Reductive elimination at an ortho-metalated iridium(III) hydride bearing a tripodal tetraphosphorus ligand

Article abstract of DOI:10.1021/om400451y

The synthesis of the novel C₃-symmetric tripodal, tetradentate ligand 1, bearing only phosphorus atoms as donor groups, is described, starting from commercially available o-tolyldiphenylphosphine, and its molecular structure has been determined by X-ray crystallographic analysis. Coordination to the cationic Ir^I precursor [Ir(COE)₂(acetone) ₂]PF₆ led to a highly unsymmetrical species (90% yield) with four inequivalent phosphorus atoms, as evidenced by ³¹P NMR spectroscopy. The corresponding ¹H NMR spectrum exhibited a pseudo doublet of quartets at δ -5.9 ppm with one large trans P-H coupling ( ²J_P-H = 115.4 Hz) and a much smaller cis coupling ( ²J_P-H = 10.8 Hz). X-ray crystallography confirmed the formation of complex 2, [Ir(H)(κ⁵P,P,P,P,C-1)]PF₆, which is a rare example of a structurally characterized mononuclear Ir hydride species bearing an ortho-metalated phosphine ligand. This species does not react with hydride sources, but addition of 1 equiv of CF₃COOH resulted in facile overall formal protonation of the Ir-C bond. DFT calculations support a pathway involving initial reductive elimination, forming the highly distorted four-coordinate Ir^I species 2′, followed by protonation at iridium to give the dicationic monohydride species 3, with an activation barrier ΔG^? of 28.2 kcal mol^-1. Deuteration experiments support this mechanism. Reductive elimination can also be induced by reaction of 2 with carbon monoxide, yielding the monocationic carbonyl complex [Ir^I(CO)(1)]PF₆ as the sole product.

Full text of DOI:10.1021/om400451y

Article
pubs.acs.org/Organometallics
Reductive Elimination at an Ortho-Metalated Iridium(III) Hydride
Bearing a Tripodal Tetraphosphorus Ligand
Yann Gloaguen,† Lianne M. Jongens,† Joost N. H. Reek,† Martin Lutz,‡ Bas de Bruin,†
and Jarl Ivar van der Vlugt*,†
†Homogeneous & Supramolecular Catalysis, van ’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904,
1098 XH Amsterdam, The Netherlands
‡Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, The Netherlands
S
* Supporting Information
ABSTRACT: The synthesis of the novel C3-symmetric tripodal, tetradentate
ligand 1, bearing only phosphorus atoms as donor groups, is described, starting
from commercially available o-tolyldiphenylphosphine, and its molecular structure
has been determined by X-ray crystallographic analysis. Coordination to the
cationic IrI precursor [Ir(COE)2(acetone)2]PF6 led to a highly unsymmetrical
species (90% yield) with four inequivalent phosphorus atoms, as evidenced by 31
P
1
NMR spectroscopy. The corresponding H NMR spectrum exhibited a pseudo
doublet of quartets at δ −5.9 ppm with one large trans P−H coupling (2JP−H
=
115.4 Hz) and a much smaller cis coupling (2JP−H = 10.8 Hz). X-ray
crystallography confirmed the formation of complex 2, [Ir(H)(κ5P,P,P,P,C-
1)]PF6, which is a rare example of a structurally characterized mononuclear Ir
hydride species bearing an ortho-metalated phosphine ligand. This species does
not react with hydride sources, but addition of 1 equiv of CF3COOH resulted in facile overall formal protonation of the Ir−C
bond. DFT calculations support a pathway involving initial reductive elimination, forming the highly distorted four-coordinate IrI
species 2′, followed by protonation at iridium to give the dicationic monohydride species 3, with an activation barrier ΔG† of
28.2 kcal mol−1. Deuteration experiments support this mechanism. Reductive elimination can also be induced by reaction of 2
with carbon monoxide, yielding the monocationic carbonyl complex [IrI(CO)(1)]PF6 as the sole product.
Chart 1. Structures of Tripodal Tetradentate Trisphosphine
Ligands NP3,3 SiP3,4 and BP3,5 Linkage Isomers A and B of
Tripodal Tetradentate All-Phosphorus Donor Ligands Based
on 3-Methylindole,5 and the Novel Ligand Scaffold 1
INTRODUCTION
■
Encapsulation of transition-metal complexes in well-defined
environments, using either supramolecular or covalent
approaches, is being actively pursued to stabilize and character-
ize species with unusual properties (reactivity, electronic
structure, geometry) that may ultimately be exploited in, for
example, catalytic reactions.1 Concerning covalent frameworks,
in particular C3-symmetric tripodal ligand systems have
provided an ideal platform to investigate new phenomena in
the reactivity of transition-metal complexes over the past few
decades.2 Among the plethora of binding motifs, ranging from
neutral to trianionic scaffolds, triphosphine ligands have taken a
prominent role, especially concerning the stabilization of late-
transition-metal complexes.
An early, prominent tetradentate ligand bearing a coordinat-
ing noncarbon bridgehead atom is Sacconi’s NP3 system,
wherein the pivot nitrogen atom is connected to three
phosphine arms via ethylene spacers.3 However, this highly
flexible tripodal structure shows hemilabile behavior of the
nitrogen donor, which complicates the coordination chemistry.
To counter this, tripodal triphosphine ligands with a strongly
coordinating monoanionic bridgehead, such as SiP3, have been
introduced (Chart 1),4 as well as the metalloboratrane analogue
BP3, where additional metal-to-boron coordination induces
structural rigidity.5 An alternative approach would be to employ
Received: May 22, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
neutral tetradentate tripodal scaffolds wherein the position of
the pivot donor is locked due to overall structural rigidity,
forcing it to become part of the metal coordination sphere.
Typical examples feature five-membered “chelation”, which
provides very favorable coordination to, for example, group 9
metals (Rh, Ir) but also automatically restricts the conforma-
tional freedom around the metal center. As an example, we
have previously reported on the formation of two linkage
isomers A and B of tripodal tetradentate all-phosphorus donor
ligands based on an indolylphosphine scaffold as well as their
sterically encumbered RhI, RhII, and RhIII complexes.6 The
highly constrained, rigid nature of the ligand was shown to
dominate the overall geometry in these Rh complexes. Inspired
by these results and building on the literature describing C3-
symmetric tetradentate ligands as well as our ongoing work on
tridentate all-phosphorus donor ligands,7,8 we sought to
construct a tripodal all-phosphorus donor with a slightly less
rigid skeleton, enabling six-membered chelation while still
possessing a strongly donating pivot, in order to accommodate
a wider range of coordination geometries for the metal center
and potentially induce additional reactivity pathways. Herein
we describe the straightforward synthesis of novel PP3 ligand 1
featuring benzyl spacers as well as its initial coordination
chemistry to iridium and subsequent reactivity of the isolated
ortho-metalated IrIII hydrido species.
Figure 1. ORTEP plot (50% probability displacement ellipsoids) of
PP3 ligand 1, tris(2-(diphenylphosphino)benzyl)phosphine. Hydrogen
atoms and the toluene solvent molecule have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): P1−C1, 1.8582(18);
P1- - -P2, 3.5299(7); P1- - -P3, 3.5043(6); P2- - -P4, 5.2926(7); C1−P1−
C20, 99.80(8); C1−P1−C39, 99.27(8); C20−P1−C39, 99.29(8).
305.74(14); P4, 306.50(14)°), likely related to the difference in
substitution (benzyl vs phenyl groups).
Coordination Behavior of Ligand 1 toward a Cationic
Ir Precursor. Reaction of ligand 1 with 1 equiv of the cationic
Ir precursor [Ir(COE)2(acetone)2]PF6 in THF resulted in an
immediate color change from orange to pale yellow, and
extractive workup gave an off-white solid in 90% isolated yield.
31P{1H} NMR spectroscopic analysis of this complex in CD2Cl2
indicated strong deviation from the ideal C3 geometry observed
for the free ligand, as four multiplet signals were observed in a
1:1:1:1 ratio at δ 33.6 (q, J = 20 Hz), 1.5 (ddd, J = 292, 20, 12
Hz), −3.6 (dd, J = 20, 12 Hz), and −73.7 (dt, J = 292, 20 Hz)
ppm. 31P NMR spectroscopy in THF-d8 at 60 °C did not result
in a higher order symmetry spectrum.
RESULTS AND DISCUSSION
■
Preparation and Characterization of Tripodal Tetra-
dentate Ligand 1. Starting from 2-tolyldiphenylphosphine,
simple lithiation of the methyl group afforded the correspond-
ing organolithium building block. Upon reaction with an
equimolar amount of PCl3 and after extractive workup, ligand 1
was obtained as a white solid in moderate yield (Scheme 1).
Scheme 1. Synthetic Procedure to PP3 Ligand 1, Starting
from Commercially Available Diphenyl-o-tolylphosphine
1
Furthermore, the corresponding H NMR spectrum did not
show any indication of coordinated cyclooctene or acetone,
suggestive of an additional substitution process after
introduction of the Ir precursor to the PP3 ligand. A complex
hydride signal was discernible at δ −5.9 ppm, which resolved as
a pseudo doublet of quartets with one large trans P−H coupling
(2JP−H = 115.4 Hz) and a much smaller cis coupling (2JP−H
=
10.8 Hz), presumably resulting from a C−H bond activation
1
process (Figure 2). A selective H{31P} NMR experiment at δ
33.6 ppm showed the disappearance of the large trans coupling
of the hydride signal, which means that this phosphorus signal
can be attributed to the pivotal P atom trans to the hydride.
The 13C NMR spectrum revealed a doublet at 120.6 ppm, with
a 2JP−C value of 41.6 Hz, indicative of a direct Ir−carbon bond.
The corresponding FAB-MS spectrum displayed a strong signal
at m/z 1049.23, which agreed very favorably with the fragment
[Ir(1)]+. On the basis of these observations, we concluded that
the ortho-metalated IrIII complex depicted in Scheme 2 is
formed, with the hydride ligand trans to the phosphorus
bridgehead of the PP3 scaffold.
We were able to obtain single crystals, suitable for X-ray
crystallographic analysis, by slow diffusion of pentane into a
solution of 2 in dichloromethane. The resulting molecular
structure is depicted in Figure 2, and bond distances, bond
angles, and torsion angles are given in Table 1. Strikingly,
reaction of 1 with the analogous Rh precursor failed to give any
distinctive reactivity according to 31P NMR spectroscopy. We
The 31P NMR spectrum of 1 reflected the anticipated highly
symmetric nature of this compound, with a quartet at δ −4.0
and a doublet at −15.9 ppm in a relative ratio of 1:3 and both
featuring a coupling constant JPP1 of 25.0 Hz. The methylene
spacer showed up nicely in the H NMR spectrum at δ 3.54
ppm as a sharp singlet and as a pseudotriplet at δ 34.1 in the
1
13C NMR spectrum with a coupling constant JPC of 21.5 Hz.
HR-MS also confirmed the formation of the intact PP3
framework at m/z 857.3 for the parent molecular ion.
Single crystals suitable for X-ray crystallographic analysis
were obtained from toluene at −20 °C; Figure 1 displays the
resulting molecular structure and selected data. The intra-
molecular P- - -P distances range from 3.4463(6) to 5.2926(7)
Å, with the pivot P1 atom in a typical pyramidal geometry and
the lone pair oriented toward the binding pocket. The P1 atom
has a slightly reduced C−P−C angle sum for P1 in comparison
to the other P atoms (P1, 298.36(14); P2, 306.15(16); P3,
B
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 2. ORTEP plots (50% probability displacement ellipsoids) for the cationic portion of [Ir(H)(κ5P,P,P,P,C-1)]PF6 (2) in bottom (left) and
side-on (right) perspectives. Hydrogen atoms, the PF6 anion, and solvent have been omitted for clarity.
Scheme 2. Preparation of Novel IrIII Species 2, with
κ5P,P,P,P,C Coordination of Ligand 1
Table 1. Selected Bond Lengths (Å), Bond Angles (deg), and
Torsion Angles (deg) for 2
Ir−P1
Ir−P2
Ir−P3
Ir−P4
2.3279(7)
2.3018(7)
2.3305(7)
2.3566(7)
3.2153(11)
3.2912(11)
87.97(2)
Ir1−C1
P1−C2
C1−C2
Ir−H1
P2- - -P3
2.133(3)
1.806(3)
1.408(4)
1.52(4)
a
P2- - -P1
3.3152(10)
4.5674(11)
67.35(8)
92.71(7)
90.05(8)
170.20(8)
86.19(9)
171.1(14)
−79.34(17)
Figure 3. HOMO of complex 2, as calculated by DFT (Turbomole,
BP86, SV(P)).
P2- - -P4
P1- - -P3
P1−Ir−P2
P1−Ir−P3
P1−Ir−P4
P2−Ir−P3
P2−Ir−P4
P3−Ir−P4
C1−Ir−P1−C2
P1−Ir−C1
P2−Ir−C1
P3−Ir−C1
P4−Ir−C1
Ir−P1−C2
P2−Ir−H1
P2−Ir−C1−C2
157.32(2)
103.33(2)
91.39(2)
306.9(2); P4, 309.6(2)°) differ significantly, as a result of the
varying coordination environments of the four phosphines in
complex 2.
89.90(2)
In an effort to intercept the supposed IrI intermediate formed
upon ligand exchange at the cationic Ir precursor, presumably
giving rise to a species such as Ir(κ4P,P,P,P)(L)]PF6 (L =
cyclooctene, acetone), we investigated the reaction between 1
and [Ir(μ-Cl)(COE)2]2. When monitored by 31P NMR
spectroscopy, this reaction did not proceed as cleanly as for
the cationic Ir precursor, but the corresponding species 2Cl was
observed as the major species in solution. This was further
corroborated by the presence of an identical hydride signal in
99.34(2)
−5.53(12)
a
Hydride H1 was refined with an isotropic displacement parameter.
are currently investigating details of this different behavior for
the second-row congener.
Mononuclear Ir hydrido species with a four-membered
ortho-metalated phosphine ligand that have been structurally
characterized are rare.9 The structure in Figure 3 exhibits a
phosphine trans to the phenyl ring and a phosphine trans to the
hydride, which was refined freely with an isotropic displace-
ment parameter and resolved at an Ir−H bond distance of
1.52(4) Å, with a P2−Ir−H1 angle of 171.1(14)°. The Ir−P
distances are all similar at around 2.30−2.35 Å. The Ir−C1
bond length is within the expected range for a cyclometalated
phenyl ring. The P1−Ir−C1 angle is very acute at 67.35(8)°,
typical for cyclometalated phenylphosphine fragments.8 The
maximum intramolecular P- - -P distance is approximately 4.5 Å
(P1- - -P3), which is significantly shorter than in free ligand 1.
The C−P−C angle sums (P1, 321.7(2); P2, 310.3(2); P3,
1
the H NMR spectrum, suggesting a favorable pathway for
intramolecular C−H activation.
Reactivity of Complex 2. To date, only four reports
mention the formation of an ortho-metalated tripodal
phosphine ligand, to the best of our knowledge.10 Two
iridium-containing complexes are known, but in both cases a
tridentate ligand with a noncoordinating pivot atom (either
C10b or B9e) was employed. Hence, complex 2 is the only Ir
species known that bears an all-phosphorus tetradentate ligand
structure. Strikingly, no details of the potential reversible
character of the M−C bond formation have been disclosed for
any of these systems, but such behavior may become relevant in
C
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
the context of cooperative catalysis and metal−ligand bifunc-
tional bond activation of small molecules.11,12 In order to
determine the nature of the “hydride” ligandthe cationic
character of the IrIII center could give rise to more “protic”
behaviorthe reactivity of 2 to various electrophilic and
nucleophilic reagents was explored. Addition of a base such as
KHDMS or LiCH2SiMe3 or a hydride donor such as NaBH4
did not result in any discernible reactivity of the Ir−H
fragment, indicating a very poorly electrophilic Ir−H system,
perhaps induced by shielding of the ligand scaffold. Weak acids
such as NH4PF6 did not induce any conversion of this species
either, and subjecting a solution of the IrIII complex to 5 bar of
H2 also did not give any reaction. No reaction was observed
when complex 2 was treated with an equimolar amount of
methyl iodide.
the Ir hydride and Ir−C bond in 2, followed by protonation of
the resulting (non-ortho-metalated) ({κ4-P}-PP3)Ir complex 2′
at iridium (see Scheme 4 for both pathways).
Scheme 4. Two Distinct Mechanisms for the Conversion of
Ortho-Metalated Ir Hydride 2 into Hydride 3 by Reaction
with Acid
The addition of ∼20 mol equiv of DCl in THF at 60 °C led
to complete conversion overnight, with disappearance of the
high-field doublet at δ ∼−75 ppm in the 31P NMR spectrum
for the ortho-metalated phenylphosphino group in 2. However,
the reaction was not selective, giving a number of unidentified
signals in the 31P NMR spectrum. Notably, Bianchini has
reported on a somewhat related Rh(H)(Cl)(PP3) species (PP3
= P(CH2CH2PPh2)3), but with a trans relation between Cl and
the pivotal P rather than the expected peripheral P in our case,
upon substitution of the coordinated phenyl fragment for a
chloride ligand.13
To induce cleaner conversion, we turned to trifluoroacetic
acid (CF3COOH, TFA) as the protonating agent. While an
equimolar amount did not give appreciable conversion of 2 at
room temperature, the use of 10 molar equiv of CF3COOH
(Scheme 3) resulted in bleaching of the pale yellow solution,
In an attempt to elaborate on the prevalent mechanism by
which the conversion from 2 to 3 proceeds, we employed
trifluoroacetic acid-d, which led to a signal at δ −9.75 ppm in
Scheme 3. Chemoselective Protonation of the Ir−C Bond in
IrIII Species 2, Resulting in Formation of the Dicationic Ir
Hydrido Complex 3
2
the H NMR spectrum for the corresponding Ir−D species,
with no indication for the installment of any CPh−D bonds.
This observation strongly supports the aforementioned
reductive elimination pathway, as direct protonation of the
Ir−CPh bond would result in a CPh−D fragment. TFA may
favorably affect the overall process by transient protonation of
the ortho-metalated ring, thereby enhancing intramolecular
reductive elimination. Further support for the reductive
elimination reaction path was obtained from submitting a
solution of complex 2 in CD2Cl2 to an atmosphere of CO (5
bar) (Scheme 5). This slow reaction (80% conversion after 2
concomitant with formation of a new hydride signal at δ −9.75
1
ppm (chemical shift Δδ of −3.85 ppm relative to 2) in the H
NMR spectrum, with coupling constants JP−H of 133.8 and 16.0
Hz. The corresponding 31P{1H} NMR spectrum displayed two
signals at δ 16.31 (pivotal phosphine) and −4.24 ppm
(peripheral phosphines), both with a JP−P value of 19 Hz.
These data imply a trans disposition of a phosphine and a
hydride ligand similar to that seen for species 2, suggesting
overall “protonation” of the Ir−C1 bond rather than
protonation of the hydride ligand.
Scheme 5. Chemoselective Reduction of 2 to the
Corresponding IrI Derivative 4 under a CO Atmosphere via
Reductive Elimination−CO Coordination
In an attempt to rationalize the observed chemoselective
protonation of the ortho-metalated fragment rather than the
“hydride” ligand, we first investigated the electronic structure of
species 2 with DFT (BP86). As is depicted in Figure 3, the
HOMO of the ortho-metalated complex shows pronounced
electron density being located in the antibonding Ir−C bond (π
character). Hence, we argued that direct protonation of the
ortho-metalated aryl fragment might be one possible pathway
for the observed conversion of 2 with acids.
weeks at room temperature) resulted in clean formation of the
new, highly symmetric species [Ir(1)(CO)]PF6 (4). The (in
situ) 31P{1H} NMR spectrum displayed only two signals (δ
43.28 (broad) 1P; −11.69 ppm (d), 3P, 2JP−P = 37.7 Hz). This
species was further characterized by IR spectroscopy, showing
the presence of a single carbonyl ligand bound to an electron-
poor iridium center (νCO 2006 cm−1).14
Alternatively, the reaction of 2 with H+ to form 3 might
proceed via reductive elimination of a CAr−H bond involving
The energy profile for the reductive elimination process from
2 to 2′ according to DFT calculations is shown in Figure 4.
D
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 4. (top) Reaction profile for reductive elimination of Ph−H from ortho-metalated species 2 as calculated by DFT (Turbomole, BP86, SV(P))
with free energies in kcal mol−1. (bottom) DFT optimized geometries for species 2 (left), TS-1 (middle), and 2′ (right).
These calculations suggest that the pathway involving initial
reductive elimination is accessible, proceeding via transition
state TS-1 with a barrier of 28.2 kcal mol−1. The reductive
elimination is endergonic, and protonation of the resulting
iridium(I) species must therefore provide the thermodynamic
driving force for the overall process. These data agree well with
the experimentally observed oxidative addition of the aromatic
C−H bond of the PP3 ligand upon binding to iridium(I)
precursors. This process has a substantially lower barrier (20.4
kcal mol−1) and is exergonic.
In summary, we have reported the synthesis of a novel
tripodal tetradentate all-phosphorus donor ligand 1 bearing a
flexible benzylic backbone and diphenylphosphine side groups
and its coordination behavior to a cationic IrI precursor. Facile
ortho metalation of one of the phenyl groups gives rise to
formation of the highly encapsulated, cationic octahedral
IrIII(hydrido) species 2+. This complex is unreactive toward
hydride sources, but it reacts smoothly with strong acid,
generating the corresponding dicationic monohydrido species
3.15 DFT calculations reveal a high-barrier reductive
elimination process of the cyclometalated Ar−H moiety.
Subsequent protonation of the thus formed cationic IrI species
provides a viable pathway for the formation of 3. Further
support for this pathway was obtained by using a deuterium-
labeled acid and from the slow but selective formation of
[Ir(1)(CO)]PF6 (4) by subjecting 2 to an atmosphere of CO
(5 bar for 2 weeks). We are currently exploring the reactivity of
PP3 scaffold 1 with other metals and the possibility of utilizing
the reductive elimination pathway for interesting reactivity with
other substrates. In addition, the effect of ligand-induced
encapsulation on the reactivity displayed by the shielded metal
center is under investigation.
EXPERIMENTAL SECTION
■
All reactions were carried out under an atmosphere of nitrogen using
standard Schlenk techniques. Reagents were purchased from
commercial suppliers and used without further purification. [Ir-
(COE)2(acetone)2]PF6 was prepared following a literature proce-
dure.16 THF, pentane, hexane, and Et2O were distilled from sodium
benzophenone ketyl. CH2Cl2 was distilled from CaH2 and toluene
from sodium under nitrogen. NMR spectra (1H, H{31P}, 31P{1H},
1
and 13C{1H}) were measured on a Varian INOVA 500 MHz, a Bruker
AV400, or a Varian MERCURY 300 MHz spectrometer. High-
resolution mass spectra were recorded on a JEOL JMS SX/SX102A
four-sector mass spectrometer; for FAB-MS, 3-nitrobenzyl alcohol was
used as a matrix. IR spectra (ATR) were recorded with a Bruker
Alpha-p FT-IR spectrometer.
Preparation of Tris((2-diphenylphosphino)benzyl)-
phosphine (1). A red solution of (diphenyl-o-tolylphosphino)-
lithium17 (896.4 mg, 3.18 mmol) in diethyl ether (15 mL) was
added to a PCl3 solution (0.09 mL, 0.62 mmol) in diethyl ether (5
mL) via a Teflon cannula. The resulting off-white milky supension was
stirred for 4 h, during which time a dark orange suspension was
formed that was subsequently concentrated in vacuo. The orange foam
was dissolved in diethyl ether (20 mL) and added to a solution of
LiAlH4 (162.7 mg, 4.29 mmol) in diethyl ether (15 mL) at −35 °C (to
reduce undesired side products, allowing for easier purification), and
the mixture was stirred for 2.5 h. The solvent was evaporated, and
toluene (30 mL) was added to the residue, followed by filtration (dual-
layer silica−Celite) and washing with toluene (4 × 5 mL). The solvent
was removed under reduced pressure. After this, the ligand was
recrystallized in toluene at −20 °C to give pure 1 in 25% yield. Mp:
1
144 °C. H NMR (400 MHz, 298 K, C6D6): δ (ppm) 7.46−7.42 (m,
9H, ArH), 7.31 (t, JHH = 7.6, JPH = 6.2 Hz, 3H, ArH), 7.21 (dd, JHH
7.1, JPH = 3.5 Hz, 3H, ArH) 7.18−7.12 (m, 18H, ArH), 7.09 (t, JHH
=
=
7.0 Hz, 3H, ArH) 6.98 (t, JHH = 7.4 Hz, 3H, ArH), 3.54 (s, 6H, CH2).
13C NMR (100 MHz, 298 K, C6D6): δ (ppm) 143.79 (dd, JPC = 26.5
and 7.3 Hz, ArC), 137.50 (d, JPC = 13.0 Hz, ArC), 136.30 (dd, JPC
13.3 and 2.6 Hz, ArC), 133.97 (d, JPC = 19.9 Hz, ArC), 130.10 (dd, JPC
=
E
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
= 9.3 and 5.4 Hz, ArC), 128.77 (s, ArC), 128.30 (d, JPC = 7.0 Hz,
ArC), 128.17 (s, ArC), 34.13 (pt, JPC = 21.5 Hz, CH2). 31P NMR (161
MHz, 298 K, C6D6): δ (ppm) −15.92 (d, J = 25.0 Hz, 3P), −3.99 (q, J
= 25.0 Hz, 1P). HR-MS (FAB+): C57H49P4 m/z calcd 857.2785, found
857.2760.
displacement parameters. Hydrogen atoms were introduced in
calculated positions. The hydride H atom of 2 was refined freely
with an isotropic displacement parameter. The PF6 anion in 2 was
disordered over two orientations and was refined with restraints for the
F−P−F angles and to approximate isotropic behavior. Geometry
calculations and checks for higher symmetry were performed with the
PLATON program.28
Preparation of [Ir(H)(κ5P,P,P,P,C-1)]PF6 (2). Tris(2-
(diphenylphosphino)phenyl)phosphine (1; 212 mg, 0.25 mmol) in
THF (18 mL) was added to [Ir(coe)2(acetone)2]PF6 in THF (168
mg, 0.25 mmol, 2 mL) via a Teflon cannula. An immediate color
change from orange to pale yellow was observed. The reaction mixture
was stirred overnight at room temperature and thereafter concentrated
to approximately 4 mL. After the solution was cooled to −35 °C,
pentane (15 mL) was added and a beige solid precipitated. The
cooling was removed, and THF (10 mL) was added, whereafter the
precipitate was filtered and washed with pentane (20 × 1 mL). The
product 2 was obtained as an off-white powder in 90% yield. Mp: >250
Details for 1: C57H48P4·C7H8, fw = 948.97, colorless block, 0.40 ×
0.34 × 0.12 mm3, triclinic, P1 (No. 2), a = 11.3975(3) Å, b =
̅
12.4827(3) Å, c = 19.9754(5) Å, α = 102.5504(10)°, β =
105.3070(10)°, γ = 98.8375(11)°, V = 2607.55(11) Å3, Z = 2, Dx =
1.209 g/cm3, μ = 0.185 mm−1. 44492 reflections measured up to (sin
θ/λ)max = 0.61 Å−1, 9710 unique reflections (Rint = 0.022), of which
8131 were observed (I > 2σ(I)), R1/wR2 (I > 2σ(I)) 0.0392/0.1039,
R1/wR2 (all reflections) 0.0500/0.1128. S = 1.031, residual electron
density between −0.31 and 0.65 e/Å3.
°C dec. 1H NMR (400 MHz, 298 K, CD2Cl2): δ (ppm) 8.37 (pt, JHH
=
Details for 2: [C57H48IrP4]PF6·CH2Cl2, fw = 1278.93, yellow block,
0.34 × 0.25 × 0.12 mm3, triclinic, P1 (No. 2), a = 12.7688(3) Å, b =
8.0 Hz, 2H), 7.68−6.52 (m, 37H), 6.27 (pt, JPH = 8.0 Hz, JHH = 6.9
̅
12.9030(3) Å, c = 17.9973(3) Å, α = 89.388(1)°, β = 71.597(1)°, γ =
68.159(1)°, V = 2592.31(10) Å3, Z = 2, Dx = 1.638 g/cm3, μ = 2.894
mm−1. 65351 reflections measured up to (sin θ/λ)max = 0.65 Å−1,
11894 unique reflections (Rint = 0.023), of which 11038 were observed
(I > 2σ(I)), R1/wR2 (I > 2σ(I)) 0.0210/0.0523, R1/wR2 (all
reflections) 0.0243/0.0537, S = 1.070, residual electron density
between −1.16 and 0.79 e/Å3.
Hz, 1H), 6.02 (pd, JPH = 4.0 Hz, JHH = 6.6 Hz, 1H), 3.90 (pt, JPH
13.6 Hz, 1H), 3.60 (pt, JPH = 13.7, JHH = 13.6 Hz, 1H), 3.36 (pt, JPH
=
=
13.2 Hz, JHH = 13.7 Hz, 1H), 3.23 (d, JPH = 8.4 Hz, JHH = 13.5 Hz,
1H), 3.00 (m, JHH = 15.0 Hz, 1H), 2.27 (m, JHH = 14.2 Hz, 1H), −5.90
(dpq, JPH = 115.4 and 10.8 Hz, hydride); the JHH coupling constants
1
are determined from the corresponding H{31P} NMR spectrum. 13C
NMR (100 MHz, 298 K, CD2Cl2): δ (ppm) 138.6 (br d, JPC = 13.0
Hz, C), 138.0 (dd, JPC = 12.0 and 3.8 Hz), 136.4 (br. d, JPC = 12.2 Hz),
136.1 (dd, JPC = 3.2 and 1.5 Hz), 134.2−133.9 (m), 133.8−133.7 (m),
133.1 (t, JPC = 7.6 Hz), 133.0−132.6 (m), 132.6−132.4 (m), 131.9−
131.8 (m), 131.8−131.3 (m), 131.2 (s), 130.2 (s), 130.1−129.9 (m),
129.8−129.6 (m), 129.5−129.3 (m), 129.0 (d, JPC = 25.6 Hz), 128.6−
128.1 (m), 128.0 (d, JPC = 9.9 Hz), 127.8−127.6 (m), 126.9 (br dd, JPC
= 27.3 and 7.5 Hz), 123.8−123.3 (m), 120.6 (br d, JPC = 41.6 Hz),
67.6 (s), 30.0−29.4 (m, CH2), 28.6 (dd, JPC = 30.2 and 9.9 Hz, CH2),
24.7 (br d, JPC = 25.6 Hz, CH2). 31P NMR (161 MHz, 298 K,
CD2Cl2): δ (ppm) 33.63 (q, J = 19.8 Hz, P2), 1.50 (ddd, J = 292.1,
21.9, 10.6 Hz, P3), −3.56 (q, J = 14.0 Hz, P4), −73.68 (dt, J = 291.8,
17.3 Hz, P1), −144.29 (hept, J = 711.4 Hz, PF6). HR-MS (FAB+):
C57H49IrP4 m/z calcd 1049.2341, found 1049.2336.
ASSOCIATED CONTENT
* Supporting Information
■
S
NMR spectra of compounds 1−3, CIF files giving crystallo-
graphic data for 1 and 2. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.I.v.d.V.: j.i.vandervlugt@uva.nl.
■
Notes
Reactivity of 2 toward Trifluoroacetic Acid and CO. Addition
of 10 molar equiv of CF3COOH (TFA) to a solution of 2 (40 mg,
33.5 μmol) in CD2Cl2 at room temperature led to clean formation of a
new species within 1 h, as indicated by 1H and 31P NMR spectroscopy.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
1H NMR (400 MHz, 298 K, CD2Cl2): δ (ppm) −9.75 (1H, JP−H
=
This work was financially supported by the European Research
Council (ERC; Starting Grant EuReCat, Grant Agreement
279097 to J.I.v.d.V.) and by the University of Amsterdam. The
EU-FP7 COST network CM0802 “PhoSciNet” is acknowl-
edged for offering stimulating scientific interactions. L.M.J.
thanks Fred Terrade, M.Sc., for support in the early stages of
the project.
133.8, JP−H = 16.0 Hz). 31P NMR (161 MHz, 298 K, CD2Cl2): δ
(ppm) 16.31 (q, 1P, JP−P = 19.0 Hz), −4.24 (overlapping doublets, 3P,
JP−P = 19.0 Hz). A solution of 2 in CD2Cl2 (20 mg, 16.7 μmol) was
stirred for 2 weeks while under a static pressure of CO (5 bar), giving
rise to 80% conversion of 2 into a highly symmetrical species,
according to in situ 31P NMR spectroscopy: 31P NMR (161 MHz, 298
K, CD2Cl2): δ (ppm) 43.28 (1P, broad), −11.69 (3P, JP−P = 37.7 Hz).
Identical spectroscopic features were present after depressurizing the
solution. ATR-IR: νCO 2006 (s) cm−1.
REFERENCES
■
(1) Selected relevant contributions: (a) Otte, M.; Kuijpers, P. F.;
Troeppner, O.; Iva novic-
Chem. Eur. J. 2013, DOI: 10.1002/chem.201301411. (b) Gadzikwa,
T.; Bellini, R.; Dekker, H. L.; Reek, J. N. H. J. Am. Chem. Soc. 2012,
DFT Calculations. Geometry optimizations were carried out with
the Turbomole program package18 coupled to the PQS Baker
optimizer19 at the ri-DFT level using the BP8620 functional and the
resolution-of-identity (ri) method.21 We used the SV(P) basis set22 for
the geometry optimizations of all stationary points. All minima (no
imaginary frequencies) and transition states (one imaginary frequency)
were characterized by numerically calculating the Hessian matrix. ZPE
and gas-phase thermal corrections (entropy and enthalpy, 298 K, 1
bar) from these analyses were calculated.
X-ray Crystal Structure Determinations. Reflections were
measured on a Bruker Kappa ApexII diffractometer with a sealed
tube and Triumph monochromator (λ = 0.71073 Å). The reflections
were integrated with the SAINT23 (compound 1) or EVAL1524 (2)
software. Absorption corrections based on multiple measured
reflections were performed with SADABS.25 The structures were
solved with direct methods using SIR-9726 (1) or SHELXS-9727 (2).
Refinement was performed with SHELXL-9727 against F2 values of all
reflections. Non-hydrogen atoms were refined freely with anisotropic
́
Burmazovic,
́
I.; Reek, J. N. H.; de Bruin, B.
134, 2860. (c) Anxolabeh
Nowak, S.; Robert, M.; Savea
́
er
̀
e-Mallart, E.; Costentin, C.; Fournier, M.;
nt, J.-M. J. Am. Chem. Soc. 2012, 134,
́
6104. (d) Inokuma, Y.; Kawano, M.; Fujita, M. Nature Chem. 2011, 3,
349. (e) Wang, Z. J.; Brown, C. J.; Bergman, R. G.; Raymond, K. N.;
Toste, F. D. J. Am. Chem. Soc. 2011, 133, 7358. (f) Wiester, M. J.;
Ulmann, P. A.; Mirkin, C. A. Angew. Chem., Int. Ed. 2011, 50, 114.
(g) van der Vlugt, J. I.; Koblenz, T. S.; Wassenaar, J.; Reek, J. N. H. In
Molecular Encapsulation: Reactions in Constrained Systems; Mieusset, J.-
L., Brinker, U. H., Eds.; Wiley: Hoboken, NJ, 2010; p 145.
(h) Koblenz, T. S.; Wassenaar, J.; Reek, J. N. H. Chem. Soc. Rev.
2008, 37, 1700. (I) Raymond, K. N. Acc. Chem. Res. 2005, 38, 349.
(2) Selected relevant contributions: (a) Siegl, W. O.; Lapporte, S. J.;
Collman, J. P. Inorg. Chem. 1971, 10, 2158. (b) Byers, P. K.; Canty, A.
J.; Skelton, B. W.; White, A. H. J. Chem. Soc., Chem. Commun. 1987,
F
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1093. (c) Klaui, W. Angew. Chem., Int. Ed. 1990, 29, 627. (d) Barbaro,
97. (e) Feldman, J. D.; Peters, J. C.; Tilley, T. D. Organometallics 2002,
21, 4050. (f) Brym, M.; Jones, C. Transition Met. Chem. 2003, 28, 595.
(g) Fang, H.; Choe, Y.-K.; Li, Y.; Shimada, S. Chem. Asian J. 2011, 6,
2512.
̈
P.; Blanchini, C.; Meli, A.; Peruzzini, M.; Vacca, A.; Vizza, F.
Organometallics 1991, 10, 2227. (e) Trofimenko, S. Chem. Rev. 1993,
93, 943. (f) Herberhold, M.; Bauer, K.; Milius, W. J. Organomet. Chem.
1995, 502, C1. (g) MacBeth, C. E.; Golombek, A. P.; Young, V. G., Jr.;
Yang, C.; Kuczera, K.; Hendrich, M. P.; Borovik, A. S Science 2000,
289, 938. (h) Castro-Rodriguez, I.; Nakai, H.; Zakharov, L. N.;
Rheingold, A. L.; Meyer, K. Science 2004, 305, 1757. (i) Turculet, L.;
Feldman, J. D.; Tilley, T. D. Organometallics 2004, 23, 2488. (j) Han,
H.; Elsmaili, M.; Johnson, S. A. Inorg. Chem. 2006, 45, 7435.
(k) Friesen, D. M.; Bowles, O. J.; McDonald, R.; Rosenberg, L. Dalton
Trans. 2006, 2671. (l) Ciclosi, M.; Llort, J.; Estevan, F.; Lahuerta, P.;
(10) (a) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Zanobini, F.
J. Am. Chem. Soc. 1988, 110, 6411. (b) Stossel, P.; Heins, W.; Mayer,
̈
H. A.; Fawzi, R.; Steimann, M. Organometallics 1996, 15, 3393.
(c) Takaoka, A.; Mendiratta, A.; Peters, J. C. Organometallics 2009, 28,
3744. See also ref 9e.
(11) Recent reviews: (a) van der Vlugt, J. I.; Reek, J. N. H. Angew.
Chem., Int. Ed. 2009, 48, 8832. (b) Gunanathan, C.; Milstein, D. Acc.
Chem. Res. 2011, 44, 588. (c) van der Vlugt, J. I. Eur. J. Inorg. Chem.
2012, 363. (d) Askevold, B.; Roesky, H. W.; Schneider, S.
ChemCatChem 2012, 4, 307. For a theoretical view on reversible
M−C reactivity, see: (e) Ghatak, K.; Mane, M.; Vanka, K. ACS Catal.
2013, 3, 920.
(12) Work from our group on cooperative bond activation: (a) van
der Vlugt, J. I.; Pidko, E. A.; Vogt, D.; Lutz, M.; Spek, A. L.; Meetsma,
A. Inorg. Chem. 2008, 47, 4442. (b) van der Vlugt, J. I.; Lutz, M.;
Pidko, E. A.; Vogt, D.; Spek, A. L. Dalton Trans. 2009, 1016. (c) van
der Vlugt, J. I.; Pidko, E. A.; Vogt, D.; Lutz, M.; Spek, A. L. Inorg.
Chem. 2009, 48, 7513. (d) van der Vlugt, J. I.; Siegler, M. A.; Janssen,
M.; Vogt, D.; Spek, A. L. Organometallics 2009, 29, 7025. (e) van der
Vlugt, J. I.; Pidko, E. A.; Bauer, R. C.; Gloaguen, Y.; Rong, M. K.; Lutz,
M. Chem. Eur. J. 2011, 17, 3850. (f) Lindner, R.; van den Bosch, B.;
Lutz, M.; Reek, J. N. H.; van der Vlugt, J. I. Organometallics 2011, 30,
499. (g) de Boer, S. Y.; Gloaguen, Y.; Lutz, M.; van der Vlugt, J. I.
Inorg. Chim. Acta 2012, 380, 336. (h) de Boer, S. Y.; Gloaguen, Y.;
Reek, J. N. H.; Lutz, M.; van der Vlugt, J. I. Dalton Trans. 2012, 41,
11276. Oldenhof, S.; de Bruin, B.; Lutz, M.; Siegler, M. A.; Patureau, F.
W.; van der Vlugt, J. I.; Reek, J. N. H. Chem. Eur. J. 2013,
DOI: 10.1002/chem.201302230.
́
́
Sanau, M.; Perez-Prieto, J. Angew. Chem., Int. Ed. 2006, 45, 6741.
(m) Whited, M. T.; Rivard, E.; Peters, J. C. Chem. Commun. 2006,
1613. (n) Leung, W.-H.; Zhang, Q.-F.; Yi, X.-Y. Coord. Chem. Rev.
2007, 251, 2266. (o) Takeda, N.; Watanabe, D.; Nakamura, T.; Unno,
M. Organometallics 2010, 29, 2839. (p) Bhadbhade, M. M.; Field, L.
D.; Gilbert-Wilson, R.; Guest, R. W.; Jensen, P. Inorg. Chem. 2011, 50,
6220. (q) Moret, M.-E.; Peters, J. C. J. Am. Chem. Soc. 2011, 133,
18118. (r) Boddien, A.; Mellmann, D.; Gartner, F.; Jackstell, R.; Junge,
̈
H.; Dyson, P. J.; Laurenczy, G.; Ludwig, R.; Beller, M. Science 2011,
333, 1733. (s) Tejel, C.; Geer, A. M.; Jimene
M. A. Organometallics 2012, 31, 2895. (t) Fernan
Seijo, M. I.; García-Fernandez, M. E. RSC Adv. 2012, 2, 1404.
́
z, S.; Lope
́ z, J. A.; Ciriano,
́
dez-Anca, D.; García-
́
(u) Moriuchi, T.; Mao, L.; Wu, H.-L.; Ohmura, S. D.; Watanabe, M.;
Hirao, T. Dalton Trans. 2012, 41, 9519. (v) Kropp, H.; King, A. E.;
Khusniyarov, M. M.; Heinemann, F. W.; Lancaster, K. M.; DeBeer, S.;
Bill, E.; Meyer, K. J. Am. Chem. Soc. 2012, 134, 15538. (w) Ziebart, C.;
Federsel, C.; Anbarasan, P.; Jackstell, R.; Baumann, W.; Spannenberg,
A.; Beller, M. J. Am. Chem. Soc. 2012, 134, 20701. (x) Broda, H.;
Hinrichsen, S.; Tuczek, F. Coord. Chem. Rev. 2013, 257, 587.
(y) Gilbert-Wilson, R.; Field, L. D.; Colbran, S. B.; Bhadbhade, M.
M. Inorg. Chem. 2013, 52, 3043.
(13) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Zanobini, F. J.
Am. Chem. Soc. 1988, 110, 6411−6423.
(3) (a) Sacconi, L.; Bertini, I. J. Am. Chem. Soc. 1967, 89, 2235.
(b) Di Vaira, M.; Midollini, S.; Sacconi, L. Inorg. Chem. 1977, 16, 1518.
(4) (a) Gossage, R. A.; McLennan, G. D.; Stobart, S. R. Inorg. Chem.
1996, 35, 1729. (b) Mankad, N. P.; Whited, M. T.; Peters, J. C. Angew.
Chem., Int. Ed. 2007, 46, 5768.
(5) (a) Bontemps, S.; Bouhadir, G.; Dyer, P. W.; Miqueu, K.;
Bourissou, D. Inorg. Chem. 2007, 46, 5149. (b) Sircoglou, M.;
Bontemps, S.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Gu, W.; Mercy,
M.; Chen, C.-H.; Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou,
D. J. Am. Chem. Soc. 2008, 130, 16729. (c) Bontemps, S.; Bouhadir, G.;
Gu, W.; Mercy, M.; Chen, C.-H.; Foxman, B. M.; Maron, L.; Ozerov,
O. V.; Bourissou, D. Angew. Chem., Int. Ed. 2008, 47, 1481. (d) Moret,
M.-E.; Peters, J. C. Angew. Chem., Int. Ed. 2011, 50, 2063. (e) Kameo,
H.; Hashimoto, Y.; Nakazawa, H. Organometallics 2012, 31, 3155.
(f) Kameo, H.; Hashimoto, Y.; Nakazawa, H. Organometallics 2012,
31, 4251. (g) Moret, M.-E.; Zhang, L.; Peters, J. C. J. Am. Chem. Soc.
2013, 135, 3792.
(14) (a) Dzik, W. I.; Smits, J. M. M.; Reek, J. N. H.; de Bruin, B.
Organometallics 2009, 28, 1631. (b) Kerfoot, D. G. E.; Mawby, R. J.;
Sgamelloiti, A.; Venanzi, L. M. Inorg. Chim. Acta 1974, 8, 195.
(15) This transformation is different from the reported protonation
of an ortho-metalated IrIII(phosphino)aryl species by Bergman and co-
workers, due to the rigid octahedral geometry and the presence of a
hydride fragment in complex 3: (a) Luecke, H. F.; Bergman, R. G. J.
Am. Chem. Soc. 1997, 119, 11538. Our case bears some similarity to
the reported reversible cyclometalation of silyl ligands; see:
(b) Aizenberg, M.; Milstein, D. Organometallics 1996, 15, 3317. It
is also related to a report by Caulton, describing similar behavior for a
nonencapsulated iridium hydride species bearing an ortho-metalated
phenylphosphine, which reacts with acetylene via reductive elimination
rather than σ-bond metathesis: (c) Cooper, A. C.; Huffman, J. C.;
Caulton, K. G. Organometallics 1997, 16, 1974.
(16) (a) Canepa, G.; Sola, E.; Martín, M.; Lahoz, F. J.; Oro, L. A.;
Werner, H. Organometallics 2003, 22, 2151. (b) Dorta, R.; Goikhman,
R.; Milstein, D. Organometallics 2003, 22, 2806.
(6) (a) Wassenaar, J.; de Bruin, B.; Siegler, M. A.; Spek, A. L.; Reek, J.
N. H.; van der Vlugt, J. I. Chem. Commun. 2010, 49, 1232−1234.
(b) Wassenaar, J.; Siegler, M. A.; Spek, A. L.; de Bruin, B.; Reek, J. N.
H.; van der Vlugt, J. I. Inorg. Chem. 2010, 49, 6495. See also:
(17) (Diphenyl-o-tolylphosphino)lithium is generated by equimolar
addition of s-BuLi to commercially available (diphenyl-o-tolylphos-
phine in the presence of TMEDA; see: (a) Longoni, G.; Chini, P.;
Canziani, F.; Fantucci, P. Chem. Commun. 1971, 470. (b) Koh, J. J.;
Rieger, P. H.; Shim, I. W.; Risen, W. M., Jr. Inorg. Chem. 1985, 24,
2312. (c) Byrne, L. T.; Engelhardt, L. M.; Jacobsen, G. E.; Leung, W.-
P.; Papasergio, R. I.; Raston, C. L.; Skelton, B. W.; Twiss, P.; White, A.
H. J. Chem. Soc., Dalton Trans. 1989, 105. (d) Braunschweig, H.; Dirk,
R.; Englert, U. Z. Anorg. Allg. Chem. 1997, 623, 1093.
(c) Penno, D.; Koshevoy, I. O.; Estevan, F.; Sanau, M.; Ubeda, M. A.;
́
́
Perez-Prieto, J. Organometallics 2010, 29, 703. For another recent
elegant addition to the class of PP3 ligands, see: (d) Ziebart, C.;
Federsel, C.; Anbarasan, P.; Jackstell, R.; Baumann, W.; Spannenberg,
A.; Beller, M. J. Am. Chem. Soc. 2012, 134, 20701.
(7) Bauer, R. C.; Gloaguen, Y.; Lutz, M.; Reek, J. N. H.; de Bruin, B.;
van der Vlugt, J. I. Dalton Trans. 2011, 40, 8822.
(8) Gloaguen, Y.; Jacobs, W.; de Bruin, B.; Lutz, M.; van der Vlugt, J.
I. Inorg. Chem. 2013, 52, 1682.
(18) Ahlrichs, R. Turbomole Version 5; Theoretical Chemistry Group,
University of Karlsruhe, Karlsruhe, Germany, 2002.
(9) (a) Del Piero, G.; Perego, G.; Zazzetta, A.; Cesari, M. Cryst.
Struct. Commun. 1974, 3, 725. (b) von Deuten, K.; Dahlenburg, L.
Cryst. Struct. Commun. 1980, 9, 421. (c) Crabtree, R. H.; Quirk, J. M.;
Felkin, H.; Fillebeen-Khan, T.; Pascard, C. J. Organomet. Chem. 1980,
187, C32. (d) Cooper, A. C.; Clot, E.; Huffman, J. C.; Streib, W. E.;
Maseras, F.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1999, 121,
(19) PQS version 2.4; Parallel Quantum Solutions, Fayettevile, AR,
2001. The Baker optimizer is available separately from PQS upon
request; see: Baker, J. J. Comput. Chem. 1986, 7, 385.
(20) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Perdew, J. P.
Phys. Rev. B 1986, 33, 8822.
G
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(21) Sierka, M.; Hogekamp, A.; Ahlrichs, R. J. Chem. Phys. 2003, 118,
9136.
(22) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97,
2571.
(23) SAINT-Plus; Bruker AXS Inc., Madison, WI, 2001.
(24) Schreurs, A. M. M.; Xian, X.; Kroon-Batenburg, L. M. J. J. Appl.
Crystallogr. 2010, 43, 70.
(25) Sheldrick, G. M. SADABS: Area-Detector Absorption Correction,
Universitat Gottingen, Gottingen, Germany, 1999.
̈
̈
̈
(26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(27) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.
(28) Spek, A. L. Acta Crystallogr., Sect. D 2009, 65, 148.
H
dx.doi.org/10.1021/om400451y | Organometallics XXXX, XXX, XXX−XXX