Synthesis and reactivity of new mono- and dinuclear hydridoirida-β- diketones - The formation and characterization of a dinuclear tris-μ-acyliridium(III) complex

Article abstract of DOI:10.1002/ejic.200600458

The hydridoirida-β-diketone [IrH{[PPh₂(o-C ₆H₄CO)]₂H}Cl] (1) reacts with silver salts of potentially coordinating anions such as tosylate (^-OTs) or triflate (^-OTf) to afford the mononuclear neutral derivatives [IrH{[PPh ₂(o-C₆H₄CO)]₂H}(X)] [X = OTs (2), OTf (3)]. In acetone solution the triflate anion in 3 is displaced by the solvent to afford the cationic complex [IrH{[PPh₂(o-C ₆H₄CO)]₂H}(acetone)]OTf (4), which is stable only in acetone solution. The reaction of 1 with halide scavengers containing less coordinating anions such as PF₆^- or BF ₄^- results in the formation of cationic compounds [{IrH[{PPh₂(o-C₆H₄CO)}₂H]} ₂(μ-Cl)]A [A = BF₄ (5), PF₆ (6)] containing a dinuclear species with a single chlorine atom bridging two hydridoirida-β-diketone fragments. Both fragments are magnetically non-equivalent and the acylphosphane groups in each hydridoirida-β-diketone fragment are chemically equivalent. This species undergoes a fluxional process in solution, with ΔH^? = 7.8 ± 0.4 kcal mol ^-1 and ΔS^? = -10.9 ± 0.5 eu. A combination of rotation around the Ir-Cl bonds and variation of the Ir-Cl-Ir angle is suggested to be responsible for the fluxionality. Complex 5 reacts further with AgBF₄ to undergo chloride abstraction along with hydrogen loss and deprotonation to give the cationic dinuclear complex [Ir ₂H{PPh₂(o-C₆H₄CO)}{μ-PPh ₂(o-C₆H₄CO)}₃]BF₄ (7), which contains an acylphosphane chelate along with three acylphosphane bridging ligands and a single hydrido ligand. Bubbling of HCl through an MeOH solution of 7 gives 1, thus making the loss of hydride, enolic protons and chloride from complex 1 a reversible process. All the complexes were fully characterized spectroscopically. Single-crystal X-ray diffraction analysis was performed on complexes 5 and 7. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600458

FULL PAPER
DOI: 10.1002/ejic.200600458
Synthesis and Reactivity of New Mono- and Dinuclear Hydridoirida-
β-diketones – The Formation and Characterization of a Dinuclear Tris-
µ-acyliridium(III) Complex
Francisco Acha,[a] María A. Garralda,*[a] Ricardo Hernández,[a] Lourdes Ibarlucea,[a]
Elena Pinilla,[b] M. Rosario Torres,[b] and Malkoa Zarandona[a]
Dedicated to Professor Victor Riera on the occasion of his retirement
Keywords: Iridium / Hydride ligands / Bridging ligands / P ligands
The hydridoirida-β-diketone [IrH{[PPh2(o-C6H4CO)]2H}Cl]
(1) reacts with silver salts of potentially coordinating anions
such as tosylate (–OTs) or triflate (–OTf) to afford the mononu-
clear neutral derivatives [IrH{[PPh2(o-C6H4CO)]2H}(X)] [X =
OTs (2), OTf (3)]. In acetone solution the triflate anion in 3 is
displaced by the solvent to afford the cationic complex
[IrH{[PPh2(o-C6H4CO)]2H}(acetone)]OTf (4), which is stable
only in acetone solution. The reaction of 1 with halide scav-
process in solution, with ∆H‡ = 7.8 0.4 kcalmol–1 and ∆S‡
= –10.9 0.5 eu. A combination of rotation around the Ir–Cl
bonds and variation of the Ir–Cl–Ir angle is suggested to be
responsible for the fluxionality. Complex 5 reacts further with
AgBF4 to undergo chloride abstraction along with hydrogen
loss and deprotonation to give the cationic dinuclear complex
[Ir2H{PPh2(o-C6H4CO)}{µ-PPh2(o-C6H4CO)}3]BF4 (7), which
contains an acylphosphane chelate along with three acyl-
phosphane bridging ligands and a single hydrido ligand.
Bubbling of HCl through an MeOH solution of 7 gives 1, thus
making the loss of hydride, enolic protons and chloride from
complex 1 a reversible process. All the complexes were fully
characterized spectroscopically. Single-crystal X-ray diffrac-
tion analysis was performed on complexes 5 and 7.
–
engers containing less coordinating anions such as PF6 or
–
BF4 results in the formation of cationic compounds
[{IrH[{PPh2(o-C6H4CO)}2H]}2(µ-Cl)]A [A = BF4 (5), PF6 (6)]
containing a dinuclear species with a single chlorine atom
bridging two hydridoirida-β-diketone fragments. Both frag-
ments are magnetically non-equivalent and the acylphos-
phane groups in each hydridoirida-β-diketone fragment are
chemically equivalent. This species undergoes a fluxional
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
[LxM(COR)(CORЈ)]– (M = Mo, W, Mn, Re, Fe, Os).[4]
Rhena-β-diketones can be deprotonated by transition metal
complexes containing basic ligands to give rhena-β-diketon-
ate derivatives of CuII, FeII, CrIII and ZnII.[5] More recently,
Steinborn et al. have reported mono- and dinuclear platina-
β-diketones obtained by the reaction of hexachloroplatinic
acid with alkynes or by the reaction of diacylhydridoplatin-
um(IV) complexes with TlPF6.[6] Partial deprotonation of
the dinuclear derivatives with amines affords platina-β-dike-
tonates of platina-β-diketones.[7] The reaction of [Ir(Cl)(H)-
{PPh2(o-C6H4CO)}(cod)] (cod = 1,5-cyclooctadiene) with
PPh2(o-C6H4CHO) in protic solvents has allowed the prep-
aration of the first hydridoirida-β-diketone [IrH{[PPh2(o-
C6H4CO)]2H}Cl].[8] Cationic mononuclear hydridoirida-β-
Introduction
Metalla-β-diketones can be considered as enol tautomers
of neutral β-diketones in which the methine group has been
substituted by a transition metal organometallic moiety.
Therefore, they may also be understood as acyl(hydroxycar-
bene) complexes that are stabilized by an intramolecular
hydrogen bond between the acyl and the hydroxycarbene
moiety (see Scheme 1). Hydroxycarbene complexes, for
which a tautomeric equilibrium with the acyl hydrides has
been reported,[1] have been proposed as important interme-
diates in CO reduction reactions[2] or in alkene hydro-
carbonylation reactions to produce alcohols.[3] Metalla-β-
diketones were synthesized for the first time by Lukehart
et al. by the protonation of diacylmetalate anions
[a] Facultad de Química de San Sebastián, Universidad del País
Vasco,
Apdo. 1072, 20080 San Sebastián, Spain
E-mail: mariaangeles.garralda@ehu.es
[b] Departamento de Química Inorgánica, Laboratorio de Difrac-
ción de Rayos X, Facultad de Ciencias Químicas,
Universidad Complutense, 28040 Madrid, Spain
Scheme 1.
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M. A. Garralda et al.
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diketones [IrH{[PPh2(o-C6H4CO)]2H}(L)]+ may undergo
reversible deprotonation/protonation reactions, and their
reaction with amines affords neutral diacylhydridoiridiu-
m(III) derivatives.[9]
We report now on the preparation of new hydridoirida-
β-diketones, including novel dinuclear species, and on the
deprotonation of the latter to afford a dinuclear tris-µ-acyl-
iridium(III) complex.
Results and Discussion
The hydridoirida-β-diketone [IrH{[PPh2(o-C6H4CO)]2-
H}Cl] (1) reacts with silver salts of potentially coordinating
anions such as tosylate (–OTs) or triflate (–OTf) to afford
the neutral complexes [IrH{[PPh2(o-C6H4CO)]2H}(X)] [X =
OTs (2), OTf (3)] with loss of AgCl, as shown in Scheme 2.
The IR spectrum of 3 indicates the presence of the coordi-
nated triflate anion, as shown by the presence of a ν(SO)
absorption at 1317 cm–1, which is shifted to higher wave-
numbers with respect to the free anion (1270 cm–1) upon
coordination, as expected.[10] The IR spectrum of 2 con-
tains a ν(SO) absorption at 1259 cm–1, which is also shifted
towards higher wavenumbers with respect to the silver tos-
ylate (1205 cm–1).[11] The FAB mass spectra show the corre-
sponding [M – X]+ peak, as expected for mononuclear com-
plexes. Both the ν(Ir–H) absorptions (2224 cm–1 for 2 and
2264 cm–1 for 3) at rather high wavenumber and the hydride
resonances (δ = –24.24 ppm for 2 and –25.89 ppm for 3) at
rather high field are in accordance with a hydrido ligand
being trans to the bonded oxygen atom of the anion.[8] The
σ-donor strength of O-coordinated anions is among the
smallest and this is reflected in the trans effect.[12] The
NMR spectroscopic data for both 2 and 3 indicate the pres-
ence of two equivalent acylphosphane fragments. The
31P{1H} NMR spectra show singlets at δ Ϸ 30 ppm and
the 13C{1H} NMR spectrum of 2 shows a doublet at δ =
256.9 ppm, in the range expected for irida-β-diketones with
acyl(hydroxycarbene) character, with a large JP,C coupling
constant of 102 Hz due to the acyl groups being trans to the
phosphorus atoms. The 1H NMR spectra show the hydride
resonances as triplets due to a JP,H coupling of about 12 Hz,
which agrees with the hydride being cis to both phosphane
ligands, and sharp, low-field singlets at δ = 22.72 ppm for 2
and 22.69 ppm for 3, which support the presence of fairly
strong O···H···O hydrogen bonds and the existence of irida-
β-diketones containing a formally tetradentate PCCP li-
gand.[8,9]
Scheme 2.
with the hydride resonance at δ = –24.03 (t, JP,H
=
1
13.25 Hz) ppm, while the H NMR spectrum of 3 shows
two hydride resonances in a 6:1 ratio according to the inte-
grals. The most abundant signal – that of the hydride at δ
= –24.59 (t, JP,H = 12.80 Hz) ppm – is due to 4 and appears
at lower field (ca. 1 ppm) than that of 3, which appears at
δ = –25.74 (t, JP,H = 13.25 Hz) ppm in CDCl3. Attempts to
obtain the acetone complex 4 proved unsuccessful and only
resulted in the isolation of complex 3.
The reaction of [IrH{[PPh2(o-C6H4CO)]2H}Cl] (1) with
halide scavengers containing noncoordinating anions such
as Et3OPF6, Et3OBF4 or AgBF4 and using Ir/scavenger ra-
tios of 2:1 results in the abstraction of only one half of the
chlorine atoms in the starting material and the formation
of the compounds [{IrH[{PPh2(o-C6H4CO)}2H]}2(µ-Cl)]A
[A = BF4 (5), PF6 (6)], which contain a cationic dinuclear
species with a single chlorine atom bridging two hydrido-
irida-β-diketone fragments (see i in Scheme 3). The spectro-
scopic data for the cation in compounds 5 and 6 are the
same. Compounds 5 and 6 show a ν(Ir–H) absorption and
a hydride resonance that agree with a hydride ligand being
trans to a chlorine atom, and a sharp, low-field singlet at
δ = 22.66 ppm that supports the presence of an O···H···O
Complex 2 behaves as nonelectrolyte in acetone solution,
whereas acetone solutions of 3 show conductivity values ex-
pected for 1:1 electrolytes.[13] This indicates that in acetone
solution the tosylate group remains bonded to the iridium
ion while the triflate anion is easily displaced by the solvent
to afford the cationic complex [IrH{[PPh2(o-C6H4CO)]2-
H}(acetone)]OTf (4), as shown in Scheme 2. To confirm
this assumption, we recorded the NMR spectra of both
1
complexes in [D6]acetone solution. The H NMR spectrum
Scheme 3. i: AgBF4, Et3OBF4 or Et3OPF6 in CH2Cl2; ii: AgBF4 in
of 2 in [D6]acetone is almost the same as that in CDCl3, CH2Cl2; iii: Et3OBF4 or Et3OPF6 in CH2Cl2; iv: HCl in MeOH.
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Mono- and Dinuclear Hydridoirida-β-diketones
FULL PAPER
fragment. They behave as 1:1 electrolytes in acetone solu- tween both moieties. For example, the average Ir–P dis-
tion and the FAB spectrum of 6 shows the [M]+ peak at tances are slightly longer [by 0.023(3) Å] in the Ir1 moiety
m/z = 1581, as expected for such a dinuclear species.
and the relative disposition of the pseudo-octahedra is
In order to ascertain the structure shown in Scheme 3, a eclipsed with a slight torsion angle of 26.71°. These facts
single-crystal X-ray diffraction study of compound 5 was mean a breaking of the C2 symmetry around the chlorine
undertaken. Selected bond lengths and angles, including the atom for the whole structure and the twofold axis is only
enolic hydrogen bond, are listed in Table 1. The crystal
structure consists of discrete, cationic dinuclear units
formed by pseudo-octahedral Ir moieties sharing the posi-
tion occupied by the chloro ligand and BF4 anions. An
Table 1. Selected bond lengths [Å] and angles [°] for Complex 5.
Ir1–P1
Ir1–P2
Ir1–C1
Ir1–C20
2.372(3)
2.364(3)
2.01(1)
2.05(1)
1.417
Ir2–P3
Ir2–P4
Ir2–C58
Ir2–C39
2.336(3)
2.354(3)
2.01(1)
2.03(1)
1.420
–
ORTEP view of the cation is given in Figure 1. Both bridg-
ing Ir–Cl distances in 5 are equal within experimental error
and are, as expected, significantly longer [2.539(3) Å] than
the terminal Ir–Cl distance in 1 [2.485(3) Å].[8] As far as we
are aware, there is only one precedent of a dinuclear iridium
complex containing a single chlorine bridge, which is trans
to an SiR2RЈ group.[14] The Ir–Cl distances in 5 are shorter
than those found in this previously reported complex and
this difference may reflect the expected stronger structural
trans influence of SiR3 groups than of hydrido ligands.[15]
The coordination around both Ir atoms is pseudo-octahe-
dral with distortions of the type usually observed in hydrido
complexes (maximal deviation from ideal angles of 19° and
16° for Ir1 and Ir2, respectively). The Ir1–Ir2 distance
(4.609 Å) and the Ir1–Cl1–Ir2 angle [130.3(1)°] exclude any
Ir–Ir interaction. This angle is similar to those reported for
related octahedral rhodium [138.15(7)°] or molybdenum
[134.0(1)°] complexes containing a single chlorine bridge
between two metal atoms.[16] The best least-squares equato-
rial planes (P1, P2, C20, C1) and (P3, P4, C39, C58) of the
Ir atoms form a dihedral angle of 54.1(2)°, in accordance
with the Ir1–Cl1–Ir2 angle. There are some differences be-
Ir1–H1A
Ir2–H1B
Ir1–Cl(1)
C1–O1
C20–O2
O2–H2A
2.535(3)
1.31(1)
1.28(1)
1.16
Ir2–Cl(1)
C39–O3
C58–O4
O3–H2B
2.544(3)
1.27(1)
1.27(1)
1.19
O1–H2A
O2···-O1
1.27
O4–H2B
O4···-O3
1.33
2.39(1)
91.7(5)
81.5(4)
168.8(3)
172.8(4)
81.6(4)
104.7(1)
89.0(3)
92.4(3)
96.4(1)
94.0(1)
104.6
83.1
90.0
71.9
165.7
159.0
130.3(1)
2.42(1)
90.3(5)
83.7(4)
173.9(4)
164.3(4)
82.2(4)
103.6(1)
98.9(3)
88.7(3)
92.8(1)
94.7(1)
77.0
C1–Ir1–C20
C1–Ir1–P1
C20–Ir1–P1
C1–Ir1–P2
C20–Ir1–P2
P1–Ir1–P2
C1–Ir1–Cl(1)
C20–Ir1–Cl(1)
P1–Ir1–Cl(1)
P2–Ir1–Cl(1)
C1–Ir1–H1A
C20–Ir1–H1A
P1–Ir1–H1A
P2–Ir1–H1A
Cl(1)–Ir1–H1A
O2–H2A–O1
Ir1–Cl(1)–Ir2
C39–Ir2–C58
C39–Ir2–P3
C58–Ir2–P3
C39–Ir2–P4
C58–Ir2–P4
P3–Ir2–P4
C39–Ir2–Cl(1)
C58–Ir2–Cl(1)
P3–Ir2–Cl(1)
P4–Ir2–Cl(1)
C39–Ir2–H1B
C58–Ir2–H1B
P3–Ir2–H1B
P4–Ir2–H1B
Cl(1)–Ir2–H1B
O3–H2B–O4
102.0
76.1
91.1
168.4
147.4
Figure 1. ORTEP view of the cation in 5 showing the atomic numbering (20% probability ellipsoids) and the intramolecular hydrogen
bonds. The hydrogen atoms, except for the four shown, and the labels of some carbon atoms have been omitted for clarity.
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M. A. Garralda et al.
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kept for the Ir cores. The C=O distances, which are in the
range 1.27–1.31 Å, are similar to those found in monomeric
irida-β-diketones. The O···O distances and O–H–O angles
are in accordance with a strong enolic character for the hy-
drogen bond and agree with those reported for other irida-
β-diketones.[8,9]
In keeping with the crystal structure, the 31P{1H} NMR
spectra of 5 and 6 show two singlets at δ = 30.7 and
18.3 ppm, respectively, at 203 K, and in the 13C{1H} NMR
spectra two doublets at δ = 257.6 (JP,C = 101 Hz) and
255.6 ppm (JP,C = 103 Hz) are observed. The 1H NMR
spectra contain a triplet at δ = –23.17 (JP,H = 14.6) ppm
and a singlet at δ = 22.66 ppm. Such a pattern is consistent
with the nonequivalence of the hydridoirida-β-diketone
fragments connected through the chlorine bridge, the equiv-
alence of the acylphosphane groups in each hydridoirida-β-
diketone fragment, and the NMR parameters of the hydride
ions and of the enolic protons of both fragments being
equal. Inspection of the 31P{1H} NMR spectra at various
temperatures shows that on raising the temperature the sin-
glets broaden and coalesce at 253 K, giving rise to a broad
resonance centered at δ = 25 ppm at room temperature (see
Figure 2). On the other hand, at room temperature the
13C{1H} NMR spectra show only a doublet at δ = 256.5
(JP,C = 101 Hz) ppm due to the bonded acyl groups. The
1H NMR spectra remain unaltered in the whole tempera-
ture range. From line-shape analysis[17] of the variable-tem-
perature 31P{1H} NMR spectra of complex 5, the activation
parameters ∆H‡
=
7.8 0.4 kcalmol–1 and ∆S‡
=
Figure 2.Variable-temperature 31P{1H} NMR spectra of 5; experi-
mental in CD2Cl2 (left) and calculated (right).
–10.9 0.5 calK–1 mol–1 have been determined. The entropy
of activation is indicative of an intramolecular rearrange-
ment process.[18] A combination of rotation around the Ir–
Cl bonds, which is restricted at low temperatures due to the respectively, with high JP,C coupling constants of about
presence of the phenyl groups, and variation of the Ir–Cl– 95 Hz, due to three acyl groups trans to phosphorus atoms.
Ir angle may account for the observed fluxional behavior.
The rather low field of the latter suggests the bridging na-
Complex 5 reacts further with AgBF4 to give complex 7, ture and significant carbene-like character for all three acyl
which contains three acylphosphane bridging groups (see ii groups.[19–21] Inspection of the NMR spectra at variable
in Scheme 3). Compound 7 shows an IR stretch at temperature shows that on raising the temperature the
1628 cm–1 due to the terminal acyl group and a strong doublet of doublets due to the hydrido ligand collapses into
stretch at 1525 cm–1 assigned to the bridging acyl groups. It a triplet at δ = –23.23 (JP,H = 18.3 Hz) ppm. The 31P{1H}
behaves as 1:1 electrolyte in acetone solution and the FAB resonances at lower field (δ = 23 and 21 ppm) show a
spectrum shows the [M]+ peak at m/z = 1543, as expected marked chemical shift temperature dependence such that ∆δ
for such a dinuclear species. At 223 K, the NMR spectra of decreases as the temperature increases and the AX system
7 are consistent with the structure shown in Scheme 3. The observed at low temperature becomes an AB system cen-
1H NMR spectrum shows only one resonance at high field tered at δ = 22.3 ppm. The two chemical shifts coincide at
(δ = –23.24 ppm) as a doublet of doublets, with a JP,H coup- room temperature, and above this temperature they ex-
ling of about 18 Hz, due to the presence of one hydrido change position. This behavior has also been reported for
ligand cis to two nonequivalent phosphorus atoms. The for- monomeric IrIII complexes.[22] Over the whole temperature
mation of three bridging acyl groups breaks the equivalence range, the corresponding JP,P value, the 31P{1H} resonances
of the acylphosphane fragments present in the starting ma- at higher field, and the 13C{1H} resonances remain un-
terial 5. The 31P{1H} NMR spectrum consists of two sets changed. A {1H,31P} HSQC experiment at room tempera-
of doublets due to the presence of four nonequivalent acyl- ture shows that the hydrido ligand is coupled to the 31P AB
phosphane fragments, two per iridium atom, and the JP,P system at δ = 22 ppm.
coupling constants agree with both phosphorus atoms
Acyl groups are well known as bridging ligands towards
bonded to the same iridium atom being mutually cis. The transition metals, although their behavior as such in iridium
13C{1H} NMR spectrum contains a singlet at δ = homodinuclear complexes is scarce,[21] and the acylphos-
209.1 ppm due to the terminal acyl group and three reso- phane chelating ligand o-PPh2(C6H4CO) has been reported
nances at δ = 266.5 (d), 264.8 (d), and 257.5 (d) ppm, to behave as a bridging acyl group only in ruthenium or
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Mono- and Dinuclear Hydridoirida-β-diketones
FULL PAPER
osmium clusters.[23] We have succeeded in isolating complex 2.12(1) Å for Ir1A–O4A, Ir2A–O1A, and Ir2A–O2A,
7 as single crystals suitable for X-ray diffraction. To the respectively] reflect the trans influence being strongest for
best of our knowledge no structural report on dinuclear the hydrido ligand, similar or slightly weaker for the acyl
transition metal complexes with three bridging acyl groups carbon atom, and weaker for the phosphorus atom. Bridg-
has been published, although a crystallographic study of a ing acyl groups can be described by acyl↔oxycarbene reso-
triacetylrhenate complex of boron has been reported.[24] nance structures and this is reflected by shorter M–C and
The crystal structure of 7 shows the presence of dinuclear longer C–O bond lengths than in terminal acyl li-
–
cations and BF4
anions packed within normal gands.[19–21] In spite of the oxycarbene character of the
van der Waals interaction distances. Two crystallographi- bridging acyl groups suggested by 13C NMR spectroscopy,
cally independent cations and anions were identified in the the Ir–C and C–O distances for the bridging groups in com-
structural determination, namely A and B. No significant plex 7 [average of 2.03(2) and 1.23(2) Å, respectively] are
differences are observed in the molecular geometries of similar to the Ir2A–C39A [1.97(2) Å] and the C39A–O3A
both. Selected bond lengths and angles are listed in Table 2, [1.26(2) Å] distances of the terminal acyl ligand. These fea-
and Figure 3 shows a molecular drawing of the cation A.
The dinuclear cation consists of two pseudo-octahedral
iridium(III) moieties, assuming that the hydrido ligand oc-
Table 2. Selected bond lengths [Å] and angles [°] for complex 7.
cupies the sixth coordination site on Ir1A, with three bridg-
ing acyl groups. Two of the corresponding carbon atoms
are bonded to the iridium atom coordinated to the hydrido
ligand such that the coordination around Ir1 is similar to
that of the parent hydridoirida-β-diketone 5. The hydrido
ligand is trans to the oxygen atom in 7 instead of to the
chlorine atom in 5 and the two oxygen atoms are bonded
to the iridium atom in 7 instead of to a proton in 5. Ir2 is
bonded to two oxygen atoms and one carbon atom of the
bridging acyl groups and six-coordination is attained with
two phosphane groups and one terminal acyl group. The
Ir–P distances in the Ir1A moiety and the Ir2A–P3A dis-
tance are equivalent [average of 2.354(4) Å] and longer than
the Ir2A–P4A distance of 2.242(4) Å as a consequence of
the weaker structural trans influence of the oxygen atom
trans to P4 than that of an acyl carbon atom trans to P1,
P2, and P3. The Ir–O distances [2.23(1), 2.19(1), and
Ir1A–P1A
Ir1A–P2A
Ir1A–O4A
2.345(4) Ir2A–P3A
2.353(4) Ir2A–P4A
2.363(4)
2.242(4)
2.185(8)
2.123(8)
1.97(2)
2.05(2)
1.26(2)
1.21(2)
2.23(1)
Ir2A–O1A
Ir2A–O2A
Ir2A–C39A
Ir2A–C58A
C39A–O3A
C58A–O4A
Ir1A–C1A
Ir1A–C20A
C1A–O1A
C20A–O2A
2.03(1)
2.02(1)
1.23(1)
1.25(1)
C1A–Ir1A–P1A
C1A–Ir1A–P2A
C20A–Ir1A–P2A
C20A–Ir1A–P1A
C20A–Ir1A–C1A
P1A–Ir1A–P2A
O1A–C1A–Ir1A
O2A–C20A–Ir1A
C58A–O4A–Ir1A
C39A–Ir2A–O1A
C39A–Ir2A–O2A
80.9(4)
C39A–Ir2A–P3A
83.2(5)
93.2(5)
102.4(2)
94.0(2)
173.2(4)
80.6(4)
172.5(3)
86.0(3)
120.1(9)
124.3(8)
128(1)
167.6(4) C39A–Ir2A–P4A
80.2(4) P4A–Ir2A–P3A
172.3(4) O1A–Ir2A–P4A
91.7(6) C58A–Ir2A–P3A
106.7(1) C58A–Ir2A–P4A
128(1)
127(1)
121(1)
O2A–Ir2A–P4A
O2A–Ir2A–O1A
C1A–O1A–Ir2A
172.9(5) C20A–O2A–Ir2A
86.9(5) O4A–C58A–Ir2A
Figure 3. ORTEP view of the cation A in complex 7 showing the atomic numbering (20% probability ellipsoids). The hydrogen atoms
and the labels of some carbon atoms have been omitted for clarity.
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M. A. Garralda et al.
FULL PAPER
a Leco CHNS-932 microanalyser. Conductivities were measured 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 re-
corded with Bruker Avance DPX 300 or Bruker Avance 500 spec-
trometers. 1H and 13C{1H} (TMS internal standard), 31P{1H}
(H3PO4 external standard) and 2D spectra were measured for
CDCl3, CD2Cl2, or [D6]acetone solutions. Mass spectra were re-
corded with a VG Autospec, by the liquid secondary ion (LSI)
technique using nitrobenzyl alcohol as matrix and a cesium gun
tures may be related to the fact that the terminal acyl ligand
is trans to the oxygen atom, which has a weak trans influ-
ence, while the carbon atoms of the bridging ligands are
trans to the phosphorus atoms, and/or to the acyl resonance
structure being a stronger contributor than the oxycarbene
resonance structure to the ground-state structure, as sug-
gested for related iridium(III) complexes.[22]
The reaction of 5 with AgBF4 to give 7 is a complex
transformation and its mechanism is not yet totally clear.
Complex 5 contains two hydrido ligands and also two eno- (Universidad de Zaragoza).
lic protons along with a chlorine atom, while complex 7
Preparation of [IrH{[PPh2(o-C6H4CO)]2H}(OTs)] (2): AgOTs
contains only one hydrido ligand; this means release of one
Cl and three H atoms. Attempts to abstract the chloride ion
from complexes 5 or 6 by using Et3OBF4 or Et3OPF6
proved unsuccessful (see iii in Scheme 3) and this indicates
that the silver salt promotes a reaction path that is not avail-
able for other halide scavengers. It is known that metathesis
reactions of silver salts may lead to the formation of dif-
ferent adducts that can involve silver coordination to the
iridium atom,[25] or formation of a halide bridge between
both metal atoms.[26] In our case, replacement of the enolic
protons by silver ions, similar to that observed in pyrazo-
lyliridium complexes,[27] can also be considered. Cationic
acyl(hydroxycarbene)platinum(II) complexes can be ob-
tained by the reaction of diacylhalohydridoplatinum(IV)
complexes with TlPF6 and may involve an intermolecular
deprotonation/protonation reaction.[28] We believe that the
silver salt is responsible for the abstraction of the chloride
(42 mg, 0.150 mmol) was added to a dichloromethane solution of
1 (60 mg, 0.075 mmol). After stirring for 24 h, the silver salts were
filtered off. Addition of diethyl ether to the solution gave a yellow
precipitate, which was filtered off, washed with diethyl ether, and
vacuum-dried (yield: 50 mg, 70%). IR (KBr): ν = 2224 (w) [ν(IrH)],
˜
1632(s) [ν(C=O)], 1259(s) [ν(SO)] cm–1. 1H NMR (CDCl3): δ =
–24.24 (t, JP,H = 12.24 Hz, 1 H, HIr), 2.19 (s, 3 H, CH3), 22.72 (s,
1 H, OHO) ppm. 13C{1H} NMR (CDCl3): δ = 256.9 (d, JP,C
=
102 Hz, CO), 21.2 (s, CH3) ppm. 31P{1H} NMR (CDCl3): δ = 29.9
(s) ppm. FAB MS: calcd. for C45H37IrO5P2S 944, found 773 [M –
OTs]+. C45H37IrO5P2S·0.25CH2Cl2 (965.25): calcd. C 56.31, H 3.92,
S 3.32; found C 56.18, H 3.89, S 3.44.
Preparation of [IrH{[PPh2(o-C6H4CO)]2H}(OTf)] (3): AgOTf
(38 mg, 0.150 mmol) was added to a dichloromethane solution of
1 (60 mg, 0.075 mmol). After stirring for 30 min, the silver salts
were filtered off. Addition of diethyl ether to the solution gave a
yellow precipitate, which was filtered off, washed with diethyl ether,
and vacuum-dried (yield: 47 mg, 68%). IR (KBr): ν = 2264 (w)
˜
ion and one proton, while evolution of H2, formed by com- [ν(IrH)], 1628 (s) [ν(C=O)], 1317 (s) [ν(SO)] cm–1. ΛM
=
=
116 Ω–1 cm2 mol–1. 1H NMR (CDCl3): δ = –25.89 (t, JP,H
bination of one hydride ion and one proton, occurs.
12.86 Hz, 1 H, HIr), 22.69 (s, 1 H, OHO) ppm. 31P{1H} NMR
(CDCl3): δ = 31.21 (s) ppm. FAB MS: calcd. for C39H30F3IrO5P2S
922; found 773 [M – OTf]+. C39H30F3IrO5P2S (921.89): calcd. C
50.81, H 3.28, S 3.48; found C 50.74, H 3.57, S 3.45.
Bubbling of HCl through an MeOH solution of 7 gives
1 (see iv in Scheme 3). This result shows that the loss of
hydrido ligands, enolic protons, and chloride ions in com-
plex 1 can be reversed; this observation has potential inter-
est in studies directed toward catalytic ionic hydrogena-
tion.[29]
Preparation of [{IrH[{PPh2(o-C6H4CO)}2H]}2(µ-Cl)]A [A = BF4
(5), PF6 (6)]: Et3OPF6 (9.42 mg, 0.038 mmol) or Et3OBF4 (7.22 mg,
0.038 mmol) was added to a dichloromethane solution of 1 (60 mg,
0.075 mmol). After stirring for 60 min, addition of diethyl ether to
the solution gave a yellow precipitate, which was filtered off,
Conclusions
washed with diethyl ether, and vacuum-dried. IR (KBr): ν = 2221
˜
(m) [ν(IrH)], 1629 (s) [ν(C=O)] cm–1. 1H NMR (CD2Cl2, 203 K): δ
= –23.17 (t, JP,H = 14.2 Hz, 1 H, HIr), 22.66 (s, 1 H, OHO) ppm.
13C{1H} NMR (CD2Cl2, 203 K): δ = 257.6 (d, JP,C = 101 Hz, CO),
255.6 (d, JP,C = 103 Hz, CO) ppm. 31P{1H} NMR (CD2Cl2, 203 K):
δ = 30.7 (s), 18.3 (s) ppm. FAB MS: calcd. for C76H60ClO4P4Ir2
Neutral, mononuclear hydridoirida-β-diketones contain-
ing labile anions have been prepared that can be used to
afford mononuclear, cationic hydridoirida-β-diketones.
Fluxional, dinuclear, cationic hydridoirida-β-diketones con-
taining a single chloride bridge can be obtained upon treat-
ment with a halide abstractor. Silver salts may afford an
asymmetric, dinuclear iridium complex with three acyl-
phosphane bridging ligands. The starting material can be
recovered by addition of HCl. The loss and recovery of hy-
dride ions and protons could be relevant to studies of cata-
lytic processes such as ionic hydrogenation.
1581; found 1581 [M]+. Data for 5: Yield: 42 mg (68%). ΛM
=
147 Ω–1 cm2 mol–1. C76H60BClF4Ir2O4P4 (1667.9): calcd. C 54.73, H
3.63; found C 54.61, H 3.57. Data for 6: Yield: 48 mg (73%). ΛM
=
179 Ω–1 cm2 mol–1. C76H60ClF6Ir2O4P5·0.5CH2Cl2 (1768.5):
calcd. C 51.96, H 3.48; found C 52.03, H 3.23.
Preparation of [Ir2H{PPh2(o-C6H4CO)}{µ-PPh2(o-C6H4CO)}3]BF4
(7): To a dichloromethane solution of 5 (125 mg, 0.075 mmol) was
added AgBF4 (29.1 mg, 0.15 mmol). After stirring for 30 min, the
silver salts were filtered. Addition of diethyl ether to the solution
gave a yellow precipitate that was filtered off, washed with diethyl
Experimental Section
ether and vacuum-dried (yield: 68 mg, 53%). IR (KBr): ν = 2189
˜
General Procedures: The preparation of the metal complexes was
carried out at room temperature under nitrogen by using standard
Schlenk techniques. [IrH{[PPh2(o-C6H4CO)]2H}Cl] (1) was pre-
pared as reported previously.[8] Microanalysis were carried out with
(w), [ν(IrH)], 1628 (s), 1525 (s) [ν(C=O)] cm–1. ΛM
=
1
152 Ω–1 cm2 mol–1. H NMR (CDCl3, 223 K): δ = –23.24 (dd, JP,H
= 19.2 and 18.3 Hz, 1 H, HIr) ppm. 31P{1H} NMR (CDCl3,
223 K): δ = 23.6 and 21.2 (d, JP,P = 12 Hz), 20.1 and 14.2 (d, JP,P
3898
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Eur. J. Inorg. Chem. 2006, 3893–3900

Mono- and Dinuclear Hydridoirida-β-diketones
FULL PAPER
Table 3. Crystal and refinement fata for 5 and 7.
5
7
Empirical formula
Mr
Crystal system
Space group
a [Å]
[C76H60Cl1O4P4Ir2]BF4·1/2CH2Cl2
[C76H56F3O4P4Ir2]BF4
1628.3
monoclinic
P21/n
1710.24
monoclinic
P21/c
14.3279(7)
15.583(1)
b [Å]
c [Å]
36.606(2)
13.235(7)
36.688(2)
23.299(2)
β [°]
97.062(1)
6888.6(6)
94.954(2)
13271(2)
V [Å3]
Z
4
8
Dcalcd. [gcm–3]
1.649
4.091
1.630
4.165
µ [mm–1]
F(000)
θ [°]
3364
1.11–25.0
6392
1.04–25.0
Data collected
No. of reflns. collected
No. of ind. reflns.
Completeness to θ
Data/restraints/parameters
R[a] [I Ͼ 2σ(I)]
(–17, –42, –14) to (15, 43, 15)
36113
12105 (Rint = 0.1195)
99.8%
12105/6/616
0.0585 (6212 obsd. reflect.)
0.16000
(–18, –40, –26) to (18, 43, 27)
102296
23299 (Rint = 0.1700)
99.6%
23299/8/1279
0.0553 (8848 obsd. reflect.)
0.1306
[b]
RwF (all data)
2
2 2
[a] ∑||Fo| – |Fc||/∑|Fo|. [b] {∑[w(Fo – Fc ) ]/∑[w(Fo2)2]}1/2
.
= 8 Hz) ppm. 13C{1H} NMR (CDCl3, 223 K): δ = 266.5 (d, JP,C
=
atoms were calculated at geometrical positions and refined as ri-
ding on their respective carbon atoms, except the hydride atoms
(H1A, H1B) and the enolic hydrogen atoms (H2A, H2B) for 5,
which were found in a difference Fourier synthesis and their coordi-
nates and thermal parameters fixed. For 7, it was impossible to
locate the hydride ions. These features led to R1 factors of 0.0585
(6212 reflections observed) and 0.0553 (8848 reflections observed)
for 5 and 7, respectively. The largest residual peaks in the final
difference map (1.54 and 1.62 eÅ–3, respectively) were found in the
91 Hz, CO), 264.5 (d, JP,C = 89 Hz, CO), 257.5 (d, JP,C = 101 Hz,
CO) 209.1 (s, CO) ppm. FAB MS: calcd. for C76H57O4P4Ir2 1543;
found 1543 [M]+. C76H57BF4O4P4Ir2·CH2Cl2 (1714.37): calcd. C
53.95, H 3.47; found C 53.65, H 3.61.
Reaction of [Ir2H{PPh2(o-C6H4CO)}{µ-PPh2(o-C6H4CO)}3]BF4 (7)
with HCl: HCl gas was bubbled at room temperature through a
methanol solution of 7 (30 mg, 0.018 mmol) for 30 min, upon
which a small amount of precipitate was formed. The solvent was
evaporated and the residue analyzed by NMR spectroscopy. Ac-
cording to the spectra, the solid contained mainly complex 1.
–
vicinity of the fluorine atoms of the BF4 groups in both com-
pounds. CCDC-606708 (5) and -606709 (7) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/datarequest/cif.
X-ray Structure Determination of 5 and 7: Yellow prismatic single
crystals of 5 and needles of 7 suitable for X-ray diffraction were
successfully grown by slow diffusion of diethyl ether into dichloro-
methane or methanol solutions, respectively. Data collection was
carried out at room temperature on a Bruker Smart CCD dif-
fractometer, using graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å), operating at 50 kV and 20 mA. In both cases, data were
collected over a hemisphere of the reciprocal space by combination
of three exposure sets. Each exposure of 10 s covered 0.3° in ω. The
first 100 frames were recollected at the end of the data collection
to monitor crystal decay after X-ray exposition; no appreciable
drop in the intensities was observed. A summary of the fundamen-
tal crystal data for the crystals is given in Table 3. The structures
were solved by direct methods and conventional Fourier tech-
niques. The refinement was done by full-matrix least squares on
F2 for 5 and by blocked full-matrix least squares on F2 for 7.[30]
Anisotropic parameters were used in the last cycles of refinement
Acknowledgments
Partial financial support by MCYT (project BQU2002-0129), UPV,
and the Diputación Foral de Guipuzcoa is gratefully acknowl-
edged.
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Received: May 16, 2006
Published Online: August 7, 2006
3900
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Eur. J. Inorg. Chem. 2006, 3893–3900