Observation of a chloride-bridged P-P bond in the phosphorus cation [L(Cl) P(μ-Cl) P(Cl)L]+ (L = NHC)

Article abstract of DOI:10.1021/om4002268

A bridging chloride anion between two electrophilic phosphorus centers was observed for the first time in the molecular structure of the novel P-P bonded cation [L^Dipp₂P₂Cl₃]⁺ (2⁺; L^Dipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene). Cation 2⁺ is prepared by the reduction of the monophosphorus species [L^DippPCl₂]⁺ (1 ⁺) with sodium. DFT calculations, AIM and mechanochemical (compliance constants) analyses are used to examine the bonding situation of this unusual species. The monochloro-substituted cation [L^Dipp₂P ₂Cl]⁺ (3⁺) was likewise observed as a reduction product of 1⁺.

Full text of DOI:10.1021/om4002268

Article
pubs.acs.org/Organometallics
Observation of a Chloride-Bridged P−P Bond in the Phosphorus
Cation [L(Cl)P(μ-Cl)P(Cl)L]+ (L = NHC)
Florian D. Henne,† Eva-Maria Schnockelborg,‡ Kai-Oliver Feldmann,† Jorg Grunenberg,§ Robert Wolf,*,‡
̈
̈
and Jan J. Weigand*,†
†TU Dresden, Department of Chemistry and Food Chemistry, 01062 Dresden, Germany
‡University of Regensburg, Institute of Inorganic Chemistry, 93040 Regensburg, Germany
§TU Braunschweig, Institute of Organic Chemistry, Hagenring 30, 38106 Braunschweig, Germany
S
* Supporting Information
ABSTRACT: A bridging chloride anion between two electro-
philic phosphorus centers was observed for the first time in the
molecular structure of the novel P−P bonded cation
[LDipp2P2Cl3]+ (2+; LDipp = 1,3-bis(2,6-diisopropylphenyl)-
imidazol-2-ylidene). Cation 2+ is prepared by the reduction
of the monophosphorus species [LDippPCl2]+ (1+) with
sodium. DFT calculations, AIM and mechanochemical
(compliance constants) analyses are used to examine the
bonding situation of this unusual species. The monochloro-substituted cation [LDipp2P2Cl]+ (3+) was likewise observed as a
reduction product of 1+.
phosphorus centers. The bonding situation in this unusual
compound is analyzed by DFT calculations and compliance
constant analysis.9
INTRODUCTION
■
Phosphorus has the highest homoatomic single bond energy
(205 kJ/mol) of any group 15 element and therefore shows a
high propensity to form P−P-bonded frameworks.1 The
chemistry of neutral and anionic polyphosphorus compounds
has therefore been flourishing for decades.2 Recently, this area
has received fresh impetus from the use of stable N-heterocyclic
carbenes (NHCs) for the preparation of P−P-bonded species
that display P2, P3, P4, and P12 frameworks.3
Several novel types of P−P-bonded phosphorus cations have
emerged in recent years.4 One interesting challenge in this area
is the synthesis of cationic polyphosphorus compounds that
carry halide substituents.5 Mono-, di-, and trichlorophospha-
nylphosphonium ions have been recently described.6 Chloride
substituents have also been incorporated into a few
oligophosphonium cations through ion transfer.7 We recently
reported a convenient protocol for the synthesis of cations
[LiPrPCl2]+ and [LiPr2PCl]2+ (LiPr = 1,3-diisopropylimidazol-2-
ylidene), using an imidazolium-transfer reagent [LiPrSiMe3]-
[OTf].8 The chlorine atoms in these reactive cations can be
substituted by cyano and azido groups.
Aiming at the synthesis of new polyphosphorus species, we
initiated a study of the reaction behavior of our [LPCl2]+
cations toward low-valent transition metalates and strong
reducing agents. Here, we describe the synthesis of the novel
cationic diphosphane derivative [LDipp2P2Cl3]+ (2+; LDipp = 1,3-
bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and the related
cation [LDipp2P2Cl]+ (3+), which are obtained via the reduction
of the novel dichloro-substituted cation [LDippPCl2]+ (1+). The
molecular structure of cation 2+ shows an unprecedented
arrangement where a chloride anion symmetrically bridges two
RESULTS AND DISCUSSION
■
[LDipp2P2Cl3][OTf] (2[OTf]) and [LDipp2P2Cl][OTf]
(3[OTf]) were initially obtained as a product mixture by
reacting the triflate salt [LDippPCl2][OTf] (1[OTf]) with the
recently reported low-valent iron(0) naphthalene complex
[K(18-crown-6){Cp*Fe(η4-naphthalene)}] (K[Fe]) (Scheme
1).10 K[Fe] acts as a two-electron reducing agent in this
reaction. The cationic complex [Cp*Fe(η6-naphthalene)]Cl
([Fe]Cl) was identified as the oxidation product by X-ray
11
1
crystallography and H NMR spectroscopy.
It is interesting to note that the ratio of 2[OTf] and 3[OTf]
formed in the reactions of 1[OTf] (2 equiv) with K[Fe]
strongly depends on the temperature and the order of addition
of the reagents (Table 1 and Figure S1.5 (Supporting
Information)). When K[Fe] is added slowly to a refluxing
solution of 1[OTf] in THF, the trichloro-substituted product
2[OTf] is formed as the major product (>90% of the total P
content, Table 1, entry 1).
Significant quantities of the monochloro-substituted species
3[OTf] are formed when the reaction is performed at lower
temperatures (Table 1, entries 2−4). Compound 3[OTf]
Special Issue: Applications of Electrophilic Main Group Organo-
metallic Molecules
Received: March 16, 2013
Published: April 9, 2013
© 2013 American Chemical Society
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Scheme 1. Formation of 2[OTf] and 3[OTf] by Reduction of
a
1[OTf]
a
See Table 1 for reducing agent, reaction conditions, and 31P{1H}
NMR spectroscopically observed product distribution.
Table 1. Ratio of Cations 2+ and 3+ Obtained in Selected
Reductions of 1[OTf] in THF According to 31P{1H} NMR
Spectra of the Reaction Mixture
a
entry
reducing agent and reaction conditions
2[OTf]:3[OTf]
1
2
3
4
5
6
7
8
1.0 equiv of K[Fe], reflux, 8 h
1.0 equiv of K[Fe], +65 °C
1.0 equiv of K[Fe], +30 °C
1.0 equiv of K[Fe], −30 °C
1.0 equiv of K[Fe], −90 °C
1.2 equiv of KC8, −78 °C
1.1 equiv of K, THF, 50 °C, ultrasonic bath
1.2 equiv of Na, THF, 50 °C, ultrasonic bath
9.9:0.1
4.5:1
1.5:1
1:2
Figure 1. ORTEP plot of the molecular structure of the cation 2+ in
2[OTf]·1.5THF. Thermal ellipsoids are given at 50% probability
(hydrogen atoms are omitted for clarity). Selected bond lengths (Å)
and angles (deg): P1−P2 = 2.242(1), P1···Cl1 = 2.602(1), P2···Cl1 =
2.594(1), P1−Cl2 = 2.138(1), P2−Cl3 = 2.142(1), P1−C1 =
1.862(3), P2−C28 = 1.852(3), C1−N1 = 1.345(4), C1−N2 =
1.346(5), C28−N3 = 1.361(4), C28−N4 = 1.351(4), C2−N1 =
1.381(5), C2−C3 = 1.349(6), C3−N2 = 1.375(4), C29−N4 =
1.376(4), C29−C30 = 1.343(5), C30−N3 = 1.361(4); C1−P1−Cl2 =
92.7(1), C1−P1−P2 = 99.9(1), P1−P2−C28 = 99.6(1), Cl2−P1−P2
= 103.57(5), N1−C1−N2 = 106.6(3), N3−C28−N4 = 105.4(3)
P1···Cl1···P2 51.1°, C1−P1−P2−C28 = 161.7(5), dihedral Cl2−P1−
P2−Cl3 = 8.0(3).
1:8
1.5:1
4:1
b
9.5:0.5
a
Ratio 2[OTf]:3[OTf] determined by integration of the 31P NMR
spectra. Side products are removed quantitatively by fractional
crystallization of 2[OTf] (CH2Cl2/n-hexane); isolated yield of 2[OTf]
60%.
b
eventually becomes the major product when a THF solution of
1[OTf] (2 equiv) is added slowly to K[Fe] in THF at −90 °C
(Table 1, entry 5). Subsequent heating of the reaction mixture
did not affect the ratio 2+:3+.
unprecedented in phosphorus chemistry, whereas halide-
bridged structures are frequently observed in transition-metal
clusters.14 A related three-membered P2B ring was recently
reported by Robinson et al., who reacted the diphosphabuta-
diene [LDipp2P2] (4)12 with BH3 to afford the boronium salt
[LDipp2P2(μ-BH2)][B2H7]. In this compound the P−P bond
length (2.199(1) Å) is only slightly shorter than that observed
in cation 2+.15 Each phosphorus atom additionally binds to an
imidazoliumyl substituent and a terminal chlorine atom with
normal P−Cl bond lengths of P1−Cl2 = 2.138(1) Å and P2−
Cl3 = 2.142(1) Å.16,17 In contrast, the bridging chlorine atom
Cl1 shows unusually long P−Cl distances of P1···Cl1 =
2.602(1) Å and P2···Cl1 = 2.594(1) Å (cf. dcov(P−Cl) = 2.09 Å
and dvdW(P−Cl) = 3.7 Å) and an acute P1−Cl1−P2 angle of
merely 51.1°. While the overwhelming majority of chloro-
substituted phosphorus compounds feature P−Cl bond lengths
between 1.95 and 2.15 Å,17 we could only find a very few
structures with a P−Cl bond length greater than 2.4 Å. The
structure of the chloro-phosphoranide [NEt4][PPh(CN)2Cl]
features a P−Cl distance of 2.810(1) Å.18 The structure of a P-
chloro-1,3,2-diazaphospholene displays P−Cl distances of
2.6915(4) and 2.759(2) Å, respectively.19 According to
quantum chemical analyses, the weakening of the P−Cl bond
in this compound results from hyperconjugation between a π
orbital of the C2N2 fragment and the σ*(P−Cl) orbital. Finally,
an N-heterocyclic carbene adduct of a P-chloroiminophosphane
The purification of compounds 2[OTf] and 3[OTf] proved
to be difficult, due to their similar solubilities and the presence
of significant amounts of the undesired byproduct [LDippH]-
[OTf], which is difficult to remove by fractional crystallization.
Subsequently, we screened other reducing agents in order to
develop a more efficient synthetic protocol. Reductions of
1[OTf] with potassium and KC8 resulted in similar product
mixtures under various conditions (Table 1, entries 6 and 7).12
Therefore, it was gratifying to finally discover that cation 2+ was
formed in a clean fashion when the reduction of 1[OTf] was
carried out with sodium (1:2) in THF at +60 °C (Table 1,
entry 8). Using this procedure, 2[OTf]·2.5CH2Cl2 was isolated
as air-sensitive orange crystals in 60% yield after crystallization
from CH2Cl2/pentane.11 Crystals of the solvate
2[OTf]·1.5THF, which contains 1.5 THF molecules in the
crystal lattice per formula unit of 2[OTf], were obtained from
THF/n-hexane. Single-crystal analysis revealed an ion-separated
arrangement of the triflate anion and the remarkable cation
[LDipp2P2Cl3]+ (2+) (Figure 1).13 The structure of the cation
shows a diphosphorus moiety (P1−P2 = 2.242(1) Å; cf.
dcov(P−P) = 2.22 A) that is bridged symmetrically by a chlorine
atom. To the best of our knowledge, this structural motif is
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also shows an elongated P−Cl bond (2.471(2) Å).20 Note that
the structure of the monophosphorus cation 1+ in 1[OTf]
features P−Cl bond lengths of 2.025(2) and 2.040(2) Å.13 The
single-crystal X-ray diffraction analysis of crystals of 3[OTf] was
complicated by severe disorder of the triflate anion. Never-
theless, the NMR spectroscopic results and the preliminary X-
ray data clearly indicate that the chlorine atom in the molecular
structure of cation 3+ interacts with one P atom only.
and are engaged in a polar covalent P−Cl bond (polarization:
30% P, 70% Cl) with a WBI of 0.81. In comparison with the
WBI of the P−Cl bond in the hypothetical dication
[L′2P2Cl2]2+ (52+) (WBI = 0.98; Figure 4), which is derived
from 2′+ by removal of the bridging chlorine atom, this
indicates a slightly increased electrostatic contribution to the
P1−Cl2 (P2−Cl3) bond.
The charges of the chlorine atoms calculated with the NBO
and atoms in molecules (AIM) definitions are summarized in
Table 2.26−28 With both methods, the bridging chlorine atom
Consistent with the crystallographically determined struc-
ture, the 31P{1H} NMR spectrum of compound 2[OTf] in
[D8]THF-d8 exclusively shows a singlet at δ −34.4 ppm (Figure
S1.3 (Supporting Information)). This resonance is shifted
significantly to lower field in comparison to Robinson’s neutral
diphosphorus species [LDipp2P2] (4), which shows a chemical
Table 2. Characteristic Topological Data of the Electron
Density in the Bond Critical Points and Charges of the
Chlorine Atoms
shift of δ −52.0 ppm.3c In the H NMR spectrum, resonances
1
∇2ρ
E
corresponding to four chemically inequivalent iPr substituents
are observed. Monochloro-substituted 3[OTf] features two
doublets at δ −22.4 and 132.1 ppm (1JPP = 388.4 Hz) in the
31P{1H} NMR spectrum in THF-d8.
ρ (electron (Laplacian
(electronic
energy)
bond
compd
density)
of ρ)
a
P1−P2
2′+
52+
6
2′+
52+
6
7+
2′+
52+
6
7+
2′+
0.112
0.116
0.109
0.111
0.123
0.133
0.135
0.146
0.159
0.149
0.146
0.046
−0.126
−0.138
−0.120
−0.123
−0.087
−0.125
−0.136
−0.094
−0.232
−0.076
−0.113
0.054
−0.052
−0.057
−0.050
−0.082
−0.107
−0.120
−0.124
−0.136
−0.156
−0.139
−0.137
−0.010
The Raman spectrum of compound 2[OTf] is highly
complex and displays a multitude of bands corresponding to
vibrations delocalized over the whole cation (vide infra for
relaxed force constants as a local bonding descriptor). On the
basis of a comparison with the experimental spectra of
[LDippSiMe3][OTf] and [LDippPCl2][OTf] (1[OTf]) and DFT
calculations, we tentatively assign bands corresponding to the
P−P stretching mode (ν[P−P] 479 cm−1), the P−Cl stretching
mode (ν[P−Cl] 402 cm−1), and a symmetric deformation of
the chlorodiphosphacyclopropane moiety (δ[P···Cl···P] 239
cm−1).11 While the P−P stretching mode is comparable to
those in related diphosphanes (e.g., ν[P−P] 506 cm−1 in
Ph(Br)P−P(Br)Ph),21 the P−Cl stretching frequency is
remarkably small. The symmetrical stretching modes of the
P−Cl bonds in PhPCl2 (ν[P−Cl] 496 cm−1)22 and 1[OTf]
(ν[P−Cl] 550 cm−1)11 are at significantly larger wavenumbers.
Apparently, the P−Cl bond in 2[OTf] is relatively weak in
comparison.
a
a
a
P1−Cl2 (P2−Cl3)
a
P1−C1 (P2−C28)
a
a
P1···Cl1 (P2···Cl1)
charge
atom
compd
AIM
NBO
Cl2 (Cl3)
2′+
52+
6
7+
2′+
52+
6
−0.555
−0.516
−0.590
−0.545
1.079
−0.115
−0.190
−0.283
−0.220
0.555
P1
1.149
0.534
Cation 2+ may be represented by a multitude of canonical
structures. The most intriguing of these, in which the central
chlorine atom is either depicted as a chloride (A) or a
chloronium (B), are shown in Figure 2. In order to shed more
1.055
0.580
7+
2′+
52+
6
7+
2′+
1.748
0.844
C1
0.635
0.042
0.533
0.095
−0.597
0.585
−0.378
0.101
Cl1
−0.633
−0.386
a
Numbering of atoms was adapted to fit the numbering of the
molecular structure of 2+.
Figure 2. Selected, plausible canonical structures for the trichloro-
substituted cation 2+.
Cl1 shows a significantly higher negative charge than the
terminal atoms Cl2 and Cl3, indicating higher bond polarity.
The charges of the terminal Cl atoms compare well with those
of the related cations [L′2P2Cl2]2+ (52+) and [L′PCl2]+ (7+) and
are expectedly less negative than in the neutral diphosphane
[Ph2P2Cl2] (6).
Further insight was gained from a topological analysis of the
electron density using the AIM formalism.27 The quantitative
data for the topological parameters ∇2ρ(r), ρ(r), and E of the
electron density in the bond critical points (BCP) of
[L′2P2Cl3]+ (2′+), [L′2P2Cl2]2+ (52+), [Ph2P2Cl2] (6), and
[L′PCl2]+ (7+) are given in Table 2. Figure 3 shows the contour
map of the Laplacian ∇2ρ(r) of the electron density ρ(r) and
the topological features of ρ(r) in the P1···Cl1···P2 plane of
2′+.27 A positive curvature (positive Laplacian ∇2ρ(r), blue
light on the bonding situation in 2+, DFT calculations were
carried out on the model compound [L′2P2Cl3]+ (2′+), where
the bulky Dipp substituents were replaced by methyl
groups.23,24 The P2Cl3 core of the optimized molecular
structure of 2′+ (C2 symmetry, M06HF/cc-pVTZ25) is in
very good agreement with the experimental structure of 2+.
A second-order perturbation theory analysis reveals signifi-
cant interactions between the lone pairs of Cl1 and the σ*
orbitals of the adjacent P1−Cl2 and P2−Cl3 bonds. The P1−
Cl1 and P2−Cl1 interactions with the bridging chlorine atom
Cl1 show a low Wiberg bond index (WBI) of 0.25. In contrast,
the terminal chlorine atoms Cl2 and Cl3 carry three lone pairs
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We completed our theoretical investigations with an analysis
of the elastic properties of cation 2′+ and compounds 52+, 6,
and 7+. Several recent papers demonstrate the additional
benefit of mechanochemical simulations by means of computed
relaxed force constants (inverse compliance constants),
especially for an understanding of bond activation, unusual
electronic situations, or eminently weak interactions.30−32
According to our calculations, the mechanical bond strength
of the P1−P2 bond (1.95 N/cm) in 2′+ is comparable to that of
other covalent two-electron P−P bonds (e.g., in P4).33 The
mechanical bond strengths of the P1−Cl2 and P2−Cl3 bonds
of only 1.1 N/cm indicate a moderate activation of these bonds
in comparison to the P−Cl bond in PCl3 (2.5 N/cm) in
dication 52+ (2.7 N/cm), monocation 7+ (2.9 N/cm), or
diphosphane 6 (2.6 N/cm), respectively.34 The P1−Cl2 (P2−
Cl3) relaxed force constant of 1.1 N/cm in our model system
2′+ is nevertheless still consistent with a covalent bond. In
marked contrast, the P1···Cl1 and P2···Cl1 interactions show
relaxed force constants of only 0.38 N/cm.
In summary, the quantum chemical analysis confirms the
predominantly electrostatic character of the P1−Cl1 and P2−
Cl1 interactions. In contrast, the terminal P1−Cl2 and P2−Cl3
bonds are typical covalent single bonds. The results support the
conclusion that cation 2+ is best regarded as a Lewis acid base
complex between the dicationic diphosphanediium derivative
[LDipp2P2Cl2]2+ and a chloride anion (structure A, Figure 2),
while a chloronium structure (structure B, Figure 2) does not
appear to be relevant.
Figure 3. Contour map of the Laplacian ∇2ρ(r) of the electron density
ρ(r) of 2′+: (black lines) bond paths; (blue lines) positive ∇2ρ(r);
(dashed red lines) negative ∇2ρ(r); (orange dots) P atoms; (green
dots) Cl atoms; (small red dots) BCPs.
lines) of the electron density dominates along the bond path
P1−Cl1 (black lines). This is a typical feature of closed-shell
interactions.29 In contrast, a negative curvature is observed
along the bond path corresponding to the P1−Cl2 bond. This
indicates an accumulation of electron density, which is also
reflected in the comparably large electron density ρ in the BCP
(0.111) and is typical for a shared interaction. The electronic
energy E at the BCP is expected to be positive for a closed-shell
interaction.29 The values of E for the BCPs of the P1−Cl1 and
P2−Cl1 bonds are only marginally negative but significantly
higher than the corresponding values for the P1−Cl2 and P2−
Cl3 bonds. Figure 4 illustrates the analogous topological
features of ρ(r) in the C1−P1−Cl2 plane of compounds 2′+,
52+, 6, and 7+. All four compounds feature very similar
characteristics of the electron density. The topological
parameters ∇2ρ(r), ρ(r), and E of the P−C, P−P, and
exocyclic P−Cl bonds are only marginally affected by the
interaction with the bridging chloride ion in compound 2′+.
CONCLUSION
■
In conclusion, we have described the unusual P−P-bonded
cation [LDipp2P2Cl3]+ (2+), which shows an unprecedented
chloride-bridged structure. According to our quantum chemical
calculations, the bonding situation in 2+ can be interpreted in
terms of an interaction between a dicationic phosphorus-based
Lewis acid and a chloride anion. The agreement between the
relaxed force constants (inverse compliance constants) on the
one hand and the experimental Raman data as well as the AIM
analysis on the other hand confirms the appropriateness of
compliance constants for the description of weak interactions.
Cation 2+ is accessible in moderate yield and high purity via the
reduction of the imidazolium salt [LDippPCl2][OTf] (1[OTf])
with sodium. The monochloro-substituted cation [LDipp2P2Cl]+
(3+) was identified as a further product of reactions of 1+ with
the low-valent naphthalene complex K[Fe], indicating that the
Figure 4. Contour maps of the Laplacian ∇2ρ(r) of the electron density ρ(r) of 2′+, 52+, 6, and 7+ as depicted below the maps; (black lines) bond
paths; (blue lines) positive ∇2ρ(r); (dashed red lines) negative ∇2ρ(r); (orange dots) P atoms; (green dots) Cl atoms; (small green dots) BCPs.
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dried in vacuo to yield analytically pure but very moisture sensitive
[LDippSiMe3][OTf]: yield 54.00 g (88.40 mmol, 93%). Mp: 188−190
°C, colorless melt. Raman (80 mW, cm−1): ν 3168 (9), 3084 (16),
3035 (6), 2979 (76), 2943 (11), 2910 (95), 2874 (38), 2773 (6), 2729
(9), 1592 (45), 1555 (22), 1469 (24), 1447 (17), 1378 (71), 1340
(31), 1305 (49), 1235 (20), 1104 (23), 1031 (57), 984 (32), 957 (12),
887 (42), 753 (17), 732 (6), 645 (25), 614 (34), 574 (15), 522 (8),
466 (9), 348 (23), 311 (31), 236 (7), 187 (20), 143 (31), 115 (17). IR
(ATR, cm−1): ν 2968 (w), 1554 (vw), 1461 (w), 1446 (vw), 1414
(vw), 1391 (vw), 1370 (vw), 1326 (vw), 1263 (vs), 1224 (w), 1208
(vw), 1146 (m), 1119 (vw), 1061 (vw), 1030 (m), 936 (vw), 848 (vs),
809 (m), 794 (vw), 781 (vw), 764 (m), 718 (vw), 636 (vs). 1H NMR
course of such reductions strongly depends on the reducing
agent and the reaction conditions. More extensive experimental
and theoretical studies are currently underway in order to
elucidate the mechanism of formation of cations 2+ and 3+.
Ongoing work in our laboratories furthermore concerns the
potential ability of other electrophilic phosphorus-based cations
to act as halide anion acceptors in a manner similar to that for
2+.
EXPERIMENTAL SECTION
■
General Remarks. All manipulations were performed in an
MBraun Unilab Glovebox or using Schlenk techniques under an
atmosphere of purified argon. Dry, oxygen-free solvents (CH2Cl2,
C6H5F, (distilled from CaH2, respectively), THF, toluene (distilled
from Na/benzophenone respectively), n-hexane (distilled from Na))
were employed. Deuterated benzene (C6D6) and THF-d8 was
purchased from Sigma-Aldrich and distilled from Na. Anhydrous
deuterated acetonitrile (CD3CN) and dichloromethane (CD2Cl2)
were purchased from Sigma-Aldrich. All distilled and deuterated
solvents were stored either over molecular sieves (4 Å; CH2Cl2,
C6H5F, toluene, THF-d8, C6D6, CD2Cl2, CD3CN, THF-d8) or
potassium mirror (n-hexane). PCl3 and Me3SiOTf were purchased
from Sigma-Aldrich. Me3SiOTf was degassed by three freeze−pump−
thaw cycles and distilled prior to use. 1,3-Bis(2,6-diisopropylphenyl)-
imidazol-2-ylidene35 and [K(18-crown-6){Cp*Fe(η4-C10H8)}] (K-
[Fe])10 were prepared according to the literature procedure. All
glassware was oven-dried at 160 °C prior to use. NMR spectra were
measured on a Bruker AVANCE (III) (1H (400.03 MHz), 13C (100.59
MHz), 31P (161.94 MHz)), a Bruker AVANCE (I) (1H (400.13
MHz), 13C (100.61 MHz), 31P (161.98 MHz)), or a Bruker AVANCE
(II) instrument (1H (200.13 MHz), 31P (81.01 MHz)) at 300 K unless
indicated otherwise. Chemical shifts were referenced to δTMS 0.00 ppm
(1H, 13C) and δH PO (85%) 0.00 ppm (31P, externally). Chemical shifts
(CD3CN, 300 K, ppm): δ −0.19 (9H, s, C8−H), 1.19 (12H, d, 3JHH
=
3
6.8 Hz, CH(CH3)2), 1.36 (12H, d, JHH = 6.8 Hz CH(CH3)2), 2.41
(4H, quart quart, pseudo sept, JHH = 6.8 Hz, 3JHH = 6.8 Hz, C7−H),
3
3
3
7.51 (4H, d, JHH = 7.8 Hz, C5−H), 7.69 (2H, t, JHH = 7.8 Hz, C6−
H), 7.95 (2H, s, C2−H). 13C{1H} NMR (CD3CN, 300 K, ppm): δ
−1.0 (s, C8), 22.4 (s, CH(CH3)2), 26.3 (s, CH(CH3)2), 30.1 (s, C7),
122.3 (quart, 1JCF = 320 Hz, CF3), 125.9 (s, C5), 129.9 (s, C2), 133.0
(s, C3), 133.5 (s, C6), 146.6 (s, C4), 153.5 (s, C1). 19F{1H} NMR
(CD3CN, 300 K, ppm): δ −79.2 (s, CF3). 29Si{1H} NMR (CD3CN,
300 K, ppm): δ −1.0 (s). Anal. Calcd for C31H45F3N2O3SSi: C, 60.95;
H, 7.43; N, 4.59. Found: C, 60.48; H, 7.13; N, 4.56.
Preparation of 1[OTf].
3
4
(δ) are reported in ppm. Coupling constants (J) are reported in Hz.
Absolute values are reported. Assignments of individual resonances
were done using 2D techniques (HMBC, HSQC) where necessary.
Melting points were recorded on an electrothermal melting point
apparatus (Barnstead Electrothermal IA9100) in sealed capillaries
under an argon atmosphere and are uncorrected. Infrared (IR) and
Raman spectra were recorded at ambient temperature using a Bruker
Vertex 70 instrument equipped with a RAM II module (Nd:YAG laser,
1064 nm). The Raman intensities are reported in percent relative to
the most intense peak and are given in parentheses. An ATR cell
(diamond) was used for recording IR spectra. The intensities are
reported relative to the most intense peak and are given in parentheses
using the following abbreviations: vw = very weak, w = weak, m =
medium, s = strong, vs = very strong. Elemental analyses were
performed on a Vario EL III CHNS elemental analyzer at the IAAC,
A suspension of [LDippSiMe3][OTf] (20.00 g, 32.70 mmol) in
fluorobenzene (100 mL) was added dropwise to a slight excess of
PCl3 (5.80 g, 3.70 mL, 42.60 mmol). After the mixture was stirred
overnight, n-hexane (150 mL) was added. A colorless precipitate was
formed, separated by filtration and washed with n-hexane (3 × 30
mL). Analytically pure but very moisture sensitive 1[OTf] was
obtained after drying in vacuo: yield 20.44 g (31.79 mmol, 98%). Dec
pt: >240 °C, yellow-brown melt. Raman (80 mW, cm−1): ν 3170 (10),
3073 (32), 3033 (5), 2984 (16), 2968 (17), 2939 (40), 2914 (14),
2869 (39), 2769 (7), 2724 (9), 1592 (55), 1540 (33), 1467 (34), 1444
(25), 1365 (91), 1325 (51), 1298 (46), 1237 (25), 1185 (6), 1105
(27), 1032 (59), 984 (32), 955 (14), 886 (50), 754 (24), 732 (14),
617 (32), 573 (11, νasym[P−Cl]), 550 (8, νsym[P−Cl]), 522 (98), 485
(10), 463 (18), 445 (12), 418 (5, ν[P−C]), 390 (8), 349 (18), 313
(14), 294 (16, δ[P−C−N−C(Me)]), 237 (20), 165 (93), 117 (33). IR
(ATR, cm−1): ν 3169 (vw), 2967 (w), 1539 (vw), 1506 (vw), 1458
(w), 1389 (vw), 1364 (vw), 1325 (vw), 1280 (vw), 1257 (s), 1223
(w), 1204 (vw), 1150 (m), 1060 (vw), 1031 (s), 936 (vw), 811 (w),
University of Munster, Germany.
̈
Preparation of [LDippSiMe3][OTf].
1
782 (vw), 759 (m), 709 (vw), 636 (vs). H NMR (CD3CN, 300 K,
ppm): δ 1.23 (12H, d, 3JHH = 6.7 Hz, CH(CH3)2), 1.33 (12H, d, 3JHH
= 6.7 Hz, CH(CH3)2), 2.37 (4 H, quart quart, pseudo sept, 3JHH = 6.7
3
Hz, 3JHH = 6.7 Hz, C7−H), 7.53 (4H, d, JHH = 7.8 Hz, C5−H), 7.74
3
(2H, d, JHH = 7.8 Hz, C6−H), 8.25 (2H, s, C2−H). 13C{1H} NMR
(CD3CN, 300 K, ppm): δ 22.8 (s, CH(CH3)2), 25.8 (s, CH(CH3)2),
A slight excess of Me3SiOTf (19.00 mL, 23.20 g, 105.00 mmol) was
slowly added at 0 °C to a suspension of 1,3-bis(2,6-diisopropyl)-
phenylimidazol-2-ylidene (37.00 g, 95.00 mmol) in fluorobenzene
(150 mL). During the course of the addition, the light red suspension
turned into a colorless solution. After ∼1 h, n-hexane (100 mL) was
added and the colorless precipitate that was formed was separated by
filtration. The precipitate was washed with n-hexane (3 × 30 mL) and
30.5 (s, C7), 122.3 (quart, 1JCF = 319.7 Hz, CF3), 126.2 (s, C6), 130.0
1
(s, C3), 131.5 (s, C2), 134.2 (s, C5), 143.5 (d, JCP = 119.0 Hz, C1),
146.5 (s, C4). 31P{1H} NMR (CD3CN, 300 K, ppm): δ 113.8 (s).
19F{1H} NMR (CD3CN, 300 K, ppm): δ −79.2 (s, CF3). Anal. Calcd
for C28H36Cl2F3N2O3PS: C, 52.58; H, 5.67; N, 4.38. Found: C, 52.09;
H, 5.50; N, 4.29.
6678
dx.doi.org/10.1021/om4002268 | Organometallics 2013, 32, 6674−6680

Organometallics
Article
Preparation of 2[OTf].
2[OTf]·1.5CH2Cl2 (C56.5H75Cl6F3N4O3P2S): C, 55.16; H, 5.99; N,
4.59. Found: C, 55.53; H, 6.19; N, 4.59 (consistent with the
1
integration of the H NMR spectrum of dissolved crystalline material
in CD2Cl2 after recrystallization from CH2Cl2/pentane at −35 °C).
Preparation of 3[OTf].
A solution of 1[OTf] (0.48 g, 0.75 mmol) in 10 mL of THF was
added dropwise to a solution of [K(18-crown-6){Cp*Fe(η4-C10H8)}]
(K[Fe], 0.23 g, 0.38 mmol) in 20 mL of THF at −90 °C. The reaction
mixture turned green at first and then yellow within 2 days. An orange
precipitate of [Fe]Cl was formed, which was isolated and characterized
as described in the Supporting Information. The mother liquor of this
crystalline precipitate was evaporated. The residue was washed with
toluene (3 × 20 mL) and dissolved in THF (20 mL). The THF
solution was filtered and layered with 20 mL of toluene. The first
fraction, containing mostly [LDippH]Cl and [LDippH][OTf], crystallized
first at −18 °C. A second crystalline fraction was obtained from the
concentrated mother liquor that contained 90% 3[OTf] and 10%
2[OTf] according to 31P NMR spectroscopy. All attempts to separate
these two compounds by crystallization were not successful: yield of
3[OTf] 0.065 g (0.06 mmol, 15%), 1H NMR (THF-d8, 300 K, ppm):
δ 0.79 (d, 6H, CH(CH3)2), 0.86 (d, 6H, CH(CH3)2), 1.00 (d, 6H,
CH(CH3)2), 1.02 (d, 6H, CH(CH3)2), 1.05 (d, 6H, CH(CH3)2), 1.09
(d, CH(CH3)2), 1.19 (d, 6H, CH(CH3)2), 1.22 (d, 6H, CH(CH3)2),
2.25 (quart quart, pseudo sept, 2H, CH(CH3)2), 2.39 (sept, 2H,
CH(CH3)2), 2.50 (overlapping sept, 4H, CH(CH3)2), 7.17 (d, 4H, m-
H Dipp), 7.25 (d, 2H, m-H Dipp), 7.32 (d, 2H, m-H Dipp), 7.44 (t,
2H, p-H Dipp), 7.49 (t, 2H, p-H Dipp), 7.49 (s, 2H, H2,3), 8.05 (s, 2H,
H29,30). 13C{1H} NMR (THF-d8, 300 K, ppm): δ 22.4 (CH(CH3)2),
23.2 (CH(CH3)2), 23.5 (CH(CH3)2), 23.6 (CH(CH3)2), 24.9
1[OTf] (1.30 g, 2.00 mmol) was combined with sodium (0.10 g, 4.00
mmol), suspended in THF (20 mL), and stirred overnight. The
colorless suspension was subsequently heated in an ultrasonic bath at
60 °C for ∼12 h. The suspension turned from colorless to orange.
This suspension was then filtered, all volatile compounds from the
filtrate were removed in vacuo, and the obtained orange solid was
dried in vacuo. 2[OTf] was obtained as a yellow solid after
recrystallization from dichloromethane/n-hexane; crystals of 2[OTf]
suitable for X-ray crystallography were obtained from THF/n-hexane:
yield 0.65 g (0.59 mmol, 60%). Recrystallization of 2[OTf] from
CH2Cl2/pentane at −35 °C yields yellow blocks of
2[OTf]·2.5CH2Cl2, which readily loses one molecule of CH2Cl2 per
formula unit when removed from the mother liquor. Dec pt: >216 °C,
yellow-brown melt. Raman (95 mW, cm−1): ν 3173 (9), 3073 (38),
3038 (5), 2968 (14), 2938 (95), 2915 (14), 2871 (48), 2765 (9), 2721
(13), 1591 (43), 1551 (19), 1466 (40), 1445 (20), 1392 (33), 1364
(47), 1328 (53), 1304 (43), 1255 (5), 1237 (24), 1182 (4), 1166 (10),
1140 (6), 1104 (24), 1045 (15), 1033 (53), 981 (22), 960 (33), 885
(43), 808 (5), 755 (19), 732 (14), 713 (4), 703 (10), 615 (29), 575
(14), 552 (6), 524 (11), 496 (15, ν[P−P]), 479 (16), 466 (5, ν[P−
C]), 449 (10, δ[C−P−P−C]), 402 (20, ν[P−Cl]), 349 (20, δ[Cl−P−
P−Cl]), 312 (29), 293 (4), 239 (34, δ[P···Cl···P]), 190 (10), 150
(50). IR (ATR, cm−1): ν 3170 (vw), 3073 (vw), 2965 (w), 2932 (vw),
2870 (vw), 1681 (vw), 1590 (vw), 1552 (vw), 1463 (w), 1442 (w),
1419 (w), 1386 (w), 1364 (w), 1328 (w), 1265 (vs), 1223 (vw), 1206
(w), 1182 (vw), 1154 (m), 1121 (vw), 1059 (w), 1030 (m), 929 (vw),
803 (w), 781 (vw), 754 (w), 730 (w), 710 (vw), 635 (s), 572 (w), 517
(w), 497 (vw), 470 (vw), 439 (w). 1H NMR (THF-d8, 300 K, ppm): δ
0.47 (6H, d, 3JHH = 6.5 Hz, CH(CH3)2 DippB), 0.84 (6H, d, 3JHH = 6.8
(CH(CH3)2), 25.6 (CH(CH3)2), 25.8 (CH(CH3)2), 26.0 (CH-
1
(CH3)2), 29.8 (CH(CH3)2), 29.9 (CH(CH3)2), 122.4 (quart, JCF
=
323 Hz, CF3), 124.9 (m-C of Dipp), 125.6 (m-C of Dipp), 126.0 (m-C
of Dipp), 126.7 (C2,3), 129.5 (C29,30), 132.1 (p-C Dipp), 132.8 (p-C
Dipp), 132.8 (i-C Dipp), 133.7 (i-C Dipp), 146.0 (o-C Dipp), 146.3
1
(o-C Dipp), 147.1 (o-C Dipp), 147.8 (o-C Dipp), 151.8 (dd, JCP
=
87.3 Hz, 2JCP = 27.4 Hz, C28), 165.7 (dd, 1JCP = 118.9 Hz, 2JCP = 34.6
Hz, C1). 31P{1H} NMR (THF-d8, 300 K, ppm): δ −22.4 (P1, d, 1JPP
=
3
382.2 Hz, PPCl), 132.1 (P1, d, 1JPP = 382.2 Hz, PPCl). 19F{1H} NMR
(THF-d8, 300 K, ppm): δ −79.1 (s, CF3).
Hz, CH(CH3)2 DippB), 1.01 (6H, d, JHH = 6.7 Hz, CH(CH3)2
3
DippA), 1.03 (6H, d, JHH = 6.8 Hz, CH(CH3)2 DippA), 1.07 (6H, d,
3
3JHH = 6.8 Hz, CH(CH3)2 DippB), 1.24 (6H, d, JHH = 6.7 Hz,
3
CH(CH3)2 DippA), 1.26 (6H, d, JHH = 6.8 Hz, CH(CH3)2 DippA),
ASSOCIATED CONTENT
* Supporting Information
1.32 (6H, d, 3JHH = 6.5 Hz, CH(CH3)2 DippB), 2.51 (2H, quart quart,
■
S
3
3
pseudo sept, JHH = 6.7 Hz, JHH = 6.7 Hz, CH(CH3)2 DippA), 2.56
3
3
Text, tables, figures, and CIF files giving experimental,
spectroscopic, and crystallographic data for compounds
1[OTf], 2[OTf], 3[OTf], 4, and [Fe]Cl. This material is
available free of charge via the Internet at http://pubs.acs.org.
CCDC files 782415−782419 also contain crystallographic data
for these compounds.
(2H, quart quart, pseudo sept., JHH = 6.8 Hz, JHH = 6.8 Hz,
CH(CH3)2 DippA), 2.59 (2H, quart quart, pseudo sept, 3JHH = 6.8 Hz,
3JHH = 6.8 Hz, CH(CH3)2 DippB), 2.69 (2H, quart quart, pseudo sept,
3JHH = 6.5 Hz, 3JHH = 6.5 Hz, CH(CH3)2 DippB), 7.04 (2H, d, 3JHH
=
7.9 Hz, m-CH DippB), 7.27 (2H, d, 3JHH = 7.9 Hz, m-CH DippB), 7.37
3
3
(2H, d, JHH = 7.6 Hz, m-CH DippA), 7.42 (2H, d, JHH = 7.6 Hz, m-
CH DippA), 7.46 (2H, t, 3JHH = 7.9 Hz, p-CH DippB), 7.57 (2H, t, 3JHH
= 7.6 Hz, p-CH DippA), 8.00 (2H, s, C2−H), 8.06 (s, 2H, C3−H).
13C{1H} NMR (THF-d8, 300 K, ppm): δ 21.6 (s, CH(CH3)2 DippB),
22.6 (s, CH(CH3)2 DippA), 23.2 (s, CH(CH3)2 DippA,B), 26.3 (s,
CH(CH3)2 DippA), 26.4 (s, CH(CH3)2 DippA,B), 26.6 (s, CH(CH3)2
DippB), 29.4 (s, CH(CH3)2 DippB), 29.9 (s, CH(CH3)2 DippA), 30.3
AUTHOR INFORMATION
Corresponding Author
■
*J.J.W.: tel, (+)49 351-46842800; e-mail, jan.weigand@tu-
dresden.de. R.W.: fax, (+)49 941 943814485; tel, (+)49 941-
9434485; e-mail, robert.wolf@ur.de.
(s, CH(CH3)2 DippA), 30.4 (s, CH(CH3)2 DippB), 122.4 (quart, 1JCF
=
321.8 Hz, CF3), 124.4 (s, m-C DippB), 125.2 (s, m-C DippA), 125.8 (s,
m-C DippB), 126.0 (s, m-C DippA), 128.4 (s, C2), 130.5 (s, C3), 132.1
(s, i-C DippB), 132.3 (s, i-C DippA), 132.9 (s, p-C DippA), 133.4 (s, p-
C DippB), 147.2 (s, o-C DippA), 147.8 (s, o-C DippA), 148.0 (s, o-C
DippB), 148.8 (s, o-C DippB), 152.0 (dd, JCP = 53.5 Hz, JCP = 46.2
Hz, C1). 31P{1H} NMR (THF-d8, 300 K, ppm): δ −34.4 (s). 19F{1H}
NMR (THF-d8, 300 K, ppm): δ −79.1 (s, CF3). Anal. Calcd for
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We dedicate this paper to Prof. Dr. Werner Uhl on the occasion
of his 60th birthday. Funding from the Deutsche Forschungs-
1
2
■
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Organometallics
Article
(15) Wang, Y.; Xie, Y.; Abraham, M. Y.; Wei, P.; Schaefer, H. F., III;
Schleyer, P. v. R.; Robinson, G. H. Chem. Commun. 2011, 47, 9224.
(16) Wiberg, N. Holleman-Wiberg: Lehrbuch der Anorganischen
Chemie, 102nd ed.; de Gruyter: Berlin, 2007; p 777.
(17) A survey in the Cambridge Crystal Structure database (CSD
version 5.33, Nov 2011) yielded 3355 entries with P−Cl distances in
the range 1.851−2.810 Å (median 2.005 Å). Out of these entries, 3196
structures showed P−Cl distances between 1.938 and 2.155 Å (median
2.004 Å).
gemeinschaft (WE 4621/2-1, WO1496/3-1, and 4-1), the
Fonds der Chemischen Industrie (fellowships to E.-M.S., K.-
O.F., R.W., and J.J.W.), and COST action CM0802
(PhosSciNet) is gratefully acknowledged, and Dr. Babak Rezaei
Rad is thanked for assistance. R.W. and J.J.W. are indebted to
Prof. W. Uhl and Prof. F. E. Hahn for their generous support
and advice.
(18) Deng, R. M. K.; Dillon, K. B.; Sheldrick, W. S. J. Chem. Soc.,
Dalton Trans. 1990, 551.
(19) (a) Gudat, D.; Haghverdi, A.; Hupfer, H.; Nieger, M. Chem. Eur.
J. 2000, 6, 3414. (b) Denk, M. K.; Gupta, S.; Lough, A. J. Eur. J. Inorg.
Chem. 1999, 41.
(20) Burford, N.; Cameron, T. S.; LeBlanc, D. J.; Phillips, A. D.;
Concolino, T. E.; Lam, K.-C.; Rheingold, A. L. J. Am. Chem. Soc. 2000,
122, 5413.
REFERENCES
■
(1) Wiberg, N. Holleman-Wiberg: Lehrbuch der Anorganischen Chemie,
102nd ed., de Gruyter: Berlin, 2007; p 310.
(2) (a) Cowley, A. H. Chem. Rev. 1965, 65, 617. (b) von Schnering,
H. G. Angew. Chem. 1981, 93, 44; Angew. Chem., Int. Ed. Engl. 1981,
20, 33. (c) Baudler, M. Angew. Chem. 1982, 94, 520; Angew. Chem., Int.
Ed. 1982, 21, 492. (d) Baudler, M. Angew. Chem. 1987, 99, 429; Angew.
Chem., Int. Ed. 1987, 26, 419. (e) Baudler, M.; Glinka, K. Chem. Rev.
1993, 93, 1623. (e) Dyker, C. A.; Bertrand, G. Science 2008, 321, 1050.
(f) Wolf, R.; Uhl, W. Angew. Chem. 2009, 121, 6905; Angew. Chem., Int.
Ed. 2009, 48, 6774. (g) Gomez-Ruiz, S.; Hey-Hawkins, E. Coord.
Chem. Rev. 2011, 255, 1360.
(21) Hassler, K.; Hofler, F. Z. Anorg. Allg. Chem. 1978, 448, 125.
̈
(22) Schindlbauer, H.; Stenzenberger, H. Spectrochim. Acta, Part A
1970, 26, 1707.
(23) Gaussian 09, Revision A.02, 2009; for a complete list of authors
see the Supporting Information.
(3) Selected recent references: (a) Masuda, J. D.; Schoeller, W. W.;
Donnadieu, B.; Bertrand, G. J. Am. Chem. Soc. 2007, 129, 14180.
(b) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G.
Angew. Chem. 2007, 119, 7182; Angew. Chem., Int. Ed. 2007, 46, 7052.
(c) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F., III;
Schleyer, P. v. R.; Robinson, G. H. J. Am. Chem. Soc. 2008, 130, 14970.
(d) Back, O.; Kuchenbeiser, G.; Donnadieu, B.; Bertrand, G. Angew.
Chem. 2009, 121, 5638; Angew. Chem., Int. Ed. 2009, 48, 5530.
(4) (a) Weigand, J. J.; Burford, N.; Decken, A.; Schulz, A. Eur. J.
Inorg. Chem. 2007, 4868. (b) Dyker, C. A.; Burford, N. Chem. Asian J.
2008, 3, 28.
(5) (a) Tarasova, R. I.; Zykova, T. V.; Shagvaleev, F. Sh.; Sitdikova,
T. Sh.; Moskva, V. V. Zh. Obshch. Khim. 1989, 60, 1775. (b) Tarasova,
R. I.; Sitdikova, T. Sh.; Zykova, T. V.; Shagvaleev, F. Sh.; Moskva, V.
V.; Kormachev, V. V.; Rusanov, V. M.; Baranov, Yu. I.; Danilov, S. D.
U.S.S.R. Patent SU 1449565, July 1, 1989; Scifinder Scholar:
1989:497499. (c) Shagvaleev, F. Sh.; Zykova, T. V.; Tarasova, R. I.;
Sitdikova, T. Sh.; Moskva, V. V. Zh. Obshch. Khim. 1990, 60, 1775.
(d) Tarasova, R. I.; Zykova, T. V.; Shagvaleev, F. Sh.; Sitdikova, T. Sh.;
Moskva, V. V. Zh. Obshch. Khim. 1991, 61, 2529. (e) Krossing, I.;
Raabe, I. Angew. Chem. 2001, 113, 4544; Angew. Chem., Int. Ed. 2001,
(24) See the Supporting Information for further details regarding the
choice of the functional and basis set and the effects of using methyl
instead of diisopropylphenyl substituents.
(25) Zhao, Y.; Truhlar, D. G. J. Phys. Chem. A 2006, 110, 13126.
(26) (a) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold,
F. NBO Version 3.1. (b) Glendening, E. D.; Reed, A. E.; Carpenter, J.
E.; Weinhold, F. Chem. Rev. 1988, 88, 899.
(27) Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Oxford
University Press: Oxford, U.K., 1995; International Series of
Monographs on Chemistry (cf. the Supporting Information).
(28) Keith, T. A. AIMAll (Version 11.08.23); TK Gristmill Software,
Overland Park KS, 2011 (aim.tkgristmill.com).
(29) Bader, R. F. W. J. Phys. Chem. A 1998, 102, 7314.
(30) Shaik, S.; Danovich, D.; Wu, W.; Su, P.; Rzepa, H. S.; Hiberty, P.
C. Nat. Chem. 2012, 4, 195.
(31) Espinosa, A.; Streubel, R. Chem. Eur. J. 2011, 17, 3166.
(b) Schreiner, P. R. Angew. Chem. 2009, 121, 8277; Angew. Chem., Int.
Ed. 2009, 48, 8133.
(32) Grunenberg, J.; Barone, G. RSC Adv. 2013, 3, 4757.
(33) (a) Katsyuba, S.; Schmutzler, R.; Grunenberg, J. Dalton Trans.
2005, 1701. (b) Brandhorst, K.; Grunenberg, J. Chem. Soc. Rev. 2008,
37, 1558.
(34) In order to test the robustness of our numerical results, we
calculated the mechanical bond properties for the experimental species
2+ with 2,6-diisopropylphenyl (Dipp) substituents applying the
M06HF method and a smaller basis set of double-ζ quality (6-
31G(d)). The mechanical bond strength is more or less unaffected
(0.40 N/m); cf. the Supporting Information.
40, 4406. (f) Gonsior, M.; Krossing, I.; Muller, L.; Raabe, I.; Jansen,
̈
M.; van Wullen, L. Chem. Eur. J. 2002, 8, 4475. (g) Krossing, I. Dalton
̈
Trans. 2002, 500. (h) Holthausen, M. H.; Feldmann, K.-O.; Schulz, S.;
Hepp, A.; Weigand, J. J. Inorg. Chem. 2012, 51, 3374.
(6) Carpenter, Y.-Y.; Burford, N.; Lumsden, M. D.; McDonald, R.
Inorg. Chem. 2011, 50, 3342.
(7) Weigand, J. J.; Burford, N.; Davidson, R. J.; Cameron, T. S.;
Seelheim, P. J. Am. Chem. Soc. 2009, 131, 17943.
(8) Weigand, J. J.; Feldmann, K.-O.; Henne, F. D. J. Am. Chem. Soc.
2010, 132, 16321.
(35) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R. Tetrahedron
1999, 50, 14523.
(9) Brandhorst, K.; Grunenberg, J. Chem. Soc. Rev. 2008, 37, 1558.
(10) (a) Wolf, R.; Schnockelborg, E.-M. Chem. Commun. 2010, 46,
̈
2832. (b) Schnockelborg, E.-M.; Weigand, J. J.; Wolf, R. Angew. Chem.
̈
2011, 123, 6786; Angew. Chem., Int. Ed. 2011, 50, 6657.
(c) Schnockelborg, E.-M.; Khusniyarov, M.; de Bruin, B.; Hartl, F.;
̈
Langer, T.; Eul, M.; Schulz, S.; Pottgen, R.; Wolf, R. Inorg. Chem.
̈
2012, 51, 6719.
(11) See the Supporting Information for details.
(12) We note that Robinson’s landmark diphosphabutadiene
[LDipp2P2] (4)3c can be isolated in high (>95%) yield by reducing
1[OTf] using a slight excess of KC8 (1:3.5) in THF (cf. the
Supporting Information).
(13) Details of the X-ray analyses of 1[OTf], 2[OTf]·1.5THF, and
[Fe]Cl are given in the Supporting Information.
(14) Shriver, D. F.; Kaesz, H. D.; Adams, R. D. The Chemistry of
Metal Cluster Complexes; Wiley-VCH: Weinheim, Germany, 1990.
6680
dx.doi.org/10.1021/om4002268 | Organometallics 2013, 32, 6674−6680