Dehydrogenation of hydridoirida-ss-diketones in methanol: The selective formation of mono- and dinuclear acyl complexes

Article abstract of DOI:10.1002/ejic.201000250

The hydridoirida-ss-diketone [IrH((PPh₂(O-C ₆H₄CO))₂H)Cl] (1) reacts with diimines (NN) or with pyridine (py) in refluxing methanol to undergo dehydrogenation. The reactions afford selectively the cis-acyl, trans-phosphane isomers of the cationic [Ir(PPh₂(o-C₆H₄CO)) ₂(NN)]⁺ (NN = 2,2′-bipyridine (2); R-N=C(CH ₃)-C(CH₃)=N-R′ [R = R′ = NH₂ (3); R = R′ = OH (4); R = OH, R′ = NH₂ (5)]} or neutral [IrCl(PPh₂(O-C₆H₄CO))₂(Py)] (6) derivatives. The reactions are faster for ligands containing amino substituents. Refluxing 1 in MeOH affords the formation of an equimolar mixture of dimer cationic species [Ir₂(μ-Cl)(μ-PPh₂(o-C ₆H₄CO))₂(PPh₂(o-C₆H ₄CO))₂]⁺ (7a and 7b) containing two acyls and a chloride as bridging groups. The isomers could be separated by fractional precipitation. Compound [3]C1, containing amino substituents in the imino functionalities, catalyses the hydrogen transfer from 2-propanol to cyclohexanone to afford cyclohexanol. All the complexes were fully characterised spectroscopically. Single crystal X-ray diffraction analysis was performed on complexes 6 and [7b]ClO₄.

Full text of DOI:10.1002/ejic.201000250

FULL PAPER
DOI: 10.1002/ejic.201000250
Dehydrogenation of Hydridoirida-β-diketones in Methanol: The Selective
Formation of Mono- and Dinuclear Acyl Complexes
Roberto Ciganda,[a] María A. Garralda,*[a] Lourdes Ibarlucea,[a] Claudio Mendicute,[a]
Elena Pinilla,[b] and M. Rosario Torres[b]
Keywords: Iridium complexes / Acyl bridging ligands / Dehydrogenation
The hydridoirida-β-diketone [IrH{(PPh2(o-C6H4CO))2H}Cl]
(1) reacts with diimines (NN) or with pyridine (py) in re-
fluxing methanol to undergo dehydrogenation. The reactions
afford selectively the cis-acyl, trans-phosphane isomers of
the cationic [Ir(PPh2(o-C6H4CO))2(NN)]+ {NN = 2,2Ј-bipyr-
idine (2); R–N=C(CH3)–C(CH3)=N–RЈ [R = RЈ = NH2 (3); R =
RЈ = OH (4); R = OH, RЈ = NH2 (5)]} or neutral [IrCl(PPh2(o-
C6H4CO))2(py)] (6) derivatives. The reactions are faster for
ligands containing amino substituents. Refluxing 1 in MeOH
affords the formation of an equimolar mixture of dimer
cationic
species
[Ir2(µ-Cl)(µ-PPh2(o-C6H4CO))2(PPh2(o-
C6H4CO))2]+ (7a and 7b) containing two acyls and a chloride
as bridging groups. The isomers could be separated by frac-
tional precipitation. Compound [3]Cl, containing amino sub-
stituents in the imino functionalities, catalyses the hydrogen
transfer from 2-propanol to cyclohexanone to afford cyclo-
hexanol. All the complexes were fully characterised spectro-
scopically. Single crystal X-ray diffraction analysis was per-
formed on complexes 6 and [7b]ClO4.
hydridoirida-β-diketone
[IrH2{(PPh2(o-C6H4CO))2H}]
Introduction
while Et3N gave [Ir2(µ-H){µ-PPh2(o-C6H4CO)}2(PPh2(o-
C6H4CO))2]Cl, with two acylphosphane chelate-bridging li-
gands and a bridging hydride.[4] In some of these reactions
dehydrogenation reactions also occurred. We report now on
the reactivity of 1 in methanol in the presence or absence
of N-donor ligands such as diimines: 2,2Ј-bipyridine (bipy),
R–N=C(CH3)–C(CH3)=N–RЈ [dihydrazone, R = RЈ = NH2
(bdh); dioxime, R = RЈ = OH (dmg); oxime hydrazone, R
= OH, RЈ = NH2 (boh)] or pyridine (py). In all cases dehy-
drogenation occurs to afford mono- or dinuclear diacyl
complexes.
Hydridoirida-β-diketones can be easily prepared by acti-
vation of aldehydes, tethered to N- or P-ligands, by hydri-
doacyliridium complexes.[1] Metalla-β-diketones, also de-
scribed as acylhydroxycarbene complexes, are rather stable
due to the formation of a strong intramolecular hydrogen
bond between the acyl and the hydroxycarbene moieties.
Recently it has been reported that this hydrogen bond is
stronger than that in acetylacetone, an organic β-di-
ketone.[2] The hydridoirida-β-diketone complex [IrH-
{(PPh2(o-C6H4CO))2H}Cl] (1) being an electronically satu-
rated species is remarkably stable. In solvents of low po-
larity, 1 is unreactive toward σ-donors such as pyridine or
triphenylphosphane. It requires the abstraction of chloride
to afford cationic mononuclear [IrH{(PPh2(o-C6H4CO))2-
H}(L)][ClO4] complexes, or the dinuclear species
[Ir2H(PPh2(o-C6H4CO)){µ-PPh2(o-C6H4CO)}3]BF4, con-
taining three acylphosphane bridging ligands and a single
terminal hydride, in a reversible process.[3] In methanol the
reaction of 1 with bases such as KOH or Et3N, at room
temperature, led to dehydrodechlorination and afforded the
acyl-bridged hydrido iridium derivative [Ir2H2(PPh2(o-
C6H4CO))2(µ-PPh2(o-C6H4CO))2]. When the reaction was
performed in refluxing methanol, KOH led to a novel di-
Results and Discussion
Complex 1 reacts with diimines in refluxing methanol,
to undergo dehydrogenation affording the cationic diacyl
derivatives [Ir(PPh2(o-C6H4CO))2(NN)]+ (NN = bipy, 2;
bdh, 3; dmg, 4; boh, 5) shown in Scheme 1. The reactions
are slow and require reaction times in a 90 min–9 h range to
reach completion. The corresponding complexes have been
isolated as perchlorate compounds by addition of sodium
perchlorate (see Exp. Sect.). High stereochemical selectivity
is observed in these reactions that afford a single isomer.
The obtained complexes show the expected features in their
IR spectra, their FAB spectra show the parent peaks and
they behave as 1:1 electrolytes in acetone solution.[5] For
complexes containing symmetric diimines, 2–4, the diimine
ligand shows one set of resonances due to equivalent imino
fragments, their 31P{1H} NMR spectra contain only one
singlet in the 27–33 ppm range, indicating equivalent P-
[a] Facultad de Química de San Sebastián, Universidad del País
Vasco,
Apdo. 1072, 20080 San Sebastián, Spain
[b] Departamento de Química Inorgánica, Laboratorio de
Difracción de Rayos X, Facultad de Ciencias Químicas,
Universidad Complutense,
28040 Madrid, Spain
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M. A. Garralda et al.
FULL PAPER
atoms and the 13C{1H} NMR spectra show also only one CH2PiPr2)2}] and hydrogenation of [RuH(PMe3){N-
singlet in the 216–224 ppm range, corresponding to equiva- (CH2CH2PiPr2)2}], via heterolytic splitting of hydrogen,
lent acyl groups. According to these data two isomers are suggest that the barrier for the hydrogen splitting may be
possible for these complexes, the cis-acyl, trans-phosphane lowered by hydrogen bond formation with added water.[8]
species or the trans-acyl, cis-phosphane compound. Taking In the present case the different dehydrogenation rates may
into account electronic considerations, the most stable iso- be related to initial hydrogen bond formation between the
mer would be the cis-acyl, trans-phosphane isomer, with the hydroxycarbene proton and the free N-donor ligand which
acyl groups trans to the imino groups, since acyls, having may lead to the proton being closer to the hydride thus
the largest trans influence and being the best σ-donors, allowing for easier formation of hydrogen when better pro-
would prefer to be trans to the imino group with the lowest ton acceptor ligands are available. X-ray diffraction studies
trans influence, being the weakest σ-donor, when compared on hydridoirida-β-diketones have shown that the iridacycle
to phosphanes.[6] This is confirmed by the reaction of 1 with comprising the acyl(hydroxycarbene) group is essentially
boh, containing nonsymmetrical imino groups, which planar.[3a] In these reactions complete dehydrogenation oc-
shows that the stereochemistry of 5 corresponds to that curs while previously we have observed that the reaction
shown in Scheme 1. The oxime hydrazone ligand shows two of 1 with Et3N in refluxing methanol led only to partial
sets of resonances due to nonequivalent imino fragments, dehydrogenation.[4] We believe that this different behaviour
the 31P{1H} NMR spectrum shows two doublets (AB may be related to the better coordinating ability of diimines,
pattern) at δ = 37.3 and 26.7 ppm corresponding to two when compared to Et3N, which may favour the removal of
nonequivalent phosphanes mutually trans [J(P,P) = 323 Hz] the hydride in the present case.
and the 13C{1H} NMR spectrum contains two acyl reso-
nances at δ = 233.9 and 214.6 ppm.
The reaction of [IrHCl{(PPh2(o-C6H4CO))2H}] (1) with
pyridine in refluxing methanol also leads to dehydrogena-
tion to afford the neutral diacyl [IrCl(PPh2(o-C6H4CO))2-
(py)] (6). Its IR spectrum contains the band due to coordi-
nated acyl groups at 1624 cm–1 and the FAB spectrum
shows the peak due to pyridine loss. The 31P{1H} NMR
spectrum contains an AB spin pattern due to trans phos-
phorus atoms [J(P,P) = 347 Hz] and the 13C{1H} NMR
spectrum contains two resonances in the 210 ppm region,
attributed to two acyl groups bonded to iridium. These
spectral features indicate trans P-atoms and cis-acyl groups
trans to chloride and to pyridine, which are the groups with
lower trans influence, as shown in Scheme 1.
Complex 6 could be characterised by single-crystal X-
ray diffraction, which confirms the spectroscopic findings.
Complex 6 crystallises in the P21/c monoclinic group. Fig-
ure 1 shows an ORTEP view of complex 6. Selected bond
lengths and angles are listed in Table 1. The coordinative
environment of the rhodium atom is distorted octahedral,
with four positions occupied by the phosphorus and carbon
atoms of the two bidentate ligands, and the other two posi-
Scheme 1. NN = bipy, 2; bdh (R = RЈ = NH2), 3; dmg (R = RЈ =
OH) 4; boh, (R = NH2, RЈ = OH), 5.
Complex 1 contains a hydride, which may behave as a tions are occupied by the nitrogen atom of the pyridine and
proton acceptor, and an alcoholic O···H···O proton. In by chloride. As also proposed for complexes 2–5, the phos-
CDCl3/CD3OD solution H/D exchange of this proton is phorus atoms are mutually trans, and the acyl groups are
observed. We believe that the dehydrogenation reaction mutually cis. A similar feature has also been observed in a
most likely occurs by interaction of H– and H+. Because of related rhodium complex.[7d] The bond lengths in 6 are in
the low rate of our reactions we were unable to observe any the expected ranges.[9] The Ir–P distances are similar and
hydrogen evolution by NMR during the dehydrogenation the Ir–N1 [2.229(4) Å] and Ir–Cl [2.515(1) Å] distances are
reaction. Nevertheless, the interaction between late transi- rather long, because of the high trans influence of the acyl
tion-metal hydrides and alcoholic or hydroxycarbene pro- groups.
tons that may result in hydrogen formation is documen-
Attempts to obtain a diacyl complex similar to 6 using
ted.[7] Furthermore, we observe some relation between the more sterically demanding ligands such as 2-methylpyridine
reaction rate and the type of ligand. The slowest reaction proved unsuccessful. Instead, the formation of an equi-
occurs for the dioxime ligand containing OH groups (ca. molar mixture of dimer cationic species [Ir2(µ-Cl)(µ-
9 h), the reaction with a good “proton acceptor” ligand PPh2(o-C6H4CO))2(PPh2(o-C6H4CO))2]+ (7a and 7b) oc-
such as bipyridine is faster (ca. 150 min) and the reaction curred (see Scheme 2). Refluxing 1 in MeOH affords also
with ligands containing amino groups, bdh or boh, are the the formation of 7. The two isomers could be separated
fastest (ca. 90 min). Recent studies on a reversible reaction by addition of NaClO4. The precipitation of [7a]ClO4 was
involving dehydrogenation of [Ru(H)2(PMe3){HN(CH2- quantitative and from the remaining solution [7b]ClO4
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Dehydrogenation of Hydridoirida-β-diketones in Methanol
Scheme 2.
Figure 1. ORTEP view of compound 6 showing the atomic num-
bering (20% probability ellipsoids). The hydrogen atoms and some
carbon atoms have been omitted for clarity.
The 13C{1H} NMR spectrum of 7a contains two dou-
blets due to acyl groups. In both resonances the coupling
to one of the phosphorus atoms is observed while the cou-
pling to the other phosphorus is unobservable. The reso-
nance at lower field is due to acyl groups with carbon atoms
trans to phosphorus atoms [J(P,C) = 99 Hz]. The chemical
shift, 264.9 ppm, is in the upper end of the range 274–
240 ppm, reported for bridging acyl groups between iridium
atoms in dinuclear complexes,[3b,4,10] and is similar to that
of the related rhodium [Rh2(µ-Cl)(µ-PPh2(o-C6H4CO))2-
(PPh2(o-C6H4CO))2]+ complex.[6d] The resonance at higher
field, 197.6 ppm, is attributed to terminal acyl groups and
appears at higher field than that of the related rhodium
derivative, 219.0 ppm. The 31P{1H} NMR spectrum con-
tains two doublets consistent with an AX pattern. For this
isomer we propose the structure depicted in Scheme 2, with
two equivalent iridium fragments, and with phosphorus
atoms trans to acyl and to chlorine. It contains the weakest
σ-donor oxygen atoms trans to the strongest σ-donor acyl
groups, which represents the most electronically favourable
geometry. Nevertheless, a disposition with phosphorus
atoms being trans to acyl and to oxygen cannot be ex-
cluded. For 7b, the spectra are due to the presence of four
nonequivalent acyl-phosphane fragments, two per iridium
atom. In the 13C{1H} NMR spectrum two close doublets
due to terminal acyl groups [ca. 198.9 ppm, J(P,C) = 8 Hz]
and two close doublets due to bridging acyl groups [ca.
264 ppm, J(P,C) = 102 Hz] are observed. The 31P{1H}
NMR spectrum consists of four doublets. The J(P,P) cou-
pling constants agree with both phosphorus atoms bonded
to the same iridium atom being mutually cis.
Table 1. Selected bond lengths [Å] and angles [°] for 6 and [7b]
ClO4.
6
[7b]ClO4
Ir–P1
Ir–P2
Ir–C20
Ir–Cl
Ir–N1
Ir–Cl
2.342(1) Ir1–P1
2.321(1) Ir1–P2
2.020(6) Ir1–C20
2.029(5) Ir1–C1
2.229(4) Ir1–Cl1
2.515(1) Ir1–O4
1.210(6) C20–O2
1.214(6) C1–O1
Ir1–Ir2
2.373(3) Ir2–P3
2.270(2) Ir2–P4
2.382(3)
2.258(3)
2.04(1)
2.01(1)
2.496(4)
2.126(7)
1.24(1)
1.22(1)
2.02(1)
2.00(1)
Ir2–C58
Ir2–C39
2.418(4) Ir2–Cl1
2.267(7) Ir2–O2
C20–O2
C1–O1
1.27(1)
1.23(1)
3.564(1)
99.1(1)
C58–O4
C39–O3
P1–Ir–P2
P1–Ir–C20 96.4(2)
P1–Ir–Cl
P1–Ir–C1
P1–Ir–N1
175.01(5) P1–Ir1–P2
P3–Ir2–P4
101.4(1)
175.3(3)
85.5(2)
99.4(1)
83.6(3)
81.7(3)
169.5(2)
101.2(1)
89.9(3)
90.9(3)
P1–Ir1–C20 177.0(3) P3–Ir2–C58
89.1(5)
84.3(2)
91.0(1)
P1–Ir1–Cl1 88.8(1)
P1–Ir1–C1
P1–Ir1–O4
P3–Ir2–O2
P3–Ir2–Cl1
P3–Ir2–C39
P4–Ir2–C58
83.8(3)
95.9(2)
P2–Ir–C20 82.4(2)
P2–Ir1–C20 82.0(2)
P2–Ir–Cl
P2–Ir–C1
P2–Ir–N1
91.9(1)
90.8(2)
93.9(1)
P2–Ir1–Cl1 168.6(1) P4–Ir2–O2
P2–Ir1–C1
P2–Ir1–O4
84.9(3)
104.0(2) P4–Ir2–C39
C58–Ir2–O2
P4–Ir2–Cl1
C20–Ir–Cl 173.3(2) C20–Ir1–Cl1 89.7(3)
C20–Ir–C1 86.1(2)
C20–Ir–N1 94.6(2)
C20–Ir1–C1 93.6(4)
C20–Ir1–O4 86.4(3)
C1–Ir1–Cl1 87.8(3)
C58–Ir2–Cl1 84.4(3)
C58–Ir2–C39 92.9(4)
C1–Ir–Cl
N1–Ir–Cl
90.6(2)
89.1(1)
O2–Ir2–Cl1
85.3(2)
82.9(3)
C1–Ir1–O4
171.0(3) O2–Ir2–C39
C1–Ir–N1 175.3(2) Cl1–Ir1–O4 83.2(2)
Ir1–Cl1–Ir2 93.0(2)
Cl1–Ir2–C39 167.6(3)
Ir1–C1–O1
Ir1–C20–O2 124.0(7) Ir2–C58–O4
Ir1–O4–C58 119.5 (7) Ir2–O2–C20
122.3(8) Ir2–C39–O3
123.4(8)
125.4(8)
123.0 (6)
It is noteworthy that by refluxing 1 in MeOH in the pres-
ence of NEt3, partial dehydrochlorination and partial dehy-
drogenation occurred, thus yielding the dinuclear [Ir2(µ-
H)(µ-PPh2(o-C6H4CO))2(PPh2(o-C6H4CO))2]Cl, with a hy-
could be obtained. Both compounds behave as 1:1 electro- dride and two acyl groups bridging the two iridium atoms.[4]
lytes in acetone solution and the FAB spectra show the An isomer, [Ir2H(PPh2(o-C6H4CO)){µ-PPh2(o-C6H4CO)}3]
[M]+ peak at 1577 as expected for such dinuclear species. BF4, containing three acylphosphane bridging ligands and
Their IR spectra show stretches at 1633 cm–1 due to the a single terminal hydride, could be obtained by complete
terminal acyl groups and a strong stretch at 1515 cm–1 that halide abstraction and partial dehydrogenation of 1 pro-
can be assigned to bridging acyl groups.
moted by halide abstractors.[3] In the present case, complete
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Figure 2. ORTEP view of the cation in compound [7b]ClO4 showing the atomic numbering (20% probability ellipsoids). The hydrogen
atoms and some carbon atoms have been omitted for clarity.
dehydrogenation leads the chloride to occupy a bridging
It is well known that metal hydrides may catalyse the
position in 7. The formation of these triply bridged iridium transfer hydrogenation of ketones.[13] Chelated IrIII bis-car-
dimers appears easy. In all cases two of the bridging groups bene complexes, proposed to involve a monohydride active
between the two iridium atoms are acyls and the nature of species, or hemilabile pincer-type hydride IrIII derivatives
the third bridge appears to depend markedly on the reac- have been reported to promote the transfer hydrogenation
tion conditions.
of cyclohexanone, reaching TOF values higher than
We succeeded in isolating compound [7b]ClO4 as single 1000 mol/h.[14] We have recently shown that in methanol
crystals suitable for X-ray diffraction. This compound crys- and in the presence of strong bases iridium acyls may afford
tallises in the P21/n monoclinic group. The asymmetric unit iridium acylhydrides,[4] and that the presence of P- and N-
–
consists of a dinuclear cation and a ClO4 anion. Figure 2 donor ligands, instead of only P-donor ligands, make the
shows an ORTEP view of the cation. Selected bond lengths corresponding iridium hydrides more useful for transfer hy-
and angles are listed in Table 1. Two acyl groups in a head- drogenation reactions of ketones.[1c] We have tested the
to-tail arrangement and a chloride bridge the Ir atoms. The catalytic activity of complexes 2–7 in the transfer hydrogen-
geometry around each Ir atom is pseudo-octahedral with ation of cyclohexanone in iPrOH, in the presence of a
the chloro ligand trans to a phosphorus atom through the strong base. From the transfer hydrogenation data it is ap-
Ir1 atom and trans to the carbon atom of a terminal acyl parent that compound [3]Cl, containing amino substituents
group through the Ir2 atom. The bridging Ir2–Cl1 distance in both the imino functionalities shows the highest activity
[2.496(4) Å] is longer than the Ir1–Cl1 distance [2.418(4) Å] reaching 88% conversion to cyclohexanol after 180 min
reflecting the higher trans influence of the acyl group.[11] (TOF[15] of 134 after 10 min). The dimer compound [7]Cl
The bridging Ir2–Cl1 distance is slightly shorter than that reaches 59% conversion after 180 min (TOF[15] of 85 after
observed in the mononuclear complex 6 [2.515(1) Å], and is 10 min) and the pyridine complex 6 shows lower activity,
similar to that reported for complexes containing a bridging reaching 44% conversion after 180 min. For compounds
chloride trans to vinyl [2.495(6) and 2.464(6) Å].[10] The Ir1– [2]Cl, [4]Cl and [5]Cl less than 10% conversion was attained
Ir2 distance [3.564(1) Å] and the Ir1–Cl1–Ir2 angle after 180 min. The corresponding perchlorate compounds
[93.0(2)°] exclude any Ir–Ir interaction. As in other dinu- show a lower activity than the chloride compounds, proba-
clear species,[12] the Ir1–Ir2 distance in 7b is longer than bly due to their low solubility. Compound [3]Cl shows a
that in the related [Ir2(µ-H)(µ-PPh2(o-C6H4CO))2(PPh2(o- comparable catalytic activity to that of Cp*IrIII complexes
C6H4CO))2]+ [2.9629(4) Å] containing hydride instead of containing functionalised carbenes.[16]
chloride as the bridge. The Ir–C and the C–O distances of
the bridging and terminal acyl groups are practically equal.
The average Ir–C and C–O bond lengths, 2.02(1) Å and
Conclusions
1.24(1) Å respectively are as expected for coordinated acyl
groups with low carbene-like character.[10] The Ir–P dis-
The hydridoirida-β-diketone [IrH{(PPh2(o-C6H4CO))2-
tances also reflect the decreasing trans influence in the H}Cl] (1) undergoes dehydrogenation in protic solvents to
series: acyl [Ir1–P1 2.373(3) and Ir2–P3 2.382(4) Å] ϾϾ afford dimer complexes with bridging acyl and chloride
chlorine [Ir1–P2 2.270(2) Å] Ͼ oxygen [Ir2–P4 2.258(3) Å]. groups. The presence of N-donors makes the dehydrogena-
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Dehydrogenation of Hydridoirida-β-diketones in Methanol
C42H36ClIrN2O8P2·CH3OH (1018.16): calcd. C 50.71, H 3.96, N
2.75; found C 50.57, H 4.10, N 2.94.
tion reaction faster, suggesting hydrogen bond formation
favouring the dehydrogenation reaction, affording selec-
tively cationic or neutral diacyl complexes of the cis-acyl,
trans-phosphane type. The dihydrazone-containing complex
can be used as a pre-catalyst for transfer hydrogenation of
ketones.
[Ir(PPh2(o-C6H4CO))2(boh)]ClO4 (5): To a methanol suspension of
[IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (50 mg, 0.062 mmol) was added
biacetyloxime hydrazone (boh) (8.7 mg, 0.062 mmol). The suspen-
sion was refluxed for 90 min whereupon a yellow solution was
formed. The solution was cooled and a methanol solution of
NaClO4·H2O (7.6 mg, 0.062 mmol) was added to afford a yellow
solid that was decanted, washed with methanol and dried under
Experimental Section
vacuum. Yield 37.3 mg, 61%. IR (KBr): ν = 3341 (w) (OH), 3395
˜
(w), 3201 (w) (NH), 1607 (s) (C=O) cm–1. ΛM (ohm–1 cm2 mol–1):
General Procedures: The preparation of the metal complexes was
carried out at room temperature under nitrogen using standard
Schlenk techniques. [IrHCl{(PPh2(o-C6H4CO))2H}] (1) was pre-
pared as previously reported.[1a] Microanalyses were carried out
with a Leco CHNS–932 microanalyser. Conductivities were mea-
sured in acetone solution with a Metrohm 712 conductimeter. IR
spectra were recorded with a Nicolet FTIR 510 spectrophotometer
in the range 4000–400 cm–1 using KBr pellets. NMR spectra were
recorded with Bruker Avance DPX 300 or Bruker Avance 500 spec-
trometers, 1H and 13C{1H} (TMS internal standard), 31P{1H}
(H3PO4 external standard), were measured from CDCl3 solutions.
Mass spectra were recorded with a VG Autospec, by liquid second-
ary ion (LSI) MS using nitrobenzyl alcohol as matrix and a caes-
ium gun (Universidad de Zaragoza).
1
94 (acetone). H NMR (CDCl3): δ = 10.6 (s, 1 H, OH); 6.17 (s, 2
H, NH); 1.72 (s, 3 H, CH3); 1.56 (s, 3 H, CH3) ppm. 31P{1H} NMR
(CDCl3): δ = 37.3 (d) and 26.7 (d) [J(P,P) = 273 Hz] ppm. 13C{1H}
NMR (CDCl3): δ = 233.9 [d, J(P,CO) = 4 Hz, IrCO]; 214.6 [d,
J(P,CO) = 4 Hz, IrCO]; 13.6 (s, CH3); 13.2 (s, CH3) ppm.
C42H37ClIrN3O7P2·CH3OH (1017,17): calcd. C 50.76, H 4.06, N
4.13; found C 50.40, H 4.01, N 4.02.
[IrCl(PPh2(o-C6H4CO))2(py)] (6): To a methanol suspension of
[IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (50 mg, 0.062 mmol) was added
pyridine (py) (5 µL, 0.062 mmol). The suspension was refluxed for
3 h whereupon a yellow solution was formed. The solution was
cooled and evaporation of the methanol solution under vacuum
afforded a yellow solid that was decanted, washed with methanol
and dried under vacuum. Yield 31.8 mg, 58%. IR (KBr): ν = 1624
˜
[Ir(PPh2(o-C6H4CO))2(bipy)]ClO4 (2): To a methanol suspension of
[IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (50 mg, 0.062 mmol) was added
2,2Ј-bipyridine (bipy) (9.7 mg, 0.062 mmol). The suspension was
refluxed for 150 min whereupon a yellow solution was formed. The
solution was cooled and a methanol solution of NaClO4·H2O
(8.7 mg, 0.062 mmol) was added to afford a yellow solid that was
decanted, washed with methanol and dried under vacuum. Yield
(s) (C=O) cm–1. 31P{1H} NMR (CDCl3): δ = 33.5 (d) and 29.0 (d)
[J(P,P) = 347 Hz] ppm. 13C{1H} NMR (CDCl3): δ = 211.4 [d,
J(P,C) = 2 Hz, IrCO]; 209.8 [d, J(P,C) = 4 Hz, IrCO] ppm. FAB-
MS: calcd. for C43H33ClIrNO2P2, 885; obsd. 806 [M – py+].
C43H33ClIrNO2P2·CH3OH (917.16): calcd. C 57.61, H 4.07, N
1.53; found C 57.30, H 3.95, N 1.84.
50.3 mg, 79%. IR (KBr):
ν =
1627 (s) (C=O) cm–1. ΛM
˜
Reaction of 1 with 2-Methylpyiridine. Formation of [Ir2(µ-Cl)(µ-
PPh2(o-C6H4CO))2(PPh2(o-C6H4CO))2]Cl [7]Cl: To a methanol
suspension of [IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (30 mg,
0.037 mmol) was added 2-methylpyridine (3.7 µL, 0.037 mmol).
The suspension was refluxed for 90 min whereupon a yellow solu-
tion was formed. The solution was cooled and evaporation of the
methanol solution under vacuum afforded an equimolar mixture
of [7a]Cl and [7b]Cl that was identified by NMR spectroscopy.
(ohm–1 cm2 mol–1): 128 (acetone). 31P{1H} NMR (CDCl3): δ = 27.2
(s) ppm. 13C{1H} NMR (CDCl3): δ = 216.0 (s) ppm. C48H36ClIr-
N2O6P2 (1026.14): calcd. C 56.17, H 3.53, N 2.73; found C 55.79,
H 3.16, N 2.71.
[Ir(PPh2(o-C6H4CO))2(bdh)]ClO4 (3): To a methanol suspension of
[IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (50 mg, 0.062 mmol) was added
biacetyldihydrazone (bdh) (7.1 mg, 0.062 mmol). The suspension
was refluxed for 90 min whereupon a yellow solution was formed.
The solution was cooled and a methanol solution of NaClO4·H2O
(8.7 mg, 0.062 mmol) was added to afford a yellow solid that was
decanted, washed with methanol and dried under vacuum. Yield
[Ir2(µ-Cl)(µ-PPh2(o-C6H4CO))2(PPh2(o-C6H4CO))2]ClO4 [7a]ClO4
and [7b]ClO4: A methanol suspension of [IrH{(PPh2(o-C6H4CO))2-
H}Cl] (1) (50 mg, 0.062 mmol) was refluxed for 10 h whereupon a
yellow solution was formed. The solution was cooled and a meth-
anol solution of NaClO4·H2O (1.8 mg, 0.031 mmol) was added to
afford a yellow solid, [7a]ClO4, which was decanted, washed with
methanol and dried under vacuum. Yield 24.9 mg, 48%. To the
remaining solution a methanol solution of NaClO4·H2O (1.8 mg,
0.031 mmol) was added to afford a yellow solid, [7b]ClO4, which
was decanted, washed with methanol and dried under vacuum.
45.2 mg, 74%. IR (KBr): ν = 3398 (m) (OH), 3299 (m), 3201 (m)
˜
(NH2), 1597 (s) (C=O) cm–1. ΛM (ohm–1 cm2 mol–1): 134 (acetone).
1H NMR (CDCl3): δ = 5.68 (s, 4 H, NH); 1.57 (s, 3 H, CH3) ppm.
31P{1H} NMR (CDCl3): δ = 31.4 (s) ppm. 13C{1H} NMR (CDCl3):
δ = 218.3 (s, IrCO); 15.1 (s, CH3) ppm. FAB-MS: calcd. for
C42H38IrN4O2P2, 885; obsd. 885 [M+]. C42H38ClIrN4O6P2·CH3OH
(1016,18): calcd. C 50.81, H 4.17, N 5.51; found C 50.62, H 4.18,
N 5.78.
Yield 15.6 mg, 30%. Data for [7a]ClO . IR (KBr): ν = 1638 (s)
˜
4
(C=O)t, 1516 (s) (C=O)b cm–1. ΛM (ohm–1 cm2 mol–1): 137 (ace-
[Ir(PPh2(o-C6H4CO))2(dmg)]ClO4 (4): To a methanol suspension
tone). 31P{1H} NMR (CDCl3): δ = 21.9 [d, J(P,P) = 3 Hz, Pa]; 9.9
of [IrH{(PPh2(o-C6H4CO))2H}Cl] (1) (50 mg, 0.062 mmol) was (d, Pb) ppm. 13C{1H} NMR (CDCl3): δ = 264.9 [d, J(P,C) = 99 Hz,
added dimethylglyoxime (dmg) (8.7 mg, 0.062 mmol). The suspen-
sion was refluxed for 9 h whereupon a yellow solution was formed.
The solution was cooled and a methanol solution of NaClO4·H2O
(7.6 mg, 0.062 mmol) was added to afford a yellow solid that was
decanted, washed with methanol and dried under vacuum. Yield
IrCaO]; 197.6 [d, J(P,C) = 6 Hz, IrCbO] ppm. FAB-MS: calcd. for
C76H56ClIr2O4P4, 1577; obsd. 1577 [M+]. C76H56Cl2Ir2O8P4·
2CH3OH (1740.22): calcd. C 53.82, H 3.71; found C 53.49, H 3.55.
Data for [7b]ClO . IR (KBr): ν = 1633 (s) (C=O) , 1515 (s) (C=O)
˜
4
t
cm–1. ΛM (ohm–1 cm2 mol–1): 95 (acetone). 31P{1H} NMR
b
29.4 mg, 48%. IR (KBr): ν = 3611 (m) (OH), 1624 (s) (C=O) cm–1.
(CDCl3): δ = 20.2 (d) and 17.4 (d) [J(P,P) = 9 Hz]; 17.8 (d) and
13.4 (d) [J(P,P) = 6 Hz] ppm. 13C{1H} NMR (CDCl3): δ = 263.8
[d, J(P,C) = 102 Hz]; 263.1 [d, J(P,C) = 102 Hz]; 198.9 [d, J(P,C) =
8 Hz] and 195.7 (m) for IrCO ppm. FAB-MS: calcd. for C76H56Cl-
˜
1
ΛM (ohm–1 cm2 mol–1): 140 (acetone). H NMR (CDCl3): δ = 1.73
(s, 3 H, CH3) ppm. 31P{1H} NMR (CDCl3): δ = 32.8 (s) ppm.
13C{1H} NMR (CDCl3): δ = 224.6 (s, IrCO); 14.7 (s, CH3) ppm.
Eur. J. Inorg. Chem. 2010, 3167–3173
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3171

M. A. Garralda et al.
FULL PAPER
Ir2O4P4, 1577; obsd. 1577 [M+]. C76H56Cl2Ir2O8P4 (1676.16): calcd.
C 54.45, H 3.37; found C 54.46, H 3.71.
refined by a least-squares fit of all reflections collected. The first
100 frames were recollected at the end of the data collection to
monitor crystal decay, and no appreciable decay was observed. In
both cases a semi-empirical absorption correction was applied. The
structures were solved by direct methods and conventional Fourier
techniques and refined by applying full-matrix least-squares on F2
with anisotropic thermal parameters for the non-hydrogen atoms,
with the exception of the oxygen atoms of the perchlorate anions
of 7b, which were refined isotropically. The hydrogen atoms were
included at their calculated positions determined by molecular ge-
ometry and refined riding on the corresponding bonded atom. All
the calculations were carried out with SHELX-97.[17]
Catalytic Reactions: The transfer hydrogenation reactions were car-
ried out under nitrogen in refluxing 2-propanol with magnetic stir-
ring. The equipment consisted of a 100-mL round-bottomed flask,
fitted with a condenser and provided with a septum cap. The cata-
lysts, as chloride compounds, were prepared “in situ” by refluxing
equimolar amounts (0.02 mmol) of 1 and the corresponding ligand
in MeOH to obtain solutions. After cooling, the methanol was
eliminated under vacuum. The solid residue was dissolved in 30 mL
of 2-propanol and 0.2 mmol of potassium hydroxide in 10 mL of
2-propanol were added. The resulting solutions were heated to
83 °C and 4 mmol of the substrate was injected. The analysis of
the catalytic reactions was carried out with a Shimadzu GC-14A
chromatograph, connected to a Shimadzu C-R6A calculation inte-
grator.
CCDC-767995 (for 6) and -767996 (for 7b) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/datarequest/cif.
X-ray Structure Determination of 6 and [7b]ClO4: Prismatic yellow
crystals of [C43H33Cl1N1O2P2Ir] and [C76H56Cl1O4P4Ir2]ClO4 suit-
able for X-ray experiments were obtained by slow diffusion of di-
ethyl ether into chloroform solutions of 6 or [7b]ClO4. A summary
of the fundamental crystal and refinement data are given in
Table 2. The crystals were resin epoxy coated and mounted on a
Bruker Smart CCD diffractometer, with graphite-monochromated
Mo-Kα (λ = 0.71073) radiation, operating at 50 kV and 20 mA.
Data were collected over a hemisphere of the reciprocal space by
combination of three exposure sets. Each frame exposure time was
of 20s, covering 0.3° in ω. The cell parameters were determined and
Acknowledgments
Financial support by Ministerio de Ciencia
(MCINN) (CTQ2008-2967/BQU), Universidad del País Vasco, and
Diputación Foral de Guipuzcoa is gratefully acknowledged.
e Innovación
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Table 2. Crystal data and structure refinement for compounds 6
and [7b]ClO4.
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Crystal data
6
[7b]ClO4
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
[C43H33Cl1IrN1O2P2]
885.29
monoclinic
P21/c
12.0866(5)
17.2053(7)
17.7139(7)
99.837(1)
3629.5(3)
4
[C76H56Cl1Ir2O4P4]ClO4
1676.39
monoclinic
P21/n
20.471(1)
11.864(1)
28.438(2)
99.352(1)
6814.5(8)
4
b [Å]
c [Å]
[°]
Volume [Å3]
Z
D(calcd.) [gcm–3]
Absorption coefficient
[mm–1]
1.620
1.634
3.879
4.130
Scan technique
F(000)
ω and φ
1752
ω and φ
3296
Range for data col-
lection [°]
1.66 to 25.00
1.14 to 25.00
Index ranges
Reflections col-
lected
–14, –20, –20 to 13,19,20 –21, –14, –33 to 24,14,22
25701
34851
Independent reflections 6091 [R(int) = 0.0450]
12015 [R(int) = 0.065]
100.0%
Completeness to theta
Data / restraints /
parameters
95.2%
6091 / 0 / 451
1.063
12015 / 0 / 805
1.082
Goodness-of-fit on F2
R[a] (refl. obsd.)
[I Ͼ 2σ(I)]
0.0303 (4490)
0.0698
0.0516 (7132)
0.1463
RwF[b](all data)
Largest diff. peak and
hole
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0.922 and –0.649 eÅ–3
1.329 and –1.181 eÅ–3
[a] Σ||Fo| – |Fc||/Σ|Fo|. [b] {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
3172
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3167–3173

Dehydrogenation of Hydridoirida-β-diketones in Methanol
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5224–5229.
[15] TOF calculated after 10 min and expressed in mol of product/
(mol of pre-catalystϫh).
[16] A. Pontes da Costa, M. Viciano, M. Sanaú, S. Merino, J. Te-
jeda, E. Peris, B. Royo, Organometallics 2008, 27, 1305–1309.
[17] G. M. Sheldrick, SHELX-97, Program for Crystal Structure
Determination, University of Göttingen, Göttingen, Germany,
1997.
Received: March 2, 2010
Published Online: May 28, 2010
Eur. J. Inorg. Chem. 2010, 3167–3173
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3173