Efficient hydridoirida-β-diketone-catalyzed hydrolysis of ammonia- or amine-boranes for hydrogen generation in air

Article abstract of DOI:10.1039/c3dt51261d

The dihydridoirida-β-diketone [IrH₂{(PPh ₂(o-C₆H₄CO))₂H}] (2) has been used as a homogeneous catalyst for the hydrolysis of ammonia- or amine-boranes to generate up to 3 equivalents of hydrogen in the presence of air. When using 0.5 mol% loading of 2, dimethylamine-borane is hydrolysed completely within 8 min at 30 °C and maintains its activity in consecutive runs. Ammonia-borane or tert-butylamine-borane is hydrolysed completely within 32 or 25 min respectively. Triethylamine-borane fails to be hydrolysed. Kinetic studies suggest a sequence of two consecutive first-order reactions, in which an intermediate builds up and finally falls, with the first step being the rate controlling step. ΔH?1 are in the range 65-85 kJ mol^-1 and negative values of ΔS?1 are obtained. A multinuclear NMR study of the catalyzed reaction shows the formation of a resting state (A) of the active catalyst proposed to be of the hydridodiacyl type [IrH(PPh ₂(o-C₆H₄CO))₂(solvent)] with a hydride trans to the acyl group. In the absence of substrate a dormant species (B) is formed. By the reaction of hydridoirida-β-diketones with ammonia, the hydridoirida-β-ketoimine [IrHCl{(PPh₂(o-C₆H ₄CO))(PPh₂(o-C₆H₄CNH))H}] (3) and the hydridobis(acylphosphane)aminoiridium(iii) complex [IrH(PPh ₂(o-C₆H₄CO))₂(NH₃)] (4), with a hydride trans to phosphane, are formed. Aromatic amines such as aniline or anisidines afford cationic [IrH{(PPh₂(o-C₆H ₄CO))₂H}(C₆H₄RNH₂)] ClO₄ (R = H (6); p-MeO (7); o-MeO (8)) hydridoirida-β-diketones with a coordinated amine group trans to the hydride. The dormant species B is proposed to be of the hydridobis(acylphosphine)aminoiridium(iii) type with a hydride trans to the amine group.

Full text of DOI:10.1039/c3dt51261d

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Efficient hydridoirida-β-diketone-catalyzed hydrolysis
of ammonia- or amine-boranes for hydrogen
generation in air†
Cite this: Dalton Trans., 2013, 42, 11652
María A. Garralda,*a Claudio Mendicute-Fierro,a Antonio Rodríguez-Diéguez,b
José M. Seco,a Carlos Ubidea and Itziar Zumetaa
The dihydridoirida-β-diketone [IrH2{(PPh2(o-C6H4CO))2H}] (2) has been used as a homogeneous catalyst
for the hydrolysis of ammonia- or amine-boranes to generate up to 3 equivalents of hydrogen in the
presence of air. When using 0.5 mol% loading of 2, dimethylamine-borane is hydrolysed completely
within 8 min at 30 °C and maintains its activity in consecutive runs. Ammonia-borane or tert-butylamine-
borane is hydrolysed completely within 32 or 25 min respectively. Triethylamine-borane fails to be hydro-
lysed. Kinetic studies suggest a sequence of two consecutive first-order reactions, in which an intermedi-
ate builds up and finally falls, with the first step being the rate controlling step. ΔH‡1 are in the range
65–85 kJ mol−1 and negative values of ΔS‡1 are obtained. A multinuclear NMR study of the catalyzed reac-
tion shows the formation of a resting state (A) of the active catalyst proposed to be of the hydridodiacyl
type [IrH(PPh2(o-C6H4CO))2(solvent)] with a hydride trans to the acyl group. In the absence of substrate a
dormant species (B) is formed. By the reaction of hydridoirida-β-diketones with ammonia, the hydrido-
irida-β-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH))H}] (3) and the hydridobis(acylphosphane)
aminoiridium(III) complex [IrH(PPh2(o-C6H4CO))2(NH3)] (4), with a hydride trans to phosphane, are
formed. Aromatic amines such as aniline or anisidines afford cationic [IrH{(PPh2(o-C6H4CO))2H}-
(C6H4RNH2)]ClO4 (R = H (6); p-MeO (7); o-MeO (8)) hydridoirida-β-diketones with a coordinated amine
group trans to the hydride. The dormant species B is proposed to be of the hydridobis(acylphosphine)-
aminoiridium(III) type with a hydride trans to the amine group.
Received 14th May 2013,
Accepted 30th June 2013
DOI: 10.1039/c3dt51261d
www.rsc.org/dalton
to now the most efficient catalysts. Several mechanisms have
Introduction
been suggested for this reaction. Ir-pincer11 and PNP-Ru10b
The catalysed dehydrogenation of ammonia- or amine-boranes complexes have been proposed to promote the cleavage of a
for hydrogen production, promoted by transition-metal cata- N–H and a B–H bond to afford hydrogen in a concerted
lysts under mild reaction conditions, has been the subject of fashion. Amidohydrido-Ru species, generated “in situ” from
recent intensive research.1 Ammonia-borane (AB) is a chemical PN-Ru complexes, may undergo an outer sphere hydrogen
hydrogen storage material with high hydrogen content, 19.6 transfer mechanism, involving amido protonation by the
weight%, is thermally and water stable at room temperature amino group of ammonia-borane followed by coordination of
and is considered to be a potential hydrogen source for porta- the resulting H3B–NH2 fragment via a hydrogen atom of the
ble fuel cells.2 The homogeneous dehydrocoupling of BH3 moiety.10a Ti-cyclopentadienyl complexes initially coordi-
ammonia- or amine-boranes catalysed by complexes of Ir,3 Ti nate a Me2NH–BH3 adduct to the Ti center via a hydrogen
or Zr,4 Rh,5 Cr,6 Re,7 Pd,8 heterobimetallic Zr–Ru,9 or Ru10 atom of the BH3 group followed by nitrogen-to-titanium hydro-
may afford up to one equivalent of hydrogen gas under an gen transfer.12 η2-Amine-borane σ-complexes have been pro-
inert atmosphere. PN- and PNP-ruthenium complexes are up posed as models for intermediate species and also as catalysts
in the dehydrogenation of amine-boranes with cationic phos-
phane rhodium complexes.13 Dehydrogenation of AB under
aFacultad de Química de San Sebastián, Universidad del País Vasco, UPV/EHU,
argon by a carbene-Ni complex affords more than two equiva-
14
Apdo. 1072, 20080 San Sebastián, Spain
bFacultad de Ciencias, Universidad de Granada, Avda. Fuenteventura s/n, 18071
lents of H2 via a H–B σ-complex-like structure
and cationic
Pd complexes release two equivalents of H2, with most of the
Granada, Spain. E-mail: mariaangeles.garralda@ehu.es
†CCDC 938743. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt51261d
hydrogen atoms obtained from the boron atom of AB.15 More
recently,
a
boron-pendant ruthenium complex has been
11652 | Dalton Trans., 2013, 42, 11652–11660
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
reported to efficiently afford up to two equivalents of H2 from
AB, under air.16
Hydrolysis reactions provide an additional method of H2
release from ammonia- or amine-boranes and can afford up to
three equivalents of hydrogen per mole of starting material.
The hydrolysis of AB to produce H2 under mild reaction con-
ditions is catalysed by the first row transition metals, sup-
ported or as nanoparticles.17 Efficient water/air-stable Ni, Pd,
Rh or Au nanoparticles have been reported recently.18 Other
noble-metal heterogeneous systems, which often require an
inert atmosphere, also allow fast H2 release from AB at room
temperature.19 Plausible mechanisms considered to account
for the heterogeneously catalysed hydrolysis of NH3BH3
include the establishment of interactions between the AB
molecule and the metal particle surface to form activated
complex species, to which attack by a H2O molecule readily
leads to concerted dissociation of the B–N bond and hydrolysis
of the resulting BH3 intermediate.17a The involvement of
boron-to-metal hydrogen transfer to form a transient M–H
bond similar to that proposed in the metal-catalysed boro-
hydride hydrolysis has also been suggested.17d More recently,
sequential dehydrogenation of H3N–BH3−n(OH)n (n = 0–2) and
hydrolysis of H2N = BH2−n(OH)n (n = 0–2) has been proposed
to account for the hydrolysis of AB catalysed by rhodium
nanoparticles.18d
Fig. 1 Experimental results of hydrogen release from AB using 0.5 mol% of 2
as a catalyst in THF–H2O mixtures.
The efficient homogeneous version of this catalysed hydro-
lysis reaction has been reported very recently using a hydrido-
irida-β-diketone,20
hydrido-PNP-iridium
complexes,21
coordinatively unsaturated Ir-carbene derivatives,22 or
dicarbonylruthenacyclic compounds.23 The latter also promotes
the anhydrous release of hydrogen, though at a much lower
rate. Following our preliminary communication on the cata-
lytic activity of the hydridoirida-β-diketone [IrHCl{(PPh2-
(o-C6H4CO))2H}] (1),20 we report now on the ability of the dihydri-
doirida-β-diketone [IrH2{(PPh2(o-C6H4CO))2H}] (2) (see Chart 1)
to catalyze the ammonia- or amine-borane hydrolysis to
produce hydrogen, including studies on mechanistic aspects
of the reaction.
Fig. 2 Hydrogen release from amine-boranes using 0.5 mol% of 2 as a catalyst
○
△
□
◊
in THF–H2O mixtures: MAB ( ), TBAB ( ), DMAB ( ) or TEAB ( ). Open marks
represent the experimental points. Solid lines represent the simulated
behaviour.
RR′HN–BH3 þ 4H2O ! RR′NH2þ þ BðOHÞ3 þ OHꢀ þ 3H2 ð1Þ
Results and discussion
A THF–H2O = 3 : 1 ratio was found to be optimal to attain
the maximum hydrogen release rate, due to low solubility of
the catalyst. Performing these reactions with higher amounts
of water led to precipitation of 2. In the presence of Hg similar
results were obtained, confirming the homogeneous nature of
the catalytic reaction.19d As shown in Fig. 1, when using an
initial AB concentration of 0.46 M and a 0.5 mol% catalyst
loading at 30 °C, complex 2 affords all 3.0 equivalents of H2
Complex 2 is an efficient homogeneous catalyst for hydrogen
generation from hydrolysis of ammonia- or amine-boranes in
THF–H2O mixtures, under mild temperatures, in the presence
of air, and releases up to three equivalents of hydrogen per
mole of borane adduct that is 100% of the maximum hydrogen
content that can be produced, according to eqn (1).
within 32 min, with a TOF of 4100 h−1 24
Hydrogen evolution
.
from amine-borane adducts containing primary amines shows
slightly lower TOF values of 2400 and 2900 h−1 for methyl-
amine-borane (MAB) and tert-butylamine-borane (TBAB)
respectively. While TBAB affords all 3 equivalents of hydrogen,
MAB affords up to 2.3 equivalents of H2, 77% of the maximum
hydrogen content that can be produced (Fig. 2). With an initial
Chart 1
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 11652–11660 | 11653

View Article Online
Paper
Dalton Transactions
substrate concentration of 0.46 M, dimethylamine-borane an intermediate (I) builds up and finally falls, such as
k1
k2
(DMAB) is hydrolysed completely within 8 min, with the S ꢀ! I ꢀ! P; where the products (P) include the catalyst in its
highest TOF of 6100 h−1, when using a 0.5 mol% loading of 2 active form. The intermediate (I) could be formed by inter-
(Fig. 2). After completion of the catalytic reactions the 11B{1H} action of the amine-borane with the iridium active species and
NMR spectra of the remaining solutions contain only singlets most likely would involve interactions with the BH3 and/or the
in the 16–20 ppm range, which indicates the transformation of NH fragments. Iridium hydride complexes with ammonia- or
the borane adducts into borate species.19b,c,22 In contrast to amine-borane adducts coordinated to iridium via the borane
this behaviour, complex 2 shows very low activity to hydrolyse fragment are known.3,26 Furthermore, triethylamine-borane,
the triethylamine-borane (TEAB) adduct (Fig. 2). This obser- lacking an NH bond, fails to undergo the hydrolysis reaction
vation suggests that suitable catalytic activity requires the pres- and the fastest reaction occurs with DMAB, containing a single
ence of an NH functionality in the amine-borane substrate. NH bond. Cleavage of the B–N bond and hydrolysis of the lib-
A blank test, under the same experimental conditions but erated borane would then render the reaction products, includ-
in the absence of 2, shows that the hydrolysis of AB is extre- ing three equivalents of hydrogen and the catalyst in a form
mely poor, affording only 5% of the maximum hydrogen ready to enter a new cycle. This sequence is in line with that
content after 30 min. MAB or DMAB afford up to 6% or 3% of suggested for the solvolysis of AB with Ir(III)–NHC complexes.22
the maximum hydrogen content and TBAB is not hydrolysed The concentration of hydrogen at any time is given by
at all.
Kinetic studies on the hydrolysis of all the substrates have
eqn (2):27
ꢀ
ꢁ
1
been performed. Fig. 1 and 2 show the experimental profiles
of hydrogen evolution along time in every case. The gas evolu-
tion shown in Fig. 2 for substrates (S) MAB, TBAB and DMAB
exhibits s-shaped profiles. These kinds of profiles have also
been observed in DMAB dehydrocoupling, catalysed by the [Rh-
(PCy3)2]+ fragment, or in DMAB hydrolysis, catalysed by Rh or
Ru nanoparticles, and have been attributed to autocata-
lysis.18d,19e,25 In the present case autocatalysis does not seem to
be involved; in fact, when the leftover solution of a completed
reaction was used as the solvent for the next, the original
profile was approximately reproduced. The reusability test in
the H2 release from Me2HNBH3 with 2 (Fig. 3) shows that after
3 runs the system is still remarkably active.
ðk2eꢀk t ꢀ k1eꢀk t
Þ
ð2Þ
1
2
½H2ꢁt ¼ 3½Substrateꢁ0 1 ꢀ
k2 ꢀ k1
When the experimental points are fitted to eqn (2) by non-
linear least-squares regression, the values of the rate constants,
k1 and k2, can be obtained (Table 1). Because no NMR signal
has been found for the intermediates (vide infra) we conclude
that I must be a labile species and its concentrations will be
low, so that the first step (k1) will be the rate controlling step,
whereas the second step (k2) will be faster, making impossible
the accumulation of the intermediate to a great extent. Simu-
lated kinetic profiles have been obtained and are represented
in Fig. 2. Good agreement can be observed in every case,
showing that the proposed sequence adequately explains the
kinetics of the hydrolysis of amine-boranes. The values of k1
and k2 can be used to characterize the evolution of the chemi-
cal system. However, the experimental results corresponding
to AB (Fig. 1) do not show a well-defined kinetic behaviour,
and no kinetic model is proposed for this substrate. The
kinetic profile initially follows a pattern similar to that
observed for the other substrates and a similar mechanism
could be proposed during a certain period of time, but after-
wards this pattern is disturbed, so that some extra complexity
in the reaction kinetics can be expected.
The experimental data of Fig. 2 can be explained by a
sequence of two consecutive first-order reactions, in which
The effect of the temperature on the rate constants was
approached by the Eyring equation in order to calculate the
activation parameters. The results obtained are also given in
Table 1. The values of the standard enthalpy of activation for
Table 1 Rate constants (30 °C) and activation parameters standard deviation,
for the hydrolysis of amine-boranes with [IrH2{(PPh2(o-C6H4CO))2H}] (0.5 mol%)
and THF–H2O = 3 : 1 ratio
ΔH‡1/
ΔS‡1/
Substrate
103k1/s−1
103k2/s−1 kJ mol−1 J mol−1 K−1
Fig. 3 Three consecutive runs of hydrogen release from Me2HNBH3 using
0.5 mol% of 2 as a catalyst in THF–H2O mixtures. Open marks represent experi-
mental points; solid lines represent the simulated behaviour.
MeH2N–BH3 (MAB)
t-BuH2N–BH3 (TBAB) 1.80 0.03 52 10
Me2HN–BH3 (DMAB) 4.80 0.03 21
1.50 0.03 80 40
79
83
68
3
6
8
–36
–22
–62 11
2
2
4
11654 | Dalton Trans., 2013, 42, 11652–11660
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
k1, ΔH‡1, between 65 and 85 kJ mol−1, are lower for the sub- observed, which rapidly disappears. The appearance of a
strate releasing hydrogen faster, DMAB. Negative values for triplet at δ = –9.07 ppm (2J(P,H) = 13.2 Hz), due to coupling to
1
ΔS‡1 were obtained, showing that the molecular disorder is two phosphorus atoms as indicated by H{31P} NMR, suggests
lower in the intermediates. The values of ΔH‡2 (for k2) are not the formation of an iridium species (A) containing a hydride
included in Table 1 because changes of k2 with temperature trans to the carbon atom of an acyl group and cis to two phos-
are small and low enthalpies with high uncertainty values are phorus atoms. In accordance with this observation the 31P{1H}
found, making the numerical values of ΔH‡2 meaningless. The NMR spectra show two resonances at δ = 7.2 (s) and 6.4 (s)
effect of the temperature in the case of AB cannot be quanti- ppm, which remain unaltered during the hydrolysis and corres-
fied in the same way, but a similar behaviour has been pond to the two phosphorus atoms mutually cis of A, as
observed.
confirmed by selective phosphorus decoupled 1H NMR
To obtain information on the course of the catalytic reac- experiments. These resonances appear as singlets due to un-
tion, a multinuclear NMR study of the catalytic hydrolysis of observable coupling constants. On completion of the catalytic
these borane adducts in a THF-d8–D2O mixture was carried reaction, complete transformation of A into a new species B
1
out. With all four substrates the H and 31P{1H} NMR spectra occurs. Opening of the tube allows a faster transformation and
show the evolution of hydrogen and the formation of new loss of hydrogen. According to the spectroscopic features
iridium species. The 11B{1H} NMR spectra show the disappear- species B contains two equivalent phosphorus atoms (δ31P
ance of the substrate at higher fields (−25 to −15 ppm) and {1H}, 21.2 (s) ppm) cis to a hydride trans to an electronegative
the increasing formation of borates (16–20 ppm). Borane inter- atom that could be nitrogen (δ1H −21.31 (t) ppm, 2J(P,H) =
1
mediates could not be observed. Fig. 4 represents the H and 17.5 Hz). A new addition of a THF-d8–D2O solution of AB to
the 31P{1H} NMR spectra of the catalytic hydrolysis of NH3BH3 the NMR tube restarts the hydrogen evolution and the immedi-
with 2. The 1H NMR spectra indicate the gradual disappear- ate transformation of B into A. From these observations we
ance of the quartet centred at δ = 1.37 ppm (1J(B,H) = 92 Hz) conclude that B is a dormant species and A a resting state of
due to AB and the formation of HD at δ = 4.52 (t) ppm (1J(D,H) the active catalyst. Attempts to obtain species B proved unsuc-
= 43 Hz) and of H2 at δ = 4.55 (s) ppm. The appearance of H2 is cessful. Species A and B have also been observed in our pre-
due to the unavoidable presence of light water vapor in heavy viously reported hydrolysis of AB with [IrHCl{(PPh2-
water in contact with air, and to the isotopic effect making the (o-C6H4CO))2H}] (1).20 Species A is also the resting state in the
reaction with H2O faster than with D2O.28 The amount of H2 hydrolysis of amine-boranes with complex 2 as the catalyst
decreases relative to HD while the reaction progresses. In the while species B is not observed when performing the hydro-
first spectrum a residual amount of 2 (δ = –8.69 ppm) is lysis of amine-boranes. Nevertheless, as confirmed in the
Fig. 4 1H- and 31P{1H} NMR spectra of the “in situ” catalytic AB hydrolysis showing the gradual disappearance of NH3BH3
) and HD ( ),
●
(
□
▲
( ), the evolution of H2
■
the disappearance of the precursor 2 ( ) and the formation of the resting state (A) and of the dormant species (B).
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 11652–11660 | 11655

View Article Online
Paper
Dalton Transactions
reusability test previously described, when using DMAB the
hydrogen evolution may also be restarted by addition of a new
amount of substrate.
We have performed some stoichiometric reactions to gain
insight into the nature of A and B. Ammonia or amines can be
present in the basic solutions and we have shown previously
that the hydridoirida-β-diketone [IrHCl{(PPh2(o-C6H4CO))2H}]
(1) reacts with primary aliphatic amines in dry THF to afford
Scheme 2 L = C6H5NH2, 6; p-MeOC6H4NH2, 7; o-MeOC6H4NH2, 8.
hydridoirida-β-ketoimines
[IrHCl{(PPh2(o-C6H4CO))(PPh2-
(o-C6H4CNR))H}] (3), with a hydride trans to the chlorine atom,
or hydridoaminodiacyl complexes [IrH(PPh2(o-C6H4CO))2(RR′
NH)] (4), with a hydride trans to the phosphorus atom, if the presence of KOH. In contrast to this behaviour, complexes 1
reaction is performed in THF–H2O mixtures. The reaction with and 2 fail to react with less basic aromatic primary amines
secondary amines led to hydridoaminodiacyl complexes 4, and such as aniline.
the tertiary amine NEt3 fails to coordinate to iridium.20,29 We
Neither 3-NH2 nor 4-NH3 show spectroscopic features
find now that ammonia behaves as aliphatic primary amines similar to species A or B observed in the catalytic reaction.
do towards 1 as shown in Scheme 1. In dry THF the hydridoirida- Trying to disclose the nature of these species we studied the
β-ketoimine
[IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH))H}] reaction of the known hydridoirida-β-diketone [IrH(OClO3)-
(3-NH2), stabilized by an intramolecular hydrogen bond {(PPh2(o-C6H4CO))2H}] (5)30 with ammonia or amines. The
between the keto and the enamine moieties, is obtained. reaction with aliphatic amines or with ammonia led to the
Complex 3-NH2 was fully characterised spectroscopically. It hydridodiacylamino complexes 4. Contrarily, the reaction of 5
contains non-equivalent cis phosphorus atoms trans to acyl or with the aromatic amine aniline, less nucleophilic, led to dis-
imino groups as shown by the doublets at 258.3 and placement of the coordinated perchlorate and formation of
222.3 ppm (2J(P,C) of 106 and 103 Hz respectively) observed in
a new cationic hydridoirida-β-diketone with coordinated
the 13C{1H} NMR spectrum. The 1H NMR spectrum shows a amine [IrH{(PPh2(o-C6H4CO))2H}(C6H5NH2)]ClO4 (6), shown in
hydride resonance in the high field region, at −20.40 ppm, as Scheme 2, as confirmed by NMR measurements. The acylphos-
a triplet due to 2J(P,H) of 14.3 Hz, which agrees with the phine groups are equivalent as shown by the appearance of a
hydride being trans to chlorine and cis to two phosphanes, and singlet at 27.7 ppm in the 31P{1H} NMR spectrum and
a low field singlet at 14.31 ppm that supports the presence of a doublet at 256.2 ppm (J(P,C) = 96 Hz) in the 13C{1H} NMR
fairly strong N⋯H⋯O hydrogen bonds and the existence of an spectrum. The 1H NMR spectrum shows a triplet for the
irida-β-ketoimine. The reaction of 1 with NH3 in THF–H2O = hydride, trans to nitrogen, at −19.84 ppm with a J(P,H) of
1/1 affords the hydridodiacylamino complex [IrH(PPh2- 14.3 Hz, along with a sharp resonance due to the O⋯H⋯O
(o-C6H4CO))2(NH3)] (4-NH3), shown in Scheme 1(ii). Its 31P{1H} group at low field, 21.84 ppm. More basic and also
NMR spectrum shows two resonances at 30.7 and 25.2 ppm. more encumbered anisidines such as p-MeOC6H4NH2 or
The 13C{1H} NMR spectrum shows a doublet at 243.0 (2J(P,C) o-MeOC6H4NH2 afford similar cationic hydridoirida-β-
of 102 Hz) and a singlet at 214.0 ppm respectively due to acyl diketones (7–8) that show similar spectroscopic features to those
groups trans or cis to phosphorus atoms and the 1H NMR spec- of 6, identical hydride chemical shifts and δ31P in the 26–29 ppm
trum shows a hydride resonance in the high field region, at range. We find now that complexes 6–8 show similar spectro-
−8.20 ppm, as a doublet of doublets due to a 2J(P,H)trans of scopic features to those of species B, especially as refers to the
2
128.5 Hz and a J(P,H)cis of 18.5 Hz. Complexes such as 4 are hydride chemical shift that agrees with a hydride trans to the
also formed by the reaction of 2 with aliphatic amines in the nitrogen atom.
An X-ray study was performed on complex 6. Its structure
consists of cationic mononuclear units [IrH(NH2C6H5)-
{(PPh2(o-C6H4CO))2H}]+, ClO4 anions and crystallization
−
dichloromethane solvent. An ORTEP perspective view is shown
in Fig. 5. The single-crystal X-ray structure of 6 reveals that the
iridium atom lies in a distorted octahedral environment
formed by the two phosphorus donors in cis positions, two
carbon atoms pertaining to the acyl groups, one nitrogen atom
of the phenylamine ligand and a hydride trans to the nitrogen
atom. The equatorial plane P1,P2,C1,C20 almost includes the
iridium atom, which deviates by 0.116 Å. The two Ir–P bond
distances are comparable (2.3387(10) and 2.362(9) Å), and the
distortion of the iridium coordination polyhedron stems
mainly from the P1–Ir1–P2 angle (104.59(3)°), distorted due to
Scheme 1 (i) NH3, dry THF; (ii) NH3, THF–H2O.
11656 | Dalton Trans., 2013, 42, 11652–11660
steric repulsion between the diphenylphosphane moieties. The
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
Scheme 3
type with a hydride trans to the amine group as shown in
Scheme 3.
Fig. 5 Asymmetric unit of the cation in 6. Thermal ellipsoids are drawn at the
50% probability level. The hydrogen atoms, except H1 and H2, the labels of
some C atoms, the perchlorate anion and the solvent molecule have been
omitted for clarity. Selected bond lengths (Å) and angles (°): Ir1–P1, 2.3622(9);
Ir1–P2, 2.3387(10); Ir1–C1, 2.048(4); Ir1–C20, 2.042(3); Ir1–N1, 2.242(3); Ir1–H1,
1.410; C1–O1, 1.279(4); C20–O2, 1.265(4); O2⋯O1, 2.407(4); C1–Ir1–C20,
90.67(15); C1–Ir1–P1, 82.05(10); C20–Ir1–P1, 170.49(10); C1–Ir1–P2, 171.03(10);
C20–Ir1–P2, 82.04(11); P1–Ir1–P2, 104.59(3); N1–Ir1–H1, 178.49; O1–H2–
O2, 174.01.
Conclusions
The dihydridoirida-β-diketone [IrH2{(PPh2(o-C6H4CO))2H}] is
an efficient and robust homogeneous catalyst for the hydro-
lysis of ammonia- or amine-borane adducts in air to produce
hydrogen. The reaction is proposed to proceed by a sequence
of two consecutive first-order reactions, in which an inter-
mediate, formed by interaction of the BH3 and/or the NH
fragments of the substrate with the iridium active species,
allows the cleavage of the B–N bond and the hydrolysis of
the liberated borane. A resting state of the catalyst and a
dormant species are proposed to be of the hydridodiacyl type
with a hydride trans to the acyl group and of the hydrido-
diacylamino type with a hydride trans to the amine group,
respectively.
Ir–C and the C–O distances comprising the chelate ligands
are in the expected ranges. The C–O distances, 1.265(4) and
1.279(4) Å, are in accord with elongated double bonds and
agree with those reported for other metalla-β-diketones.29,30
The Ir–N distance is similar to those found for complexes in
which the hydride and the nitrogen atom are in trans posi-
tions.31,32 Around the iridium atom, cis and trans angle values
are in the ranges 82.04(11)–104.59(3)° and 170.49(10)–178.49°.
A short distance between O1 and O2 (2.407(4) Å) is observed,
in accordance with a strong hydrogen bond interaction,30,33
and the O1–H2–O2 angle (174.01°) is consistent with a nearly
Experimental section
General procedures
linear O⋯H⋯O bridge. This hydrogen bond is responsible for All reagents were purchased from commercial sources and
the coplanarity of the two aromatic rings pertaining to the acyl used without further purification. The hydridoirida-
groups and the reason why the iridium atom is almost β-diketones [IrHX{(PPh2(o-C6H4CO))2H}] (X = Cl (1); H (2); OClO3
included in the equatorial P1,P2,C1,C20 plane. As expected the (5)) were prepared as previously reported.29,30 The preparation
metallocycle IrC1C2C3P1 and the phenyl ring C2C3C4C5C6C7 of the metal complexes was carried out at room temperature
are practically planar, forming a dihedral angle of 7.69°. The under nitrogen by using standard Schlenk techniques.
metallocycle IrC20C21C22P1 forms a dihedral angle of 6.54° Ammonia-, tert-butylamine- and dimethylamine-borane were
with the phenyl ring C21C22C23C24C25C26, whereas the purchased and used as received. Methylamine-borane was
planes formed by the two metallocycles show a dihedral angle prepared according to literature methods.10a Microanalyses
of 6.15°.
were carried out with a Leco CHNS-932 microanalyser. Con-
On account of the catalytic and stoichiometric observations ductivities were measured in acetone solution with a Metrohm
we propose that A, the resting state of the catalyst, is of the 712 conductimeter. IR spectra were recorded with a Nicolet
hydridodiacyl type and can be unsaturated or saturated with FTIR 6700 spectrophotometer in the range 4000–400 cm−1
1
solvent (S). A is stable only in the presence of substrate, which using KBr pellets. NMR spectra, H and 13C{1H} (TMS internal
most likely undergoes cleavage of the B–N bond and hydrolysis standard), 31P{1H} and 31P (H3PO4 external standard) and
of the borane fragment to produce hydrogen. Upon disappear- 11B{1H} (BF3·OEt2 external standard) were recorded with Bruker
ance of the substrate, A transforms into a dormant species B, Avance DPX 300 or Bruker Avance 500 spectrometers.
which is suitable to reform A upon addition of the corres-
Warning! Perchlorate salts and perchlorate transition metal
ponding borane adduct. The presence of free amine is feasible; complexes may be explosive. Preparations at a larger scale than
therefore B is proposed to be of the hydridodiacylamino that reported herein should be avoided.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 11652–11660 | 11657

View Article Online
Paper
Dalton Transactions
Dehydrogenation of RR′R″N–BH3 with complex 2
(CDCl3): δ 27.7 (s). 13C{1H}NMR (CDCl3): δ 256.2 (d, 2J(P,C) =
96 Hz, IrCvO). Data for 7. Yield: 26.7 mg, 79%. ΛM (ohm−1 cm−2
mol−1): 132 (acetone). IR (cm−1): 3309 (w), 3055 (w), ν(NH);
2204 (m), ν(IrH); 1618 (s), ν(CvO). Anal. calc. for C45H39ClIr-
NO7P2: C, 54.30; H, 3.96; N, 1.41; found: C, 54.91; H, 3.82; N,
1.78. 1H NMR (CDCl3): δ 21.89 (s, 1H, O⋯H⋯O); 3.89 (s, br,
2H, NH); −19.84 (t, 1H, 2J(P,H) = 14.6 Hz, IrH). 31P{1H}NMR
(CDCl3): δ 26.9 (s). 13C{1H}NMR (CDCl3): δ 255.9 (d, 2J(P,C) =
97 Hz, IrCvO). Data for 8. Yield: 23 mg, 68%. ΛM (ohm−1
cm−2 mol−1): 117 (acetone). IR (cm−1): 3309 (w), 3055 (w),
ν(NH); 2163 (m), ν(IrH); 1615 (s), ν(CvO). Anal. calc. for
C45H39ClIrNO7P2·0.5CH2Cl2: C, 52.65; H, 3.88; N, 1.35; found:
C, 52.40; H, 3.46; N, 1.33. 1H NMR (CDCl3): δ 21.49 (s, 1H,
O⋯H⋯O); 3.37 (s, br, 2H, NH); −19.65 (t, 1H, 2J(P,H) =
14.1 Hz, IrH). 31P{1H}NMR (CDCl3): δ 28.7 (s). 13C{1H}NMR
(CDCl3): δ 255.7 (d, 2J(P,C) = 95 Hz, IrCvO).
A typical dehydrogenation experiment is described here for the
hydrolysis of H3N–BH3 using THF–H2O = 3 : 1 mixtures and
0.5 mol% catalyst loading: a solution of 42.5 mg (1.38 mmol)
of H3N–BH3 in 0.75 ml of H2O was prepared in a round
bottom 40 ml flask fitted with a gas outlet and with a side arm
sealed with a tight-fitting septum cap. The flask was connected
via the gas outlet to a water-filled gas burette. The solution was
warmed to the required temperature and allowed to equilibrate
for at least 10 minutes. A warmed solution of 5.3 mg
(0.007 mmol) of 2 in 2.25 ml of dry THF was then syringed
through the septum, magnetic stirring was performed and
timing started. Gas evolution began immediately and the
amount of gas evolved was determined periodically by measur-
ing the displacement of water in the burette. Volumes were
measured at atmospheric pressure in the 25–45 °C range.
X-Ray data collection and structure refinement
Preparation of [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH))H}]
(3-NH2)
Suitable crystals of 6 were mounted on a glass fiber and used
for data collection. Data were collected with a Bruker AXS
APEX CCD area detector equipped with graphite monochro-
mated Mo Kα radiation (λ = 0.71073 Å) by applying the ω-scan
method. The data were processed with APEX234 and corrected
for absorption using SADABS.35 The structures were solved by
direct methods using SIR97,36 revealing the positions of all
non-hydrogen atoms. These atoms were refined on F2 by a full
matrix least-squares procedure using anisotropic displacement
parameters. All hydrogen atoms were located in difference
Fourier maps and included as fixed contributions riding on
attached atoms with isotropic thermal displacement para-
meters 1.2 times those of the respective atom. Final R(F),
wR(F2) and goodness of fit agreement factors, details on the
data collection and analysis can be found in Table 2. Crystallo-
graphic data (excluding structure factors) for the reported
structure have been deposited with the Cambridge
To a THF solution of 1 (40 mg, 0.049 mmol) was added 2.0 M
NH3 solution in THF (2.5 ml, 5.0 mmol) whereupon a solution
was obtained. Stirring for 24 h and evaporation of the solvent
gave a yellow solid that was washed with diethyl ether and
vacuum dried. Yield: 22.5 mg, 56%. IR (cm−1): 2193 (m),
ν(IrH); 1584 (s), 1571 (s), ν(CvO) and ν(CvN). Anal. calc. for
C38H31ClIrNOP2: C 56.54, H 3.87, N 1.73; found: C 56.27, H
4.36, N 1.59. 1H NMR (CDCl3): δ 14.31 (s, 1H, N⋯H⋯O);
−20.40 (t, 1H, J(P,H) = 14.3 Hz, IrH). 31P{1H}NMR (CDCl3): δ
2
30.7 (s); 19.3 (s). 13C{1H}NMR (CDCl3): δ 258.3 (d, 2J(P,C) =
106 Hz, IrCvO); 222.3 (d, 2J(P,C) = 103 Hz, IrCvN).
Preparation of [IrH(PPh2(o-C6H4CO))2(NH3)] (4-NH3)
To a THF–H2O = 1 : 1 suspension of 1 (30 mg, 0.037 mmol)
was added 2.0 M NH3 solution in THF (1.5 ml, 3.0 mmol). Stir-
ring for 1 h and decantation gave a pale yellow solid that was
washed with diethyl ether and vacuum dried. Yield: 12.3 mg,
42%. IR (cm−1): 3339 (m), 3277 (w), ν(NH); 2027 (s), ν(IrH);
1597 (s), 1562 (s), ν(CvO). Anal. calc. for C38H32IrNO2P2: C
Table 2 Crystal data and structure refinement for C45H39Cl3IrNO6P2
1
Identification code
Empirical formula
Formula weight
CCDC 938743
C45H39Cl3IrNO6P2
1050.26
57.86, H 4.09, N 1.78; found: C 58.34, H 5.58, N 1.65. H NMR
2
2
(CDCl3): −8.20 (dd, 1H, J(P,H)cis = 18.5 Hz; J(P,H)trans = 128.5
Hz, IrH). 31P{1H}NMR (CDCl3): δ 30.7 (s); 25.2 (s). 13C{1H}NMR
(CDCl3): δ 243.0 (d, 2J(P,C) = 102 Hz, IrCvO); 214.0 (s, IrCvO).
T (K)
λ (Å)
100(2)
0.71069
Crystal system
Space group
Triclinic
P1
ˉ
Preparation of [IrH{(PPh2(o-C6H4CO))2H}H2NR]ClO4
(R = C6H5, 6; R = p-MeOC6H4, 7; R = o-MeOC6H4, 8)
a/Å
b/Å
c/Å
α/°
β/°
γ/°
11.2547(15)
13.1302(18)
14.795(2)
101.098(2)
98.513(2)
99.049(2)
2082.6(5)
2
To a dichloromethane solution of 5 (30 mg, 0.034 mmol) was
added the corresponding ligand (3.1 μl, 4.7 mg or 3.9 μl
respectively, 0.034 mmol). Stirring for 30 min and evaporation
gave yellow solids that were washed with diethyl ether and
vacuum dried. Data for 6. Yield: 22 mg, 67%. ΛM (ohm−1 cm−2
mol−1): 136 (acetone). IR (cm−1): 3303 (m), 3058 (w), ν(NH);
2175 (s), ν(IrH); 1607 (s), ν(CvO). Anal. calc. for C44H37IrCl-
NO6P2: C 54.74, H 3.86, N 1.45; found: C 54.64, H 4.14, N 1.43.
1H NMR (CD2Cl2): δ 21.84 (s, 1H, O⋯H⋯O); 3.62 (s, br, 2H,
V/Å3
Z
Density (g cm−3
)
1.675
3.525
µ (mm−1
)
Unique reflections
R(int)
24 066
0.043
1.046
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R1 = 0.033, wR2 = 0.072
NH); −19.84 (t, 1H, 2J(P,H) = 14.3 Hz, IrH). 31P{1H}NMR R(F) = Σ[||Fo| − |Fc||]/Σ|Fo|. wR(F2) = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}1/2
.
11658 | Dalton Trans., 2013, 42, 11652–11660
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
Crystallographic Data Centre as supplementary publication
No. CCDC 938743.
7 Y. Jiang, O. Blacque, T. Fox, C. M. Frech and H. Berke, Organo-
metallics, 2009, 28, 5493–5504.
8 A. Rossin, G. Bottari, A. M. Lozano-Vila, M. Paneque,
M. Peruzzini, A. Rossi and F. Zanobini, Dalton Trans., 2013,
42, 3533–3541.
Acknowledgements
9 T. Miyazaki, Y. Tanabe, M. Yuki, Y. Miyake and
Y. Nishibayashi, Organometallics, 2011, 30, 2394–2404.
10 (a) N. Blaquiere, S. Diallo-Garcia, S. I. Gorelsky, D. A. Black
and K. Fagnou, J. Am. Chem. Soc., 2008, 130, 14034–14035;
(b) M. Käβ, A. Friedrich, M. Drees and S. Schneider, Angew.
Chem., Int. Ed., 2009, 48, 905–907; (c) D. F. Schreiber,
C. O’Connor, C. Grave, Y. Ortin, H. Müller-Bunz and
A. D. Phillips, ACS Catal., 2012, 2, 2505–2511.
Financial support by Ministerio de Ciencia e Innovación
(CTQ2011-24859/BQU), Universidad del País Vasco, and
Diputación Foral de Gipuzkoa is gratefully acknowledged. IZ is
grateful to Gobierno Vasco for a scholarship.
11 A. Paul and C. B. Musgrave, Angew. Chem., Int. Ed., 2007,
46, 8153–8156.
References
1 (a) T. B. Marder, Angew. Chem., Int. Ed., 2007, 46, 8116– 12 Y. Luo and K. Ohno, Organometallics, 2007, 26, 3597–
8118; (b) F. H. Stephens, V. Pons and R. T. Baker, Dalton 3600.
Trans., 2007, 2613–2626; (c) P. Wang and X. D. Kang, Dalton 13 (a) T. M. Douglas, A. B. Chaplin, A. S. Weller, X. Yang and
Trans., 2008, 5400–5413; (d) C. W. Hamilton, R. T. Baker,
A. Staubitz and I. Manners, Chem. Soc. Rev., 2009, 38, 279–
293; (e) N. C. Smythe and J. C. Gordon, Eur. J. Inorg. Chem.,
2010, 509–521; (f) A. Staubitz, A. P. M. Robertson and
M. B. Hall, J. Am. Chem. Soc., 2009, 131, 15440–15456;
(b) A. B. Chaplin and A. S. Weller, Angew. Chem., Int. Ed.,
2010, 49, 581–584; (c) R. Dellanegra, A. B. Chaplin, J. Tsim
and A. S. Weller, Chem. Commun., 2010, 46, 3092–3094.
I. Manners, Chem. Rev., 2010, 110, 4079–4124; 14 (a) R. J. Keaton, J. M. Blacquiere and R. T. Baker, J. Am.
(g) A. Staubitz, A. P. M. Robertson, M. E. Sloan and
I. Manners, Chem. Rev., 2010, 110, 4023–4078;
(h) A. B. Chaplin and A. S. Weller, Inorg. Chem., 2010, 49,
1111–1121.
2 (a) H. W. Langmi and G. S. McGrady, Coord. Chem. Rev.,
2007, 251, 925–935; (b) T. Umegaki, J. M. Yan, X. B. Zhang,
Chem. Soc., 2007, 129, 1844–1845; (b) X. Yang and
M. B. Hall, J. Am. Chem. Soc., 2008, 130, 1798–1799;
(c) P. M. Zimmerman, A. Paul, Z. Zhang and
C. B. Musgrave, Angew. Chem., Int. Ed., 2009, 48, 2201–
2205; (d) P. M. Zimmerman, A. Paul and C. B. Musgrave,
Inorg. Chem., 2009, 48, 5418–5433.
H. Shioyama, N. Kuriyama and Q. Xu, Int. J. Hydrogen 15 S. K. Kim, W. S. Han, T. J. Kim, T. Y. Kim, S. W. Nam,
Energy, 2009, 34, 2303–2311.
M. Mitoraj, L. Piekos, A. Michalak, S. J. Hwang and
3 (a) M. C. Denney, V. Pons, T. J. Hebden, D. M. Heinekey
S. O. Kang, J. Am. Chem. Soc., 2010, 132, 9954–9955.
and K. I. Goldberg, J. Am. Chem. Soc., 2006, 128, 12048– 16 B. L. Conley, D. Guess and T. J. Williams, J. Am. Chem. Soc.,
12049; (b) B. L. Dietrich, K. I. Goldberg, D. M. Heinekey, 2011, 133, 14212–14215.
T. Autrey and J. C. Linehan, Inorg. Chem., 2008, 47, 8583– 17 (a) Q. Xu and M. Chandra, J. Power Sources, 2006, 163, 364–
8585.
370; (b) J. M. Yan, X. B. Zhang, S. Han, H. Shioyama and
Q. Xu, Angew. Chem., Int. Ed., 2008, 47, 2287–2289;
(c) S. B. Kalidindi, M. Indriani and B. R. Jagirdar, Inorg.
Chem., 2008, 47, 7424–7429; (d) S. B. Kalidindi, U. Sanyal
and B. R. Jagirdar, Phys. Chem. Chem. Phys., 2008, 10,
5870–5874; (e) H. L. Jiang, T. Akita and Q. Xu, Chem.
Commun., 2011, 47, 10999–11001; (f) P. Z. Li, A. Aijaz and
Q. Xu, Angew. Chem., Int. Ed., 2012, 51, 6753–6756;
(g) M. Kaya, M. Zahmakiran, S. Özkar and M. Volkan, ACS
Appl. Mater. Interfaces, 2012, 4, 3866–3873.
4 (a) T. J. Clark, C. A. Russell and I. Manners, J. Am. Chem.
Soc., 2006, 128, 9582–9583; (b) M. E. Sloan, A. Staubitz,
T. J. Clark, C. A. Russell, G. C. Lloyd-Jones and I. Manners,
J. Am. Chem. Soc., 2010, 132, 3831–3841; (c) T. Beweries,
S. Hansen, M. Kessler, M. Klahn and U. Rosenthal, Dalton
Trans., 2011, 40, 7689–7692; (d) A. M. Chapman,
M. F. Haddow and D. F. Wass, J. Am. Chem. Soc., 2011, 133,
8826–8829; (e) H. Helten, B. Dutta, J. R. Vance, M. E. Sloan,
M. F. Haddow, S. Sproules, D. Collison, G. R. Whittell,
G. C. Lloyd-Jones and I. Manners, Angew. Chem., Int. Ed., 18 (a) J. M. Yan, X. B. Zhang, S. Han, H. Shioyama and Q. Xu,
2013, 52, 437–440.
Inorg. Chem., 2009, 48, 7389–7393; (b) Y. Li, L. Xie, Y. Li,
J. Zheng and X. Li, Chem.–Eur. J., 2009, 15, 8951–8954;
(c) J. M. Yan, X. B. Zhang, T. Akita, M. Haruta and Q. Xu,
J. Am. Chem. Soc., 2010, 132, 5326–5327; (d) M. Fetz,
R. Gerber, O. Blacque and C. M. Frech, Chem.–Eur. J., 2011,
17, 4732–4736; (e) B. Kilic, S. Sencanli and O. Metin, J. Mol.
Catal., 2012, 361–362, 104–110.
5 (a) C. A. Jaska, K. Temple, A. J. Lough and I. Manners,
J. Am. Chem. Soc., 2003, 125, 9424–9434; (b) C. A. Jaska and
I. Manners, J. Am. Chem. Soc., 2004, 126, 9776–9785;
(c) Y. Chen, J. L. Fulton, J. C. Linehan and T. Autrey, J. Am.
Chem. Soc., 2005, 127, 3254–3255; (d) M. E. Sloan,
T. J. Clark and I. Manners, Inorg. Chem., 2009, 48, 2429–
2435.
19 (a) F. Cheng, H. Ma, Y. Li and J. Chen, Inorg. Chem., 2007,
46, 788–794; (b) M. Chandra and Q. Xu, J. Power Sources,
2006, 156, 190–194; (c) M. Chandra and Q. Xu, J. Power
6 B. Bera and B. R. Jagirdar, Inorg. Chim. Acta, 2011, 372,
200–205.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 11652–11660 | 11659

View Article Online
Paper
Sources, 2007, 168, 135–142; (d) T. J. Clark, G. R. Whittell
Dalton Transactions
A. Guerri, A. Lledós, M. Peruzzini and F. Zanobini,
Eur. J. Inorg. Chem., 2009, 3055–3059; (g) T. J. Hebden,
M. C. Denney, V. Pons, P. M. B. Piccoli, T. F. Koetzle,
A. J. Schulz, W. Kaminsky, K. I. Goldberg and
D. M. Heinekey, J. Am. Chem. Soc., 2008, 130, 10812–10820.
and I. Manners, Inorg. Chem., 2007, 46, 7522–7527;
(e) S. Caliskan, M. Zahmakiran, F. Durap and S. Özkar,
Dalton Trans., 2012, 41, 4976–4984; (f) G. Chen, S. Desinan,
R. Rosei, F. Rosei and D. Ma, Chem.–Eur. J., 2012, 18, 7925–
7930; (g) G. Chen, S. Desinan, R. Rosei, F. Rosei and D. Ma, 27 J. H. Espenson, Chemical Kinetics and Reaction Mechanisms,
Chem. Commun., 2012, 48, 8009–8011; (h) X. Wang, D. Liu, McGraw Hill, New York, 2nd edn, 2002, p. 71.
S. Song and H. Zhang, Chem. Commun., 2012, 48, 10207– 28 G. Guella, C. Zanchetta, B. Patton and A. Miotello, J. Phys.
10209. Chem., 2006, 110, 17024–17033.
20 R. Ciganda, M. A. Garralda, L. Ibarlucea, E. Pinilla and 29 F. Acha, R. Ciganda, M. A. Garralda, R. Hernández,
M. R. Torres, Dalton Trans., 2010, 39, 7226–7229.
21 T. W. Graham, C. W. Tsang, X. Chen, R. Guo, W. Jia,
L. Ibarlucea, E. Pinilla and M. R. Torres, Dalton Trans.,
2008, 4602–4611.
S. M. Lu, C. Sui-Seng, C. B. Ewart, A. Lough, D. Amoroso 30 M. A. Garralda, R. Hernández, L. Ibarlucea, E. Pinilla and
and K. Abdur-Rashid, Angew. Chem., Int. Ed., 2010, 49,
8708–8711.
22 G. C. Fortman, A. M. Z. Slawin and S. P. Nolan, Organo-
metallics, 2011, 30, 5487–5492.
23 C. Boulho and J. P. Djukic, Dalton Trans., 2010, 39, 8893–
8905.
M. R. Torres, Organometallics, 2003, 22, 3600–3603.
31 (a) K. D. Atkinson, M. J. Cowley, S. B. Duckett, P. I. P. Elliot,
G. G. R. Green, J. Lopez-Serrano, I. G. Khazal and
A. C. Whitwood, Inorg. Chem., 2009, 48, 663–670;
(b) M. Rosales, T. González, R. Atencio and A. Sanchez-
Delgado, Dalton Trans., 2004, 2952–2956.
24 TOFs were calculated as moles of hydrogen per mole of 32 R. Ciganda, M. A. Garralda, L. Ibarlucea, C. Mendicute-
precatalyst × h at 30% conversion.
25 L. J. Sewell, G. C. Lloyd-Jones and A. S. Weller, J. Am. Chem.
Soc., 2012, 134, 3598–3610.
26 (a) H. C. Johnson, A. P. M. Robertson, A. B. Chaplin,
L. J. Sewell, A. L. Thompson, M. F. Haddow, I. Manners
and A. S. Weller, J. Am. Chem. Soc., 2011, 133, 11076–11079;
Fierro, M. C. Torralba and M. R. Torres, Inorg. Chem., 2012,
51, 1760–1768.
33 (a) C. M. Lukehart and J. V. Zeile, J. Am. Chem. Soc., 1976,
98, 2365–2367; (b) M. Gerisch, F. W. Heinemann, C. Bruhn,
J. Scholz and D. Steinborn, Organometallics, 1999, 18,
564–572.
(b) C. Y. Tang, A. L. Thompson and S. Aldridge, J. Am. 34 Bruker Apex2, Bruker AXS Inc, Madison, Wisconsin, USA,
Chem. Soc., 2010, 132, 10578–10591; (c) C. Y. Tang, 2004.
A. L. Thompson and S. Aldridge, Angew. Chem., Int. Ed., 35 G. M. Sheldrick, SADABS, Program for Empirical Adsorption
2010, 49, 921–925; (d) C. Y. Tang, N. Phillips, J. I. Bates,
A. L. Thompson, M. J. Gutmann and S. Aldridge, Chem.
Correction, Institute for Inorganic Chemistry, University of
Göttingen, Germany, 1996.
Commun., 2012, 48, 8096–8098; (e) C. Y. Tang, N. Phillips, 36 A. Altomare, M. C. Burla, M. Camilla, G. L. Cascarano,
M. J. Kelly and S. Aldridge, Chem. Commun., 2012, 48,
11999–12001; (f) A. Rossin, M. Capolari, L. Gonsalvi,
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
11660 | Dalton Trans., 2013, 42, 11652–11660
This journal is © The Royal Society of Chemistry 2013