Cyclometalated iridium complexes of bis(aryl) phosphine ligands: Catalytic C-H/C-D exchanges and C-C coupling reactions

Article abstract of DOI:10.1021/ic400759r

This work details the synthesis and structural identification of a series of complexes of the (η⁵-C₅Me₅)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR′(Ar) ₂, for R′ = Me and Ar = 2,4,6-Me₃C₆H ₂, 1b; 2,6-Me₂-4-OMe-C₆H₂, 1c; 2,6-Me₂-4-F-C₆H₂, 1d; R′ = Et, Ar = 2,6-Me₂C₆H₃, 1e. Both chloride-and hydride-containing compounds, 2b-2e and 3b-3e, respectively, are described. Reactions of chlorides 2 with NaBAr_F (BAr_F = B(3,5-C ₆H₃(CF₃)₂)₄) in the presence of CO form cationic carbonyl complexes, 4⁺, with ν(CO) values in the narrow interval 2030-2040 cm^-1, indicating similar π-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBAr_F forces κ⁴-P,C,C′,C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C-C coupling reaction converts the κ⁴ species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD₃OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir-H and Ir-CH ₂ sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported.

Full text of DOI:10.1021/ic400759r

Article
pubs.acs.org/IC
Cyclometalated Iridium Complexes of Bis(Aryl) Phosphine Ligands:
Catalytic C−H/C−D Exchanges and C−C Coupling Reactions
Jesus Campos, María F. Espada, Joaquín Lopez-Serrano, and Ernesto Carmona*
́
́
Departamento de Química Inorgan
Investigaciones Científicas, Avda. Amer
́
ica, Instituto de Investigaciones Químicas (IIQ), Universidad de Sevilla, Consejo Superior de
́
ico Vespucio 49, 41092, Spain
S
* Supporting Information
ABSTRACT: This work details the synthesis and structural
identification of a series of complexes of the (η5-C5Me5)Ir(III)
unit coordinated to cyclometalated bis(aryl)phosphine ligands,
PR′(Ar)2, for R′ = Me and Ar = 2,4,6-Me3C6H2, 1b; 2,6-Me2-
4-OMe-C6H2, 1c; 2,6-Me2-4-F-C6H2, 1d; R′ = Et, Ar = 2,6-
Me2C6H3, 1e. Both chloride- and hydride-containing com-
pounds, 2b−2e and 3b−3e, respectively, are described.
Reactions of chlorides 2 with NaBArF (BArF = B(3,5-
C6H3(CF3)2)4) in the presence of CO form cationic carbonyl
complexes, 4+, with ν(CO) values in the narrow interval
2030−2040 cm−1, indicating similar π-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBArF forces κ4-
P,C,C′,C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far
encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C−C
coupling reaction converts the κ4 species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using
CD3OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3
experience only D incorporation into the Ir−H and Ir−CH2 sites. Mechanistic schemes that explain this diversity have come to
light thanks to experimental and theoretical DFT studies that are also reported.
Complexes of the [(η5-C5Me5)Ir] metal unit stabilized by
INTRODUCTION
■
coordination to cyclometalated phosphines (see general
formulation B in Scheme 1) are known,16 and some members
of this series induce C−H activation at higher rates than
nonmetalated analogs.16c,e As briefly mentioned, we have
reported lately a set of cyclometalated rhodium and iridium
complexes of the type shown in Scheme 1 (structure C) that
stem from a bis(o-xylyl) phosphine, PMeXyl2 (Xyl = 2,6-
Me2C6H3), which possesses 12 benzylic positions.6 Cyclo-
metalation of PMeXyl2 is a facile reaction that occurs under
mild conditions yielding a five-membered ring structure which
is stable toward β-H elimination. Because of the existence of
two xylyl groups in the phosphine, the cationic unsaturated
species that form upon abstraction of the halide ligand in C
(and the Rh analog)6 undergoes facile exchange of the
metalated and nonmetalated xylyl units. This key structural
feature confers to these complexes valuable and unusual
reactivity properties.6,17 Furthermore, it also appears to be
responsible for the uncommon binding of the metalated
phosphine arm, which coordinates as a κ4-P,C,C′,C″ five-
electron donor ligand.6a,d,17
The cationic Ir(III) complex [(η5-C5Me5)Ir(Me)(PMe3)-
(ClCH2Cl)]+ of Bergman and co-workers (Scheme 1)1 has
served for many years as a model for studies on C−H bond
activation reactions,2 due to its ability to promote this
transformation in a range of organic molecules, including
methane and other hydrocarbons.1 Somewhat surprisingly, the
rhodium analog is more stable thermally and considerably less
reactive.3 Related Ir(III) complexes supported also by the η5-
C5Me5 ancillary group, but containing different phosphorus
donor4 and N-heterocyclic carbene5 ligands, have been
investigated too.
We have recently developed a series of rhodium and iridium
complexes in which the phosphine and alkyl functionalities are
constituents of an aryl phosphine ligand which has undergone
metalation at one of its benzylic positions (see Scheme 1).6
Transition metal metallacycles are an important family of
coordination and organometallic complexes. Comprehensive
studies on these compounds over the past decades7,8 have
discovered plentiful applications in different areas of research,
encompassing catalysis,9 medicinal chemistry,10 and material
science.11 In particular, some iridium complexes of this type
exhibit outstanding catalytic properties. Thus, iridacycles
constructed around pincer ligands12 feature an exceptional
capacity to promote alkane dehydrogenation9a,12c,13 and
hydrogen release from aminoboranes.14 Moreover, they also
display great potential as light-emitting diodes.15
As an extension of this work, we now report the preparation
of iridium complexes like C but derived from bis(aryl) PR′Ar2
phosphines (R′ = Me, Et; see Scheme 2) in which the xylyl
Received: March 27, 2013
© XXXX American Chemical Society
A
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Scheme 1. Some (η5-C5Me5)Ir(III) Structures Relevant to the Present Work
and bis-xylyl phosphine ligands.6,17,22 In a related approach, we
concentrate attention now on cyclometalated Ir(III) complexes
of some bis(aryl)phosphines (Scheme 2). The synthesis of
these ligands was effected utilizing the general, classical
procedure depicted in Scheme 3. Reaction of the corresponding
Scheme 2. Alkyl Bis(aryl) Phosphine Ligands Employed in
This Work (1b−1e) and Studied Previously (1a)6
Scheme 3. General Synthesis of the Phosphine Ligands 1
groups have been modified to accommodate a third R
substituent (R = Me, OMe, F; 1b−1d) in the 4-position of
the aromatic ring. The analogous complex of the ethyl
phosphine, PEtXyl2, 1e, has been studied too. Besides
ascertaining possible electronic effects created by the R
subtituent in the donor properties of the cyclometalated
phosphine, the main objective of this work was to confirm that
the unsual reactivity exhibited by these complexes is in fact due
to the existence of two phosphine aryl rings with benzylic
subtituents prone to cyclometalation. Adding to current interest
in hydrogen isotope exchange reactions,6,17 we also address in
this contribution the diverse catalytic C−H/C−D exchanges
shown by chloride and hydride complexes of type C, albeit
resulting from the metalation of phosphines 1b−1e, and
provide a full mechanistic picture substantiated by experimental
and computational studies. In addition, choosing as a
representative example the cyclometalated iridium complexes
that originate from the fluorophosphine 1d, we describe a
dehydrogenative C−C coupling reaction6d that generates a
hybrid olefin-phosphine (phosphepine) ligand, which adds to
other ligands of this kind already known mostly because of their
numerous applications in catalysis.19
Mg(Ar)Br with PCl3 in a 2:1 molar ratio yielded the expected
bis(aryl)halophosphine as a mixture of the chloro and bromo
derivatives PXAr2, which converted into the desired PMeAr2
(1b−1d) upon reaction with Mg(Me)Br. The synthesis of
PEtXyl2, 1e, was accomplished similarly, employing Mg(Et)Br.
Derivatives 1a−1e were isolated as white solids in yields around
80% (see Experimental Section).
Neutral Cyclometalated Ir(III) Chloride and Hydride
Compounds. The new cyclometalated iridium chloride
complexes 2b−2e were generated with the procedure already
reported6b,d for the PMeXyl2 analog, 2a. As summarized in
Scheme 4, the room temperature reaction of {[(η5-C5Me5)-
IrCl2]2} with 1 equiv of the phosphine in the presence of
2,2,6,6-tetramethylpyperidine (TMPP) allowed isolating com-
plexes 2b−2e as crystalline yellow solids in ca. 70% yield.
Under these conditions, all compounds except the OMe
substituted 2c formed as the single stereomers shown in
Scheme 4, for which steric pressure is relieved thanks to the syn
distribution of the Ir−Cl and P−R (R = Me, Et) units. This
proposal was conclusively demonstrated for 2a6b,c and has now
been additionally inferred from NOESY studies carried out with
the hydride analogs, 3 (vide infra). However, it is difficult to
explain the appearance for 2c of a 60:40 diastereomer mixture,
which remained unchanged upon prolonged heating at 40 °C in
RESULTS AND DISCUSION
■
Synthesis of Bis(aryl)phosphines, PR′Ar2, 1. Phosphine
ligands have played a pivotal role in organometallic chemistry.20
They generally behave as spectator ligands and are capable of
stabilizing a range of oxidation states and a diversity of
organometallic functionalities and structures. In recent years,
bulky phosphines have proved irreplaceable in preparing
molecules of biological interest as well as in promoting
challenging chemical transformations,21 particularly when
combined with a suitable source of Pd(0).
Recently, we have uncovered unusual reactivity modes in Rh,
Ir, and Pt complexes stabilized by coordination to bulky mono-
B
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Scheme 4. Synthesis of the Cyclometalated Iridium Chloride Complexes, 2b−2e
Scheme 5. Synthesis of Ir(III) Hydride Compounds, 3b−3e
a 1:1 mixture of CH2Cl2 and CH3OH. Since under the latter
conditions, the kinetic 70:30 mixture of the syn and anti
stereomers of 2a converted into the syn structure by partial
dissociation of the chloride ligand,6b,c it seems plausible that the
chloride dissociation from compound 2c finds a higher kinetic
barrier that prevents its isomerization. This assumption is also
in agreement with the observation of nearly one stereomer of
hydride 3c (90:10 mixture) upon reaction of 2c with LiAlH4
(vide infra).
Chloride complexes 2b−2e converted into their related
hydrides, 3b−3e, upon reaction with LiAlH4 in THF at 45 °C
for ca. 2 h (Scheme 5). Once more, we observed only the syn
Ir−H/P−R stereomers for 3b, 3d, and 3e but a 90:10 syn/anti
mixture for isolated samples of 3c. All hydrides feature a weak
Ir−H stretching vibration in the IR spectrum between 2075 and
1
2125 cm−1 and a salient, strongly shielded H NMR doublet
resonance at ca. −17 ppm (2JHP ∼ 35 Hz). Corresponding
31P{1H} resonances are only slightly shifted with respect to the
chloride precursors (between 3 and 6 ppm for 3b−3d and at
28.5 ppm for the PEtXyl2 derivative 3e). The proposed syn
structure was deduced from NOESY studies (Experimental
Section) carried out for 3c, which revealed that the major
stereoisomer has a syn structure.
The solution molecular structure of compounds 2 was
unequivocally inferred from their NMR properties. Since they
are similar to those described for the X-ray characterized 2a,
only some selected data will be analyzed here, while
comprehensive lists of the NMR parameters are provided in
the Experimental Section and in the Supporting Information
(SI). For all compounds, a noticeable doublet is found for the
Cationic Complexes Generated by Chloride Abstrac-
tion from Compounds 2. To determine if the structural
variations introduced by the R and R′ substituents in the
phosphine ligands 1a−1e of Scheme 2 have any detectable
effect in the electronic properties of the iridium center of the
cyclometalated complexes studied in this work, we prepared the
cationic carbonyl species 4b+−4e+ by treatment of the
4
C5Me5 protons between 1.4 and 1.6 ppm, with a JHP value of
about 1.6 Hz. The diastereotopic hydrogen atoms of their
metallacyclic moieties give rise to two multiplets between δ 3.5
and 3.8, as expected for ABX spin systems where X is 31P.
31P{1H} resonances appear in the range 3−10 ppm for 2b−2d
(11.3 ppm for 2a) and at a somewhat higher frequency for 2e
(22.8 ppm).
corresponding chloro derivatives 2 with NaBArF (BArF
=
[B(3,5-C6H3(CF3)2)4]) in the presence of 1.5 bar of CO
C
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Scheme 6. Synthesis of Cationic Carbonyl Complexes, 4b+−4e+
Scheme 7. Formation of Complex 5d-BArF with κ4-P,C,C′,C″ Coordination of the Cyclometalated Phosphine (A) and Suggested
Intermediates, D and E, to Explain the Facile Solution Exchange of Its Aryl Groups (B)
Scheme 8. (A) Bronsted−Lowry Base-Catalyzed Rearrangement of Complex 5d-BAr and (B) Key Cationic Alkyl−Alkylidene
̈
F
Intermediate F in the Generation of the Hydride-Phosphepine Complex 6d-BArF
D
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2
(Scheme 6). We found that with the exception of the fluoro-
substituted cation, 4d+, which features ν(CO) at a slightly
higher wavenumber (2040 cm−1), all other compounds,
including 4a+, present this IR band in the narrow interval
2030−2035 cm−1. The solid-state molecular structure of 4e-
BArF has been determined by X-ray crystallography (Figure S6
in SI).
appear at 3.90, 3.32 (Ir-CH2; d, JHH = 14.4 Hz), −12.77 (s),
2
and −13.10 ppm (d, JHP = 16 Hz).
C−H/C−D Exchanges in Chloride (2) and Hydride (3)
Complexes. We reported previously that the parent chloride
and hydride complexes 2a and 3a, respectively, undergo facile
C−H/C−D exchanges using CD3OD as a deuterium source.6c
As recalled in Scheme 9, the exchange affected all benzylic sites
Effecting the above reaction of 2d in the absence of CO
yielded the new compound 5d-BArF (Scheme 7A, the
analogous complex 5e-BArF was obtained similarly). Unequiv-
Scheme 9. C−H/C−D Reactions Reported for Complexes 2a
and 3a6c
1
ocal analogies between the H, 13C{1H}, and 31P{1H} NMR
spectra and those recorded for 5a-BArF,6d as well as for the
rhodium complex analog,6a evidenced the reorganization of the
electronic structure of the cyclometalated phosphine ligand that
leads to the κ4-P,C,C′,C″ coordination mode. As stated earlier,
achieving this unusual binding appears to necessitate a second
aryl unit in the phosphine ligand. Besides, the existence of the
two aryls permits the facile intramolecular exchange of two
degenerate ground-state structures through the low-energy
intermediates D and E shown in Scheme 7B for the fluoro-
containing compound 5d.6d Similarly to 5a-BArF, in the room
1
temperature H NMR spectrum of 5d+ only the signals due to
the η5-C5Me5 and P-Me fragments can be discerned clearly (δ
2
2
1.85, JHP = 2.0 and 2.31 ppm, JHP = 12.7, respectively). The
benzylic protons of the two aryl fragments give a broad peak at
2.43 ppm, but upon cooling at −60 °C the aryl methyl groups
resonate at 2.45 (6H) and 2.05 (3H) ppm, whereas the
diastereotopic Ir−CH2 protons yield two multiplets at 3.01 (t,
3
3
2JHH = JHP = 4.7 Hz) and 1.21 ppm (dd, JHP = 16.2 Hz).
The stirring of a dichloromethane solution of 5d-BArF at 20
°C, in the presence of a catalytic amount of aqueous NaHCO3,
led to the formation of two new compounds (Scheme 8A)
identified as 6d-BArF and 7d-BArF on the basis of their IR and
NMR spectra. By analogy with the previously studied6d reaction
that originated 6a-BArF, the C−C coupling that gives rise to
the phosphepine ligand implied, most probably, an irreversible
migratory insertion of the Ir−CH2 linkage of intermediate F in
Scheme 8B onto the IrCH functionality. Diagnostic
spectroscopic data for 6d+ are (i) an Ir−H IR stretching at
2140 cm−1 and a corresponding 1H NMR signal at −12.93 ppm
of chloride 2a with the same rate, but only the Ir−H and Ir−
CH2 positions (simultaneously too) of hydride 3a. Further-
more, whereas deuteration of 2a was almost imperceptibly
influenced by Bronsted−Lowry acids, a remarkable acid
̈
catalysis ensued for 3a. In the first instance, experimental
data supported the participation of a cationic methanol adduct
generated by momentary chloride dissociation, but for the
second we could only speculate with the possible participation
of a cationic alkylidene species, and a clear mechanistic picture
did not emerge. To settle this question, we have performed
analogous deuteration experiments with the new compounds
2b−2e and 3b−3e, as well as additional assays with the parent
chloride 2a. A simple, general mechanistic scenario that
explains the diverse deuteration of the two sets of compounds
has come to light. This mechanism finds theoretical support in
DFT calculations that are reported. However, contrary to our
initial suggestion,6c the new results do not back the
participation of iridium alkylidenes in the C−H/C−D
exchanges in complexes 3.
(d, JHP = 28 Hz) and (ii) olefinic H and 13C{1H} NMR
resonances recorded respectively at 4.89 and 4.42 ppm (1H)
and 61.4 and 54.8 ppm (13C), which exhibit the expected
couplings to other magnetically active nuclei. The analogous
complexes 6e-BArF and 7e-BArF have also been investigated
(see SI).
2
1
Under ordinary conditions, cation 7d+ was the minor
product of the reaction represented in Scheme 8A. Moreover,
upon prolonged stirring at 20 °C of the 6d+ plus 7d+ mixture,
7d+ converted into 6d+ in a process that became accelerated by
removing volatile materials under a vacuum. However,
performing the reaction in a sealed NMR tube furnished a
1:1 mixture of the two cations.6d These observations, along
with its characteristic spectroscopic data (see below), support
the formulation of 7d+ as the bis(hydride)Ir(V) species
represented in Scheme 8A. Hence, in the reaction depicted in
Scheme 8A, complex 7d+ resulted from the fast reaction of the
H2 liberated in the C−C coupling leading to 6d+ with the still
unreacted 5d+. Indeed, in the presence of H2, 5d+ yielded
cleanly 7d+. Like 7a+, the new complex 7d+ undergoes at room
temperature the exchange of the Ir-(H)2 and Ir-CH2 protons,
which results in the observation of a broad, average signal
centered at −4.55 ppm. At −80 °C, four individual resonances
C−H/C−D exchange reactions of the parent 2a and the new
chlorides 2b−2d occurred with comparable rates for the four
compounds (t1/2 ca. 500−600 min at room temperature), again
with no observable differences among the 11 benzylic sites
(Scheme 10). Nevertheless, the deuteration of the PEtXyl2
derivative 2e was appreciably faster, with a half-life of ca. 25
min. For solubility reasons, CD2Cl2/CD3OD solvent mixtures
were employed, with the rate of deuteration increasing with the
concentration of CD3OD (t1/2 of ca. 490 min for 1:1 mixtures
and of about 900 min for 3:1 mixtures). For a cationic NCMe
adduct derived from 2a by chloride elimination (by action of
NaBArF) in the presence of acetonitrile,6d the half-life of the
exchange in 1:1 CD2Cl2/CD3OD mixtures was of only 30 min,
reflecting the need for Cl− dissociation. These data comple-
ment those already described6c and support the mechanistic
exchange represented in Scheme 11, whose key step is D+
E
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Scheme 10. H/D Exchange Reactions for Compounds 2a−2e
Scheme 11. Proposed Mechanism for C−H/C−D Exchange in Iridium(III) Chloride Complexes
Figure 1. DFT-calculated potential energy profiles (ΔE, kcal·mol−1) for H/D exchange in the chloride 2a (G) and hydride 3a (7a+) complexes and
DFT-optimized geometries (most hydrogens are omitted) of the transition states for the corresponding H transfer steps. This step is rate limiting for
the reaction with 2a, whereas it is fast for the reaction with 3a.
transfer from the coordinated CD3OD in cationic intermediate
G to the Ir−CH2 bond. The faster deuteration of the PEtXyl2
derivative 2e results probably from the larger steric require-
ments of the P-Et substituent in comparison with the P-Me
F
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Scheme 12. Proposed Mechanism for the CD3OD Deuteration of 3a
Scheme 13. H/D Exchange Reactions of 7a+ with D2 at Variable Temperature, with a Reaction Time of 45 min
analogs of 2a−2d. Electronic effects, although not manifested in
the ν(CO) values of the cationic carbonyls 4+, would also play
into the same direction. The DFT calculations we have now
developed for 2a provided theoretical reinforcement of this
proposal (Figure 1) and disclosed that the above D+ transfer
reaction needs to surmount a barrier of ca. 30 kcal·mol−1. The
resulting agostic structure H could experience C−H (or C−D)
activation at all benzylic sites, following CAr−CH3 and P−CAr
bond rotations, along with the exchange of the aryl units. No
transition states were located for CAr−CH3, P−CAr, and Ir−P
bond rotations. Accordingly, corresponding barriers (all below
20 kcal·mol−1) were estimated by relaxed coordinate Potential
Energy Surface (PES) scans.
of p-TsOH deuteration of Ir−H and Ir−CH2 was immediate,
whereas the half-life for o-CH3 was around 650 and 150 min,
respectively).
A plausible mechanism that explains these observations and
is backed by the DFT calculations discussed below is shown in
Scheme 12. The key assumption is that the protonation
(deuteration) of 3a by CD3OD (to yield the hydride/deuteride
species 7a−d+) as well as the formation of the cationic agostic
hydride isotopomer I are fast, reversible processes, whereas the
barriers for the exchange of the agostic and nonagostic methyl
groups of the latter species (isotopomers I′ and I″, right-hand
side of Scheme 12) are so large that they cannot be overcome
at appreciable rates at very low concentrations of H+/D+ (pKa
of CH3OH, 15.54), similarly to the results observed when using
variable catalytic amounts of p-TsOH for the deuteration of 3a.
Indeed, DFT calculations disclose that protonation/deuteration
of either the Ir or the Ir-CH2 sites yields two fast-
interconverting intermediates (7a+ and I in Scheme 12) with
small and comparable forward and reverse barriers (ca. 7.6 and
7.9 kcal·mol−1 respectively). Then, whereas rotation around the
CAr−CH3 bond is facile (ca. 2.9 kcal·mol−1), other rotations
(P−CAr and Ir−P bonds) that would permit D incorporation
into the remaining benzylic positions encounter significantly
higher barriers (Figure 1).
All hydride compounds 3a−3e underwent H/D exchanges
with similar rates (CD2Cl2/CD3OD mixtures, 20 °C; t1/2
between 120 and 150 min) to give the corresponding d3
isotopologues with specific deuterium incorporation at the
Ir−H and Ir−CH2 positions. The exchange was inhibited by
added bases (NaOH or NaOMe) but was significantly
enhanced by catalytic amounts of p-toluensulfonic acid or
acetic acid, to the point that suffiently large H+ concentrations
(5 × 10−3 M, against 2.5 × 10−2 M of 2a) led to immediate
deuteration of all benzylic sites. Interestingly, an intermediate
situation is observed when using lower concentrations of p-
TsOH, which results in full deuteration of the hydride and
methylene positions and only partial exchange at the non-
To complete this isotopic exchange study, we analyzed the
reactivity toward D2 of the cationic bis(hydride) 7a+, a key
intermediate in the deuteration mechanistic path proposed in
metalated benzylic sites (i.e., with 1.5 × 10−3 M or 2 × 10−3
M
G
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1
Scheme 14. Labeling Scheme for the H and 13C NMR Assignment of Compounds 2−7-BArF
Scheme 12. As discussed earlier, 7a+, and the F-subtituted
EXPERIMENTAL SECTION
■
analog 7d+, undergo facile solution exchange by NMR of the
General. All operations were performed under an argon
atmosphere using standard Schlenk techniques, employing dry
solvents and glassware. Microanalyses were performed by the
two hydrides and the two Ir-CH2 sites,6d with an energy barrier
ΔG‡ ≈ 11 kcal·mol−1 measured at 300 K (calculated ΔG‡ ≈ 10
kcal·mol−1). We set up four parallel experiments that were
performed at temperatures of −40, −20, 0, and 25 °C. For each
of them, 7a+ was generated by reacting a CD2Cl2 solution of
5a+ with H2. Excess of the gas was eliminated by cooling with
liquid N2 and pumping under a vacuum, and the resulting
solution of 7a+ was charged with 0.5 bar of D2 and stirred for
ca. 45 min at the desired temperature. Scheme 13 summarizes
the results of this experiment, which induced deuterium
incorporation only at the hydride position at −40 °C (no D-
incorporation at all at −60 °C after stirring for 2 h) and at the
hydride and methylene sites at −20 °C. Partial and complete
C−H/C−D exchange at all benzylic positions took place at
respectively 0 and 25 °C. These results are in excellent
agreement with the mechanistic proposal of Scheme 12
regarding C−H/C−D exchanges in the hydride complexes 3.
In summary, the use of the methyl- and ethyl-bis(aryl)
phosphines PR′Ar2, 1, with differently substituted Ar groups
does not seem to affect significantly the electronic properties of
the Ir(III) complexes investigated. The existence of the two
identical benzylic Ar units in the phosphine, one metalated and
the other free, explains their facile solution exchange in the
cationic, Lewis base-free complexes 5+ and also seems
responsible for the adoption of the rare κ4-P,C,C′,C″ binding
mode of the metalated appendage. So far, this coordination
mode remains unobserved in related complexes with only one
benzylic Ar group. Additionally, these two substituents
participate in an intramolecular, dehydrogenative, base-
catalyzed C−C coupling reaction that culminates in the
formation of a hybrid phosphine-olefin ligand.
́
Microanalytical Service of the Instituto de Investigaciones Quimicas
(Sevilla, Spain). Infrared spectra were recorded on a Bruker Vector 22
spectrometer. The NMR instruments were Bruker DRX−500, DRX−
400, and DRX−300 spectrometers. Spectra were referenced to external
SiMe4 (δ 0 ppm) using the residual proton solvent peaks as internal
standards (1H NMR experiments), or the characteristic resonances of
the solvent nuclei (13C NMR experiments), while 31P{1H} spectra
were referenced to external H3PO4 [Scheme 14 gives the labeling
1
scheme for the H and 13C NMR assignment of compounds 2−7-
BArF]. Spectral assignments were made by routine one- and two-
dimensional NMR experiments where appropriate. The dimer [(η5-
C5Me5)IrCl2]2,23 NaBArF,24 and 4-bromo-3,5-dimethylanisol25 were
prepared according to literature procedures, as well as complexes 2a,6b
6d
3a,6b and 1-H2 . In the H NMR spectra, all aromatic couplings are
of ca. 7.5 Hz, and signals corresponding to the BArF counterion were
invariant for different complexes (CD2Cl2; δ 7.74 (s, 8 H, Ho), 7.57 (s,
4 H, Hp).
+
1
Synthetic procedures and characterization data for representative
complexes are given below. Those for the remaining compounds
studied can be found in the Supporting Information.
COMPUTATIONAL DETAILS
■
DFT calculations were performed with the Gaussian 09 package26 and
were carried out using Truhlar’s hybrid meta-GGA functional M06.27
The Ir atom was represented by the Stuttgart/Dresden Effective Core
Potential and the associated basis set28 as implemented in Gaussian 09
(SDDALL). The remaining H, C, P, and Si atoms were represented by
means of the 6-31G(d,p) basis set.29−31 The geometries for all species
described were optimized in the gas phase without symmetry
restrictions. Frequency calculations were performed on the optimized
structures at the same level of theory to characterize the stationary
points, as well as for the calculation of gas-phase enthalpies (H),
entropies (S), and Gibbs energies (G) at 298.15 K. The nature of the
intermediates connected was determined by Intrinsic Reaction
H
dx.doi.org/10.1021/ic400759r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Coordinate (IRC) calculations or by perturbing the transition states
along the TS coordinate and optimizing to a minimum.
1:2 mixture of CH2CL2/pentane. Compound 4b+. HRMS (FAB), m/z
calcd. for C30H39IrOP: 639.2365. Found: 639.2368. IR (Nujol): 2032
1
cm−1. H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.26, 7.14, 6.93, 6.90
General Synthesis of Phosphine Ligands. Phosphine ligands
were prepared according to the procedure depicted in Scheme 3. As a
representative phosphine, the preparation of PMe(Xyl)2 is described in
detail in the SI. Other phosphines were prepared by the same
procedure and isolated as white crystalline materials in yields of
around 80%. In the case of PEt(Xyl)2, a solution of EtMgBr was
employed instead of the methyl Grignard reagent.
2
3
(br. s., 1H each, Ha/b/c/d), 3.68 (dd, 1H, JHH = 14.1, JHP2 = 2.7 Hz,
2
IrCHH), 3.15 (d, 1H, JHH = 14.0, IrCHH), 2.60 (d, 3H, JHP = 10.0
Hz, PMe), 2.55, 2.39, 2.36, 2.06, 1.48 (s, 3H each, Meα/β/γ/δ/ε), 1.80
4
(d, 15H, JHP = 2.0 Hz, C5Me5). 13C{1H} NMR (100 MHz, CD2Cl2,
2
2
25 °C): δ 167.2 (d, JCP = 11 Hz, CO), 153.4 (d, JCP = 27 Hz, C1),
142.9, 142.8 (d, 4JCP = 3 Hz, C4/8), 141.8 (d, 2JCP = 10 Hz, C5/7), 140.6
(d, 2JCP = 10 Hz, C5/7), 139.9 (d, 2JCP = 4 Hz, C3), 133.3 (d, 1JCP = 68
Synthesis of Chloride Complexes, 2. [(η5-C5Me5)IrCl2]2 (1g,
1.25 mmol) was dissolved in dry CH2Cl2 (30 mL) in a Schlenk flask
provided with a stir bar. The solution was cooled to 0 °C and the
phosphine (2.5 mmol) dissolved in CH2Cl2 (10 mL) was added,
followed by the addition of 2,2,6,6-tetramethyl piperidine (425 μL, 2.5
mmol). The reaction mixture was allowed to warm to room
temperature and additionally stirred for 2 h. The solvent was then
removed in vacuo and the product extracted with toluene in the air.
The solution was evaporated to dryness and the solid washed with
pentane to yield a bright yellow powder in ca. 70% yield. Complex 2c
was obtained as a mixture of two isomers (60:40). Crystallization from
CH2Cl2/pentane (1:2) provided analytically pure samples of the
desired products. Compound 2b. Anal. Calcd. for C29H39ClIrP: C,
Hz, C2), 131.8, 131.6, 130.8 (d, 3JCP = 9 Hz, CHb/c/d), 127.1 (d, 3JCP
=
1
2
15 Hz, CHa), 120.3 (d, JCP = 54 Hz, C6), 102.4 (d, JCP = 2 Hz,
3
1
C5Me5), 25.1 (d, JCP = 6 Hz, Meγ/ε), 25.0 (d, JCP = 47 Hz, PMe),
22.9 (d, 3JCP = 8 Hz, Meγ/ε), 20.5 (Meα/δ), 20.0 (d, 4JCP = 4 Hz, Meβ),
10.3 (IrCH2), 8.1 (C5Me5). 31P{1H} NMR (160 MHz, CD2Cl2, 25
°C): δ 0.18.
Synthesis of 5d-BArF. To a mixture of 2d (100 mg, 0.15 mmol)
and NaBArF (133 mg, 0.15 mmol) was added 5 mL of CH2Cl2 under
argon. The reaction mixture was stirred for 10 min at room
temperature, after which the solution turned from orange to yellow.
The resulting suspension was filtered and the solvent evaporated under
reduced pressure to obtain compounds 5-BArF as yellow solids in ca.
95% yield. For further purification, the complexes can be crystallized
from a 1:2 mixture of CH2Cl2/pentane. Compound 5d-BArF. 1H
NMR (400 MHz, CD2Cl2, −60 °C): δ 7.23 (d, 1H, 3JHF = 7.9 Hz, Ha),
1
53.9; H, 6.1. Found: C, 53.8; H, 6.2. H NMR (400 MHz, CDCl3, 25
°C): δ 7.12 (s, 1H, Ha), 6.91 (s, 1H, Hd), 6.66 (s, 1H, Hc), 6.57 (s, 1H,
Hb), 3.64 (d, 1H, 2JHH = 14.9 Hz, IrCHH), 3.47 (dd, 1H, 2JHH = 14.7,
3JHP = 4.1 Hz, IrCHH), 2.56 (s, 3H, Meε), 2.25 (s, 3H, Meδ), 2.23 (s,
3H, Meβ), 2.20 (d, 3H, 2JHP = 10.3 Hz, PMe), 1.91 (s, 3H, Meα), 1.43
3
3
6.76 (d, 1H, JHF = 6.8 Hz, Hc/d), 6.68 (d, 1H, JHF = 7.9 Hz, Hc/d),
3
2
3
6.45 (d, 1H, JHF = 8.7 Hz, Hb), 3.01 (t, 1H, JHH = JHP = 4.7 Hz,
2
IrCHα), 2.45 (s, 6H, Meα, Meγ), 2.18 (d, 3H, JHP = 12.6 Hz, PMe),
4
(d, 15H, JHP = 1.5 Hz, C5Me5), 1.42 (s, 3H, Meγ). 13C{1H} NMR
2.05 (s, 3H, Meβ), 1.66 (s, 15H, C5Me5), 1.21 (dd, 1H, 2JHH = 5.5, 3JHP
2
(125 MHz, CDCl3, 25 °C): δ 157.7 (d, JCP = 31 Hz, C1), 141.5 (d,
1
= 16.2 Hz, IrCHβ). H NMR (400 MHz, CD2Cl2, 25 °C): δ 6.94 (m,
2JCP = 9 Hz, C5), 139.8 (d, 2JCP = 8 Hz, C7), 139.5 (d, 4JCP = 2 Hz, C4),
4H, Ha/b/c/d), 2.43 (br. s, 11H, Meα, Meβ, Meγ, IrCH2), 2.31 (d, 3H,
138.9 (d, 4JCP = 3 Hz, C8), 138.8 (d, 2JCP = 3 Hz, C3), 137.1 (d, 1JCP
=
2JHP = 12.7 Hz, PMe), 1.85 (d, 15H, JHP = 2.0 Hz, C5Me5). 31P{1H}
4
62 Hz, C23), 130.6 (d, 3JCP = 8 Hz, CHd), 130.3 (d, 3JCP = 8 Hz, CHc),
NMR (160 MHz, CD2Cl2, 25 °C): δ −44.2 (br. s). 19F{1H} NMR
(160 MHz, CD2Cl2, 25 °C): δ −104.8 (br. s).
3
128.2 (d, JCP = 7 Hz, CHa), 128.0 (d, JCP = 15 Hz, CHb), 127.6 (d,
1JCP = 48 Hz, C6), 91.7 (d, 2JCP = 3 Hz, C5Me5), 25.2 (d, 3JCP = 5 Hz,
Synthesis of 6d-BArF. A mixture of 2d (100 mg, 0.15 mmol) and
NaBArF (133 mg, 0.15 mmol) placed in a Schlenk flask was suspended
in CH2Cl2 (5 mL) under argon. A saturated aqueous solution of
NaHCO3 (5 μL) was added to the reaction mixture, which was stirred
for 16 h with intermittent vacuum−argon cycles to pump out the
produced molecular hydrogen. The yellow solution was filtered and
the solvent evaporated under reduced pressure to obtain a pale yellow
solid, which was washed with pentane to yield 6d-BArF in 90% yield.
For further purification, 6-BArF can be recrystallized from a 1:1
mixture of CH2Cl2/pentane. Compound 6d-BArF. IR (Nujol): 2140
3
Meε), 22.6 (d, JCP = 8 Hz, Meγ), 20.7 (Meδ), 20.6 (Meβ), 20.5
(IrCH2), 20.3 (d, 3JCP = 3 Hz Meα), 18.0 (d, 1JCP = 40 Hz, PMe), 8.0
(C5Me5). 31P{1H} NMR (160 MHz, CD2Cl2, 25 °C): δ 9.2.
Synthesis of Hydride Complexes, 3. The corresponding
chloride precursor 2b−2e (0.153 mmol) was dissolved in THF (5
mL), and a solution of LiAlH4 in THF (1M, 0.49 mL) was added
under argon. The reaction mixture was heated at 45 °C for 2 h and
quenched with H2O (40 μL). The solvent was removed under a
vacuum and the residue extracted with pentane and then evaporated to
dryness, to provide the product as a pale yellow powder.
Recrystallization from pentane yielded the product as pale yellow
crystals. Complexes 3b−3d were obtained in ca. 40% yield, whereas 3e
was isolated in ca. 70% yield. Compound 3b. Anal. Calcd. for
C29H401IrP: C, 56.9; H, 6.6. Found: C, 56.4; H, 6.4. IR (Nujol): 2080
1
cm−1. H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.12 (m, 2H, Ha, Hd),
6.76, 6.69 (d, 1H each, 3JHF = 9.2 Hz, Hb, Hc), 4.89 (dd, 1H, 3JHH = 8.7
4
3
Hz, JHP = 4.1 Hz, CHα), 4.42 (d, 1H, JHH = 8.5 Hz, CHβ), 2.59 (d,
3H, 2JHP = 13.2 Hz, PMe), 2.53, 2.50 (s, 3H each, Meα, Meβ), 2.01 (s,
15H, C5Me5), −12.93 (d, 1H, JHP = 27.9 Hz, IrH). 13C{1H} NMR
2
cm−1. H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.07 (s, 1H, Ha), 6.92
1
(100 MHz, CD2Cl2, 25 °C): δ 164.1 (d, JCF = 251 Hz, C4/8), 163.3
2
1
(s, 1H, Hd), 6.69 (s, 1H, Hc), 6.57 (s, 1H, Hb), 3.35 (dt, 1H, JHH
=
(d, JCF = 257 Hz, C4/8), 150.8 (C5), 146.6 (C1), 139.3, 138.4, 135.4,
3
3
2
134.8 (C2, C3, C6, C7), 117.7, 117.0 (dd, 2JCF = 21, 3JCP = 11 Hz, CHb,
CHc), 114.0 (dd, 2JCF = 23, 3JCP = 16 Hz, CHa/d), 112.3 (dd, 2JCF = 22,
15.5, JHH = JHP = 2.9 Hz, IrCHH), 2.80 (d, 1H, JHH = 15.2 Hz,
IrCHH), 2.55 (s, 3H, Meε), 2.28 (s, 3H, Meδ), 2.27 (s, 3H, Meβ), 2.23
(d, 3H, 2JHP = 9.9 Hz, PMe), 1.90 (s, 3H, Meα), 1.70 (s, 15H, C5Me5),
3JCP = 11 Hz, CHa/d), 100.7 (C5Me5), 61.4 (t, JCF = JCP = 3 Hz,
4
2
1.43 (s, 3H, Meγ), −17.81 (d, 1H, JHP = 34.4 Hz, Ir-H). 13C{1H}
2
2
4
CHβ), 54.8 (dd, JCP = 8, JCF = 2 Hz, CHα), 22.2, 21.7 (Meα, Meβ),
12.3 (d, 1JCP = 37 Hz, PMe), 9.1 (C5Me5). 31P{1H} NMR (160 MHz,
CD2Cl2, 25 °C): δ 6.3. 19F{1H} NMR (160 MHz, CD2Cl2, 25 °C): δ
−34.2, −34.9.
2
NMR (125 MHz, CD2Cl2, 25 °C): δ 160.3 (d, JCP = 31 Hz, C1),
142.0 (d, 2JCP = 9 Hz, C5), 141.3 (d, 1JCP = 62 Hz, C2), 139.7 (d, 2JCP
=
3
8 Hz, C7), 139.4 (C3), 139.3 (C8), 138.6 (C4), 130.8 (d, JCP = 8 Hz,
CHd, CHc), 129.5 (d, 1JCP = 41 Hz, C6), 128.3 (d, 3JCP = 7 Hz, CHb),
Synthesis of 7d-BArF. To a mixture of 2d (100 mg, 0.15 mmol)
and NaBArF (142 mg, 0.16 mmol) placed in a thick-wall vessel was
added 3 mL of CH2Cl2. The reaction mixture was stirred for 30 min at
room temperature under 1 bar of H2, after which the original solution
with intense yellow color became almost colorless. Workup of the
reaction in the absence of hydrogen led to the release of H2 and
formation of 5d-BArF. Thus, characterization of 7d-BArF by 1D- and
2D-NMR spectroscopy was carried out in a Young NMR tube under a
H2 atmosphere. 1H NMR (400 MHz, CD2Cl2, 25 °C, H2 atmosphere):
δ 7.12 (dt, 1H, 4JHP = 1.8, 3JHF = 8.9 Hz, Ha), 7.06 (dt, 1H, 4JHP = 2.9,
3JHF = 9.0 Hz, Hc/d), 6.91 − 6.79 (m, 2H, Hb, Hc/d), 2.61 (s, 3H,
Meβ/γ), 2.57 (d, 3H, 2JHP = 10.4 Hz, PMe), 2.01 (s, 3H, Meα), 1.84 (d,
3
2
127.7 (d, JCP = 14 Hz, CHa), 92.1 (d, JCP = 3 Hz, C5Me5), 31.4 (d,
1JCP = 45 Hz, PMe), 25.5 (d, JCP = 4 Hz, Meε), 21.8 (d, 3JCP = 9 Hz,
3
Meγ), 21.2 (Meβ, Meδ), 20.9 (Meα), 9.8 (C5Me5), 3.8 (IrCH2).
31P{1H} NMR (160 MHz, C6D6, 25 °C): δ 6.1.
Synthesis of 4b+−4e+. To a solid mixture of the corresponding
chloride precursor 2b−2e (0.08 mmol) and NaBArF (0.08 mmol)
placed in a thick-wall vessel was added 5 mL of CH2Cl2. The reaction
mixture was stirred for 10 min at room temperature under 1.5 bar of
CO. The solution was filtered, and the solvent was then evaporated
under reduced pressure to obtain pale white (4e-BArF) or yellow
powders in ca. 95% yield. These complexes can be recrystallized from a
I
dx.doi.org/10.1021/ic400759r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4
15H, JHP = 1.7 Hz, C5Me5), 1.55 (s, 3H, Meβ/γ), −4.55 (br. s, 4H,
2002, 124, 5100. (b) Corkey, B. K.; Felicia, F. L.; Bergman, R. G.;
Brookhart, M. Polyhedron 2004, 23, 2943.
IrCH2, Ir−H2). 1H NMR (400 MHz, CD2Cl2, −80 °C, H2
atmosphere): δ 7.02 (d, 1H, Ha), 6.91 (d, 1H, Hc/d), 6.67 − 6.63
(m, 2H, Hb, Hc/d), 3.90 (d, 1H, 2JHH = 14.4 Hz, IrCHH), 3.32 (d, 1H,
2JHH = 14.4 Hz, IrCHH), 2.47 (m, 6H, Meβ/γ, PMe), 1.91 (s, 3H,
Meα), 1.66 (s, 15H, C5Me5), 1.35 (s, 3H, Meβ/γ), −12.77 (s, 1H,
(4) (a) Meredith, J. M.; Goldberg, K. I.; Kaminsky, W.; Heinekey, D.
M. Organometallics 2009, 28, 3546. (b) Janowicz, A. H.; Bergman, R.
G. J. Am. Chem. Soc. 1983, 105, 3929. (c) Tellers, D. M.; Yung, C. M.;
Arndtsen, D. R.; Adamson, D. R.; Bergman, R. G. J. Am. Chem. Soc.
2002, 124, 1400. (d) Tellers, D. M.; Bergman, R. G. Organometallics
2001, 20, 4819.
IrHH), −13.10 (d, 1H, JHP = 16.1 Hz, IrCHH). 13C{1H} NMR (125
2
MHz, CD2Cl2, 25 °C, H2 atmosphere): δ 165.3 (d, 1JCF = 254 Hz, C4),
1
2
4
163.9 (d, JCF = 255 Hz, C8), 155.4 (dd, JCP = 32, JCF = 9 Hz, C1),
(5) Meredith, J. M.; Robinson, R., Jr.; Goldberg, K. I.; Kaminsky, W.;
Heinekey, D. M. Organometallics 2012, 31, 1879.
144.4 (dd, 2JCP = 9, 3JCF = 11 Hz, C7/5), 143.4 (t, 2JCP = 3JCF = 10 Hz,
C7/5), 141.8 (dd, 2JCP = 5, 3JCF = 9 Hz, C3), 131.7 (dd, 1JCP = 68, 4JCF
=
́ ́
(6) (a) Campos, J.; Esqueda, A. C.; Lopez-Serrano, J.; Sanchez, L.;
2 Hz, C2), 119.0 (br. d, 1JCP = 46 Hz, C6), 117.9, 117.4, 116.8 (dd, 3JCP
Cossio, F. P.; Cozar, A.; Alvarez, E.; Maya, C.; Carmona, E. J. Am.
Chem. Soc. 2010, 132, 16765. (b) Campos, J.; Esqueda, C.; Carmona,
2
3
2
= 10, JCF = 21 Hz, CHc, CHd, CHb), 112.6 (dd, JCP = 18, JCF = 21
1
Hz, CHa), 104.0 (C5Me5), 29.5 (br. d, JCP = 65 Hz, PMe), 24.7 (d,
́
E. Chem.Eur. J. 2010, 16, 419. (c) Campos, J.; Alvarez, E.; Carmona,
3JCP = 5 Hz, Meβ/γ), 23.3 (d, 3JCP = 7 Hz, Meβ/γ), 20.2 (d, 3JCP = 3 Hz,
Meα), 9.9 (br. s, IrCH2), 8.5 (C5Me5). 31P{1H} NMR (160 MHz,
CD2Cl2, 25 °C): δ 0.9 (br. s). 19F{1H} NMR (160 MHz, CD2Cl2, 25
°C): δ −108.8 (br. s).
E. New. J. Chem. 2011, 35, 2122. (d) Campos, J.; Lop
́
ez-Serrano, J.;
́
Alvarez, E.; Carmona, E. J. Am. Chem. Soc. 2012, 134, 7165.
(7) (a) Albrecht, M. Chem. Rev. 2010, 110, 576. (b) van der Boom,
M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759. (c) Reichard, H. A.;
Micalizio, G. C. Chem. Sci. 2011, 2, 573.
ASSOCIATED CONTENT
* Supporting Information
(8) (a) Baratta, W.; Herdtweck, E.; Martinuzzi, P.; Rigo, P.
Organometallics 2001, 20, 305. (b) Baratta, W.; Ballico, M.; Del
Zotto, A.; Zangrando, E.; Rigo, P. Chem.Eur. J. 2007, 13, 6701.
(c) Li, L.; Jiao, Y.; Brennessel, W. W.; Jones, W. D. Organometallics
■
S
General synthesis, analytical, and spectroscopic data of
phosphine ligands; analytical and spectroscopic data of
complexes 2c−2e, 3c−3e, 4c+−4e+, 5d+, 5e+, and 6d+;
hydrogen/deuteration exchange reactions; X-ray structure
analysis of 4e+; tables of the optimized geometries (Cartesian
coordinates, in Ångstroms) for the calculated species. This
material is available free of charge via the Internet at http://
pubs.acs.org.
2010, 29, 4593. (d) Donnelly, K. F.; Lalrempuia, R.; Muller-Bunz, H.;
̈
Albrecht, M. Organometallics 2012, 31, 8414. (e) Pollock, J. B.; Cook,
T. R.; Stang, P. J. J. Am. Chem. Soc. 2012, 134, 10607. (f) Wu, X.; Xiao,
J. Chem. Commun. 2007, 2449. (g) Daugulis, O.; Brookhart, M.
́
Organometallics 2004, 23, 527. (h) Prades, A.; Corberan, R.; Poyatos,
M.; Peris, E. Chem.Eur. J. 2008, 14, 11474.
(9) (a) Gottker-Schnetmann, I.; White, P.; Brookhart, M. J. Am.
̈
Chem. Soc. 2004, 126, 1804. (b) Saidi, O.; Marafie, J.; Ledger, A. E. W.;
AUTHOR INFORMATION
Corresponding Author
*E-mail: guzman@us.es.
Notes
Liu, P. M.; Mahon, M. F.; Kociok-Kohn, G.; Whittlesey, M. K.; Frost,
C. G. J. Am. Chem. Soc. 2011, 133, 19298. (c) Feng, J.-J.; Chen, X.-F.;
Shi, M.; Duan, W.-L. J. Am. Chem. Soc. 2010, 132, 5562. (d) Selander,
̈
■
N.; Szabo,
́
K. J. Dalton Trans. 2009, 6267. (e) Bedford, R. B. Chem.
, R.; Poyatos, M.; Peris,
Commun. 2003, 1787. (f) Prades, A.; Corberan
́
The authors declare no competing financial interest.
E. Chem.Eur. J. 2009, 15, 4610.
(10) (a) Severin, K.; Bergs, R.; Beck, W. Angew. Chem., Int. Ed. 1998,
37, 1634. (b) Dyson, P. J.; Sava, G. Dalton Trans. 2006, 1929.
(c) Ryabov, A. D.; Sukharev, V. S.; Alexandrova, L.; Lagadec, R. L.;
Pfeffer, M. Inorg. Chem. 2001, 40, 6529.
ACKNOWLEDGMENTS
Financial support (FEDER support) from the Spanish
Ministerio de Ciencia e Innovacion
17476) and Consolider-Ingenio2010 (No. CSD2007/0000)
and the Junta de Andalucia (Projects Nos. FQM-119 and P09-
FQM-4832) is gratefully acknowledged. J.C. thanks the
́
Ministerio de Educacion for a research grant (ref
AP20080256). M.F.E. thanks the Universidad de Sevilla for a
research grant. J.L.-S. is thankful to the Spanish Minitry of
■
́
(Project No. CTQ2010-
(11) (a) Patoux, C.; Launay, J.-P.; Beley, M.; Chodorowski-kimmes,
S.; Collin, J.-P.; James, S.; Sauvage, J.-P. J. Am. Chem. Soc. 1998, 120,
3717. (b) Isozaki, K.; Takaya, H.; Naota, T. Angew. Chem., Int. Ed.
2007, 119, 2913. (c) Wadman, S. H.; Lutz, M.; Tooke, D. M.; Spek, A.
L.; Havenith, R. W. A.; Klink, G. P. M. V.; Van Koten, G. Inorg. Chem.
2009, 48, 1887. (d) Wadman, S. H.; Kroon, J. M.; Bakker, K.; Lutz,
M.; Spek, A. L.; van Klink, G. P. M.; van Koten, G. Chem. Commun.
2007, 1907.
(12) (a) Ben-Ar, E.; Cohen, R.; Gandelman, M.; Shimon, J. L. W.;
Martin, J. M. L.; Milstein, D. Organometallics 2006, 25, 3190.
(b) Gosh, R.; Kanzelberguer, M.; Emge, T. J.; Hall, G. S.; Goldman, A.
S. Organometallics 2006, 25, 5668. (c) Haibach, M. C.; Kundu, S.;
Brookhart, M.; Goldman, A. S. Acc. Chem. Res. 2012, 45, 947−958.
(d) Campos, J.; Kundu, S.; Pahls, D. R.; Brookhart, M.; Carmona, E.;
Cundari, T. R. J. Am. Chem. Soc. 2013, 135, 1217. (e) Findlater, M.;
Bernskoetter, W.; Brookhart, M. J. Am. Chem. Soc. 2010, 132, 4534.
(f) Findlater, M.; Cartwright-Sykes, A.; White, P. S.; Schauer, C. K.;
Brookhart, M. J. Am. Chem. Soc. 2011, 133, 12274.
Science and Innovation (MICINN) for a Ramon y Cajal
Contract. The use of computational facilities of the Super-
computing Centre of Galicia (CESGA) is also acknowledged.
́
DEDICATION
■
Dedicated to Professor Antonio Laguna on the occasion of his
65th birthday.
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