Reversible C-H bond activation of a bifunctional phosphine bridging ligand across two unbonded metal centers

Article abstract of DOI:10.1021/om0001671

Reaction of [{Ir(μ-Cl)(cod)}₂] with the short-bite bifunctional N,P-donor ligand (1-benzyl-2-imidazolyl) diphenylphosphine (Ph₂PBzIm) gives the yellow complex [IrCl (Ph₂PBzIm)(cod)] (2). A further addition of [{Ir (μ-Cl)(cod)}₂] to 2 results in the reversible metalation of a phenyl ring across two unbonded iridium centers to give orange crystals of [IrCl(cod){μ-PPh(C₆H₄)-BzIm}IrHCl (cod)] (1). Complex 1 is in equilibrium with the mononuclear complex [IrCl(Ph₂-PBzIm)(cod)] and the active species undergoing the sp²-C-H activation, [{IrCl(cod)}₂ (μ-Ph₂PBZIm)], in solution. Abstraction of one chloride ligand from 1 with AgBF₄ produces the deinsertion of the C-H bond yielding the cationic complex [{Ir(cod)}₂(μ-Ph₂ PBzIm)(μ-Cl)]-BF₄, which regenerates 1 upon addition of a chloride-soluble salt. The cationic complex [{Ir- (cod)}₂(μ-Ph₂PBzIm)(μ-Cl)]BF₄ is inactive for the above-mentioned sp²-C-H bond activation and can be prepared alternatively from the reaction of 2 with [Ir(cod) (CH₃CN)₂]BF₄. A related binuclear sp²-C-H bond activation across two unbonded metals also occurs in the reaction of dppm with [{Ir(μ-Cl)(cod)}₂] in a 1:1 molar ratio. This reaction leads to a mixture in equilibrium of [{IrCl(cod)}₂(μ-dppm)] and the hydride complex [IrCl(cod){μ-PPh(C₆H₄)CH₂-PPh₂)}IrHCl (cod)] in a 1.5:1 molar ratio, respectively, in dichloromethane at 20°C. The structure of the mixed-valence complex 1 was solved by X-ray diffraction studies.

Full text of DOI:10.1021/om0001671

Organometallics 2000, 19, 3115-3119
3115
Rever sible C-H Bon d Activa tion of a Bifu n ction a l
P h osp h in e Br id gin g Liga n d a cr oss Tw o Un bon d ed Meta l
Cen ter s
Cristina Tejel,† Rita Bravi,† Miguel A. Ciriano,*,† Luis A. Oro,*,†
Marta Bordonaba,‡ Claudia Graiff,‡ Antonio Tiripicchio,‡ and Alfredo Burini§
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain, Dipartimento di Chimica Generale
ed Inorganica, Chimica Analitica, Chimica Fisica, Centro di Studio per la Strutturistica
Diffrattometrica del CNR, Universita` di Parma, Parco Area delle Scienze 17A,
I-43100 Parma, Italy, and Dipartimento di Scienze Chimiche, Universita` degli Studi
di Camerino, I-62032 Camerino, Italy
Received February 23, 2000
Reaction of [{Ir(µ-Cl)(cod)}2] with the short-bite bifunctional N,P-donor ligand (1-benzyl-
2-imidazolyl)diphenylphosphine (Ph2PBzIm) gives the yellow complex [IrCl(Ph2PBzIm)(cod)]
(2). A further addition of [{Ir(µ-Cl)(cod)}2] to 2 results in the reversible metalation of a phenyl
ring across two unbonded iridium centers to give orange crystals of [IrCl(cod){µ-PPh(C6H4)-
BzIm}IrHCl(cod)] (1). Complex 1 is in equilibrium with the mononuclear complex [IrCl(Ph2-
PBzIm)(cod)] and the active species undergoing the sp2-C-H activation, [{IrCl(cod)}2(µ-
Ph2PBzIm)], in solution. Abstraction of one chloride ligand from 1 with AgBF4 produces the
deinsertion of the C-H bond yielding the cationic complex [{Ir(cod)}2(µ-Ph2PBzIm)(µ-Cl)]-
BF4, which regenerates 1 upon addition of a chloride-soluble salt. The cationic complex [{Ir-
(cod)}2(µ-Ph2PBzIm)(µ-Cl)]BF4 is inactive for the above-mentioned sp2-C-H bond activation
and can be prepared alternatively from the reaction of 2 with [Ir(cod)(CH3CN)2]BF4. A related
binuclear sp2-C-H bond activation across two unbonded metals also occurs in the reaction
of dppm with [{Ir(µ-Cl)(cod)}2] in a 1:1 molar ratio. This reaction leads to a mixture in
equilibrium of [{IrCl(cod)}2(µ-dppm)] and the hydride complex [IrCl(cod){µ-PPh(C6H4)CH2-
PPh2)}IrHCl(cod)] in a 1.5:1 molar ratio, respectively, in dichloromethane at 20 °C. The
structure of the mixed-valence complex 1 was solved by X-ray diffraction studies.
In tr od u ction
centers, and we give evidence for both the assistance of
the second metal center to enter in the binuclear sp2-
C-H activation and the active species undergoing this
reaction.
Short-bite bifunctional N,P ligands such as 2-(diphen-
ylphosphino)pyridine (Ph2PPy) have been the focus of
much interest in building dinuclear complexes holding
the metal atoms in close proximity, and a rich chemistry
for them has been developed.1 However, to the best of
our knowledge, C-H bond activation of these ligands
is very rare, despite the ability of phenyl and pyridyl
groups to undergo ortho-metalation reactions.2 Some
examples of P-C bond activation in reactions with
ruthenium clusters3 and ortho metalation of a phenyl
ring of Ph2PPy across a multiple Re-Re bond have been
previously reported.4
Resu lts a n d Discu ssion
Reaction of [{Ir(µ-Cl)(cod)}2] with 1 molar equiv of
1-benzyl-2-imidazolyldiphenylphosphine (Ph2PBzIm) in
dichloromethane gives orange crystals analyzed as
[{IrCl(cod)}2(µ-Ph2PBzIm)] after layering the reaction
mixture with hexanes overnight. Interestingly, this
reaction involves a C-H bond activation process under
smooth conditions, indicated by the detection of a
We report here on reversible C-H bond activation
reactions of a hybrid P,N (phosphine-imidazolyl) ligand
and of dppm in dinuclear complexes leading to the ortho
metalation of a phenyl ring across two unbonded iridium
hydride ligand as a doublet at δ -12.90 ppm (J H-P
)
1
9.3 Hz) in the H NMR spectrum of these crystals. As
this spectrum is too complicated to establish unambigu-
ously the source of the hydride ligand (Figure 1), the
complete characterization of the orange crystals as [IrCl-
(cod){µ-PPh(C6H4)BzIm}IrHCl(cod)] (1) was fully elu-
cidated by a X-ray diffraction study.
† Universidad de Zaragoza-CSIC.
‡ Universita` di Parma.
§ Universita` degli Studi di Camerino.
(1) Zhang, Z.-Z.; Cheng, H. Coord. Chem. Rev. 1996, 147, 1.
(2) For a review see: Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997,
97, 2879 and references therein.
(3) (a) Deeming, A. J .; Smith, M. B. J . Chem. Soc., Dalton Trans.
1993, 2041. (b) Lugan, N.; Lavigne, G.; Bonnet, J . J . Inorg. Chem. 1987,
26, 585.
The molecular structure of the Ir(I)-Ir(III) complex
[IrCl(cod)[{µ-PPh(C6H4)BzIm}IrHCl(cod)] (1) is shown
in Figure 2 together with the atomic numbering system.
Selected bond distances and angles are given in Table
1. The two iridium atoms, separated by 4.475(3) Å, are
bridged by the PPh(C6H4)BzIm ligand (through the N(1)
(4) Barder, T. J .; Tetrick, S. M.; Walton, R. A.; Cotton, F. A.; Powell,
G. L. J . Am. Chem. Soc. 1983, 105, 4090.
10.1021/om0001671 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 07/08/2000

3116 Organometallics, Vol. 19, No. 16, 2000
Tejel et al.
F igu r e 1. 1H NMR spectrum of crystals of 1 in CDCl3 showing the resonances of 1, [{Ir(µ-Cl)(cod)}2] (b), [IrCl(Ph2PBzIm)-
(cod)], and [{IrCl(cod)}2(µ-Ph2PBzIm)] (O). The asterisk (*) denotes the CH2Cl2 of crystallization.
than the typical for a hydride cis to a phosphine in
iridium complexes. However, X-ray data indicate that
this bridge, if it exists, is very unsymmetrical (Ir(2)‚‚‚
H(1) ) 2.59(7) Å). Therefore, the large coupling constant
could arise from a large scalar coupling through four
bonds due to the close proximity between these atoms
in the molecule.
Solutions of 1 in CDCl3 invariably show three P-
containing species in a concentration-dependent equi-
librium (with signals in the 31P{1H} NMR spectrum at
δ 25.2, 10.8, and 7.0 ppm in a 75:10:15 molar ratio for
a concentrated solution) and [{Ir(µ-Cl)(cod)2]. The spec-
troscopic data for the main species including H,H-COSY
and H,H-NOESY experiments are consistent with the
hydrido complex 1. A second species identified in the
equilibrium is the yellow mononuclear complex [IrCl-
(Ph2PBzIm)(cod)] (2) with the P atom bonded to the
metal, which is easily prepared by reaction of [{Ir(µ-
F igu r e 2. View of the structure of compound 1 together
Cl)(cod)}2] with 2 molar equiv of (1-benzyl-2-imidazolyl)-
with the atomic numbering system.
diphenylphosphine (Ph2PBzIm) in dichloromethane.
Finally, the broad singlet in the 31P{1H} NMR spectrum
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 1a
at δ 10.8 is attributed to [{IrCl(cod)}2(µ-Ph2PBzIm)] (A),
which could not be isolated. These species are related
by the equilibria
Ir(1)-Cl(1)
Ir(1)-N(1)
Ir(1)-M(1)
Ir(2)-P(1)
Ir(2)-M(3)
N(1)-C(1)
N(2)-C(1)
N(2)-C(4)
2.489(3)
2.067(6)
2.077(9)
2.292(2)
2.010(9)
1.329(10)
1.353(10)
1.487(11)
Ir(1)-H(1)
Ir(1)-C(18)
Ir(1)-M(2)
Ir(2)-CI(2)
Ir(2)-M(4)
N(1)-C(2)
N(2)-C(3)
1.60(6)
2.034(8)
2.195(9)
2.356(2)
2.095(9)
1.360(10)
1.358(11)
1/2[{Ir(µ-Cl)(cod)}2] + [IrCl(Ph2PBzIm)(cod)] h
[{IrCl(cod)}2(4-Ph2PBzIm)] h 1
To identify the active species undergoing the C-H
bond activation, the reaction was performed stepwise
by the successive additions of the “Ir(cod)” moiety and
chloride to 2. Thus, reaction of 2 with [Ir(cod)(CH3CN)2]-
BF4 in dichloromethane gives the purple complex [{Ir-
(cod)2(µ-Ph2PBzIm)(µ-Cl)]BF4 (3) (Scheme 1). The cat-
ionic compound 3, in which the P,N ligand is coordinated
to both iridium atoms, remains unaltered in solution
for days. A further addition of the chloride-soluble salt
PPNCl to 3 gives the mixture containing mainly the
hydrido complex 1 in a few minutes (Scheme 1). Both
steps are accomplished by the direct reaction of the
mononuclear 2 with [{Ir(µ-Cl)(cod)2] in a 1:0.5 molar
ratio (Scheme 1). These experiments evidence that the
active species which undergoes the sp2-C-H activation
reaction is the neutral complex [{IrCl(cod)}2(µ-Ph2-
PBzIm)] (A; Scheme 2), while the related cationic
complex 3 is inactive under identical conditions.
C(18)-Ir(1)-N(1)
N(1)-Ir(1)-Cl(1)
C(1)-P(1)-Ir(2)
N(1)-C(1)-P(1)
N(I)-C(1)-N(2)
86.5(3)
C(18)-Ir(1)-Cl(1)
89.3(3)
89.71(9)
123.8(5)
130.4(6)
85.71(19) P(1)-Ir(2)-Cl(2)
115.7(3)
119.6(6)
109.8(7)
C(1)-N(1)-Ir(1)
N(2)-C(1)-P(1)
a
M(1), M(2), M(3), and M(4) are the midpoints of the double
bonds C(23)-C(24), C(27)-C(28), C(31)-C(32), and C(35)-C(36),
respectively.
and P(1) atoms), which also interacts with Ir(1) through
the C(18) atom from the ortho-metalated phenyl. The
hydrogen atom H(1) coming from the C-H activation
is terminally bound to the Ir(1) atom (Ir(1)-H(1) )
1.60(6) Å). If the midpoints of the double bonds of the
cod ligands are considered as coordination sites, the Ir(1)
and Ir(2) atoms exhibit octahedral and square-planar
coordinations, respectively, as expected for Ir(III) and
Ir(I) atoms.
The hydride ligand located in the solid state on the
iridium atom coordinated at the N-donor end could be
thought to bridge the two iridium atoms, since the
coupling with the phosphorus nucleus is slightly smaller
The key to this distinctive reactivity of A versus 3
probably relies on the ability of one phenyl ring on the
Ph2P-Ir(1) moiety to interact with the metal in the

C-H Bond Activation of a Phosphine Ligand
Organometallics, Vol. 19, No. 16, 2000 3117
Sch em e 1
The Ph2PBzIm ligand is not particularly needed to
reverse the reaction, since either of the two donor
entities of the P,N hybrid ligand is enough to fulfill this
process. Thus, complex 1 reacts with PPh3 to render an
equimolecular mixture of 2 and [IrCl(PPh3)(cod)] and
with N-benzylimidazole to give 2 and [IrCl(N-benzylimi-
dazole)(cod)].6
As this unusual assisted reaction and mechanism
should not be restricted to this N,P ligand, we undertook
the study of a similar reaction with the much used
diphenylphosphine ligand (dppm).7 Some examples of
P-C and C-H bond activations of metal-metal bonds
in the reactions of dppm with ruthenium and osmium
clusters have been described,8,9 and cyclometalation of
a phenyl ring of dppm taking place at the same metal
to which the phosphorus is bound has been observed in
a heterodinuclear complex.10 Supporting this idea, a
binuclear sp2-C-H bond activation across the two
metals also occurs in the reaction of dppm with [{Ir(R-
Cl)(cod)2] in a 1:1 molar ratio in dichloromethane. After
workup, an orange microcrystalline solid analyzed as
[{IrCl(cod)}2(µ-dppm)] is isolated. Solutions of this solid
in CD2Cl2 or d6-benzene at 20 °C and those prepared
from [IrCl(cod)(dppm)] and [{Ir(µ-Cl)(cod)}2] in a 1:0.5
molar ratio in CD2Cl2 contain an equilibrium mixture
of [{IrCl(cod)}2(µ-dppm)] and the hydride complex [IrCl-
(cod){µ-PPh(C6H4)CH2PPh2)}IrHCl(cod)] (4) in a 1.5:1
molar ratio, respectively.
Sch em e 2
The characterization of 4 relies on spectroscopic data,
and the compound seems to be similar to complex 1
(Figure 3a). In particular, the resonance for the hydride
ligand appears as a multiplet at δ -15.39 ppm in the
1H NMR spectrum, due to the coupling with the two
phosphorus nuclei, one in a cis position and the other
on the neighboring iridium atom. The close proximity
of the hydride ligand with two olefinic protons of cod in
cis positions is clearly indicated by the cross-peaks in
the H,H-NOESY spectrum (Figure 3b), and therefore,
cod and hydride occupy fac positions in the octahedral
environment.
In separate experiments, the mononuclear [IrCl-
(dppm)(cod)] (5) and the cationic [Ir2(µ-Cl)(µ-dppm)-
(cod)2]BF4 (6) complexes were isolated and characterized
to discard their presence in the above-mentioned equi-
librium. As for the hybrid P,N ligand, the cationic
complex [Ir2(µ-Cl)(µ-dppm)(cod)2]BF4 (5) is inactive for
the phenyl C-H activation, remaining unaltered for
other half of the complex, Ir(2)-N(BzIm). The close
proximity of Ir and phenyl groups is allowed in complex
A by a free rotation of half of the binuclear complex
around the P-C(BzIm) bond (Scheme 2), while it is
prevented in 3 by the bridging chloride ligand.
Molecular models show that this rotation in A allows
the approach of the ortho CH of a phenyl group to the
second iridium center, which is necessary to start the
CH activation process. A frozen structure of such an
intermediate with a bridging dppm between two plati-
num atoms in (NBu4)[(C6F5)3Pt{µ-Ph2PCH2PPh(η2-Ph)}-
Pt(C6F5)2] has just been described.5 Moreover, the
stereochemistry of 1, in which the ortho carbon and
hydride are cis, is consistent with a concerted oxidative
addition of the C-H bond. The reaction leading to 1
represents a rare example of ortho metalation across
two metal centers due to the assistance between the two
metals, since the first iridium center coordinates the
Ph2P fragment while the second one undergoes the sp2-
C-H bond activation reaction giving 1. No insertion of
the hydride ligand into one of the olefinic bonds is
observed, despite the right stereochemistry for this
reaction in the molecular structure of 1.
(6) Bonati, F.; Oro, L. A.; Pinillos, M. T.; Tejel, C.; Apreda, M. C.;
Foces-Foces, C.; Cano, F. H. J . Organomet. Chem. 1989, 369, 253.
(7) (a) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99. (b) Chaudret,
B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191. (c)
Adams, R. D. In The Chemistry of Metal Cluster Compounds; Shriver,
D. F., Kaesz, H. D., Adams, R. D., Eds.; VCH: Weinheim, Germany,
1990; Chapter 3.
A further remarkable feature of the transformation
of 3 into 1 by addition of chloride is that it is fully
reversible. The abstraction of one chloride ligand from
1 by addition of AgBF4 regenerates 3 quantitatively.
This reversibility involves the corresponding formation
and rupture of the C-H bond. Moreover, the formation
of the C-H bond from the hydride and the ortho-
metalated carbon is also achieved by addition of Ph2-
PBzIm to 1, which regenerates 2 in quantitative yield.
(8) (a) Lavigne, G.; de Bonneval, B. In Catalysis by Di- and
Polynuclear Metal Cluster Compounds; Adams, R. D., Cotton, F. A.,
Eds.; Wiley-VCH: New York, 1998, Chapter 2, p 39. (b) Sappa, E. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Elsevier: Oxford, U.K., 1995; Vol. 7, Chapter
14.
(9) (a) Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J . Can. J . Chem.
1995, 73, 3, 903. (b) Bruce, M. I.; Hinchliffe, J . R.; Surynt, R.; Skelton,
B. W.; White, A. H. J . Organomet. Chem. 1994, 469, 89. (c) Harding,
M. M.; Kariuki, B.; Mathews, A. J .; Smith, A. K.; Braunstein, P. J .
Chem. Soc., Dalton Trans. 1994, 33. (d) Bruce, M. I.; Humphrey, P.
A.; Miyamae, H.; Skelton, B. W.; White, A. H. J . Organomet. Chem.
1992, 429, 187.
(5) Casas, J . M.; Fornie´s, J .; Martinez, F.; Rueda, A. J .; Tomis, M.;
Welch, A. J . Inorg. Chem. 1999, 38, 1529.
(10) Hilts, R. W.; Franchuk, R. A.; Cowie, M. Organometallics 1991,
10, 1297.

3118 Organometallics, Vol. 19, No. 16, 2000
Tejel et al.
solvent and 85% phosphoric acid as references, respectively.
The phase-sensitive H,H-NOESY experiments were carried out
on the Bruker spectrometer using the pulse program NOE-
SYST with 512 FID’s and a mixing time of 1000 ms. Conduc-
tivities were measured in (4-5) × 10-4 M acetone solutions
using a Philips PW 9501/01 conductimeter.
[Ir Cl(cod){µ-P P h (C6H4)BzIm }Ir HCl(cod)] (1). Solid [IrCI-
(Ph2PBzIm)(cod)] (2; 135.6 mg, 0.20 mmol) was added to a
solution of [{Ir(µ-Cl)(cod)}2] (67.1 mg, 0.10 mmol) in dichloro-
methane (10 mL) to give a red solution. This solution was
concentrated to ca. 2 mL and layered with hexanes. During
the diffusion, the initial red solution became orange and orange
monocrystals, suitable for X-ray diffraction studies, were
deposited. The crystals were washed with hexane and vacuum-
dried. Yield: 182.4 mg (90%). Anal. Calcd for C38H43N2Cl2PIr2:
C, 45.01; H, 4.27; N, 2.76. Found: C, 45.91; H, 3.88; N, 2.57.
31P{1H} NMR (room temperature, CDCl3): δ 25.2 (74%,
corresponding to 1); 10.8 (12%, attributed to [{IrCl(cod)2(4-
Ph2PBzIm)] (A), and 7.0 (14%, corresponding to 2). Molecular
weight in CHCl3: calcd 1014, found 1005.
[Ir Cl(P h 2P BzIm )(cod )] (2). Solid [{Ir(µ-Cl)(cod)}2] (134.2
mg, 0.20 mmol) was added to a solution of Ph2PBzIm (137.2
mg, 0.40 mmol) in dichloromethane (10 mL). After it was
stirred for 1 h, the orange solution was concentrated to ca. 1
mL and layered with hexanes (20 mL) to give orange micro-
crystals overnight. The solution was decanted, and the crystals
were washed with hexane and vacuum-dried. Yield: 250 mg
(92%). Anal. Calcd for C30H31N2ClPIr2: C, 53.13; H, 4.61; N,
4.13. Found: C, 52.84; H, 4.30; N, 3.96. 31P{1H} NMR (room
temperature, CDCl3): δ 7.0. 1H NMR (room temperature,
CDCl3): δ 7.673 (m, 4H, HoPh2PBzIm); 7.358 (br, 12H, Ph2-
PCH2PhIm); 6.938 (s, 1H, Ph2PCH2PhIm); 6.214 (s, 2H,
Ph2PCH2PhIm); 5.191 (br, 2H) and 2.790 (br, 2H) (HCd cod),
2.094 (br, 4H) and 1.578 (br, 4H) (CH2 cod).
F igu r e 3. (a) Proposed structure for 4. (b) Section of of
the H,H-NOESY spectrum of 4 in CD2Cl2 at 27 °C, showing
the positive cross-peaks due to proximity between the
hydride and one diasterotopic proton (CH2) of dppm, two
olefinic protons of the cod in cis positions, and two olefinic
protons of the other cod ligand.
days in solution, but addition of a soluble chloride drives
the reaction to the equilibrium mixture.
[{Ir (cod )}2(µ-P h 2P BzIm )(µ-Cl)]BF 4 (3). Solid [IrCI(Ph2-
PBzIm)(cod)] (2; 67.8 mg, 0.10 mmol) was added to a solution
of [Ir(cod)(CH3CN)2]BF4 (46.9 mg, 0.10 mmol) in dichloro-
methane (10 mL). The color of the solution changed inmedi-
ately from yellow to dark red. After evaporation of the
dichloromethane to ca. 1 mL the solution was carefully layered
with diethyl ether (15 mL) to render dark red microcrystals
overnight. The solution was decanted and the solid washed
with diethyl ether and vacuum-dried. Yield: 89.0 mg (91%).
Anal. Calcd for C38H43N2ClPIr2BF4: C, 42.84; H, 4.07; N, 2.63.
Found: C, 42.73; H, 4.27; N, 1.78. 31P{1H} NMR (223 K, d6-
acetone): δ 11.1. 1H{31P} NMR (223 K, HDA): δ 8.020 (d, 1.50
Hz, 1H) and 7.585 (d, 1.50 Hz, 1H) (Ph2PBzIm); 7.859 (d, 7.23
In conclusion, intramolecular reversible sp2-C-H
activation reactions of frequently used short-bite bi-
nucleating ligands across two unbonded metals can take
place under smooth conditions in binuclear iridium
complexes, and they involve the assistance of the second
metal center. The key to these activations seems to be
also related to the presence of a single bridging ligand
that provides the flexibility needed for the initial
approach of a phenyl group to the second metal center.
Hz, 2H, Ho), 7.790 (d, 7.07 Hz, 2H, Ho′), 7.723 (m, 3H, Hm′+p′
)
Exp er im en ta l Section
and 7.587 (m, 3H, Hm+p) (Ph2PBzIm); 7.171 (t, 7.29 Hz, 1H,
Hp), 7.062 (t, 7.29 Hz, 2H, Hm), and 6.284 (d, 7.29 Hz, 2H, Ho)
(Ph2PBzIm); 4.976 (d, 15.28 Hz, 1H) and 4.715 (d, 15.28 Hz,
1H) (Ph2PCH2PhIm); 5.402 (m, 1H), 4.964 (m, 1H), 4.387 (m,
1H), 4.365 (m, 1H), 4.071 (m, 2H), 3.857 (m, 1H), and 3.142
(m, 1H) (HCd cod); 2.635 (m, 3H), 2.198 (m, 9H), 1.644 (m,
1H), and 1.429 (m, 3H) (CH2 cod). ΛM (4.9 × 10-4 M in acetone)
Gen er a l Con sid er a tion s. All the reactions were carried
out under argon using standard Schlenk techniques. Those
with silver salts were protected from light with black photo-
graphic paper. The complex [{Ir(µ-Cl)(cod)}2]11 and (1-benzyl-
2-imidazolyl)diphenylphosphine12 were prepared according to
literature methods. Solvents were dried and distilled under
argon before use by standard methods. Carbon, hydrogen, and
nitrogen analyses were performed in a Perkin-Elmer 2400
microanalyzer. IR spectra were recorded with a Nicolet 550
spectrophotometer. Mass spectra were recorded in a VG
Autospec double-focusing mass spectrometer operating in the
FAB+ mode. Ions were produced with the standard Cs+ gun
at ca. 30 kV; 3-nitrobenzyl alcohol (NBA) was used as matrix.
Molecular weights were determined with a Knauer osmometer
using chloroform solutions. 1H and 31P{1H} NMR spectra were
recorded on Bruker ARX 300 and Varian UNITY 300 spec-
) 102 S cm2 mol-1
.
[Ir Cl(cod ){µ-P P h (C6H4)CH2P P h 2)}Ir HCl(cod )] (4) was
prepared as for 1, starting from [IrCl(dppm)(cod)] (5; 72.0 mg,
0.10 mmol) and [{Ir(µ-Cl)(cod)}2] (33.6 mg, 0.050 mmol) in
dichloromethane to yield an orange solid after layering with
hexanes. A second crop was obtained from the mother liquor
after concentration. Overall yield: 90 mg (82%). Anal. Calcd
for C41H46Cl2P2Ir2: C, 46.63; H, 4.39. Found: C, 46.69; H, 4.63.
31P{1H} NMR (room temperature, CD2Cl2): δ 20.7 (d, J P-P
)
12 Hz), -17.1 (d, J P-P ) 12 Hz) (40%, 4), 13.6 (br s, 60%,
attributed to [{IrCl(cod)}2(µ-dppm)]).
[Ir Cl(d p p m )(cod )] (5). Addition of solid [{Ir(µ-Cl)(cod)}2]
(150 mg, 0.22 mmol) to a solution of dppm (171.6 mg, 0.44
mmol) in dichloromethane (10 mL) gives a yellow solution in
a few minutes. Evaporation of this solution under vacuum to
ca. 1 mL followed by layering with hexanes (10 mL) yields a
1
trometers operating at 300.13 and 299.95 MHz for H, respec-
tively. Chemical shifts are reported in parts per million and
referenced to SiMe4 using the residual signal of the deuterated
(11) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.
(12) Burini, A.; Pietroni, R. B.; Galassi, R.; Valle, G.; Calogero, S.
Inorg. Chim. Acta 1995, 229, 299.

C-H Bond Activation of a Phosphine Ligand
Organometallics, Vol. 19, No. 16, 2000 3119
Ta ble 2. Cr ysta l Da ta a n d Da ta Collection a n d
Refin em en t for Com p lex 1
microcrystalline yellow solid. The solution was decanted, and
the solid was washed with hexanes and dried under vacuum.
Yield: 279 mg (87%). Anal. Calcd for C33H34ClP2Ir: C, 55.03;
H, 4.76. Found: C, 54.42; H, 4.93. 31Pt{1H} NMR (room
chem formula
fw
C38H43Cl2Ir2N2P‚0.25CH2Cl2
1035.25
1
temperature, CD2Cl2): δ -54.9. H NMR (room temperature,
cryst size, mm
cryst syst
space group
a, Å
0.23 × 0.20 × 0.30
CD2Cl2): δ 7.46 (m, 8H), 7.36 (m, 12H) (Ph2PCH2PPh2); 4.835
(m, 2H, Ph2PCH2PPh2); 3.999 (br s, 4H, HCd cod); 2.36 (m,
4H) and 1.94 (m, 4H) (CH2 cod). Molecular weight in CHCl3:
calcd 720, found 745.
monoclinic
P21/n
26.335(5)
b, Å
13.860(4)
c, Å
9.961(3)
[Ir 2(µ-Cl)(µ-d p p m )(cod )2]BF 4 (6) was prepared as de-
scribed for 3, starting from [IrCl(dppm)(cod)] (140.0 mg, 0.20
mmol) and [Ir(cod)(CH3CN)2]BF4 (93.8 mg, 0.20 mmol), to
render orange microcrystals. Yield: 197.0 mg (89%). Anal.
Calcd for C41H46ClP2Ir2BF4: C, 44.47; H, 4.19. Found: C, 43.91;
â, deg
91.93(6)
2670.5(14)
V, Å3
Z
D
4
calcd, g cm-3
1.891
75.69
20
µ(Mo KR), cm-1
temp, °C
1
H, 3.93. 31P{1H} NMR (223 K, CD2Cl2): δ 19.4. H NMR (223
scan type
θ/2θ
K, CD2Cl2): δ 7.571 (br s, 20H, Ph2PCH2PPh2); 3.750 (t, J H-P
) 9.30 Hz, 2H, Ph2PCH2PPh2); 4.565 (br s, 4H) and 2.567 (br
s, 4H) (HCd cod); 1.763 (m, 12H) and 1.349 (m, 3H) (CH2 cod).
scan speed, deg/min
0 range, deg
no. of measd rflns
no. of unique rflns
R1a
3-10
5-30
11 162
ΛM (5.0 × 10-4 M in acetone) ) 102 S cm2 mol-1
.
10620 (I >2σ(I)) (Rint ) 0.0946)
0.0427 (0.1045, all data)
0.1102 (0.1439, all data)
0.942
Cr ysta l Str u ctu r e Deter m in a tion of Com p lex 1‚1/4CH2-
Cl2. The intensity data of 1‚1/4CH2Cl2 were collected at room
temperature (293(2) K) on a Siemens AED single-crystal
diffractometer using graphite-monochromated Mo KR radia-
tion (λ ) 0.710 73 Å) and the θ/2θ scan technique. Crystal-
lographic and experimental details are summarized in Table
2. A correction for absorption was made for the complex
(maximum and minimum values for the transmission coef-
ficient were 1.0000 and 0.716).13 The structure was solved by
Patterson and Fourier methods and refined by full-matrix
least-squares procedures (based on Fo2) with anisotropic
thermal parameters in the last cycles of refinement for all the
non-hydrogen atoms, except the atoms of the CH2Cl2 solvent,
which were found disordered in two positions around the
center of inversion. All hydrogen atoms were placed at their
geometrically calculated positions and refined riding on their
parent atoms, except for the hydride, which was localized in
the final ∆F map and refined isotropically. The weighting
scheme w ) 1/[(σ2(Fo2) + (0.0817 P)2] was used in the last cycles
wR2b
GOFc
R1(F2) ) ∑||Fo| - |Fc||/∑|Fo|. wR2(F2) ) [∑[w(Fo - Fc2)2]/
a
b
2
∑[w(Fo2)2]]1/2
.
c GOF ) {[w(Fo - Fc2)2]/(n - p)}1/2, where n is the
2
number of reflections and p is the total number of parameters
refined.
The details of the crystal structure investigation have been
deposited at the Cambridge Crystallographic Data Center as
supplementary publication no. CCDC-146826. Copies of the
data can be obtained free of charge on application to the CCDC,
12 Union Road, Cambridge CB2 1EZ, U.K. (fax, int. code +
44(1223)336-033; e-mail, deposit@ccdc.cam.ac.uk).
Ack n ow led gm en t. Generous financial support from
the DGES (Projects PB95-221-Cl and PB94-1186 and a
fellowship to M.B.) and from the Universita` di Camerino
for a fellowship (to R.B.) is gratefully acknowledged.
2
of refinement, where P ) (Fo + 2Fc2)/3. All calculations were
carried out on the DIGITAL Alpha Station 255 computers of
the “Centro di Studio per la Strutturistica Diffrattometrica”
del CNR, Parma, Italy, using the SHELX-97 systems of
crystallographic computer programs.14
Su p p or tin g In for m a tion Ava ila ble: Listings of full
experimental details of the structure determination, atomic
coordinates, thermal parameters, hydrogen coordinates, and
bond distances and angles for 1‚1/4CH2Cl2 and a section of the
H,H-NOESY spectrum of 1. This material is available free of
charge via the Internet at http://pubs.acs.org.
(13) (a) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39,
158. (b) Ugozzoli, F. Comput. Chem. 1987, 11, 1099.
(14) Sheldrick, G. M. SHELX-97 Program for the Solution and the
Refinement of Crystal Structures; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
OM0001671