Complexes with hybrid phosphorus-NHC ligands: Pincer-type Ir hydrides, dinuclear Ag and Ir and tetranuclear Cu and Ag complexes

Article abstract of DOI:10.1021/ic302854t

Three types of hybrid phosphorus-imidazolium salts, 1-methyl-3-(3- ((diphenylphosphino)methyl)benzyl)-1H-imidazol-3-ium hexafluorophosphate (2·PF₆), 1-methyl-3-(3-(di-tert-butylphosphinooxy)phenyl) imidazolium iodide (8a), and 3-(3-((diphenylphosphoryl)methyl)phenyl)-1-methyl- 1H-imidazol-3-ium iodide (11) have been prepared and used as precursors to phosphine-NHC, phosphinite-NHC, and phosphoryl-NHC metal complexes, respectively. The structure of 11 has been determined by X-ray diffraction. The Ag(I) and Ir(I) complexes of the phosphine-NHC ligand, [Ag(μ-P-NHC,κC, κP)]₂(PF₆)₂ (3) and [Ir(cod)(μ-P-NHC, κC,κP)]₂(PF₆)₂ (4), were obtained and characterized by NMR, ESI-MS, elemental analysis, and X-ray diffraction. Both complexes are dinuclear and dicationic, with two P-NHC ligands bridging the two metal centers. The presence of the P donor led for 3 to an unprecedented structure compared to that of related Ag(I) complexes with trans spanning bis-NHC ligands. Complex 4 is the first example of a dinuclear iridium complex with a hybrid P-NHC ligand. The new hydrido, Ir(III) pincer-type complex [IrH(C_NHCCC_NHC)(MeCN)]PF₆ (7) is suggested to have a square-pyramidal structure. The tetranuclear Ag(I) complex with the phosphinite-NHC ligand, [Ag₂(μ₃-I)(μ-PO-NHC, κP,κC_NHC)]₂ (9a) has a cubane-type structure, with alternating silver and iodine apexes and two PO-NHC ligands bridging opposite edges of the Ag₄ tetrahedron. The Ir(III) pincer complexes [IrH(I)(PO-NHC,κP,κC,κC_NHC)^Me] (10a) and [IrH(I)(PO-NHC,κP,κC,κC_NHC)^n-Bu] (10b), with Me or n-Bu substituents on the nitrogen atom, respectively, have been prepared and characterized. Ag(I) and Cu(I) complexes with the phosphoryl-NHC ligand are reported and the centrosymmetric structure of the latter, [Cu(OP-NHC,κC_NHC)₂(μ-I){Cu(μ-I)}]₂ (13), was established by X-ray diffraction and consists of a central Cu ₂(μ-I)₂ rhombus connected by single iodide bridges to two Cu(OP-NHC,κC_NHC)₂ moieties. The Ir(III) hydride pincer complexes 10a,b were tested as catalyst precursors for the C-H bond activation of alkanes. Although their efficiency was significantly lower for transfer dehydrogenation from cyclooctane (coa) to t-butylethylene (tbe) than that of known PCP-Ir systems, these results represent the first attempts to study the catalytic properties of hybrid P-NHC iridium pincer complexes.

Full text of DOI:10.1021/ic302854t

Article
pubs.acs.org/IC
Complexes with Hybrid Phosphorus-NHC Ligands: Pincer-Type Ir
Hydrides, Dinuclear Ag and Ir and Tetranuclear Cu and Ag
Complexes
Xianghao Liu and Pierre Braunstein*
Laboratoire de Chimie de Coordination, Institut de Chimie, UMR 7177 CNRS, Universite
90032, 67081 Strasbourg Cedex, France
́
de Strasbourg, 4 rue Blaise Pascal, CS
S
* Supporting Information
ABSTRACT: Three types of hybrid phosphorus-imidazolium
salts, 1-methyl-3-(3-((diphenylphosphino)methyl)benzyl)-1H-
imidazol-3-ium hexafluorophosphate (2·PF6), 1-methyl-3-(3-
(di-tert-butylphosphinooxy)phenyl)imidazolium iodide (8a),
and 3-(3-((diphenylphosphoryl)methyl)phenyl)-1-methyl-1H-
imidazol-3-ium iodide (11) have been prepared and used as
precursors to phosphine-NHC, phosphinite-NHC, and
phosphoryl-NHC metal complexes, respectively. The structure
of 11 has been determined by X-ray diffraction. The Ag(I) and
Ir(I) complexes of the phosphine-NHC ligand, [Ag(μ-P-
NHC, κC , κP)]2 (PF6 )2 (3 ) and [Ir(cod )(μ- P -
NHC,κC,κP)]2(PF6)2 (4), were obtained and characterized by NMR, ESI-MS, elemental analysis, and X-ray diffraction. Both
complexes are dinuclear and dicationic, with two P-NHC ligands bridging the two metal centers. The presence of the P donor led
for 3 to an unprecedented structure compared to that of related Ag(I) complexes with trans spanning bis-NHC ligands. Complex
4 is the first example of a dinuclear iridium complex with a hybrid P-NHC ligand. The new hydrido, Ir(III) pincer-type complex
[IrH(CNHCCCNHC)(MeCN)]PF6 (7) is suggested to have a square-pyramidal structure. The tetranuclear Ag(I) complex with the
phosphinite-NHC ligand, [Ag2(μ3-I)(μ-PO-NHC,κP,κCNHC)]2 (9a) has a cubane-type structure, with alternating silver and
iodine apexes and two PO-NHC ligands bridging opposite edges of the Ag4 tetrahedron. The Ir(III) pincer complexes
[IrH(I)(PO-NHC,κP,κC,κCNHC)Me] (10a) and [IrH(I)(PO-NHC,κP,κC,κCNHC n‑Bu] (10b), with Me or n-Bu substituents on the
)
nitrogen atom, respectively, have been prepared and characterized. Ag(I) and Cu(I) complexes with the phosphoryl-NHC ligand
are reported and the centrosymmetric structure of the latter, [Cu(OP-NHC,κCNHC)2(μ-I){Cu(μ-I)}]2 (13), was established by
X-ray diffraction and consists of a central Cu2(μ-I)2 rhombus connected by single iodide bridges to two Cu(OP-NHC,κCNHC
)
2
moieties. The Ir(III) hydride pincer complexes 10a,b were tested as catalyst precursors for the C−H bond activation of alkanes.
Although their efficiency was significantly lower for transfer dehydrogenation from cyclooctane (coa) to t-butylethylene (tbe)
than that of known PCP-Ir systems, these results represent the first attempts to study the catalytic properties of hybrid P-NHC
iridium pincer complexes.
Chart 1. Pincer-Type Complexes with Phosphorus (a) or
NHC Donor Groups (b)
INTRODUCTION
■
Since the seminal work of Shaw and Moulton,1 phosphorus-
based pincer-type complexes have been increasingly studied
because of their intrinsic interest and involvement in numerous
aspects of fundamental and applied modern organometallic
chemistry (Chart 1a).2,3 Many of them display interesting
structural/electronic properties and behave as efficient catalysts
in a number of reactions.4−7 Another family of ligands, the N-
heterocyclic carbenes (NHC), has received increasing attention
over the past few years in coordination/organometallic
chemistry and homogeneous catalysis where they behave as
valuable alternatives to phosphorus ligands for transition metals
because of their strong σ-donating and weak π-accepting
properties which limit their dissociation from the metal center
to which they are coordinated.8,9 With the objective to associate
within the same molecule the beneficial properties of each class
of ligands, a diversity of metal complexes with pincer-type
NHC ligands have been prepared (Chart 1b) (with, e.g.,
10−23
24−33
or CNHC∧N∧CNHC
C
NHCCCNHC
donor sets). NHC
metal complexes generally exhibit advantages over their
Received: December 28, 2012
© XXXX American Chemical Society
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phosphorus analogues in terms of, for example, improved air
and thermal stability, which are highly desirable properties in
organometallic chemistry and homogeneous catalysis.34,35
Consistent with the often unique properties that hybrid
ligands, that is, which contain chemically different donor
functions, confer to their metal complexes,36−39 phosphorus-
based hybrid ligands have attracted considerable interest,37,40
while the importance of NHC-based hybrid ligands in metal-
catalyzed reactions has been recently emphasized.41 There are
still relatively few examples of hybrid phosphine-NHC
ligands,42 and they include bidentate43−70 (Chart 2a),
their relatively higher stability compared to the corresponding
Rh and Co complexes.85 The combined use of monodentate
phosphine and NHC ligands in iridium complexes was first
reported by Buriak and coworkers,86 and this was followed by
other research groups87−94 (Chart 4). We were interested to
Chart 4. General Formula of Ir Complexes Containing
Monodentate Phosphine and NHC Ligands
Chart 2. Examples of Hybrid Phosphine-NHC Ligands
extend these studies by connecting these donor functions
within the same ligand and to synthesize new metal complexes,
in particular of iridium, containing P-functionalized NHCs
because of the conceivable diversity and tunability of such
ligands and the beneficial contribution of the chelate effect.
Although the first P-NHC iridium complex was developed
for asymmetric hydrogenation by Bolm in 2004,53 iridium
complexes with hybrid P-NHC ligands remain rare. Except for
Bolm′s complex (Chart 5),53 they all contain an alkyl chain as
tridentate PCNHCP71−77 (Chart 2b), and macrocyclic
P2(CNHC)2 (Chart 2c) ligands.78 This triggered our interest
for the synthesis and coordination chemistry of such PCNHC
ligands. The ligand backbone was chosen to consist in a 1,3-
disubstituted aryl ring that could potentially be metalated at the
2-position and thus lead to a pincer-type system.
Chart 5. Relevant Ir Complexes with P-NHC Hybrid Ligands
(See Text)
In terms of synthetic efforts, Ag(I)-NHC complexes have
received most attention among the coinage metal-NHCs owing
to their ease of preparation, from an imidazolium precursor and
Ag2O, and their ability to transfer the resulting NHC ligand to
other metal centers by a transmetalation reaction.79 This is
particularly useful when a convenient, high yield direct
synthesis of a transition metal-NHC complex is not available.
In the case of hybrid phosphorus/NHC ligands, Helmchen et
al. synthesized the rhodium complex of a chiral P-functionalized
NHC ligand by a transmetalation reaction from the
corresponding dinuclear silver complex (Chart 3),45 and Lee
et al. used the trinuclear Ag(I) complex of a tridentate pincer
phosphine/NHC ligand to prepare the corresponding Pd(II),80
Ru(II),72 and Rh(I)81 complexes (Chart 3).
Chart 3. Previously Reported Ag(I) Complexes with P-NHC
Hybrid Ligands Used for Transmetalation Reactions
spacer between the P and NHC donor groups of the chelating
P-NHC ligand.52,57,59,65,70,95−98 We will describe below the first
example, to the best of our knowledge, of a dinuclear Ir
complex with a hybrid P-NHC ligand, which extends the range
of known P-NHC Ir complexes to a new class of dimetallacyclic
complexes.
To vary the nature of the phosphorus donor function
associated with the NHC moiety, we have used two different
P(III) functions (phosphine and phosphinite) and one P(V)
donor (phosphine oxide). We thus report the synthesis of: (i)
1-methyl-3-(3-((diphenylphosphino)methyl)benzyl)-1H-imida-
zol-3-ium hexafluorophosphate and its use as precursor to a
phosphine-NHC hybrid ligand that could behave in a bidentate
or a pincer-type manner in Ag(I) and Ir(I) complexes; (ii) 1-
methyl-3-(3-(di-tert-butylphosphinooxy)phenyl)imidazolium
iodide and its use as precursor to a phosphinite-NHC hybrid
ligand that could also behave in a bidentate or a pincer-type
manner in Ag(I) and Ir(I) complexes, and (iii) 3-(3-
((diphenylphosphoryl)methyl)phenyl)-1-methyl-1H-imidazol-
Among the transition metals which have been most
investigated, besides silver for the reasons given above, those
with potential applications in homogeneous catalysis have
attracted special attention. Much research has been performed
on iridium complexes, in particular since the report of
Crabtree′s hydrogenation catalyst,82 and of new applications
found for iridium complexes in the dehydrogenation of
alkanes.83,84 For the latter, significant progress has been made
recently which has led to more active catalysts as a result of
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3-ium iodide and its use as precursor to a phosphoryl-NHC
hybrid ligand in Cu(I) and Ag(I) complexes.
Ag1−P1i 172.94(2)°] (Figure 1). As a result, the aromatic rings
of the spacer are thus parallel to each other, their mean planes
RESULTS AND DISCUSSION
■
Phosphine-NHC Hybrid Ligand. The phosphine-imida-
zolium salt 2·PF6 was prepared from 1,3-bis(chloromethyl)-
benzene by modifying a reported procedure (Scheme 1).99 To
Scheme 1. Synthesis of the Phosphine-Imidazolium
Precursor
Figure 1. (top): ORTEP of the molecular structure of the dicationic
complex [Ag(μ-P-NHC,κP,κCNHC)]2 in 3 with 30% probability
thermal ellipsoids. Hydrogen atoms and anions omitted for clarity.
Selected bond lengths [Å] and angles (deg): Ag1−C1 2.104(5), Ag1−
P1i 2.366(1); C1−Ag1−P1i 172.94(2), C1−N1−C3 104.7(5).
(bottom) Perspective view of the molecular structure of 3 (Diamond
software).
limit possible problems associated with the air-sensitivity of an
uncoordinated phosphine group, we introduced the P-donor
moiety in the final step of the preparation. Diethyl ether was
used as the solvent in the first step of the synthesis to
precipitate the monosubstituted derivative 1, thus preventing
further substitution even though 1,3-bis(chloromethyl)benzene
was present in large excess. Highly hygroscopic 2·Cl was treated
with KPF6 to give the phosphine-imidazolium salt associated
with the noncoordinating hexafluorophosphate anion, which is
easier to handle.
To obtain the corresponding Ag(I) NHC complex, a
dichloromethane solution of the phosphine-imidazolium salt
was reacted with 0.5 equiv of Ag2O at room temperature under
the protection against light. This reaction afforded a white
precipitate of the Ag(I) complex 3 (Scheme 2). Its 31P{1H}
being 6.607 Å apart and their centroids separated by 6.783 Å,
and the P−Ag−CNHC vectors are in a mutual antiparallel
orientation. A comparison between this structure and that of
other Ag(I) complexes containing either phosphorus or NHC
ligands (Chart 6a-c)99−101 demonstrates the structural diversity
brought about by the hybrid P-NHC ligands. When halides are
present, they usually behave as ligands in neutral Ag(I)
complexes, whereas noncoordinating anions such as OTf−,
Scheme 2. Synthesis of the Ag(I) Complex [Ag(μ-P-
NHC,κP,κCNHC)]2(PF6)2 (3)
Chart 6. Ag(I) Complexes with Phosphorus or NHC Ligands
Related to the Hybrid Ligand Present in 3
NMR spectrum contains a doublet of doublets resonance at δ
1
12.19 ppm [1J(P-107Ag) = 488 Hz, J(P-109Ag) = 555 Hz)].
Single crystals of this complex suitable for X-ray diffraction
were obtained by slow diffusion of diethyl ether into a saturated
acetonitrile solution of the complex.
In the centrosymmetric structure of the cationic complex, the
two phosphine-NHC ligands bridge two Ag metal centers
(Ag···Ag 6.304(6) Å), which have a linear coordination
geometry defined by the Ag−P and Ag−CNHC bonds [C1−
C
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−
−
PF6 , or BF4 favor the linear coordination of neutral donors
around a cationic metal center.101−103
and coordinated by a phosphorus and a carbene donor from
two different P-NHC ligands, thus reaching a 16e environment.
The separation between the two Ir centers is 9.725(6) Å. This
dicationic, 18-membered dimetallacycle with μ-P-NHC units is
obviously preferred to a mononuclear 9-membered ring
structure with P-NHC chelating ligands. Similary to the
Ag(I) complex 3, the aromatic rings which separate the NHC
and P donor groups in each ligand are parallel to each other,
the distance between their mean planes is 1.585 Å and that
between their centroids is 7.054 Å. The two bridging ligands
are in an extended-type conformation in comparison to 3 where
it is more “contracted”. In Crabtree’s work on Ir complexes, it
was shown that imidazolium salts associated with a halogen
anion led preferentially to classical NHCs, whereas non-
The poor solubility of the Ag(I) complex 3 hampered further
transmetalation reactions. This triggered our efforts for a direct
synthesis of iridium complexes from 2·PF6. Thus, a solution of
2·PF6 was reacted with [Ir(cod)(μ-Cl)]2 and Cs2CO3 in
acetonitrile for 3 h, which gave an Ir(I) complex in excellent
yield (Scheme 3). A singlet appeared in the 31P{1H} NMR
Scheme 3. Synthesis of the Dinuclear Ir(I) Complex 4
−
−
coordinating anions, such as BF4 or PF6 , mostly give rise to
abnormal NHCs.104 However, here we did not observe the
formation of any abnormal NHC.
It is interesting to compare the structure of 4 with that of two
other dinuclear iridium complexes: (a) the dinuclear pincer-
type Ir(III) complex [Ir(μ-I)(I)(CNHCCCNHC)]2 with iodides
as bridging ligands (Chart 7a), obtained by transmetalation
spectrum at δ 16.88 ppm (low field shifted from the value of δ
−7.74 ppm for the free ligand). The 13C{1H} NMR spectrum
contained a resonance at δ 175.1 ppm for the NHC carbon
coordinated to Ir. Single crystals of 4·2THF suitable for X-ray
diffraction studies were obtained by slow diffusion of
tetrahydrofuran (THF) in a saturated CH2Cl2 solution of the
complex.
Chart 7. Dinuclear Ir(III) (a) and Ir(I) (b) Complexes with
Chelating or Bridging Bis-carbene Ligands
The centrosymmetric structure of the dinuclear cation in 4 is
shown in Figure 2. Each Ir(I) center is chelated by a cod ligand
from a Zr(IV) intermediate;19 (b) a dimetallacyclic, helical Ir(I)
complex with an arrangement of the 20-membered ring formed
by the bis-carbene bridging ligands resulting in a figure-of-eight
conformation, which was obtained by in situ deprotonation of
the imidazolium precursor (Chart 7b).23
In the course of studies extending the latter system to the
iridium(I) complex 6, obtained from the bis-imidazolium salt 5
having methyl substituents in the 4 and 6 positions of the aryl
ring (Scheme 4),100 and of H NMR investigations of the
1
stereodifferentiation in solution of its P and M enantiomers,105
we noted that using the more labile precursor [Ir(coe)2(μ-Cl)]2
led instead to a pincer-type iridium hydride complex,
formulated as 7.
1
Whereas the H NMR spectra of complexes 5 and 6 were
consistent with a symmetrical structure, that of 7 suggested a
nonsymmetrical conformation. In addition to the AB spin
system observed for the NCH2 protons, consistent with the
lack of symmetry element passing through this group, a
doubling of all the resonances was observed, except for the
arene hydrogen (C···CH···C), which shifted from δ 7.23
(ligand) to 6.47 ppm. This would be consistent with the two
twisted NHC arms being inequivalent, which in turn suggests
for 7 a square-pyramidal coordination geometry with transoid
H and MeCN ligands, similar to the situation observed in
recently reported Ir(III) NHC pincer complexes.11 Moreover,
the resonance of the hydrogen attached to the arene carbon C2
has disappeared and a singlet at δ −22.09 ppm provided
Figure 2. Top: ORTEP of the molecular structure of the dicationic
complex [Ir(cod)(μ-P-NHC,κP,κCNHC)]2 in 4·2THF with 30%
probability thermal ellipsoids. The 2 molecules of THF, the anions,
and the hydrogen atoms have been omitted for clarity. Selected bond
lengths [Å] and angles [deg]: Ir1i−C1 2.043(7), Ir1i−P1i 2.316(2);
C1−Ir1i−P1i 91.5(2), N1−C1−N2 104.0(6). Bottom: Perspective
view of the molecular structure of the dicationic complex in 4
(Diamond software).
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atom, we prepared the imidazolium salts 8a and 8b, with slight
modifications for the former of the procedure reported earlier
for 8b (Scheme 5).106
Scheme 4. Synthesis of Ir(I) or Ir(III) Complexes as a
Function of the Metal Precursor
Scheme 5. Synthesis of the Phosphinite-Imidazolium Salts
By analogy with the reaction with 8b,106 2 equiv of the N-
methyl substituted ligand 8a were reacted with Ag2O in the
presence of 2 equiv of AgI to afford the cubane-type silver
cluster 9a (Scheme 6), which was characterized by X-ray
diffraction (Figure 3).
Scheme 6. Synthesis of the Silver PO-NHC Cluster [Ag2(μ3-
I)(μ-PO-NHC,κP,κCNHC)]2 (9a)
evidence for the formation of an Ir−H bond. MS-ESI data
presented a main peak at (m/z) 528.2 [M-PF6]+ and another
peak at (m/z) 487.1 [M-MeCN-PF6]+, indicating coordination
of a neutral solvent molecule (MeCN) to the metal center,
giving rise to a penta-coordinated complex. Unfortunately, we
could not obtain single crystals of this complex suitable for X-
ray diffraction.
These results illustrate the influence that the iridium-
coordinated ligands cod or coe of the precursor complexes
may have on their reactivity. In complex 6, the cod ligand
remains chelated to the Ir center and the two bridging bis-NHC
ligands connect the Ir(I) centers in such a way that each metal
is bonded to two mutually cis carbene donors. This results in a
dicationic 20-membered dimetallacycle. Because coe is a more
labile olefin than cod, it was easily displaced by the solvent
molecule MeCN, which coordinates to the Ir center through its
nitrogen atom in complex 7. The requirement for shorter
reaction times (compared to the reaction using [Ir(cod)(μ-
Cl)]2 also indicated the higher lability of the complex due to a
more weakly bound coe ligand compared to cod. Unlike the
situation in 6, with its figure-of-eight loop structure, the aromatic
ring has been metalated in complex 7, as a result of oxidative-
addition and formation of Ir−C and Ir−H bonds. Mixtures of
solvents were used to increase the solubility of the ligand
(soluble in MeCN) and [Ir(coe)2(μ-Cl)]2 (soluble in THF).
Interestingly, MeCN appears to have significantly stabilized the
pincer-type Ir(III) hydride complex 7 because when the bis-
imidazolium dibromide precursor, which is soluble in THF, was
treated under similar conditions but in the absence of MeCN,
only decomposition of the iridium precursor was observed.
The chelating cod ligand in the Ir complexes 4 and 6 and in
that of Chart 7b is responsible for the mutual cis arrangement
of the NHC donors (in 6 and Chart 7b) and of the P and NHC
donor functions (in 4), while in the Ag(I) complex 3, there is
no constraint preventing the P-NHC ligands to adopt a
conformation allowing a trans arrangement of the P and NHC
donor groups and a linear coordination geometry about the
Ag(I) centers.
Figure 3. ORTEP of 9a in 9a·CH2Cl2 with 30% probability thermal
ellipsoids. Hydrogen atoms omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Ag1−C1 2.176(8), Ag2−P1 2.451(2), Ag3−
C19 2.156(9), Ag4−P2 2.460(2), Ag1−I1 2.9740(9), Ag1−I2
2.887(1), Ag1−I3 2.987(1), Ag1−Ag2 3.084(1), Ag3−Ag4 3.045(1);
N1−C1−N2 103.3(7), C1−Ag1−I1 104.5(2), C1−Ag1−I2 123.4(2),
C1−Ag1−I3 127.6(2), I1−Ag1−I2 113.96(3), I1−Ag1−I3 93.80(3),
I2−Ag1−I3 90.29(3).
Phosphinite-NHC Hybrid Ligands. To examine the
consequences of replacing the CH2 spacer between the
phosphorus and the aryl ring with an isoelectronic oxygen
E
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The molecular structure of 9a is similar to that of known
9b106 and exhibits a rare ligand/metal arrangement, despite the
diversity encountered in the structural chemistry of Ag-NHC
complexes.79,102,103 The distorted Ag4I4 cubane-like core, with
alternating Ag and I vertices, features iodide ligands capping
three metal centers and two PO-NHC ligands bridging
opposite edges of the Ag4 tetrahedron. The corresponding
Ag···Ag distances of 3.084(1) and 3.045(1) Å are compatible
with the existence of d10-d10 interactions.107 The Ag···Ag
distances and the P−Ag bond lengths are in the range of the
corresponding values in [Ag4I4(PPh3)4].108,109 The pronounced
deformation of the pseudocubane arrangement in 9a is due to
I···I separations being significantly longer than the Ag···Ag
ones. The NHC-Ag distances (Ag1−C1 2.176(8) and Ag3−
C19 2.156(9) Å) are similar to those in 9b. The 31P{1H} NMR
spectrum of 9a exhibits a broad signal at 158.3 ppm, and the
to a phosphoryl-NHC hybrid ligand was synthesized according
to Scheme 8.
Scheme 8. Synthesis of the Precursor to a Phosphoryl-NHC
Hybrid Ligand
1
two J(P−Ag) couplings were not resolved.
The similarities between 9a and 9b show that PO-NHC
ligands with different N-substituents behave as bridging rather
than chelating ligands and that the change of N-substituent
from n-Bu to methyl does not significantly affect the structure
of the corresponding tetrasilver complexes obtained according
to Scheme 6.
The salt 11 was characterized by X-ray diffraction (Figure 4).
Whereas no intramolecular H-bonding interaction involving the
Since attempts to use 9a for transmetalation to Ir(I)
complexes failed, we attempted the direct synthesis of what
should be the first examples of iridium complexes with a P-
containing NHC pincer ligand. We reacted the corresponding
imidazolium salts 8a,b with the Ir(I) precursor complex in the
presence of weak bases, as detailed in Scheme 7, and obtained
the corresponding Ir(III) complexes 10a,b.
Scheme 7. Synthesis of Iridium(III) Pincer Complexes
[IrH(I)(PO-NHC,κP,κC,κCNHC)] (10a,b) with a PO-NHC
Ligand
Figure 4. ORTEP of 11 with 30% probability thermal ellipsoids.
Selected bond lengths [Å] and angles [deg]: N1−C1 1.312(3), N2−
C1 1.337(4), P1−O1 1.483(2); N1−C1−N2 109.2(3), C11−P1−O1
114.1(1).
oxygen atom was detected, some intermolecular interactions
between the oxygen atom and the imidazole olefinic hydrogen
atom of an adjacent molecule were detected (CH···OP:
3.100 Å). It is interesting to compare the X-ray structure of this
salt, which contains a C−PO linkage, with that of 8b and its
C−O−P moiety.106 Whereas the imidazolium and aromatic
rings are coplanar in 11, their mean planes formed an angle of
22.7(2)° in 8b. The iodide counterion in both 8b and 11 forms
an intramolecular contact with the NCHN hydrogen (CH···I:
3.672 and 3.760 Å respectively). In 11, another iodide
(belonging to another entity) is situated in the vicinity of C3
and C10 (C3H···I: 3.122 Å and C10H···I: 3.061 Å). Other
metrical data within the cation are as expected.
To synthesize the corresponding NHC silver complex, the
salt 11 was reacted with 0.5 equiv of Ag2O in dichloromethane
at room temperature, under the protection against light.
Although we could not obtain single crystals of the product
formed, it was characterized by NMR spectroscopy and
elemental analysis and formulated as [Ag(11−H)I]n (12). The
value of the 31P{1H} NMR chemical shift (27.72 ppm) is
almost identical to that in 11 (27.67 ppm), indicating that the
oxygen is not coordinated to the metal. We are lacking
sufficient data to suggest a structure for 12, and we will see
1
Like in the case of 7, the H NMR spectrum of 10a,b
revealed the presence of a hydride resonance at δ −26.88 (d,
2J(PH) = 17.6 Hz) and −31.72 (br s) ppm, respectively.
Compared with the spectrum of 8a,b, the two tert-butyl groups
of 10a,b appeared nonidentical (both in the 1H and 13C NMR).
The 31P{1H} NMR resonance is downfield shifted from δ 159.9
(8a) and 159.5 (8b) to 174.6 (10a) and 173.1 (10b) ppm,
respectively. Although the poor quality of the crystals available
and of the X-ray diffraction data of 10b prevented a full
refinement of the structure, tridentate coordination of the
pincer ligand and iodide coordination trans to carbon were
unambiguously established. We thus assume for 10a,b a square
pyramidal coordination geometry similar to those reported for
PCP and POCOP pincer iridium hydride complexes, which
also contain a halide ligand trans to carbon.110−113
Phosphoryl-NHC Hybrid Ligand. To evaluate the
influence of the chelate or of the pincer ring size and of the
nature of the donor atom associated with the NHC function on
the structure and properties of the metal complexes, a precursor
F
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below that the Cu(I) complex with this ligand has indeed an
unexpected structure, while retaining a 1:1 M/NHC ratio.
We then attempted to prepare the corresponding Cu(I)
complex and, unexpectedly, obtained in high yield a complex,
13, of which the structure could fortunately be established by
X-ray diffraction. Complex 13 has a centrosymmetric,
tetranuclear structure, with a central Cu2(μ-I)2 unit (Scheme
9).
Chart 8. Structural Unit Generally Encountered in Cu(I)-
NHC Complexes with Bridging Halides
M/NHC/I ratio of 4:2:4 in the Ag(I) cubane-type complexes
9a,b with that of 4:4:4 in 13. Since the additional PO
functionality in 13 does not participate in the bonding to the
metals, the structural arrangement observed in 13 could have a
more widespread occurrence.
Scheme 9. Synthesis of the Tetranuclear Cu(I) Complex
[Cu(OP-NHC,κCNHC)2(μ-I){Cu(μ-I)}]2 (13)
Attempted Transfer Dehydrogenation of Cyclooctane
Using the Iridium Complexes 4, 6, 7, 10a, and 10b as
Precatalysts. Iridium complexes of the PCP pincer-type
ligands have shown very promising properties in catalytic C−H
bond activation of alkanes.127−129 Considering that complexes
with NHC ligands generally exhibit higher thermal stability
than their phosphine analogues, and that an increased
electronic density around the metal center would be beneficial
for the C−H oxidative-addition of the C−H bond,35 NHC-
based Ir complexes could represent good candidates for the
homogeneous catalytic dehydrogenation of alkanes.
Since the initial reports of transfer dehydrogenation of
cyclooctane (coa) using PCP130,131 and POCOP132,133 iridium
pincer complexes these systems have served as benchmarks for
this reaction (Scheme 10).83,85,112,134−146
Scheme 10. Transfer Dehydrogenation of coa in the
Presence of tbe
As shown in Figure 5, there are two types of coordination
environments for the Y-shaped coordinated Cu(I) centers: (1)
Preliminary studies using the dicationic Ir(I) complexes 4
and 6 or the cationic Ir(III) hydride complex 7 revealed no
catalytic activity, probably because of their poor solubility in
neat alkanes. The synthesis of a neutral Ir(III) dihydride
complex from 7 using KOt-Bu in the presence of dihydrogen
was also unsuccessful, because of decomposition initiated by
the reactivity of the CH2 position under such basic conditions.
The solubility of the neutral iridium complexes 10a and 10b,
however, is significantly better than that of 6 or 7, and these
were tested for the transfer dehydrogenation of coa. Each of
these precatalysts was tested for 5 and 10 h reaction time. The
results of the catalytic experiments are summarized in Table 1.
Figure 5. ORTEP of the Cu(I) complex 13 with 30% probability
thermal ellipsoids. Hydrogen omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Cu1−C1 1.912(8), Cu1−C26 1.930(9), Cu1−
I1 3.119(1), Cu2−I1 2.522(2), Cu2−I2, 2.576(2); C1−Cu1−C26
162.6(4), C1−Cu−I1 97.7(3), Cu1−I1−Cu2 121.99(5), I2−Cu2−I2i
108.37(6).
Cu1 is surrounded by two NHC ligands and an iodide; (2) Cu2
has three iodide ligands. All the PO functions are dangling.
Despite the structural diversity encountered with NHC Cu(I)
complexes containing halide ligands, most published examples
containing a Cu2(μ-X)2 core have the NHC ligand directly
coordinated to this unit (Chart 8).114−126
Table 1. Catalytic Transfer Dehydrogenation of Cyclooctane
in the Presence of tert-Butylethene with 10a and 10b
entry
catalyst
time/h
TOF/h−1
1
2
3
4
10a
10a
10b
10b
5
0.85
0.52
1.27
1.46
The structure of 13 may be viewed as constituted of two
Cu(NHC)2-type cations associated with a [Cu2(μ-I)2I2]2−
10
5
dianion. This is consistent with the bending of the CNHC
Cu−CNHC angle (162.6(4)°). It is interesting to compare the
−
10
G
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performed by the “Service de microanalyses”, Universite de
́
Strasbourg. Electrospray mass spectra (ESI-MS) were recorded on a
microTOF (Bruker Daltonics, Bremen, Germany) instrument using
nitrogen as drying agent and nebulizing gas. The syntheses of 5, 6, 8b,
and 9b have been reported before.100,105,106
In a preliminary investigation, a red suspension of 10a (6.4
mg, 10 μmmol) or 10b (6.8 mg, 10 μmmol) in a mixture of
cyclooctane (coa; 4.0 mL, 30.3 mmol) and tert-butylethene
(tbe; 0.45 mL, 3.5 mmol), in sealed tubes under argon, was
heated to 200 °C. Gas chromatographic analysis of the products
indicated that, for entry 4 (Table 1) 0.48% of the cyclooctane
was converted to cis-cyclooctene (coe) at a turnover freguency
(TOF) of 1.46 h−1, indicating that the transfer dehydrogenation
reaction did occur, although at a rate significantly lower than
previously found in PCP-Ir systems.112,130−133,144 Such low
catalytic activities compared with those of PCP-Ir systems
operating at similar temperatures and thus with similar
concentrations of tbe cannot be due to a too low concentration
of tbe in solution at 200 °C. According to the observations
made with PCP pincer complexes, high concentrations of tbe
tend to inhibit the catalytic reaction.130,131,147 The stronger σ-
donor properties of the NHC ligands compared to phosphines
should facilitate the C−H oxidative-addition step while
disfavoring the reductive elimination of the product during
the catalytic cycle. Further work is needed to improve the
catalytic performances.
Synthesis of 1-(3-(Chloromethyl)benzyl)-1H-imidazol-3-ium
Chloride (1). N-methyl-imidazole (0.165 g, 158 μL, 2.01 mmol) was
added to a Et2O solution (10 mL) of m-xylene dichloride (1.751 g,
10.00 mmol) at room temperature. After it was refluxed for 7 days, the
suspension was allowed to cool to room temperature and filtered. The
crude solid was washed with Et2O (2 × 10 mL) leading to an off-white
product. (0.190 g, 0.736 mmol, 37% based on N-methyl-imidazole).
1H NMR (CDCl3): δ 10.84 (1H, s, NCHN), 7.52 (1H, s), 7.45 (1H,
m), 7.40−7.37 (3H, m), 7.35−7.33 (1H, m), 5.61 (2H, s, N−CH2),
4.55 (2H, s, Cl-CH2), 4.03 (3H, s, N−CH3); 13C{1H} NMR (CDCl3):
δ 138.8 (s, Carom.), 138.0 (s, Carom.), 133.9 (s, Carom.), 129.9 (s, Carom.),
129.6 (s, Carom.), 129.0 (s, Carom.), 129.0 (s, Carom.), 123.7 (s, Cimid.),
122.0 (s, Cimid.), 52.8 (s, N−CH2), 45.6 (s, Cl-CH2), 36.6 (s, N−CH3)
ppm. ESI-MS (m/z): 221.1 [M-Cl]+. The hygroscopic nature of this
compound prevented the recording of satisfactory elemental analyses.
Synthesis of 1-Methyl-3-(3-((diphenylphosphino)methyl)
benzyl)-1H-imidazol-3-ium Hexafluorophosphate (2·PF6). A
THF solution of potassium diphenylphosphide (0.500 M, 2.00 mL,
1.00 mmol) was added dropwise to a solution of 1 (0.258 g, 1.00
mmol) in dimethylsulfoxide (DMSO, 5 mL). The mixture was stirred
at room temperature for 3 h, and DMSO was removed under reduced
pressure. Methanol (5 mL) was then added and after the mixture was
stirred for 20 min, all volatiles were removed under reduced pressure.
The residue was then dissolved in dichloromethane (15 mL), and the
suspension was filtered to remove inorganic salts. The solvent was
then removed under vacuum to afford 1-methyl-3-(3-
((diphenylphosphino)methyl) benzyl)-1H-imidazol-3-ium chloride as
a foam after washing with diethyl ether (3 × 10 mL). This product was
used directly for the synthesis of the PF6 salt, and a large excess of
KPF6 (0.900 g, 4.89 mmol) was added to its suspension in acetone (10
mL). The mixture was stirred at room temperature for 8 h. Acetone
was then removed under reduced pressure and dichloromethane (15
mL) was added to this residue. A clear solution was obtained after
filtration. Removal of the solvent followed by addition of diethyl ether
gave an oil which solidified slowly at room temperature in Et2O to give
2·PF6 a white solid (0.346 g, 0.668 mmol, 67% based on 1). 1H NMR
(d6-DMSO): δ 9.13 (1H, br s, NCHN), 7.71 (1H, pseudo t, 3J(HH) =
CONCLUSION
■
The coordination chemistry of functional NHC ligands
associated with three different types of phosphorus donors, of
the phosphine, phosphinite, and phosphine-oxide type, has
been explored. The phosphine-NHC ligand present in the
Ag(I) and Ir(I) complexes 3 and 4, respectively, behaved as a
bidentate, bridging ligand and did not form PCCNHC pincer-
type complexes. The presence of the P donor led for 3 to an
unprecedented structure when compared to that of related
trans-spanning bis-NHC donors (Chart 6c). The steric bulk of
the diphenylphosphino group may be responsible for the
formation of a dinuclear rather than a mononuclear Ag
complex.101 It is interesting to compare the metal/NHC/
halide ratios in complexes 9a,b (4:2:4) with that in 12 (4:4:4).
Since the additional PO functionality does not participate in
the bonding to the metals, the structural arrangement found in
12 could have a more widespread occurrence in complexes with
a formula of the common type MX(NHC). We observed that
the use of NHC Ag(I) complexes as transmetalating agents
suffers from limitations, which may be due to their low
solubility, as with 3, or to a lack of reactivity, as with 9a, where
the stability of the cubane structure may disfavor NHC transfer.
In both cases however, a direct access to Ir NHC complexes
was successful, which reduces the number of steps.
3
4
4J(HH) = 1.7 Hz, CHimid), 7.61 (1H, pseudo t, J(HH) = J(HH) =
1.7 Hz, CHimid); 7.45−7.35 (10H, m, CHarom.), 7.24 (1H, pseudo q,
4
5
3J(HH) = J(HH) = J(HH) = 7.8 Hz, C···CH···C), 7.18−7.13 (3H,
m, CHarom.), 5.31 (2H, s, NCH2), 3.87 (3H, s, NCH3), 3.54 (2H, s, P-
CH2); 13C{1H} NMR (DMSO): δ 138.6 (d, J(PC) = 8.1 Hz, Carom.),
137.6 (d, J(PC) = 15.5 Hz, Carom.), 136.5 (s, Carom.), 134.6 (s, Carom.),
132.6 (d, J(PC) = 18.8 Hz, Carom.), 130.6 (d, J(PC) = 9.2 Hz, Carom.),
129.5 (d, J(PC) = 6.8 Hz, Carom.), 128.9 (d, J(PC) = 6.5 Hz, Carom.),
128.8 (s, Carom.), 128.7 (d, J(PC) = 1.3 Hz, Carom.), 128.5 (d, J(PC) =
6.6 Hz, Carom.), 125.7 (d, J(PC) = 2.4 Hz, Carom.), 123.9 (s, Cimid),
122.2 (s, Cimid), 51.7 (s, NCH2), 35.8 (s, NCH3), 34.1 (d, J(PC) =
15.1 Hz, PCH2); 31P{1H} NMR (d6-DMSO): δ −7.74 (s, PPh2),
−143.10 (sept, 1J(PF) = 711 Hz, PF6) ppm. ESI-MS (m/z): 371.2 [M-
PF6]+. Anal. Calcd for C24H24F6N2P2 (516.40): C, 55.82; H, 4.68; N,
5.42. Found: C, 55.58; H, 4.80; N, 5.70%.
The reactivity of the pincer-type iridium(III) hydrido
complexes 10a,b deserves further investigations. Preliminary
experiments performed with the latter as catalyst precursors for
the C−H bond activation of alkanes showed that they were less
active than PCP-Ir systems. These experiments still provide the
first attempts to study the catalytic properties of hybrid P-NHC
iridium pincer complexes and remain promising.
Synthesis of [Ag(μ-P-NHC,κP,κCNHC)]2(PF6)2 (3). Solid Ag2O
(0.023 g, 0.10 mmol) was added to a Schlenk tube containing a
CH2Cl2 solution of 2·PF6 (0.103 g, 0.199 mmol) under argon. The
Schlenk tube was protected against light, and the solution was stirred
at room temperature until the black solid disappeared and a white
precipitate formed. The solid was collected by filtration and
redissolved in MeCN. The solution was filtered again to remove any
unreacted Ag2O and concentrated to 5 mL. Diethyl ether (15 mL) was
added to precipitate an off-white solid, which was collected and
washed with diethyl ether to afford the product. (0.157 g, 0.126 mmol,
63%). Single crystals suitable for X-ray diffraction studies were
obtained by slow diffusion of diethyl ether into a saturated acetonitrile
EXPERIMENTAL SECTION
■
General Considerations. All reactions were performed under a
dry argon atmosphere using standard Schlenk techniques. All solvents
were distilled under argon from the appropriate drying agents and
1
stored under argon. H, 13C{1H}, and 31P{1H} NMR spectra were
recorded on a Bruker AV-300 spectrometer at 300.13, 75.48, and
121.49 Hz, respectively, using TMS as external standard, with
downfield shifts reported as positive. All NMR spectra were measured
at 298 K, unless otherwise specified. Elemental analyses were
1
solution of the complex. H NMR (CD3CN): δ 7.57−7.42 (10H, m,
H
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CHarom.), 7.21 (1H, d, J(HH) = 7.1 Hz, CHarom.), 7.08 and 7.05 (2H,
ppm. ESI-MS (m/z): 528.2 [M-PF6]+, 487.1 [M-MeCN-PF6]+. Anal.
Calcd for C20H25F6IrN5P (672.63): C, 35.71; H, 3.75; N, 10.41.
Found: C, 35.10 ; H, 3.30 ; N 9.90%. Despite several attemps, no
better analysis data were obtained, owing to the air- and moisture-
sensitivity of this complex.
AB spin system, CHimid.,
3J(HH) = 1.6 Hz), 7.04 (1H, overlap,
CHarom.), 6.96 (1H, d, J(HH) = 6.8 Hz, CHarom.), 6.87 (1H, s,
C···CH···C), 4.93 (2H, s, NCH2), 3.87 (3H, s, NCH3), 3.71 (2H, br,
PCH2); 13C{1H} NMR (CD3CN): δ 138.4 (s, Carom.), 136.3 (s,
Carom.), 134.1 (s, Carom.), 134.0 (s, Carom.), 132.0 (s, Carom.), 130.2 (s,
Carom.), 130.1 (s, Carom.), 130.0 (s, Carom.), 129.5 (s, Carom.), 126.9 (s,
Carom.), 123.9 (s, Cimid.), 122.8 (s, Cimid.), 55.1 (s, NCH2), 39.2 (s,
NCH3), 34.1 (s, PCH2), the resonance of the coordinated NHC
carbon could not be observed, probably because of the poor solubility
of the complex in CD3CN; 31P{1H} NMR (CD3CN): δ 12.22 (dd,
1J(P-107Ag) = 488 Hz, 1J(P-109Ag) = 555 Hz), −142.91 (sept., 1J(PF) =
711 Hz, PF6) ppm. ESI-MS (m/z): 371.2 (ligand), 477.1 [1/2(M−
2PF6)]+. Anal. Calcd for C48H46N4P4F12Ag2 (1246.52): C, 46.25; H,
3.72; N, 4.49. Found: C, 45.95; H, 3.90; N, 4.55%.
Synthesis of 1-Methyl-3-(3-hydroxyphenyl)imidazolium Io-
dide. Solid 1-(3-hydroxyphenyl)-imidazole (0.512 g, 3.20 mmol) and
iodomethane (5.0 mL) were mixed and stirred for 3 h. The suspension
was filtered. The crude solid was washed with Et2O (2 × 30 mL)
leading to a gray product. Recrystallization from MeOH/Et2O/
pentane yielded the product as a white solid (0.863 g, 2.86 mmol,
1
89%). H NMR (d6-DMSO): δ 10.23 (1H, br s, OH), 9.72 (1H, br s,
NCHN), 8.25 (1H, br s, CHimid.), 7.95 (1H, br s, CHimid.), 7.44 (1H, t,
2
3J(HH) = 6.7 Hz, CHarom.), 7.18 (1H, d, J(HH) = 6.7 Hz, CHarom.),
2
7.11 (1H, s, CHarom.), 6.98 (1H, d, J(HH) = 6.7 Hz, CH CHarom.),
3.95 (3H, s, NCH3); 13C{1H} NMR (d6-DMSO): δ 159.2 (C−OH),
136.3 (Carom.), 136.2 (NCN), 131.6 (Carom.), 124.9 (Cimid.), 121.4
(Cimid.), 117.1 (Carom.), 112.6 (Carom.), 109.3 (Carom.), 36.7 (NCH3)
ppm. ESI-MS (m/z): 175.1 [M-I]+. Anal. Calcd for C10H11IN2O
(302.11): C, 39.76; H, 3.67; N, 9.27. Found: C, 39.73; H, 3.81; N,
9.06%.
Synthesis of [Ir(cod)(μ-P-NHC,κP,κCNHC)]2(PF6)2 (4). Solid 2·PF6
(0.103 g, 0.200 mmol), [Ir(cod)(μ-Cl)]2 (0.067 g, 0.10 mmol), and
Cs2CO3 (0.098 g, 0.30 mmol) were mixed and heated in acetonitrile
(15 mL) at 60 °C for 3 h. The suspension was then allowed to cool to
room temperature and the solvent was removed under reduced
pressure. The orange solid was dissolved in CH2Cl2 (10 mL), and the
solution was filtered, concentrated to 5 mL, and diethyl ether was
added to precipitate an orange solid. (0.13 g, 0.080 mol, 80%). Single
crystals of 4·2THF suitable for X-ray diffraction studies were obtained
by slow diffusion of THF into a saturated CH2Cl2 solution of the
Synthesis of 1-Methyl-3-(3-(di-tert-butylphosphinooxy)-
phenyl)imidazolium Iodide (8a). 1-Methyl-3-(3-hydroxyphenyl)
imidazolium iodide (0.863 g, 2.86 mmol) and excess NEt3 (1.00 mL,
7.17 mmol) were mixed in THF (50 mL). Di-tert-butyl-chlorophos-
phine (0.584 mL, 3.00 mmol) was added via a syringe and the reaction
mixture was stirred at room temperature for 15 h. The resulting
suspension was filtered, and the solvent was removed in vacuo. The
crude solid was recrystallized from THF/Et2O, yielding the pure
product as a white solid. (0.597 g, 1.34 mmol, 47%). 1H NMR
1
complex. H NMR (CD3CN): δ 7.51−7.48 (3H, m, CHarom.), 7.40−
7.32 (6H, m, CHarom.), 7.25 (1H, d, 3J(HH) = 2.0 Hz, CHimid.), 7.19−
3
7.11 (4H, m, CHarom.), 6.78 (1H, d, J(HH) = 2.0 Hz, CHimid.), 5.94
(1H, br s, C···CH···C), 5.80 (1H, A part of an AB spin system,
simulated, 2J(HH) = 14.9 Hz, NCHH), 5.03 (1H, B part of an AB spin
4
2
(CDCl3): δ 10.60 (pseudo t, J(HH) = 1.5 Hz, 1H, NCHN), 7.64
system, simulated, J(HH) = 14.9 Hz, NCHH), 4.51 (4H, m, cod),
3
4
(pseudo t, J(HH) = J(HH) = 1.7 Hz, 1H, CHimid.), 7.61 (pseudo t,
4.07 (3H, s, N−CH3), 3.87 (2H, m, cod), 3.68 (2H, m, cod), 3.56
(1H, A part of an AB spin system, simulated, 2J(HH) = 7.7 Hz,
PCHH), 3.51 (2H, B part of an AB spin system, simulated, 2J(HH) =
7.7 Hz, PCHH), 3.10 (2H, m, cod), the other cod protons are partly
masked by the solvent; 13C{1H} NMR (CD3CN): δ 175.1 (NCN),
136.4 (d, J(PC) = 12.2 Hz, Carom.), 135.8 (s, Carom.), 133.6 (d, J(PC) =
10.0 Hz, Carom.), 132.9 (s, Carom.), 131.9 (s, Carom.), 130.9 (d, J(PC) =
3.8 Hz, Carom.), 130.0 (d, J(PC) = 4.2 Hz, Carom.), 129.8 (s, Carom.),
129.7 (s, Carom.), 129.6 (s, Carom.), 125.3 (s, Cimid.), 122.9 (s, Cimid.),
88.8 (d, J = 11.8 Hz, cod), 87.3 (d, J = 11.8 Hz, cod), 82.3 (s, cod),
79.0 (s, cod), 55.0 (s, NCH2), 38.6 (s, NCH3), 37.1 (d, J(PC) = 26.2
Hz, PCH2), 33.2 (d, J(PC) = 41.6 Hz, cod), 29.4 (d, J(PC) = 48.0 Hz,
cod); 31P{1H} NMR (CD3CN): δ 16.88 (s, PPh2), −143.44 (sept,
1J(PF) = 706 Hz, PF6) ppm. ESI-MS (m/z): 671.2 [M−2(PF6)]2+.
Anal. Calcd for (C32H35F6IrN2P2)2 (1631.58): C, 47.11; H, 4.32; N,
3.43. Found: C, 46.82; H, 4.28; N, 3.33%.
4
3J(HH) = J(HH) = 1.7 Hz, 1H, CHimid.), 7.44−7.51 (m, 2H), 7.39−
3
7.43 (m, 2H), 4.29 (s, 3H, NCH3), 1.20 [d, J(PH) = 12.0 Hz, 18H,
CH3, P(t-Bu)2]; 13C{1H} NMR (CDCl3): δ 161.3 (d, J(PC) = 4.9
2
Hz, C−O), 136.1 (Carom.), 135.3 (NCN), 131.5 (Carom.), 124.3 (Cimid.),
3
120.7 (Cim3 id.), 120.2 (d, J(PC) = 11.8 Hz, Carom.), 115.0 (Carom.),
1
111.8 (d, J(PC) = 11.2 Hz, Carom.), 37.4 (NCH3), 35.7 [d, J(PC) =
2
25.0 Hz, Cquart., 2 × P(t-Bu)2], 27.1 [d, J(PC) = 15.4 Hz, CH3, 2 ×
P(t-Bu)2]; 31P{1H} NMR (CDCl3): δ 159.92 ppm. ESI-MS (m/z):
319.2 [M-I]+. Anal. Calcd for C18H28IN2OP (446.31): C, 48.44; H,
6.32; N, 6.28. Found: C, 48.17; H, 6.29; N, 6.07%.
Synthesis of the Tetranuclear Silver Cluster [Ag2(μ3-I)2(μ-OP-
NHC,κP,κCNHC)]2 (9a). In a Schlenk tube, Ag2O (0.023 g, 0.10 mmol)
and AgI (0.047 g, 0.20 mmol) were added to a solution of 1-methyl-3-
(3-(di-tert-butylphosphinooxy)phenyl)imidazolium iodide (0.089 g,
0.20 mmol) in CH2Cl2 (15 mL). The mixture was stirred at room
temperature for 15 h. The solvent was removed in vacuo, and the solid
obtained was recrystallized from CH2Cl2/Et2O, yielding the product as
a colorless solid (0.16 g, 0.087 mmol, 87%). Single crystals of
9a·CH2Cl2 suitable for X-ray diffraction studies were obtained by slow
diffusion of Et2O into a saturated dichloromethane solution of the
Synthesis of [IrH(CNHCCCNHC)(MeCN)]PF6 (7). Solid 1,1′-((4,6-
dimethyl-1,3-phenylene)bis(methylene)) bis (3-methyl-1H-imidazol-
3-ium) dihexafluorophosphate (5) (0.231 g, 0.394 mmol), [Ir-
(coe)2(μ-Cl)]2 (0.180 g, 0.200 mmol) and Cs2CO3 (0.326 g, 1.00
mmol) were mixed and heated in a stirred solution of acetonitrile (35
mL) and THF (15 mL) at 85 °C for 3 h. The suspension was then
allowed to cool to room temperature and the solution was filtered. The
filtrate was concentrated to 5 mL and ether was added to precipitate a
pale yellow solid. (0.201 g crude, 0.299 mmol, 75.8% yield based on
1
complex. H NMR (CD2Cl2): δ 7.55 (br s, 1H, CHarom.), 7.38 (t,
3J(HH) = 8.0 Hz, 1H, CHarom.), 7.20 (d, 3J(HH) = 1.8 Hz, 1H,
3
CHimid.), 7.11−7.16 (m, 2H, CHarom.), 7.10 (d, J(HH) = 1.8 Hz, 1H,
3
CHimid.), 3.97 (s, 3H, NCH3), 1.41 [d, J(PH) = 14.6 Hz, 18H, P(t-
Bu)2]; 13C{1H} NMR (CD2Cl2): δ 158.6 (C−O), 142.1 (C−N),
130.2 (Carom.), 122.3 (Cimid.), 121.7 (Cimid.), 121.1 (d, 3J(PC) = 2.7 Hz,
Carom.), 119.4 (Car1om.), 118.0 (d, 3J(PC) = 8.1 Hz, Carom.), 39.5
(NCH3), 39.2 [d, J(PC) = 0.8 Hz, Cquart., 2 × P(t-Bu)2], 28.2 [d,
2J(PC) = 10.0 Hz, CH3, 2 × P(t-Bu)2], the resonance of the
coordinated NHC carbon could not be observed, probably because of
the poor solubility of the complex in CD2Cl2; 31P{1H} NMR
1
3
Ir). H NMR (CD3CN): δ 7.27 (1H, d, J(HH) = 1.9 Hz, CHimid.),
7.26 (1H, d, 3J(HH) = 1.9 Hz, CHimid.), 7.07 (1H, d, 3J(HH) = 1.9 Hz,
CHimid.), 7.01 (1H, d, 3J(HH) = 1.9 Hz, CHimid.), 6.47 (1H, s,
2
CHarom.), 5.19 (2H, m, A part of an AB spin system, J(HH) = 13.9
Hz, CHH), 5.16 (2H, m, a part of an AB spin system, J(HH) = 15.0
2
Hz, CHH), 5.06 (2H, m, b part of an AB spin system, 2J(HH) = 15.0
Hz, CHH), 4.38 (2H, m, B part of an AB spin system, 2J(HH) = 13.9
Hz, CHH), 3.88 (3H, s, N−CH3), 3.67 (3H, s, N−CH3), 2.30 (3H, s,
C−CH3), 2.27 (3H, s, C−CH3), −22.07 (1H, s, Ir−H); 13C{1H}
NMR (CD3CN): δ 164.5 (NCN), 164.1 (NCN), 139.0 (Carom.), 138.7
(Carom.), 135.0 (Carom.), 132.5 (Carom.), 131.9 (Carom.), 127.2 (Carom.),
122.4 (Cimid.), 122.0 (Cimid.), 121.9 (Cimid.), 121.4 (Cimid.), 56.1 (CH2),
53.4 (CH2), 38.2 (NCH3), 37.2 (NCH3), 20.6 (CH3), 20.5 (CH3);
1
(CD2Cl2): δ 158.33 (br, J(P−Ag) not resolved) ppm. ESI-MS (m/
z): 1576.6 [M+H]+, 1468.7 [M+2H−Ag]+, 1340.8 [M+H−AgI]+,
1234.9 [M-AgI2]+. Anal. Calcd for C36H54Ag4I4N4O2P2·3CH2Cl2
(1830.68): C, 25.59; H, 3.30; N, 3.06. Found: C, 25.14; H, 3.26; N,
3.15%.
Synthesis of [IrH(I)(PO-NHC,κP,κC,κCNHC)
Me] (10a). Solid 8a
1
31P{1H} NMR (CD3CN): δ −144.71 (sept., J(PF) = 709 Hz, PF6)
(0.178 g, 0.399 mmol), [Ir(coe)2(μ-Cl)]2 (0.180 g, 0.200 mmol), and
I
dx.doi.org/10.1021/ic302854t | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
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Cs2CO3 (0.163 g, 0.500 mmol) were mixed and heated in THF (50
mL) at 65 °C for 3 h. The suspension was then allowed to cool to
room temperature, and the solvent was removed in vacuo. Toluene
(15 mL) was added to extract the product, and the suspension was
filtered. The filtrate was concentrated to 3 mL and layered with
pentane to give some red crystals at 0 °C in low yield (0.020 g, 0.031
mmol, 7.7% based on Ir). 1H NMR (C6D5CD3): δ 6.84 (2H, m,
J(PC) = 7.9 Hz), 132.59 (d, J(PC) = 5.3 Hz), 132.05, 131.61 (d,
J(PC) = 2.8 Hz), 131.42 (d, J(PC) = 5.3 Hz), 131.35 (d, J(PC) = 5.5
Hz), 130.69 (d, J(PC) = 9.2 Hz), 129.53 (d, J(PC) = 2.9 Hz), 129.40
(d, J(PC) = 2.5 Hz), 128.35 (d, J(PC) = 5.1 Hz), 128.18 (d, J(PC) =
11.8 Hz), 128.16, 37.38 (d, J(PC)= 65.7 Hz, PCH2); 31P{1H} NMR
(CDCl3): δ 29.32 ppm; ESI-MS (m/z): 371.0 [M+H]+. Anal. Calcd
for C19H16BrOP (371.21): C, 61.48; H, 4.34. Found: C, 61.80; H,
4.45%.
3
CHarom.), 6.58 (1H, br s, CHimid.), 6.40 (1H, d, J(HH) = 7.3 Hz,
CHarom.), 5.99 (1H, br s, CHimid.), 3.98 (3H, s, NCH3), 1.48 (9H, d,
Synthesis of 3-(3-((Diphenylphosphoryl)methyl)phenyl)-1-
methyl-1H-imidazol-3-ium Iodide (11). First, (3(1H-imidazol-1-
yl)benzyl)diphenylphosphine oxide was prepared by reacting (3-
bromobenzyl)diphenylphosphine oxide (1.12 g, 3.02 mmol), imidazole
(0.336 g, 4.94 mmol), K2CO3 (0.692 g, 5.00 mmol), and CuO (0.046
g, 0.58 mmol) in DMSO (5 mL). The solution was heated at 150 °C
for 48 h. The mixture was cooled, and the DMSO was distilled off
under reduced pressure. CH2Cl2 (15 mL) was added, and the
suspension was filtered. The filtrate was concentrated to 5 mL, and
diethyl ether (15 mL) was added to precipitate an off-white solid,
which was collected and dried. Then, to a flask containing a larger
quantity of (3-(1H-imidazol-1-yl)benzyl)diphenylphosphine oxide
(1.79 g, 5.00 mmol) iodomethane (10 mL) was added, and the
suspension was stirred at room temperature for 3 h until the color of
the solid turned to light yellow. It was then filtered, washed with
diethyl ether (3 × 30 mL), and an off-white solid was obtained. (1.50
3J(PH) = 13.9 Hz, C(CH3)3), 1.33 (9H, d, 3J(PH) = 14.1 Hz,
2
C(CH3)3), −26.88 (1H, d, J(PH) = 17.6 Hz, IrH). 13C{1H} NMR
(C6D5CD3): δ 175.2 (NCN), 166.2 (Carom.−O), 145.0 (C arom.−N),
3
122.1 (C imid.), 120.7 (d, J(PC) = 4.7 Hz, Carom.), 114.8 (C imid.),
3
1
107.6(d, J(PC) = 9.6 Hz, Carom.), 105.0 (Carom.), 43.5 [d, J(PC) =
15.1 Hz, Cquart., P(t-Bu)2], 39.7 [d, 1J(PC) = 21.0 Hz, Cquart., P(t-Bu)2],
37.7 (NCH3), 27.2 [CH3, P(t-Bu)2], 27.0 [CH3, P(t-Bu)2], the
resonance of one of the aromatic carbon (supposed to be present
around δ 130 ppm) may overlap with the solvent peaks; 31P{1H}
NMR (C6D5CD3): δ 174.61 ppm. Anal. Calcd for C18H28IIrN2OP
(638.52): C, 33.86; H, 4.42; N, 4.39. Found: C, 33.35 ; H, 4.10: N,
4.15. The air- and moisture-sensitivity of this complex precluded better
elemental analysis data to be obtained.
Synthesis of [IrH(I)(PO-NHC,κP,κC,κCNHC)
n‑Bu] (10b). Solid 1-
butyl-3-(3-(di-tert-butylphosphinooxy)phenyl) imidazolium iodide
(8b) (0.195 g, 0.399 mmol), [Ir(coe)2(μ-Cl)]2 (0.180 g, 0.200
mmol), and Cs2CO3 (0.163 g, 0.500 mmol) were mixed and heated in
THF (50 mL) at 65 °C for 3 h. The suspension was then allowed to
cool to room temperature, and the solvent was removed in vacuo.
Toluene (15 mL) was added to extract the product, and the
suspension was filtered. The filtrate was concentrated to 3 mL and
layered with pentane to give some dark red crystals at 0 °C in low yield
(0.025 g, 0.037 mmol, 9.2% based on Ir). Their poor quality and that
of the X-ray diffraction data prevented a full refinement of the
structure (a = 10.7577(5) Å, b = 20.0596(13) Å, c = 11.8999(7) Å, α =
γ = 90.00°, β = 113.069(3)°, V = 2362.6(2) Å3, Z = 4). However,
tridentate coordination of the pincer ligand and iodide coordination
trans to carbon were unambiguously established. 1H NMR
(C6D5CD3): δ 6.84 (2H, m, CHarom.), 6.67 (1H, br s, CHimid.), 6.43
(1H, d, 3J(HH) = 7.1 Hz, CHarom.), 6.26 (1H, br s, CHimid.), 4.97 (1H,
br s, A part of an AB spin system, NCHH), 4.49 (1H, br s, B part of an
AB spin system, NCHH), 1.75 (2H, m, NCH2CH2), 1.48 (11H, m,
CH2CH3 + C(CH3)3), 1.36 (9H, d, 3J(PH) = 14.9 Hz, C(CH3)3), 0.92
(3H, t, CH2CH3), −31.72 (1H, br s, IrH); 13C{1H} NMR
(C6D5CD3): δ 175.4 (NCN), 166.7 (Carom.−O), 146.1 (Carom.−N),
122.7 (Cimid.), 120.1 (d, 3J(PC) = 2.7 Hz, Carom.), 114.7 (C imid.),
1
g, 3.00 mmol, 60%). H NMR (d6-DMSO): δ 9.66 (1H, s, NCHN),
8.10 (1H, s, CHimid.), 7.94 (1H, s, CHimid.), 7.84 (4H, m, CHarom.), 7.66
(1H, s, CHarom.), 7.55 (8H, m, CHarom.), 7.30 (1H, m, CHarom.), 4.05
2
(2H, d, J(P−H) = 13.8 Hz, PCH2), 3.94 (3H, s, NCH3); 13C{1H}
NMR (d6-DMSO): δ 135.80 (Carom.), 135.04 (d, J(P−C) = 8.1 Hz,
Carom.), 134.30 (d, J(PC) = 2.6 Hz, Carom.), 133.54 (Carom.), 132.24
(Carom.), 131.73 (d, J(PC) = 2.5 Hz, Carom.), 131.05 (d, J(PC) = 5.3
Hz, Carom.), 130.60 (d, J(P−C) = 9.3 Hz, Carom.), 129.74 (d, J(PC) =
2.1 Hz, Carom.), 128.58 (d, J(PC) = 11.5 Hz, Carom.), 124.55 (Cimid),
123.27 (d, J(PC) = 5.1 Hz, Carom.), 120.65 (Cimid), 119.91 (d, J(PC) =
2.7 Hz, Carom.), 36.13 (NCH3), 35.79 (d, J(PC) = 64.9 Hz, PCH2);
31P{1H} NMR (d6-DMSO): δ 27.67 ppm. ESI-MS (m/z): 373.2 [M−
I]+. Anal. Calcd for C23H22IN2OP (500.31): C, 55.21; H, 4.43; N, 5.60.
Found: C, 55.27; H, 4.50; N, 5.53%.
Synthesis of the Ag(I) Complex of the Phosphoryl-NHC
Ligand (12). Ag2O (0.023 g, 0.099 mmol) was added to a CH2Cl2
solution of 11 (0.100 g, 0.200 mmol). The suspension was stirred at
room temperature overnight under the protection against light. It was
then filtered to remove unreacted Ag2O, and the filtrate was
concentrated to 5 mL. Diethyl ether (30 mL) was added, and an
off-white solid precipitated. The solid was collected through filtration,
1
3
yielding the Ag(I) complex 12 (0.089 g, 0.15 mmol, 73%). H NMR
107.5(d, J(PC) = 8.1 Hz, Carom.), 104.7 (Carom.), 51.3 (NCH2), 43.4
1
1
(d6-DMSO): δ 7.86−7.79 (4H, m, CHarom.), 7.66 (1H, br s, CHimid.),
[d, J(PC) = 14.4 Hz, Cquart., P(t-Bu)2], 40.3 [d, J(PC) = 18.2 Hz,
Cquart., P(t-Bu)2], 34.6 (CH2), 27.3 [CH3, P(t-Bu)2], 27.1 [CH3, P(t-
Bu)2], 21.9 (CH2), 14.3 (CH3), the resonance of one of the aromatic
carbon (supposed at around δ 130 ppm) may be masked by the
solvent peaks; 31P{1H} NMR (C6D5CD3): δ 173.13 ppm. ESI-MS (m/
z): 594.2 [M-I+2H +K]+, 552.2 [M-HI]+. Anal. Calcd for
C21H34IIrN2OP (680.60): C, 37.06; H, 5.04; N, 4.12. Found: C,
36.55 ; H, 4.70: N, 3.85. The air- and moisture-sensitivity of this
complex precluded better elemental analysis data to be obtained.
Synthesis of (3-Bromobenzyl)diphenylphosphine Oxide. A
solution of potassium diphenylphosphide in THF (0.50 M, 10 mL, 5.0
mmol) was added dropwise to a solution of 1-bromo-3-
(bromomethyl)benzene (1.25 g, 5.00 mmol) in DMSO (10 mL).
The mixture was stirred at 60 °C overnight and then cooled to room
temperature. Dichloromethane (50 mL) was added, and the mixture
was washed with brine (20 mL). The organic layer was collected and
dried with anhydrous Na2SO4. Air was bubbled through the filtered
solution, and stirring was maintained for 1 h. The solvent was then
removed under vacuum to afford (3-bromobenzyl)diphenylphosphine
oxide as a white solid after washing with diethyl ether (3 × 10 mL).
7.59 (1H, br s, CHimid.), 7.58−7.46 (8H, m, CHarom.), 7.27−7.22 (2H,
2
m, CHarom.), 3.98 (2H, d, J(P−H) = 13.8 Hz, PCH2), 3.82 (3H, s,
NCH3), the broadness of some resonances could be due to some
dynamic behavior; 13C{1H} NMR (d6-DMSO): δ 139.27 (d, J(P−C)
= 2.8 Hz, Carom.), 134.43 (d, J(P−C) = 7.9 Hz, Carom.), 133.75 (s,
Carom.), 132.50 (s, Carom.), 131.68 (d, J(PC) = 3.0 Hz, Carom.), 130.55
(d, J(PC) = 9.1 Hz, Carom.), 129.18 (d, J(PC) = 2.8 Hz, Carom.), 128.85
(s, Carom.), 128.58 (d, J(PC) = 11.6 Hz, Carom.), 128.16 (s, Carom.),
125.39 (d, J(PC) = 7.4 Hz, Carom.), 124.05 (s, Cimid.), 122.88 (s, Carom.),
121.80 (Cimid.), 38.39 (s, NCH3), 35.66 (d, J(PC) = 65.0 Hz, PCH2);
31P{1H} NMR (d6-DMSO): δ 27.72 ppm. ESI-MS (m/z): 373.1 [M−
AgI]+. Anal. Calcd for C23H21AgIN2OP (607.17): C, 45.50; H, 3.49;
N, 4.61. Found: C, 45.01; H, 3.58; N, 4.31%. Despite several attempts,
no better elemental analysis data could be obtained.
Synthesis of the Phosphoryl-NHC Cu(I) Complex [Cu(OP-
NHC,κCNHC)2(μ-I){Cu(μ-I)}]2 (13). A suspension of 11 (0.100 g, 0.200
mmol), [Cu(NCMe)4]PF6 (0.074 g, 0.20 mmol) and Cs2CO3 (0.098
g, 0.30 mmol) in acetonitrile (10 mL) was stirred at 60 °C for 1 h
under an inert atmosphere. The suspension was then allowed to cool
to room temperature, and the solvent was removed under vacuum.
The resulting colorless solid was then treated with CH2Cl2 (10 mL),
and the solution was filtered. The filtrate was concentrated to 5 mL,
and diethyl ether was added to precipitate a white solid.
1
(0.76 g, 2.0 mmol, 41%). H NMR (CDCl3): δ 7.72−7.66 (5H, m,
CHarom.), 7.52−7.43 (5H, m, CHarom.), 7.31−7.29 (1H, m, CHarom.),
7.24−7.18 (2H, m, CHarom.), 7.08 (1H, s, CHarom.), 3.60 (2H, d,
2J(PH) = 13.6 Hz, PCH2); 13C{1H} NMR (CDCl3): δ 133.08 (d,
J
dx.doi.org/10.1021/ic302854t | Inorg. Chem. XXXX, XXX, XXX−XXX

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Article
Table 2. X-ray Data Collection and Structure Refinement Parameters
compound
chemical formula
formula Mass
crystal system
a/Å
3
4·2THF
C64H70Ir2N4P2·C8H16O2·2PF6
1775.73
9a·CH2Cl2
C36H54Ag4I4N4O2P2·CH2Cl2
1660.78
11
13
C48H46Ag2N4P2·2PF6
1246.51
monoclinic
11.9233(3)
10.5074(5)
19.8377(8)
90.00
C23H22IN2OP
500.30
C92H84Cu4I4N8O4P4
2251.31
triclinic
monoclinic
20.4549(6)
12.3814(2)
25.1919(6)
90.00
triclinic
triclinic
10.0347(6)
14.2909(6)
14.4418(7)
62.225(3)
9.4993(7)
11.2175(9)
12.0230(15)
108.775(2)
107.405(2)
103.001(2)
1081.80(18)
173(2)
13.0030(7)
13.7427(8)
14.3145(6)
72.152(3)
76.698(3)
63.608(2)
2167.82(19)
173(2)
b/Å
c/Å
α/deg
β/deg
93.315(2)
90.00
72.114(3)
123.518(2)
90.00
γ/deg
85.688(3)
unit cell volume/Å3
temperature/K
space group
Z
2481.17(17)
173(2)
1738.17(15)
173(2)
5319.2(2)
193(2)
P21/n
P1
̅
1
P21/c
P1
P1
̅
̅
2
4
2
1
absorption coefficient,
μ/mm−1
1.003
3.997
3.966
1.570
2.522
no. of reflections measured
8209
4855
10687
6819
34450
12190
14190
5231
12341
7685
no. of independent
reflections
Rint
0.0348
0.0530
0.1402
0.0423
0.0530
0.1082
0.0691
0.0619
0.1502
0.0359
0.0306
0.0581
0.0529
0.0759
0.1614
final R1 values (I > 2σ(I))
final wR(F2) values (I >
2σ(I))
final R1 values (all data)
0.0837
0.0801
0.1210
1.030
0.0998
0.1667
1.101
0.0517
0.0638
1.029
0.1317
0.1810
1.041
final wR(F2) values (all data) 0.1743
goodness of fit on F2
1.139
Recrystallization was carried out by layering Et2O onto a MeCN
solution of the white solid, which afforded colorless crystals (0.10 g,
0.044 mmol, 88%). Single crystals suitable for X-ray diffraction studies
were obtained by slow vapor diffusion of pentane into a saturated
dichloromethane solution of the complex. 1H NMR (CD3CN): δ
7.77−7.70 (4H, m, CHarom.), 7.54−7.44 (8H, m, CHarom.), 7.18−7.12
(4H, m, CHarom.), 3.75 (2H, d, 2J(PH) = 13.6 Hz, PCH2), 3.69 (3H, s,
NCH3); 31P{1H} NMR (CD3CN): δ 27.46 ppm. The broadness of the
13C{1H} NMR resonances, probably because of quadrupolar effects
and/or dynamic behavior of the Cu(I) complex, prevented their full
identification. Anal. Calcd for C92H84Cu4I4N8O4P4 (2251.40): C,
49.08; H, 3.76; N, 4.98. Found: C, 48.85 ; H, 3.45 ; H, 4.85.
X-ray Data Collection and Structure Refinement for All
Compounds. Suitable crystals for the X-ray analysis were obtained as
described above. The intensity data were collected at 173(2) K on a
Kappa CCD diffractometer148 (graphite monochromated Mo−Kα
radiation, λ = 0.71073 Å). Crystallographic and experimental details
for the structures are summarized in Table 2. The structures were
solved by direct methods (SHELXS-97) and refined by full-matrix
least-squares procedures (based on F2, SHELXL-97)149 with
anisotropic thermal parameters for all the non-hydrogen atoms.
CCDC 852587−852591 contain the supplementary crystallographic
data for this paper that can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
data_request/cif.
ACKNOWLEDGMENTS
■
We thank the Centre National de la Recherche Scientifique, the
Ministere de l′Enseignement Superieur et de la Recherche
(Paris), the Universite de Strasbourg, and the International
̀
́
́
Center for Frontier Research in Chemistry, Strasbourg (icFRC,
www.icfrc.fr), the China Scholarship Council and the French
Embassy in Beijing (grant to X.L.) for financial support. We are
very grateful to Johnson Matthey PLC for the loan of iridium
salts and to Drs. Roberto Pattacini and the Service de
Radiocristallographie, Institut de Chimie, Strasbourg, for the
resolution of the structures by X-ray diffraction and to Dr. A. A.
Danopoulos for discussions.
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S
* Supporting Information
The CIF of compounds 3, 4·2THF, 9a·CH2Cl2, 11, and 13.
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Notes
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K
dx.doi.org/10.1021/ic302854t | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
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