). While the phosphorus-containing
complexes 5 and 6 undergo in DCM irreversible oxidation
ox
ox
processes (Ep = +1.022 V (5), Ep = +0.952 V (6) vs Fc/
Fc+), the triazole-based compounds 7 and 8 show quasi-
reversible oxidation waves (Eox = +0.909 V (7), Eox = +0.917 V
(8) vs Fc/Fc+). In the electrochemical reduction of 5−8
(THF), all complexes show irreversible reduction processes
(Epred = −2.56 V (5), Epred = −2.56 V (7), Epred = −2.135 V (8),
Ep = −2.357 V (6) vs Fc/Fc+). Similar to the observations
red
made for the free ligands, the Re(I) complexes containing the
triazaphophole ligand are slightly more difficult to reduce than
the triazole-based systems, while the coordination compounds
t
containing a Bu group at the 5-position of the heterocycle are
more difficult to reduce in comparison to those containing a
SiMe3 group, due to the electron-withdrawing character of that
particular substituent.
In comparison to the only nitrogen-containing triazoles, both
the IR spectroscopic and cyclic voltammetric measurements
nicely demonstrate that there is indeed the postulated influence
of the phosphorus atom and the additional substituent at the
PC moiety on the electronic properties of the novel
heterocycles and the corresponding transition-metal complexes.
E
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Chem. 2010, 3307−3316. (f) Nylaszi, L.; Csonka, G.; Ref
́
fy, J.;
pounds in more detail are currently being carried out in our
laboratories.
Veszprem
́
i, T.; Heinicke, J. J. Organomet. Chem. 1989, 373, 49−56.
(8) For reviews and selected examples see: (a) Struthers, H.; Mindt,
T. L.; Schibli, R. Dalton Trans. 2010, 39, 675. (b) Crowley, J. D.
McMorran, D. In Topics in Heterocyclic Chemistry; Kosmrlj, J., Ed.;
Springer: Berlin/Heidelberg, Germany, 2012; Vol. 28, p 31.
(c) Schweinfurth, D.; Deibel, N.; Weisser, F.; Sarkar, B. Nachr.
Chem. 2011, 59, 937. (d) Schulze, B.; Friebe, C.; Hager, M. D.; Winter,
A.; Hoogenboom, R.; Goerls, H.; Schubert, U. S. Dalton Trans. 2009,
787. (e) Urankar, D.; Pevec, A.; Kosmrlj, J. Cryst. Growth Des. 2010,
10, 4920. (f) Schweinfurth, D.; Pattacini, R.; Strobel, S.; Sarkar, B.
Dalton Trans. 2009, 9291. (g) Schweinfurth, D.; Su, C.-Y.; Wei, S.-C.;
Braunstein, P.; Sarkar, B. Dalton Trans. 2012, 41, 12984. (h) Wolff,
M.; Munoz, L.; Francois, A.; Carrayon, C.; Seridi, A.; Saffon, N.;
Picard, C.; Machura, B.; Benoist, E. Dalton Trans. 2013, 42, 7019.
(i) Urankar, D.; Pinter, B.; Pevec, A.; de Proft, F.; Turel, I.; Kosmrlj, J.
Inorg. Chem. 2010, 49, 4820.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text giving full experimental details for compounds 1−8 and
CIF files giving crystallographic data for compounds 5−8. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*C.N.: fax, (+) 49 (0)30 838 45004; e-mail, c.mueller@fu-
berlin.de; web, www.bcp.fu-berlin.de/ak-mueller.
Notes
(9) Choong, S. L.; Nafady, A.; Stasch, A.; Bond, A. M.; Jones, C.
Dalton Trans. 2013, 42, 7775−7780.
The authors declare no competing financial interest.
(10) (a) Chapyshev, S. V. Synlett 2009, 1, 1−8. (b) Chapyshev, S. V.;
Bergstraßer, U.; Regitz, M. Chem. Heterocycl. Compd. 1996, 32, 59.
̈
ACKNOWLEDGMENTS
■
(11) Choong, S. L.; Jones, C.; Stasch, A. Dalton Trans. 2010, 39,
5774−5776.
The Free University of Berlin, Institute for Chemistry and
Biochemistry, is gratefully acknowledged for financial support.
We thank Dipl. Chem. Mrs. Naina Deibel for technical
assistance with the CV measurements and Dr. Andreas Springer
for collecting the mass spectrometry data.
(12) Pardin, C.; Roy, I.; Lubell, W. D.; Keillor, J. W. Chem. Biol. Drug
Des. 2008, 72, 189−196.
(13) Becker, G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, B36, 16.
(14) (a) Mansell, S. M.; Green, M.; Kilby, R. J.; Murray, M.; Russell,
C. A. C. R. Chem. 2013, 13, 1073−1081. (b) Cordaro, J. G.; Stein, D.;
Ruegger, H.; Grutzmacher, H. Angew. Chem., Int. Ed. Engl. 2006, 45,
̈
̈
REFERENCES
■
6159−6162.
(1) See for example: (a) Muller, C.; Vogt, D. In Catalysis and
̈
(15) For 1,3-azaphospholes, benzopyrido[b] or pyrido[c] annulated,
as well as 1,3(benz)oxaphospholes and 1,3-(benzo)thiaphospholes
with π-donor atoms in conjugation to phosphorus a chemical shift
value of δ (ppm) 65−80 is observed in the 31P{1H} NMR spectrum,
while in 2-SiMe3-substituted benzazaphospholes a signal at δ (ppm)
120 ppm is usually observed. The rather low value observed for the N-
donor-containing triazaphospholes is related to the π-deficient
properties of the two σ2N atoms.
Material Science Applications; Peruzzini, M., Gonsalvi, L., Eds.;
Springer: Heidelberg, Germany, 2011; Vol. 36, Chapter 6. (b) Muller,
̈
C. in Phosphorus(III) Ligands in Homogeneous Catalysis: Design and
Synthesis; Kamer, P. C. J., van Leeuwen, P. W. N. M., Eds.; Wiley-
VCH: Weinheim, Germany, 2012. (c) Douglas-Tessier, J.; Conrad, E.
D.; Dake, G. R.; Gates, D. P. In Phosphorus Ligand Effects in
Homogeneous Catalysis: Design and Synthesis; Kamer, P. C. J., van
Leeuwen, P. W. N. M., Eds.; Wiley-VCH: Weinheim, Germany, 2012.
(16) Michaels, H. A.; Zhu, L. Chem. Asian J. 2011, 6, 2825−2834.
(17) (a) Crowley, J. D.; Bandeen, P. H.; Hanton, L. R. Polyhedron
2010, 29, 70−83. (b) Anderson, C. B.; Elliott, A. B. S.; McAdam, C. J.;
Gordon, K. C.; Crowley, J. D. Organometallics 2013, 32, 788−797.
(d) Muller, C.; Broeckx, L. E. E.; de Krom, I.; Weemers, J. J. M. Eur. J.
̈
Inorg. Chem. 2013, 187. (e) Bates, J. I.; Dugal-Tessier, J.; Gates, D. P.
Dalton Trans. 2010, 39, 3151−3159.
(2) (a) Muller, C.; Wasserberg, D.; Weemers, J. J. M.; Pidko, E. A.;
̈
Hoffmann, S.; Lutz, M.; Spek, A. L.; Meskers, S. C. J.; Janssen, R. A. J.;
van Santen, R. A.; Vogt, D. Chem. Eur. J. 2007, 13, 4548−4559.
(b) Campos Carrasco, A.; Pidko, E. A.; Masdeu-Bulto,
́
A. M.; Lutz, M.;
Spek, A. L.; Vogt, D.; Muller, C. New J. Chem. 2010, 34, 1547−1550.
̈
(c) Campos-Carrasco, A.; Broeckx, L. E. E.; Weemers, J. J. M.; Pidko,
E. A.; Lutz, M.; Masdeu-Bulto,
J. 2011, 17, 2510−2517. (d) de Krom, I.; Broeckx, L. E. E.; Lutz, M.;
Muller, C. Chem. Eur. J. 2013, 19, 3676−3684. (e) de Krom, I.; Pidko,
́
A. M.; Vogt, D.; Muller, C. Chem. Eur.
̈
̈
E. A.; Lutz, M.; Muller, C. Chem. Eur. J. 2013, 19, 7523−7531.
̈
(3) Rosch, W.; Regitz, M. Angew. Chem., Int. Ed. Engl. 1984, 23, 900.
̈
(4) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2001, 40, 2004−2021. (b) Rostovtsev, V. V.; Green, L. G.; Fokin,
V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596.
(c) Tornoe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67,
3057.
(5) Janssen, M. C. C.; Muller, C.; Vogt, D. Adv. Synth. Catal. 2009,
̈
351, 313−318.
́ ́ ́
(6) (a) Nyulaszi, L.; Vespremi, T.; Reffy, J.; Burkhardt, B.; Regitz, M.
J. Am. Chem. Soc. 1992, 114, 9080−9084. (b) Nylas
́
zi, L. Chem. Rev.
2001, 101, 1229−1246.
(7) (a) Ghalib, M.; Konczol, L.; Nyulas
́
zi, L.; Jones, P. G.; Palm, G. J.;
̈
̈
Heinicke, J. W. Dalton Trans. 2014, 43, 51−54. (b) Ghalib, M.; Jones,
P. G.; Palm, G. J.; Heinicke, J. W. RSC Adv. 2013, 3, 17726−17731.
(c) Niaz, B.; Iftikhar, F.; Kindermann, M. K.; Jones, P. G.; Heinicke, J.
Eur. J. Inorg. Chem. 2013, 4220−4227. (d) Aluri, B. R.; Niaz, B.;
Kindermann, M. K.; Jones, P. G.; Heinicke, J. Dalton Trans. 2011, 40,
211−224. (e) Adam, M. S. S.; Jones, P. G.; Heinicke, J. Eur. J. Inorg.
F
dx.doi.org/10.1021/om4010077 | Organometallics XXXX, XXX, XXX−XXX