Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes and the isolation of the hydride insertion product with an alkene

Article abstract of DOI:10.1016/j.jorganchem.2011.01.036

Reaction of the Ir(I)-Xantphos complex [Ir(κ²-Xantphos) (COD)][BAr^F₄] (Xantphos = 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene, Ar^F = C₆H₃(CF ₃)₂) with H₂

Full text of DOI:10.1016/j.jorganchem.2011.01.036

Journal of Organometallic Chemistry 696 (2011) 2870e2876
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Journal of Organometallic Chemistry
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Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes
and the isolation of the hydride insertion product with an alkene
*
Ashley J. Pontiggia, Adrian B. Chaplin, Andrew S. Weller
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, UK
a r t i c l e i n f o
a b s t r a c t
Reaction of the Ir(I)eXantphos complex [Ir(k2eXantphos)(COD)][BArF4] (Xantphos ¼ 4,5-bis(diphenyl-
phosphino)-9,9-dimethylxanthene, ArF ¼ C6H3(CF3)2) with H2 in acetone or CH2Cl2/MeCN affords the
Ir(III)ehydrido complexes [Ir(k3eXantphos)(H)2(L)][BArF4], L ¼ acetone or MeCN, whereas in non-coor-
Article history:
Received 14 January 2011
Received in revised form
28 January 2011
dinating CH2Cl2 solvent dimeric [Ir(k3eXantphos)(H)( -H)]2[BArF
m ] is formed. A common intermediate
4 2
Accepted 28 January 2011
in these reactions that invokes a (s, h
2-C8H13) ligand is reported. Addition of excess tert-butylethene
(tbe) to [Ir(k3eXantphos)(H)2(MeCN)][BArF4] results in insertion of a hydride into the alkene to form
[Ir(k3eXantphos)(MeCN)(CH2CH2C(CH3)3)(H)][BArF4], an Ir(III) alkylehydrido-Xantphos complex. This
reaction is reversible, and heating (80 ꢀC) results in the reformation of [Ir(k3eXantphos)(H)2(MeCN)]
[BArF4] and tbe. These complexes have been characterised by NMR spectroscopy, ESI-MS and single-
crystal X-ray diffraction. They show variable coordination modes of the Xantphos ligand: cis-k2eP,P, fac
Keywords:
Iridium
Phosphine
Pincer
X-ray
Hydride
Xantphos
e
k3eP,O,P and mer-k3eP,O,P with the later coordination mode like that found in related PNPepincer
complexes.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
application in CeH activation chemistry [14e18]. We report here
a preliminary study into their synthesis and reactivity.
Transition-metal complexes involving tridentate “pincer”
ligands, especially with the later transition metals, are an important
class of materials as they mediate many interesting, and contem-
porary, transformations such as the activation of EeH bonds [1e4].
Within the complexes of group 9 metals, those with formally
neutral PNP-type ligands (Chart 1) are distinct from (formally
anionic) PCP-type ligands as they often result in an overall positive
charge on the metal centre. In this regard they are similar to POP-
type ligands such a DPEphos and Xanthphos that have found
application in a number of catalytic process, especially carbonyla-
tion reactions such as hydroformylation [5e7]. Xantphos (Chart 1)
is a particularly interesting comparison, as it is relatively rigid and
thus might be expected to coordinate in a manner similar to
PNPeligands [8,9]. However well-characterised P,O,Pek3ecoordi-
nation modes of Xantphos are, surprisingly, rare, there being
2. Results and discussion
Complex 1 [Ir(k2eXantphos)(COD)][BArF4] (COD ¼ 1,5-cyclo-
octadiene, ArF ¼ C6H3(CF3)2) that is the precursor to the studies
reported here is readily synthesised by addition of Xantphos to
[Ir(COD)Cl]2 in CH2Cl2 solvent in the presence of the halide
abstracting agent Na[BArF4] Scheme 1. X-ray quality crystals of dark
orange 1 allowed for the solid-state structure to be determined, as
shown in Fig. 1. This demonstrates a pseudo-square planar envi-
ronment around the Ir(I) centre with cis phosphines and an oxygen
atom that is not coordinated with the metal (Ir1/O1, 2.544(2) Å).
Although the coordination environment is distorted somewhat
from being ideal square planar, with the IreP distances differing by
0.1 Å and the COD ligand twisted [planes defined by P1eIr1eP2 and
the Ir1ecentroid(C1,C2)ecentroid(C5,C6) 21.99(3)ꢀ] the cation
approximates to Cs symmetry in the solid-state. Other cis-
k2eXantphos complexes have been structurally characterised
[10,19e22]. In contrast to the solid-state structure, in solution the 1H
only
a handful of fully characterised examples [8e12]. The
P,Pek2ecoordination mode (i.e. with the Oedonor atom not bound)
is far more common. We have recently reported upon this unusual
k
3 coordination mode using Rh-based systems, e.g. A [13], and were
interested in extending this to iridium to afford complexes that are
directly analogues to IrePNP systems that have found much recent
NMR spectrum of 1 shows equivalent methyl protons (
at room temperature and a single alkene COD environment (
4H), i.e. apparent C2v symmetry. The 31P {1H} spectrum shows
a singlet at 14.26 demonstrating equivalent phosphine environ-
ments. These data are consistent with rapid inversion of the
d
1.75, 6H)
d
3.85,
d
* Corresponding author.
E-mail address: andrew.weller@chem.ox.ac.uk (A.S. Weller).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.01.036

A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
2871
Chart 1.
Xantphos ligand on the NMR timescale in solution, possibility via
k3eintermediate [12]. Similar NMR data are observed for the
analogous Rhenorbornadiene complex [13].
doublets of triplets, collapsing to doublets on decoupling 31P. The
coupling constants show cis 1He31P coupling (J(PH) ¼ 13.8 and
14.0 Hz respectively), with no trans coupling observed. Inequivalent
a
Addition of hydrogen (w4 atm) to 1 in d6-acetone solution
resulted in a colour change from orange to colourless, and ulti-
Xantphos methyl protons (
were also observed. There is no indication of any COD alkene or allyl
signals in the range 3e5. These data point towards a structure for
d 1.99 and 1.77) and free C8H16 (d 1.52)
mately
(24
h)
affords
the
dihydride
complex
d
[Ir(k3eXantphos)(H)2(acetone)][BArF4], 3, and the hydrogenation of
COD to cyclooctane (COA). Initially formed, however, is an inter-
mediate, spectroscopically characterised in situ as the mono-
3 as shown in Scheme 2. We assign the remaining coordination site
to be occupied by a molecule of solvent (acetone). Similar struc-
tures have been reported for Rh [13] and Ru [8] Xantphos
complexes while the close chemical shift of the hydrides points to
a similar trans donor atom (i.e. O) for each. Strong peaks observed
by ESI-MS at m/z ¼ 831.208 ([IrC42H40O2P2]þ calc. 831.213) and
773.168 ([M]þ ꢁ acetone, calc. 773.171) support this formulation.
We were unable to isolate crystalline samples of either 2 or 3 and
thus neither a solid-state structural determination nor micro-
analytical data were obtained. Nevertheless spectroscopic and ESI-
MS data are unequivocal for their determination.
hydrido complex [Ir(k3eXantphos)(H)( 2-C8H13)][BArF
s, h ] 2
4
(Scheme 2). The 1H NMR spectrum of the reaction mixture after
10 min shows this intermediate to be the dominant species in
solution. Two alkene peaks at
d 4.94 and 4.24 that integrate each to
1H relative to [BArF4] and a doublet of doublets at
d
ꢁ7.28 (dd, 1H)
that shows cis couplings to the phosphines (J(PH) ¼ 17.9, 27.5 Hz) are
observed. This hydride signal collapses into a singlet on decoupling
31P. Two Xantphos methyl environments are observed (
d 1.99, 1.41).
The alkene peaks correlate with each another (COSY) and also to
signals at 84.4 and 76.3 in the 13C {1H} NMR spectrum (HSQC) which
lie in the region associated with bound alkene ligands. A relatively
Repeating the hydrogenation in very weakly-coordinating
solvent CD2Cl2 with an added 2 eq of MeCN (per 1) led to
the formation of a new colourless complex [Ir(k3eXantphos)
(H)2(MeCN)][BArF4] 4 after 24 h, which was characterised by
NMR spectroscopy, ESI-MS, and a single-crystal X-ray diffraction
experiment (Scheme 3). The NMR data of 4 are very similar to those
high frequency signal in the 1H NMR spectrum (
d 3.58) does not
couple with the alkene peaks (COSY) and shows a strong correlation
to a carbon signal at 16.1. This carbon signal is also the lowest
frequency one in the 13{1H} NMR spectrum and shows no corre-
lation to other protons, suggesting an IreCHR2 group. The 31P {1H}
spectrum shows a pair of AB-roofed doublets (d 7.4, 3.2) with
a magnitude of coupling constant that demonstrates trans-orien-
tated phosphines (J(PP) ¼ 288 Hz). ESI-MS (ElectroSpray Ionisation-
Mass Spectrometry) demonstrates the dominant parent ion at m/
z ¼ 881.267 ([IrC47H46P2O1]þ calc. 881.265) that fits the suggested
formulation. These data are fully consistent with partial hydroge-
nation of COD to form a (
against alternative formulations as an allyl [23e25] or vinyl[17]
ligands. The formation of a
2-C8H13 ligand from insertion of
s, h
2-C8H13) ligand. These data also argue
s, h
a hydride into a coordinated COD ligand has been reported pre-
viously [26,27].
Over a period of 24 h compound 2 smoothly converts to
a new compound, characterised as [Ir(k3eXantphos)(H)2(acetone)]
[BArF4], 3. The 31P {1H} spectrum of 3 shows a single environment at
d
32.26 as a singlet, while two hydride environments are observed
in the 1H NMR spectrum at
d
ꢁ26.01 and ꢁ26.90, both of which are
[BArF
]
4
O
Xantphos
Ph2
[IrCl(COD)]2
P
P
Ir
Na[BArF
]
Fig. 1. The molecular crystal structure of the cationic portion of 1, only the major
disordered component of the COD ligand shown. Hydrogen atoms and anion are
omitted for clarity. Thermal ellipsoids are shown at the 30% probability level. Selected
bond distances (Å): Ir1eP1, 2.3258(8); Ir1eP2, 2.4209(9); Ir1eC1, 2.161(4); IreC2,
2.161(4); Ir1eC5, 2.300(4); Ir1eC6, 2.208(4); Ir/O1, 2.544(2). Selected angle (ꢀ):
P1eIr1eP2, 101.22(3).
4
CH2Cl2
Ph2
1
Scheme 1.

2872
A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
[BArF
]
[BArF
]
[BArF
]
Ph2
P
4
Ph2
P
4
4
H
H
H2
H2
O
H
O
Ir
O
Ir
Ph2
P
P
O
Ir
d6-acetone
– COA
P
P
Ph2
24 hours
10 minutes
Ph2
Ph2
2
1
3
Scheme 2.
of 3. The 1H NMR spectrum of isolated material demonstrates two
hydride environments at
doublets of triplets, J(PH) ¼ 12.8, 15.4 Hz respectively, and show
a mutual 1He1H coupling of J(HH) ¼ 7.4 Hz. Although similar to 3,
the larger chemical shift dispersion for the hydrides in 4 reflects
couplings, especially those to the hydride signal at
d
ꢁ22.81, are
d
ꢁ18.55 and ꢁ26.79 both of which are
much smaller (<20 Hz) indicative of cis-coupling. In the 1H {31P}
spectrum these hydride multiplicities reduce to two simple triplets
with J(HH) ¼ 3.4 Hz. The 13C {1H} NMR spectrum shows a single
environment for C(CH3)2 while two environments for C(CH3)2
are observed. The 31P {1H} NMR spectrum shows a single envi-
different trans ligands (O and N) and we assign the signal at
to the hydride trans to the acetonitrile ligand [28]. In the alkyl region
of the spectrum peaks for coordinated acetonitrile ( 1.90) and
inequivalent Xantphos methyl protons ( 1.50 and 1.18) are
d
ꢁ18.55
ronment at
d 22.90. These data suggest a ratio of Xantphos ligand
d
to hydrides of 1:2, and a rather symmetric structure. The dimeric
formulation of 5 was revealed by ESI-MS which showed m/
z ¼ 773.180 ([C78H68P4O2Ir2]2þ calc. 773.171) consistent with a
dimer with a þ2 charge, that is to say an increase between each
isotopomer of m/z ¼ 0.5 and an overall isotope pattern that clearly
indicated a dimeric {Ir2}2þ formulation.
d
observed. The 31P {1H} NMR spectrum shows a single environment
at
d
27.97. ESI-MS shows a peak at m/z ¼ 814.196 ([C41H37P2NOIr]þ
calc. 814.198). These data are consistent with the formation of an
acetonitrile analogue of the Xantphos acetone adduct 4 in which the
Xantphos ligand is trans spanning and the acetonitrile ligand is
bound trans to a hydride. The solid-state structure of 4 is shown in
Fig. 2 and confirms the coordination geometry as determined by
NMR spectroscopy. In particular it demonstrates a PeIreP bond
angle of 164.10(4)ꢀ, and a MeCN ligand trans to a hydride. As seen for
the formation of 3, the intermediate 2 was observed during the
initial stages of the reaction. Addition of acetone (ca. 2 eq) to
a CD2Cl2 solution of 4 resulted in a mixture of 3 and 4 in a 1:5 ratio
respectively. This demonstrates exchange of the bound MeCN
ligand, which at the 18-electon Ir(III) centre must be via a dissocia-
tive process. Complexes 3 and 4 are directly analogous to PNP-type
pincer complexes [14e16,18], such as [Ir(PNP)(H)2(NCMe)][BF4] [17]
(PNP ¼ [2,6-bis-(di-tert-butylphosphinomethyl)pyridine]).
These data point to a formulation for 5 which is a centrosym-
metric dimer with bridging hydrides. A crystal structure determi-
nation confirmed this to be the case (Fig. 3), showing the Xantphos
ligand binding in as k3 e with a facial coordination geometry, the
oxygen coordinating to the Ir(III) centre (Ir1eO1, 2.220(3) Å). This
distance is not appreciably different from that found for the k3
e
meridional binding mode (e.g. 4 and 6, vide infra). The hydride
ligands were not located in the final difference map, but an
apparent vacant site in the coordination sphere trans to O1 is the
likely location of the terminal hydride, while the bridging hydrides
sit trans to P1 and P2, consistent with the NMR data. The IreIr
distance of 2.6460(4) Å is consistent with a formal twice protonated
M]M double bond, or alternatively an 18eelectron configuration
can be obtained by treating each bridging hydride as a 3-centre 2-
electron bond. The bonding in such dimeric species has been dis-
cussed previously [29]. Similar structures for Ir2 dimeric species
with bridging hydrides have been reported, which show similar
IreIr separations [23,30]. As far as we are aware 5 is the first
In contrast to the hydrogenation of 1 in acetone or CH2Cl2/
MeCN solvents, both of which are relatively coordinating and
reveal final products that have coordinated solvent, hydrogenation
in CD2Cl2 forms a bi-metallic complex with no coordinated
solvent: [Ir(k3eXantphos)(H)( -H)]2[BArF4]2, 5 (Scheme 4), as
m
characterised by NMR spectroscopy, X-ray crystallography and ESI-
MS. Complex 2 was once again observed as an intermediate, which
changed smoothly to 5 over 24 h. The 1H NMR spectrum of 5
crystallographically characterised example of a
with facial coordination geometry. Changes in coordination
geometry from
3-fac to 3-mer have previously been observed in
k
3-Xantphos ligand
k
k
showed two sets of Xantphos methyl protons at
d
2.16 and 2.14.
related Rhecomplexes of DPEphos [31]
Complex second-order multiplets observed at
d
ꢁ6.68 and ꢁ22.81,
The synthesis of 5 on a large scale (>10 mg) proved problematic
as hydrogenation in CH2Cl2 led to trace impurities that could not be
removed by recrystallisation. However, addition of H2 to 1 in flu-
orobenzene (C6H5F) solvent resulted in the clean formation of 5 and
allowed its isolation in a yield of 53% as bright orange crystals that
precipitated out of solution as analytically pure material.
Addition of MeCN to complex 5 resulted in the quantitative
formation of 4 after 2 h. A deep-red intermediate was observed
in the early stages of the reaction, but this was short lived and we
both integrating as 2H, are assigned to the hydrides. The former
resonance is characteristic in both chemical shift and coupling
constants for hydride ligands that bridge two metal centres, while
the latter is characteristic for terminal hydrides. Line-shape
analysis of these hydride resonances in an AA0BB0XX0X00X000 system
gave a satisfactory, if not perfect fit, and reveals a coupling
constant between the bridging hydride (
phine of w64 Hz suggesting a trans orientation, while the other
d
ꢁ6.68) and the phos-
[BArF
]
[BArF
]
Ph2
P
4
4
H2
H
O
H
O
Ir
Ph2
P
P
N
Ir
CD2Cl2 / 2 equiv. MeCN
C
Me
P
Ph2
24 hours
Ph2
1
4
Scheme 3.

A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
2873
Fig. 2. The molecular crystal structure of the cationic portion of 4. Hydrogen atoms,
apart from the hydrides, and anion are omitted for clarity. Hydride ligands were
located in the difference Fourier map. Thermal ellipsoids are shown at the 30% prob-
ability level. Selected bond distances (Å): Ir1eP1, 2.2649(11); Ir1eP2, 2.2771(11);
IreO1, 2.249(3); IreN1, 2.105(4). Selected angles (ꢀ): P1eIr1eP2, 164.10(4);
O1eIr1eN1, 95.86(12).
Fig. 3. The molecular crystal structure of the cationic portion of 5. Hydrogen atoms are
omitted for clarity. The hydride atoms were not located in the difference Fourier map.
Selected bond distances (Å): Ir1eP1, 2.2827(13); Ir1eP2, 2.2461(14); IreO1, 2.220(3);
Ir1eIr0, 2.6460(4). Selected Angles (ꢀ): P1eIr1eP2, 105.24(5); O1eIr1eP1, 82.34(9);
O1eIr1eP2, 82.74(10).
have not been able to definitely characterise it. NMR spectroscopy
after 15 min shows a broad environment in the 13P{1H} NMR
m/z ¼ 898.291 ([IrC47H49O2P2]þ calc. 898.29, i.e. 4 þ tbe), which is
consistent with this. A crystal structure confirmed the structure as
[Ir(k3eXantphos)(MeCN)(CH2CH2C(CH3)3)(H)][BArF4] 6 (Scheme 6,
Fig. 4). Key structural metrics that identify the alkyl hydride are the
C1eC2 distances 1.495(8) Å, that identifies it as a CeC single bond
rather than a C]C double bond (c.f. 1.30(1) Å in trans-Ir{(CH]
spectrum at
spectrum
(fwhm w 40 Hz) set of signals are observed at
respectively, of approximate equal intensity. Given the similarly of
this data to 5 we tentatively assign this complex as the MeCN
adduct of the dimer 5 in which the Xantphos ligand remains cis
coordinated but the oxygen is no longer bound (Scheme 5).
d
0.1 ppm, while in the hydride region in the 1H NMR
very broad (fwhm 500 Hz) and sharper
ꢁ11 and ꢁ17.1
a
w
d
d
CHC(CH2CH2Ph)2CH3}(CO)(PPh3)2) [37] and 1.299(7)
Å
in
Tp0Rh(CNneo)(CH]CHCMe3)Cl [38]), and that the Ir1eC1eC2
angle (116.8(4)ꢀ) is also much smaller than expected for a vinyl
group (w130ꢀ [38]). The hydride ligand was located in the final
difference map and sits trans to the MeCN ligand.
A well-reported hydrogen acceptor is tert-butylethene (tbe),
which has found considerable use in the generation of active, low-
coordinate, Ir(I) species from Ir(III)ehydrido complexes [32]. When
tbe was added in excess to the dimeric 5 in CD2Cl2 solvent no
reaction was observed after 4 days, even on mild heating (40 ꢀC).
This possibly suggests that tbe does not break up the dimeric
structure, unlike MeCN (i.e. 5 to 4). In contrast, addition of an excess
of tbe to the monomeric acetonitrile adduct 4 in CD2Cl2 resulted in
the formation of a new species, which was the sole-product after
20 h. No intermediates were observed, with 4 cleanly transforming
In 6 the tbe ligand has undergone insertion into one of the
hydride ligands in 4, presumably via dissociation of the MeCN
ligand (as suggested in the reaction with acetone), alkene coor-
dination and hydride migration. The formation of the linear
product is consistent with insertion favouring the least sterically
crowded complex. Related Iridium(III)ePNP [15,39] and
Iridium(III)ePCP[40,41] pincer complexes that are alkyl, aryl or
vinylehydrido species have been reported previously. A charac-
teristic reactivity profile of these is reductive elimination of
alkane, arene or alkene respectively to give Ir(I) species, that
themselves can often undergo oxidative addition [14,15,40,41]. On
heating 6 in C6H5F solvent at 80 ꢀC for 2 h we see no evidence for
the formation of a stable Ir(I) species, however under these
conditions complex 4 is reformed cleanly alongside 1 eq of tbe (by
1H NMR spectroscopy). A likely mechanism is reversible dissoci-
into the new product. In the 1H NMR spectrum a triplet at
d
ꢁ18.20
(1H) with a cis 1He31P coupling constant of J(PH) ¼ 15.2 Hz,
a singlet at d
0.55 that integrated as 9H is assigned to the tBu group
and two methyl environments for the Xantphos ligand were
observed. Signals assigned to methylene groups at 1.93 and 1.02
d
(2H each) were seen, while no signals characteristic to a coordi-
nated tbe ligand [33,34] or a vinyl ligand (i.e. IreCH]CHR) [35e38]
were observed. The 31P {1H} NMR spectrum only showed a singlet
at
d
21.34, which in combination with the other spectroscopic data,
ation of MeCN and b-elimination from the alkyl group to reform
suggests a trans conformation of the Xantphos ligand. These data
suggest that tbe coordination and hydride insertion have occurred
to give an alkyl hydride. ESI-MS showed the dominant parent ion as
tbe. Given this observation, presumably it is the excess tbe used in
the synthesis of 6 from 4 that provides the driving force for its
formation.
[BArF
]
4 2
[BArF
]
4
O
Ir
H
H2
O
Ph2
P
P
Ph2
H
P
P
Ph2
P
P
Ir
CD2Cl2
Ir
H
Ph2
Ph2
O
24 hours
Ph2
H
5
1
Scheme 4.

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A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
[BArF
]
4 2
[BArF
]
4
Me
Ph2
P
O
C
H
N
Ph2
P
P
excess MeCN
CD2Cl2
Ph2
H
H
P
P
Ir
Ir
5
H
4
O
Ir
H
Ph2
N
Ph2
C
H
N
C
2 hours
Me
O
P
Ph2
Me
Scheme 5.
3. Conclusions
5. Crystallography
Cationic k3epincer-type complexes of Ir(III)edihydrides have
been synthesised from reaction of a precursor Ir(I)eXantphos
complex. These complexes show variable coordination modes of
the Xantphos ligand: cis-k2eP,P, facek3eP,O,P and mer-k3eP,O,P;
with the last coordination mode like that found in PNPepincer
complexes. Related to this analogy, an alkylehydrido-Xantphos
complex has been isolated from reaction of a dihydride with an
alkene (tbe), that is closely related to alkylehydridoePNP species
that are precursor complexes for CeH activation process by Ir(I)
reactive intermediates. The formation of this complex is reversible,
and heating isolated material reforms the dihydride and alkene.
The coordination chemistry of Xantphos thus shows very inter-
esting parallels with that of PNPeligands [8,9], with the added
spice of having flexible coordination modes. It will be interesting to
see whether these facets can be harnessed in catalytic cycles that
are also mediated by PNP-type complexes.
Relevant crystallographic data are given in Table 1. Data was
acquired on an Enraf Nonius Kappa CCD diffractometer using
graphite monochromated Mo K
a
radiation (
l
¼ 0.71073 Å) and
a low-temperature device (150 K); data was collected using
COLLECT, reduction and cell refinement was performed using
DENZO/SCALEPACK [46,47]. Structures were solved by direct
methods using SIR2004 (1, 4, 6) or by Patterson interpretation using
SHELXS-86 (5), and refined full-matrix least squares on F2 using
SHELXL-97 [48,49]. All non-hydrogen atoms were refined aniso-
tropically. Hydride ligands were located in the difference Fourier
map for complexes 4 and 6. Problematic solvent disorder in the
structure of 5 and 6 was treated using the SQUEEZE algorithm [50].
Further details of disorder modelling are documented in the
crystallographic information files under the heading _refine_s-
pecial_details. Restraints to thermal parameters were applied were
necessary in order to maintain sensible values.
5.1. [Ir(k2eXantphos)(COD)][BArF4] 1
4. Experimental
A solution of Xantphos (169.7 mg, 0.29 mmol) in CH2Cl2 (3 mL)
was added dropwise to a stirred CH2Cl2 (6 mL) suspension of
[Ir(cod)Cl]2 (98.5 mg, 0.15 mmol) and Na[BArF4] (260.6 mg,
0.29 mmol). The dark orange solution was then stirred at ambient
temperature for a further 2 h. The solution was filtered via cannula
and the solvent removed in vacuo to yield a dark orange solid,
which was recrystallised from CH2Cl2/pentane. Yield: 398.1 mg
(78.0%). Crystals suitable for X-ray diffraction were obtained by
recrystallisation from CH2Cl2/pentane at room temperature.
All manipulations were carried out under an atmosphere of Argon
using standard Schlenk and glove-box techniques. Glassware was
oven dried at 130 ꢀC overnight and flamed under vacuum prior to use.
Unless otherwise stated, all solvent reagents were placed under an
Argonatmosphere before use using threefreezeepumpethawcycles.
Dichloromethane, acetonitrile, pentane and hexane were dried using
a Grubbs-type solvent purification system (MBraun SPS-800) [42].
Acetone and d6-acetone were stirred over 3 Å molecular sieves
overnight then distilled under vacuum. CD2Cl2, and C6H5F
were distilled under vacuum from CaH2 and stored over 3 Å
molecular sieves. The Xantphos ligand was used as purchased from
SigmaeAldrich. Na[BArF4] and [Ir(cod)Cl]2 were prepared according
to published literature methods or variations thereof. [43,44] NMR
spectra were recorded on Varian 500 MHz, Bruker 500 MHz and
Varian 300 MHz spectrometers. Chemical shifts are quoted in ppm
and coupling constants in Hz. ESI-MS was carried out on a Bruker
MicroTOF instrument interfaced to a glove box [45]. Samples were
diluted with the appropriate solvent before being injected via a gas-
tight syringe. Microanalyses were performed by Elemental Micro-
analysis Ltd.
1H (500 MHz, CD2Cl2, 298 K):
d
7.72 (s, 8H, BArF4), 7.61 (m, 2H,
phenyl), 7.56 (s, 4H, BArF4), 7.37 (8H, m, aryl), 7.24 (m, 16H, aryl),
3.85 (s, 4H, cod), 1.75 (s, 6H, CH3), 1.72 (m, 4H, cod), 1.35 (m, 4H,
cod). 31P {1H} NMR (202 MHz, CD2Cl2, 298 K):
d
14.26 (s). 13C {1H}
(125 MHz, CD2Cl2, 298 K):
d
162.31 (q, JCB ¼ 49.6, BArF4), 161.48 (d,
JCP ¼ 4.3, aryl), 137.72 (d, JCP ¼ 5.7, aryl), 135.36 (s, BArF4), 133.79 (s,
aryl), 132.57 (d, JCP ¼ 11.4, phenyl), 132.04 (dd, JCP ¼ 43.9, 2.86,
PeCphenyl), 131.16 (s, aryl), 129.42 (d, JCP ¼ 10.5, phenyl), 129.41 (qq,
JCF ¼ 32, 2.8, BArF4), 129.14 (s, aryl), 128.62 (d, JCP ¼ 5.7, aryl), 125.25
(q, JCF ¼ 272.7, BArF4), 124.37 (d, JPC ¼ 42.9, PeCaryl), 124.07 (s, aryl),
118.04 (sept, JCF ¼ 3.8, BArF4), 65.84 (t, cod), 38.22 (s, C(CH3)2), 31.76
(s, cod), 27.04 (s, CH3). ESI-MS (CH2Cl2, 100 ꢀC, 4.5 kV): m/z calc. for
[BArF
]
Ph2
P
[BArF
]
4
excess, 298 K
tBu
Ph2
P
4
tBu
H
H
O
Ir
6
H
O
Ir
4
N
N
C
C
Me
Me
80ºC
tBu
P
P
Ph2
Ph2
–
Scheme 6.

A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
2875
1.70 (m, 1H, CH2), 1.41 (s, 3H, CH3), 1.39 (m, 1H, CH2), 1.35e1.15 (m,
3H, CH2), 0.95 (m, 2H, CH2), 0.58 (m, 2H, CH2) ꢁ7.28 (dd, 1H,
J(PH) ¼ 17.9, 27.5). 31P {1H} NMR (202 MHz, (CD3)2CO, 298 K):
d 7.4
(d, JPP ¼ 288), 3.2 (d, JPP ¼ 288). ESI-MS (CH2Cl2, 60ꢀC, 4.5 kV): m/z
calc. for [IrC47H46P2O1]þ 881.265, obs. 881.267.
5.2.2. Complex 3
1H NMR (500 MHz, (CD3)2CO, 298 K):
d 8.17 (m, 4H, aryl), 8.08
(dd, 2H, JHH ¼ 7.63, 1.8, 2H, aryl), 7.85 (s, 8H, BArF4), 7.72 (m, 12H,
aryl), 7.58 (m, 8H, aryl), 7.33 (m, 4H, aryl), 1.99 (s, 3H, CH3), 1.73 (s,
3H, CH3), ꢁ26.01 (dt, JHP ¼ 14.8, JHH ¼ 9.0, 1H, Ir-H), ꢁ26.90 (dt,
JHP ¼ 13.0, JHH ¼ 9.0, 1H, IreH). 31P {1H} NMR (202 MHz, (CD3)2CO,
298 K): d d 8.17
32.26 (s). 1H {31P} NMR (500 MHz, (CD3)2CO, 298 K):
(d, JHH ¼ 7.1, 4H, aryl), 7.33 (d, JHH ¼ 7.1, 4H, aryl), ꢁ26.01 (d,
JHH ¼ 9.0, 1H, IreH), ꢁ26.90 (d, JHH ¼ 9.0, 1H, IreH). ESI-MS (CH2Cl2,
60ꢀC, 4.5 kV): m/z calc. for [IrC42H40O2P2]þ 831.213 obs. 831.208. m/
z calc. for [IrC39H34,P2O]þ 773.171, obs. 773.168.
5.3. [Ir(k3eXantphos) (H)2(MeCN)][BArF4] 4
Fig. 4. Molecular crystal structure of cationic portion of 6. Thermal ellipsoids are
shown at the 30% probability level. Only the major disordered component of tBu and
phenyl groups shown. The hydride ligand was located in the difference Fourier map.
Ir1eP1, 2.2844(12); Ir1eP2, 2.2594(12); IreO1, 2.271(3); IreN1, 2.103(4); Ir1eC1,
2.086(5); C1eC2, 1.496(8); C2eC3, 1.565(7); Selected angles (ꢀ): P1eIr1eP2, 163.43(4);
O1eIr1eN1, 89.04(12); Ir1eC1eC2, 116.8(4).
A CH2Cl2 solution (2 mL) of [Ir(cod)(Xantphos)][BArF4] (41.7 mg,
0.023 mmol) and CH3CN (1.9 ml, 2 eq) was placed under H2 (1 atm)
for 24 h before placing under Ar using three freezeepumpethaw
cycles. Layering with pentane yielded colourless crystals after 48 h
at ꢁ4 ꢀC. Yield: 15.2 mg (56.8%).
1H NMR (500 MHz, CD2Cl2, 298 K):
d 7.87 (m, 4H, aryl), 7.67 (m,
þ
12H, aryl), 7.47 (m, 22 H, aryl),1.90 (s, 3H, CH3),1.55 (s, 3H, CH3),1.18
(s, 3H, CH3), ꢁ18.55 (dt, JHP ¼ 15.4, JHH ¼ 7.4, 1H, IreHtransCH3CN),
ꢁ26.79 (dt, JHP ¼ 12.8, JHH ¼ 7.37, 1H, IreHtransO). 31P {1H} NMR
[IrP2OC47H44
]
879.249, obs. 879.251. Microanalysis: calc. for
C79H56BF24OP2Ir: C, 54.46; H, 3.24. Found C, 54.93; H, 3.27.
(202 MHz, CD2Cl2, 298 K):
d
27.97 (s). 1H {31P} NMR (500 MHz,
5.2. [Ir(k3eXantphos)(H)( 2-C8H13)][BArF4] 2 and
s, h
CD2Cl2, 298 K):
d
7.87 (d, J ¼ 7.0, 4H, aryl), 7.72 (s, 8H, BArF4), 7.71 (s,
[Ir(k3eXantphos)H2(acetone)][BArF4] 3
2H, aryl), 7.69 (d, JHH ¼ 1.1, 1H, aryl), 7.57 (s, 1H, aryl), 7.55 (s, 4H,
BArF4), 7.54 (s, 1H, aryl), 7.52 (m, 2H, aryl), 7.51 (m, 1H, aryl), 7.47 (d,
JHH ¼ 2.2, 4H, aryl), 7.05 (m, 4H, aryl), 7.39 (m, 6H, aryl), ꢁ18.55 (d,
JHH ¼ 7.4, 1H), ꢁ26.79 (d, JHH ¼ 7.4, 1H). ESI-MS (CH2Cl2, 100 ꢀC,
4.5 kV): m/z calc. for [C41H37P2NOIr]þ 814.198, obs. 814.196.
AhighpressureYoung’s NMR tubecontaining a d6-acetone (500 ml)
solution of [Ir(cod)(Xantphos)][BArF4] (10 mg, 5.74 ꢂ10ꢁ3 mmol) was
placed under H2 (w4 atm) resulting in the immediate formation of 2,
which slowly evolved over 24 h to afford 3. Attempts to isolate a solid
or crystals were unsuccessful.
m ] 5
5.4. [Ir(k3eXantphos)(H)( -H)]2[BArF
4 2
5.2.1. Complex 2
1H NMR (500 MHz, (CD3)2CO, 298 K):
d
8.18 (m, 2 H, aryl),
A
fluorobenzene solution (4 mL) containing 1 (78 mg,
7.90e7.33 (m, 22H, aryl and BArF4), 4.94 (m, 1H, alkene), 4.24 (m,
0.045 mmol) was placed under H2 (4 atm) at ambient temperature
1H, alkene), 3.58 (s br, 1H, CH), 2.18 (m, 1H, CH2), 1.99 (s, 3H, CH3),
for w48 h, resulting in the formation of the product as orange
Table 1
Crystallographic data for compounds.
1
4
5
6
CCDC
808103
808105
808104
808106
Formula
M
C
79H56BF24IrOP2
C73H49BF24IrNOP2
1677.08
C142H88B2F48Ir2O2P4
3268.02
C79H61BF24IrNOP2
1761.24
1742.19
Cryst syst
Space group
a [Å]
b [Å]
c [Å]
Monoclinic
P21/n
15.42730(10)
22.2336(2)
21.8498(2)
Triclinic
P ꢁ 1
Triclinic
P ꢁ 1
Triclinic
P ꢁ 1
14.20740(10)
15.6396(2)
18.5741(2)
90.6863(4)
108.7335(5)
115.2006(6)
3482.81(6)
2
12.9166(3)
17.5298(4)
18.3009(5)
113.8708(11)
94.1716(12)
93.6085(11)
3759.85(16)
1
12.9313(2)
18.3388(4)
18.6381(3)
71.7289(8)
70.5417(9)
88.8237(8)
3939.95(12)
2
a
b
g
[deg]
[deg]
[deg]
107.4412(5)
V [Å3]
7150.01(10)
4
1.618
Z
Density [g cmꢁ3
]
1.599
2.072
1.443
1.917
1.485
1.836
m
(mmꢁ1
)
2.022
q
Range [deg]
5.11 ꢃ
q
ꢃ 26.37
5.10 ꢃ
q
ꢃ 26.37
5.11 ꢃ
q
ꢃ 26.37
5.10 ꢃ
q
ꢃ 26.37
Reflns collected
No. of data/param/restr
R1 [I > 2 (I)]
14504 (Rint ¼ 0.0305)
14504/1102/224
0.0338
14147 (Rint ¼ 0.0391)
14147/993/144
0.0401
14625 (Rint ¼ 0.0392)
14625/1043/201
0.0524
15835 (Rint ¼ 0.0313)
15835/1169/904
0.0416
s
wR2 [all data]
0.0825
0.0875
0.1419
0.1036
GoF
1.056
1.714, ꢁ1.345
1.028
2.206, ꢁ1.143
1.058
3.701, ꢁ1.530
1.064
1.378, ꢁ1.125
Largest diff. pk and hole [e Åꢁ3
]

2876
A.J. Pontiggia et al. / Journal of Organometallic Chemistry 696 (2011) 2870e2876
[7] M.-N. Birkholz, Z. Freixa, P.W.N.M. van Leeuwen, Chem. Soc. Rev. 38 (2009)
1099e1118.
crystals. Yield: 38.2 mg (52.2%). Crystals suitable for X-ray diffrac-
tion were obtained by placing a concentrated dichloromethane
solution of [Ir(cod)(Xantphos)][BArF4] under H2 (1 atm) and layer-
ing with pentane under an atmosphere of H2. Pale yellow crystals
were precipitated after 6 h at ambient temperature.
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1H NMR (500 MHz, CD2Cl2, 298 K):
d
8.01 (dd, JHH ¼ 7.8, 1.12, 4H,
aryl), 7.75 (s, 16H, BArF4), 7.67 (t, JHH ¼ 7.6, 4H, aryl), 7.57 (s, 8H,
BArF4), 7.55 (m, 2H, aryl), 7.33 (m, 8H, aryl), 7.11 (t, 4H, JHH ¼ 7.5,
aryl), 7.05 (t, JHH ¼ 7.5, 4H, aryl), 6.68 (t, JHH ¼ 7.8, 8H, aryl), 6.60 (t,
JHH ¼ 7.8, 8H, aryl), 6.29 (m, 8H, aryl), 2.16 (s, 6H, CH3), 2.14 (s, 6H,
CH3), ꢁ6.68 (m, 2H, Hbridging), ꢁ22.81 (m, 2H, Hterminal). 31P {1H}
NMR (202 MHz, CD2Cl2, 298 K):
CD2Cl2, 298 K):
d
22.90 (s). 1H {31P} NMR (500 MHz,
7.33 (dd, JHH ¼ 8.2,1.1, 8H, aryl), 6.29 (dd, JHH ¼ 8.6,
d
1.1, 8H, aryl), ꢁ6.68 (t, JHH ¼ 3.4, 2H, Hbridging), ꢁ22.81 (t, JHH ¼ 3.4,
2H, Hterminal). 13C {1H} NMR (125 MHz, CD2Cl2, 298 K): 162.3 (q,
JCB ¼ 49.6, BArF4), 161.38 (m, aryl), 139.69 (s, aryl), 135,37 (s, BArF4),
134.02 (m, aryl), 132.64 (s, aryl), 132.13 (s, aryl), 131.79 (s, aryl),
131.39 (br, aryl), 130.85 (s, aryl), 129.63 (m, aryl), 129.43 (qq, BArF4),
128.91 (m, aryl), 125.10 (q, JCF ¼ 272.7, BArF4), 118.04 (sep, BArF4),
39.76 (s, C(CH3)2), 30.90 (s, CH3), 22.69 (s, CH3). ESI-MS (CH2Cl2,
60ꢀC, 4.5 kV): m/z calc. for [C78H68P4O2Ir2]2þ 773.171, obs. 773.180.
Microanalysis: calc. for C142H92B2F48O2P4Ir2: C, 52.12; H, 2.83.
Found C, 52.99; H, 2.70.
5.5. [Ir(k3eXantphos)(MeCN)(CH2CH2C(CH3)3)(H)][BArF4] 6
Tbe (5 eq, 5
m
l) was added via syringe to a dichloromethane
solution (500
m
l) containing [Ir(Xantphos)(CH3CN)H2][BArF4] (11 mg,
6.6 ꢂ 10ꢁ3 mmol) in a Young’s NMR tube. After 24 h the product was
characterised in situ by NMR spectroscopy. Colourless crystals suit-
able for X-Ray diffraction were obtained, in low yield, by recrystalli-
sation from CH2Cl2/tbe/pentane at ꢁ4 ꢀC 1H NMR (500 MHz, CD2Cl2,
298 K):
d
7.94 (m, 4H, aryl), 7.72 (s, 8H, BArF4), 7.67 (dd, J ¼ 7.6, 1.7, 2H,
aryl), 7.56 (s, 4H, BArF4), 7.63e7.28 (m, 24H, aryl), 1.91 (m, 2H, CH2),
1.87 (s, 3H, CH3),1.54 (s, 3H, CH3),1.22 (s, 3H, CH3CN), 0.55(s, 9H, CH3),
ꢁ18.20 (t, JHP ¼ 15.2, 1H, IreH). 31P {1H} (202 MHz, CD2Cl2, 298 K):
d
21.34(s). ESI-MS(CH2Cl2, 60ꢀC,4.5kV):m/zcalc. for[IrC47H46P2ON]þ
898.290, obs 898.291.
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4829e4844.
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Chem. Soc. 122 (2000) 11017e11018.
Acknowledgements
The University of Oxford and the EPSRC for support. Dr Thomas
Douglas and Romaeo Dallanegra for useful discussions.
[37] M. Itazaki, C. Yoda, Y. Nishihara, K. Osakada, Organometallics 23 (2004)
5402e5409.
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Chem. Soc. 125 (2003) 4714e4715.
Appendix. Supplementary material
[40] X. Zhang, T.J. Emge, R. Ghosh, A.S. Goldman, J. Am. Chem. Soc. 127 (2005)
8250e8251.
[41] J. Choi, Y. Choliy, X. Zhang, T.J. Emge, K. Krogh-Jespersen, A.S. Goldman, J. Am.
Chem. Soc. 131 (2009) 15627e15629.
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metallics 15 (1996) 1518e1520.
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre under CCDC 808103e808106. These
data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
[43] J.L. Herde, J.C. Lambert, C.V. Senoff, Inorg. Synth. 15 (1974) 18e20.
[44] W.E. Buschmann, J.S. Miller, K. Bowman-James, C.N. Miller, Inorg. Synth. 33
(2002) 83e85.
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