Synthesis and crystal structure of iridium-1,4-benzoquinone complexes of tris(3,5-dimethylpyrazolyl)methane ligand: Decarbonylation, protonation, and substitution reactions

Article abstract of DOI:10.1021/om300439c

Complexes [κ²-Tpm^Me2Ir(2,3,5,6-η-2-R-1,4- benzoquinone)Cl] (R = H, 1a; Cl, 1b; Ph, 1c; ^tBu, 1d; Tpm ^Me2 = tris(3,5-dimethylpyrazolyl)methane) and [κ³- Tpm^Me2Ir(2,3,5,6-η-1,4-benzoquinone)][

Full text of DOI:10.1021/om300439c

Article
pubs.acs.org/Organometallics
Synthesis and Crystal Structure of Iridium-1,4-benzoquinone
Complexes of Tris(3,5-dimethylpyrazolyl)methane Ligand:
Decarbonylation, Protonation, and Substitution Reactions
Martín Hernandez-Juarez,†,‡ Veronica Salazar,‡ Efren V. García-Baez,† Itzia I. Padilla-Martínez,*,†
́
́
́
́
́
Herbert Hopfl,§ and Maria de Jesus Rosales-Hoz⊥
̈
†Departamento de Ciencias Bas
Avenida Acueducto s/n Barrio la Laguna Ticoman
‡Centro de Investigaciones Químicas, Universidad Auton
́
icas, Unidad Profesional Interdisciplinaria de Biotecnología del Instituto Politec
́
nico Nacional,
́
, Mexico, D. F. 07340, Mexico
́
́
oma del Estado de Hidalgo, Carretera Pachuca a Tulancingo Km 4.5, 42184,
Mineral de la Reforma, Hidalgo, Mexico
§Centro de Investigaciones Químicas, Universidad Auton
62210, Mexico
́
oma del Estado de Morelos, Avenida Universidad 1001, Cuernavaca Morelos
⊥Departamento de Química, CINVESTAV-IPN, Avenida Instituto Politec
́ ́
nico Nacional 2508, Col. San Pedro Zacatenco, Mexico D.
F. 07360, Mexico
S
* Supporting Information
t
ABSTRACT: Complexes [κ2-TpmMe2Ir(2,3,5,6-η-2-R-1,4-benzoquinone)Cl] (R = H, 1a; Cl, 1b; Ph, 1c; Bu, 1d; TpmMe2
=
tris(3,5-dimethylpyrazolyl)methane) and [κ3-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)][BF4], 2a-BF4, have been prepared from
the dimeric complex [Ir(μ-Cl)(coe)2]2 and structurally characterized. Compounds 1a−d were then thermally transformed to the
corresponding iridacyclohexa-2,5-dien-4-one complexes [κ3-TpmMe2Ir(1,5-η-CHC(R)C(O)CHCH−)(CO)][BF4], 3-BF4,
and for 1a the reactivity toward CO, phosphines, and HBF4−OEt2 was examined. Compounds 1a, 1b, 2a-BF4, 3a-BF4, 3b-BF4,
carbonyl complex [κ3-TpmMe2Ir(2,3-η-1,4-benzoquinone)(CO)][Ir(CO)2Cl2], 4-[Ir(CO)2Cl2], phosphine complexes [(PR3)2Ir-
(2,3,5,6-η-1,4-benzoquinone)Cl] (PR3 = PPh3, PPhMe2, PMe3), 5−7, and [(μ-PPh2CH2CH2PPh2)Ir(2,3,5,6-η-1,4-
benzoquinone)Cl]2, 8, were characterized by X-ray diffraction analysis. Treatment of 1a with HBF4 led, through the
intermediacy of [κ2-TpmMe2Ir(2-6-η-semiquinone)Cl][BF4], 9-BF4, to the isolation of hydroquinone [κ2-TpmMe2Ir(1-6-η-1,4-
hydroquinone)Cl][BF4]2, 10-(BF4)2, and treatment of 3-BF4 with HSO3CF3 led to dicationic iridaphenol complexes [κ3-
t
TpmMe2Ir(1,5-η-CHC(R)-C(OH)CH−CH)(CO)][SO3CF3]2 (R = H, Bu), 11-(O3SCF3)2.
in spite of their wide use in organometallic chemistry as
ancillary ligands. Important scorpionate ligands are those
derived from 3,5-dimethylpyrazole such as the anionic
tris(3,5-dimethylpyrazolyl)borate (TpMe2) or the neutral
analogue tris(3,5-dimethylpyrazolyl)methane (TpmMe2). Both
ligands are versatile hard N-donor ligands that can coordinate
in a mono-, bi-, or tridentate fashion to the metal center.7
Despite the similarity of the two ligands, TpMe2 has widespread
use in organometallic and coordination chemistry; in contrast,
the TpmMe2 ligand has received comparatively little attention.
However, this ligand can act as more than a simple spectator in
the course of the chemical reactions experienced by their
compounds, because of the possibility of temporary changes in
INTRODUCTION
■
1,4-Benzoquinones (BQ) are an important class of compounds
that play key roles in chemistry and biology. They are useful
synthons in organic synthesis and building blocks for
hormones, pigments, and other derivatives.1,2 Their potential
as anticancer drugs and as central components of antibiotics has
also been reported.1
Quinonoid complexes of transition metals have been known
since the late 1950s.3 However, the organometallic chemistry of
hydroquinone−benzoquinone complexes has emerged only in
the past 30 years, using soft donors such as phosphines and
principally π-acceptors such as carbonyl, allyl, COD, COT,
indenyl, cyclopentadienyl, and arene ligands.4 Hard N-donor
ligands containing bipy and imine functions have been used
also,5 but there is only one report on a complex containing
simultaneously a benzoquinone and a scorpionate-type ligand,6
Received: May 21, 2012
Published: July 13, 2012
© 2012 American Chemical Society
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denticity and its ambidentate nature after the removal of the
CH(PzMe2)3 proton.8 More recently the syntheses of Co, Pd,
and Ir complexes with ditopic ligands that combine quinonoid
and bis-pyrazolyl-methane moieties have been reported.9 These
ligands exhibit κ2- and κ3-coordination modes or can act like a
bridge, leading to heterodinuclear complexes.
Only a few metal complexes have been reported in which
quinonoids are coordinated to heavier elements, mainly with
Pt.10 In the particular case of iridium,5a,11,12 only COD and
Cp* have been used as ancillary ligands so far. In both cases the
synthesis started from the cationic 1-6-η-hydroquinone
complex A, which after deprotonation with a strong base
gave the corresponding 2,3,5,6-η-quinone complex B (Scheme
1). In the case of Cp* as intermediate, the 2-6-η-semiquinone
HBF4 and HSO3CF3 were performed on 1a and 3-BF4,
respectively, and are also discussed.
RESULTS AND DISCUSSION
■
1H and 13C{1H} NMR data corresponding to the BQ ligand in
complexes 1a−d, 2a-BF4, 3a−d-BF4, 4-[Ir(CO)2Cl2], 5−8, 9-
BF4, 10-(BF4)2 and 11a,d-(O3SCF3)2 are listed in Table 1.
Selected bond distances and angles of 1a, 2a-BF4, 3a-BF4, 3b-
BF4, 4-[Ir(CO)2Cl2], 5, and 8 are given in the corresponding
captions of Figures 1, 2, and 4−8. A full list of data is found in
the Supporting Information, SI.
Benzoquinone Complexes [κ2-TpmMe2Ir(2,3,5,6-η-2-R-
1,4-benzoquinone)Cl]. The iridium benzoquinone complex
1a [κ2-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] was easily
synthesized as an air-stable solid in 85% yield by reaction of
[Ir(μ-Cl)(coe)2]2 with two equivalents of 1,4-benzoquinone
and tris(3,5-dimethylpyrazolyl)methane (TpmMe2), at room
temperature (Scheme 2).
Scheme 1. Reported Synthesis of 1,4-Benzoquinone Ir
Complexes by Deprotonation of the Corresponding
Hydroquinone Derivatives11,12
The IR spectrum of complex 1a shows a couple of medium-
intensity bands characteristic of CO vibrations at 1643 and
1563 cm−1. These frequencies are very similar to those
observed for uncoordinated 1,4-benzoquinone at 1640 and
1589 cm−1. The 1H and 13C{1H} NMR spectra are in
agreement with an η4:π2 coordination mode of the BQ ligand
to the Ir(I) center: in 1H NMR a singlet at δ 4.55, equivalent to
four protons, and in 13C{1H} NMR two signals at δ 64.4 (CH,
1JC−H = 173 Hz) and 169.2 (CO). Comparison with the
chemical shifts of the free BQ ligand, δ 6.77, 136.7 (CH, 1JC−H
= 169 Hz) and 187.4 (CO), showed that the alkenyl atoms are
strongly shielded by the nearby metal center. The symmetry
exhibited by the TpmMe2 ligand in complex 1a is in agreement
with Cs point group symmetry: two single signals with 2:1
intensities at δ 6.25 and 5.91 for the pyrazole CH protons, four
signals at δ 2.65, 2.51, 2.08, and 1.53 (intensities 2:2:1:1) for
the Me groups, and a single signal at δ 7.61 corresponding to
the methine CH(PzMe2)3 proton. A similar pattern is observed
in the 13C{1H} NMR spectrum: four signals at δ 158.4, 150.6,
144.3, and 140.0 (2:2:1.1) for the six quaternary carbons of
complex C was observed. Herein, a general synthesis of a series
of iridium complexes of the composition [κ2-TpmMe2Ir(2,3,5,6-
t
η-2-R-1,4-benzoquinone)Cl] (R = H, 1a; Cl, 1b; Ph, 1c; Bu,
1d) and [κ3-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)][BF4], 2a-
BF4, are reported, starting from the dimeric complex [Ir(μ-
Cl)(coe)2]2. After thermal treatment of 1a−d several novel
compounds resulted. Further, substitution reactions of complex
1a with CO and PR3 as well as reactions with the mineral acids
1
1
Table 1. Selected H and 13C NMR Data, δ in ppm and JC−H in Hz
compound
H2
H3
H5
H6
C1
C2 (1JC−H
)
C3 (1JC−H
)
C4
C5 (1JC−H
)
C6 (1JC−H
)
CH(Pz)3
1a
1b
1c
1d
4.55
4.55
5.05
5.45
5.2
4.55
4.13
3.96
3.10
5.45
6.89
7.18
7.05
6.88
6.56
4.22
4.70
4.84
4.88
4.39
5.39
7.79
7.79
4.55
4.81
4.85
4.93
5.45
8.73
8.67
8.61
8.25
4.89
4.22
4.70
4.84
4.88
6.1
169.2
165.4
165.9
163.1
177.5
197.5
188.1
195.9
198.1
161.2
166.4
162.4
162.3
163.3
176.4
152.1
198.7
198.9
64.4 (171)
71.5
64.4
53.6
169.2
169.5
171.4
172.4
177.5
158.8
64.4
74.6
64.4
76.6
7.61
7.62
7.60
7.61
8.15
8.23
8.24
8.22
8.23
8.24
71.6
54.0
70.1
75.0
88.7
50.1
65.1
77.4
a
2a-BF4
5.45
8.73
8.86
8.78
8.42
4.89
4.22
4.70
4.84
4.88
6.1
5.45
6.89
61.6
61.6
61.6
61.6
3a-BF4
135.8
127.6
133.8
125.8
138.6
81.0 (170)
80.8
136.7
129.8
140.1
144.3
28.2
136.7
138.4
137.8
139.1
28.2
135.8
134.3
132.6
129.5
138.6
f
3b-BF4
NO
3c-BF4
159.2
159.6
3d-BF4
a
4-[Ir(CO)2Cl2]
6.56
4.22
4.70
4.84
4.88
4.39
5.39
7.79
5
6
7
8
81.0 (170)
80.8
81.0 (170)
80.8
81 (170)
162.4
162.3
163.3
152.4
152.1
155.0
156.1
80.8
79.8
80.9
79.8
79.8
79.8
80.9
80.9
80.9
a
9-BF4
61.7 (177)
74.6
82.7 (178)
74.6
82.7 (178)
74.6
61.7 (177)
74.6
8.45
8.38
8.12
8.12
b
10-(BF4)2
5.39
11.02
11.67
5.39
11.02
10.50
cd
,
11a-(O3SCF3)2
11d-(O3SCF3)2
177.4
169.3
132.2 (158)
134.7
132.2 (158)
149.8
177.4
ce
,
165.9
a
b
c
d
e
Measured in (CD3)2OD. Measured in CD3OD. Measured in CD2Cl2. All other compounds were reported in CDCl3. δ OH: 13.65. δ OH:
f
13.44. NO = not observed.
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Figure 3. Quantification of the distortion from planarity of metal-
coordinated BQ rings: angles α and β.
Figure 1. Molecular structure of the neutral iridium complex 1a
(drawn at the 30% probability level). H atoms and water molecule are
omitted for clarity. Selected bond lengths (Å) and angles (deg): Ir1−
N12 2.151(4), Ir1−N14 2.139(4), Ir1−Cl1 2.364(3), Ir1···Cg(C2,C3)
2.004(4), Ir1···Cg(C5,C6) 2.066(4), C2−C3 1.445(6), C5−C6
1.401(6), C1−O1 1.236(5), C4−O4 1.232(5); N12−Ir1−N14
83.75(12), Cl1−Ir1−N12 86.95(10), N12−Ir1−C2 119.33(14),
N14−Ir1−C2 156.83(13), Cl1−Ir1−C2 91.76(11), Cl1−Ir1−C3
92.97(11), Cl1−Ir1−C5 156.25 (11), Cl1−Ir1−C6 154.42(10).
Figure 4. Molecular structure of cationic iridium(III) complex 3a-BF4
(drawn at the 30% probability level). H atoms and BF4 anion omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ir1−N12
2.106(3), Ir1−N14 2.165(4), Ir1−N16 2.149(4), Ir1−C1 1.869(6),
Ir1−C2 2.028(5), Ir1−C6 2.037(7), C2−C3 1.334(8), C3−C4
1.468(10), C4−O4 1.234(7), C1−O1 1.119(7); N12−Ir1−N14
85.77(13), N12−Ir−N16 84.07(14), N12−Ir−C2 92.13(17), N12−
Ir1−C6 91.74(18), N14−Ir1−C2 175.9(2), N14−Ir1−C6 95.1(2),
N16−Ir1−C6 174.54(18), C2−Ir1−C6 88.5(3), C3−C4−C5
118.9(5), Ir1−C1−O1 173.6(5).
κ3-coordination mode of the TpmMe2 ligand to give either
neutral [κ2-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] or cati-
onic [κ3-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)]Cl.
Single-crystal X-ray diffraction analysis confirmed the
presence of the chlorine atom in the coordination sphere of
the metal and the κ2-coordination mode of the TpmMe2 ligand
(Figure 1). Compound 1a crystallized in the monoclinic crystal
system, space group C2/c, with one water molecule in the
asymmetric unit. The geometry around the Ir(I) center in
compound 1a is distorted trigonal-bipyramidal (tbpy). The
TpmMe2 ligand occupies the two equatorial positions with a
N12−Ir1−N14 bite angle of 83.75(12)° and a mean Ir−N
bond length of 2.145(4) Å. The BQ ligand is coordinated in
η4:π2 fashion to the Ir(I) center through the C2−C3 and C5−
C6 double bonds, the former occupying the remaining
equatorial position and the latter the axial position opposed
to the chlorine atom, with a mean Cl1−Ir1−C(5−6) angle of
155.3(10)°. The Ir1−C(5,6) are elongated and the C5−C6
bond lengths are shortened, in both cases by approximately
0.05 Å, when compared to the corresponding Ir1−C(2,3) and
Figure 2. Molecular structure of the cationic complex 2a-BF4 (drawn
at the 30% probability level). H atoms, BF4 anion, and acetone
molecule are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ir1−N12 2.116(3), Ir1−N14 2.224(3), Ir1−N16 2.185(3),
Ir1···Cg(C2,C3) 2.002(3), Ir1···Cg(C5,C6) 2.083(3), C2−C3
1.443(5), C5−C6 1.405(5), C1−O1 1.226(4), C4−O4 1.225(4);
N12−Ir1−N14 86.62(11), N12−Ir1−N16 82.72(10), N12−Ir1−C2
95.88(12), N12−Ir1−C3 95.96(12), N12−Ir1−C5 156.88(12), N12−
Ir1−C6 158.37(12), N14−Ir1−C2 117.42(12).
pyrazole, two signals at δ 111.0 and 110.0 (2:1) for the three
pyrazole CH, four signals at δ 14.4, 13.5, 11.7, and 10.6
(2:2:1:1) for the six methyl groups, and one signal for the
CH(PzMe2)3 carbon atom at δ 74.0. On the basis of the IR and
NMR data it was not possible to differentiate between a κ2- and
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Table 2. Ring Puckering Parameters of the BQ Rings (C1/
C2/C3/C4/C5/C6) in Compounds 1a, 1b, 2a-BF4, 4-
[Ir(CO)2Cl2] and 5−8; and (Ir/C2/C3/C4/C5/C6) for 3a-
BF4, and (Ir/C2/C3/C4/C3a/C2a) for 3b-BF4
parameter
compound
Q/Å
θ/deg
φ/deg
1a
1b
0.451(5)
0.460(13)
0.529(4)
0.360(5)
0.418(8)
0.117(5)
0.437(9)
0.368(11)
0.412(11)
0.466(5)
92.7(6)
92.7(16)
90.4(4)
74.0(9)
73.6(13)
0.4(6)
2.1(17)
2a-BF4
−2.4(4)
0.2(10)
3a-BF4
3b-BF4
360.0(13)
3(3)
4-[Ir(CO)2Cl2]
87(2)
5
6
7
8
93.5(12)
96.1(17)
90.5(15)
87.7(6)
180.8(11)
179.8(16)
356.7(15)
180.2(6)
2-substituent in the BQ ligand destroys the symmetry in the 1H
and 13C{1H} NMR spectra of the corresponding complexes,
and the signals appear at lower frequencies, as a consequence of
the metal shielding effect, but exhibit a pattern similar to the
corresponding free 2-R-1,4-benzoquinone (R = Cl, b; Ph, c).
With regard to complex 1b, as an example, the signals at δ 5.05
(d, 4J = 3.0 Hz), 4.81 (d, 3J = 9.0 Hz), and 4.13 (dd, 4,3J = 3.0,
9.0 Hz) were assigned to protons H-3, H-6, and H-5 of the 2-
Cl-BQ ligand. In the 13C{1H} NMR spectrum the correspond-
ing signals appear at δ 53.6, 76.6, and 74.6, respectively,
whereas the carbonyl signals appear at δ 169.5 and 165.4. The
lack of symmetry is observed also in the signal patterns arising
from the ancillary ligand TpmMe2: one 1H NMR signal at δ 7.62
for CH(PzMe2)3, three signals for pyrazole CH in the range δ
6.27−5.90, and six signals for the methyl groups in the range δ
2.62 to 1.50. The 13C{1H} NMR spectrum gave six signals at δ
158.8−150.9 and 145.0−140.2, three signals at δ 111.2−109.9,
for the quaternary and CH carbons of the pyrazole rings, one at
δ 74.0 for CH(PzMe2)3, and six for the methyl groups in the
range δ 14.6 to 10.4 ppm. The molecular structure of 1b was
confirmed by single-crystal X-ray diffraction analysis. Com-
pound 1b crystallized in the monoclinic crystal system, space
group P21/c, and the geometry is very similar to that observed
for compound 1a (see the SI). The mean Cl1−Ir1−(C5, C6)
angle for the higher order axis is 156.4(3)°, the N12−Ir1−N14
bite angle is 85.2(4)°, and the mean Ir−N bond length is
2.12(9) Å.
Figure 5. Molecular structure of complex 3b-BF4 (drawn at the 30%
probability level). Cl3 and H3 atoms are disordered (occ = 0.5 each).
H atoms and BF4 anion are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ir1−N12 2.154(6), Ir1−N14 2.106(10), Ir1−
C1 1.870(12), Ir1−C2 2.016(8), C2−C3 1.329(12), C3−C4
1.509(11), C4−O4 1.226(14), C3−C13 1.679(9), C1−O1
1.127(12); N12−Ir1−N14 84.3(3), N12−Ir−C2 93.8(3), N14−Ir1−
C2 92.2(3), N12−Ir1−C2a 175.7(3), C2−Ir1−C2a 88.8(5), C3−C4−
C3a 117.8(10), Ir1−C1−O1 173.2(10).
C2−C3 bond lengths located in the equatorial plane. These
geometric features are in agreement with the favorable
disposition of the equatorial ligands to a better orbital
overlapping with the metal center. Upon coordination, the
BQ ligand is bent to a boat-like conformation, according to the
Cremer and Pople12 parameters, Q = 0.451(5) Å, θ = 92.7(6)°,
φ = 0.4(6)°, Table 2. The rigid conformation exhibited by the
BQ ligand in compound 1a in the solid state contrasts with the
fluxional behavior observed in solution. On the NMR time
scale, at room temperature, the BQ ligand is in fast rotation,
which would explain the high symmetry observed in solution.
The reaction of [Ir(μ-Cl)(coe)2]2 with benzoquinones and
TpmMe2 is quite general; thus, the analogous products 1b and
1c could be obtained starting from the corresponding 2-Cl and
2-Ph-1,4-benzoquinone in 78% and 93% yield, respectively. The
When the bulky 2-tBu-1,4-benzoquinone is reacted with the
[Ir(μ-Cl)(coe)2]2 dimer and TpmMe2 under the already
described conditions, a mixture of 1d and the corresponding
Scheme 2. Synthesis of Complexes 1, 2a-BF4, and 3-BF4
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cationic complex 3d-Cl is obtained in a relation of 1:1. If the
reaction is performed at −40 °C, the isolated ratio changes to
1:4. Attempts to isolate 1d in pure form were unsuccessful, and
we observed that solutions of 1d always progress with an
increase of 3d-Cl (vide infra). At this point it is worth noting
that the related Ir(I) complexes [Cp*Ir(2,3,5,6-η-BQ)]12 and
[CODIr(2,3,5,6-η-BQ)]−11b were synthesized by deprotonation
of the corresponding hydoquinone complexes with a strong
base, whereas the synthesis of complexes 1a−d is achieved by
before for 1a,b, the BQ ligand presents a boat conformation, in
which the vertices C2−C1−C6 and C3−C4−C5 are pointing
away from the metal center but the carbonyl tips are pointing
toward the metal. Such a distortion from planarity has been
observed previously in duroquinone Rh complexes17 and
quantified by angles α and β (Figure 3), of which the former
is the angle formed between the mean planes of the olefin
carbon atoms C2/C3/C5/C6 and the CC(O)C segments C6/
C1/C2 and C3/C4/C5 and the latter is the angle formed
between the CO group and the plane of the three neighboring
carbon atoms. Herein, α1 and β1 are reserved for the planes
involving segment C2−C1(O1)−C6, while α4 and β4 are used
for fragment C3−C4(O4)−C5. The corresponding values are
listed in Table 3. This asymmetric representation has to be
t
direct coordination of the 2-R-BQ ligand (R = H, Cl, Ph, Bu).
Besides, upon coordination, the 1H and 13C{1H} NMR
chemical shifts of the BQ ligand in 1a−d are shifted to lower
frequencies, whereas the IR frequency of the CO group and
1JC−H remain almost unchanged with regard to free BQ, in
agreement with reported data for the analogous neutral
[Cp*Ir(2,3,5,6-η-BQ)]12 and anionic [(CO)3Mn(2,3,5,6-η-
Table 3. Angles between the Mean Planes within the BQ
Rings of Compounds 1a, 1b, 2a-BF4, 3a-BF4, 3b-BF4, 4-
[Ir(CO)2Cl2], and 5−8
14
BQ)]− complexes.
Benzoquinone Complex [κ3-TpmMe2Ir(2,3,5,6-η-1,4-
benzoquinone)][BF4]. Addition of one equivalent of AgBF4
to a CH2Cl2 solution of 1a at 4 °C resulted in the formation of
the cationic complex 2a-BF4 in 53% yield (Scheme 2). This
Ir(I) complex can also be synthesized starting from [Ir(μ-
Cl)(coe)2]2 and BQ, under the simultaneous addition of the
TpmMe2 ligand and AgBF4. This procedure does not require the
isolation of 1a and improves the yield to 88%. Compound 2a-
a
angle between planes
compound
α1
β1
α4
β4
1a
1b
25.4(2)
25.8(5)
30.8(1)
18.7(2)
21.7(1)
8.2(4)
10.7(2)
10.2(5)
8.6(1)
28.7(2)
29.7(5)
32.1(2)
13.4(3)
14.4(0)
7.0(3)
8.3(2)
8.4(5)
7.9(2)
0.8(3)
0.6(0)
2.6(3)
4.6(4)
2.9(4)
3.6(5)
7.3(4)
5.1(2)
2a-BF4
3a-BF4
1
BF4 is highly fluxional in solution, and both H and 13C{1H}
3b-BF4
1
4-[Ir(CO)2Cl2]
2.2(3)
3.9(4)
5.1(4)
6.3(5)
5.3(4)
3.5(2)
NMR spectra are highly symmetric. The H NMR spectrum
5
29.6(4)
26.0(4)
25.7(5)
25.5(4)
29.5(2)
23.9(4)
18.4(4)
18.1(5)
26.5(4)
26.3(2)
gave one signal at δ 6.40 for the three pyrazole CH hydrogens,
two single signals at δ 2.80 and 2.50 for the six methyl groups of
the TpmMe2 ligand, and in addition one singlet at δ 8.15
corresponding to the CH(PzMe2)3 proton. The corresponding
signals in the 13C{1H} NMR spectrum are at δ 112.7 (3CHPz),
15.4 and 12.4 (6MePz), and 70.6 (CH(PzMe2)3), besides a pair
of signals for the six quaternary pyrazole carbon atoms at δ
161.0 and 146.0. The NMR data for the BQ ligand are in
agreement with a η4:π2-coordination mode to the Ir(I) center:
the olefin atoms give rise to signals at δ 5.45 and at 61.6 (1JC−H
= 171 Hz) in the 1H and 13C{1H} NMR, respectively, besides a
signal at δ 177.5 for CO-BQ. These data strongly resemble
those observed for the highly fluxional complex [κ3-TpmMe2Ir-
(1,2-η-C2H4)2]PF6.15 The positive charge at the metal center
deshields the 1H and 13CO NMR chemical shifts of the
coordinated BQ ligand, which in comparison with 1a appear at
higher frequencies, approximately 1 and 8 ppm, respectively, in
the cationic complex 2a-BF4. The deshielding effect is also
exerted in the resonance of the CH(PzMe2)3 proton of the
ancillary ligand by a shift of 0.5 ppm (Table 1).
The structure of 2a-BF4 was unambiguously confirmed by
single-crystal X-ray diffraction analysis (Figure 2). This complex
crystallized as an acetone solvate in a monoclinic crystal system
with space group P21/c. The ancillary ligand TpmMe2 is
coordinated to the metal center in a κ3 fashion; thus two
pyrazole rings are located in equatorial positions with a N12−
Ir1−N16 bite angle of 82.72(10)°. The axial positions are
occupied by the third pyrazole nitrogen and the C5−C6 double
bond, with a mean N12−Ir1−C(5,6) angle of 157.6(12)°. As
observed for 1a,b, the Ir−Cax(C5,C6) bond is longer than the
Ir−Ceq(C2,C3) bond by 0.07 Å, and the C5−C6 bond is
shorter than the C2−C3 bond by 0.04 Å. This structure closely
resembles that of [κ3-TpIr(1,2-η-C2H4)2].16 The replacement
of Cl (1a) with pyrazole (2a-BF4) in the coordination sphere of
the Ir(I) center does not significantly change the geometric
parameters associated with the ligand TpmMe2. As mentioned
6
6A
7
8
a
α1: angle between planes C2/C3/C5/C6 and C2/C1/C6 for
compounds 1a, 1b, 2a-BF4, and 4−8, and C2/Ir/C6 for compounds
3a-BF4, 3b-BF4; α4: angle between planes C2/C3/C5/C6 and C3/
C4/C5 for compounds 1a, 1b, 2a-BF4, 4-[Ir(CO)2Cl2], and 5−8.
employed for complexes 1a, 1b, and 2a-BF4, because one vertex
is more bent than the other, even when the Ir−C(olefin)
distances are similar. The magnitude of the largest bending is
sensitive to the coordination mode of the TpmMe2 ligand: α4
has a larger value (α4 = 32.1(2)°) in [κ3-TpmMe2Ir(2,3,5,6-η-
1,4-benzoquinone)][BF4], 2a-BF4, than in [κ2-TpmMe2Ir-
(2,3,5,6-η-1,4-benzoquinone)Cl], 1a, α4 = 28.7(2)°, or [κ2-
TpmMe2Ir(2,3,5,6-η-2-Cl-1,4-benzoquinone)Cl], lb, α4 =
29.7(5)°. Larger values of α are associated with smaller values
of β in compounds 1a and 1b, but in compound 2a-BF4 it is the
opposite. Nevertheless β values are smaller than α values. A
comparison among several known complexes of the general
composition [LM-2,3,5,6,-η-BQ] makes clear that the BQ
bending can be attributed mainly to steric effects caused by the
size of the metal M, the bulkiness of the ligand L (Cp*Ir,13 α =
15.4 6°; Cp*Rh,18 α = 12.9 9°; CODRh,19 α = 8.0 0.1°),
or the presence of bulky substituents in the benzoquinone ring
([Cp*Rh-2,3,5,6,-η-di-tBu-BQ],17 α = 24.5
2.5°; [κ3-
1.3°). Thus,
B(Pz)4Rh-2,3,5,6,-η-duroquinone],5a α = 25.3
the bending observed in complexes 1a, 1b, and 2a-BF4 is the
largest so far reported for Ir(I) complexes, which, however, is
not unexpected because of the large cone angle of the TpmMe2
ligand (239°).20
Iridacyclohexa-2,5-dien-4-one Complexes [κ3-
TpmMe2Ir(1,5-η-CHC(R)C(O)CHCH−)(CO)][BF4] (R =
t
H, Cl, Ph, Bu). When complex 2a-BF4 is refluxed in CH2Cl2
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for 6 h, Ir(III) complex 3a-BF4 is afforded in 92% yield
(Scheme 2). This reaction was monitored by 1H NMR, heating
a DMSO-d6 solution of compound 1a to 60 °C at regular time
intervals. After 4.5 h, compound 1a has been completely
transformed into a mixture of 3a-Cl and free TpmMe2 in a 4:1
ratio. Under these conditions also some decomposition occurs
because of the strongly coordinating solvent. Characteristic IR
features for complex 3a-BF4 are stretching bands at 2066 and
1614 cm−1, respectively, for the terminal IrCO and RCO
carbonyls, which generate signals at δ 197.5 and 158.8 ppm in
the 13C{1H} NMR spectrum. The vinyl hydrogen atoms are
observed as a pair of doublets at δ 8.73 and 6.89 (3JH2−H3= 9
Hz), which, on the basis of NOE experiments using the
pyrazole methyl groups, have been assigned to the IrCH and
COCH hydrogens, respectively, in the 1H NMR spectrum. The
corresponding signals in the 13C{1H} NMR are observed at δ
135.8 (C-2,6, JC−H = 159 Hz) and 136.7 (C-3,5, JC−H = 153
Hz). For the ancillary ligand TpmMe2, the typical signal pattern
for molecules with Cs symmetry is observed, similar to that
described for compound 1a. This 2a-BF4 → 3a-BF4 trans-
formation probably proceeds through the intermediacy of the
corresponding 16-electron complex iridacyclohepta-3,6-diene-
2,5-dione, D, which might be formed by insertion of the Ir
atom into the C−CO BQ bond of 2a-BF4 and the
subsequent migration of CO to form the 18-electron
iridacyclohexa-2,5-dien-4-one complex 3a-BF4 (Scheme 3).
This change is in agreement with the tendency of the
TpmMe2 ligand to favor d6 Ir(III) over d8 Ir(I) systems,
enforcing octahedral coordination to the metal center.21
octahedral geometry around the Ir(III) center. The C2−C3
(1.334(8) Å) and C5−C6 (1.326(8) Å) distances of the alkenyl
fragments, the C4−O4 (1.234(7) Å) distance of the carbonyl
group, and the C3−C4 (1.468(10) Å) and C4−C5 (1.479(9)
Å) distances are very close to the values observed for free BQ
with values of 1.333(11), 1.222(13), and 1.478(11) Å,
respectively.23 Thus, 3a-BF4 can be considered as an
iridacyclohexa-2,5-dien-4-one complex. In general, the bond
lengths and angles found in 3a-BF4 are similar to the cationic
iridacyclohexa-3,5-dien-2-one isomer [(PMe3)4Ir(1,5-η-C(O)-
C(Me)CH-C(Me)CH−)][O3SCF3], which, however, is
almost planar.22
Addition of AgBF4 to complex 1b at room temperature gave
3b-BF4 in 87% yield. This transformation was performed also
under simultaneous addition of TpmMe2 and AgBF4 starting
from [Ir(μ-Cl)(coe)2]2 and 2-Ph and 2-tBu-1,4-benzoquinone
to obtain 3c-BF4 (78%) and 3d-BF4 (81%), respectively
(Scheme 2). In neither case were the intermediate compounds
analogous to 2a-BF4 observed.
1
1
From these results and the fact that compound 1d is
spontaneously transformed into 3d-Cl (vide supra), it becomes
clear that the transformation of 1 into 3-BF4 is made faster by
the influence of steric effects in the BQ ring. Complex 3b-BF4
crystallized in the orthorhombic crystal system with space
group Pnma. The molecular structure of this compound is very
similar to 3a-BF4, but H-5 and the chlorine atoms are
disordered over two positions (occ = 0.50) (Figure 5). The
iridacycles in compounds 3a-BF4 and 3b-BF4 present boat-like
conformations13 (Table 2) similar to those described for
complexes 1a,b and 2a-BF4. The bending of the Ir vertex (angle
α1) from the central diolefin plane in complexes 3a-BF4 and
3b-BF4 is larger, 18.7(2)° and 21.7(1)°, than the bending of the
CO vertex (angle α4), with values of 13.4(3)° and 14.4(0)°,
respectively (Table 3), and the CO tip becomes almost
coplanar with the C3/C4/C5 fragment (β values close to zero).
Substitution Reactions of 1a with CO and Phos-
phines. Cationic compound [κ3-TpmMe2Ir(2,3-η-1,4-
benzoquinone)(CO)][Ir(CO)2Cl2], 4-[Ir(CO)2Cl2], was iso-
lated from the reaction of compound 1a with CO (1 atm) in
CH2Cl2 solution at room temperature in 71% yield. This
Scheme 3. Pathway Proposed for the Transformation of 2a-
BF4 to 3a-BF4
1
reaction was monitored by H NMR spectroscopy, using the
appropriate pressure tube. After 5 min the solution changed
from pale yellow to green-yellow, and the free ligands BQ and
TpmMe2 and complexes 1a and 4+ were observed in 1:1:1:1
proportion. The reaction proceeds with depletion of 1a in 50
min; afterward polycarbonylated species appear, which were
not further characterized. Compound 4+ is similar to the
complex [κ3-TpmMe2Ir(1,2-η-C2H4)(CO)]+ reported as an
intermediate in the carbonylation of [κ3-TpmMe2Ir(1,2-η-
(C2H4)2]+.15 Characteristic IR features for 4-[Ir(CO)2Cl2]
include two IrCO stretching bands observed at ν 2042 and
1957 cm−1, corresponding to cationic and iridate fragments,
respectively. It is worth mentioning that in the 13C{1H} NMR
spectrum only the Ir−CO signal corresponding to the cationic
fragment is observed at δ 198.9. According to the symmetry of
The chemical shift of Ir−13CH (δ 135.8) in compound 3a-
BF4 is comparable with the value reported for the
iridacyclohexa-3,5-dien-2-one isomer (δ 136.7) [(PMe3)4Ir-
(1,5-η-C(O)-C(Me)CH-C(Me)CH−)][CF3SO3], already
known.22 It is worth highlighting that these complexes were
synthesized by treating the iridabenzene complex [(PMe3)3Ir-
(1,5-ηCH-C(Me)CH-C(Me)CH−)] with N2O, which
was obtained after several steps, in contrast to the simplicity of
the method reported herein. The structure of 3a-BF4 was
unambiguously confirmed by single-crystal X-ray diffraction
analysis (Figure 4). Complex 3a-BF4 crystallized in a
monoclinic crystal system, space group P21/c. The ancillary
ligand is κ3-coordinated with almost equal values for the three
orthogonal N−Ir−C angles, mean value of 175(1)°, and a mean
N−Ir−N bite angle of 85(1)°. The π-acceptor ability of CO
forces a strong electron release from N12 toward the metal, and
as a consequence, the Ir1−N12 bond is 0.05 Å shorter than the
equatorial Ir1−N14 and Ir−N16 bonds. The C2−Ir1−C6 angle
is 88.5(3)°, and the Ir1−C2 and Ir1−C6 distances are
practically identical, with a mean value of 2.03(1) Å. These
geometric data are in agreement with the slightly distorted
1
the molecule, two singlets appear at δ 4.89 and 6.56, in the H
NMR, and at δ 28.2 and 138.6 in the 13C{1H} NMR spectra,
which were assigned to coordinated and free alkenyl CH,
respectively. The typical pattern for a Cs-symmetric molecule
1
was observed in both H and 13C{1H} NMR for the ancillary
ligand TpmMe2. The molecular structure of compound 4-
[Ir(CO)2Cl2] was undoubtedly established by X-ray analysis
(Figure 6). This compound crystallized in the monoclinic
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Figure 6. Molecular structure of the cationic complex 4-[Ir(CO)2Cl2]
(drawn at the 30% probability level). H atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ir1−N12 2.184(4), Ir1−
N14 2.142(3), Ir1−N16 2.147(3), Ir1−C2 2.114(4), Ir1−C3
2.121(4), Ir1−C7 1.843(5), Ir2−C26 1.819(6), Ir2−Cl1 1.224(6),
C7−O7 1.141(7), C1−C2 1.476(6), C2−C3 1.470(6), C3−C4
1.485(6), C4−C5 1.472(8), C5−C6 1.331(7), C1−C6 1.475(7),
O1−C1 1.224(6), O4−C4 1.229(6), N12−Ir1−N14 82.75(14), N12−
Ir1−N16 82.35(13), N12−Ir1−C2 92.32(14), N14−Ir1−C2
116.28(14), N12−Ir1−C3 93.87(15), N14−Ir1−C3 156.73(15),
C2−C1−C6 117.1(4), C3−C4−C5 118.4(4), C1−C2−C3 120.2(4),
C4−C5−C6 122.7(5), Cl1−Ir2−C26 91.7(2).
Figure 8. Molecular structure of dimer complex 8 (drawn at the 30%
probability level). H atoms have been omitted for clarity. Selected
bond lengths (Å) and angles (deg): Ir1−P1 2.328(9), Ir1−P2
2.326(8), Ir1−Cl 2.460(10), Ir1···Cg(C2,C3) 2.085(7), Ir1···Cg-
(C5,C6) 2.147(7), C1−O1 1.217(6), C4−O4 1.232(6); P1−Ir1−P2
95.41(3), Cl1−Ir1−P1 95.46(3), Cl1−Ir1−P2 96.07(3), Cl1−
Ir1···Cg(C2,C3) 112.7(3), Cl1−Ir1···Cg(C5,C6) 102.8(3), C3−C4−
C5 109.2(4), C2−C1−C6 107.6(4).
C2−C3 = 1.470(6) Å, than that of the uncoordinated bond,
C5−C6 = 1.331(7) Å. The BQ ring is almost planar, as
indicated by the ring puckering parameters (Table 2) and the
smaller values for angles α1 and α4 (Table 3).
The reaction proceeds through the intermediacy of the
neutral species [κ2-TpmMe2Ir(2,3-η-1,4-benzoquinone)(CO)-
Cl], E, which was fortuitously crystallized (see the SI). CO
displaces one alkenyl bond, changing the coordination mode of
the BQ ligand from η4:π2, in 1a, to η2:π, in intermediate E. In
the presence of CO, E rapidly disproportionates, with
elimination of one molecule of TpmMe2 and BQ ligands, into
the more stable cationic Ir(I) complex 4+, generating in situ the
anion [Ir(CO)2Cl2]− (Scheme 4). This reaction is probably
promoted by the trans effect of the already coordinated CO.
On the other hand, when complex 1a is reacted with two
equivalents of PPh3 at room temperature, the TpmMe2 ligand is
replaced with two PPh3 moieties to give [(PPh3)2Ir(2,3,5,6-η-
1,4-benzoquinone)Cl], 5, in 91% yield (Scheme 5). Initially,
the reaction was performed using one equivalent of PPh3, and
in this case only a half-equivalent of the metal complex was
converted. The fluxional compound 5 is symmetric, and the
NMR data are in agreement with a complex having Cs
Figure 7. Molecular structure of complex 5 (drawn at the 30%
probability level). H atoms have been omitted for clarity. Selected
bond lengths (Å) and angles (deg): Ir1−P1 2.346(2), Ir1−P2
2.340(2), Ir1−Cl1 2.456(2), Ir1···Cg(C2,C3) 2.137(12), Ir1···Cg-
(C5,C6) 2.099(12), C1−O1 1.239, C4−O4 1.252(9), C2−C3
1.413(10), C5−C6 1.407(11); P1−Ir1−P2 96.87(6), Cl1−Ir1−P1
95.28(6), Cl1−Ir1−P2 94.94(6), Cl1−Ir1···Cg(C2,C3) 105.8(2),
Cl1−Ir1···Cg(C5,C6) 109.6(2), P1−Ir1···Cg(C2,C3) 94.60(2), P1−
Ir1···Cg(C5,C6) 152.79(2), P2−Ir1···Cg(C2,C3) 155.25(2), P2−
Ir1···Cg(C5,C6) 91.81(2).
1
symmetry: in H NMR only the signal for the phenyl protons
was observed as well as one signal at δ 4.22 for the protons of
coordinated BQ; in 13C{1H} NMR the CO signal was located
at δ 166.4 (3JC−P= 2.2 Hz) and the alkenyl carbons gave signals
at δ 81.0 (1JC−H = 169, 2JC−P = 5.9 Hz). 31P{1H} NMR showed
a signal at δ −13.6, characteristic for coordinated PPh3.
This reaction is quite general, and analogous complexes with
PMe2Ph (δ 31P{1H} = −33.1) 6 and PMe3 (δ 31P{1H}= −39.4)
7 could be obtained also, in 83% and 31% yield, respectively.
crystal system with space group P21/c. The TpmMe2 ligand is
coordinated in a facial shape with C7O and N12 atoms in the
apical positions, N12−Ir1−C7 = 171.79(17)°, and the BQ
ligand is positioned in the equatorial plane of a tbpy. As
expected, the bond length of the coordinated olefin is longer,
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Scheme 4. Proposed Reaction Sequence for the Combination of 1a with CO
which passes through both carbonyl groups, is aligned with the
vertical axis of the molecule, one of them being almost eclipsed
by the Ir−Cl bond. The largest deviation was observed in the
PMe3 derivative 7 (O1−C1−Ir1−Cl1 = −11.0(3)°). The values
for the olefin bonds C2−C3 and C5−C6 are almost equal in
compounds 5 (PPh3), 8 (PPh2(CH2)2Ph2P), and 6 (PPhMe2),
but for compounds 6A (PPhMe2) and 7 (PMe3) a mean
difference of 0.06(2) Å was detected. Although the structures of
the phosphine derivatives 5−8 are rather similar, some
structural trends arise because of the stereoelectronic effects
inherent to the nature of the phosphine. The triphenylphos-
phine complex 5 has the largest P1−Ir−P2 angle, 96.87(7)°,
and the smallest was measured in the dimethylphenylphosphine
complex 6A, 92.56(10)°. The coordinated BQ adopts a boat-
like conformation, in which both carbonyls are displaced out of
the diene plane, as suggested by the ring puckering parameters
(Table 2). In all cases, one of the two carbonyl vertexes is more
deviated from the central diolefin plane than the other, as
indicated by the angles formed between the mean planes
(Table 3). The magnitudes of the largest α value follow the
order PPh3 (29.6(4)°) ≈ DPPE (29.5(2)° mean value of 6 and
6A) > PPhMe2 (25.9(4)°) ≈ PMe3 (26.5(4)°), in agreement
with the tendency of the corresponding cone angles.25 Is worth
noting that β values for phosphine complexes are almost half of
the values corresponding to TpmMe2 complexes and thus more
sensitive to steric crowding.
Reactions with Acids. Reaction of 1a with one equivalent
of HBF4 always led to a mixture of semiquinone 9-BF4 and
hydroquinone 10-(BF4)2 (Scheme 7). Other approaches to
isolate 9-BF4 were unsuccessful, and in solution an equilibrium
mixture of 10-(BF4)2 and 1a was always established. Thus, the
titration of 1a with aqueous HBF4 (48 wt %) was monitored by
1H NMR in (CD3)2CO solution. The highest concentration of
semiquinone 9-BF4 was achieved after addition of 0.75 molar
equivalents of the acid (Figure 9). We then selected these
conditions to prepare and characterize this compound by
NMR, but using HBF4−OEt2 instead of the aqueous HBF4
solution to improve the solubility. Protonation of 1a with 0.8
molar equivalents of HBF4−OEt2 lead to a mixture of
semiquinone (SQ) [κ2-TpmMe2Ir(2-6-η-semiquinone)Cl][BF4],
9-BF4, and unreacted 1a in 1:3 proportion, respectively. The
SQ ring gave a pair of doublets at δ 6.11 and 4.39 with 3JH3−H2
= 6 Hz and were assigned to H-3 and H-2, respectively. The
corresponding carbon atoms gave signals at δ 82.7 (1JC−H = 180
Scheme 5. Reactivity of 1a with Phosphines and Synthesis of
Complexes 5−7
The displacement reaction with PMe3 leads to a complex
1
mixture of unidentified compounds observed by H NMR;
however, no further efforts were undertaken for a more
complete analysis and separation. In order to avoid the
adventitious reactions observed with PMe3, we performed the
reaction also with the bidentate ligand Ph2PCH2CH2PPh2
(DPPE), but instead the dimeric cyclic compound 8 (δ
31P{1H} = 32.8) was obtained in 80% yield (Scheme 6).
Compounds 5−8 can be synthesized alternatively with
similar yields by addition of two equivalents of BQ to a
suspension of [Ir(μ-Cl)(coe)2]2 in CH2Cl2, followed by
addition of four equivalents of PR3 (two in the case of
DPPE). This reaction and that described for 2a (vide supra)
probably proceed through the formation of [Ir(μ-Cl)(2,3,5,6-η-
benzoquinone)]2, which is formed by displacement of the coe
ligand from the coordination sphere of the Ir(I) center by
chelating BQ. Neither this latter method nor the displacement
of the TpmMe2 ligand gave better yields of compound 7. The
molecular structures of compounds 5−8 were confirmed by
single-crystal X-ray diffraction analysis. The X-ray structures of
compounds 5 and 8 are show in Figures 7 and 8, respectively,
and those corresponding to compounds 6 and 7 are in the SI.
The phosphine complexes 5 and 7 crystallized in the
monoclinic crystal system with space group P21/c, and the
crystal structures of compounds 6 (two independent molecules
in the asymmetric unit) and 8 belong to the triclinic system,
with space group P1. In all cases the geometry around the Ir(I)
̅
center is in agreement with a distorted square-based pyramid
(sbpy) with the chlorine atoms in apical position. The τ
parameter24 were calculated to establish the percentage of the
sbpy character: 5 (τ = 0.04, 96%), 6 (τ = 0.09, 91%), 6A (τ =
0.07, 93%), 7 (τ = 0.19, 81%), 8 (τ = 0.11, 89%). The BQ
ligand is coordinated to the Ir center in a η4:π2 fashion,
occupying two neighboring positions of the square base,
opposite the phosphine ligands. The C2 axis of the BQ ligand,
Scheme 6. Reaction of 1a with the Bidentate Ligand DPPE Leads to Dimer 8
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Scheme 7. Protonation of 1a with HBF4
equilibria. The acid medium modifies the chemical shifts of 3a+
to higher frequencies; nevertheless, the signals for 112+ were
clearly different from 3a+. The addition of 10 equivalents of
HSO3CF3 in THF solution were required to complete the
transformation for preparative purposes, and under these
conditions the irida-4-phenol 11a-(SO3CF3)2 was isolated in
70% yield (Scheme 8).
Scheme 8. Synthesis of the Iridaphenol Complex 11-
(SO3CF3)2
Figure 9. 1H NMR titration experiments of 1a with aqueous HBF4 in
(CD3)2CO.
Hz) and 61.7 (1JC−H = 178 Hz), respectively, and the signals at
δ 176.4 and 152.4 were assigned to the CO and C−OH
carbon atoms. To completely shift the equilibrium to the
dicationic HQ compound 10-(BF4)2, addition of two
equivalents of HBF4−OEt2 to 1a in CH2Cl2 solution was
The spectroscopic data of 11a-(SO3CF3)2 is in agreement
with the proposed structure: the O−H group gave a broad
signal at δ 13.65 (1H NMR) and a band at ν 3420 cm−1 (IR);
the IrCH and OCCH ring protons appeared at δ 11.02 and
7.79 as doublets (3JH2−H3 = 9 Hz), respectively, and were
assigned by the NOE effect observed when irradiating IrCH
protons on the pyrazole methyl groups; the corresponding
signals in the 13C{1H} NMR appeared at δ 177.4 and 132.2
(1JC−H = 158 Hz) for the CH functions; at δ 155.0 for C−OH;
and at δ 198.7 for IrCO (ν 2085 cm−1 in IR). The
coordinated TpmMe2 ligand displayed a signal pattern
consistent with Cs symmetry. The spectroscopic data of
complex 11a-(SO3CF3)2 bear close similarity to those of the
irida-2-phenol isomer [(PMe3)3-Ir(1,5-η-CHC(Me)-CH
C(Me)-C(OH)−)(O3SCF3)]O3SCF3 reported by Bleeke.22
Transformation of 3a-BF4 into the irida-4-phenol 11a-
(SO3CF3)2 is reversible in (CD3)3CO solution, and it seems
that the weak basic nature of this solvent assists in shifting the
equilibrium. Thus, after one week crystals of the starting 3a-
SO3CF3 complex were isolated from this experiment. This is in
contrast to the already reported irida-2-phenol isomers
[(PMe3)3-Ir(1,5-η-CHC(Me)-CHC(Me)-C(OH)−)X]-
1
necessary (93% yield). The H and 13C{1H} NMR signals
corresponding to the coordinated HQ ligand appeared at δ
1
5.39, 74.6 (CH, JC−H = 179 Hz) and 152.1 (C−OH),
respectively. For both complexes the NMR signals of the
ancillary TpmMe2 ligand were consistent with Cs point group
symmetry, showing a similar pattern to the one already
described for 1a. The NMR data are in agreement with a
localized bonding in the SQ ring of the 9-BF4 complex, in
contrast to the delocalized bonding observed for [(CO)3Mn(2-
6-η-SQ)] species.26 This difference could be attributed to the
steric effects exerted by both the ancillary ligand TpmMe2 and
the BQ ligands carrying a bulky group, as observed in complex
[(CO)3Mn(2-6-η-tBu-SQ)].14
Metallabenzenes have been synthesized from the correspond-
ing metallacyclohexadienes by treatment with acids such as
HBF4, CH3COOH, or HSO3CF3.27 Thus, the aromatization of
the iridacycle 3a-BF4 to form the corresponding iridabenzene
seems to be a feasible reaction. Several preparative efforts were
carried out in CH2Cl2 solutions, using up to 10 equivalents of
HSO3CF3, but only unreacted 3a-BF4 was isolated. The
reaction was followed by 1H NMR in CD3OD solution,
showing that addition of 10 equivalents of the strong acid
HSO3CF3 leads to a mixture of 3a+ and irida-4-phenol 112+ in
1:4 proportion. Addition of the acid in increments of 10
equivalents up to a total of 80 displaces the equilibrium to a
steady state of 1:9 proportion. In spite of the excess of acid
used, the transformation was not complete, probably because of
the involvement of the polar solvent CD3OD in the acid−base
SO3CF3 (X = CF3SO3 or CF3COO−), which are formed by
−
addition of 1.5 equivalents of HSO3CF3 or CF3COOH.27 The
low reactivity of 3a-BF4 may be due to several factors inherent
to the iridacyclohexa-2,5-dien-4-one ring including the furthest
position from the metal center of the carbonyl group, the
strong distortion from planarity, and the nonalternated
disposition of the diolefin bonds, thus limiting π-electron
delocalization within the ring. A further contribution might
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result from an electronic effect on the metal, provided by the
hard TpmMe2 ligand, which does not realize back-bonding.
The aromatization of the bulkier iridacyclohexadien-4-one
complex 3d-BF4 was performed with one equivalent of
HSO3CF3 in CH2Cl2 solution to lead to the isolation of [κ3-
TpmMe2Ir(1,5-η-CHC(tBu)-C(OH)CH−CH)(CO)]-
[O3SCF3]2, 11d-(O3SCF3)2, in 85% yield. In fact two
additional equivalents of the acid were just added to guarantee
the full exchange of the anion. This result highlights the
participation of steric effects in the aromatization of 3-BF4 into
11-(O3SCF3)2. In contrast to the relatively simple methodology
reported herein, iridabenzenes from the closely related ligand
TpMe2 have been synthesized27 by contraction of the
iridacycloheptatriene complex [κ3-TpMe2Ir(1,6-η-C(R)C(R)-
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under a
dry, oxygen-free N2 atmosphere, following conventional Schlenk
techniques. Solvent evaporation, filtering, and drying procedures were
performed under vacuum. Solvents were dried by standard methods
(hexane and dichloromethane with CaH2 and diethyl ether and THF
with Na/benzophenone) and distilled under nitrogen prior to use.
[Ir(μ-Cl)(coe)2]2 was obtained by the published procedure,29 whereas
TpmMe2 was synthesized by a modified procedure of the method
reported by Elguero.30,15 All other chemicals, including ammonium
hexachloroiridate(IV), 2-Cl-1,4-benzoquinone, 2-Ph-1,4-benzoqui-
none, 2-tBu-1,4-benzoquinone, PMe3, PMe2Ph, PPh3, and DPPE,
were used as received except for 1,4-benzoquinone, which was
sublimed before use. Melting points were measured on an Electro-
thermal IA9100 apparatus and were uncorrected. IR spectra were
recorded neat using a Varian 3100 FT-IR spectrophotometer of the
Excalibur Series equipped with an ATR system. 1H, 13C, and 31P NMR
spectra were recorded on a Varian Mercury 300 (1H, 300.08; 13C,
75.46; 31P, 121.47 MHz) instrument in deoxygenated and deuterated
solvents. Spectra were referenced to external SiMe4 (δ = 0 ppm) using
the residual protio solvent peaks as internal standards (1H NMR) or
characteristic resonances of the solvent nuclei (13C NMR). For
31P{1H} NMR spectroscopy, 85% H3PO4 was used as the reference.
Spectral assignments were made by means of routine one- and two-
dimensional NMR experiments where appropriate. Microanalyses were
performed by the Microanalytical Service of the Centro de
t
C(R)C(R)C(R)C(R)(H2O)] using BuOOH as oxidizing
agent28a or by expansion of the iridacyclopentadiene complex
[(TpMe2)Ir(1,4-η-CHC(R)C(R)C(R))(H2O)] (R =
CO2Me) by reaction with propene.28b The synthesis and
structure of TpMe2-iridabenzenes have been recently revie-
wed.28c
CONCLUSIONS
■
The synthesis of a series of complexes of the type [κ2-
TpmMe2Ir(2,3,5,6-η-2-R-BQ)Cl] (R = H, Cl, Ph, Bu) 1a−d
t
́
́
Investigaciones Quimicas de la Universidad Autonoma del Estado de
starting from [Ir(μ-Cl)(coe)2]2 and the appropriate 2-R-BQ
and TpmMe2 ligands is feasible. The combined steric effects of
the R substituent and the TpmMe2 ligand lead to the formation
of novel iridaciclohexa-2,5-dien-4-one complexes, 3-BF4, after
activation of the C(sp2)−C(sp2)O double bond and decarbon-
ylation of 1a−d. This unprecedented transformation for
coordinated 1,4-BQ is promoted by steric hindrance, character-
istic of the κ3-coordination mode of the ancillary ligand
TpmMe2, and proceeds through the intermediacy of [κ3-
TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)][BF4], 2a-BF4, species.
This contribution expands by twofold the available range of
currently known Ir(I) compounds of composition [LIr(2,3,5,6-
η-1,4-benzoquinone]m. The neutral compound 1 is analogous
to an anionic COD complex, and the cationic compound 2a-
BF4 is analogous to a neutral Cp* complex; thus the range of
charged compounds (m = −1, 0, 1) is widened.
Hidalgo (UAEH) and Micro Analysis Inc. (Wilmington, DE, USA).
Due to the strong tendency of these ionic complexes to retain
crystallization solvent, the calculated elemental analyses for some of
them are reported considering CH2Cl2, Et2O, and adventitious H2O
content.
XRD Experiments. Single-crystal X-ray diffraction data for
molecules 1a and 1b were collected at 100(2) or 173(2) K for
molecules 2a-BF4, 3a-BF4, and 3b-BF4, on Bruker Apex II and Nonius
Kappa diffractometers equipped with area detectors using Mo Kα
radiation, λ = 0.71073 Å, and at 293(2) K (5−8 and E) on a CrysAlis
Pro diffractometer with an area detector and Cu Kα radiation, λ =
1.54178, and 4-[Ir(CO)2Cl2] with Mo Kα radiation, λ = 0.71073 Å.
Summaries of crystal data and collection parameters are listed in
Tables 6 and 7 (SI). Either a semiempirical absorption correction was
applied using SADABS31 and the program SAINT,32 or the CrysAlis
Pro program33 was used for integration of the diffraction profiles. The
structures were solved by direct methods using SHELXS9734 in the
WinGX package.35 The final refinement was performed by full-matrix
least-squares methods on F2 with SHELXTL97.32 H atoms on C, N,
and O were positioned geometrically and treated as riding atoms, with
C−H = 0.93−0.98 Å, and with Uiso(H) = 1.2 Ueq(C, N, O). The
program Mercury was used for visualization, molecular graphics, and
analysis of crystal structures.36 Software used to prepare material for
publication was PLATON.37 The molecules in the crystal structure of
3b-BF4 are disordered over two positions at the sites corresponding to
Cl and H3 atoms; they were refined with occupancy factors of 0.50
each. In compound 8, CH2Cl2 solvent molecules were disordered over
three positions (occ = 0.45, 0.18, and 0.37). Disorder was treated with
PART1-3 instructions. Crystals suitable for single-crystal X-ray
diffraction analysis were obtained by slow evaporation of a solution
of compound 3a-BF4, 4-[Ir(CO)2Cl2], or E in acetone or slow
diffusion of Et2O into saturated CH2Cl2 solutions of complexes 1a, 1b,
2a-BF4, 3b-BF4, and 5−8.
Phosphines displace the TpmMe2 ligand in compound 1a
selectively, leading to the formation of Ir(I) complexes 5−8,
whereas the BQ ligand remains in the coordination sphere of
the metal. The exchange of the ligand TpmMe2 is accompanied
with a change of the coordination geometry at the metal center
from accentuated tbpy in 1a to sbpy in complexes 5−8.
Conversely, CO sequentially displaces the BQ double bonds,
giving compound 4-[Ir(CO)2Cl2] in the first place; however,
carbonylation continues, generating polycarbonylated species
and making evident the preference of the metal for stronger
bonds. Protonation of 1a with HBF4 allowed the isolation of
the dicationic hydroquinone complex 10-(BF4)2. The mono-
protonated semiquinone complex 9-BF4 is little favored when
less than one equivalent of acid is added, and the equilibrium is
shifted to unprotonated 1a. In contrast, more than one
equivalent of acid shifts the equilibrium to complex 10-(BF4)2.
Finally, irida-4-phenol complexes [κ3-TpmMe2Ir(1,5-η-CH
[κ2-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] (1a). In a
Schlenk flask equipped with a stir bar and immersed in an ice−
water bath was suspended 500 mg (0.558 mmol) of the [Ir(μ-
Cl)(coe)2]2 dimer in 15 mL of CH2Cl2. Then, 121 mg (1.11 mmol) of
1,4-benzoquinone in 5 mL of CH2Cl2 was added, followed, after 1 h,
by 333 mg (1.11 mmol) of TpmMe2 ligand in 1 mL of CH2Cl2,
whereupon the mixture was allowed to react for 1 h at room
temperature. The solvent was evaporated, and the resulting solid was
washed with Et2O (3 × 3 mL), filtered, and dried to obtain a pale
t
C(R)-C(OH)CH−CH)(CO)][O3SCF3]2 (R = H, Bu),
11-(O3SCF3)2, were formed by aromatization, in acid media, of
iridacyclohexa-2,5-dien-4-one complexes 3-BF4, in spite of
unfavorable geometric features associated with the coordinated
BQ ligand and the hard donor nature of the TpmMe2 ligand.
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yellow solid in 85% yield (598 mg, 0.943 mmol). Mp = 178 °C. IR
νneat (cm−1): (CO) 1643, 1563.1H NMR (CDCl3): δ 7.61 (s, 1H,
CH(Pz)3), 6.25, 5.91 (s, 3H, CHPz (2:1)), 4.55 (s, 4H, CHBQ), 2.65,
2.51, 2.08, 1.53 (s, 18H, 6MePz (2:2:1:1)). 13C{1H} NMR (CDCl3): δ
169.2 (2COBQ), 158.4, 150.6, 144.3, 140.0 (6CqPz, 2:1:2:1), 111.0,
110.0 (3CHPz (1:2)), 74.0 (CH(Pz)3), 64.4 (4CHBQ), 14.4, 13.5, 11.7,
10.6 (6 MePz, 2:2:1:1). Anal. Calcd for C22H26N6O2ClIr (634.14 g/
mol): C, 41.6; H, 4.1; N, 13.2. Found: C, 41.5; H, 4.2; N, 13.5.
[κ2-TpmMe2Ir(2,3,5,6-η-2-Cl-1,4-benzoquinone)Cl] (1b). This
compound was prepared following a procedure similar to that
described for 1a, but with 200 mg of [Ir(μ-Cl)(coe)2]2 (0.223
mmol), 7 mL of CH2Cl2, 63.6 mg (0.446 mmol) of 2-Cl-1,4-
benzoquinone, and 133 mg (0.446 mmol) of TpmMe2. A dark yellow
solid was obtained in 78% yield (232 mg, 0.348 mmol).
Decomposition without melting occurred at 166 °C. IR νneat
obtain a greenish-yellow solid in 88% yield (673 mg, 0.981 mmol).
Decomposition without melting occurred at 111 °C. IR νneat (cm−1):
1
(CO) 1662, 1569. H NMR [(CD3)2CO]: δ 8.15 (s, 1H, CH(Pz)3),
6.40 (s, 3H, HPz), 5.45 (s, 4H, HBQ), 2.80, 2.50 (s, 9H each, 6MePz).
13C{1H} NMR [(CD3)2CO]: δ 177.5 (2COBQ), 161.0, 146.0 (6CqPz),
112.7 (3CHPz), 70.6 (CH(Pz)3), 61.6 (4CHBQ), 15.4, 12.4 (6MePz).
Anal. Calcd for C22H26N6O2Ir BF4·(685.50 g/mol): C, 38.5; H, 3.8; N,
12.2. Found: C, 38.7; H, 3.8; N, 12.4.
[κ3-TpmMe2Ir(1,5-η-CHCHC(O)CHCH−)(CO)][BF4] (3a-
BF4). In a Schlenk flask equipped with a stir bar were placed 100
mg (0.146 mmol) of compound 1a and 12 mL of CH2Cl2. The yellow
solution was stirred at 60 °C for 6 h to give a brown solution. After
solvent evaporation, a brown solid was obtained in 92% yield (92 mg,
0.134 mmol). Decomposition without melting occurred at 149 °C. IR
1
νneat (cm−1): (IrCO) 2066, (CO) 1614, (B−F) 1053. H NMR
1
(cm−1): (CO) 1645, 1563. H NMR [CDCl3, J(Hz)]: δ 7.62 (s, 1H,
3
[CDCl3, J(Hz)]: δ 8.73 (d, 2H, JH2−H3 = 9, H-2,6), 8.23 (s, 1H,
4
3
CH(Pz)3), 6.27, 6.24, 5.90 (s, 1H each, CHPz), 5.05 (d, 1H, JH3−H5
=
CH(Pz)3), 6.89 (d, 2H, JH3−H2 = 9, H-3,5), 6.31, 6.10 (s, 3H, HPz
3.0, H-3), 4.81 (d, 1H, 3JH6−H5 = 9.0, H-6), 4.13 (dd, 1H, 4JH5−H3 = 3.0,
3JH5−H6 = 9.0, H-5), 2.62, 2.52, 2.51, 2.50, 2.08, 1.50 (s, 3H each,
6MePz). 13C{1H} NMR (CDCl3): δ 169.5, 165.4 (2COBQ), 158.8,
158.6, 150.9, 145.0, 144.7, 140.2 (6CqPz), 111.2, 110.2, 109.9 (3CHPz),
76.6 (C-6), 74.6 (C-5), 74.0 (CH(Pz)3), 71.5 (C−Cl), 53.6 (C-3), 14.6,
14.4, 13.7, 11.9, 11.8, 10.4 (6MePz). Anal. Calcd for C22H25 N6O2Cl2Ir
(668.58 g/mol): C, 39.5; H, 3.7; N, 12.5. Found: C, 39.2; H, 4.0; N,
12.4.
(2:1)), 2.79, 2.76, 2.39, 2.19 (s, 18H, 6MePz (2:1:2:1)). 13C{1H} NMR
[CDCl3]: δ 197.5 (CO-Ir), 158.8 (CO), 158.4, 154.8, 144.4, 136.6
(6CqPz, 2:1:2:1), 136.7 (2C-3,5), 135.8 (2C-2,6), 110.8, 109.9,
(3CHPz, 1:2), 69.8 (CH(Pz)3), 14.2, 14.1, 11.2, 11.1, (6MePz
(2:1:2:1)). Anal. Calcd for C22H26N6O2IrBF4 (685.50 g/mol): C,
38.5; H, 3.8; N, 12.2. Found: C, 38.3; H, 3.9; N, 12.3.
[κ3-TpmMe2Ir(1,5-η-CHC(Cl)C(O)CHCH−)(CO)][BF4] (3b-
BF4). In a Schlenk flask equipped with a stir bar were placed 200
mg (0.299 mmol) of compound 1b, 58.2 mg (0.299 mmol) of AgBF4
and 12 mL of CH2Cl2, and the reaction mixture was allowed to react at
room temperature for 90 min. The AgCl precipitate was removed by
filtration and washed with CH2Cl2 (2 × 3 mL). The resulting red
solution was evaporated to dryness to obtain a dark brown solid in
87% yield (187 mg, 0.260 mmol). Decomposition without melting
occurred at 138 °C. IR νneat (cm−1): (IrCO) 2061, (CO) 1624, (B−
F) 1053. 1H NMR [CDCl3, J(Hz)]: δ 8.86 (s, 1H, H-2), 8.67 (d, 1H,
3JH6−H5 = 9, H-6), 8.24 (s, 1H, CH(Pz)3), 7.18 (d, 1H, 3JH5−H6 = 9, H-5)
[κ2-TpmMe2Ir(2,3,5,6-η-2-Ph-1,4-benzoquinone)Cl] (1c). This
compound was prepared following a procedure similar to that
described for 1a, but with 150 mg of [Ir(μ-Cl)(coe)2]2 (0.167
mmol), 6 mL of CH2Cl2, 61.7 mg (0.334 mmol) of 2-Ph-1,4-
benzoquinone, and 99.9 mg (0.334 mmol) of TpmMe2. A dark brown
solid in 93% yield (221 mg, 0.311 mmol) was obtained.
Decomposition without melting occurred at 136 °C. IR νneat
1
(cm−1): (CO) 1624, 1563. H NMR [CDCl3, J(Hz)]: δ 8.16−8.13
(m, 2H, Ho), 7.60 (s, 1H, CH(Pz)3), 7.41−7.29 (m, 3H, Hm‑p), 6.26,
4
6.20, 5.95 (s, 3H, HPz (1:1:1)), 5.45 (d, 1H, JH3−H5 = 2.4, H-3), 4.85
6.33, 6.32, 6.13 (s, 1H each, HPz), 2.80, 2.79, 2.76, 2.41, 2.40, 2.20 (s,
3H each, 6MePz). 13C{1H} NMR [CDCl3]: δ 188.1 (CO-Ir), not
observed (CO), 158.4, 157.9, 155.1, 155.0, 144.9, 144.8, (6CqPz),
138.4 (C-5), 134.3 (C-6), 129.8 (C−Cl), 127.6 (C-2), 111.0, 110.1,
110.0 (3CHPz), 69.9 (CH(Pz)3), 14.4, 14.3, 13.3, 11.5, 11.3, 11.2
(6MePz). Anal. Calcd for C22H25N6O2ClIrBF4 (719.94 g/mol): C,
36.7; H, 3.4; N, 11.6. Found: C, 36.9; H, 3.4; N, 11.3.
(d, 1H, 3JH6−H5 = 7.5, H-6), 3.96 (dd, 1H, 3JH5−H6 = 7.5, 4JH5−H3 = 2.4,
H-5), 2.67, 2.50, 2.48, 2.46, 2.10, 1.54 (s, 3H each, 6MePz). 13C{1H}
NMR (CDCl3): δ 171.4, 165.95 (2COBQ), 158.8, 158.4, 150.8, 144.8,
144.5, 140.3 (6Cqpz), 134.4 (CqPh), 129.1 (2CHo), 128.2 (2CHm),
127.8 (CHp), 111.3, 110.5, 109.8 (3CHPz), 75.0 (C-6), 74.0 (CH(Pz)3),
71.6 (C-Ph), 70.1 (C-5), 54.0 (C-3), 15.1, 14.9, 13.8, 11.9, 11.8, 10.3
(6MePz). Anal. Calcd for C28H30N6O2ClIr·H2O (728.26 g/mol): C,
46.2; H, 4.4; N, 11.5. Found: C, 46.5; H, 4.3; N, 11.2.
[κ3-TpmMe2Ir(1,5-η-CHC(Ph)C(O)CHCH−)(CO)][BF4] (3c-
BF4). The same procedure as for the synthesis of 1a was followed,
but 100 mg (0.111 mmol) of [Ir(μ-Cl)(coe)2]2, 14 mL of CH2Cl2, and
41.1 mg (0.223 mmol) of 2-Ph-1,4-benzoquinone were used. Then
66.6 mg (0.223 mmol) of TpmMe2 and 43.4 mg (0.223 mmol) of
AgBF4 were simultaneously added. After solvent evaporation, the solid
was washed with Et2O (3 × 3 mL) and dried. The remaining solid was
dissolved in CH2Cl2, and the solution was filtered to separate AgCl
and evaporated to obtain a brown solid in 78% yield (132 mg, 0.174
mmol). Decomposition without melting occurred at 134 °C. IR νneat
(cm−1): (IrCO) 2057, (CO) 1614, (B−F) 1051. 1H NMR [CDCl3,
[κ2-TpmMe2Ir(2,3,5,6-η-2-tBu-1,4-benzoquinone)Cl] (1d) in a
Mixture with 3d-Cl. The reaction was performed as described for 1a,
but with 50 mg of [Ir(μ-Cl)(coe)2]2 (0.056 mmol), 4 mL of CH2Cl2,
18.3 mg of 2-tBu-1,4-benzoquinone immersed in a liquid nitrogen−
methanol cooling bath (−40 °C), and 33.3 mg (0.111 mmol) of
TpmMe2 during 80 min at −40 °C. After workup, 67 mg of a dark
brown solid was obtained as an inseparable mixture of compounds 1d
and 3d-Cl in a 4:1 ratio, respectively. The mixture melts at 123 °C.
Spectroscopic data for 1d: IR νneat (cm−1): (CO) 1648, 1564. 1H
NMR [CDCl3, J(Hz)]: δ 7.61 (s, 1H, CH(pz)3), 6.29, 6.21, 5.95 (s, 1H
each, HPz), 5.21 (d, 1H, 4JH3−H5 = 3, H-3), 4.93 (d, 1H, 3JH6−H5 = 9, H-
6), 3.10 (dd, 1H, 3JH5−H6 = 9, 4JH5−H3 = 3, H-5), 2.72, 2.63, 2.52, 2.46,
3
J(Hz)]: δ 8.78 (s, 1H, H-2), 8.61 (d, 1H, JH6−H5 = 9, H-6), 8.22 (s,
1H, CH(Pz)3), 7.34−7.22 (m, 5H, HPh), 7.05 (d, 1H, 3JH5−H6 = 9, H-5),
6.31, 6.29, 6.10 (s, 1H each, CHPz), 2.77, 2.76, 2.73, 2.44, 2.40, 2.24 (s,
3H each, 6MePz). 13C{1H} NMR [CDCl3]: δ 195.9 (CO-Ir), 159.2
(CO), 158.2, 154.9, 154.7, 146.8, 144.5, 144.4, (6CqPz), 140.1(C-Ph),
137.8 (C-5), 133.8 (C-2), 132.6 (C-6), 130.2 (CqPh), 128.6, 128.0,
127.2 (5CHPh, 2:2:1), 110.8, 109.9, 109.8 (3CHPz), 69.9 (CH(Pz)3),
14.4, 14.2, 13.3, 11.4, 11.2, 11.1 (6 MePz). Anal. Calcd for
C28H30N6O2IrBF4 (761.59 g/mol): C, 44.1; H, 3.9; N, 11.0. Found:
C, 44.4; H, 4.0; N, 10.7.
t
2.04, 1.55 (s, 3H each, 6MePz), 1.45 (s, 9H, Bu). 13C{1H} NMR
(CDCl3): δ 172.4, 163.1 (2COBQ), 158.5, 158.3, 150.2, 144.8, 144.6,
140.1 (6CqPz), 111.0, 110.9, 109.4 (3CHPz), 88.7 (C-tBu), 77.4 (C-6),
73.9 (CH(Pz)3), 65.1 (C-5), 50.1 (C-3), 36.1 (CqtBu), 27.4 (3MetBu
)
15.7, 14.9, 13.6, 12.0, 11.8, 10.0 (6MePz).
[κ3-TpmMe2Ir(2,3,5,6-η-1,4-benzoquinone)][BF4] (2a-BF4).
Method A. In a Schlenk flask equipped with a stir bar and immersed
in an ice−water bath were placed 150 mg (0.0236 mmol) of
compound 1a, 46 mg (0.0236 mmol) of AgBF4, and 8 mL of CH2Cl2.
The mixture was allowed to react for 50 min at 4 °C, whereupon the
AgCl precipitate was filtered off and washed with CH2Cl2 (2 × 3 mL).
The CH2Cl2 solution was evaporated to dryness to obtain a greenish-
yellow solid in 53% yield (87.5 mg, 0.100 mmol). Method B. The
same procedure as for the synthesis of 1a was followed, but 217 mg
(1.1 mmol) of AgBF4 was added together with the TpmMe2 ligand, to
[κ3-TpmMe2Ir(1,5-η-CHC(tBu)C(O)CHCH−)(CO)][BF4] (3d-
BF4). This compound was prepared as described for 3c-BF4, but
100 mg (0.111 mmol) of [Ir(μ-Cl)(coe)2]2, 14 mL of CH2Cl2, 36.6
mg (0.223 mmol) of 2-tBu-1,4-benzoquinone, 66.6 mg (0.223 mmol)
of TpmMe2, and 43.4 mg (0.223 mmol) of AgBF4 were used. A brown
solid was obtained in 81% yield (134 mg, 0.180 mmol).
Decomposition without melting occurred at 134 °C. IR νneat
(cm−1): (IrCO) 2052, (CO) 1609, (B−F) 1051. 1H NMR
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3
[CDCl3, J(Hz)]: δ 8.42 (s, 1H, H-2), 8.25 (d, 1H, JH6−H5 = 9, H-6),
allowed to react for 1.5 h to obtain a dark yellow solid after solvent
evaporation, which was washed with Et2O (3 × 4 mL) and dried. The
resulting solid was redissolved in 4 mL of CH2Cl2, and 3 mL of Et2O
was added. The resulting solution was discarded after filtration, and
the remaining solid was treated as before. After drying, 24 mg (0.048
mmol) of a yellow solid was obtained in 31% yield. Decomposition
without melting occurred at 163 °C. IR νneat (cm−1): (CO) 1614,
3
8.23 (s, 1H, CH(Pz)3), 6.88 (d, 1H, JH5−H6 = 9, H-5), 6.31, 6.29, 6.11
(s, 1H each, HPz), 2.79, 2.78, 2.76, 2.36, 2.36, 2.19 (s, 3H each, 6MePz),
1.23 (s, 9H, 3MetBu). 13C{1H} NMR [CDCl3]: δ 198.1 (CO-Ir), 159.6
(CO), 158.1, 154.8, 154.5, 151.9, 144.4, 144.4 (6CqPz), 144.3 (C-tBu),
139.1 (C-5), 129.5 (C-6), 125.8 (C-2), 110.7, 109.8, 109.7 (3CHPz),
69.9 (CH(Pz)3), 38.1 (CqtBu), 30.2 (3MetBu), 14.1, 14.1, 12.9, 11.4, 11.3,
11.2 (6MePz). Anal. Calcd for C26H34N6O2BF4Ir (741.60 g/mol): C,
42.1; H, 4.6; N, 11.3. Found: C, 42.3; H, 4.9; N, 11.2.
1
1583, (P−C) 1293, (CC) 1695. H NMR [CDCl3]: δ 4.84 (s, 4H,
2
HBQ), 1.72 (virtual d, 9H, JH−P = 9, P(CH3)3). 13C NMR [CDCl3,
3
2
[κ3-TpmMe2Ir(2,3-η-1,4-benzoquinone)(CO)][Ir(CO)2Cl2] (4-[Ir-
(CO)2Cl2]). In a Fisher-Porter glass pressure vessel equipped with a stir
bar was placed 150 mg (0.236 mmol) of compound 1a, and after three
cycles of treatment with N2/vacuum 12 mL of CH2Cl2 was added and
the reactor was charged with 1 atm of CO. The mixture was allowed to
react at room temperature during 50 min; then it was transferred to a
Schlenk flask, and half the solvent was evaporated under reduced
pressure. Then, 8 mL of Et2O was added until saturation, and the
solution was cooled to 4 °C until precipitation. The ethereal solution
was discarded, and the resulting solid was washed twice with 2 mL of
Et2O. The yellow solid was dried under vacuum to give 4 in 71% yield
(80 mg, 0.084 mmol). Decomposition without melting occurred at
179 °C. IR νneat (cm−1): (IrCO) 2042, 1957 (CO) 1648, 1566,
(CC) 1697. 1H NMR [(CD3)2CO, J(Hz)]: δ 8.24 (s, 1H, CH(Pz)3),
6.56 (s, 2H, H-5,6), 6.49, 6.31 (s, 3H,HPz, 2:1), 4.89 (s, 2H, H-2,3),
2.84, 2.82, 2.53, 2.30 (s, 18H, 6CHPz, 2:1:1:2). 13C{1H} NMR
[(CD3)2CO]: δ 198.9 (Ir-CO), 161.2 (2CO), 158.3, 157.4, 145.8,
145.2 (6CqPz, 1:2:1:2), 138.6 (C-5,6), 112.8, 109.8 (3CHPz, 1:2), 70.3
(CH(Pz)3), 28.2 (C-2,3), 14.1, 13.4, 11.9, 11.2 (6MePz, 2:1:1:2). Anal.
Calcd for C25H26N6O5Cl2Ir2 (985.85 g/mol): C, 31.7; H, 2.8; N, 8.9.
Found: C, 32.0; H, 2.8; N, 8.5.
J(Hz)]: δ 162.3 (t, 2CO, JC−P = 2.6), 78.9 (t, 4CHBQ, JC−P = 3.8),
16.4−15.6 (m, 6CH3). 31P{1H} NMR (CDCl3): δ −39.4 (PMe3).
Anal. Calcd for C12H22O2P2ClIr·0.25Et2O (508.97 g/mol): C, 30.7; H,
5.3. Found: C, 30.6; H, 5.1.
[(μ-PPh2CH2CH2PPh2)Ir(2,3,5,6-η-1,4-benzoquinone)Cl]2 (8).
This compound was prepared as described for 5 (method A), but
60 mg (0.094 mmol) of 1a, 5 mL of CH2Cl2, and a solution of 39.6 mg
(0.099 mmol) of 1,2-bis(diphenylphosphino)ethane in 5 mL of
CH2Cl2 were used. Washing was performed with a 70:30 mixture of
hexane−ethyl acetate (4 × 3 mL) followed by Et2O (2 × 3 mL). After
workup an orange solid was obtained in 80% yield (112 mg, 0.076
mmol). Decomposition without melting occurred at 144 °C. IR νneat
(cm−1): (CO) 1638, 1607, (P−C) 1434, 1332, (CCarom) 1483,
(CC) 1723. 1H NMR [CDCl3, J(Hz)]: δ 7.57−7.29 (m, 20H, HPh),
4.88 (s, 4H, HBQ), 3.08, 2.35 (m, 2H each, P(CH2)). 13C{1H} NMR
[CDCl3, J(Hz)]: δ 163.3 (t, 2CO, 3JC−P = 2.1), 132.9 (t, 4CHo, 2JC−P
=
3
5.5), 132.7 (t, 4CHm, JC−P = 4.5), 131.9, 131.6 (2CHp), 129.2 (t,
4CHm, 3JC−P = 5.4), 128.8 (t, 4CHo, 2JC−P = 5.5), 80.9 (t, 4CHBQ, 2JC−P
1
1
= 5.4), 27.9 (d, 2CH2, JC−P = 4.2), 27.4 (d, 2CH2, JC−P = 4.2).
31P{1H} NMR (CDCl3): δ 32.81 (1,2-bis(diphenylphosphino)ethane).
Anal. Calcd for C64H56O4P4Cl2Ir2·CH2Cl2 (1553.29 g/mol): C, 50.3;
H, 3.8. Found: C, 50.2; H, 3.6.
[(PPh3)2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] (5). Method A. In a
Schlenk flask equipped with a stir bar were placed 100 mg (0.157
mmol) of compound 1a, 10 mL of CH2Cl2, and 82.7 mg (0.315
mmol) of PPh3, and the mixture was allowed to react for 2 h at room
temperature. Then, the bright yellow solution was evaporated to
dryness, and the resulting dark yellow solid was washed with Et2O (3
× 4 mL) and dried under vacuum to obtain a yellow solid in 91% yield
(123 mg, 0.143 mmol). Method B. Into a Schlenk flask equipped with
a stir bar and immersed in an ice−water bath were placed 100 mg
(0.111 mmol) of [Ir(μ-Cl)(coe)2]2, 8 mL of CH2Cl2, and 24 mg
(0.223 mmol) of 1,4-benzoquinone. The mixture was allowed to react
for 1 h, whereupon 117 mg (0.446 mmol) of PPh3 was added. The
reaction mixture was allowed to react for 1.5 h at RT, whereby it
turned from dark orange to light orange. The solvent was evaporated,
and the resulting solid was washed with Et2O (3 × 3 mL), filtered, and
dried to obtain an orange solid in 87% yield (168 mg, 0.195 mmol).
Decomposition without melting occurred at 197 °C. IR νneat (cm−1):
(CO) 1675, 1630, (P−C) 1434, (CCarom) 1482. 1H NMR [CDCl3]:
δ 7.36−7.18 (m, 30H, HPPh3), 4.22 (s, 4H, HBQ). 13C{1H} NMR
[CDCl3, J(Hz)]: δ 166.4 (t, 2CO, 3JC−P = 2.2), 134.3 (t, 12CHm, 3JC−P
[κ2-TpmMe2Ir(2-6-η-semiquinone)Cl][BF4] (9-BF4) in a Mixture
with 1a. In a Schlenk flask equipped with a stir bar and immersed in
an ice−water bath was dissolved 100 mg (0.157 mmol) of 1a in 8 mL
of CH2Cl2, whereupon 17 μL (0.126 mmol) of HBF4−OEt2 was
added. Immediately, a pale yellow solid appeared. The mixture was
allowed to react for 1 h under vigorous stirring and allowed to reach
RT during one more hour. The solvent was evaporated to dryness, and
the resulting solid was dissolved in (CD3)CO to give a mixture of 9-
1
1
BF4−1a in 1:3 proportion as established from H NMR. H NMR
[(CD3)23CO]: δ 8.45 (s, 1H, CH(Pz)3), 6.52, 6.11 (s, 3H, HPz, 2:1), 6.11
3
(d, 2H, JH3−H2 = 6, H-3), 4.39 (d, 2H, JH2−H3 = 6, H-2), 2.79, 2.58,
2.10, 1.64 (s, 18H, 6CHPz, 2:2:1:1). 13C{1H} NMR [(CD3)2CO]: δ
176.4 (CO), 159.5, 150.8, 148.6, 142.6 (6CqPz, 2:1:2:1), 152.4 (C−
1
OH), 111.5, 110.8 (3CHPz, 1:2), 82.7 (2C-3, JC−H= 180), 75.6
1
(CH(Pz)3), 61.7 (2C-2, JC−H = 178), 14.8, 14.4, 11.7, 11.3 (6MePz,
2:1:2:1).
[κ2-TpmMe2Ir(1-6-η-1,4-hydroquinone)Cl][BF4]2 (10-(BF4)2). In
a Schlenk flask immersed in an ice−water bath and equipped with a
stir bar were placed 100 mg (0.157 mmol) of compound 1a, 12 mL of
CH2Cl2, and 47 μL (0.347 mmol) of a HBF4−OEt2 solution.
Immediately, a pale yellow solid appeared. The reaction mixture was
allowed to react for 1 h at 4 °C and for 1 h at room temperature. The
solvent was evaporated, and the remaining solid was washed with Et2O
(3 × 4 mL) and evaporated to dryness. A pale yellow solid was
obtained in 93% yield (118 mg, 0.146 mmol). Decomposition without
melting occurred at 75 °C. IR νneat (cm−1): (O−H) 3561, (C−O)
1062, 1032, (CC) 1676, 1569, (B−F) 1049. 1H NMR [(CD3)2CO]:
δ 8.55 (s, 1H, CH(Pz)3), 6.61, 6.19 (s, 3H, HPz, 2:1), 5.49 (br, 4H,
HHQ), 2.82, 2.60, 2.12, 1.67 (s, 18H, 6CHPz, 2:2:1:1).1H NMR
[CD3OD]: δ 8.38 (s, 1H, CH(Pz)3), 6.53, 6.12 (s, 3H, HPz, 2:1), 5.39
(s, 4H, HHQ), 2.66, 2.59, 2.15, 1.65 (s, 18H, 6CHPz, 2:2:1:1). 13C{1H}
NMR [(CD3)2CO]: δ 159.6, 151.3, 149.4, 143.1 (6CqPz, 2:1:2:1),
112.1, 111.4 (3CHPz, 1:2), 75.8 (CH(Pz)3), 74.6 (br, 4CHHQ), not
observed (COH), 15.1, 13.3, 11.8, 10.4 (6MePz, 2:1:2:1). 13C{1H}
NMR [CD3OD]: δ 160.2, 152.0, 149.6, 143.3 (6CqPz, 2:1:2:1), 152.1
1
= 4.5), 131.9 (virtual t, 6CqPh, JC−P = 28.3), 130.8 (6CHp), 128.2 (t,
12CHo, JC−P = 5.2), 81.0 (t, 4CHBQ,2JC−P = 5.9). 31P{1H} NMR
2
[CDCl3]: δ −13.6 (PPh3). Anal. Calcd for C42H34O2P2ClIr·H2O
(878.35 g/mol): C, 57.4; H, 4.1. Found: C, 57.1; H, 3.9.
[(PMe2Ph)2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] (6). This com-
pound was prepared as described for 5 (method A), but 45.0 μL
(0.315 mmol) of PMe2Ph was used to obtain a pale orange solid in
83% yield (80.5 mg, 0.131 mmol). Decomposition without melting
occurred at 162 °C. IR νneat (cm−1): (CO) 1644, 1603, (P−C) 1437,
1309, (CC) 1683. 1H NMR [CDCl3, J(Hz)]: δ 7.47−7.41 (m, 10H,
HPh), 4.70 (s, 4H, HBQ), 1.84, 1.71 (d, 6H each,2JH−P = 10.8,
P(CH3)2). 13C{1H} NMR [CDCl3, J(Hz)]: δ 162.4 (t, 2CO, JC−P
=
3
3
2.5), 131.4 (2CHp), 130.5 (t, 4CHm, JC−P = 4.6), 129.1 (t, 4CHo,
2JC−P = 5.1), 80.8 (t, 4CHBQ, 2JC−P = 4.8), 15.1 (t, 2CH3, 1JC−P = 20),
13.4 (t, 2CH3, JC−P = 20). 31P{1H} NMR (CDCl3): δ −33.1
1
(PMe2Ph). Anal. Calcd for C22H26O2P2ClIr (612.06 g/mol): C, 43.2;
H, 4.3. Found: C, 43.3; H, 4.2.
(C−OH), 112.4, 111.6 (3CHPz, 1:2), 76.2 (CH(Pz)3), 74.6 (4CHHQ
,
1JC−H = 179), 15.1, 13.3, 11.7, 10.4 (6MePz, 2:1:2:1). Anal. Calcd for
C22H28N6O2F8B2ClIr·H2O (827.79 g/mol): C, 31.9; H, 3.7; N, 10.2.
Found: C, 31.9; H, 3.4; N, 9.9.
[(PMe3)2Ir(2,3,5,6-η-1,4-benzoquinone)Cl] (7). This compound
was prepared as described for 5 (method A), but 331.0 μL of a 1.0 M
solution of PMe3 in THF was used (0.311 mmol). The mixture was
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Organometallics
Article
[κ3-TpmMe2Ir(1,5-η-CHCH-C(OH)CH−CH)(CO)]-
[O3SCF3]2 (11a-(O3SCF3)2). In a Schlenk flask equipped with a stir bar
was suspended 100 mg (0.145 mmol) of 3a-BF4 in 15 mL of THF.
The brown suspension turned to a light brown solution after dropwise
addition of 129 μL (1.45 mmol) of HSO3CF3 under vigorous stirring,
and after 30 min it turned gelatinous. After solvent evaporation, the
remaining brown oil was crushed in 15 mL of Et2O until a yellow solid
appeared. The solvent was removed by filtration, and the solid was
washed with Et2O (3 × 2 mL) and dried to obtain a pale yellow solid
in 70% yield (94.1 mg, 0.102 mmol). Decomposition without melting
occurred at 199 °C. IR νneat (cm−1): (O−H) 3420, (IrCO) 2085,
8, and E are available. Ortep drawings of compounds 1b, 6, 7,
and E are also available. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ipadillamar@ipn.mx.
Notes
The authors declare no competing financial interest.
1
(CC) 1571, 1470, (C−OH) 1255, (SO) 1307, 1166. H NMR
[CD2Cl2, J(Hz)]: δ 13.65 (br, 1H, OH), 11.02 (d, 2H, 3JH2−H3 = 9, H-
ACKNOWLEDGMENTS
2,6), 8.12 (s, 1H, CH(Pz)3), 7.79 (d, 2H, 3JH3−H2 = 9, H-3,5), 6.38, 6.16
■
1
The authors thank CONACYT (grants 33438-E and 83378
(I.I.P.M.), Scholarship 214238 (M.H.J.)) and Secretaria de
(s, 3H, HPz, 2:1), 2.76, 2.71, 2.37, 1.85 (s, 18H, 6CHPz, 2:1:2:1). H
́
NMR [CD3OD, J(Hz)]: δ not observed (OH), 11.52 (br d, 2H, H-
2,6), 7.92 (s, 1H, CH(Pz)3), 7.68 (d, 2H, 3JH3−H2 = 9, H-3,5), 6.16, 5.97
(s, 3H, HPz, 2:1), 2.49, 2.46, 2.13, 1.54 (s, 18H, 6CHPz, 2:1:2:1).
13C{1H} NMR [CD2Cl2, J(Hz)]: δ 198.7 (Ir-CO), 177.4 (C-2,6),
158.7, 156.5, 145.5, 145.4 (6CqPz, 2:1:2:1), 155.0 (C-OH), 132.2 (C-
́
́
Posgrado e Investigacion del Instituto Politecnico Nacional
(SIP-IPN) for financial support.
REFERENCES
1
■
3,5, JC−H = 158), 111.1, 110.6 (3CHPz, 1:2), 70.1 (CH(Pz)3), 14.9,
12.2, 11.9, 11.7 (6MePz, 2:1:1:2). 13C{1H} NMR [CD3OD, J(Hz)]: δ
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196.9 (Ir-CO), 187.1 (br, C-2,6), 157.5, 155.9, 144.9, 144.7 (6CqPz,
1
2:1:2:1), 153.9 (C-OH), 129.0 (C-3,5, JC−H = 158), 109.9, 109.6
(3CHPz, 1:2), 69.6 (CH(Pz)3), 13.5, 10.4, 10.4, 10.2 (6MePz, 2:1:1:2).
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3.2; N, 9.2. Found: C, 31.5; H, 3.1; N, 8.9.
[κ3-TpmMe2Ir(1,5-η-CHC(tBu)-C(OH)CH-CH)(CO)]-
[O3SCF3]2 (11d-(O3SCF3)2). In a Schlenk flask equipped with a stir
bar were placed 164 mg (0.221 mmol) of 3d-BF4 in 4 mL of CH2Cl2.
The brown solution turned orange after dropwise addition of 59 μL
(0.663 mmol) of HSO3CF3 under vigorous stirring, and after 30 min
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mL of Et2O until an orange solid appeared. The solvent was removed
by filtration, and the solid was washed with Et2O (3 × 2 mL) and dried
to obtain a pale orange solid in 85% yield (178.6 mg, 0.187 mmol).
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(O−H) 3471, (IrCO) 2089, (CC) 1562, 1468, (C−OH) 1257,
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1
(SO) 1311, 1149. H NMR [CD2Cl2, J(Hz)]: δ 13.44 (br, 1H,
OH), 11.67 (s, 1H, H-2), 10.50 (d, 1H, 3JH6−H5 = 9, H-6), 8.12 (s, 1H,
3
CH(Pz)3), 7.79 (d, 1H, JH5−H6 = 9, H-5), 6.39, 6.37, 6.17 (s, 1H each,
HPz), 2.76, 2.75, 2.72, 2.35, 2.35, 1.86 (s, 3H each, 6CHPz), 1.35 (s,
9H, 3MetBu). 13C{1H} NMR [CD2Cl2]: δ 198.9 (Ir-CO), 169.3 (C-2),
165.9 (C-6), 158.4, 156.3, 155.9, 145.3, 145.5, 145.1 (6CqPz), 156.1
(C-OH), 149.8 (C-5), 134.7 (C-tBu), 110.9, 110.4, 110.4 (3CHPz),
70.1 (CH(Pz)3), 39.4 (CqtBu), 29.9 (3MetBu), 14.8, 14.7, 11.9, 11.8, 11.6,
11.6 (6Mepz). Anal. Calcd for C28H36N6O8F6S2Ir·0.75CH2Cl2
(1012.89 g/mol): C, 33.5; H, 3.7; N, 8.3. Found: C, 33.8; H, 4.0;
N, 8.1.
Titration of 1a with Aqueous HBF4 (48 wt %). Eight independent
samples were prepared starting from 10 mg of 1a in CH2Cl2 and
adding the acid solution in aliquots of 0.25 molar equivalents in the
NMR tubes to complete two molar equivalents in tube No. 8. After
solvent evaporation each reaction mixture was washed with Et2O, to
remove the remaining H2O, and dried. The resulting solid was
1
dissolved in deuterated acetone for H NMR.
Monitoring Reaction of 1a with CO (1 atm.). In an NMR tube
with a J. Young valve was placed 25 mg (0.039 mmol) of compound
1a, and after three cycles of alternate N2/vacuum application, 0.5 mL
of CD2Cl2 was added and the solution was immersed in a bath with
liquid N2. The tube was charged with 1 atm of CO, and after
1
defrosting the solution to room temperature, H NMR spectra were
recorded at regular time intervals.
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ASSOCIATED CONTENT
■
S
* Supporting Information
CIFs, structure factors, tables of crystallographic data and
comparative tables of selected bond lengths and angles of
complexes 1a, 1b, 2a-BF4, 3a-BF4, 3b-BF4, 4-[Ir(CO)2Cl2], 5−
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Organometallics
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NOTE ADDED AFTER ASAP PUBLICATION
■
This paper was published on the Web on July 13, 2012, with
errors in Scheme 1 and refs 12 and 13 and their associated
citations. The corrected version was reposted on July 17, 2012.
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