Dihydrogen catalysis of the reversible formation and cleavage of C - H and N - H bonds of aminopyridinate ligands bound to (η5-C5Me5)IrIII

Article abstract of DOI:10.1002/chem.201405340

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵-C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵

Full text of DOI:10.1002/chem.201405340

DOI: 10.1002/chem.201405340
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Isomerisation |Hot Paper|
Dihydrogen Catalysis of the Reversible Formation and Cleavage
of CꢀH and NꢀH Bonds of Aminopyridinate Ligands Bound to (h5-
C5Me5)IrIII
Ana Zamorano, Nuria Rendꢀn, Joaquꢁn Lꢀpez-Serrano, Josꢂ E. V. Valpuesta,
Eleuterio ꢃlvarez, and Ernesto Carmona*[a]
Abstract: This study focuses on a series of cationic com-
plexes of iridium that contain aminopyridinate (Ap) ligands
bound to an (h5-C5Me5)IrIII fragment. The new complexes
have the chemical composition [Ir(Ap)(h5-C5Me5)]+, exist in
the form of two isomers (1+ and 2+) and were isolated as
tropic rearrangement that changes the nature and coordina-
tion mode of the aminopyridinate ligand between the well-
known k2-N,N’-bidentate binding in 1+ and the unprece-
dented k-N,h3-pseudo-allyl-coordination mode in isomers 2+
through activation of a benzylic CꢀH bond and formal
proton transfer to the amido nitrogen atom. Experimental
and computational studies evidence that the overall rear-
rangement, which entails reversible formation and cleavage
of HꢀH, CꢀH and NꢀH bonds, is catalysed by dihydrogen
under homogeneous conditions.
ꢀ
salts of the BArF anion (BArF =B[3,5-(CF3)2C6H3]4). Four Ap li-
gands that differ in the nature of their bulky aryl substitu-
ents at the amido nitrogen atom and pyridinic ring were
employed. In the presence of H2, the electrophilicity of the
IrIII centre of these complexes allows for a reversible proto-
Introduction
have been scrutinised with the aim of exploiting their es-
teemed properties as anti-cancer drugs and cell-imaging
agents,[10a] and as hosts in molecular-recognition studies.[10b]
Recently, we have investigated the potential of (h5-C5Me5)MIII
complexes of Rh and Ir that contain cyclometallated phos-
phines as stoichiometric and catalytic reagents in CꢀH and Hꢀ
H bond-activation reactions. We have also examined other rel-
evant applications, such as catalytic hydrogen-isotope ex-
change, hydrosilylation of carbonyl groups and other unsatu-
rated functionalities, as well as the formation of CꢀC bonds.[5-
Half-sandwich rhodium and iridium complexes of the ancillary
C5Me5 ligand are useful reagents for an ample variety of chemi-
cal transformations.[1] The steric protection that the permethy-
lated cyclopentadienyl group provides and its excellent donor
properties confer unique reactivity to complexes based on (h5-
C5Me5)M (M=metal) fragments and permit stabilisation of
high-oxidation-state intermediates.[2,3a–d] Indeed, in recent de-
cades compounds of this type have led to valuable discoveries
in different areas of organometallic chemistry and catalysis.
These comprise CꢀH bond-activation reactions,[4,5] cyclometal-
lation reactions[1a,d] and a plethora of homogeneous catalytic
reactions: water oxidation,[2,3] hydrogenation and hydrogen-
transfer catalysis,[1b–e,6] hydrogen isotope exchanges[7,8] and
other processes.[4e–f,9] Moreover, half-sandwich Rh and Ir deriva-
tives, including [Ir(Cp’)(L^L’)X]n+ complexes (Cp’ represents
C5Me5 or C5Me4Ar (Ar=aryl or biaryl substituent), X is Clꢀ or
a related group and L^L’ is a bidentate C^N or N^N ligand)
d,8a–b,11,12]
Related complexes that accommodate N^N or N^C
mono-anionic ligands, rather than P^C ligands, also display
rich and versatile chemistry.[1,2,6]
Accordingly, we commenced an investigation of the chemis-
try of complexes in which the (h5-C5Me5)MIII core is stabilised
by coordination to an aminopyridinate (Ap) ligand
(Figure 1).[13,14] Besides finding great utility for stabilisation of
complexes of electropositive metals (early-transition elements
[a] Dr. A. Zamorano, Dr. N. Rendꢀn, Dr. J. Lꢀpez-Serrano, Dr. J. E. V. Valpuesta,
Dr. E. ꢁlvarez, Prof. Dr. E. Carmona
Instituto de Investigaciones Quꢂmicas (IIQ)
Departamento de Quꢂmica Inorgꢃnica and
Centro de Innovaciꢀn en Quꢂmica Avanzada (ORFEO-CINQA)
Consejo Superior de Investigaciones Cientꢂficas (CSIC)
and Universidad de Sevilla, Av. Amꢄrico Vespucio 49
Isla de la Cartuja, 41092 Sevilla (Spain)
Fax: (+34)954460565
E-mail: guzman@us.es
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405340.
Figure 1. Aryl-substituted aminopyridinate ligands employed in this work.
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and some lanthanides),[14,15] latterly these ligands have been
employed, mainly by Kempe and co-workers, to stabilise the
quintuple CrꢀCr bond.[16] Similarly to other ligands of the
amino-amide type, for instance H2NCH(Ph)CH(Ph)NTsꢀ (Ts=
tosyl),[6] the amido terminus of aminopyridinates can function
as a s-donor and/or p-donor ligand depending upon the elec-
tronic requirements of the bound metal atom.[17] This electron-
ic versatility facilitates some important transformations, such
as the activation of H2 and other small molecules, and explains
the high efficiency of many group 8 and 9 metal complexes
with amine-amido ligands as bifunctional molecular catalysts
for hydrogen transfer and heterolytic hydrogenation
reactions.[6,18,19]
Results and Discussion
To broaden the utilisation of aminopyridinate ligands to the
chemistry of late-transition metals, in particular to the coordi-
nation chemistry of the (h5-C5Me5)IrIII fragment, and with the
additional goal of ascertaining the generality of the H2-cata-
lysed isomerisation of aminopyridinate groups within an Ir–Ap
linkage (Scheme 1), we studied iridium complexes of amino-
pyridinate ligands with diverse aryl substitution (Figure 1). The
synthesis of ligand a was reported previously.[14] The remaining
ligands b–d were obtained similarly, by a three-step procedure
from the appropriate bromoaryl (Scheme 2a) and aniline com-
pounds (Scheme 2c).
In addition to compounds already cited, many Rh and Ir
complexes of mono-anionic, chelating N^N ligands are
known,[20] although information for M–Ap complexes is
scarce.[21] Notwithstanding, preliminary work from our group[12]
led to a cationic aminopyridinate complex [Ir(Ap)(h5-C5Me5)]+
(1a+; Figure 1), which displays a five-coordinate structure but
an eighteen-electron count thanks to the p-donor action of
the aminopyridinate amido nitrogen atom.[12] Interestingly, be-
sides irreversible reaction with H2 to form the known binuclear
compound[22] [(h5-C5Me5)Ir(m-H)3Ir(h5-C5Me5)]+ (isolated as the
ꢀ
BArF salt; BArF =B[3,5-(CF3)2C6H3]4), this complex undergoes
spontaneous and reversible isomerisation of its aminopyridi-
nate ligand from a classical k2-N,N’ coordination mode to an
unprecedented k-N,h3-pseudo-allyl binding mode (Scheme 1)
in a process efficiently catalysed by dihydrogen. Although
coordination of H2 to 1a+ and 2a+ was not observed, the
corresponding carbonyl adducts 1a·CO+ and 2a·CO+ were
isolated.[12]
Scheme 2. Synthesis of the new aminopyridinate ligands employed in this
work following the procedure reported in references [14a] and [14b]] for re-
lated ligands. [Pd2(dba)3]=tris(dibenzylideneacetone)dipalladium(0),
dppp=1,3-bis(diphenylphosphanyl)propane.
Synthetic details are provided in the Supporting Information.
The free amines, HAp, were isolated as white crystalline solids
(the p-fluoro-substituted aminopyridine was characterised by
X-ray crystallography; see Figure S1 in the Supporting Informa-
tion) and generated in gram or multi-gram (5–10 g) quantities.
The corresponding lithium amides, LiAp, were generated in
situ prior to their use by the reported procedure.
Scheme 1. The H2-catalysed isomerisation of aminopyridinate ligands report-
ed in this work. Ar is either 2,6-iPr2C6H3 or 2,6-Me2C6H3.
Aside from playing a fundamental role in some biological
processes,[23] the dihydrogen molecule is an indispensable re-
actant for homogeneous and heterogeneous catalytic process-
es of paramount importance.[24] Moreover, H2 has become the
ideal energy carrier.[25] Notwithstanding its significance, the cat-
alytic action of H2 is almost unknown.[12] We therefore decided
to ascertain the generality of the H2-catalysed rearrangement
Neutral and cationic (C5Me5)IrIII–Ap compounds
The low-temperature (ꢀ508C) addition of a solution of LiAp in
toluene to a suspension of the IrIII dimer [Ir(C5Me5)Cl2]2 in the
same solvent and subsequent stirring at room temperature for
about 14 h permitted isolation of the yellow or orange crystal-
line complexes 1a·Cl–1d·Cl, which exhibited the expected k2-
N,N’ coordination of the aminopyridinate group (Scheme 3). In
solution in CH2Cl2, these compounds readily underwent elimi-
nation of the chloride ligand by action of NaBArF to form dark-
grey, almost black, solutions of cations 1a+–1d+, which were
represented in Scheme 1. We have studied
a series of
[Ir(Ap)(h5-C5Me5)]+ complexes of substituted Ap ligands
(Figure 1) and analysed their Lewis acid reactivity toward sever-
al Lewis bases. Most importantly, we have investigated their re-
actions with dihydrogen by experimental and computational
methods. In this contribution we provide full details[12] of this
work.
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Scheme 3. Synthesis of neutral (1a·Cl–1d·Cl) and cationic (1a+–1d+) ami-
nopyridinate complexes of the (C5Me5)IrIII fragment.
ꢀ
isolated as salts of the BArF anion. The base-free cations dis-
play five-coordinate structures but an electron count of eight-
een on the assumption that the amido nitrogen atom behaves
as a p-donor ligand toward the cationic IrIII centre.[6,17] X-ray
studies (see below) support this conjecture. Moreover, the very
dark colour of these cations has been previously observed for
complexes with MꢀN and MꢀO bonds stabilised by p donation
and has been attributed to ligand-to-metal charge-transfer
p!d electronic transitions.[6a–e,17,26,27]
Figure 2. X-ray structures of complexes 1a·Cl (top) and 1a+ (bottom). Anion
The neutral complexes 1a·Cl–1d·Cl and their corresponding
cationic derivatives 1a+–1d+ were characterised by conven-
tional structural techniques. 1H and 13C NMR spectroscopic
studies (1D and 2D experiments) provide convincing evidence
for the formulation proposed in Scheme 3. The chlorides
1a·Cl–1d·Cl are chiral at iridium and the lack of symmetry be-
BArFꢀ is omitted for clarity.
(ꢁ2.11 ꢅ), as expected. For the two cations 1a+ and 1d+
both the IrꢀNpy and the IrꢀNamido bond lengths are shorter than
in the neutral chlorides, most probably a consequence of the
lower coordination number. Importantly, whereas the decrease
in the IrꢀNpy bond length is small (roughly 0.03 ꢅ), that of the
IrꢀNamido bond is much larger at 0.15 ꢅ (for instance,
2.1085(17) ꢅ in 1a·Cl and 1.965(2) ꢅ in 1a+). These data hint
at significant IrꢀNamido p bonding in 1a+ but less, or none, in
1a·Cl, a hypothesis that can be extended to the rest of the
complexes in Scheme 3. The reactivity of the cationic com-
plexes 1+ towards Lewis bases and natural bond order (NBO)
analyses on model compounds (see below) furnish additional
support for this proposal. These data compare well with those
reported in the literature for somewhat related
compounds.[6,28]
1
comes apparent in their H and 13C NMR spectra. For instance,
for 1a·Cl, which contains 2,6-iPr2C6H3 and 2,6-Me2C6H3 (Xyl) aryl
substituents, two septets (d=3.39 and 4.42 ppm) and four
doublet resonances (d=1.21, 1.32, 1.36 and 1.41 ppm) are re-
corded for the iPr groups along with two singlets (d=2.10 and
2.67 ppm) attributed to the methyl groups of the Xyl ring. In
contrast, the Cs symmetry of the cationic molecules of 1a+ is
concluded from the observation of only one septet (d=
3.61 ppm) and two doublets (d=1.15 and 1.42 ppm) for the
iPr groups and one singlet (d=2.28 ppm) for the Xyl methyl
protons. Complete of NMR data for these complexes is provid-
ed in the Experimental Section.
The molecular structures of complexes 1a·Cl, 1b·Cl, 1a+
and 1d+ were determined by X-ray crystallography (Figure 2;
Figures S3 and S5 in the Supporting Information). Besides the
six-coordinate structures of the neutral chlorides compared
with the less-common five-coordinate geometries of the cat-
ionic species, there are other significant structural differences
that mainly concern the binding of the Ap ligand in the two
types of compound. Thus, in the neutral derivatives, the IrꢀN
bond lengths for the pyridinic (Npy; N1 in Figure 2) and amido
(Namido; N2 in Figure 2) nitrogen atoms are quite similar, with
the former (ꢁ2.15 ꢅ) somewhat longer than the latter
Lewis base adducts of cations [Ir(Ap)(h5-C5Me5)]+
As represented in Scheme 4 for 1a+, addition of the N- and C-
donors NH3, 4-dimethylaminopyridine (DMAP), CO and CNXyl,
led to an immediate and abrupt colour change from the very
dark, nearly black colouration of 1a+ to the yellow-orange
characteristic colour of the six-coordinate adducts 1a·L+. In ad-
dition to 1a·CO+, the remaining carbonyl species 1b·CO+
–1d·CO+ were also isolated.
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The IR spectra of the carbonyl adducts 1a·CO+–1d·CO+ ex-
hibit the expected carbonyl stretching frequency that appears
in the narrow interval n˜ =2060–2050 cmꢀ1 (see Table S1 in the
Supporting Information). In all likelihood, the high n˜(CO) values
are a reflection of low back-donation from the cationic IrIII
centre to the p* antibonding orbitals of the CO ligand. This is
a common observation for many cationic IrIII–CO complex-
es[6d,30] and, more generally, for cationic carbonyl complexes of
the transition metals,[31] including other late-transition
metals.[32] The subtle differences recorded for this series of
complexes (Dn˜(CO)ꢁ10 cmꢀ1) are striking and do not appear
to correlate with the electron-donor properties of the amino-
pyridinate aryl substituents. In particular, Dn˜(CO) between the
para-NMe2-substituted complex 1c·CO+ and the para-F-substi-
tuted analogue 1d·CO+ is only 3 cmꢀ1. This observation sug-
gests that the pyridyl aryl substituents have little, or no, influ-
ence on the electron-donating properties of the aminopyridi-
nate ligands. In fact, it is possible that the small changes mea-
sured for n˜(CO) in our complexes are meaningless in terms of
M–CO electronic interaction and may be due to polarisation of
the carbon–oxygen sigma bond of the coordinated molecule
of CO by the positively charged IrIII centre.[31] Crystallographic
Scheme 4. Reactions of complex 1a+ with different Lewis bases.
+
The ammonia and DMAP derivatives, 1a·NH3 and 1a·
DMAP+ exhibited dynamic behaviour at room temperature
1
+
that was not investigated. The H NMR spectrum of 1a·NH3
recorded at 08C (CD2Cl2, 500 MHz) features, in addition to sig-
nals due to the C5Me5 and Ap ligands (see the Experimental
Section), a resonance at d=2.16 ppm with a relative intensity
that corresponded to three hydrogen atoms, which was as-
signed to the coordinated NH3 molecule. Crystallographic anal-
ysis of the BArF salts of these cations (Figure 3) revealed unex-
ceptional structural features. For example, the IrꢀNH3 bond of
+
1a·NH3 has a length of 2.164(5) ꢅ, which is comparable to
that found in other (C5Me5)IrIII–NH3 complexes.[6d,28d,29]
ꢀ
studies performed with the BArF salts of 1a·CO+ and 1b·CO+
(Figure 4) furnished IrꢀCO distances of about 1.89 ꢅ and CꢀO
bond lengths of about 1.11 ꢅ, which are consistent with the
high n˜(CO) values observed and reinforce the notion of very
low p basicity of the iridium centre in these complexes.[6d,30]
Solutions of 1a+ in dichloromethane were also reacted with
stoichiometric amounts of the aryl isocyanide CNXyl. An in-
stant reaction took place marked, once again by a noticeable
colour change from black to yellow-orange, and provided the
desired compound [1a·CNXyl]BArF in essentially quantitative
yield. Aryl isocyanides are efficient p-acid ligands,[33] which act
mostly, or exclusively, as s donors when confronted with metal
fragments of scarce p-donor capacity.[34] Similarly to CO, isocya-
nides bind to metal centres with donation of electron density
from a molecular orbital polarised at the isocyanide carbon
atom, which possesses some antibonding character. According-
!
ly, M CꢂNAr s donation reinforces the CꢂN bond and results
in an increase of n˜(CꢂN).[33,34] In the IR spectrum of 1a·CNXyl+,
the target n˜(CꢂN) band appears with a high wavenumber of
2155 cmꢀ1, which is roughly 40 cmꢀ1 shifted toward higher
energy relative to free CNXyl. Thus, the positive shift strength-
ens the perception of the very weak capability of a cationic
[IrIII(Ap)(C5Me5)]+ core to act as a p donor toward efficient p-
acid ligands like CO and aryl isocyanides. Figure 5 illustrates
the molecular structure of 1a·CNXyl+, which exhibits IrꢀNpy
and IrꢀNamido bond lengths that match those determined for
other 1a·L+ adducts and an IrꢀCNXyl bond length of
1.961(2) ꢅ, which is somewhat longer than the IrꢀCO bond
length in 1a·CO+ (1.884(7) ꢅ).
Reactions of cationic complexes [Ir(Ap)(h5-C5Me5)]+ with H2
The study of the reactivity of transition-metal complexes with
the dihydrogen molecule is an essential part of organometallic
chemistry because the resulting hydride or dihydrogen com-
+
Figure 3. X-ray structures of complexes 1a·NH3 (top) and 1a· DMAP+
(bottom). Anion BArFꢀ is omitted for clarity.
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Scheme 5. Reaction of aminopyridinate complexes 1a+–1d+ with an excess
of dihydrogen.
nate complexes 1a+–1d+, evidenced in the reactivity studies
already discussed, prompted us to investigate their interaction
with H2. As depicted in Scheme 5, all complexes reacted irre-
versibly at room temperature with an excess of H2 to produce
the known[22] binuclear hydride complex [{(h5-C5Me5)Ir}2(m-
H)3]BArF, together with the corresponding free- and protonat-
ed-aminopyridine, HAp and [H2Ap]BArF, respectively. For iden-
tification purposes, the formation of the latter species was
1
monitored by H NMR spectroscopy and its identity was con-
firmed by protonation of HAp with HBArF. Interestingly, since
the early description of the above binuclear complex by Maitlis
et al.[22] it has been identified as the product of hydrogena-
tion of different cationic complexes of the (h5-C5Me5)IrIII
fragment.[3b,22b,39]
The reactions of complexes 1+ with stoichiometric or sub-
stoichiometric concentrations of H2 (Scheme 5) are fast once
they start but feature ill-defined kinetics and may be avoided,
particularly if low relative concentrations of H2 (less than
40 mol%) are employed at room temperature or below. Under
these conditions, an interesting and unprecedented reversible
isomerisation of the Ir–Ap linkage of cations 1+ was observed
(Scheme 1), which allowed for the isolation of complexes
[2a]BArF–[2d]BArF. As can be seen, isomerisation of complexes
1+ necessitates benzylic CꢀH bond activation with formal
proton transfer to the amido nitrogen atom, which becomes
uncoordinated. Thus, the most characteristic details of the
NMR spectra of the new complexes are those pertinent to
these functionalities. For example, with reference to the equi-
librium 1a+Ð2a+ (Scheme 6) the singlet at d=2.28 ppm due
to the Xyl methyl protons of 1a+ (relative intensity=6H) con-
verts into a singlet (d=2.48 ppm; 3H), two doublets (d=3.68
and 2.07 ppm; 1H each; 2J(H,H)=4.5 Hz) and one slightly
broad resonance attributed to the amine proton of 2a+ (d=
5.94 ppm; 1H). In the 13C NMR spectrum of 2a+ the h3-benzyl-
ic terminus is responsible for signals at d=100.4 (IrꢀCH2Cq),
94.1 (IrꢀCq) and 34.9 ppm (IrꢀCH2; 1J(C,H)average =155 Hz).
The described rearrangement of the Ap ligand was structur-
ally authenticated by X-ray studies of complexes 2a+–2c+
(Figure 6; Figure S12 in the Supporting Information). In the
three complexes, the IrꢀNpy bonds have similar lengths (2a+:
2.073(6) ꢅ; 2b+: 2.098(4) ꢅ; 2c+: 2.083(5) ꢅ) and the Ir-(h3-ben-
zylic) moieties possess one relatively short IrꢀCH2 bond
(ꢁ2.12 ꢅ), an intermediate IrꢀCH2Cq distance of about 2.25–
2.30 ꢅ and a longer Ir···Cq contact of about 2.40 ꢅ.
Figure 4. X-ray structures of complexes 1a·CO+ (top) and 1b·CO+ (bottom).
Anion BArF is omitted for clarity.
ꢀ
Figure 5. X-ray structure of complex 1a·CNXyl+; anion BArFꢀ is omitted for
clarity.
plexes are often active participants in homogeneous catalytic
reactions.[18a,23b,24b,35–38] The electrophilicity of the five-coordi-
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play little sensitivity to changes in the aminopyridi-
nate aryl substituents, with values of Keq =4ꢄ0.5 for
the 1a+/2a+ and 1b+/2b+ couples and of Keq =2ꢄ
0.5 for the 1d+/2d+ couple. The same equilibrium
mixtures were reached starting from the pure h3-ben-
zylic complexes 2a+, 2b+ and 2d+, although longer
reaction times were needed. These Keq values reveal
that the two isomeric structures have similar thermo-
dynamic stability, although in comparative terms the
k-N,h3-pseudo-allyl Ap coordination mode in 2c+
Scheme 6. Reversible isomerisation of complexes 1a+ and 2a+ catalysed by H2.
leads to enhanced stability, most likely due to the
electron-donating properties of the para-NMe2 substituent.
The rate of the 1+!2+ redistribution reaction is dependent
upon the H2 concentration. Thus, t1/2 values of about 2.5 h and
30 min were measured for the conversion of 1a+ into 2a+ at
208C in CD2Cl2 for concentrations of H2 in solution of 6 and
32 mol%, respectively (see above for additional data). Al-
though isomerisation rates were of comparable magnitude for
all the compounds investigated, the 1a+Ð2a+ reorganisation
was comparatively slower, perhaps due to steric hindrance ex-
erted by the 2,6-iPr2C6H3 aryl substituent. A sufficiently detailed
kinetic study of the 1+Ð2+ interconversions was unfortunate-
ly unattainable. This was due to the somewhat erratic and un-
predictable tendency of complexes 1+ to react irreversibly
with H2 (discussed above) in the manner shown in Scheme 5.
Countless hydrogenation reactions both stoichiometric and
catalytic are known. Even if it would not be surprising that
a molecule of H2 functions not only as a reagent but also as
a catalyst, literature precedent for H2-catalysed reactions is
very limited.[12,40] In the system under scrutiny, H2 behaves as
an efficient homogeneous catalyst and promotes the forma-
tion and cleavage of CꢀH and NꢀH bonds of Ap ligands
bound to the (h5-C5Me5)IrIII fragment. Sola and co-workers dem-
onstrated a fast catalysis by H2 of the syn–anti isomerisation of
five-coordinate iridium mono-hydride complexes stabilised
by
k3-P,P’,Si-binding
of
the
PSiP
pincer
ligand
ꢀSi(Me){(CH2)3PPh2}2.[41] In accordance with NMR spectroscopic
and computational studies, no exchange between IrꢀH and H2
took place during the syn–anti isomerisation, although such an
Figure 6. X-ray structures of complexes 2a+ (top) and 2c+ (bottom). Anion
BArFꢀ is omitted for clarity.
exchange could be possible in
intermediate.[41]
a low-energy tri-hydride
Complexes 1+ did not undergo any observable change
upon prolonged stirring either at room temperature or 50–
608C in the absence of H2. Furthermore catalytic concentra-
tions of H2 as low as 2–5 mol% (measured by 1H NMR spectros-
copy in solution in CD2Cl2) efficiently promoted the 1+Ð2+ re-
arrangement, although longer reaction periods were needed.
For instance, a H2 load of about 1.6 mol% induced the 1a+
Ð2a+ interconversion at 208C with a half-life (t1/2) of about
9.1 h. Thus, the isomerisation of the aminopyridinate ligand of
these complexes was catalysed by dihydrogen. Extensive prep-
arative and NMR spectroscopic studies of this reaction system
demonstrated that complexes 1a+–1d+ exist in solution in dy-
namic equilibrium with their 2a+–2d+ counterparts.
A series of experiments were developed to demonstrate
beyond any doubt the proposed homogeneous and catalytic
nature of the isomerisation depicted in Scheme 6.[42] The ex-
periments included discarding a heterogeneous process[43] pro-
moted by iridium colloidal particles, as well as unnoticed catal-
ysis by water or other Brønsted–Lowry acids or bases.[6d,44] In
addition, besides commercially available H2 (and D2, see
below), dihydrogen was chemically generated by well-estab-
lished procedures.[42] In the course of these experiments it was
found that 1a+ underwent no observable change when treat-
ed with H2 in the presence of the weakly coordinating base
TMPP (2,2,6,6-tetramethylpiperidine), whereas its pseudo-allylic
isomer 2a+ reacted to yield the neutral hydride 1a·H
(Scheme 7), which was alternatively generated by the action of
NaBH4 on the parent chloride 1a·Cl. The analogous hydride
1b·H was also obtained (see the Experimental Section).
With the exception of the 4-dimethylamino-substituted com-
plex 1c+, which converts almost quantitatively (ꢃ95% by
1H NMR spectroscopy) into its 2c+ isomer, the equilibria dis-
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/2c·CO+), may be taken as suggestive of the moderately
better electron-donating properties of the h1-benzylic ligand in
complexes 2·CO+ than for the Namido functionality present in
complexes 1·CO+.
In summary, some relevant characteristics of this unusual re-
action system are:
1) The isomeric complexes 1+ and 2+ have similar thermody-
namic stabilities.
2) In solution they exist in a dynamic equilibrium that can be
reached starting from either side.
3) Isomer equilibration requires the formation and rupture of
CꢀH and NꢀH bonds and occurs at room temperature or
below under homogeneous dihydrogen catalysis.
4) Dihydrogen activation, that is HꢀH bond cleavage, is not
rate limiting.
Scheme 7. Two different syntheses of the hydride complex 1a·H.
Computational studies and mechanistic proposal
With reference to complexes 1a+ and 2a+, chosen as models
for this theoretical analysis, the experimental efforts to eluci-
date a mechanism for their isomerisation were completed with
DFT (B3LYP) calculations. Initial explorations, previously com-
municated,[12] used a model system with a cyclopentadienyl
(C5H5) instead of a C5Me5 ligand and two Xyl fragments on the
aminopyridinate ligand (Cp·1b+), but the results discussed
herein correspond to calculations based on the cation com-
plexes of the real species 1a+ and 2a+, unless stated other-
wise. Thermodynamic data are relative free energies in the gas
phase and energy barriers correspond to relative electronic en-
ergies in the gas phase.
Further experimental work was accomplished. Use of D2 pro-
vided a kinetic isotopic effect (KIE) with kH/kD =1.3, which sug-
gested that HꢀH bond cleavage had no important contribution
to the rate-determining step. KIE values close to 1 are com-
monly found for reactions of H2 with unsaturated com-
plexes.[34,45] When D2 was utilised as the catalyst, selective deu-
terium incorporation was realised, firstly in complex 2a+ at the
amido nitrogen atom (which converts into an amine, >NH or
>ND) and the CH2 and CH3 sites of the metallated Xyl group,
and secondly, if sufficient time was allowed, at the Xyl methyl
positions of isomer 1a+.
The facile, H2-promoted reversible rearrangement, 1+Ð2+,
suggested that similar to complexes 1+, the pseudo-allylic de-
rivatives 2+ should also exhibit electrophilic character and
react readily with Lewis bases with a concomitant benzylic co-
ordination change from h3 to k-C. Bubbling CO through solu-
tions of the two complexes chosen for this study, 2a+ and
2c+, in CH2Cl2 confirmed this prediction and led to quantita-
tive formation of the carbonyl adducts 2a·CO+ and 2c·CO+
(Scheme 8). The two compounds display a strong IR absorption
with nearly the same wavenumber (n˜(CO)=2030 cmꢀ1; see
Table S1 in the Supporting Information), which is somewhat
shifted to lower energy relative to the corresponding band for
isomers 1a·CO+ and 1c·CO+. The shift, albeit modest (20 cmꢀ1
for the 1a·CO+/2a·CO+ couple and 28 cmꢀ1 for 1c·CO+
The calculations at this level indicate that the energies of
the two isomers are comparable, consistent with the two com-
pounds existing in equilibrium; 1a+ is favoured over 2a+ by
3.1 kcalmolꢀ1. However this may be an effect of the functional.
Use of M06, which has been claimed to give a better account
of dispersive forces in large molecules[46] (see the Supporting
Information), leads to a greater stability of 2a+ by 0.5 kcal
molꢀ1, and equates to an equilibrium constant of 2.3.
Despite experimental evidence that establishes a role for di-
hydrogen in the isomerisation, a mechanism was explored
without H2 participation and was discarded. Oxidative addition
of one benzylic CꢀH bond of 1a+ has an energy barrier (DE°)
of 38.1 kcalmolꢀ1, too high for a room temperature process.
Furthermore, migration of the resulting iridium hydride to the
amido nitrogen atom yields an even higher overall barrier from
1a+ of 45.1 kcalmolꢀ1 (see Figure S15 in the Supporting
Information).
The calculations indicate that H2 coordination to 1a+ is en-
dergonic (DG=20.4 kcalmolꢀ1) and the resulting dihydrogen
complex (A) undergoes a reduction in the molecular symmetry
(from Cs in 1a+ to C1, see Figure 7) and an elongation of the
IrꢀNamido bond from 1.98 to 2.15 ꢅ. NBO analysis of the simpli-
fied model Cp·1b+ showed that the natural localised molecu-
lar orbital (NLMO) derived from the lone pair on the amido ni-
trogen atom has a 10.2% contribution from Ir and 73.9% from
Scheme 8. Formation of carbonyl complexes 2a·CO+ and 2c·CO+.
Chem. Eur. J. 2014, 20, 1 – 13
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Figure 7. Views of the DFT-optimised structures of cations 1b+ (top left)
and A (top right). The bottom structure shows the p (Namido-Ir) natural lo-
calised molecular orbital (NLMO) of Cp·1b+ with a significant contribution
from Ir.
its parent NBO. Upon H2 coordination the contribution from Ir
to the corresponding NLMO becomes less than 1%, which is
consistent with a decrease in the double-bond character of the
IrꢀNamido interaction in intermediate A and other adducts
1a·L+.
Figure 9. DFT-optimised geometries of the transition states for the protona-
tion of the Namido (TSA!B) and the activation of one benzylic CꢀH of B’
(TSB!C). Calculated distances are in ꢅ.
The dihydrogen intermediate A is in fast equilibrium with
the corresponding IrV dihydride, A-(H)2 according to the calcu-
lations, which predict that the dihydride complex is more
stable (DGꢁ2 kcalmolꢀ1). The activation of H2 from A is
almost barrier-less, however the overall barrier from 1a+
amounts to 20 kcalmolꢀ1 (see Figure 8). Protonation of the
Namido atom takes place from the dihydride complex (see
Figure 9; no transition state was located for the corresponding
elemental step from the dihydrogen intermediate A at this
this bond is dependent on the steric interaction between the
C5Me5 and the Ap ligands (see the Supporting Information for
details), whereas all calculations predict that species B’ has
a relative energy comparable to (or lower than) that of 1a+ +
H2 (ꢀ0.3 kcalmolꢀ1).
Activation of one benzylic CꢀH unit of B’ yields a new IrV di-
hydride C-(H)2, with a relative energy of 14.5 kcalmolꢀ1. This di-
hydride is in rapid equilibrium with the corresponding dihydro-
gen complex C (as in the case of A and A-(H)2, the dihydride
and the dihydrogen species have similar energies). Finally, the
latter can eliminate H2 to yield 2a+.
level of theory) with
a
barrier of DE° =12.2 kcalmolꢀ1
(Figure 8). The resulting IrIII monohydride (B) lies above 1a+ +
H2 (DG=8.3 kcalmolꢀ1) and features an interaction between
the Ir atom and NH moiety (2.33 ꢅ). The next step requires ac-
tivation of one benzylic CꢀH bond (see Figure 9 for transition-
state geometry) but needs a conformational change to replace
the Ir–NH interaction with an h2 interaction with the Xyl sub-
stituent of the pyridine moiety.[47] Calculations at various levels
of theory and with different models suggest that the extent of
On the basis of the experimental and theoretical data pre-
sented thus far, the equilibrium between the isomeric species
1a+Q2a+ may occur as represented in Scheme 9. It seems
likely that reactive, undetected iridium s-dihydrogen com-
plexes could be generated by coordination of dihydrogen to
the electrophilic iridium centres of 1a+ and 2a+.[23b,35–37] Dihy-
drogen intermediates A and C would be structurally analogous
to the adducts 1a·CO+ and 2a·CO+ discussed already. Proto-
nation of the IrꢀNamido bond may occur by heterolytic rupture
of the HꢀH bond to give Hꢀ, which links to the metal with for-
mation of the hydride ligand, and H+, which migrates intramo-
lecularly to protonate the amide group (intermediate B). Alter-
natively, homolytic rupture could occur to form a cationic bis-
hydride complex of Ir(V). From B, activation of a CꢀH bond
from a methyl group of the Xyl substituent followed by elimi-
nation of H2 would lead to the h3-benzylic isomer 2a+.
Conclusion
The experimental and computational studies described in this
paper demonstrate that aminopyridinate ligands with a 2,6-di-
methyl-substituted aryl group at the 6-position of the pyridinic
terminus can bind to the (h5-C5Me5)IrIII fragment in two differ-
Figure 8. Calculated free energy profile (kcalmolꢀ1; data in parentheses cor-
respond to electronic energies) of the dihydrogen-assisted isomerisation
1a+Ð2a+. The inset represents the optimised geometries of the intermedi-
ate B’ (most hydrogen atoms are omitted). Calculated distances are in ꢅ.
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2
1
Ar), 129.2 (q, J(C,F)=31 Hz; m-Ar), 124.9 (q, J(C,F)=273 Hz; CF3),
117.8 ppm (p-Ar). The synthesis and characterisation of ligands b–
d, compounds 1a·Cl–1d·Cl, [1a]BArF–[1d]BArF, [1a·CO]BArF–
[1d·CO]BArF and [1a·L]BArF are reported in the Supporting
Information.
Synthesis and characterisation
Compound [2a]BArF: A solution of compound [1a]BArF (0.1 g,
0.065 mmol) in CH2Cl2 (5 mL) at 08C was treated with H2 (0.5 bar)
and the mixture was stirred for 6 h. 1H NMR analysis of the reaction
mixture revealed the formation of complex 2a+ and its isomer
1a+ in approximately a 1:1 ratio. [2a]BArF was separated by frac-
tional crystallisation from Et2O/hexane mixtures at ꢀ238C as
orange crystals. 1H NMR (500 MHz, CD2Cl2, 258C): d=7.72 (m,
3
3J(H,H)ꢁ7.5 Hz, 1H; CHXyl), 7.59 (t, J(H,H)ꢁ7.5 Hz, 1H; CHPyridine(Pyr)),
7.48 (t, 3J(H,H)=8.2 Hz, 1H; CHDiisopropylphenyl(Dipp)), 7.45 (t, 3J(H,H)
ꢁ7.5 Hz, 1H; CHXyl), 7.37 (d, 3J(H,H)ꢁ7.5 Hz, 1H; CHXyl), 7.30 (d,
3J(H,H)=8.2 Hz, 1H; CHDipp), 7.01 (d, 3J(H,H)=8.2 Hz, 1H; CHDipp),
6.11 (d, 3J(H,H)ꢁ7.5 Hz, 1H; CHPyr), 6.04 (d, 3J(H,H)ꢁ7.5 Hz, 1H;
2
CHPyr), 5.94 (s, 1H; NH), 3.68 (d, J(H,H)=4.5 Hz, 1H; IrꢀCHH), 3.19
(septet, 3J(H,H)ꢁ7.0 Hz, 1H; CHiPr), 2.78 (septet, 3J(H,H)ꢁ7.0 Hz,
1H; CHiPr), 2.48 (s, 3H; 1ꢆMexyl), 2.07 (d, 2J(H,H)=4.5 Hz, 1H; Irꢀ
CHH), 1.61 (s, 15H; 5ꢆMeCp*), 1.30 (d, 3J(H,H)ꢁ7.0 Hz, 3H; MeiPr),
1.28 (d, 3J(H,H)ꢁ7.0 Hz, 3H; MeiPr), 1.26 (d, 3J(H,H)ꢁ7.0 Hz, 3H;
MeiPr), 1.01 ppm (d, J(H,H)ꢁ7.0 Hz, 3H; MeiPr); 13C NMR (125 MHz,
3
CD2Cl2, 258C): d=157.1 (Cq-Pyr), 154.2 (Cq-Pyr), 148.0 (Cq-Dipp), 147.7
Scheme 9. Proposed mechanism for the H2-catalysed isomerisation between
species 1a+ and 2a+.
(Cq-Dipp), 146.2 (Cq-Dipp), 141.4 (CHPyr), 137.7 (Cq-Xyl), 134.0, 130.0,
129.6, 129.4, 125.3, 125.1 (CHXyl, CHDipp), 117.8 (CHPyr), 107.5 (CHPyr),
1
100.4 (IrꢀCH2-Cq), 94.1 (IrꢀCq-xyl), 90.2 (Cq-Cp*), 34.9 (d, J(C,H)average
=
ent forms (complexes 1a+–1d+ and 2a+–2d+). We have
found that H2 catalyses a prototropic rearrangement, which in-
terchanges a hydrogen atom between one of the 2,6-benzylic
positions and the amido site of the aminopyridinate ligands
under homogeneous conditions with high efficiency. The pro-
cess implies reversible formation and cleavage of HꢀH, CꢀH
and NꢀH bonds.
155 Hz; IrꢀCH2), 29.4 (CHiPr), 28.6 (CHiPr), 25.6 (MeiPr), 23.7 (MeiPr),
23.6 (MeiPr), 23.1 (MeiPr), 20.5 (Mexyl), 8.9 ppm (MeCp*); IR (Nujol): n˜ =
3420 cmꢀ1 (br; NH); elemental analysis calcd (%) for C67H56BF24IrN2:
C 52.0, H 3.7, N 1.8; found: C 52.0, H 3.7, N 1.8.
Compounds [2b]BArF–[2d]BArF: See the Supporting Information
for synthetic details and characterisation data.
Compound 1a·H:
Method a: Tetramethylpiperidine (5 equiv) was added to an equilib-
rium mixture of 1a+ and 2a+ in CD2Cl2 and the resulting mixture
was treated with H2 (1 atm). The reaction was monitored by
1H NMR spectroscopy until 2a+ had reacted to form 1a·H.
Experimental Section
General procedures
Method b: To a solution of 1a·Cl (0.05 g, 0.072 mmol) in THF
(5 mL), NaBH4 (ꢁ10 equiv) and methanol (3 mL) were added. The
reaction mixture was stirred at RT for 14 h and the colour of the
solution changed from orange to yellow. Distilled water (3 mL) was
added and the product was extracted with toluene. The organic
phase was dried over MgSO4 and the solvent was evaporated
Microanalyses were performed by the Microanalytical Service of
the Instituto de Investigaciones Quꢁmicas (Seville, Spain). Infrared
spectra were obtained with a Bruker Vector 22 spectrometer. Mass
spectra were obtained at the Mass Spectroscopy Service of the
University of Seville. NMR spectra were recorded with a Bruker
DRX-500, DRX-400 or DPX-300 spectrometer. Spectra were refer-
enced to external SiMe4 (d=0 ppm) by using the residual protic
solvent peaks as internal standards (1H NMR experiments) or the
characteristic resonances of the solvent nuclei (13C NMR experi-
ments). Spectral assignments were made by routine one- and two-
dimensional NMR experiments if appropriate. All manipulations
were performed under dry, oxygen-free N2, by using conventional
Schlenk techniques. Crystal structures were determined with
1
under vacuum. Analysis by H NMR spectroscopy revealed quanti-
tative conversion into 1a·H. Note: 1a·H converts into 1a·Cl in the
presence of chlorinated solvents. An analytically pure sample of
1a·H could not be obtained due to its slow decomposition in solu-
1
tion when crystallising. H NMR (300 MHz, C6D6, 258C): d=7.24 (m,
3
3H; 3ꢆCHDipp), 7.05 (m, 1H; CHXyl), 6.94 (t, J(H,H)ꢁ7.5 Hz, 2H; 2ꢆ
CHXyl), 6.73 (t, 3J(H,H)ꢁ7.5 Hz, 1H; CHPyr), 5.70 (d, 3J(H,H)ꢁ7.5 Hz,
1H; CHPyr), 5.28 (d, 3J(H,H)ꢁ7.5 Hz, 1H; CHPyr), 3.97 (septet,
3
a
Bruker–Nonius, X8Kappa diffractometer. Metal complex
3J(H,H)=7.0 Hz, 1H; CHiPr), 3.64 (septet, J(H,H)=7.0 Hz, 1H; CHiPr),
[48]
[49]
[IrCl2Cp*]2 and NaBArF were prepared as previously described.
The lithium salts of the Ap ligands were prepared according to
2.46 (s, 3H; MeXyl), 2.20 (s, 3H; MeXyl), 1.41 (s, 15H; 5ꢆMeCp*), 1.38
(d, 3J(H,H)ꢁ7.0 Hz, 6H; 2ꢆMeiPr), 1.27 (d, 3J(H,H)ꢁ7.0 Hz, 3H;
publisheꢀd procedures.[14a] The H and 13C{1H} NMR spectral data for
MeiPr), 1.16 (d, J(H,H)ꢁ7.0 Hz, 3H; MeiPr), ꢀ7.39 ppm (s, 1H; IrꢀH);
1
3
the BArF anion in CD2Cl2 are identical for all complexes and there-
13C NMR (75 MHz, C6D6, 258C): d=170.7 (Cq-Pyr), 157.2 (Cq-Pyr), 146.7
(Cq-Dipp), 145.8 (Cq-Dipp), 139.9 (Cq-Xyl), 138.4 (Cq-Xyl), 137.6 (Cq-Dipp),
136.5 (Cq-Xyl), 134.1 (CHPyr), 104.8 (CHPyr), 104.0 (CHPyr), 128.2 (CHXyl),
127.9 (CHXyl), 126.8 (CHXyl), 124.9 (CHDipp), 123.8 (CHDipp), 122.9
1
fore are not repeated for each individual case below. H NMR (500
MHz, CD2Cl2): d=7.75 (s, 8H; o-Ar), 7.58 ppm (s, 4H; p-Ar); 13C NMR
(125 MHz, CD2Cl2): d=162.1 (q, 1J(C,B)=37 Hz; ipso-Ar), 135.3 (o-
Chem. Eur. J. 2014, 20, 1 – 13
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(CHDipp), 84.2 (Cq-Cp*), 27.9 (CHiPr), 26.6 (CHiPr), 25.1 (MeiPr), 24.5
(MeiPr), 24.2 (MeiPr), 23.1 (MeiPr), 20.2 (MeXyl), 19.7 (MeXyl), 10.0 ppm
(MeCp*).
([2b]BArF) and 1024992 ([2c]BArF) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Compound 1b·H: See the Supporting Information for synthetic de-
tails and characterisation data.
Compound [2a·CO]BArF: CO (g) was bubbled through a solution
of [2a]BArF (0.1 g, 0.065 mmol) in CH2Cl2 (5 mL) at RT for 5 min.
The solution immediately changed colour from orange to yellow.
The solvent was removed under reduced pressure and 1H NMR
analysis of the reaction product showed quantitative conversion
into 2a·CO+. The product was washed with pentane and dried
Acknowledgements
Financial support (FEDER contribution and ESF) from the Span-
ish Ministry of Science (projects CTQ2013-42501-P and Consol-
ider Ingenio 2010 CSD 2007-0006) and the Junta de Andalucꢁa
(grant FQM-119 and project P09-FQM-4832) is acknowledged.
N.R. and J.L.-S. thank the Spanish Ministry of Science and the
University of Seville for two “Ramꢀn y Cajal” contracts.
1
3
under vacuum. H NMR (400 MHz, CD2Cl2, 258C): d=7.56 (t, J(H,H)
ꢁ7.5 Hz, 1H; CHPyr), 7.12 (d, 3J(H,H)ꢁ7.5 Hz, 1H; CHPyr), 6.22 (d,
3
3J(H,H)ꢁ7.5 Hz, 1H; CHPyr), 7.51 (t, J(H,H)ꢁ7.5 Hz, 1H; CHDipp), 7.38
(m, 3J(H,H)ꢁ7.5 Hz, 2H; 2ꢆCHDipp), 7.30 (t, 3J(H,H)ꢁ7.5 Hz, 1H;
CHXyl), 7.24 (t, 3J(H,H)ꢁ7.5 Hz, 1H; CHXyl), 7.11 (d, 3J(H,H)ꢁ7.5 Hz,
1H; CHXyl), 6.68 (s, 1H, NH), 3.78 (d, 2J(H,H)ꢁ11 Hz, 1H; IrꢀCHH),
Keywords: CꢀH activation · dihydrogen catalysis · iridium ·
ligand isomerisation · NꢀH activation
2
2.98 (d, J(H,H)ꢁ11 Hz, 1H; IrꢀCHH), 3.04 (septet, 3J(H,H)ꢁ7.0 Hz,
1H; CHiPr), 2.94 (septet, 3J(H,H)ꢁ7.0 Hz, 1H; CHiPr), 2.34 (s, 3H;
3
MeXyl), 1.68 (s, 15H; 5ꢆMeCp*), 1.27 (d, J(H,H)ꢁ7.0 Hz, 3H; MeiPr),
1.26 (d, 3J(H,H)ꢁ7.0 Hz, 3H; MeiPr), 1.15 (d, 3J(H,H)ꢁ7.0 Hz, 3H;
[1] a) Y.-F. Han, G.-X. Jin, Chem. Soc. Rev. 2014, 43, 2799–2823; b) C. Wang,
B. Villa-Marcos, J. Xiao, Chem. Commun. 2011, 47, 9773–9785; c) T.
Suzuki, Chem. Rev. 2011, 111, 1825–1845; d) M. Albrecht, Chem. Rev.
2010, 110, 576–623; e) S. Kuwata, T. Ikariya, Dalton Trans. 2010, 39,
2984–2992; f) J. Liu, X. Wu, J. A. Iggo, J. Xiao, Coord. Chem. Rev. 2008,
252, 782–809; g) T. Ikariya, A. J. Blacker, Acc. Chem. Res. 2007, 40, 1300–
1308.
[2] a) U. Hintermair, S. W. Sheehan, A. R. Parent, D. H. Ess, D. T. Richens, P. H.
Vaccaro, G. W. Brudvig, R. H. Crabtree, J. Am. Chem. Soc. 2013, 135,
10837–10851; b) J. Graeupner, U. Hintermair, D. L. Huang, J. M. Thom-
sen, M. Takase, J. Campos, S. M. Hashmi, M. Elimelech, G. W. Brudvig,
R. H. Crabtree, Organometallics 2013, 32, 5384–5390; c) U. Hintermair,
S. M. Hashmi, M. Elimelech, R. H. Crabtree, J. Am. Chem. Soc. 2012, 134,
9785–9795; d) R. H. Crabtree, Organometallics 2011, 30, 17–19.
[3] a) C. Zuccaccia, G. Bellachioma, G. Bortolini, A. Bucci, A. Savini, A. Mac-
chioni, Chem. Eur. J. 2014, 20, 3446–3456; b) A. Savini, A. Bucci, G. Bella-
chioma, L. Rocchigiani, C. Zuccaccia, A. Llobet, A. Macchioni, Eur. J.
Inorg. Chem. 2014, 690–697; c) C. Zuccaccia, G. Bellachioma, S. BolaÇo,
L. Rocchigiani, A. Savini, A. Macchioni, Eur. J. Inorg. Chem. 2012, 1462–
1468; d) D. G. H. Hetterscheid, J. N. H. Reek, Chem. Commun. 2011, 47,
2712–2714; e) W. I. Dzik, S. E. Calvo, J. N. H. Reek, M. Lutz, M. A. Ciriano,
C. Tejel, D. G. H. Hetterscheid, B. de Bruin, Organometallics 2011, 30,
372–374.
[4] a) J. F. Hartwig, Acc. Chem. Res. 2012, 45, 864–873; b) N. Kuhl, M. N.
Hopkinson, J. Wencel-Delord, F. Glorius, Angew. Chem. Int. Ed. 2012, 51,
10236–10254; Angew. Chem. 2012, 124, 10382–10401; c) G. E. Dober-
einer, R. H. Crabtree, Chem. Rev. 2010, 110, 681–703; d) D. Balcells, E.
Clot, O. Eisenstein, Chem. Rev. 2010, 110, 749–823; e) D. A. Colby, A. S.
Tsai, R. G. Bergman, J. A. Ellman, Acc. Chem. Res. 2012, 45, 814–825;
f) G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651–3678.
[5] For examples see: a) B. A. Arndtsen, R. G. Bergman, Science 1995, 270,
1970–1973; b) P. Burger, R. G. Bergman, J. Am. Chem. Soc. 1993, 115,
10462–10463; c) J. M. Meredith, R. Robinson, Jr., K. I. Goldberg, W. Ka-
minsky, D. M. Heinekey, Organometallics 2012, 31, 1879–1887; d) J.
Campos, J. Lꢀpez-Serrano, E. ꢃlvarez, E. Carmona, J. Am. Chem. Soc.
2012, 134, 7165–7175.
[6] See, for instance: a) A. J. Blacker, E. Clot, S. B. Duckett, O. Eisenstein, J.
Grace, A. Nova, R. N. Perutz, D. J. Taylor, A. C. Whitwood, Chem.
Commun. 2009, 6801–6803; b) A. Nova, D. J. Taylor, A. J. Blacker, S. B.
Duckett, R. N. Perutz, O. Eisenstein, Organometallics 2014, 33, 3433–
3442; c) K. Ishiwata, S. Kuwata, T. Ikariya, J. Am. Chem. Soc. 2009, 131,
5001–5009; d) Z. M. Heiden, T. B. Rauchfuss, J. Am. Chem. Soc. 2009,
131, 3593–3600; e) Z. M. Heiden, B. J. Gorecki, T. B. Rauchfuss, Organo-
metallics 2008, 27, 1542–1549; f) Z. M. Heiden, T. B. Rauchfuss, J. Am.
Chem. Soc. 2007, 129, 14303–14310; g) J. Campos, U. Hintermair, T. P.
Brewster, M. K. Takase, R. H. Crabtree, ACS Catal. 2014, 4, 973–985; h) U.
Hintermair, J. Campos, T. P. Brewster, L. M. Pratt, N. D. Schley, R. H. Crab-
tree, ACS Catal. 2014, 4, 99–108.
3
MeiPr), 1.14 ppm (d, J(H,H)ꢁ7.0 Hz, 3H; MeiPr); 13C NMR (100 MHz,
CD2Cl2, 258C): d=168.4 (IrꢀCO), 161.6 (Cq-Pyr), 155.0 (Cq-Pyr), 147.6
(Cq-Dipp), 146.9 (Cq-Dipp), 144.8 (Cq-Xyl), 140.0 (CHPyr), 138.4 (Cq-Xyl), 137.7
(Cq-Xyl), 131.0 (Cq-Dipp), 117.7 (CHPyr), 130.2 (CHDipp), 129.8 (CHXyl), 129.0
(CHXyl), 126.6 (CHDipp), 126.5 (CHDipp), 123.2 (CHXyl), 108.1 (CHPyr),
101.8 (Cq-Cp*), 29.1 (CHiPr), 28.7 (CHiPr), 24.9 (MeiPr), 24.8 (MeiPr), 23.8
(MeiPr), 23.5 (MeiPr), 21.7 (MeXyl), 9.7 (dd, 1J(C,H)=142 Hz, IrꢀCH2),
8.6 ppm (MeCp*); IR (Nujol): n˜ =3355 (NH), 2030 cmꢀ1 (CO); elemen-
tal analysis calcd (%) for C67H56BF24IrN2: C 51.8, H 3.6, N 1.8; found:
C 51.6, H 3.8, N 1.6.
Compound [2c·CO]BArF: See the Supporting Information for syn-
thetic details and characterisation data.
Computational Details
All calculations were performed by using the Gaussian 09 series of
programs[50] with the B3LYP functional.[51,52] An effective core po-
tential[53] and its associated double-z LANL2DZ basis set were used
for iridium. C, H and N atoms were represented by means of the
6–31G(d,p) basis set (BS1).[54–56] Additional calculations were carried
out with Truhlar’s M06 functional[46] and the SDD core potential for
iridium[57] (BS2). The latter calculations agree qualitatively with the
B3LYP results. The structures of the reactants, intermediates, transi-
tion states and products were fully optimised in the gas phase
without any symmetry restriction. Frequency calculations were per-
formed on all optimised structures at the same levels of theory to
characterise the stationary points and the transitions states, as well
as for the calculation of gas-phase zero-point energies (ZPE), en-
thalpies (H), entropies (S) and Gibbs energies (G) at T=298.15 K.
The nature of the intermediates connected by transition states was
determined by intrinsic reaction coordinate (IRC) calculations or by
perturbing the transition states along the TS coordinate and opti-
mising to a minimum. NBO analysis[58] was performed with the
NBO 3.1 program as implemented in Gaussian 09.
X-ray structure analysis
X-ray details are given in the Supporting Information. CCDC-
1024982 (ligand d), 1024983 (1a·Cl), 1024984 (1b·Cl), 859075
([1a]BArF), 1024985 ([1d]BArF), 1024986 ([1a·CO]BArF), 1024987
([1a·NH3]BArF), 1024988 ([1a·dmap]BArF), 1024989 ([1a·CNXyl]-
BArF), 1024990 ([1b·CO]BArF), 859076 ([2a]BArF), 1024991
&
&
Chem. Eur. J. 2014, 20, 1 – 13
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10
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[7] a) J. Atzrodt, V. Derdau, T. Fey, J. Zimmermann, Angew. Chem. Int. Ed.
2007, 46, 7744–7765; Angew. Chem. 2007, 119, 7890–7911; b) J. R.
Heys, J. Labelled Compd. Radiopharm. 2007, 50, 770–778.
12713; c) W. H. Bernskoetter, E. Lobkovsky, P. J. Chirik, Organometallics
2005, 24, 6250–6259; d) P. H. M. Budzelaar, N. N. P. Moonen, R. de Geld-
er, J. M. M. Smits, A. W. Gal, Eur. J. Inorg. Chem. 2000, 753–769;
e) P. H. M. Budzelaar, R. de Gelder, A. W. Gal, Organometallics 1998, 17,
4121–4123; f) C. Tejel, L. Asensio, M. P. del Rꢁo, B. de Bruin, J. A. Lꢀpez,
M. A. Ciriano, Eur. J. Inorg. Chem. 2012, 512–519; g) C. Tejel, M. P.
del Rꢁo, L. Asensio, F. J. van den Bruele, M. A. Ciriano, N. T. i Spithas,
D. G. H. Hetterscheid, B. de Bruin, Inorg. Chem. 2011, 50, 7524–7534;
h) C. Tejel, M. A. Ciriano, M. P. del Rꢁo, F. J. van den Bruele, D. G. H. Het-
terscheid, N. T. i Spithas, B. de Bruin, J. Am. Chem. Soc. 2008, 130, 5844–
5945.
[8] See, for instance: a) J. Campos, M. Rubio, A. C. Esqueda, E. Carmona, J.
Labelled Compd. Radiopharm. 2012, 55, 29–38; b) J. Campos, A. C. Es-
queda, J. Lꢀpez-Serrano, L. Sꢇnchez, F. P. Cossio, A. de Cozar, E. ꢃlvarez,
C. Maya, E. Carmona, J. Am. Chem. Soc. 2010, 132, 16765–16767; c) G.
Ciancaleoni, S. BolaÇo, J. Bravo, M. Peruzzini, L. Gonsalvi, A. Macchioni,
Dalton Trans. 2010, 39, 3366–3368; d) J. A. Brown, S. Irvine, A. R. Ken-
nedy, W. J. Kerr, S. Andersson, G. N. Nilsson, Chem. Commun. 2008,
1115–1117; e) R. Corberꢇn, M. Sanaffl, E. Peris, J. Am. Chem. Soc. 2006,
128, 3974–3979; f) C. M. Yung, M. B. Skaddan, R. G. Bergman, J. Am.
Chem. Soc. 2004, 126, 13033–13043; g) S. R. Klei, J. T. Golden, T. D. Tilley,
R. G. Bergman, J. Am. Chem. Soc. 2002, 124, 2092–2093; h) J. T. Golden,
R. A. Andersen, R. G. Bergman, J. Am. Chem. Soc. 2001, 123, 5837–5838.
[9] a) G. Zeng, S. Sakaki, K. Fujita, H. Sano, R. Yamaguchi, ACS Catal. 2014,
4, 1010–1020; b) A. Prades, R. Corberꢇn, M. Poyatos, E. Peris, Chem. Eur.
J. 2009, 15, 4610–4613; c) A. Prades, R. Corberꢇn, M. Poyatos, E. Peris,
Chem. Eur. J. 2008, 14, 11474–11479; d) L. Li, Y. Jiao, W. W. Brennessel,
W. D. Jones, Organometallics 2010, 29, 4593–4605; e) A. P. da Costa, M.
Viciano, M. Sanaffl, S. Merino, J. Tejeda, E. Peris, B. Royo, Organometallics
2008, 27, 1305–1309.
[10] a) Z. Liu, P. J. Sadler, Acc. Chem. Res. 2014, 47, 1174–1185; b) D. P. Smith,
H. Chen, S. Ogo, A. I. Elduque, M. Eisenstein, M. Olmstead, R. H. Fish, Or-
ganometallics 2014, 33, 2389–2404.
[11] a) J. Campos, M. F. Espada, J. Lꢀpez-Serrano, E. Carmona, Inorg. Chem.
2013, 52, 6694–6704; b) M. Rubio, J. Campos, E. Carmona, Org. Lett.
2011, 13, 5236–5239; c) J. Campos, A. C. Esqueda, E. Carmona, Chem.
Eur. J. 2010, 16, 419–422.
[12] J. E. V. Valpuesta, N. Rendꢀn, J. Lꢀpez-Serrano, M. L. Poveda, L. Sꢇnchez,
E. ꢃlvarez, E. Carmona, Angew. Chem. Int. Ed. 2012, 51, 7555–7557;
Angew. Chem. 2012, 124, 7673–7675.
[13] D. Barr, W. Clegg, R. E. Mulvey, R. Snaith, J. Chem. Soc. Chem. Commun.
1984, 469–470.
[21] N. Kanematsu, M. Ebihara, T. Kawamura, Inorg. Chim. Acta 1999, 292,
244–248.
[22] a) C. White, A. J. Oliver, P. M. Maitlis, J. Chem. Soc. Dalton Trans. 1973,
1901–1907; b) T. M. Gilbert, R. G. Bergman, J. Am. Chem. Soc. 1985, 107,
3502–3507.
[23] a) R. K. Thauer, Eur. J. Inorg. Chem. 2011, 919–921, and other articles in
this issue on hydrogenases; b) J. C. Gordon, G. J. Kubas, Organometallics
2010, 29, 4682–4701.
[24] a) Handbook of Heterogeneous Catalysis (Eds.: G. Ertl, H. Knçzinger, F.
Schüth, J. Weitkamp), Wiley-VCH, Weinheim, 2008; b) J. F. Hartwig in Or-
ganotransition Metal Chemistry, University Science Books, Sausalito,
2010. A related role for dihydrogen as a co-catalyst in metal-catalysed
isomerisation of olefins, or in olefin polymerisation (as a chain-transfer
reagent) is also known. See, for example: c) R. Cramer, R. V. Lindsey, J.
Am. Chem. Soc. 1966, 88, 3534–3544; d) N. M. G. Franssen, J. N. H. Reek,
B. de Bruin, Chem. Soc. Rev. 2013, 42, 5809–5832; e) A. Guyot, R. Spitz,
C. Bobichon, J. L. Lacombe in Catalytic Olefin Polymerization (Eds.: T.
Keii, K. Soga), Elsevier Science, Amsterdam, 1990, Chap. 3; f) A. S. Hoff-
man, B. A. Fries, P. C. Condit, J. Polym. Sci. Part C 1963, 4, 109–126.
[25] See, for example: a) U. Eberle, M. Felderhoff, F. Schüth, Angew. Chem.
Int. Ed. 2009, 48, 6608–6630; Angew. Chem. 2009, 121, 6732–6757;
b) N. Armaroli, V. Balzani, Angew. Chem. Int. Ed. 2007, 46, 52–66; Angew.
Chem. 2007, 119, 52–67.
[26] P. Espinet, P. M. Bailey, P. M. Maitlis, J. Chem. Soc. Dalton Trans. 1979,
1542–1547.
[27] A. W. Holland, D. S. Glueck, R. G. Bergman, Organometallics 2001, 20,
2250–2261.
[28] See, for example: a) J. Yuan, R. P. Hughes, A. L. Rheingold, Organometal-
lics 2009, 28, 4646–4648; b) A. C. Sykes, P. White, M. Brookhart, Organo-
metallics 2006, 25, 1664–1675; c) J. Zhao, A. S. Goldman, J. F. Hartwig,
Science 2005, 307, 1080–1082; d) M. Kanzelberger, X. Zhang, T. J. Emge,
A. S. Goldman, J. Zhao, C. Incarvito, J. F. Hartwig, J. Am. Chem. Soc.
2003, 125, 13644–13645.
[14] a) N. M. Scott, T. Schareina, O. Tok, R. Kempe, Eur. J. Inorg. Chem. 2004,
3297–3304; b) N. M. Scott, R. Kempe, Eur. J. Inorg. Chem. 2005, 1319–
1324; c) W. P. Kretschmer, A. Meetsma, B. Hessen, T. Schmalz, S.
Qayyum, R. Kempe, Chem. Eur. J. 2006, 12, 8969–8978; d) D. M. Lyubov,
C. Dçring, S. Y. Ketkov, R. Kempe, A. A. Trifonov, Chem. Eur. J. 2011, 17,
3824–3826.
[15] a) D. M. Lyubov, G. K. Fukin, A. V. Cherkasov, A. S. Shavyrin, A. A. Trifo-
nov, L. Luconi, C. Bianchini, A. Meli, G. Giambastiani, Organometallics
2009, 28, 1227–1323; b) D. M. Lyubov, C. Dçring, G. K. Fukin, A. V. Cher-
kasov, A. S. Shavyrin, R. Kempe, A. A. Trifonov, Organometallics 2008, 27,
2905–2907.
[29] D. Rais, R. G. Bergman, Chem. Eur. J. 2004, 10, 3970–3978.
[30] a) J. M. Meredith, K. I. Goldberg, W. Kaminsky, D. M. Heinekey, Organo-
metallics 2009, 28, 3546–3551; b) D. Wang, R. J. Angelici, Inorg. Chem.
1996, 35, 1321–1331; c) P. J. Alaimo, B. A. Arndtsen, R. G. Bergman, J.
Am. Chem. Soc. 1997, 119, 5269–5270.
[16] a) E. S. Tamne, A. Noor, S. Qayyum, T. Bauer, R. Kempe, Inorg. Chem.
2013, 52, 329–336; b) A. Noor, T. Bauer, T. K. Todorova, B. Weber, L. Ga-
gliardi, R. Kempe, Chem. Eur. J. 2013, 19, 9825–9832; c) F. R. Wagner, A.
Noor, R. Kempe, Nat. Chem. 2009, 1, 529–536; d) A. Noor, G. Glatz, R.
Müller, M. Kaupp, S. Demeshko, R. Kempe, Nat. Chem. 2009, 1, 322–
325; e) A. Noor, F. R. Wagner, R. Kempe, Angew. Chem. Int. Ed. 2008, 47,
7246–7249; Angew. Chem. 2008, 120, 7356–7359.
[31] A. S. Goldman, K. Krogh-Jespersen, J. Am. Chem. Soc. 1996, 118, 12159–
12166.
[32] a) J. C. Thomas, J. C. Peters, Inorg. Chem. 2003, 42, 5055–5073;
b) H. V. R. Dias, C. Dash, M. Yousufuddin, M. A. Celik, G. Frenking, Inorg.
Chem. 2011, 50, 4253–4255.
[33] a) P. M. Treichel, Adv. Organomet. Chem. 1973, 11, 21–86; b) Y. Yamamo-
to, Coord. Chem. Rev. 1980, 32, 193–233.
[17] a) K. G. Caulton, New J. Chem. 1994, 18, 25–41; b) T. J. Johnson, K. Folt-
ing, W. E. Streib, J. D. Martin, J. C. Huffman, S. A. Jackson, O. Eisenstein,
K. G. Caulton, Inorg. Chem. 1995, 34, 488–489; c) M. Jimꢂnez-Tenorio,
M. C. Puerta, P. Valerga, Eur. J. Inorg. Chem. 2004, 17–32; d) C. Tejel,
ˇ
M. P. del Rꢁo, M. A. Ciriano, E. J. Reijerse, F. Hartl, S. Zꢇlis, D. G. H. Het-
[34] a) S. D. Stults, R. A. Andersen, A. Zalkin, Organometallics 1990, 9, 115–
122; b) M. M. Conejo, J. S. Parry, E. Carmona, M. Schultz, J. G. Brennann,
S. M. Beshouri, R. A. Andersen, R. D. Rogers, S. Coles, M. Hursthouse,
Chem. Eur. J. 1999, 5, 3000–3009.
[35] a) G. J. Kubas, J. Am. Chem. Soc. 1984, 106, 451–452; b) G. J. Kubas,
Metal Dihydrogen and s-Bond Complexes: Structure, Bonding and Reac-
tivity, Kluwer Academic/Plenum, New York, 2001; c) G. J. Kubas, J. Orga-
nomet. Chem. 2014, 751, 33–49.
[36] a) R. H. Crabtree, Angew. Chem. Int. Ed. Engl. 1993, 32, 789–805; Angew.
Chem. 1993, 105, 828–845; b) P. G. Jessop, R. H. Morris, Coord. Chem.
Rev. 1992, 121, 155–284.
[37] a) D. M. Heinekey, A. Lledꢀs, J. M. Lluch, Chem. Soc. Rev. 2004, 33, 175–
182; b) S. Sabo-Etienne, B. Chaudret, Coord. Chem. Rev. 1998, 178–180,
381–407; c) R. N. Perutz, S. Sabo-Etienne, Angew. Chem. Int. Ed. 2007,
terscheid, N. T. i Spithas, B. de Bruin, Chem. Eur. J. 2009, 15, 11878–
11889.
[18] a) R. Noyori, Angew. Chem. Int. Ed. 2002, 41, 2008–2022; Angew. Chem.
2002, 114, 2108–2123; b) C. A. Sandoval, T. Ohkuma, N. Utsumi, K. Tsut-
sumi, K. Murata, R. Noyori, Chem. Asian J. 2006, 1, 102–110; c) T.
Ohkuma, N. Utsumi, K. Tsutsumi, K. Murata, C. Sandoval, R. Noyori, J.
Am. Chem. Soc. 2006, 128, 8724–8725.
[19] a) T. Liu, X. Wang, C. Hoffmann, D. L. DuBois, R. M. Bullock, Angew.
Chem. Int. Ed. 2014, 53, 5300–5304; b) T. R. Simmons, V. Artero, Angew.
Chem. Int. Ed. 2013, 52, 6143–6145; Angew. Chem. 2013, 125, 6259–
6261; c) C. S. Letko, Z. M. Heiden, T. B. Rauchfuss, S. R. Wilson, Inorg.
Chem. 2011, 50, 5558–5566.
[20] a) M. R. Kelley, J.-U. Rohde, Dalton Trans. 2014, 43, 527–537; b) J. L.
McBee, J. Escalada, T. D. Tilley, J. Am. Chem. Soc. 2009, 131, 12703–
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
11
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
46, 2578–2592; Angew. Chem. 2007, 119, 2630–2645; d) M. Besora, A.
Lledꢀs, F. Maseras, Chem. Soc. Rev. 2009, 38, 957–966.
[48] C. White, A. Yates, P. M. Maitlis, D. M. Heinekey, Inorg. Synth. 1992, 29,
228–234.
[38] a) G. J. Kubas, Chem. Rev. 2007, 107, 4152–4205; b) M. R. Dubois, D. L.
Dubois, Chem. Soc. Rev. 2009, 38, 62–72; c) M. R. Dubois, D. L. Dubois,
Acc. Chem. Res. 2009, 42, 1974–1982; d) F. Gloaguen, T. B. Rauchfuss,
Chem. Soc. Rev. 2009, 38, 100–108.
[39] a) T. M. Gilbert, F. J. Hollander, R. G. Bergman, J. Am. Chem. Soc. 1985,
107, 3508–3516; b) C. S. Letko, Z. M. Heiden, T. B. Rauchfuss, Eur. J.
Inorg. Chem. 2009, 4927–4930; c) S. M. Whittemore, J. Gallucci, J. P.
Stambuli, Organometallics 2011, 30, 5273–5277.
[40] a) R. Asatryan, Chem. Phys. Lett. 2010, 498, 263–269; b) H. Kim, G. A.
Ferguson, L. Cheng, S. A. Zygmunt, P. C. Stair, L. A. Curtiss, J. Phys.
Chem. C 2012, 116, 2927–2932; c) S. Vogt-Geisse, A. Toro-Labbꢂ, J.
Chem. Phys. 2009, 130, 244308; d) R. K. Joshi, M. Yoshimura, K. Tanaka,
K. Ueda, A. Kumar, N. Ramgir, J. Phys. Chem. C 2008, 112, 13901–13904.
[41] E. Sola, A. Garcꢁa-Camprubꢁ, J. L. Andrꢂs, M. Martꢁn, P. Plou, J. Am. Chem.
Soc. 2010, 132, 9111–9121.
[49] M. Brookhart, B. Grant, A. F. Volpe, Organometallics 1992, 11, 3920–
3922.
[50] Gaussian 09 (Revision B.01), M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2010.
[42] See Section II of the Supporting Information for full details for these ex-
periments
[51] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[43] D. R. Anton, R. H. Crabtree, Organometallics 1983, 2, 855–859.
[44] a) N. M. Weliange, E. Szuromi, P. R. Sharp, J. Am. Chem. Soc. 2009, 131,
8736–8737; b) M. Findlater, W. H. Bernskoetter, M. Brookhart, J. Am.
Chem. Soc. 2010, 132, 4534–4535.
[52] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[53] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299–310.
[54] W. J. Hehre, R. Ditchfield, J. A. Pople, J. Phys. Chem. 1972, 56, 2257–
2261.
[45] See, for example: a) M. Gꢀmez-Gallego, M. A. Sierra, Chem. Rev. 2011,
111, 4857–4963; b) G. Parkin, J. Labelled Compd. Radiopharm. 2007, 50,
1088–1114; c) K. E. Janak in Comprehensive Organometallic Chemistry,
3rd ed. (Eds.: D. M. P. Mingos, R. H. Crabtree), Elsevier, Amsterdam, 2007,
Chap. 1.20; d) See chapter 7 of Ref. [35b]].
[55] P. C. Hariharan, J. A. Pople, Theor. Chim. Acta. 1973, 28, 213–222.
[56] M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. De-
Frees, J. A. Pople, J. Chem. Phys. 1982, 77, 3654–3665.
[57] D. Andrae, U. Haeussermann, M. Dolg, H. Stoll, H. Preuss, Theor. Chem.
Acc. 1990, 77, 123–141.
[46] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215–241.
[47] No transition state was located that connects the two conformers at
this level of theory, however previous calculations based on the simpli-
fied model Cp·1b+ predict a low energy barrier of 12.0 kcalmolꢀ1 for
this transformation.
[58] A. E. Reed, L. A. Curtis, F. Weinhold, Chem. Rev. 1988, 88, 899–926.
Received: September 19, 2014
Published online on && &&, 0000
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FULL PAPER
&
Isomerisation
A. Zamorano, N. Rendꢀn,
J. Lꢀpez-Serrano, J. E. V. Valpuesta,
E. ꢁlvarez, E. Carmona*
&& – &&
Aminopyridinate (Ap) complexes of
composition [Ir(Ap)(h5-C5Me5)]+ exist in
the form of two isomers 1a+–1d+ and
2a+–2d+ that equilibrate in the pres-
ence of H2 by means of a reversible pro-
totropic rearrangement within the Ap
ligand. The isomerisation reaction is cat-
alysed by dihydrogen and implies rever-
sible formation and cleavage of HꢀH,
CꢀH and NꢀH bonds.
Dihydrogen Catalysis of the Reversible
Formation and Cleavage of CꢀH and
NꢀH Bonds of Aminopyridinate
Ligands Bound to (h5-C5Me5)IrIII
Chem. Eur. J. 2014, 20, 1 – 13
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These are not the final page numbers! ÞÞ