C-H activation on a diphosphine and hydrido-bridged diiridium complex: Generation and detection of an active IrII-IrII species [(Cp*Ir)2(μ-dmpm)(μ-H)]+

Article abstract of DOI:10.1039/b803626h

Reaction of [Cp*Ir(μ-H)]₂ (5) (Cp* = η⁵-C₅Me₅) with bis(dimethylphosphino) methane (dmpm) gives a new neutral diiridium complex [(Cp*Ir) ₂(μ-dmpm)(μ-H)₂] (3). Treatment of 3 with methyl triflate at -30 °C results in the formation of [(Cp*Ir)(H)(μ-dmpm) (μ-H)(Me)(IrCp*)][OTf] (6). Warming a solution of 6 above 0 °C brings about predominant generation of 32e^- Ir^II-Ir ^II species [(Cp*Ir)(μ-dmpm)(μ-H)(IrCp*)][OTf] (7). Further heating of the solution of 7 up to 30 °C for 14 h leads to quantitative formation of a new complex [(Cp*Ir)(H)(μ-Me ₂PCH₂PMeCH₂)(μ-H)(IrCp*)][OTf] (8), which is formed by intramolecular oxidative addition of the methyl C-H bond of the dmpm ligand. Intermolecular C-H bond activation reactions with 7 are also examined. Reactions of 7 with aromatic molecules (benzene, toluene, furan, and pyridine) at room temperature result in the smooth sp² C-H activation to give [(Cp*Ir)(H)(μ-dmpm)(μ-H)(Ar)(IrCp*)][OTf] (Ar = Ph (9); Ar = m-Tol (10a) or p-Tol (10b); Ar = 2-Fur (11)) and [(Cp*Ir)(H) (μ-dmpm)(μ-C₅H₄N)(H)(IrCp*)][OTf] (12), respectively. Complex 7 also reacts with cyclopentene at 0 °C to give [(Cp*Ir)(H)(μ-dmpm)(μ-H)(1-cyclopentenyl)(IrCp*)][OTf] (13). Structures of 3, 8 and 12 have been confirmed by X-ray analysis.

Full text of DOI:10.1039/b803626h

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C–H activation on a diphosphine and hydrido-bridged diiridium
complex: generation and detection of an active IrII–IrII species
[(Cp*Ir)2(l-dmpm)(l-H)]+†
Yoshinori Takahashi,a Mitsuru Nonogawa,a Ken-ichi Fujita*a,b and Ryohei Yamaguchi*a
Received 3rd March 2008, Accepted 1st May 2008
First published as an Advance Article on the web 27th May 2008
DOI: 10.1039/b803626h
5
Reaction of [Cp*Ir(l-H)]2 (5) (Cp* = g -C5Me5) with bis(dimethylphosphino)methane (dmpm) gives a
new neutral diiridium complex [(Cp*Ir)2(l-dmpm)(l-H)2] (3). Treatment of 3 with methyl triflate at
−30 ◦C results in the formation of [(Cp*Ir)(H)(l-dmpm)(l-H)(Me)(IrCp*)][OTf] (6). Warming a
solution of 6 above 0 ◦C brings about predominant generation of 32e− IrII–IrII species
[(Cp*Ir)(l-dmpm)(l-H)(IrCp*)][OTf] (7). Further heating of the solution of 7 up to 30 ◦C for 14 h
leads to quantitative formation of a new complex [(Cp*Ir)(H)(l-Me2PCH2PMeCH2)(l-
H)(IrCp*)][OTf] (8), which is formed by intramolecular oxidative addition of the methyl C–H bond of
the dmpm ligand. Intermolecular C–H bond activation reactions with 7 are also examined. Reactions
of 7 with aromatic molecules (benzene, toluene, furan, and pyridine) at room temperature result in the
smooth sp2 C–H activation to give [(Cp*Ir)(H)(l-dmpm)(l-H)(Ar)(IrCp*)][OTf] (Ar = Ph (9); Ar =
m-Tol (10a) or p-Tol (10b); Ar = 2-Fur (11)) and [(Cp*Ir)(H)(l-dmpm)(l-C5H4N)(H)(IrCp*)][OTf]
(12), respectively. Complex 7 also reacts with cyclopentene at 0 ◦C to give [(Cp*Ir)(H)(l-dmpm)(l-H)(1-
cyclopentenyl)(IrCp*)][OTf] (13). Structures of 3, 8 and 12 have been confirmed by X-ray analysis.
H)]+, which would be generated by base-induced nucleophilic
Introduction
deprotonation of 1 and 2. Although intermediacy of IrII–IrII
(or mixed-valent IrI-IrIII) species in C–H activation by diiridium
complexes has been proposed by Bergman et al.8a and Oro et al.,8b
direct detection of such species has never been reported.9
In this article, we report the synthesis and reactivity of a
new neutral diiridium complex [(Cp*Ir)2(l-dmpm)(l-H)2] (3): (1)
treatment of 3 with methyl triflate results in the net abstraction
of hydride to successfully afford the proposed 32e− intermediate,
(2) this 32e− complex can be detected for the first time by NMR
spectroscopy, and (3) it becomes evident that the detected active
species readily brings about intramolecular sp3 and intermolecular
sp2 C–H bond activation.
The study on C–H bond activation of hydrocarbons has been
attracting much attention in organometallic chemistry,1 since they
are becoming increasingly important as elemental reactions in the
functionalization of the inert but abundant organic molecules.2
During recent decades, it has been revealed that a number of
transition metal complexes are capable of activating C–H bonds.
As for iridium complexes, (C5R5)Ir(L) [R = Me (Cp*), H (Cp)]
complexes are well known to be capable of such activation,3 and
catalytic applications have been also reported.4
Meanwhile, much attention has been paid to the activa-
tion of organic molecules on multinuclear complexes in ex-
pectation of the synergetic effect of the multi-metal centers,5
and various multimetallic systems capable of C–H activa-
tion have been disclosed.6 In the course of our studies on
the synthesis and reactivity of diphosphine- and dihydrido-
bridged dicationic diiridium complexes [(Cp*Ir)2(l-diphos)(l-
H)2]2+ [diphos = bis(dimethylphosphino)methane (dmpm) (1) as
well as bis(diphenylphosphino)methane (dppm) (2)],7 we reported
that the reaction of 1 and 2 with base resulted in the activation
of aromatic C–H bonds.7c The active species in these reactions
was assumed to be a 32e− IrII–IrII species, [(Cp*Ir)2(l-diphos)(l-
Chart 1
aGraduate School of Human and Environmental Studies, Kyoto Univer-
sity, Sakyo-ku, Kyoto 606-8501, Japan. E-mail: yama@kagaku.mbox.
media.kyoto-u.ac.jp; Fax: +81 75 753 6634; Tel: +81 75 753 6840
Results and discussion
Preparation of a neutral dmpm and dihydrido-bridged dinuclear
iridium complex 3
bGraduate School of Global Environmental Studies, Kyoto University, Sakyo-
ku, Kyoto 606-8501, Japan. E-mail: fujitak@kagaku.mbox.media.kyoto-
u.ac.jp; Fax: +81 75 753 6634; Tel: +81 75 753 6827
As reported earlier, we have demonstrated that treatment of
diphosphine and dihydrido-bridged dicationic diiridium complex
1 and 2 with base induced the C–H bond activation and proposed
that the 32e− IrII–IrII species might play an important role at the
† Electronic supplementary information (ESI) available: Crystallographic
details for complex 3, 8 and 12. CCDC reference numbers 680332–680334.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b803626h
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critical stage of the activation.7c However, such C–H activation
reactions were relatively sluggish (20 h at room temperature)
probably because of the low solubility of the starting dicationic
complexes and base (NaOtBu), making it very difficult to carry out
further investigations and direct detection of the true active 32e−
IrII–IrII species. Thus, we have designed a new neutral diiridium
complex bridged by dmpm and dihydrides, [(Cp*Ir)2(l-dmpm)(l-
H)2] (3), anticipating that 3 would be more soluble and could be
converted into the active species by the abstraction of one of the
bridging hydride as a form of hydride (H−).10
(1)
Fig. 1 ORTEP drawing of the neutral complex 3 with 50% thermal
probability ellipsoids. Hydrogen atoms are omitted for◦clarity. Selected
◦
˚
bond distances (A), angles ( ), and a torsion angle ( ): Ir(1)–Ir(2) =
2.7618(3); Ir(1)–P(1) = 2.200(2); Ir(2)–P(2) = 2.193(2); Ir(2)–Ir(1)–P(1) =
86.75(5); Ir(1)–Ir(2)–P(2) = 84.94(5); P(1)–Ir(1)–Ir(2)–P(2) = 43.96(8).
Treatment of [(Cp*Ir)2(l-H)3]+ (4) with KOtBu followed by an
addition of dmpm to a solution of resulting [Cp*Ir(l-H)]2 (5) in
11
benzene gave [(Cp*Ir)2(l-dmpm)(l-H)2] (3) in high yield (eqn 1).
The complex 3 was highly soluble in non-polar solvent as expected,
and was isolated by the extraction with hexane in 93% yield. The
NMR spectra of 3 indicated C2v symmetry in solution. In the 1H
NMR spectrum of 3, signals due to two Cp* ligands (d 2.15) and
four methyl groups of the dmpm ligand (d 1.47) were observed
equivalently as well as the signals due to two hydrides (d −17.76).
[(Cp*Ir)(l-dmpm)(l-H)(IrCp*)]+ (7) (Scheme 1). It should be
noted that a net abstraction of a hydride can be achieved by these
successive reactions.
When methyl triflate (1.0 equiv.) was added to a dichloro-
methane solution of 3 at −30 ◦C and the solution was stirred
for 2 h, we found that methyl dihydride complex 6 was formed
quantitatively (Scheme 1). The structure of complex 6 was
identified by NMR spectroscopy below −30 ◦C because of its
thermal instability. In the 1H NMR spectrum, a signal due to the
iridium-bound methyl group was observed at d 0.51 as a doublet.
1
In the 31P{ H} NMR, a singlet resonance was found at d −46.7. All
NMR data for 3 are consistent with the proposed structure. If the
bridging hydride is regarded as a two-electron ligand, 3 would be
a 34e− complex. Cooling the hexane solution of 3 gave the brown
single crystals suitable for X-ray diffraction study. An ORTEP
drawing of 3 is shown in Fig. 1. The iridium–iridium distance
1
In the 13C{ H} NMR spectrum, a characteristic signal due to the
iridium-bound methyl carbon was observed at d −32.7 as a doublet
coupled to one of the phosphorus atoms. Signal patterns of Cp*
˚
(2.7618(3) A) is slightly longer than that of the dicationic complex
1
1
1
and dmpm in H, 13C{ H}, and 31P{ H} NMR were similar to
1 (2.7237(3) A), reflecting the difference between the 34e− (3)
7a
˚
those of C–H activated complexes so far reported by us.7c
and the 32e− (1) characters. Although a large torsion angle of
P(1)–Ir(1)–Ir(2)–P(2) was inconsistent with the higher symmetry
observed in the NMR analysis, it would be rationalized by the fast
ring flip of the Ir2P2C framework at room temperature in solution.
Then, we traced the reaction of 6 by variable-temperature NMR
spectroscopy by raising the temperature from −30 to 30 ◦C.
1H NMR spectra of the hydride region and a possible reaction
pathway are summarized in Fig. 2 and Scheme 1. Upon warming
the solution of complex 6, the signals of hydrides (d −16.86 for
terminal and d −25.25 for bridging) and the methyl group bound
to iridium (d 0.51) of 6 disappeared. Instead, a new triplet signal
of a species 7 appeared at d −20.23 with an integration value
corresponding to 1H, which was◦predominantly observed around
Abstraction of a hydride from the neutral complex 3 by the reaction
with methyl triflate: generation and detection of a highly active
IrII–IrII species [(Cp*Ir)2(l-dmpm)(l-H)]+ (7)
At first, we attempted several reactions of 3 using the reagents for
abstraction of hydride such as (Ph3C)+ in order to generate a 32e−
active species directly from 3, but these reactions gave complicated
mixtures.12 Then, we anticipated that the reaction of 3 with methyl
cation would give a methyl dihydrido intermediate [(Cp*Ir)(H)(l-
dmpm)(l-H)(Me)(IrCp*)]+ (6), from which reductive elimination
of methane could occur to generate the desired 32e− active species
1
1
the temperature range of 0 to 20 C. 13C{ H} and 31P{ H} spectra
◦
1
of 7 were also measured at −10 C in addition to H NMR. In
the H and 13C{ H} NMR, signals due to two Cp* ligands were
equivalently observed at d 1.77 (1H) and d 11.5 (13C), respectively,
indicating the high symmetrical structure of 7. Signals due to
the four methyl groups of dmpm were also observed equivalently
1
1
Scheme 1
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Fig. 2 Monitoring of the reaction of 6 in dichloromethane-d2 by 1H NMR analysis from −30 to 30 ◦C. Signals due to the iridium hydrides are shown.
1
at d 1.75 (1H) and d 20.2 (13C). In the 31P{ H} NMR, only one signal
was observed at d 10.6, also supporting the proposed symmetrical
structure of 7. From these NMR analyses, the structure of 7
was confirmed to be 32e− IrII–IrII, [(Cp*Ir)2(l-dmpm)(l-H)]+, as
illustrated in Scheme 1.13 Further heating of the solution of 7 up to
30 ◦C for 14 h resulted in the quantitative formation of the complex
8, formed by intramolecular oxidative addition of the methyl C–H
bond of dmpm ligand to the diiridium core (vide infra).
The above successful generation and detection of the true active
IrII–IrII intermediate 7 prompted us to investigate the scope of C–H
activation. The brown solid of 6 was converted to the purple solid
of 7 by the simple procedures, which consisted of the gen◦eration
of 6 followed by the removal of volatiles in vacuo at −30 C and
warming to room temperature (see the Experimental section for
details). Using the desired purple solid 7, we have performed the
Fig. 3 ORTEP drawing of the cationic part of 8 with 30% thermal
C–H activation reactions with several organic molecules as shown
below.14
probability ellipsoids. Hydrogen◦atoms are omitted for clarity. Selected
˚
bond distances (A) and angles ( ): Ir(1)–Ir(2) = 3.0189(4); Ir(1)–P(1) =
2.257(2); Ir(2)–P(2) = 2.235(2); Ir(1)–C(25) = 2.154(8); P(1)–Ir(1)–C(26) =
80.3(2); P(1)–Ir(1)–Ir(2) = 89.38(6); Ir(1)–Ir(2)–P(2) = 66.10(5).
Intramolecular activation of sp3 C–H bond in dmpm ligand
◦
When a solution of 7 in dichloromethane was kept at 40 C for
24 h, the complex 8 was formed quantitatively (eqn 2).15 The
structure of 8 was determined by spectroscopic analysis and X-ray
crystallography. The 1H NMR spectrum of 8 showed signals due
to two hydrides at d −16.78 (terminal) and −24.47 (bridging) and
signals due to non-equivalent methylene protons of the activated
Intermolecular activation of sp2 C–H bonds by complex 7
We next investigated intermolecular aromatic C–H bond activa-
tion reactions of benzene, toluene, and hetero aromatics. As soon
as benzene was added to pre-formed 7 at room temperature, the
purple solid of 7 was dissolved and turned into a red–orange
solution. After stirring for 75 min, [(Cp*Ir)(H)(l-dmpm)(l-
H)(Ph)(IrCp*)]+ (9) was produced in 89% yield (eqn 3). The
spectral data of 9 were identical to those we have previously
reported.7c This C–H activation reaction of benzene apparently
proceeded much faster compared to the reaction starting with the
dicationic complex 1 (20 h, 44% isolated yield), and the yield of
9 was also higher. Using similar procedures, the C–H activation
reactions of toluene and furan were also accomplished to give 10
(45%) and 11 (89%), respectively (eqn 3). While the activation of
toluene gave a mixture of the meta- and para-activated products
in a ratio of 1 : 1.617 comparable to those of our earlier report (1 :
2)7c and others,3g,18 the activation of furan gave the 2-furyl product
11 as a single product in high yield (89%) and the 3-furyl product
was not detected.
1
methyl group at d 2.84 and 0.85. In the 13C{ H} NMR spectrum,
the methylene carbon bound to the iridium center was observed at
d −8.2 as a doublet. The structure of 8 was finally confirmed by X-
ray diffraction study. The molecular geometry is shown in Fig. 3.
˚
˚
The iridium–iridium distance (3.0189(4) A) is 0.17 A shorter than
that of phenyl complex 9 (3.190(1) A).7c The iridium–carbon bond
length (2.154(8) A) is a typical value compared to those in sp
˚
3
˚
carbon–iridium bonds.16
(2)
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next examined. A large excess of cyclopentene was added to
the dichloromethane solution of 7 at −30 ◦C and the solution
was stirred at 0 ◦C for 18 h. These procedures brought about
the activation of the olefinic C–H bonds of cyclopentene to
give [(Cp*Ir)(H)(l-dmpm)(l-H)(1-cyclopentenyl)(IrCp*)]+ (13) in
56% yield (eqn 5).19 Complex 13 was relatively unstable and
(3)
1
its structure was elucidated by NMR analysis. In the H NMR
spectrum of 13, signals due to hydrides were observed at d −17.20
1
(terminal) and −25.80 (bridging). In the 13C{ H} NMR spectrum,
We further examined the C–H activation of a hetero aromatic
compound. The similar activation of pyridine by pre-formed 7
gave [(Cp*Ir)(H)(l-dmpm)(l-C5H4N)(IrCp*)(H)]+ (12) in 74%
characteristic signals due to olefinic carbons were observed at d
131.4 and 130.2 and the latter signal at d 130.2 (d, J = 14 Hz) was
coupled to one of the phosphorus atoms in the dmpm ligand. All
NMR data were consistent with the proposed structure.
1
yield (eqn 4). In the H NMR spectra of 12, signals due to two
non-equivalent hydrides were observed in the terminal hydride
region (d −14.92 and −14.99). It was deduced from the signal
pattern of aromatic protons that the C–H bond at the 2-position
of the pyridine ring was selectively cleaved.19 The structure
of 12 was unequivocally confirmed by X-ray diffraction. The
molecular geometry and atom-numbering system are shown in
Fig. 4. It is apparent that the two iridium centers are bridged
by the pyridine ring at the nitrogen and the carbon at the ortho-
(5)
˚
position. The iridium–iridium distance is 4.0287(4) A, indicating
the absence of a bonding interaction between the two iridium
Conclusions
˚
centers. The lengths of the iridium–carbon bond (2.054(8) A) and
˚
We have accomplished the synthesis of electronically neutral
dmpm and dihydrido-bridged diiridium(II) complex 3 and dis-
closed that treatment of 3 with methyl triflate results in a net
abstraction of a hydride from 3, leading to successful generation
of a highly reactive 32e− IrII–IrII species 7 that can be detected for
the first time by means of variable-temperature NMR analysis.
Using pre-formed 7 derived from the neutral complex 3 as a
precursor, rapid activation of aromatic and olefinic C–H bonds
can be achieved under very mild conditions.
the iridium–nitrogen bond (2.159(8) A) are typical of iridium–
aromatic carbon single bonds and iridium–pyridine dative bonds,
respectively.20 Formation of this 36e− complex 12 indicates that
other C–H activated 34e− complexes (8–11) could be potentially
coordinatively unsaturated.
(4)
Experimental
General
All reactions and manipulations were carried out under an
atmosphere of argon by means of standard Schlenk techniques.
1
1
1H, 13C{ H}, 19F, and 31P{ H} NMR spectra were recorded using
a JEOL A-500 and EX-270 spectrometers. 31P{ H} NMR were
1
referenced to an 85% H3PO4 external standard. 19F NMR were
referenced to a CF3CO2Et external standard. Melting points were
determined using a Yanagimoto micro melting point apparatus.
Elemental analyses were carried out at the Microanalysis Center
of Kyoto University.
Materials
Solvents were subjected to freeze–thaw–degas cycles three times
after being dried by using standard procedures and were distilled
prior to use. [(Cp*Ir)2(l-H)3]Cl (4) was prepared following the
literature method.21 Dmpm, methyl triflate and potassium tert-
butoxide were used as obtained from commercial sources. Other
reagents were used after distillation.
Fig. 4 ORTEP drawing of the cationic part of 12 with 30% thermal
probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected
◦
˚
(bond) distances (A) and angles ( ): Ir(1)–Ir(2) = 4.0287(4); Ir(1)–P(1)
= 2.240(2); Ir(2)–P(2) = 2.247(2); Ir(1)–C(26) = 2.054(8); Ir(2)–N(1) =
2.159(8); P(1)–Ir(1)–C(26) = 84.1(2); P(2)–Ir(2)–N(1) = 94.23(19).
Preparation of [(Cp*Ir)2(l-dmpm)(l-H)2] (3)
By the C–H activation methodology using the neutral complex
3 as a precursor, the activation of olefinic C–H bonds was
In a 10 mL Schlenk tube, [(Cp*Ir)2(l-H)3](Cl) (4) (692 mg,
0.998 mmol) and potassium tert-butoxide (133 mg, 1.19 mmol)
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were placed. After addition of benzene (6 mL), the mixture was
stirred for 2 hours at room temperature. The color of the solution
turned brown. Dmpm (150 mg, 1.10 mmol) was added, and the
mixture was further stirred for 24 hours at room temperature.
After evaporation of the volatiles, the residue was extracted with
hexane. Removal of hexane in vacuo afforded a brown solid 3
(735 mg, 0.927 mmol, 93%). Single crystals suitable for X-ray
diffraction were obtained by recrystallization from a hot hexane
thus obtained confirmed quantitative formation of 7. Then, C–H
activation reactions were conducted as described below.
Intramolecular C–H bond activation to give 8
After the generation of 7 (from 0.190 mmol of 3), the purple solid
was dissolved in dichloromethane (12 mL). Heating the solution at
40 ◦C for 24 h gave the C–H bond activated product 8. Extraction
with toluene gave the brown oil 8 (173 mg, 0.184 mmol, 97%).
Single crystals suitable for X-ray analysis were obtained by cooling
1
solution of 3. H NMR (500 MHz, C6D6): d 2.61 (2H, t, J =
10 Hz, PCH2P), 2.15 (30H, s, Cp*), 1.47 (12H, br s, PMe), −17.76
1
the toluene solution of 8. H NMR (500 MHz, CD2Cl2): d 3.38
1
(2H, t, J = 17 Hz, Ir–H–Ir). 13C{ H} NMR (126 MHz, C6D6): d
(1H, m, PCHHP), 2.84 (1H, m, PCHHIr), 2.03 (15H, s, Cp*),
2.01 (1H, m, PCHHP), 1.91 (15H, d, J = 3 Hz, Cp*), 1.73 (3H,
d, J = 11 Hz, PMe), 1.60 (3H, d, J = 10 Hz, PMe), 1.52 (3H,
d, J = 10 Hz, PMe), 0.85 (1H, m, PCHHIr), −16.78 (1H, d, J =
90.6 (s, C5Me5), 56.6 (t, J = 36 Hz, PCH2P), 16.0 (s, PMe), 12.40
1
(s, C5Me5). 31P{ H} NMR (202 MHz, C6D6): d −46.7 (s). M.p.
173.3–175.0 ◦C. Anal. Calcd for C26H46Ir2P2: H, 5.85; C, 37.86.
Found: H, 5.82; C, 37.96.
1
28 Hz, IrH,), −24.47 (1H, m, Ir–H–Ir). 13C{ H} NMR (126 MHz,
CD2Cl2): d 121.2 (q, J = 322 Hz, CF3), 94.0 (d, J = 3 Hz, C5Me5),
93.2 (d, J = 3 Hz, C5Me5), 36.4 (t, J = 38 Hz, PCH2P), 21.0 (m,
PMe), 19.8 (dd, J = 37 Hz, 4 Hz, PMe), 13.8 (dd, J = 36 Hz, 3 Hz,
PMe), 11.1 (d, J = 4 Hz, C5Me5), 10.1 (d, J = 4 Hz, C5Me5), −8.2
(d, J = 37 Hz, PCH2Ir). 19F NMR (470 MHz, CD2Cl2) d −78.3
Generation and detection of 6 and 7 by the reaction of 3 with
MeOTf using low-temperature and variable-temperature
NMR analysis
A two-necked 30 mL flask was charged with 3 (242 mg,
0.305 mmol) and dichloromethane (12 mL) at −30 ◦C. Methyl
triflate (49.8 mg, 0.303 mmol) was added to ◦the solution, and the
reaction mixture was stirred for 2 h at −30 C. After removal of
the solvent in vacuo at −30 ◦C, CD2Cl2 (1.0 mL) was added. The
1
(s). 31P{ H} NMR (202 MHz, CD2Cl2): d −22.7 (d, J = 46 Hz),
−43.6 (d, J = 46 Hz). M.p. 169 ◦C (decomp.). Anal. Calcd for
C26H45F3Ir2O3P2S: C, 33.18; H, 4.82. Found: C, 33.47; H, 4.76.
◦
solution was transferred into an NMR tube at −40 C, and the
General procedure for the C–H activation reaction of aromatic
molecules to give 9–12
tube was flame sealed. The tube was kept below −80 ◦C before
being placed in a pre-cooled (−80 ◦C) NMR probe. The probe
temperature was elevated by 10 ◦C every 30 min from −50 to
30 ◦C.
After the generation of 7, aromatic solvent was added to the purple
solid of 7 and stirred for 75 min. The color of the solution turned
from purple to orange–red within 10–15 min. After removal of the
volatiles, complexes 9–12 were isolated. The spectral data of 9, 10
and 11 are identical to those we have previously reported.7c
6: H NMR (500 MHz, CD2Cl2, at −40 ◦C): d 4.60 (1H, m,
1
PCHHP), 2.10 (1H, m, PCHHP), 1.92 (15H, s, Cp*), 1.76 (15H, s,
Cp*), 1.64 (3H, d, J = 10 Hz, PMe), 1.55 (3H, d, J = 9 Hz, PMe),
1.39 (3H, d, J = 10 Hz, PMe), 1.38 (3H, d, J = 10 Hz, PMe), 0.51
(3H, d, J = 6 Hz, IrMe), −16.86 (1H, dd, J = 37 Hz, 2 Hz, IrH,),
C–H activation reaction of benzene to give 9
1
−25.25 (1H, m, Ir–H–Ir). 13C{ H} NMR (126 MHz, CD2Cl2, at
After removal of benzene in vacuo, the residue was washed with
benzene and hexane to give 9 as an orange powder (756 mg,
0.741 mmol, 89%).
−40 ◦C): d 120.5 (q, J = 321 Hz, CF3), 94.2 (d, J = 2 Hz, C5Me5),
94.0 (d, J = 3 Hz, C5Me5), 25.5 (d, J = 44 Hz, PCH2P), 17.3 (d,
J = 34 Hz, PMe), 14.8 (d, J = 43 Hz, PMe), 11.8 (d, J = 35 Hz,
PMe), 11.7 (d, J = 35 Hz, PMe), 10.6 (s, C5Me5), 9.8 (s, C5Me5),
C–H activation reaction of toluene to give 10
1
−32.7 (d, J = 9 Hz, IrMe). 31P{ H} NMR (202 MHz, CD2Cl2, at
−40 ◦C): d −30.9 (d, J = 42 Hz), −40.5 (d, J = 42 Hz).
After removal of toluene in vacuo, the residue was chro-
matographed on silica gel, and subsequent recrystallization from
toluene gave a mixture of 10a and 10b as an orange powder
(119 mg, 0.115 mmol, 45%). The ratio of products was determined
by 1H NMR.
◦
1
7: H NMR (500 MHz, CD2Cl2, at 10 C): d 2.33 (2H, t, J =
10 Hz, PCH2P), 1.77 (30H, s, Cp*), 1.75 (12H, br s, PMe2), −20.23
(1H, t, J = 10 Hz, Ir–H–Ir). 13C{ H} NMR (126 MHz, CD2Cl2,
1
◦
at −10 C): d 120.9 (q, J = 322 Hz, CF3), 93.5 (s, C5Me5), 36.7
(t, J = 35 Hz, PCH2P), 20.2 (app. triplet, AAꢀX system, RJPC
=
44 Hz, PMe), 11.5 (d, J = 4 Hz, C5Me5). 19F NMR (470 MHz,
C–H activation reaction of furan to give 11
◦
CD2Cl2, at 10 C) d −78.4 (s). 31P{ H} NMR (202 MHz, CD2Cl2,
1
at −10 ◦C): d 10.6 (s).
After removal of furan in vacuo, the residue was washed with
toluene and hexane to give 11 as a light yellow powder (832 mg,
0.824 mmol, 89%).
General procedures for the C–H activation reactions: concise
generation of 32e− complex 7
C–H activation reaction of pyridine to give 12
A two-necked 30 mL flask was charged with 0.30 mmol of 3 and
◦
12 mL of dichloromethane at −30 C. Methyl triflate (0.30 mol,
After removal of pyridine in vacuo, the residue was washed with
toluene and extracted with dichloromethane to give the light
yellow powder (219 mg, 0.215 mmol, 74%). 1H NMR (500 MHz,
acetone-d6): d 9.16 (1H, d, J = 8 Hz, aromatic), 7.59 (1H, d, J =
9 Hz, aromatic), 7.01 (1H, t, J = 9 Hz, aromatic), 6.45 (1H, t,
1.0 equiv.) was added to the solution and the reaction mixture
was stirred for 2 h at −30 ◦C. After removal of the volatiles in
vacuo at −30 ◦C, the flask was warmed to room temperature, and
the brown solid turned purple. NMR analyses of the purple solid
3550 | Dalton Trans., 2008, 3546–3552
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J = 7 Hz, aromatic), 2.66 (1H, m, PCHHP), 1.96 (3H, d, J =
10 Hz, PMe), 1.95 (15H, s, Cp*), 1.90 (3H, d, J = 10 Hz, PMe),
1.85 (15H, s, Cp*), 1.81 (3H, d, J = 11 Hz, PMe), 1.76 (1H, m,
PCHHP), 1.32 (3H, d, J = 10 Hz, PMe), −14.92 (1H, d, J =
4.10 (1H, m, PCHHP), 2.47 (1H, m, PCHHP), 2.31 (2H, m,
=CHCH2CH2), 2.18 (2H, m, IrCCH2CH2), 1.97 (15H, d, J =
3 Hz, Cp*), 1.81 (15H, s, Cp*), 1.68 (3H, d, J = 10 Hz, PMe), 1.65
(3H, d, J = 10 Hz, PMe and overlapped CH2CH2CH2), 1.62 (3H,
d, J = 10 Hz, PMe), 1.47 (3H, d, J = 11 Hz, PMe), −17.20 (1H,
1
22 Hz, Ir–H), −14.99 (1H, s, Ir–H). 13C{ H} NMR (126 MHz,
1
acetone-d6): d 179.5 (d, J = 17 Hz, Ir–C), 163.7 (s, aromatic),
144.1 (s, aromatic), 132.5 (s, aromatic), 122.4 (q, J = 321 Hz,
CF3), 118.4 (s, aromatic), 96.6 (d, J = 3 Hz, C5Me5), 93.7 (d, J =
3 Hz, C5Me5), 29.9 (dd, J = 25 Hz, 31 Hz, PCH2P), 26.7 (dd, J =
48 Hz, 7 Hz, PMe), 19.3 (d, J = 38 Hz, PMe), 17.0 (d, J = 39 Hz,
6 Hz, PMe), 10.9 (d, J = 34 Hz, PMe), 10.41 (s, C5Me5), 9.96 (s,
dd, J = 34 Hz, 5 Hz, IrH), −25.80 (1H, m, Ir–H–Ir). 13C{ H}
NMR (126 MHz, CD2Cl2): d 131.4 (d, J = 4 Hz, IrC=CH–CH2),
130.2 (d, J = 14 Hz, Ir–C=CH–CH2), 121.3 (q, J = 320 Hz, CF3),
96.3 (d, J = 3 Hz, C5Me5), 95.3 (d, J = 2 Hz, C5Me5), 52.3 (s,
IrC–CH2–CH2), 52.1 (dd, J = 31 Hz, 36 Hz, PCH2P), 35.4 (s,
CH–CH2–CH2), 26.3 (s, CH2–CH2–CH2), 24.3 (dd, J = 44 Hz,
6 Hz, PMe), 18.3 (dd, J = 34 Hz, 2 Hz, PMe), 16.2 (dd, J = 45 Hz,
3 Hz, PMe), 13.1 (dd, J = 37 Hz, 7 Hz, PMe), 11.2 (s, C5Me5),
1
C5Me5). 31P{ H} NMR (109 MHz, CD2Cl2): d −22.6 (d, J = 7
Hz), −25.8 (d, J = 7 Hz). M.p. 163 ◦C (decomp.). Anal. Calcd for
C31H50F3Ir2NO3P2S: C, 36.50; H, 4.94; N, 1.37. Found: C, 36.30;
H, 4.72; N, 1.31.
1
10.6 (s, C5Me5). 31P{ H} NMR (202 MHz, CD2Cl2): d −27.8 (d,
J = 37 Hz), −38.6 (d, J = 37 Hz).
C–H activation reaction of cyclopentene to give 13
X-Ray structure analyses of 3, 8, and 12
To the pre-formed 7 (0.209 mmol), cyclopentene (4 mL) and
dichloromethane (2 mL) were added and the mixture was stirred
for 18 h at 0 ◦C. After removal of the solvent in vacuo, the
residue was washed with toluene and hexane to give 13 as an
orange powder (119 mg, 0.118 mmol, 56%) with a small amount
of contaminants probably because of the thermal decomposition
of 13. 1H NMR (500 MHz, CD2Cl2): d 5.12 (1H, s, CH2CH=CIr),
Crystal data and structure refinement parameters for 3, 8 and
12 are summarized in Table 1. Diffraction data were obtained
using a Rigaku AFC-5S. The reflection intensities were monitored
by three standard reflections every 150 measurements. An empir-
ical absorption correction based on azimuthal scans of several
reflections was applied. The data were corrected for Lorentz
and polarization effects. The structure was solved by heavy-atom
Table 1 Crystal data and structure refinement parameters for 3, 8 and 12
3
8
12
Description of crystal
Color, habit
Orange, block
0.60 × 0.50 × 0.30
Monoclinic
P21/c (#14)
8.505(6)
16.341(7)
20.088(4)
90
96.95(3)
90
2771.2(23)
4
Orange, block
0.60 × 0.30 × 0.30
Triclinic
Orange, block
0.40 × 0.35 × 0.35
Monoclinic
P21/a (#14)
17.7878(14)
12.3618(17)
18.402(2)
90
117.595(7)
90
3586.1(7)
4
Max dimensions/mm
Crystal system
Space group
¯
P1 (#2)
˚
a/A
9.771(3)
10.880(3)
15.431(3)
80.24(2)
83.09(2)
86.91(3)
1604.0(8)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
V/A
Z
3
˚
Formula
C25H46P2Ir2
793.03
1.901
C26H45O3F3P2SIr2
941.08
1.948
C31H50NO3F3P2SIr2
1020.18
1.889
Mw
D
calc/g cm−3
Data collection
˚
˚
˚
˚
Radiation k/A
MoKa (k = 0.71069A)
MoKa (k = 0.71069A)
MoKa (k = 0.71069A)
T/K
203
296
293
Scan technique
x-2h
(1.26 + 0.30 tanh)
55.0
x-2h
(1.31 + 0.30 tanh)
55.0
x-2h
(1.15 + 0.30 tanh)
55.0
Scan width/◦
◦
2hmax
/
Reflections collected
Structure determination
Observed reflections (I > 3.00r(I))
No. of variables
6744
7637
8475
5326
306
17.41
0.023–0.054
0.0638
0.0447
0.0738b
0.1518
1.004
5063
377
13.43
0.063–0.078
0.0197
0.0375
0.0498c
0.1111
1.020
5785
436
13.27
0.042–0.069
0.0230
0.0426
0.0598d
0.1352
1.007
Reflection/parameter ratio
Transmission factor
Rint
R (I > 3.00r(I))a
Rw (I > 3.00r(I))a
wR2 (all data)e
Goodness of fit indicator
2
1/2
2
2
a R = RꢁFo| − |Fcꢁ/R|Fo|, Rw = [Rw(|Fo| − |Fc|)2/RwFo
]
.
b w = 1/[0.0048Fo + 1.0000r(Fo2)]. c w = 1/[0.0016Fo + 1.0000r(Fo2)]. d w =
1/[0.0025Fo + 1.0000r(Fo2)]. e wR2 = {R[w(Fo − Fc2)2]/R[w(Fo2)2]}
.
2
2
1/2
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Patterson methods22 and expanded using Fourier techniques.23
The non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were refined using the riding model. Atomic scattering
factors, anomalous dispersion terms and the values for the mass
attenuation coefficients were taken from the literature.24 The
hydrogen atoms were located on idealized positions except for
metal hydrides. Metal hydrides in 3, 8, and 12 were not located.
All calculations were performed using the CrystalStructure25,26
crystallographic software package.
F. J. Lahoz and L. A. Oro, Angew. Chem., Int. Ed., 2002, 41,
1208.
9 Oxidative addition of dihydrogen to a characterized IrII–IrII (or IrI–
IrIII) complex has been reported: (a) D. M. Heinekey, D. A. Fine and D.
Barnhart, Organometallics, 1997, 16, 2530; (b) M. V. Jime´nez, E. Sola,
J. A. Lo´pez, F. J. Lahoz and L. A. Oro, Chem.–Eur. J., 1998, 4, 1398.
10 Intermolecular C–H activation via abstraction of a hydride by a Lewis
acid such as AlMe3 or B(C6F5)3 has been reported: L.-C. Liang, P.-S.
Chien and Y.-L. Huang, J. Am. Chem. Soc., 2006, 128, 15562.
11 (a) Z. Hou, A. Fujita, T. Koizumi, H. Yamazaki and Y. Wakatsuki,
Organometallics, 1999, 18, 1979; (b) Z. Hou, T. Koizumi, A. Fujita, H.
Yamazaki and Y. Wakatsuki, J. Am. Chem. Soc., 2001, 123, 5812.
12 We have also attempted the reaction of 3 with HOTf to generate the ac-
tive species. However, the reaction brought about simple protonation to
give [(Cp*Ir)(H)(l-dmpm)(l-H)(IrCp*)(H)][OTf] as a stable product.
13 19F NMR spectra of 7 and 8 were also measured: a single resonance
was observed at d −78.4 for 7 and d −78.3 for 8, respectively. It has
been reported that 19F resonances due to the uncoordinated triflate are
usually found around d −78 to −79 in CD2Cl2, while the coordinated
one is observed downfield by 1–2 ppm. Since the triflate ion in 8 was
evidently uncoordinated, it is highly probable that the triflate ion in 7
would also be uncoordinated: (a) T. Hayashida, H. Kondo, J. Terasawa,
K. Kirchner, Y. Sunada and H. Nagashima, J. Organomet. Chem., 2007,
692, 382; (b) A. C. Ontko, J. F. Houlis, R. C. Schnabel and D. M.
Roddick, Organometallics, 1998, 17, 5467, see also ref. 8b.
Acknowledgements
This work was partially supported by a Grant-in-Aid for Young
Scientists (B) #14750666 and #17750052 from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
Notes and references
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14 We have also conducted the reaction of 7 with CO, which gave
a
carbonyl-bridged IrII–IrII complex, [(Cp*Ir)(l-CO)(l-dmpm)(l-
H)(IrCp*)]+, in 95% yield. The same complex was also obtained by the
reaction of the dicationic complex 1 with CO in the presence of strong
base (NaOtBu). The spectroscopic data and X-ray structure analysis of
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15 Intramolecular activation of sp3 C–H bond in dmpm starting with the
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3552 | Dalton Trans., 2008, 3546–3552
This journal is
The Royal Society of Chemistry 2008
©