An iridium-mediated C-H activation/CO2-carboxylation reaction of 1,1-bisdiphenylphosphinomethane

Article abstract of DOI:10.1039/c0dt00230e

The reaction of 1,1-bisdiphenylphosphinomethane (dppm, 4 eq.) with [IrCl(coe)₂]₂ results in a solvent dependent equilibrium from which the complexes [IrCl(dppm)(dppm-H)(H)] (1) and [Ir(dppm) ₂]Cl (2) were isolated. When 2 is dissolved in methanol, [IrCl(dppm)₂(H)][OCH₃] (4) is formed as dominant species in solution. The C-H activation reaction which leads to 1 and 4 can be suppressed by adding an additional dppm ligand per iridium center resulting in the formation of [Ir(dppm)₃]Cl (5). If the reaction of dppm with [IrX(coe)₂]₂ (X = Cl, I) is performed under an atmosphere of CO₂ the complexes [IrX(dppm)(H){(Ph₂P) ₂C-COOH}] (6: X = Cl; 7: X = I) are formed by a CH activation/CO ₂ carboxylation sequence. The reaction of 6 with NH₄PF yields [IrCl(dppm)₂(H)]PF₆.(10). Additionally the lithium compounds [Li(dme)₂(dppm-H)] (3) and [Li(dme){(Ph₂P) ₂CHCOO}]₂ (8) were prepared for comparison. The molecular structures of the compounds 1, 3, 5, 7, 8 and of the related iridium complex [IrCl(dppm)₂(H)]I (11) are reported. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00230e

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www.rsc.org/dalton | Dalton Transactions
An iridium-mediated C–H activation/CO2-carboxylation reaction of
1,1-bisdiphenylphosphinomethane†
Jens Langer,*a Mar´ıa Jose´ Fabra,b Pilar Garc´ıa-Ordun˜a,b Fernando J. Lahoz,b Helmar Go¨rls,a Luis A. Oro*b
and Matthias Westerhausena
Received 30th March 2010, Accepted 4th June 2010
First published as an Advance Article on the web 23rd July 2010
DOI: 10.1039/c0dt00230e
The reaction of 1,1-bisdiphenylphosphinomethane (dppm, 4 eq.) with [IrCl(coe)2]2 results in a solvent
dependent equilibrium from which the complexes [IrCl(dppm)(dppm-H)(H)] (1) and [Ir(dppm)2]Cl (2)
were isolated. When 2 is dissolved in methanol, [IrCl(dppm)2(H)][OCH3] (4) is formed as dominant
species in solution. The C–H activation reaction which leads to 1 and 4 can be suppressed by adding an
additional dppm ligand per iridium center resulting in the formation of [Ir(dppm)3]Cl (5). If the
reaction of dppm with [IrX(coe)2]2 (X = Cl, I) is performed under an atmosphere of CO2 the complexes
[IrX(dppm)(H){(Ph2P)2C–COOH}] (6: X = Cl; 7: X = I) are formed by a CH activation/CO2
carboxylation sequence. The reaction of 6 with NH4PF yields [IrCl(dppm)2(H)]PF6.(10). Additionally
the lithium compounds [Li(dme)2(dppm-H)] (3) and [Li(dme){(Ph2P)2CHCOO}]2 (8) were prepared for
comparison. The molecular structures of the compounds 1, 3, 5, 7, 8 and of the related iridium complex
[IrCl(dppm)2(H)]I (11) are reported.
active in such C–H activation reactions14 and several examples for
Introduction
CO2 activation by this metal have been reported,1 too, making
The use of CO2 as renewable, cheap and non-toxic carbon source is
iridium complexes a promising choice for further studies.
highly desirable but limited by its high stability and low reactivity.
English and Herskovitz demonstrated that iridium compounds
are able to mediate the carboxylation of acetonitrile by CO2,15 but
the formed products were not isolated. Later Behr et al. observed
a similar reactivity, using the more acidic malonodinitrile (pKa =
12) as substrate. In this case, several iridium compounds con-
taining the anion [HOOCC(CN)2]- were isolated and completely
characterized.16,17
We preliminary reported the iridium mediated transformation
of the less acidic dppm (1,1-bisdiphenylphosphinomethane, pKa =
29.9 18) into the unpredicted anionic ligand [(Ph2P)2C–COOH]- via
a C–H activation/carboxylation sequence (see Scheme 1).19
For instance, the direct carboxylation of hydrocarbons with CO2
is a straightforward route to carboxylic acids. Besides the reaction
of CO2 with strong carbon nucleophiles like Grignard reagents,
the transition metal mediated oxidative coupling of unsaturated
hydrocarbons with CO2 offers an attractive route to such acids
or their derivatives. Electrochemical or photochemical activation
offer additional ways to initiate a reaction between CO2 and
hydrocarbons.1
In case of aromatic hydrocarbons a carboxylation with CO2
can be achieved under either basic or acidic conditions.2,3 The
production of hydroxybenzoic acid derivatives from the related
alkali metal phenoxides (Kolbe–Schmitt reaction)4–6 is one of the
rare examples of a synthesis using CO2 as a carbon source in
industrial scale. Additionally, related alkali metal phenoxides have
been used as CO2 transfer agents in the carboxylation of C–H
acidic compounds.7–11
The carboxylation of less or none activated alkanes requires
more forcing conditions. The vanadium catalyzed carboxylation
of methane with CO2 in fuming H2SO4 to form acetic acid in
presence of K2S2O8 as oxidizing agent was reported.12,13
The transition metal mediated C–H activation followed by
carboxylation using CO2 may offer an alternative approach under
milder conditions. Various iridium compounds are known to be
Scheme 1
Herein more detailed results will be given.
aInstitute of Inorganic and Analytical Chemistry, Friedrich-Schiller-
University Jena, August-Bebel-Str. 2, 07743, Jena, Germany. E-mail:
j.langer@uni-jena.de
Results
bDepartamento de Qu´ımica Inorga´nica, Instituto Universitario de Cata´lisis
Homoge´nea, Instituto de Ciencia de Materiales de Arago´n, Universidad de
Zaragoza-Consejo Superior de Investigaciones Cient´ıficas, 50009, Zaragoza,
Spain. E-mail: oro@unizar.es; Fax: +34 976 761143; Tel: +34 976 761143
The C–H activation of dppm
The reaction of dppm with [Ir2(m-Cl)2(coe)4] (coe = cyclooctene)
in a 4 to 1 ratio was first described by Cowie and coworkers.20
The product obtained from the reaction in benzene was
† CCDC reference numbers 770462–770467. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00230e
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recrystallized from CH2Cl2 and identified as the pentacoordi-
nated iridium(I) complex [IrCl(dppm)2] on basis of its NMR
data. Later on, Tejel et al. found that this species exists in
solution in a solvent dependent equilibrium with an iridium(III)
compound formed via C–H activation of one of the dppm
ligands.21 They isolated [IrCl(dppm)(dppm-H)(H)] (dppm-H =
1,1-bisdiphenylphosphinomethanide) from a toluene solution.
Reinvestigation of this equilibrium in various nonchlorinated
solvents confirmed the existence of [IrCl(dppm)(dppm-H)(H)] (1)
while [IrCl(dppm)2] was not directly observed under the applied
conditions. However, the red, ionic compound [Ir(dppm)2]Cl
(2) was instead identified as the dominating species in more
polar solvents like acetone and acetonitrile. Compound 1 can be
obtained in crystalline form from toluene 19 or dimethoxy ethane
(dme). The molecular structure is shown in Fig. 1.
Fig. 2 Molecular structu◦re of 3 (H-atoms are omitted for clarity). Selected
˚
distances (A) and angles ( ) are: Li–P1 2.896(3), Li–O1 2.1184(12), Li–O2
2.114(2), P1–C1 1.7308(11), O1–Li–O2 80.43(7), O1–Li–P1 100.31(8),
P1–Li–P1A 60.35(7), P1–C1–P1A 114.46(11).
be treated rather as a contact ion pair than as a covalently bound
molecule. Besides 3 other solvent adducts of [Li(dppm-H)]n for
instance with thf or tmeda are known.26,27,28
While the colourless iridium(III) complex 1 was easily obtained
in pure form from various solvents, the isolation of the related red
iridium(I) compound 2 was found to be more challenging. The
use of more polar solvents like acetone or acetonitrile shifts the
equilibrium towards 2 as indicated by the formation of dark red
solutions from the reaction of dppm and [Ir2(m-Cl)2(coe)4]. How-
ever, only crystals of 1 were obtained upon cooling. Finally the use
of ethanol enables the isolation of 2. Although red crystals of 2
were obtained several times as described below (see experimental
section) the given procedure tends to be somewhat irreproducible.
Since the iridium(I) species formed slowly reacts with ethanol
at room temperature, rapid crystallization is necessary, but the
reaction mixture tends to oversaturate. In such cases dominantly
iridium(III) hydrido complexes are formed by dehydrogenation of
the alcohol.
Fig. 1 Molecular structure of 1 (most of the H-atoms and cocrysta◦ llized
˚
dme are omitted for clarity). Selected distances (A) and angles ( ) are:
Ir1–P1 2.3333(19), Ir1–P2 2.330(2), Ir1–P3 2.3300(19), Ir1–P4 2.3273(19),
Ir1–Cl 2.5129(18), P1–C1 1.724(8), P2–C1 1.720(8), P3–C26 1.852(7),
P4–C26 1.855(8), P1–Ir1–P4 174.71(7), P2–Ir1–P3 174.21(7), P1–C1–P2
100.0(4), P3–C26–P4 93.3(4).
Like in related diphosphanylmethanide complexes, the formed
four membered ring Ir1,P1,C1,P2 is planar.22,23 The observed
Once isolated, 2 is only sparingly soluble in thf due to its ionic
nature. The crystals show dichroism (red/greenish brown) and a
red luminescence when irradiated with UV radiation (366 nm) like
previously reported for a similar compound containing the cation
[(dppm)2Ir]+.21,29 Unfortunately, the crystals isolated from ethanol
were not suitable for X-ray measurement. When those crystals
were dissolved in a mixture of ethanol and d8-THF the 31P NMR
spectrum shows two singlets at d = -35.7 and -53.9. The signal
first mentioned which slowly decreases in intensity was assigned to
2 by comparison with the values reported for related compounds
containing the same cation (see compound 9 and 30). The second
signal belongs to the compound [[IrCl(dppm)2(H)]+[OEt]- (4a)
which most likely results from deprotonation of ethanol by 1
formed as an intermediate from 2. While in ethanol this reaction is
rather slow, which allowed the isolation of 2 in the first place, the
use of more acidic methanol as solvent results in rapid formation
of a pale yellow solution which contains [IrCl(dppm)2(H)]+[OMe]-
(4b) as sole product. The reaction of 2 in d4-methanol indicates
that there still is an equilibrium between 1 and 4 as shown
by the rapid exchange of all protons of the P–CH2–P groups
˚
˚
distances Ir1–P1 (2.333(19) A) and Ir1–P2 (2.330(2) A) are
slightly longer than found in [Ir(dppm-H)(H)(tp)] (2.276 and
2.269 A).24 The narrow angle of the ligand backbone P1–C1–P2 of
˚
100.0(4) reflects the high orbital contribution in the ligand bonding
resulting in compression of this angle to achieve better overlapping
of the phosphorus lone pair with iridium based orbitals.
In order to further address this aspect the lithium complex
[Li(dme)2(dppm-H)] (3) was prepared from [Li(dppm-H)]n.25 The
use of the harder lithium should result in a lower affinity to the
soft phosphorus donor atoms and overall in a decreased orbital
contribution in ligand bonding.
In 3, the lithium atom is also in an octahedral coordination
sphere (see Fig. 2) but the coordinated diphosphanylmethanide
ligand shows some remarkable differences. The more electrostatic
nature of the ligand bonding leads to an opening of the backbone
angle of the dppm-H ligand to 114.46◦ while the P–C bonds
˚
˚
(1.731 A) are only slightly longer then in 1 (av. 1.722 A). The
˚
distance Li–P(1) of 2.896(3) A is huge and suggests that 3 should
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Table 1 Comparison of selected bond lengths and angles of the iridium complexes 1, 5, 11 and the lithium complex 3
chelating dppm
dppm-H
P–C–P (av.) [◦] M–P (av.) [A]
others
M–P (av.) [A] P–C (av.) [A]
P–C (av.) [A]
P–C–P [◦]
Distances [A]
Bonds
˚
˚
˚
˚
˚
Ir complexes
1
2.329(2)
2.334(2)
2.330(3)
1.854(8)
1.843(5)
1.841(13)
93.3(4)
95.2(2)
94.6(5)
2.332(2)
—
—
1.722(8)
—
—
100.0(4)
—
—
2.513(2)
2.360(2)
2.467(3)
Ir1–Cl1
Ir1–P5
Ir1–Cl1
5
11
[IrH(dppm-H)(Tp)]24
2.2724(13)
1.727(5)
97.5(3)
Li complex
3
—
—
—
2.896(3)
1.731(1)
114.5(1)
2.116(2)
Li–O (av.)
by deuterium, while the hydride signal is not affected. The
irreversible formation of [IrCl(dppm)2(H)]+[OH]- by the reaction
of 1 and H2O was previously reported.21 The formation of 1
and 4 from the iridium(I) compound 2 in methanol can be
suppressed by adding an additional equivalent of dppm. From the
resulting orange coloured solution, crystals of the 18VE complex
[Ir(dppm)3]Cl·6MeOH (5) were isolated.
iridium phosphorus distances range from 2.2989(13) (Ir–P3) to
˚
2.3896(13) A (Ir–P1). The backbone angles of the chelating dppm
ligands of 95.7(2)◦ (P1–C1–P2) and 94.7(2) ◦ (P3–C26–P4) lie in a
typical region for iridium dppm complexes (see Table 1) while
the backbone angle of the monodentate dppm of 117.0(3)◦ is
much bigger than the value observed for uncoordinated dppm
(106.2(3)◦)34 due to the increased steric pressure resulting from the
attachment of the iridium substituent to P5.
Despite the broad range of application of dppm in transition
metal chemistry, only a few mononuclear tris(dppm) complexes
of the general formula [M(dppm)3]n+ have been reported so
far. Besides the crystal structures of two rhenium compounds,
containing the cation [Re(dppm)3]+ with three chelating dppm
While such 18VE compounds of iridium(I) are rather common
with electron withdrawing ligands like CO, the only other struc-
turally characterized example of such a compound containing
only phosphorus donors is [Ir(QP)(Ph3P)][BPh4] [QP = tris-(o-
diphenylphosphinophenyl)phosphine] reported by Venanzi et al.35
Complex 5 shows fluxional behaviour in methanol solution and
only a very broad signal in the 31P NMR spectra at d = -57
was observed at room temperature. At -50 ◦C this signal splits
into three signals at d = -13.4, -24.4 and -64.1 with relative
intensities of 1 to 1 to 4. Even at this temperature only broad signals
ligands (anions: I- or ReO4 ),31,32 only the crystal structure of the
-
tetrahedral nickel compound [Ni(dppm)3] with one chelating and
two monodentate dppm ligands is known.33
As shown in Fig. 3, the iridium(I) atom in compound 5
is in a distorted trigonal bipyramidal environment with two
chelating dppm ligands and an additional monodentate one. The
phosphorus atoms P1 and P3 as well P5 of the monodentate
dppm are in equatorial positions while P2 and P4 adopt the
axial positions with an angle of 165.51◦ between them. The
1
were observed in the H NMR spectra. Scheme 2 summarizes
the compounds observed from the reaction of dppm with [Ir2(m-
Cl)2(coe)4].
CO2 activation by diphosphanylmethanide complexes
Among the isolated products and postulated intermediates (see
Scheme 2), present in the equilibrium observed from the irid-
ium mediated C–H activation of dppm, are several species
with potential reaction sites for CO2. It is known, that several
iridium and rhodium complexes of the type [(L « L)2M]Cl
with chelating phosphorus and arsenic ligands react with CO2
forming metallacarboxylates of the type [(L « L)2MCl(CO2)] 36,37
and one may expect that [Ir(dppm)2]Cl, present in the above
described equilibrium, is suitable for this reaction too. Fur-
thermore, [IrCl(coe)(PMe3)3], [IrCl(PMe2Ph)3] and [Ir(PMe3)4]Cl
are known to form an iridacycle by oxidative coupling of two
CO2 molecules.38–40 A compound of the type [IrCl(PR3)3] can be
assumed to be the reactive species in those cases and the proposed
intermediate [IrCl(h -dppm)(h -dppm)]21 is expected to have a
similar geometry at the iridium center and therefore maybe similar
reactivity. When the reaction of [Ir2(m-Cl)2(coe)4] and dppm (1
to 4 ratio) was performed under a CO2 atmosphere in various
solvents (for instance toluene, thf, acetone or acetonitrile), a
white precipitate rapidly formed. As preliminary reported, this
compound was identified as [IrCl(dppm)(H){(Ph2P)2C–COOH}]
(6).19 The infrared spectrum of 6 shows strong broad bands at
1580 and 1270 cm-1, while its insolubility in nearly all common
2
1
Fig. 3 Molecular structure of the cation of 5 (H-atoms and cocrys-
tallized methanol are omitted for clarity). Selected distances (A) and
˚
angles (◦) are: Ir1–P1 2.3896(13), Ir1–P2 2.3153(13), Ir1–P3 2.2989(13),
Ir1–P4 2.3327(13), Ir1–P5 2.3598(13), P1–Ir1–P2 71.18(4), P1–Ir1–P3
123.17(4), P1–Ir1–P4 109.25(4), P1–Ir1–P5 101.34(4), P2–Ir1–P3 95.91(5),
P2–Ir1–P4 165.51(5), P2–Ir1–P5 97.99(5), P3–Ir1–P4 1.48(4), P3–Ir1–P5
135.48(5), P4–Ir1–P5 96.11(4), P1–C1–P2 95.7(2), P3–C26–P4 94.7(2),
P5–C51–P6117.0 (3).
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Scheme 2 Equilibria observed in the reaction of dppm with [Ir2(m-Cl)2(coe)4]
solvents prevents further investigations in solution by NMR. The
identity of 6 was undoubtfully established by elemental analysis
in combination with a X-ray diffraction study of crystals of 6,
obtained directly from the reaction mixture in acetone. Similar
results were obtained when crude [Ir2(m-I)2(coe)4] prepared in
analogy to a known procedure41 was used. In this case, the corre-
sponding iodo compound [IrI(dppm)(H){(Ph2P)2C–COOH}] (7)
was isolated in good yields. The presence of the iodide ligand
in 7 results in a shift of the hydride band to 2165 cm-1 due to
its differing trans influence when compared to 6 (2185 cm-1).
Fig. 4 shows the molecular structure of 7. Like the isostructural
C1 and C2 clearly exhibit sp2 hybridizations (bond angles around
C1 and C2 summing up to 359.3 and 360.0 and the P–C1 bonds
˚
(average 1.774(10) A) are significantly shorter than in the standard
˚
coordinated dppm (av. 1.847(3) A), consistent with a P–C partially
multiple bond character and with the delocalization of the negative
charge in the P1–C1–P2 fragment. However, these P–C distances
are significantly longer then in the diphosphanylmethanide ligand
in 1. The carboxylic acid group is nearly coplanar with the
P1–C1–P2 fragment forming a dihedral angle of 9.18◦, very similar
to that observed in the neutral carbodiphosphorane CO2 adduct
(Ph3P)2C–CO2 (10.0◦).42 Like other carboxylic acids, 6 and 7 form
dimers in the solid state through a double hydrogen bond (O1–
¯
6, compound 7 crystallizes in the space group P1. The iridium
˚
centre is surrounded by four phosphorus atoms, a hydride and a
iodide ligand in a slightly distorted octahedral environment. In
the formed anionic (Ph2P)2C–COOH ligand the carbon atoms,
O2¢ 2.606 A). As mentioned above the compounds 6 and 7 are
closely related to carbodiphosphorane CO2 and CS2 adducts and
should be treated as their metal containing counterparts. Table 2
summarizes some of the structural features of these adducts
together with those of 6 and 7. Although the C1–C2 bond in
the carbodiphosphorane adducts is quite short, calculations have
shown that the contribution of attractive p-orbital interactions to
this bond is rather small.42 The even shorter C1–C2 bond (see
Table 2) in the iridium complexes 6 and 7 may indicate a higher
degree of a multiple bond character and higher contribution of the
resonance structure B (see Scheme 3) to the real bonding situation.
Scheme 3 Mesomeric forms of 6 and 7.
The observed structure of the newly formed ligand is in
contrast to the lithium salt which arises from the reaction
of [Li(dppm-H)]n with CO2. In this case, the formation of a
bis(diphenylphosphino)acetate ligand was reported but further
analytical data was not available.25 Therefore, the formation
of [Li{(Ph2P)2CHCOO}] was reinvestigated and recrystallization
from dme was found to produce suitable crystals of the dinuclear
complex [Li(dme){(Ph2P)2CHCOO}]2 (8) for X-ray diffraction
experiments. The same compound was formed when a solution
of the above mentioned lithium complex 3 was exposed to a
CO2 atmosphere. The molecular structure of 8 (molecule A of
two independent molecules) shown in Fig. 5 illustrates, that in
this complex indeed the other tautomeric form of the ligand
known from the iridium complexes is observed. As expected,
the geometries of those two ligands are quite different (see
Fig. 4 Molecular structure of 7 (top) and dimeric unit (bottom), (most of
the H-atoms and co-crystallized acetone are omitted for clarity; disorder
◦
˚
of a phenyl ring is not shown). Selected distances (A) and angles ( )
are: Ir1–P1 2.343(2), Ir1–P2 2.363(2), Ir1–P3 2.344(2), Ir1–P4 2.334(2),
Ir1–I 2.7369(10), P1–C1 1.771(10), P2–C1 1.776(9), P3–C27 1.853(10),
P4–C26 1.844(10), C1–C2 1.407(14), C2–O1 1.323(11), C2–O2 1.274(11),
P1–Ir1–P3 176.42(7), P2–Ir1–P4 172.00(8), P1–C1–P2 99.9(5), P3–C27–P4
96.03(5), O1–C2–O2 119.8(9).
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Table 2 Selected bond lengths and angles of the complexes 6, 7, 8 and of related carbodiphosphorane adducts
Distances (av.) [A]
Angles (av.) [◦]
P–C–P
˚
Compound
P–C
C–C
C–O (or S)
P–C–C
C–C–O (or S)
O–C–O (or S)
Reference
[(Ph3P)2C–CO2]
1.721
1.751
1.764
1.761
1.871
1.494
1.469
1.421
1.428
1.534
1.259
1.691
1.296
1.298
1.249
135.2
127.3
100.2
100.8
104.9
112.2
116.4
129.6
129.3
112.7
116.2
117.6
119.9
119.9
116.8
127.7
124.8
120.2
120.1
126.5
42
42
19
—
—
[(Ph3P)2C–CS2]
6
7
8
react with 6 within days under release of CO2. While the cation
[IrCl(dppm)2(H)]+ was the only phosphorus containing species
detected in dichloromethane, a untraceable mixture of products
was formed in chloroform. The products formed may stem from
the reaction of 6 with HCl slowly formed in those chlorinated
solvents. A similar reactivity towards other acidic compounds like
NH4PF6 supports this hypothesis.
This reaction leads to the formation of [IrCl(dppm)2(H)]PF6
(10) (see Scheme 4) which was identified an basis of its NMR
spectra. Carbodiphosphorane CO2 adducts react in a comparable
way with acids underlining the similarity of 6 and 7 to those
compounds.44 Crystals of 10 obtained from acetone, acetonitrile
or ethanol suffer from twining and were not suitable for X-ray
diffraction experiments.
Fig.
5 Molecular structure of 8 (carbon atoms of dme and
most of the H-atoms are omitted for clarity). Selected distances
(A) and angles (◦) are: Li1A–O1A 1.867(6), Li1A–O3A 1.894(6),
˚
Li1A–O5A 2.052(6), Li1A–O6A 2.068(6), O1A–C2A 1.256(4), O2A–C2A
1.240(4), C1A–C2A 1.533(4), P1A–C1A 1.871(3), P2A–C1A 1.870(3).
O1A–Li1A–O3A 129.5(3), O1A–Li–O5A 102.1(3), O1A–Li1A–O6A
105.7(3), O1A–C2A–O2A 126.6(3), O1A–C2A–C1A 116.8(3),
O2A–C2A–C1A 116.5(3), P1A–C1A–P2A 104.77(16), P1A–C1A–C2A
109.3(2), P2A–C1A–C2A 114.8(2).
Table 2) and the ligand observed in the lithium salt truly is a
bis(diphenylphosphino)acetate. NMR measurements of 8 in d8-thf
confirm, that the same tautomeric form of the ligand is observed
in solution as well. Besides the signals of the dme ligand and the
phenyl groups a triplet at d = 4.11 in the 1H NMR spectrum and a
triplet at d = 48.2 in the 13C NMR spectrum were observed for the
PCHP group. Additionally, the signal of the carboxylate function
was found at d = 174.8 in the 13C NMR spectrum.
Scheme 4 Acid induced decarboxylation of 6.
However, the related compound [IrCl(dppm)2(H)]I (11) con-
taining the same cation as 4 and 10 was obtained as side product
of the reaction of [Ir2(m-I)2(coe)4], dppm and CO2 in toluene. 11
arises from impurities of the used starting material. The molecular
structure of 11 is shown in Fig. 6.
In compound 11 the iridium atom has the same donor set
consisting of four phosphorus atoms, a hydride and a chloride
as the one in compound 1. The distances and angles of the
coordinated dppm ligands in those complexes are similar. As
expected the main difference is the shorter Ir1–Cl bond of
The formation of the iridium complexes 6 and 7 can be explained
by the initial C–H bond activation of dppm in the complex 2
leading to intermediate 1 or its iodo analog. As shown in Scheme 2,
a coordinating anion is necessary for this reaction. Therefore
the related compound [Ir(dppm)2]PF6 (9) containing the weakly
-
˚
coordinating PF6 anion was prepared in analogy to the known
2.467(3) A in the cation of 11 when compared to the Ir1–Cl bond
trifluoroacetate derivative.30 Its composition was established by
NMR measurement. In solution no C–H activation of coordinated
dppm of 9 was observed and no reactivity towards CO2 was found
as well under the employed conditions.
˚
of 2.513(2) A in neutral 1.
Finally, it should be mentioned that no insertion of CO2 into
the Ir–H bonds of the reported complexes was observed under
the applied conditions (room temperature, CO2 pressure up to 0.4
bar).
The next steps in the formation of 6 and 7 are the nucleophilic
attack of CO2 by the methanide carbon followed by a proton shift
to the formed carboxylate function resulting in formal insertion
of CO2 into the C–H bond of the diphosphanyl methanide
anion. Ruiz et al. reported a similar insertion of alkynes into
the C–H bond of a coordinated diphosphanyl methanide ligand
in fac-[Mn(CNtBu)(CO)3{(PPh2)2C–H}].43 The low solubility of
6 and 7 in common organic solvents prevents their further
investigation in solution. Chlorinated solvents slowly dissolve and
Conclusions
The reaction between dppm and [IrX(coe)2]2 results in the
formation of various products partially connected which each
other via different equilibria. The variation of the solvent and
the ligand to metal ratio allows the isolation of some of those
products (1, 2, 5; X = Cl). When such a reaction mixture is
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Synthesis of [Ir(dppm)]Cl (2) and formation of
[IrCl(dppm)2(H)][OR] (4a: R = Et; 4b: R = Me)
Ethanol (8 ml) was added to a mixture of solid [Ir2(m-Cl)2(coe)4]
(67 mg, 0.075 mmol) and dppm (115 mg, 0.299 mmol). The
obtained suspension was stirred until all solids were dissolved
resulting in a red solution. This solution was stored at -20 ◦C
over night. Afterwards the volume was reduced in a vacuum to
approximately 2 ml until crystallization of a red compound started.
Then the stirring was stopped and the solution was allowed to
stand 1 h at room temperature resulting in the formation of red
crystals of 2. The mother liquor was decanted and the residue
was rapidly washed with 2 ml of a mixture of thf and ethanol (2
to 1) and dried in vacuo. The crystals partially lose cocrystallized
ethanol on drying. Yield: 85 mg. dP(81.0 MHz, d8-THF–EtOH):
-35.7 (s, 2), -53.9 (s, 4a).
A sample of red 2 was dissolved im d4-Methanol. The obtained
pale yellow solution contained [IrCl(d2-dppm)2(H)][OCD3] (4b) as
sole iridium containing product. dH(200 MHz, d4-MeOH): -16.45
(1H, quint., 2JH,P 12.0, Ir–H), 1.17 (~6H, t, 3JH,H 7.0, CH3 EtOH),
3.60 (~4H, q, JH,H 7.0, CH2 EtOH), 7.2–7.6 (40 H, m, CH Ph).
dP(81.0 MHz, d4-MeOH): -53.9 (s).
Fig. 6 Molecular structure of 11 (most of the H-at◦oms are omit-
˚
ted for clarity). Selected distances (A) and angles ( ) are: Ir1–P1
2.342(3), Ir1–P2 2.311(3), Ir1–P3 2.349(3), Ir1–P4 2.316(3), Ir1–Cl
2.467(3), P1–C1 1.861(13), P2–C1 1.823(11), P3–C26 1.833(11), P4–C26
1.848(12), P1–Ir1–P4 171.65(10), P2–Ir1–P3 173.35(10), P1–C1–P2
95.1(5), P3–C26–P4 94.2(5).
3
Synthesis of [Li(dme)2(dppm-H) (3)
exposed to a CO2 atmosphere, the surprisingly selective formation
of [IrX(dppm)(H){(Ph2P)2C–COOH}] (6: X = Cl, 7: X = I)
was observed containing an unique anionic ligand. This ligand
is most likely formed from dppm by a C–H activation/CO2
carboxylation sequence mediated by iridium. Comparison with
related lithium compounds indicates that the iridium center with
its strong preference for the phosphorus donors of the ligand is
responsible for its tautomerisation while in case of lithium the
expected diphosphinoacetate ligand was observed.
The observed tautomer in 6 and 7 shows some remarkable
similarities with carbodiphosphorane-CO2 adducts making com-
plexes with this ligand an interesting subject for further studies if
derivatives with higher solubility can be found.
[Li(dppm-H)]n25 (0.52 g, 1.33 mmol) was dissolved in dme (20 ml),
stirred for 30 min and evaporated to dryness. The pale yellow
residue was washed with cold diethyl ether (2 ¥ 5 ml) and dried in a
vacuum. Yield 0.59 g (78%). Found: C, 69.0; H, 7.2% C33H41LiO4P2
requires C, 69.5; H, 7.2%. dH(400 MHz, d8-THF) 1.61 (1H, t, 2JH,P
8.4, CH), 3.27 (12H, s, CH3 dme), 3.44 (8H, s, CH2 dme), 6.97 (4H,
m, p-CH Ph), 7.08 (8H, m, m-CH Ph), 7.56 (8H, m, o-CH Ph).
dC(50.3 MHz, d8-THF) 18.5 (1C, t, 1JC,P 17.8, P2CH), 58.8 (4C, s,
CH3 dme), 72.6 (4C, s, CH2 dme), 125.4 (4C, s, p-CH Ph), 127.3
(8C, t, J 2.8, m-CH-Ph), 132.0 (8C, t, J 7.9, o-CH Ph), 152.5 (4C, t,
J 3.4, i-C Ph). dP(81.0 MHz, d8-THF) 3.1(s). Suitable crystals for
X-ray measurement were obtained by cooling a saturated solution
of 3 in dme from room temperature to -20 ◦C.
Synthesis of [Ir(g1-dppm)(g2-dppm)2]Cl*6CH3OH (5)
Experimental
Dppm (70 mg, 0.182 mmol) was added to a suspension of [Ir2(m-
Cl)2(coe)4] (25 mg, 0.028 mmol) in methanol (6 ml) and the
resulting mixture was stirred for 4h. Afterwards the solution was
filtered and concentrated to 2 ml in a vacuum. Storage at -40 ◦C
resulted in formation of yellow orange crystals within a week. The
supernatant solution was decanted and the residue was dried in
a vacuum. The compound loses the cocrystallized methanol on
prolonged drying in vacuo. Yield 63 mg (85%). Found: C, 65.0;
H, 4.8% C75H66IrClP4 requires C, 65.2; H, 4.8%; dP(81.0 MHz,
d8-THF, 223 K) -13.4 (1P, q, 2JP,P 29.3), -24.4 (1P, d, 2JP,P 29.5),
-64.1 (4P, d, 2JP,P 29.2).
General data
All manipulations were carried out under an argon atmosphere
using standard Schlenk techniques. The solvents were dried
according to common procedures and distilled under argon,
deuterated solvents were dried over sodium, degassed, and sat-
urated with argon. Acetone was dried with CaCl2 and distilled
before used. [Ir2(m-X)2(coe)4] was prepared according (X = Cl) 45
or in analogy (X = I) to literature methods.41 Crude impure [Ir2(m-
I)2(coe)4] obtained this way was used without further purification.
Dppm was purchased from Aldrich. CO2 (99.999%) was purchased
from Air Liquide and used without further purification. The
1H and 13C{ H} NMR spectra were obtained on a Bruker AC
1
Synthesis of [IrCl(dppm)(H){(Ph2P)2C–COOH}] (6)
400 MHz or 200 MHz spectrometer. Chemical shifts are reported
in parts per million and referenced to SiMe4 using the residual
signal of the deuterated solvent as reference and 85% phosphoric
acid, respectively. Infrared spectra were recorded using a Perkin–
Elmer Spectrum One spectrometer. Carbon and hydrogen analyses
were performed with a Perkin–Elmer 2400 microanalyzer.
Dppm (102 mg, 0.27 mmol) in toluene (5 ml) was added to a
stirred suspension of [Ir2(m-Cl)2(coe)4] (56 mg, 0.062 mmol) in
toluene (5 ml). The initially red solution bleached to yellow and
the argon atmosphere was replaced by CO2 resulting in further
bleaching topale yellow andprecipitationofa colourless solid. The
7818 | Dalton Trans., 2010, 39, 7813–7821
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reaction mixture was stirred for additional three hours. Afterwards
the supernatant solution was decanted and the remaining white
residue was washed with toluene (2 ¥ 5 ml) and diethyl ether (2 ¥
5 ml). The obtained product 6·0.5toluene was dried in a vacuum.
Yield 131 mg (96%). Found: C, 60.3; H, 4.5% C54.5H48IrClO2P4
requires C, 60.25; H, 4.45%. nmax/cm-1 2185w (Ir–H), 1580br
(COO), 1270br (COO).
Similar results were obtained in thf, acetone or acetonitrile. 6 is
insoluble in common organic solvents like toluene, diethyl ether,
thf or acetone, and dissolves slowly and decomposes in chlorinated
solvents like CHCl3 and CH2Cl2.
Synthesis of [Li2{OOC–CH(PPh2)2}2(dme)2] (8)
[Li{OOC–CH(PPh2)2}]25 was recrystallized from dimethoxy-
ethane. 8 was obtained as colourless crystals.
dH(400 MHz, d8-THF) 3.28 (12H, s, CH3 dme), 3.44 (8H, s,
2
CH2 dme), 4.11 (2H, t, JH,P 2.8, CH), 7.03–7.13 (24H, m, CH
Phenyl), 7.41–7.48 (8H, m, CH Ph), 7.52–7.59 (8H, m, CH Ph);
dC(50.3 MHz, d8-THF) 48.2 (2C, t, 1JC,P 25.7, P2CH), 58.8 (4C, s,
CH3 dme), 72.6 (4C, s, CH2 dme), 128.0–128.4 (12C, m, CH Ph),
134.3 (4C, t, J 10.8, o-CH–Ph), 135.2 (4C, t, J 11.4 Hz, o-CH Ph),
140.1 (2C, t, J 5.7, i-C Ph), 140.9 (2C, t, J 4.8, i-C Ph), 174.8 (2C, s,
COO); dP(81.0 MHz, d8-THF) -9.8 (s). nmax/cm-1 1625 (COO).
Suitable crystals of the composition 6·3acetone for X-ray
measurement were obtained directly from a reaction mixture in
acetone.
Synthesis of [Ir(dppm)2]PF6 (9)
[Ir(dppm)2]PF6 was prepared in analogy to [Ir(dppm)2]OTf.30
dH(400 MHz, d6-acetone) 5.22 (4H, br, PCH2P), 7.3–7.6 (40H,
m, Ph); dP(162.0 MHz, d6-acetone) -35.7 (4P, s, dppm), -144.0
(1P, sept, 1JP,F 711, PF6).
Synthesis of [IrI(dppm)(H){(Ph2P)2C–COOH}] (7)
A solution of dppm (72 mg, 0.19 mmol) in thf (4 ml) was added
to a stirred suspension of [Ir2(m-I)2(coe)4] (51 mg, 0.047 mmol) in
thf (5 ml). The resulting brown solution was pressured with CO2
(0.2 bar) and was allowed to stand overnight. Afterwards the su-
pernatant solution was decanted from the formed microcrystalline
solid. The residue was washed with diethyl ether (2 ¥ 5 ml) and
dried in a vacuum. Yield 85.5 mg (80%). nmax/cm-1 2165w (Ir–H),
1590br (COO), 1265br (COO).
Similar results were obtained in toluene or acetone. Suitable
crystals of the composition 7·3acetone for X-ray measurement
were obtained directly from a reaction mixture in acetone. Suitable
crystals of compound 11 for X-ray measurement were obtained as
an impurity from the mother liquor of the reaction in toluene.
Synthesis of [IrCl(dppm)2(H)]PF6 (10)
NH4PF6 (14.7 mg, 0.09 mmol) was added to a stirred suspension
of 6 (77.2 mg, 0.074 mmol) in acetone (5 ml). Within 1 h a clear
colourless solution formed and the solvent was removed in a
vacuum. The remaining solid was washed with diethyl ether (3 ¥
4 ml) and dried in a vacuum. Yield: 85 mg (crude product, contains
the excess of NH4PF6). As judged from the 31P nmr, 10 is the only
dppm containing product formed. A sample recrystallized from
acetone was used for elemental analysis. Found: C, 52.7; H, 4.0%
Table 3 Crystal data and refinement details for the X-ray structure determinations
Compound
Formula
1
3
5
7
8
11
C50H44ClIrP4
0.5·(C4H10O2)
1041.44
-90(2)
Monoclinic
P21/c
9.9857(3)
21.0322(6)
21.3775(7)
90
94.868(2)
90
4473.5(2)
4
1.546
32.26
30048
6285
10210/0.1292
0.1268
0.0603
1.007
1.975/-1.039
NONE
770462
C33H41LiO4P2
[C75H66IrP6]+ Cl-
6·(CH4O)
1573.00
-90(2)
Monoclinic
P21/c
20.9095(3)
13.8595(2)
27.8469(5)
90
111.662(1)
90
7500.0(2)
4
1.393
19.96
49853
11474
17055/0.0942
0.1232
0.0524
1.033
C51H44IIrO2P4
3·(C3H6O)
1306.16
-173(2)
Triclinic
C60H62Li2O8P4
[C50H45ClIr P4]+ I-
fw/g mol-1
570.54
-90(2)
Monoclinic
C2/c
16.2326(6)
9.2525(2)
21.7101(7)
90
106.354(2)
90
3128.76(17)
4
1.211
1.74
10804
2844
3572/0.0384
0.1037
0.0359
1.015
0.263/-0.239
NONE
770463
1048.86
-90(2)
Triclinic
1124.29
-90(2)
Monoclinic
P21/c
12.7210(5)
16.1700(3)
25.2040(7)
90
120.220(3)
90
4479.9(2)
4
1.667
39.06
41253
7899
10225/0.0910
0.2321
0.0833
1.031
1.614/-1.599
NONE
770467
T/◦
C
Crystal system
Space group
¯
¯
P1
P1
˚
a/A
12.3388(7)
13.1005(7)
17.6742(10)
84.285(2)
79.868(2)
79.862(2)
2761.5(3)
2
1.571
31.4
25015
8418
11.5057(2)
15.9886(4)
32.4517(6)
92.367(1)
90.741(1)
110.614(1)
5580.4(2)
4
1.248
1.89
31591
15912
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
r/g cm-3
m/mm-1
measured data
data with I > 2s(I)
unique data (Rint
)
9747/0.0766
0.1739
0.0606
23791/0.0341
0.2019
0.0769
wR2 (all data, on F2)a
R1 (I > 2s(I))a
sb
1.018
1.009
-3
˚
Res. dens./e A
absorpt method
CCDC No.
1.762/-0.896
NONE
770464
2.263/-4.982
empirical
770465
0.881/-0.781
NONE
770466
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
2
2
a Definition of the R indices: R1 = ( ||Fo| -|Fcꢀ)/ |Fo|; wR2 = { [w(Fo - Fc2)2]/ [w(Fo2)2]} with w-1 = s (Fo2) + (aP)2. b s = { [w(Fo
-
1/2
Fc2)2]/(No - Np)}
.
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Dalton Trans., 2010, 39, 7813–7821 | 7819
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View Article Online
C50H45IrClF6P5 requires C, 52.6; H, 4.0%. nmax/cm-1 2198w (Ir–
H). dH(400 MHz, CD2Cl2) -16.39 (1H, quint., JH,P 12.1, Ir–H),
5.1–5.25 (2H, m, CHH’), 5.30–5.45 (2H, m, CHH’), 7.1–7.25
9 D. Walther, U. Ritter, S. Geßler, J. Sieler and M. Kunert, Z. Anorg. Allg.
2
Chem., 1994, 620, 101–106.
10 R. Fischer, D. Walther and H. Go¨rls, Eur. J. Inorg. Chem., 2004, 1243–
1252.
(32H, m, CH Ph), 7.35–7.45 (8H, m, CH Ph); dC(75 MHz, CD2Cl2)
11 R Fischer, H. Gorls and D. Walther, Z. Anorg. Allg. Chem., 2004, 630,
¨
1
1387–1394.
50.1 (2C, quint., JC,P 15.6, P–CH2–P), 128.0 (4C, quint., J 15.5,
12 M. Zerella, S. Mukhopadhyay and A. T. Bell, Org. Lett., 2003, 5,
3193.
i-C Ph), 129.0 (8C, quint., J 2.6, CH Ph), 129.5 (8C, quint., J 2.6,
CH Ph), 131.2 (4C, quint., J 15.2, i-C Ph), 132.1 (4C, s, p-CH Ph),
132.5 (4C, s, p-CH Ph), 133.0 (8C, quint., J 3.2, CH Ph), 133.4
(8C, quint., J 2.9, CH Ph). dP(121.5 MHz, CD2Cl2) -55.2 (4P, s,
dppm), -144.2 (1P, sept., 1JP,F 711.3, PF6).
13 Y. Fujiwara, Y. Taniguchi, K. Takaki, M. Kurioka, T. Jintoku and T.
Kitamura, Stud. Surf. Sci. Catal., 1997, 107, 275.
14 For reviews on C–H activation see: K. R. Campos, Chem. Soc. Rev.,
2007, 36, 1069–1084; J. A. Labinger and J. E. Bercaw, Nature, 2002,
417, 507–514; C. Slugovc, I. Padilla-Martinez, S. Sirol and E. Carmona,
Coord. Chem. Rev., 2001, 213, 129–157; G. Dyker, Angew. Chem., Int.
Ed., 1999, 38, 1698–1712; A. E. Shilov and G. B. Shul’pin, Chem. Rev.,
1997, 97, 2879–2932.
A related complex [IrCl(dppm)2(H)]BF4 has been previously
reported.21
15 A. D. English and T. Herskovitz, J. Am. Chem. Soc., 1977, 99, 1648–
Crystal structure determinations
1649.
16 A. Behr, E. Herdtweck, W. A. Herrmann, W. Keim and W. Kipshagen,
J. Chem. Soc., Chem. Commun., 1986, 1262–1263.
17 A. Behr, E. Herdtweck, W. A. Herrmann, W. Keim and W. Kipshagen,
Organometallics, 1987, 6, 2307–2313.
18 F. G. Bordwell, W. S. Matthews and N. R. Vanier, J. Am. Chem. Soc.,
1975, 97, 442–443.
19 J Langer, M. J. Fabra, P. Garc´ıa-Ordun˜a, F. J. Lahoz and L. A. Oro,
Chem. Commun., 2008, 4822–4824.
20 R. H. Hitts, R. A. Franchuk and M. Cowie, Organometallics, 1991, 10,
1297.
The intensity data for the compounds 1, 3, 5, 8 and 11 were
collected on a Nonius KappaCCD diffractometer using graphite-
˚
monochromated Mo-Ka radiation (l = 0.71073 A). Data were
corrected for Lorentz and polarization effects but not for ab-
sorption effects.46,47 The structures were solved by direct methods
(SHELXS)48 and refined by full-matrix least squares techniques
against Fo (SHELXL-97) (Table 3).49 All hydrogen atoms were
2
included at calculated positions with fixed thermal parameters. All
non-disordered non-hydrogen atoms were refined anisotropically.
The intensity data for 7 was recorded at 100(2) K on a Bruker-AXS
Smart CCD diffractometer, using a w scan technique with Mo-Ka
radiation. The structure was solved by direct methods (SHELXS-
97)48 and refined on F2 by full-matrix least-squares techniques us-
ing the SHELXL-97 program.49 Non-hydrogen atoms were refined
with anisotropic displacement parameters, and most hydrogen
atoms were refined from observed positions. The hydride ligand
was included from electrostatic potential calculations (HYDEX
program).50 XP (SIEMENS Analytical X-ray Instruments, Inc.)
was used for structure representations.
21 C. Tejel, M. A. Ciriano, S. Jime´nez, L. A. Oro, C. Graiff and A.
Tiripicchio, Organometallics, 2005, 24, 1105–1111.
22 D. E. Chebi, P. E. Fanwick and I. P. Rothwell, Organometallics, 1990,
9, 2948–2952.
23 J. R. Torkelson, O. Oke, J. Muritu, R. McDonald and M. Cowie,
Organometallics, 2000, 19, 854–864.
24 J. S. Wiley and D. M. Heinekey, Inorg. Chem., 2002, 41, 4961–4966.
25 K. Issleib and H. P. Abicht, J. Prakt. Chem., 1970, 312, 456–465.
26 D. J. Brauer, S. Hietkamp and O. Stelzer, J. Organomet. Chem., 1986,
299, 137–142.
27 H. H. Karsch, B. Deubelly and G. Mu¨ller, J. Organomet. Chem., 1988,
352, 47–59.
28 J. Langer, K. Wimmer, H. Go¨rls and M. Westerhausen, Dalton Trans.,
2009, 2951–2957.
29 R Brady, W. V. Miller and L. Vaska, J. Chem. Soc., Chem. Commun.,
1974, 393–394.
30 D. Yakhvarov, P. Barbaro, L. Gonsalvi, S. M. Carpio, S. Midollini, A.
Orlandini, M. Peruzzini, O. Sinyashin and F. Zanobini, Angew. Chem.,
Int. Ed., 2006, 45, 4182–4185.
Acknowledgements
31 M. Rivero, C. Kremer, J. Gancheff, E. Kremer, L. Suescun, A. Mombru´,
R. Mariezcurrena, S. Dom´ıngues, A. Mederos and S. Midollini,
Polyhedron, 2000, 19, 2249–2254.
32 K. H. Whitmire, D. R. Derringer and K. R. Kongkasuwan, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2002, 58, m363.
33 R. Fischer, J. Langer, H. Go¨rls, A. Malassa, D. Walther and G.
Vaughan, Chem. Commun., 2006, 2510–2512.
This work was supported by the Deutsche Forschungsgemein-
schaft (DFG, Bonn-Bad Godesberg, Germany; Grants LA
2474/1-1 and LA 2474/1-2) and by MEC (Grants CTQ2006-
01629 and CONSOLIDER INGENIO-2010 CSD2006-0015).
34 H. Schmidbaur, G. Reber, A. Schier, F. E. Wagner and G. Mu¨ller, Inorg.
Chim. Acta, 1988, 147, 143–150.
Notes and references
35 L. M. Venanzi, R. Spagna and L. Zambonelli, Chem. Commun., 1971,
1570–1571.
1 For reviews on CO2 activation and utilization see: S. N. Riduan and
Y. Zhang, Dalton Trans., 2010, 39, 3347–3357; M. Aresta and A.
Dibenedetto, Dalton Trans., 2007, 2975–2992; T. Sakakura, J.-C. Choi
and H. Yasuda, Chem. Rev., 2007, 107, 2365–2387; N. Getoff, Radiat.
Phys. Chem., 2006, 75, 514–523; M. Tokuda, J. Nat. Gas Chem., 2006,
15, 275–281; X. Yin and J. R. Moss, Coord. Chem. Rev., 1999, 181,
27; D. H Gibson, Chem. Rev., 1996, 96, 2063–2095; W. Leitner, Coord.
Chem. Rev., 1996, 153, 257; P. Braunstein, D. Matt and D. Nobel, Chem.
Rev., 1988, 88, 747; A. Behr, Angew. Chem., 1988, 100, 681; D. Walther,
Coord. Chem. Rev., 1987, 79, 135.
2 F. Thomas, G. Garo and F. Susan, (Shell Oil), WO-A1 01/16072.
3 G. A. Olah, A. Torok, J. P. Joschek, I. Bucsi, P. M. Esteves, G. Rasul
and G. K. S. Prakash, J. Am. Chem. Soc., 2002, 124, 11379–11391.
4 H. Kolbe, Liebigs Ann. Chem., 1860, 113, 125–127.
36 T. Herskovitz, J. Am. Chem. Soc., 1977, 99, 2391–2392.
37 J. C. Calabrese, T. Herskovitz and J. B. Kinney, J. Am. Chem. Soc.,
1983, 105, 5914–5915.
38 T. Herskovitz and L. J. Guggenberger, J. Am. Chem. Soc., 1976, 98,
1615–1616.
39 T. Herskovitz, Inorg. Synth., 1982, 21, 99–103.
40 J. Langer, W. Imhof, M. J. Fabra, P. Garc´ıa-Ordun˜a, H. Go¨rls, F. J.
Lahoz, L. A. Oro and M. Westerhausen, Organometallics, 2010, 29,
1642–1651.
41 T. Yamagata, M. Nagata, K. Mashima and K. Tani, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2007, 63, m2402.
42 W Petz, C. Kutschera, M. Heitbaum, G. Frenking, R. Tonner and B.
Neumu¨ller, Inorg. Chem., 2005, 44, 1263–1274.
5 H. Kolbe and E. Lautemann, Liebigs Ann. Chem., 1860, 115, 157–206.
6 For a recent example see: Y. Kosugi, Y. Imaoka, F. Gotoh, M. A. Rahim,
Y. Matsui and K. Sakanishi, Org. Biomol. Chem., 2003, 1, 817–821.
7 G. Bottaccio and G. P. Chiusoli, Chem. Commun., 1966, 618.
8 G. Bottaccio and G. P. Chiusoli, Z. Naturforsch., 1968, 23B(561), 1016.
43 J. Ruiz, R. Quesada, V. Riera, E. Castellano and O. Piro,
Organometallics, 2004, 23, 175–177.
44 C. N. Matthews, J. S. Driscoll and G. H. Birum, Chem. Commun., 1966,
736–737.
7820 | Dalton Trans., 2010, 39, 7813–7821
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
45 A. Van Der Ent and A. L. Onderdelinden, Inorg. Synth., 1990, 28, 91.
46 COLLECT, Data Collection Software B. V. Nonius, Netherlands, 1998.
47 Processing of X-Ray Diffraction Data Collected in Oscillation Mode,
Z. Otwinowski, W. Minor, in C. W. Carter, R. M. Sweet (ed.), Methods
in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, pp.
307–326, Academic Press, San Diego 1997.
48 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 1990,
46, 467–473.
49 G. M. Sheldrick, SHELXL-97 (Release 97-2), University of Go¨ttingen,
Germany, 1997.
50 A. G. Orpen, J. Chem. Soc., Dalton Trans., 1980, 2509–
2516.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 7813–7821 | 7821
©