Transmission of trans effects in dinuclear complexes

Article abstract of DOI:10.1021/ja016213l

The substitution of a terminal hydride ligand in the complexes [Ir₂(μ-H)(μ-Pz)₂H₃(L)PⁱPr ₃)₂] (L = NCCH₃ (1) or pyrazole (3)) by chloride provokes a significant change in the lability of the L ligand, despite the fact that the substituted hydride and the L ligand lie in opposite extremes of the diiridium(III) complexes. Detailed structural studies of complex 3 and its chloro-trihydride analogue [Ir₂(μ-H)(μ-Pz)₂H₂Cl(HPz)(P ⁱ-Pr₃)₂] (4) have shown that this behavior is a consequence of the transmission of ligand trans effects from one extreme of the molecule to the other, with the participation of the bridging hydride. Extended Hueckel calculations on model diiridium complexes have suggested that such trans effect transmissions are due to the formation of molecular orbitals of ρ symmetry extended along the backbones of the complexes. This is also an expected feature for metal - Metal bonded complexes. The feasibility of the transmission of ligand trans effects and trans influences through metal - Metal bonds and its relevance to the understanding of both the reactivity and structures of metal - Metal bonded dinuclear compounds have been substantiated through structural studies and selected reactions of the diiridium(II) complexes [Ir₂(μ-1,8-(NH)₂naphth)I(CH₃)(CO) ₂(PⁱPr₃)₂] (isomers 6 and 7) and their cationic derivatives [Ir₂(μ-1,8-(NH)₂naphth)(CH₃)(CO) ₂(PⁱPr₃)₂](CF₃SO ₃) (isomers 8 and 9).

Full text of DOI:10.1021/ja016213l

J. Am. Chem. Soc. 2001, 123, 11925-11932
11925
Transmission of Trans Effects in Dinuclear Complexes
Eduardo Sola, Francisco Torres, M. Victoria Jime´nez, Jose A. Lo´pez, Silvia E. Ruiz,
Fernando J. Lahoz, Anabel Elduque, and Luis A. Oro*
Contribution form the Departamento de Quimica Inorga´nica, Instituto de Ciencia de Materiales de
Arago´n, UniVersidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
ReceiVed May 16, 2001
Abstract: The substitution of a terminal hydride ligand in the complexes [Ir2(µ-H)(µ-Pz)2H3(L)PiPr3)2] (L )
NCCH3 (1) or pyrazole (3)) by chloride provokes a significant change in the lability of the L ligand, despite
the fact that the substituted hydride and the L ligand lie in opposite extremes of the diiridium(III) complexes.
Detailed structural studies of complex 3 and its chloro-trihydride analogue [Ir2(µ-H)(µ-Pz)2H2Cl(HPz)(Pi-
Pr3)2] (4) have shown that this behavior is a consequence of the transmission of ligand trans effects from one
extreme of the molecule to the other, with the participation of the bridging hydride. Extended Hu¨ckel calculations
on model diiridium complexes have suggested that such trans effect transmissions are due to the formation of
molecular orbitals of σ symmetry extended along the backbones of the complexes. This is also an expected
feature for metal-metal bonded complexes. The feasibility of the transmission of ligand trans effects and
trans influences through metal-metal bonds and its relevance to the understanding of both the reactivity and
structures of metal-metal bonded dinuclear compounds have been substantiated through structural studies
and selected reactions of the diiridium(II) complexes [Ir2(µ-1,8-(NH)2naphth)I(CH3)(CO)2(PiPr3)2] (isomers 6
and 7) and their cationic derivatives [Ir2(µ-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2](CF3SO3) (isomers 8 and 9).
Introduction
do not involve concerted actions of the various metal moieties
on a substrate, but the transmission of information from one
metal to another. The characterization of possible sources and
mechanisms for such information transmission constitutes a
challenge in the chemistry of polynuclear compounds, and may
also enlighten the rational design of catalysts by exploiting
cooperative reactivity.
The cooperative reactivity of the metal centers in dinuclear
and polynuclear compounds can drive unique chemistry and
catalysis.1 This cooperation can arise from the proximity of the
metal centers, which may favor the formation of metal-metal
bonds or interactions and the existence of multimetallic coor-
dination and reaction sites. Such features can bring advantageous
mechanistic alternatives for substrate activation and subsequent
reactions,2 thus leading to unusual reactivities or enhanced
catalytic activities. However, along with the species having close
metal centers, other dinuclear species with related but distant
metals can also exhibit cooperative reactivity.3 It has been shown
that distant metal centers can “talk to each other” via the
bridging ligand system, through reorganizations in the ligands
(mechanical coupling) or electronic influences (through-bond
coupling).4
Recently, we have reported on the reactivity of some
diiridium(III) polyhydrides, which suggested that the trans
effects of ligands could be transmitted from one metal center
to another via hydride bridges.5 Such transmission was inferred
from the reactivity differences displayed by compounds 1 and
2 (Figure 1), since the substitution of the axial hydride of 1 by
the less trans labilizing chloride ligand rendered the labile
acetonitrile ligand at the other extreme of the molecule nonlabile.
Further studies on the catalytic activity of complex 1 provided
evidence for a dinuclear hydrogenation mechanism resulting
from the facile migration of coordination vacancies along the
dinuclear complex.6 Such vacancy migrations could be under-
stood as the result of ligand trans effects being transmitted from
one side of the molecule to the other. These preliminary data,
which have inspired the present study, strongly suggest the
relevance of trans effect transmissions to cooperative reactivity
and bimetallic catalysis. The selected examples of reactivity,
structural data, and theoretical calculations on diiridium com-
plexes discussed herein indicate that dinuclear trans effects and
influences are not exclusive features of hydride-bridged com-
plexes, and illustrate the potential importance of such concepts
in the understanding of both the structure and reactivity of
dinuclear compounds.
These latter cooperation pathways are different from those
operating in compounds with close metal centers because they
(1) (a) Catalysis by Di- and Polynuclear Metal Cluster Complexes;
Adams, R. A., Cotton, F. A., Eds.; Wiley-VCH: New York, 1998. (b)
Braunstein, P.; Rose´, J. In Metal Clusters in Chemistry; Braunstein, P.,
Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, Germany, 1999;
p 616. (c) Van der Beuken, E. K.; Feringa, B. L. Tetrahedron 1998, 54,
12985.
(2) For some representative examples in dinuclear compounds, see: (a)
Torkelson, J. R.; Antwi-Nsiah, F. H.; McDonald, R.; Cowie, M.; Pruis, J.
G.; Jalkanen, K. J.; DeKock, R. L. J. Am. Chem. Soc. 1999, 121, 3666. (b)
Torkelson, J. R.; McDonald, R.; Cowie, M. J. Am. Chem. Soc. 1998, 120,
4047. (c) Fryzuk, M. D.; Love, J. B.; Rettig, D. J.; Young, V. G. Science
1997, 275, 1445. (d) Tada, K.; Oishi, M.; Suzuki, H.; Tanaka, M.
Organometallics 1996, 15, 2422. (e) Baranger, A. M.; Bergman, R. G. J.
Am. Chem. Soc. 1994, 116, 3822. (f) Broussard, M. E.; Juma, B.; Train, S.
G.; Peng, W. J.; Laneman, S. A.; Stanley, G. G. Science 1993, 260, 1784.
(g) Fryzuk, M. D.; Piers, W. E. Organometallics 1990, 9, 986.
(3) (a) Zhang, X. X.; Wayland, B. J. Am. Chem. Soc. 1994, 116, 7897.
(b) Esteruelas, M. A.; Garcia, M. P.; Lo´pez, A. M.; Oro, L. A. Organo-
metallics 1991, 10, 127.
(5) Sola, E.; Bakhmutov, V. I.; Torres, F.; Elduque, A.; Lo´pez, J. A.;
Lahoz, F. J.; Werner, H.; Oro, L. A. Organometallics 1998, 17, 683.
(6) Torres, F.; Sola, E.; Elduque, A.; Martinez, A. P.; Lahoz, F. J.; Oro,
L. A. Chem. Eur. J. 2000, 6, 2120.
(4) Bosnich, B. Inorg. Chem. 1999, 38, 2554.
10.1021/ja016213l CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/02/2001

11926 J. Am. Chem. Soc., Vol. 123, No. 48, 2001
Sola et al.
program.7 This structure was used as the starting point for a
full-geometry optimization based on DFT calculations. For these
calculations, the PiPr3 ligands were replaced by PH3 groups with
constrained rotation around the Ir-P axis. The distances of the
complex backbone resulting from this optimization are shown
below the X-ray structure of 4 in Figure 2, and are consistent
with our proposal of a bridging hydride equidistant between
the metals. A similar DFT optimization was carried out for the
tetrahydride complex 3, starting from a structure similar to that
of 4 but replacing the chloride ligand by a hydride at a typical
distance of 1.6 Å. These calculations converged to give the
backbone distances depicted below the X-ray structure of 3 in
Figure 2, which are consistent with those resulting from the
X-ray structural determination (Table 1).
Figure 1. Proposed structures of the complexes [Ir2(µ-H)(µ-
Pz)2H2X(NCCH3)(PiPr3)2] (X ) H (1), Cl (2)) and their 1H NMR signals
corresponding to the bridging hydrides.
The structural results described above are also consistent with
previous studies on other dinuclear compounds containing
bridging hydrides. Similar nonsymmetric M(µ-H)M bridges have
been found by X-ray diffraction in complexes such as [Et4N]-
[Mo2(µ-H)(CO)9PPh3]8 and [Ru2(µ-H)(µ-Pz)2H(HPz)(cod)2],9
and by neutron diffraction analysis in the compound [Pt2(µ-
H)H(dppe)2].10 In these examples, the bridging hydride coor-
dinates trans to ligands having very different trans influences,
hence accounting for the nonsymmetric position of the hydride.
In agreement with this explanation, the neutron diffraction
analysis of the complex [Pt2(µ-H)(Ph)2(PMe3)4][BPh4], in which
the hydride coordinates trans to two phenyl ligands, revealed
two equal Pt-H distances.11 Furthermore, in the compound [Pt2-
(µ-H)(H)(Ph)2(PMe3)2][BPh4], with two good trans labilizing
ligands (H and Ph) trans to the bridging hydride, two nearly
equal Pt-H distances were observed by neutron diffraction.12
Scheme 1
Compound 3 undergoes facile substitution of the pyrazole
ligand by CO, to give the previously reported complex [Ir2(µ-
H)(µ-Pz)2H3(CO)(PiPr3)2] (5).5 The equivalent substitution in
complex 4 is not observed even under harsh reaction conditions
(Scheme 1). Given that such substitution reactions have been
shown to follow dissociative mechanisms,5 the reason for the
different behavior of complexes 3 and 4 can be straightforwardly
deduced from their X-ray structures, since the Ir-N(pyrazole)
distance is considerably longer in complex 3 (Ir(1)-N(5) 2.142-
(4) Å) than in 4 (2.057(7) Å). The lengthening of the Ir-
pyrazole bond in 3 (Figure 2) can be attributed to the sequential
transmission of trans influence along the backbone of the
complex. Thus, the larger trans influence of hydride compared
to chloride pushes away the trans located bridging hydride,
which consequently binds more strongly to the other iridium
atom, and exerts a larger trans influence on the pyrazole ligand.
From the kinetic point of view, this sequential transmission of
trans influences results in the effective transmission of the
hydride trans effect from one side of the molecule to the other.
Results and Discussion
In our previous study of complexes 1 and 2,5 we proposed
that the reactivity change induced by substitution of an axial
hydride by chloride was accompanied by a subtle change in
the position of the bridging hydride. Such a positional change,
which suggested an active role of the bridge in the transmission
1
of trans effects, was inferred from the H NMR signals of the
bridging hydrides shown in Figure 1. Thus, the signal for
complex 2, which shows two equal JHP coupling constants, was
consistent with a bridging hydride equidistant from both metal
centers. In turn, the two different JHP coupling constants
observed in the corresponding signal of compound 1 suggested
an asymmetric position for this hydride bridge. This proposal,
attributing the different magnitude of the JHP couplings to
different H-Ir distances, could not be corroborated by the X-ray
diffraction study of 1, since the quality of its crystals was too
low to allow the proper location and refinement of the hydrides.
Crystals of sufficient quality to accomplish such a study have
been obtained for the related derivative [Ir2(µ-H)(µ-Pz)2H3(HPz)-
(PiPr3)2] (3) (Scheme 1), the structure of which is shown in
Figure 2. Even though hydride locations based on X-ray
diffraction methods have to be considered with caution, the
asymmetric position of the bridging hydride in this structural
determination (Ir-H distances 1.61 and 2.00(7) Å) is consistent
with the above-mentioned proposal since the NMR data of 3
are similar to those of 1. A parallel structural study was
attempted on the product resulting from the replacement of the
axial hydride of 3 by chloride, the complex [Ir2(µ-H)(µ-Pz)2H2-
Cl(HPz)(PiPr3)2] (4), although in this case the low quality of
the crystals and problems with disorder finally precluded the
proper location of the hydrides. The structure of 4 depicted in
Figure 2 shows the hydride ligands as positioned by the HYDEX
This communication between metal centers can also be
understood in terms of the molecular orbital schemes depicted
in Figure 3. To offer the most simple and straightforward
molecular orbital description of these compounds, calculations
(7) Orpen, A. G. J. Chem. Soc., Dalton Trans. 1980, 2509.
(8) Darensbourg, M. Y.; Atwood, J. L.; Burch, R. R., Jr.; Hunter, W.
E.; Walker, N. J. Am. Chem. Soc. 1979, 101, 2632.
(9) (a) Ashworth, T. V.; Liles, D. C.; Singleton, E. J. Chem. Soc., Chem.
Commun. 1984, 1317. (b) Albers, M. O.; Crosby, S. F. A.; Liles, D. C.;
Robinson, D. J.; Shaver, A.; Singleton, E. Organometallics 1987, 6, 2014.
(10) Chiang, M. Y.; Bau, R.; Minghetti, G.; Bandini, A. L.; Banditelli,
G.; Koetzle, T. F. Inorg. Chem. 1984, 23, 122.
(11) Albinati, A.; Chaloupka, S.; Eckert, J.; Venanzi, L. M.; Wolfer, M.
K. Inorg. Chim. Acta 1997, 259, 305.
(12) Albinati, A.; Bracher, G.; Carmona, D.; Jans, J. H. P.; Klooster,
W. T.; Koetzle, T. F.; Macchioni, A.; Ricci, J. S.; Thouvenot, R.; Venanzi,
L. M. Inorg. Chim. Acta 1997, 265, 255.

Transmission of Trans Effects in Dinuclear Complexes
J. Am. Chem. Soc., Vol. 123, No. 48, 2001 11927
Figure 2. Molecular structures determined by X-ray diffraction of complexes 3 (left) and 4a (right). Thermal ellipsoids are drawn at the 50%
probability level. (Below) Bond distances (Å) involved in the backbones of the complexes obtained from DFT optimizations.
Table 1. Selected Crystallographic Bond Distances (Å) and Angles
(deg) for Complexes 3 and 4aa
extent. Figure 3 (left) represents the five σ molecular orbitals
contributed by the ligands on the backbone of a symmetrical
molecule with terminal chlorides and a bridging hydride. The
three orbitals of lowest energy (1-3) are filled in the diiridium-
(III) complex. The replacement of one axial chloride by a
hydride (Figure 3, center) substantially modifies the features
of the filled orbitals 1 and 2, in a way that is consistent with
our experimental observations. Thus, orbital 2, which does not
involve the bridging hydride in the symmetric model, shows
antibonding character at the position trans to the axial hydride
in the asymmetric molecule. Consequently, a bonding contribu-
tion of similar magnitude appears at the other side of the
bridging hydride. Also, the metal-axial ligand bonding con-
tribution at the opposite extreme from the axial hydride
disappears in orbital 1.
The above model calculations allow us to rationalize the
experimentally observed transmission of trans effects as a
consequence of the formation of σ molecular orbitals extended
along the backbone of the dinuclear complex. However, these
molecular orbitals are not an exclusive feature of complexes
connected by bridging hydrides, being also present in more
common types of compounds such as those containing metal-
metal bonds. This observation is illustrated by the molecular
orbital scheme depicted in Figure 3 (right), which has been
calculated for a model metal-metal bonded diiridium(II)
compound. The formal similarity between the molecular orbital
descriptions of all those dinuclear species would suggest that
the transmission of trans effects and influences could also affect
the reactivity and structure of metal-metal bonded dinuclear
complexes. Indeed, the transmission of trans influences through
Au(II)-Au(II) bonds has been previously suggested to rational-
ize the structural features of bis(ylide) complexes containing
L-Au-Au-L′ backbones, since the Au-L bond distances of
these compounds seem to be controlled by the trans influence
of L′.14
3
4a
4b
Ir(l)‚‚‚Ir(2)
Ir(1)-P(1)
Ir(1)-N(1)
Ir(1)-N(3)
Ir(l)-N(5)
Ir(1)-H(30)
Ir(l)-H(31)
Ir(2)-P(2)
Ir(2)-N(2)
Ir(2)-N(4)
Ir(2)-H(30)
Ir(2)-H(32)/C1
lr(2)-H(33)
3.0413(7)
2.3090(16)
2.197(4)
2.123(4)
2.142(4)
1.61(7)
2.8784(8)
2.298(4)
2.164(9)
2.065(10)
2.060(9)
2.8793(8)
2.288(4)
2.213(11)
2.081(10)
2.053(10)
1.53(7)
2.2679(15)
2.127(5)
2.182(5)
2.00(7)
1.33(5)
1.55(6)
2.284(4)
2.061(10)
2.143(10)
2.276(4)
2.088(10)
2.141(9)
2.390(3)
2.394(3)
P(1)-Ir(1)-N(1)
P(l)-Ir(l)-N(3)
P(l)-Ir(l)-N(5)
98.11(13)
172.22(13)
101.20(14)
85(2)
101.6(3)
176.7(3)
93.0(3)
102.0(3)
175.7(3)
93.2(3)
P(1)-Ir(1)-H(30)
P(1)-Ir(l)-H(3 1)
N(1)-Ir(1)-N(3)
N(1)-Ir(1)-N(5)
N(1)-Ir(1)-H(31)
N(3)-Ir(1)-N(5)
N(5)-Ir(1)-H(30)
H(30)-Ir(1)-H(31)
P(2)-Ir(2)-N(2)
P(2)-Ir(2)-N(4)
P(2)-Ir(2)-H(30)
P(2)-Ir(2)-H(32)/Cl
P(2)-Ir(2)-H(33)
N(2)-Ir(2)-N(4)
N(2)-k(2)-H(32)/Cl
N(4)-Ir(2)-H(32)/C1
N(4)-Ir(2)-H(33)
H(30)-Ir(2)-H(32)
H(30)-Ir(2)-H(33)
H(32)-Ir(2)-H(33)
Ir(1)..Ir(2)-H(32)/Cl
N(5)-Ir(1)..Ir(2)
90(3)
86.55(18)
92.56(17)
168(3)
84.74(18)
168(2)
81.5(4)
96.5(4)
81.0(4)
97.5(4)
87.8(4)
89.4(4)
75(3)
175.75(13)
96.64(13)
89(2)
83(2)
85(2)
87.61(17)
97(2)
98(2)
173(2)
172(3)
90(3)
89(3)
159(2)
145.18(13)
174.9(3)
102.3(3)
176.1(3)
101.5(3)
92.26(14)
91.85(13)
82.2(4)
89.8(3)
92.5(3)
82.2(4)
89.1(3)
93.0(3)
152.01(9)
153.8(3)
152.80(9)
155.9(3)
An experimental system capable of illustrating the transmis-
sion of trans effects and influences and their consequences in
metal-metal bonded complexes was found in the diiridium
compounds depicted in Scheme 2. The complex [Ir2(µ-1,8-
(NH)2naphth)I(CH3)(CO)2(PiPr3)2] (6) has been recently reported
to be the kinetic product of methyl iodide oxidative addition to
the diiridium(I) complex [Ir2(µ-1,8-(NH)2naphth)(CO)2(Pi-
a 4a and 4b correspond to the two crystallographic independent
molecules of 4.
were carried out by extended Hu¨ckel methods13 in linear model
complexes containing only hydride and chloride ligands, since
neither the bending of the molecule nor the charge of the
compound influences the results of such calculations to a large
(13) (a) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397. (b) Hoffmann,
R.; Lipscomb, W. N. J. Chem. Phys. 1962, 36, 2179. (c) Hoffmann, R.;
Lipscomb, W. N. J. Chem. Phys. 1962, 36, 2872.
(14) (a) Murray, H. H.; Fackler, J. P., Jr.; Trzcinska-Bancroft, B.
Organometallics 1985, 4, 1633. (b) Laguna, A.; Laguna, M.; Jime´nez, J.;
Lahoz, F. J.; Olmos, E. J. Organomet. Chem. 1992, 435, 235.

11928 J. Am. Chem. Soc., Vol. 123, No. 48, 2001
Sola et al.
Figure 3. Molecular orbitals obtained by extended Hu¨ckel calculations on some model diiridium complexes: (left) symmetric and hydride bridged
diiridium(III), (center) asymmetric with axial and bridging hydrides diiridium(III), (right) symmetric metal-metal bonded diiridium(II).
Scheme 2
rather different in isomers 8 and 9, given the different inter-
metallic distances observed for the compounds (Table 2). This
could be primarily attributed to the different trans influences
of CH3 and PiPr3 ligands, since a sterically induced lengthening
of the intermetallic distance in 8 is unlikely for a transoid
arrangement of the phosphine ligands. Moreover, the existence
of any destabilizing contribution of steric origin in the structure
of 8 would not be consistent with the fact that 8 is the
thermodynamically stable isomer.
Isomers 8 and 9 offer an excellent system to compare the
behavior of coordination vacancies subjected to nearly equal
steric constraints but different electronic environments as a result
of the different spatial distribution of the ligands around the
neighboring metal atom. Such electronic effects did not affect
the reactivity of the isomeric compounds toward a strong
nucleophile such as iodide, which in both cases reformed the
neutral precursors 6 and 7. The electronic effects were apparent
upon reaction with a weaker nucleophile such as pyrazole. Thus,
isomer 9 readily formed the isolable pyrazole compound [Ir2(µ-
1,8-(NH)2naphth)(CH3)(HPz)(CO)2(PiPr3)2](CF3SO3) (10) (Scheme
2), whereas no evidence for adduct formation was observed in
the solutions containing 8 and pyrazole, even at low temperature.
The structure of 10 determined by X-ray diffraction is shown
in Figure 5; relevant bond distances and angles are listed in
Table 2. As expected from the long Ir-N(pyrazole) distance
observed in this structure, 2.233(6) Å, compound 10 was found
to be very labile, since its solutions slowly produced the
unsaturated complex 8 and free pyrazole when warmed to room
temperature.
The reactivity differences displayed by complexes 8 and 9
toward pyrazole can be rationalized in terms of the transmission,
through the metal-metal bond, of the trans labilizing properties
of the phosphine and methyl ligand, since the instability of the
pyrazole adduct of 8 can be readily attributed to the larger trans
influence expected for a methyl ligand. By extrapolation of what
is often observed in mononuclear unsaturated compounds, it
could be expected that good trans labilizing ligands direct the
coordination vacancy to the trans position in the ground state
structure of an unsaturated dinuclear complex. In agreement with
Pr3)2].15 Compound 6 was found slowly to isomerize in solution
to give the thermodynamic product of the reaction, the isomer
7. Iodide abstraction with silver triflate from these two isomers
has allowed the isolation of two isomeric cationic compounds
of formula [Ir2(µ-l,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2](CF3SO3)
(8, 9), the structures of which are shown in Figure 4. Handling
of isomer 9 in solution required low temperature, since its
isomerization to 8 was found to be fast at room temperature.
On the basis of previous studies on unsaturated compounds
related to 8 and 9,15,16 these isomers should be described as
Ir(III)-Ir(I) mixed valence compounds, in which the metal
atoms are connected by a weak Ir(I)-Ir(III) dative metal-metal
bond. The relative strength of this dative Ir-Ir bond could be
(16) (a) Oro, L. A.; Sola, E.; Lo´pez, J. A.; Torres, F.; Elduque, A.; Lahoz,
F. J. Inorg. Chem. Commun. 1998, 1, 64. (b) Jime´nez, M. V.; Sola, E.;
Lo´pez, J. A.; Lahoz, L. A. Chem. Eur. J. 1998, 4, 1396. (c) Jimenez, M.
V.; Sola, E.; Martinez, A. P.; Lahoz, F. J.; Oro, L. A. Organometallics
1999, 18, 1125.
(15) Jime´nez, M. V.; Sola, E.; Egea, M. A.; Huet, A.; Francisco, A. C.;
Lahoz, F. J.; Oro, L. A. Inorg. Chem. 2000, 39, 4868.

Transmission of Trans Effects in Dinuclear Complexes
J. Am. Chem. Soc., Vol. 123, No. 48, 2001 11929
Figure 4. Molecular structures of the cations of complexes 8 (left) and 9a (right). Thermal ellipsoids are drawn at the 50% probability level.
Table 2. Selected Crystallographic Bond Distances (Å) and Angles
(deg) for Complexes 8-10a
8
9a
9b
10
Ir(l)-Ir(2)
Ir(l)-P(1)
Ir(l)-N(1)
Ir(l)-N(2)
Ir(l)-N(3)
Ir(l)-C(29)
Ir(2)-P(2)
Ir(2)-N(l)
Ir(2)-N(2)
Ir(2)-C(31)
lr(2)-C(32)
2.7243(8)
2.300(2)
2.105(8)
2.114(8)
2.6209(7)
2.288(4)
2.124(8)
2.064(9)
2.6127(7)
2.283(3)
2.077(8)
2.130(9)
2.5766(5)
2.311(2)
2.142(6)
2.136(6)
2.233(6)
1.805(9)
2.336(2)
2.194(6)
2.035(8)
1.786(11)
2.113(7)
1.831(10)
2.343(3)
2.121(7)
2.085(9)
1.877(15)
2.088(9)
1.777(13)
2.282(3)
2.062(8)
2.140(9)
1.779(13)
2.062(11)
1.746(13)
2.287(3)
2.141(8)
2.050(7)
1.787(15)
2.088(13)
P(l)-Ir(l)-Ir(2)
P(l)-Ir(l)-N(1)
P(l)-Ir(l)-N(2)
P(l)-Ir(l)-N(3)
P(l)-Ir(l)-C(29)
N(l)-Ir(l)-N(2)
N(l)-Ir(l)-N(3)
125.85(7)
97.5(2)
171.6(2)
120.14(8)
170.3(2)
102.4(3)
127.07(8)
100.1(3)
174.4(2)
116.05(6)
101.96(19)
166.2(2)
98.17(19)
86.3(3)
71.1(3)
94.4(2)
159.9(3)
94.4(3)
96.7(3)
136.54(17)
102.6(3)
105.4(3)
153.32(7)
111.11(17)
103.5(2)
92.6(3)
Figure 5. Molecular structure of the cation of complex 10. Thermal
ellipsoids are drawn at the 50% probability level.
89.9(3)
74.2(3)
90.4(4)
72.0(3)
91.0(4)
74.3(3)
N(l)-Ir(l)-C(29) 167.8(4)
N(2)-Ir(l)-N(3)
94.6(5)
163.9(5)
94.6(4)
N(2)-Ir(1)-C(29) 98.4(4)
N(3)-Ir(l)-Ir(2)
166.2(5)
N(3)-Ir(l)-C(29)
C(29)-Ir(l)-Ir(2) 117.7(3)
116.2(4)
154.66(9)
105.8(2)
115.6(3)
90.8(4)
92.4(4)
71.7(3)
163.3(4)
89.3(4)
99.4(4)
149.2(4)
111.0(4)
92.2(4)
99.1(3)
111.1(4)
153.62(8)
114.4(2)
105.3(3)
92.4(4)
91.3(3)
74.6(3)
99.2(5)
151.4(4)
162.3(5)
87.2(4)
110.4(4)
91.5(6)
P(2)-Ir(2)-Ir(l)
P(2)-Ir(2)-N(l)
P(2)-Ir(2)-N(2)
P(2)-Ir(2)-C(31)
P(2)-Ir(2)-C(32)
N(1)-Ir(2)-N(2)
N(l)-Ir(2)-C(31)
119.66(7)
169.2(2)
97.9(2)
90.2(3)
93.3(3)
74.4(3)
96.5(4)
92.3(2)
71.9(2)
102.6(3)
152.8(3)
163.9(3)
89.7(3)
110.8(3)
89.6(3)
N(1)-Ir(2)-C(32) 95.1(3)
N(2)-Ir(2)-C(31) 169.1(4)
N(2)-Ir(2)-C(32) 97.1(4)
C(31)-Ir(2)-Ir(l) 119.5(3)
C(31)-Ir(2)-C(32) 89.7(4)
C(32)-Ir(2)-Ir(l) 133.5(3)
Figure 6. Dependence of the reaction rate upon iodide concentration
for the isomerization of 6 into 7.
100.8(3)
100.4(2)
Scheme 3
a 9a and 9b correspond to the two crystallographic independent
molecules of 9.
this, complex 8, with a mutually trans disposition of the methyl
ligand and the vacancy, is the thermodynamic isomer of the
unsaturated cation [Ir2([µ-1,8-(NH)2naphth)(CH3)(CO)2(Pi-
Pr3)2]+.
Arguments similar to those presented above may help to
rationalize the structure of 7 (Scheme 2), the thermodynamically
stable isomer of the neutral complex [Ir2(µ-1,8-(NH)2naphth)I-
(CH3)(CO)2(PiPr3)2]. When the thermally induced isomerization
of complex 6 into 7 was carried out in CDCl3 or acetone-d6, in
the presence of a 10-fold excess of [NBu4]Br, the reaction
product consisted of a 1:10 mixture of isomer 7 and its
isostructural bromide complex [Ir2(µ-1,8-(NH)2naphth)Br-
(CH3)(CO)2(PiPr3)2] (11) (Scheme 3). Substitution of iodide by
bromide in the precursor 6 was not observed during the reaction,
suggesting that iodide dissociation is a necessary step within
the isomerization mechanism. Pseudo-first-order rate constants
for the isomerization of 6 into 7 (kobs) were obtained by 31P
NMR spectroscopy at 328 K in the presence of different
concentrations of [NBu4]I, giving values around 7-8 × 10-5
s-1, irrespective of the complex/iodide ratio. This zero-order

11930 J. Am. Chem. Soc., Vol. 123, No. 48, 2001
Sola et al.
were measured in ca. 3 × 10-4 M solutions with a Philips PW 9501/
01 conductimeter.
Scheme 4
Synthesis. All reactions were carried out with exclusion of air by
using standard Schlenk techniques. Solvents were dried by known
procedures and distilled under argon prior to use.17 The complexes [Ir2-
(µ-H)(µ-Pz)2H3(HPz)(PiPr3)2] (3)5 and [Ir2(µ-1,8-(NH)2naphth)I-
(CH3)(CO)2(PiPr3)2] (isomers 6 and 7)15 were prepared by known
procedures. All other reagents were obtained from commercial sources
and were used as received. All the compounds whose preparations are
described below are air sensitive in solution.
Preparation of [Ir2(µ-H)(µ-Pz)2H2Cl(HPz)(PiPr3)2] (4). A solution
of [Ir2(µ-H)(µ-Pz)2H3(HPz)(PiPr3)2] (3) (100 mg, 0.11 mmol) in
chloroform (2 mL) was heated for 30 min under reflux. The solvent
was removed in vacuo, and the residue was treated with methanol to
give a pale orange solid. The liquid phase was decanted, and the solid
washed with methanol before drying in vacuo. Yield: 86 mg. Single
crystals of 4 were grown from a concentrated chloroform solution,
layered with hexane. Both the solid and the crystals gave microanalysis
consistent with the presence of 1.5 molecules of CHCl3 per molecule
of 4, just as found in the structural analysis by X-ray diffraction. Anal.
Calcd for C27H55CIr2N6P2‚1.5CHCl3: C, 30.44; H, 5.02; N, 7.47.
dependence upon iodide concentration (Figure 6) is consistent
with the mechanism for isomerization of 6 to 7 depicted in
Scheme 4. The intramolecular iodide dissociation from 6 is the
initial and rate-determining step.
The mechanism shown in Scheme 4 together with the results
discussed earlier, suggest that the transmission of trans effects
and influences is the driving force for this isomerization reaction.
Thus, isomerization would be favored by the lability of the
iodide ligand of 6, which is induced by the large trans effect of
the methyl ligand. In turn, the smaller trans influence of the
phosphine compared to that of methyl can account for the greater
thermodynamic stability of isomer 7.
1
Found: C, 30.04; H 5.31; N, 7.06. H NMR (C6D6, 293 K) δ -32.98
(tt, JHP ) JHP′ ) 9.9, JHH ) JHH′ ) 2.1, 1H, Ir(µ-H)Ir), -21.86 (dd,
JHP ) 19.5, JHH ) 2.1, 1H, IrH), -21.07 (dd, JHP ) 18.5, JHH ) 2.1,
1H, IrH), 0.85 (dd, JHP ) 13.5, JHH ) 6.9, 9H, PCHCH3), 1.03 (dd,
JHP ) 12.9, JHH ) 7.2, 9H, PCHCH3), 1.06 (dd, JHP ) 13.2, JHH ) 7.2,
9H, PCHCH3), 1.17 (dd, JHP ) 12.9, JHH ) 7.2, 9H, PCHCH3), 2.23,
2.50 (both m, 3H, PCHCH3), 5.83 (m, 2H, CH), 6.03 (dt, JHP ) 1.8,
JHH ) 1.5, 1H, CH), 6.32 (dd, JHH ) 2.7, 2.1, 1H, CH), 7.45 (d, JHH
) 2.7, 1H, CH), 7.54 (m, 1H, CH), 7.76 (m, 1H, CH), 7.93 (d, JHH
)
2.1, 1H, CH), 8.06 (d, JHH ) 1. 8, 1H, CH), 10.65 (br, 1H, NH). 31P-
{1H} NMR (C6D6, 293 K) δ 4.28, 6.05 (both s).
Reactions of 3 and 4 with CO. Carbon monoxide was bubbled
during ca. 2 min into solutions of the corresponding complex (ca. 20
mg) in CDCl3 (0.5 mL), in an NMR tube, at room temperature. After
this manipulation, the 1H and 31P {1H} NMR of the samples were
measured. The sample corresponding to the initial solution of complex
3 was completely transformed into a mixture of free pyrazole and a
complex, which on the basis of its NMR features was identified as
[Ir2(µ-H)(µ-Pz)2H3(CO)(PiPr3)2] (5).5 The sample corresponding to
complex 4 only showed unreacted starting material. This sample was
sealed under CO atmosphere and heated for 24 h at 333 K. After this
period the only detectable complex in the solution was 4.
Preparation of [Ir2(µ-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2]-
(CF3SO3) (8). The synthesis of this complex starting from the diiridium-
(I) compound [Ir2(µ-1,8-(NH)2naphth)(CO)2(PiPr3)2] has been previously
described.15 Alternatively, the complex can be obtained as follows: A
Schlenk tube containing a solution of complex [Ir2(µ-1,8- (NH)2-
naphth)I(CH3)(CO)2(PiPr3)2] (isomer 6) (200 mg, 0.19 mmol) in acetone
(10 mL) was protected from the light and placed into a cooling bath at
ca. 250 K. Silver triflate (49.5 mg, 0.19 mmol) was added to the
solution, and the resulting suspension was stirred for 1 h. The suspension
was filtered through Celite and the recovered solution was dried in
vacuo to give a red oil. The oil was treated with diethyl ether to give
a red solid, which was decanted, washed with ether and hexane, and
dried in vacuo. Yield: 140 mg (75%). Single crystals of 8 were grown
from acetone solutions, layered with diethyl ether. The microanalysis
and NMR features of 8 in acetone-d6 coincide with those already
published.
Conclusion
The dinuclear compounds described in this paper together
with their reactivity have revealed the feasibility of the transmis-
sion of ligand trans effects and influences along the backbone
of dinuclear complexes. Such transmission probably occurs
through molecular orbitals of σ symmetry extending along the
dinuclear complexes, a situation that has been found to be
favored by the presence of bridging hydrides or metal-metal
bonds. This type of information transmission between metal
centers allows the nature and spatial arrangement of the ligands
coordinated to one metal to exert a profound influence upon
the structure and reactivity of the neighboring metal containing
fragment. In view of these results, we believe that these concepts
of dinuclear trans effect and dinuclear trans influence may
constitute useful tools for a better understanding of the chemistry
of dinuclear compounds and, furthermore, to advance in the
development of applications based on intermetallic cooperative
reactivity.
Experimental Section
Physical Measurements. Infrared spectra were recorded as Nujol
mulls on polyethylene sheets with use of a Nicolet 550 spectrometer.
C, H, N, and S analyses were carried out in a Perkin-Elmer 2400
CHNS/O analyzer. NMR spectra were recorded on Varian UNITY,
Varian Gemini 2000, or Bruker ARX, 300 MHz spectrometers. 1H (300
MHz) and 13C (75.19 MHz) NMR chemical shifts were measured
relative to partially deuterated solvent peaks but are reported in ppm
relative to tetramethylsilane. 31P (121 MHz) NMR chemical shifts were
measured relative to H3PO4 (85%). Coupling constants, J, are given in
Preparation of [Ir2(µ-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2]-
(CF3SO3) (9). The complex was prepared as a red solid (123 mg, 63%
yield) following the procedure described for 8 but starting from complex
7. Single crystals of 9 were grown from acetone solutions cooled at
ca. 250 K, and layered with diethyl ether. Anal. Calcd for C32H53F3-
Ir2O5N2P2S: C, 35.55; H, 4.94; N, 2.59. Found: C, 35.67; H, 5.03; N,
2.60. IR (cm-1) 3310, 3281 ν(NH), 2010, 1983 ν(CO). MS (FAB+,
m/z (%)) 932 (10) [M+]. ΛM (acetone) ) 125 Ω-1 cm2 mol-1 (1:1). 1H
1
Hertz. Generally, spectral assignments were achieved by H COSY,
NOESY, and 13C DEPT experiments. MS data were recorded on a VG
Autospec double-focusing mass spectrometer operating in the positive
mode; ions were produced with the Cs+ gun at ca. 30 kV, and
3-nitrobenzyl alcohol (NBA) was used as the matrix. Conductivities
(17) (a) Shriver, D. F. The Manipulation of Air-sensitiVe Compounds;
McGraw-Hill: New York, 1969. (b) Armarego, W. L. F.; Perrin, D. D.
Purification of Laboratory Chemicals, 4th ed.; Butterworth-Heinmann;
Oxford, 1996.

Transmission of Trans Effects in Dinuclear Complexes
J. Am. Chem. Soc., Vol. 123, No. 48, 2001 11931
NMR (acetone-d6, 293 K) δ 0.73 (dd, JHP ) 14.4, JHH ) 7.2, 9H,
PCHCH3), 1.13 (m, 3H, IrCH3), 1.21 (dd, JHP ) 15.0, JHH ) 7.2, 9H,
PCHCH3), 1.30 (dd, JHP ) 14.0, JHH ) 6.9, 9H, PCHCH3), 1.35 (dd,
JHP ) 14.4, JHH ) 7.2, 9H, PCHCH3), 2.77, 1.91 (both m, 3H,
PCHCH3), 6.84 (br, 1H, NH), 7.23 (t, JHH ) 7.9, 13 1H, CH), 7.29
(br, 1H, NH), 7.23 (t, JHH ) 7.9, 1H, CH), 7.47 (d, JHH ) 7.5, 1H,
CH), 7.57 (d, JHH ) 8.1, 1H, CH), 7.71 (d, JHH ) 8.1, 1H, CH), 7.75
(d, JHH ) 7.5, I1H, CH). 31P{1H} NMR (acetone-d6, 293 K) δ 42.82,
8.91 (both d, JPP ) 8.4). 13C{1H} NMR (acetone-d6, 233 K) δ -19.70
(m, IrCH3), 17.75 (d, JCP ) 3.8, PCHCH3), 19.11, 19.69, 20.06 (all s,
PCHCH3), 24.18 (d, JCP ) 28.5, PCHCH3), 25.46 (d, JCP ) 29.9,
PCHCH3), 112.21, 120.78 (both s, CH), 121.41 (s, C), 122.71, 127.78,
128.14 (all s, CH), 135.85 (s, C), 146.21 (d, JCP ) 2.4, C), 148.71 (m,
C), 174.45 (d, JCP ) 7.9, CO), 177.24 (d, JCP ) 10.6, CO).
experimental data used in these determinations are included in the
Supporting Information.
Computational Experimental Details. The computational method
used for geometry optimization of models of compounds 3 and 4 was
density functional theory in its B3LYP formulation,18 using the
Gaussian9819 series of programs. The basis sets used were the LanL2DZ
effective core potential for iridium atoms: 6-31G** for chlorine,
phosphorus and nitrogen atoms, and hydride ligands, and 6-31G for
carbon and the rest of the hydrogen atoms. Calculations of the extended
Hu¨ckel type13 were carried out by using a modified version of the
Wolfsberg-Helmholz formula.20 The calculations and drawings were
made with the program CACAO,21 and the atomic parameters used
are those implemented in this program.
Structural Analysis of Complexes 3, 4, 8, 9, and 10. X-ray data
were collected for all complexes at low temperature (see crystal data
below) on four-circle Siemens P4 (3) or Stoe-Siemens AED-2 diffrac-
tometers (8), or in a Bruker SMART APEX CCD diffractometer (4, 9,
and 10) with graphite monochromated Mo KR radiation (λ ) 0.710 73
Å) using ω/2θ (3 and 8) or ω scans (4, 9, and 10). Data were corrected
for absorption by using a psi-scan method22 (3 and 8) or a multiscan
method applied with the SADABS program.23
The structures for all five compounds were solved by direct methods
with SHELXS-86.24 Refinement, by full-matrix least squares on F2 with
SHELXL97,24 was similar for all complexes, including isotropic and
subsequently anisotropic displacement parameters for all non-hydrogen
nondisordered atoms. Particular details concerning the presence of
solvent, static disorder, and hydrogen refinement are listed below. All
the highest electronic residuals were observed in close proximity of
the Ir centers and make no chemical sense.
Crystal data for 3: C27H56Ir2N6P2, M ) 911.12; colorless prismatic
block, 0.38 × 0.26 × 0.20 mm3; triclinic, P1h; a ) 10.693(2) Å, b
) 12.514(3) Å, c ) 14.836(3) Å, R ) 74.30(3)°, â ) 75.73(3)°, γ
) 69.95(3)°; Z ) 2; V ) 1769.2(6) Å3; Dc ) 1.710 g/cm3; µ )
7.629 mm-1, minimum and maximum transmission factors 0.1596
and 0.3107; 2θmax ) 28.0°; temperature 123(1) K; 10325 reflections
collected, 8398 unique [R(int) ) 0.0452]; number of data/restrains/
parameters 8398/0/457; final GoF 1.064, R1 ) 0.0311 [6832 reflections,
I > 2σ(I)], wR2 ) 0.0714 for all data; largest difference peak 1.594
e‚Å-3; extinction coefficient 0.00069(8). Most of the hydrogen atoms
were located in the difference maps; thus, pyrazole and pyrazolate
hydrogens were refined as free isotropic atoms, while those of the
phosphine ligands were refined by using a restricted riding mode. All
the hydride ligands were located and refined in the last cycles of
refinement as free isotropic atoms.
Preparation of [Ir2(µ-1,8-(NH)2naphth)(CH3)(HPz)(CO)2(PiPr3)2]-
(CF3SO3) (10). A solution of 9 (100 mg, 0.09 mmol) in acetone (5
mL) was treated at ca. 250 K with pyrazole (6.47 mg, 0.09 mmol),
and the mixture was stirred for 1 h. The resulting yellow solution was
concentrated to ca. 0.5 mL and diethyl ether was added to produce a
yellow precipitate. The solid was separated by decanting the solution,
washed with diethyl ether, and dried in vacuo. Yield: 95 mg (72%).
Single crystals of 10 were grown from acetone solutions cooled at ca.
250 K and layered with diethyl ether. Anal. Calcd for C35H57F3-
Ir2N4O5P2S: C, 36.58; H, 5.00; N, 4.87; S, 2.79. Found: C, 36.98; H,
5.02; N, 5.10; S 2.69. IR (cm-1) 3336, 3286, 3155 ν(NH), 1998, 1988
1
ν(CO). H NMR (acetone-d6, 293 K) δ 0.71 (dd, JHP ) 13.5, JHH
)
7.2, 9H, PCHCH3), 1.14 (dd, JHP ) 13.2, JHH ) 6.9, 9H, PCHCH3),
1.24 (d, JHP ) 2.4, 3H, IrCH3), 1.35 (dd, JHP ) 14.7, JHH ) 7.5, 9H,
PCHCH3), 1.42 (dd, JHP ) 13.8, JHH ) 7.2, 9H, PCHCH3), 1.84, 2.71
(both m, 3H, PCHCH3), 5.83 (dd, JHH ) 2.4, 2.1, 1H, CH), 6.04, 6.48
(both br, 1H, NH), 7.05 (d, JHH ) 7.8, 1H, CH), 7.09 (d, JHH ) 7.2,
1H, CH), 7.15 (d, JHH ) 7.2, 1H, CH), 7.47 (m, 4H, CH), 7.67 (d, JHH
) 7.5, 1H, CH), 12.07 (m, 1H, NH). 31P{1H} NMR (acetone-d6, 293
K) δ 26.23, -4.16 (both s). 13C{1H} NMR (acetone-d6, 273 K) δ
-24.76 (dd, JCP ) 8.7, 5.4, IrCH3), 18.02 (d, JCP ) 3.7, PCHCH3),
19.32 (d, JCP ) 2.3, PCHCH3), 19.61, 20.13 (both s, PCHCH3), 24.04
(d, JCP ) 24.9, PCHCH3), 25.53 (d, JCP ) 29.0, PCHCH3), 105.82,
111.65 (both s, CH), 113.02 (d, JCP ) 3.7, CH), 120.63 (s, CH), 121.42
(s, C), 121.57 (s, CH), 122.13 (q, JCF ) 320.4, CF3SO3), 127.64 (s,
CH), 136.34 (s, C), 146.71 (d, JCP ) 2.7, C), 150.16 (d, JCP ) 2.3, C),
174.93 (dd, JCP ) 11.4, 1.9, CO), 177.70 (dd, JCP ) 8.2, 5.0, CO).
Isomerization of 6 into 7 in the Presence of [NBu4]Br. An NMR
tube containing a solution of complex 6 (20 mg, 0.019 mmol) and
[NBu4]Br (60.7 mg, 0.19 mmol) in acetone-d6 (0.5 mL) was placed
into an oil bath at 323 K. The course of the reaction was monitored by
1H and 31P{1H} NMR over a period of 3 days. The starting complex 6
disappeared, giving rise to a mixture of 7 and a new complex 11 in a
1:10 molar ratio. No products other than 6, 7, and 11 were observed.
Complex 11 was identified as the compound [Ir2([µ-1,8-(NH)2naphth)-
Br(CH3)(CO)2(PiPr3)2], the bromide analogue of isomer 7, on the basis
Crystal data for 4: C27H55ClIr2N6P2‚1.5CHCl3, M) 1124.61; yellow
irregular block, 0.35 × 0.31 × 0.25 mm3; triclinic, P1h; a ) 12.187(3)
Å, b ) 16.457(3) Å, c ) 22.246(5) Å, R ) 88.294(4)°, â ) 83.524-
(4)°, γ ) 82.862(3)°; Z ) 4; V) 4398.3(16) Å3; Dc ) 1.698 g/cm3;
µ ) 6.478 mm-1, minimum and maximum transmission factors
(18) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. ReV. B 1998, 37, 785.
of its NMR features and MS spectra. Data for 11: MS (FAB+, m/z
1
(%)) 1012 (10) [M+]. H NMR (acetone-d6, 293 K) δ 0.28 (d, JHH
)
(19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-
Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe,
M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.7;
Gaussian, Inc.: Pittsburgh, PA, 1998.
1.5, 3H, IrCH3), 0.68 (dd, JHP ) 12.6, JH ) 6.9, 9H, PCHCH3), 1.09
(dd, JHP ) 14.4, JHH ) 6.9, 9H, PCHCH3) [18H, PCHCH3 and 3H,
PCHCH3 were hidden under the NBu4 signals], 2.83 (m, 3H, PCHCH3),
5.36, 5.76 (both br, 1H, NH), 6.98 (dd, JHH ) 8.1, 7.5, 1H, CH), 7.06
(dd, JHH ) 7.5, 6.9, 1H, CH), 7.18 (d, JHH ) 6.9, 1H, CH), 7.40 (d,
JHH ) 8.1, 1H, CH), 7.48 (d, JHH ) 7.5, 1H, CH), 7.52 (d, JHH ) 7.5,
1H, CH). 31P{1H} NMR (acetone-d6, 293 K) δ 23.36, -6.23 (both s).
Kinetics of Isomerization of 6 into 7. A solution of complex 6 in
CDCl3 (0.057 M) was prepared and stored at low temperature. Each
sample was prepared by taking 0.5 mL of this solution into a NMR
tube and dissolving the necessary amount of the soluble salt [NBu4]I
to obtain the desired iodide concentration. The decrease in the intensity
of the 31P{1H} NMR signals of 6 was measured at intervals after the
sample was stabilized at 328 K. The pseudo-first-order rate constants
(20) Ammeter, J. H.; Bdrgi, H. B.; Thibeault, J. C.; Hoffmann, R. J.
Am. Chem. Soc. 1978, 100, 3686.
(21) Mealli, C.; Proserpio, D. M. J. Chem. Edu. 1990, 67, 399.
(22) North, C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr. 1986,
A24, 351.
(23) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. SADABS:
Area-detector absorption correction, 1996, Bruker-AXS, Madison, WI.
(24) SHELXTL Package v. 6.10, 2000, Bruker-AXS, Madison, WI.
Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
k
obs (s-1) were obtained from the slopes of the plots of normalized signal
integral vs time (s), under pseudo-first-order conditions (i.e. the first
10% of the reaction), using a least-squares approach. The values
obtained were the following (kobs (s-1)/[NBu4]I concentration (M)): 7.97
E-5/0.052, 8.75 E-5/0.285, 6.75 E-5/0.57, 6.99 E-5/1.14. The

11932 J. Am. Chem. Soc., Vol. 123, No. 48, 2001
Sola et al.
0.1867 and 0.3249; 2θmax ) 27.0°; temperature 173(2) K; 32072
reflections collected, 18706 unique [R(int) ) 0.0531]; number of data/
restrains/parameters 18706/172/768; final GoF 0.940, R1 ) 0.0628
[10632 reflections, I > 2σ(I)], wR2 ) 0.1739 for all data; largest
difference peak 2.476 e‚Å-3. The crystal structure reveals the presence
of three chloroform molecules of solvation together with the two
independent dinuclear complexes; one chloroform molecule was
observed disordered over two positions and was refined isotropically
with complementary occupancies and geometric restrains. Additionally,
three isopropyl groups of the phosphine ligands were also found to be
disordered; they were refined with two isotropic models for each
disordered moiety with fixed complementary occupancy. Hydrogens
were only included for the pyrazole and pyrazolate ligands in calculated
positions and were refined by using a riding model. The hydride ligands
were included in the last cycles of refinement in the positions estimated
from electrostatic potential calculations7 and refined riding on Ir atoms.
Crystal data for 8: C31H53ClIr2N2O6P2‚C3H6O, M ) 1089.62; red
prismatic block, 0.55 × 0.35 × 0.27 mm3; monoclinic, P21/c; a )
20.598(4) Å, b ) 12.756(3) Å, c ) 16.001(3) Å, â ) 110.03(2)°; Z )
4; V ) 3949.9(14) Å3; Dc ) 1.832 g/cm3; µ ) 6.926 mm-1, minimum
and maximum transmission factors 0.1148 and 0.2602; 2θmax ) 25.1°;
temperature 100(1) K; 8693 reflections collected, 6931 unique [R(int)
) 0.0541]; number of data/restrains/parameters 6931/1/459; final GoF
0.996, Rl ) 0.0459 [5135 reflections, I > 2σ(I)], wR2 ) 0.1144 for all
data; largest difference peak 2.004 e‚Å-3; extinction coefficient 0.00013-
(5). The carbon atoms of one phosphine were found to be disordered
and refined with isotropic displacement parameters; two models were
included to take account of this disorder. All hydrogen atoms were
included from calculated positions and refined riding on their corre-
sponding C or N atoms. An acetone molecule of solvation was also
found to be disordered in the asymmetric unit; two disordered models
were included to complete one acetone molecule.
0.4113 and 0.7288; 2θmax ) 28.8°; temperature 173(2) K; 30883
reflections collected, 18373 unique [R(int) ) 0.0891]; number of data/
restrains/parameters 18373/21/949; final GoF 0.746, R1 ) 0.0568 [7879
reflections, I > 2σ(I)], wR2 ) 0.0923 for all data; largest difference
peak 3.576 e‚Å-3. A diethyl ether molecule of solvation was detected
and refined anisotropically. Hydrogen atoms were included from
idealized positions and refined riding on their C or N atoms. No
hydrogen was included for the solvent molecule.
Crystal data for 10: C35H57F3Ir2N4O5P2S‚1.25 C4H10O, M )
1241.90; yellow irregular block, 0.22 × 0.18 × 0.17 mm3; monoclinic,
P21/c; a ) 11.8839(8) Å, b ) 19.9638(13) Å, c ) 20.7764(13) Å, â
) 91.4000(10)°; Z ) 4; V ) 4927.7(6) Å3; Dc ) 1.674 g/cm3; µ )
5.560 mm-1, minimum and maximum transmission factors 0.3783 and
0.4463; 2θmax ) 28.7°; temperature 173(2) K; 32237 reflections
collected, 11613 unique [R(int) ) 0.0576]; number of data/restrains/
parameters 11613/17/530; final GoF 0.992, R1 ) 0.0462 [6955
reflections, I > 2σ(I)], wR2 ) 0.0926 for all data; largest difference
peak 3.205 e‚Å-3. Two molecules of diethyl ether were observed in
the asymmetric unit. One of them was refined as a disordered molecule
with two complementary moieties. For the second a partial occupation
was assumed (0.25). Hydrogens in calculated positions were refined
with a riding model.
Acknowledgment. We thank the Plan Nacional de Inves-
tigacio´n, MCYT, for the support of this research (Project No.
BQU2000-1170).
Supporting Information Available: Drawings and tables
of atomic coordinates for the DFT-optimized structures of the
PH3 models for complexes 3 and 4, and tables of 31P{1H} NMR
signal integrals of 6 vs time and least-squares-fits used for the
determination of complex 6 isomerization rates (PDF); an X-ray
crystallographic file containing full details of the structural
analysis of the five structures (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
Crystal data for 9: C32H53F3Ir2N2O5P2S‚0.5C4H10O, M ) 1118.22;
red irregular block, 0.16 × 0.06 × 0.05 mm3; triclinic, P1h; a ) 11.7846-
(11) Å, b ) 18.3407(18) Å, c ) 20.285(2) Å, a ) 100.799(2)°, â )
102.636(2)°, y ) 102.471(2)°; Z ) 4; V ) 4048.5(7) Å3; Dc ) 1.835
g/cm3; µ ) 6.753 mm-1, minimum and maximum transmission factors
JA016213L