Preparation and reactivity of the heterobimetallic ReIr face-shared bioctahedral compounds Cp*Ir(μ-Cl)3Re(CO)3 and Cp*Ir(μ-SC6H4Me-4)3Re(CO) 3: X-ray diffraction structures and redox behavi

Article abstract of DOI:10.1016/j.poly.2009.04.023

Thermolysis of the dinuclear compound [Cp*IrCl₂]₂ (1) with ClRe(CO)₅ (2) leads to the formation of the confacial bioctahedral compound Cp*Ir(μ-Cl)₃Re(CO)₃ (3) in high yield. Whereas the substitution o

Full text of DOI:10.1016/j.poly.2009.04.023

Polyhedron 28 (2009) 2294–2300
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Preparation and reactivity of the heterobimetallic ReIr face-shared bioctahedral
compounds Cp*Ir(l-Cl)3Re(CO)3 and Cp*Ir(
l-SC6H4Me-4)3Re(CO)3: X-ray
diffraction structures and redox behavior
b
b,
Xiaoping Wang a, , Casey Hammons , Michael G. Richmond
*
*
a Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6460, United States
b Department of Chemistry, University of North Texas, Denton, TX 76203, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Thermolysis of the dinuclear compound [Cp*IrCl2]2 (1) with ClRe(CO)5 (2) leads to the formation of the
Received 22 December 2008
Accepted 15 April 2009
Available online 3 May 2009
confacial bioctahedral compound Cp*Ir(
chloride ligands in 3 is observed on treatment with excess p-methylbenzenethiol to furnish the sul-
fido-bridged compound Cp*Ir( -SC6H4Me-4)3Re(CO)3 (4), 3 undergoes fragmentation upon reaction with
l-Cl)3Re(CO)3 (3) in high yield. Whereas the substitution of the
l
tertiary phosphines [PPh3 and P(OMe)3] to furnish the mononuclear compounds Cp*IrCl2P and fac-ClRe-
(CO)3P2. Both 3 and 4 have been isolated and fully characterized in solution by IR and 1H NMR spectros-
copies, and their solid-state structures have been established by X-ray crystallography. The redox
properties of 3 and 4 have been explored by cyclic voltammetry, and the results are discussed relative
to extended Hückel MO calculations.
Keywords:
Rhenium–iridium compounds
Halide-bridged compounds
Sulfido-bridged compounds
Heterobimetallic compounds
X-ray crystallography
Ó 2009 Elsevier Ltd. All rights reserved.
O
1. Introduction
Os
SnPh3
R3P Pt
The catalysis of organic reactions using dinuclear mixed-metal
compounds remains under active investigation, with synergistic
bimetallic participation in C–H and C–C bond activation processes
promoting altered product distributions relative to the corre-
sponding homometallic systems [1]. An undisputed paradigm of
cooperative bimetallic reactivity involving alkyne coordination
and insertion into a metal–hydride bond has recently been demon-
strated by Adams et al. in the case of the mixed-metal compound
O
H
H
(R = But)
R3P
Os
SnPh3
Pt
H
Ph
H
ð1Þ
Ph
Ph
H
HOsPtð COÞ ðSnPh3ÞðPBut3Þ. Eq. (1) shows this particular reaction,
H
4
and control experiments and MO calculations confirm the fact that
the platinum metal serves as the initial site for alkyne coordina-
tion, leading to a weakened Os–H bond, which in turn facilitates
the ensuing alkyne insertion and formation of the vinylidene spe-
R3P
SnPh3
Pt
Os
cies OsPtðCOÞ ðSnPh3ÞðPBut3Þ½
l
ꢀ HC2ðHÞPhꢁ [2]. The role played by
4
Severin and co-workers have shown that heterobimetallic com-
pounds based on a M(
-X)3M0 architecture can serve as highly ac-
heterobimetallic species in Fischer–Tropsch chemistry, alkyl and
CO insertion reactions, alkyne and alkene hydrogenations, and
the reversible reduction of hydronium ions to H2 by FeNi hydrog-
enases continues to receive attention, and the mechanistic insight
afforded by the mixed-metal species in these different reactions
cannot be underscored in terms of modeling heterogeneous cata-
lysts and biological processes [3].
l
tive catalyst precursors in Oppenauer-type oxidations of alcohols
and atom-transfer radical addition (ATRA) reactions to alkenes
[4]. Accordingly, the directed synthesis of new heterobimetallic
systems is warranted if a full understanding of the cooperative
synergism between dissimilar metals is to be unraveled in the
above catalytic reactions. Severin has outlined several different
synthetic methodologies that may be employed in the synthesis
of M(
compound and a ‘‘lightly activated” or weakly bound solvent com-
l
-X)3M0 compounds, with the union of a halide-containing
* Corresponding authors. Tel.: +1 940 565 3548; fax: +1 940 565 4318 (M.G.
Richmond).
E-mail addresses: wangx@ornl.gov (X. Wang), cobalt@unt.edu (M.G. Richmond).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.04.023

X. Wang et al. / Polyhedron 28 (2009) 2294–2300
2295
plex providing a clean route that leads to the formation of a pleth-
ora of different M(
-X)3M0 derivatives [5]. An elegant example
demonstrating this concept involves the synthesis of (
6-arene)R-
u( -Br)3Re(CO)3 (where arene = benzene, cymene, 1,3,5-Et3C6H3)
from the reaction of [(
6-arene)RuBr2]2 with [ReBr(THF)(CO)3]2,
Innovative Technology solvent purification system. All distilled sol-
vents were stored in Schlenk storage vessels equipped with high-
vacuum Teflon stopcocks [10]. The combustion analysis on 3 was
performed by Atlantic Microlab, Norcross, GA.
The reported IR data were recorded on a Nicolet 6700 FT-IR
spectrometer, while all 1H spectra were recorded at 500 MHz on
a Varian VXR-500 spectrometer. The ESI-APCI mass spectrum of 4
was recorded at the UC San Diego mass spectrometry facility in
the positive ionization mode.
l
g
l
g
as depicted in Eq. (2). Here the formal loss of THF and splitting of
the halide bridges in the latter dimer afford the mononuclear rhe-
nium species ‘‘BrRe(CO)3” that is readily scavenged by the donating
halide ligands associated with the (g
6-arene)RuBr2 fragment. The
driving force for this and related reactions is entropically driven,
and the formation of new bridging metal–halogen bonds in the
binuclear RuRe product compensates for the loss of the weakly
bound THF molecules.
2.2. Synthesis of Cp*Ir(l-Cl)3Re(CO)3 from the thermolysis of
[Cp*IrCl2]2 with ClRe(CO)5
To 10 mg (0.013 mmol) of 1 in a 100 mL Schlenk round-bottom
flask under argon flush was added 20 mL of CH2Cl2, followed by
9.1 mg (0.025 mmol) of 2. The solution was then heated at reflux
over night and allowed to cool to room temperature, at which time
TLC analysis revealed the consumption of the latter starting mate-
rial and a large spot at the origin of the TLC plate belonging to the
desired compound 3. The solvent was removed under vacuum and
the residue recrystallized from a minimum amount of CH2Cl2/ben-
zene to yield 3 as a golden-yellow solid in 91% yield (16 mg). IR
R
Br
Br
Br
Ru
Ru
Br
R
(CH2Cl2): t .
(CO) 2037 (s), 1919 (s, broad) cmꢀ1 1H NMR (CDCl3):
THF
Re
Br
d 1.90 (s, Cp*). Anal. Calc. for C13H15Cl3IrO3Reꢂ1/8C6H6: C, 23.12;
ð2Þ
H, 2.21. Found: C, 22.87; H, 2.22%.
Re
2.3. Synthesis of Cp*Ir(
methylbenzenethiol
l-SC6H4Me-4)3Re(CO)3 from 3 and p-
Br
R
THF
Br
Br
Ru
To a 250 mL Schlenk round-bottom flask was added 50 mg
(0.071 mmol) of 3, followed by the addition of 50 mL of toluene
via cannula. The slurry was stirred for several minutes to ensure
complete dissolution of 3, after which time 35 mg (0.28 mmol;
slight excess) of p-methylbenzenethiol was added in one portion
and the contents heated at reflux for 1.5 h. TLC analysis of the
crude reaction solution in CH2Cl2/hexane (1:9) revealed the pres-
ence of the desired product 3 as a bright yellow spot at Rf = 0.86,
along with a trace amount of an orange spot at Rf = 0.80 ascribed
-THF
Re
Br
Recently, we reported our results on the synthesis of the chlo-
rine-bridged compound ( -
6-cymene)Ru( -Cl)3Re(CO)3 from [(g6
g
l
cymene)RuCl2]2 and ClRe(CO)5. Here we capitalized on known
lability of the CO groups in the latter reagent to generate the unsat-
urated species ‘‘ClRe(CO)4” under thermal and photochemical acti-
vation, which in turn reacts with the starting ruthenium dimer to
furnish the observed heterobimetallic end-product [6]. The trap-
ping of an in situ generated unsaturated species upon loss of CO
to Cp*Ir(l-Cl)(l-SC6H4Me-4)2Re(CO)3 and some material that re-
mained at the origin. 3 was subsequently isolated by column chro-
matography over silica gel using the aforementioned mobile phase
in 64% yield (44 mg). IR (CH2Cl2): t(CO) 2012 (s), 1902 (s, broad) -
cmꢀ1 1H NMR (CDCl3): d 1.30 (s, 15 H, Cp*), 2.32 (s, 9 H, Me-4),
.
7.06 (d, 6 H, 3J = 8 Hz, aryl), 7.61 (d, 6 H, 3J = 8 Hz, aryl). ESI-MS
(m/z): 988.97 [3+Na]+, 845.01 [3-SC6H4-Me-p]+.
represents an alternative protocol for the preparation of M(
X)3M0 compounds. Herein we present our data on the synthesis
and physical characterization of Cp*Ir( -Cl)3Re(CO)3 (3) and
the corresponding sulfido-bridged product Cp*Ir( -SC6H4Me-
l-
l
2.4. X-ray crystallographic data
l
4)3Re(CO)3 (4). Preliminary reactions between 3 and phosphine
ligands support the fragmentation of the starting heterobimetallic
compound to mononuclear species.
Single crystals of 3 and 4ꢂ1/2CH2Cl2 suitable for diffraction anal-
ysis were grown from CH2Cl2 solutions containing each compound
that had been layered with hexane. The X-ray data for 3 and
4ꢂ1/2CH2Cl2 were collected on an APEX II CCD-based diffractome-
ter at 100(2) K. The frames were integrated with the available
APEX2 [11] software package using a narrow-frame algorithm, and
the structures were solved and refined using the SHELXTL program
package [12]. Each molecular structure was checked using PLATON
[13], and all nonhydrogen atoms were refined anisotropically.
The hydrogen atoms in 3 and 4ꢂ1/2CH2Cl2 were assigned calculated
positions and allowed to ride on the attached carbon heavy atom.
The refinement for 3 converged at R = 0.0534 and Rw = 0.1575 for
2. Experimental
2.1. General
The starting materials [Cp*IrCl2]2[7] and ClRe(CO)5[8] used in
the synthesis of 3 were prepared by established literature proce-
dures. The chemicals IrCl3ꢂxH2O (Engelhard), Re2(CO)10 (Pressure
Chemical), and p-methylbenzenethiol (Aldrich) were used as re-
ceived, while the pentamethylcyclopentadiene employed in the
synthesis of 1 was prepared from 2-bromo-2-butenes (isomeric
mixture) [9], the latter which was purchased from Aldrich. The
reaction solvents were either distilled from an appropriate drying
agent under argon using Schlenk techniques or obtained from an
3179 independent reflection with I > 2
ues for 4ꢂ1/2CH2Cl2 obtained at R = 0.0181 and Rw = 0.0374 for
7729 independent reflection with I > 2 (I). The X-ray data and pro-
r(I), with convergence val-
r
cessing parameters are reported in Table 1, with selected bond dis-
tances and angles quoted in Table 2.

2296
X. Wang et al. / Polyhedron 28 (2009) 2294–2300
Table 1
auxiliary electrode, and the reference electrode utilized a silver wire
as a quasi-reference electrode. The reported potential data were
standardized against the formal potential of the Cpꢃ2Fe=Cpꢃ2Feþ
(internally added) redox couple, taken to have E1/2 = ꢀ 0.20 V [14].
X-ray crystallographic data and processing parameters for 3 and 4ꢂ1/2CH2Cl2.
Compound
3
4ꢂ1/2CH2Cl2
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P2(1)/n
9.622(1)
14.776(2)
12.045(2)
triclinic
ꢀ
P1
10.037(2)
12.102(2)
15.679(3)
75.35(3)
84.78(3)
73.06(3)
1762.3(6)
C34.5H37ClIrO3ReS3
1009.67
2.6. Extended Hückel MO calculations
The extended Hückel calculations reported here were carried
out using the original program developed by Hoffmann and Lips-
comb [15], as modified by Mealli and Proserpio [16]. The weighted
Hij’s contained in the program were used in the calculations, and
the input Z-matrices for 3 and 4 were constructed from the avail-
able X-ray data, with the predefined CACAO packaged Cp moiety
replacing the Cp* ligand in each compound and methyl groups
substituted for the p-tolyl groups in 4.
a
(°)
b (°)
90.003(1)
c
(°)
V (Å3)
1712.6(4)
C13H15Cl3IrO3Re
611.86
Molecular formula
Formula weight
Formula units per cell (Z)
Dcalc. (Mg/m3)
4
2
2.730
0.71073
15.296
1.903
0.71073
7.489
k (Mo K
a
)
) (Å)
l
(mmꢀ1
Absorption correction
semi-empirical
from equivalents
0.6243/0.1928
15508
semi-empirical
from equivalents
0.1772/0.1197
21693
3. Results and discussion
Absorption correction factor
Total reflections
Independent reflections
3179
3179/78/197
0.0534
0.1575
1.167
7729
7729/4/416
0.0181
0.0374
1.095
3.1. Syntheses and X-ray diffraction structure of Cp*Ir(l-Cl)3Re(CO)3
(3)
Data/restraints/parameters
a
R1 [I P 2
r
(I)]
b
wR2 (all data)
Goodness-of-fit (GOF) on F2
Thermolysis of 1 and 2 (equimolar in metal) in refluxing CH2Cl2
furnishes the new heterobimetallic compound 3, as assessed by IR
and NMR analysis of the reaction solution before formal work-up;
heating 1 and 2 in either 1,2-dichloroethane or toluene also affords
3 without complications. Scheme 1 shows the reaction leading to 3.
Compound 3 could not be purified by column chromatography
employing traditional supports such as silica gel and alumina be-
cause of the irreversible binding of 3 to the chromatographic sup-
D
q
(max),
D
q
(min) (e/Å3)
3.174, ꢀ3.866
0.774, ꢀ0.768
a
R1
R2 ¼ f
¼
R
R
kFo j ꢀ j Fck= j Fo j.
R
2
2
1=2
½wðF2o ꢀ F2c Þ ꢁ=
R
½wðF2oÞ ꢁg
.
b
Table 2
Selected bond distances (Å) and angles (°) in 3 and 4ꢂ1/2CH2Cl2.
Compound 3
Bond distances
Cl
Cl
Re(1)–C(13)
Re(1)–C(12)
Re(1)–Cl(2)
Ir(1)–Cl(1)
Ir(1)–Cl(3)
1.89(2)
1.92(2)
2.510(5)
2.439(4)
2.461(4)
Re(1)–C(11)
Re(1)–Cl(1)
Re(1)–Cl(3)
Ir(1)–Cl(2)
1.90(2)
2.504(4)
2.512(4)
2.452(4)
1.7663(5)
*CpIr
IrCp*
Cl
Re
Cl
Cl
Ir(1)–centroida
Bond angles
1:2 stoichiometry
C(13)–Re(1)–C(11)
C(11)–Re(1)–C(12)
Ir(1)–Cl(2)–Re(1)
O(1)–C(11)–Re(1)
O(3)–C(13)–Re(3)
86.3(8)
87.7(8)
84.7(1)
178(2)
176(2)
C(13)–Re(1)–C(12)
Ir(1)–Cl(1)–Re(1)
Ir(1)–Cl(3)–Re(1)
O(2)–C(12)–Re(2)
88.4(8)
85.1(1)
84.4(1)
177(2)
Cl
Cl
Compound 4ꢂ1/2CH2Cl2
Bond distances
Re(1)–C(3)
Re(1)–C(1)
Re(1)–S(2)
compound 3
Cp*Ir
Re
1.910(3)
1.926(3)
2.5030(9)
2.3973(9)
2.406(1)
Re(1)–C(2)
Re(1)–S(3)
Re(1)–S(1)
Ir(1)–S(2)
1.924(3)
2.515(1)
2.509(1)
2.403(1)
1.8058(1)
Cl
Ir(1)–S(3)
Ir(1)–S(1)
Ir(1)–centroidb
p-MeC6H4SH (excess)
Bond angles
C(3)–Re(1)–C(2)
C(2)–Re(1)–C(1)
S(1)–Re(1)–S(3)
S(3)–Ir(1)–S(2)
S(2)–Ir(1)–S(1)
90.3(1)
92.3(1)
75.70(3)
79.83(3)
80.56(4)
C(3)–Re(1)–C(1)
S(2)–Re(1)–S(3)
S(2)–Re(1)–S(1)
S(3)–Ir(1)–S(10
90.0(1)
75.73(3)
76.68(3)
79.85(3)
a
*
*
Mean Ir(1)–C distance for the Cp carbons C(1)–C(5).
S
S
b
Mean Ir(1)–C distance for the Cp carbons C(4)–C(8).
compound 4
Cp*Ir
Re
2.5. Electrochemical studies
The reported cyclic voltammetry data were recorded on a PAR
Model 273 potentiostat/galvanostat, equipped with positive feed-
back circuitry to compensate for iR drop. The homemade three-elec-
trode cell that was employed allowed the cyclic voltammograms to
be recorded under oxygen- and moisture-free conditions. A plati-
num disk (area = 0.0079 cm2) was utilized as the working and
S
Scheme 1.

X. Wang et al. / Polyhedron 28 (2009) 2294–2300
2297
Fig. 1. Thermal ellipsoid plot of 3 (left) and 4ꢂ1/2CH2Cl2 (right) showing the thermal ellipsoids at the 50% probability level. The accompanying solvent molecule in the latter
structure has been omitted for clarity.
ports, necessitating the use of recrystallization in order to purify 3.
Isolated yields of 3 ranged from good to excellent and were readily
achieved through recrystallization of the crude reaction material
using the non-coordinating solvents CH2Cl2 and benzene. 3 was
isolated as an air-stable golden-yellow solid, and samples of 3
maintained under argon did not exhibit any visible sign of decom-
position over the course of several months; however, exposure of 3
to atmospheric moisture led to the slow decomposition of 3. This
same decomposition was noticeably accelerated by directly treat-
ing 3 with water, consistent with the reactive nature of the halide
the solid-state structure of 3 and reveals a molecular motif predi-
cated on a triply bridged confacial bioctahedral geometry, where
the three chlorines function as the common face-sharing ligands.
Assuming the occupation of three coordination sites by the Cp*
ligand, each metal center in 3 is formally six-coordinate and
electronically saturated according to the Effective Atomic Number
(EAN) rule when the bridging chlorides are treated as 3e-donating
ligands. The structure of 3 is analogous to the bromine-bridged
derivative Cp*Ir(l-Br)3Re(CO)3 prepared by Severin and co-work-
ers [22], and represents the only heterobimetallic ReIr derivative
containing face-sharing chlorine ligands on file with the Cam-
bridge Structural Data Center [23]. The internuclear Re(1)ꢂ ꢂ ꢂIr(1)
distance of 3.3424(8) Å in 3 precludes any significant metal–metal
bonding when contrasted with the Re–Ir single-bond lengths of
2.8081(6), 2.9013(6), and 2.8519(2) Å reported for the heterobime-
bridging ligands in related M(l
-Cl)3M0 dimers and formation of
hydrolysis-derived species representing a significant decomposi-
tion manifold [17].
CO dissociation in XRe(CO)5 has been shown to be facile and
facilitated by the ancillary halide ligand, facts experimentally
established by different research groups over three decades ago
[18]. Essentially quantitative yields of 3 may also be achieved by
making use of the lability of the CO groups in 2 in the presence
of the weak donor solvent MeCN. The cis labilization exerted by
the chloride ligand in 2 leads to facile loss of cis CO groups and
the in situ generation of the ‘‘lightly activated” compound fac-
ClRe(CO)3(MeCN)2.[19] Moreover, the thermolysis of 2 has been
kinetically studied and found to proceed by a rapid first-order pro-
cess involving dissociative CO loss, exhibiting a t1/2 ca. 25 min at
60 °C [20]. Reaction of the in situ generated fac-ClRe(CO)3(MeCN)2
with 1 then gives the desired product 3.1 The proposed reaction se-
quence was verified by a control experiment between independently
synthesized fac-ClRe(CO)3(MeCN)2 and 1, which afforded 3 in >90%
yield. Finally, 3 may be synthesized by a photochemical route
employing near-UV irradiation (366 nm). Loss of CO in 2 upon opti-
cal excitation leads to the unsaturated intermediate ClRe(CO)4 [21],
which in turn is free to react with 1, followed by an accompanying
redistribution of a Cp*IrCl2 fragment.
tallic compounds Cp*(CO)Ir(
CB10H11], and [Cp*Ir(PMe3)(
[24]. The structural absence of a metal–metal bond in 3 has, in fact,
been theoretically confirmed in related L3M( -X)ML3 compounds
l
-CO)2Re(CO)Cp*, [ReIr(CO)3Cp*(
g
5-7-
l
-S)2Re(NC6H3Me2-2,6)2], respectively
l
by extended Hückel MO calculations [25]. Here the tethering of
the d6-[CpIr]2+ and d6-[Re(CO)3]+ fragments by three chloride li-
gands (Clꢀ) gives rise to a filled set of low-energy d orbitals incapa-
ble of metal–metal bonding.2 The Re–Cl distances range from
2.504(4) Å [Re(1)–Cl(1)] to 2.5123(4) Å [Re(1)–Cl(3)] and display a
mean distance of 2.509 Å, while the slightly shorter Ir–Cl distances
range from 2.439(4) Å [Ir(1)-Cl(1)] to 2.461(4) Å [Ir(1)–Cl(3)] and re-
veal a mean length of 2.484 Å. Both sets of metal–halides distances
are in excellent agreement with the mean Re–Cl and Ir–Cl bond dis-
tances tabulated by Orpen et al.[26]. The remaining bond distances
and angles are unremarkable and require no comment.
3.2. Syntheses and X-ray diffraction structure of Cp*Ir(l-SC6H4Me-
4)3Re(CO)3 (4)
3 was characterized by IR and 1H NMR spectroscopies, combus-
tion analysis, and X-ray crystallography. The IR spectrum exhibits
two terminal carbonyl stretching bands for the Re–CO groups at
Due to the interest in functionalized dendrimers and star-
shaped molecules based on M2( -SR)3 cores, we next explored
l
2037 and 1919 cmꢀ1 consistent with the idealized C3 symmetry
the functionalization of 3 with p-methylbenzenethiol [27]. Facile
substitution of the three chloride ligands in 3 by p-methylbenze-
nethiol (slight excess) is observed in refluxing toluene to afford
v
displayed by the Re(CO)3 moiety, while the 1H NMR spectrum re-
veals a single resonance at d 1.90 for the Cp* ligand. Fig. 1 shows
1
A control experiment (1H NMR) involving the reaction of MeCN with 1 was
2
conducted to explore the formation of the solvated species Cp*IrCl2(MeCN) which, in
principal, could then undergo reaction with fac-ClRe(CO)3(MeCN)2 to furnish 3. While
no direct NMR evidence for the MeCN-induced fragmentation of 1 was observed, our
The formal union of two d6-ML3 moieties is net non-bonding because of the filled
t2g set of orbitals belonging to each metal. Inclusion of bridging ligands having
p
character does not change the situation due to the existence of the appropriate
symmetry-adopted linear combination orbitals (SALCs) that negate any net bonding
between the metal centers.
data do not rule out
a small equilibrium concentration (<5%) of the ligand-
substitution product Cp*IrCl2(MeCN).

2298
X. Wang et al. / Polyhedron 28 (2009) 2294–2300
the sulfido-bridged compound 4 as the major product, along
with a trace amount of material whose spectroscopic properties
were indicative of the bis-substituted sulfido-bridged species
The reaction of 3 with the rigid bidentate phosphine 4,5-
bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) was also
probed by 31P NMR spectroscopy, given our longstanding interest
in the coordination chemistry and activation of this particular
ligand by polynuclear metal clusters [30]. As in the above reactions
Cp*Ir(l-Cl)(l-SC6H4Me-4)2Re(CO)3. This latter material was exam-
ined for its reactivity with added p-methylbenzenethiol and found
to give 4. Whereas 3 was unstable with respect to chromatographic
supports, 4 could be readily purified by column chromatography
over silica gel. 4 was characterized in solution by IR spectroscopy,
with monodentate phosphines, rapid fragmentation of
3 is
observed upon treatment with a measured amount of bpcd (1:2 ra-
tio), with new 31P resonances recorded at d 22.28 and ꢀ26.91 that
are readily assignable to the known chelated rhenium compound
which revealed two strong t
(CO) bands at 2013 and 1902 cmꢀ1
consistent with the A and E symmetry bands belonging to the
fac-ClRe(CO)3(bpcd) (cf.: d 22.29) and the ionic compound
fac-Re(CO)3 moiety. The observed ca. 20 cmꢀ1 shift to lower fre-
[Cp*IrCl(bpcd)][Cl], respectively [31,32]. The latter product is
assumed to derive from chloride loss upon ring-closure of the
quency of each carbonyl band in 4 vis-a-vis the
is consistent with the presence of the stronger
t
(CO) bands in 3
r
donating sulfido
pendent phosphine in the intermediate species Cp*IrCl2(
Having established the lability of in phosphine-promoted
g
1-bpcd).
ligands in the former compound. The 1H NMR spectrum of 4 exhib-
ited two high-field resonances at d 1.30 and 2.32 that are readily
ascribed to the Cp* and p-Me moieties, respectively, with the aryl
hydrogens at d 7.06 and 7.61 exhibiting a classic AX pattern having
3
fragmentation reactions, further substitution studies were
abandoned.
a J/Dd value of 0.03. Finally, the ESI mass spectrum of 4 displayed
3.4. Redox properties and MO data for 3 and 4
two prominent peaks at m/z 988.97 and 845.01 that are attributed
to a pseudo-molecular ion for [3+Na]+ and the loss of a single sul-
fido ligand for [3-SC6H4-Me-p]+, respectively, consistent with the
formulated structure. The unequivocal identity of 4, as the CH2Cl2
solvate, was subsequently established by X-ray diffraction analysis.
The thermal ellipsoid plot of 4 in Fig. 1 establishes the presence of
the three bridging sulfido groups and the local octahedral coordi-
nation about the Re(1) and Ir(1) centers. 4 is unique insomuch as
it represents, to our knowledge, the first structurally characterized
sulfido-bridged heterobimetallic ReIr compound exhibiting a con-
facial bioctahedral geometry. The overall molecular structure is
identical to that of 3, and the internuclear Re(1)ꢂ ꢂ ꢂIr(1) distance
of 3.3718(7) Å is elongated by 0.030 Å compared to the corre-
sponding distance found in 3. The formation of 4 in near quantita-
tive yield, along with the collective spectroscopic and mass
spectral data, confirm the fact that metal redistribution to give
The electrochemical properties of 3 and 4 were next investi-
gated the cyclic voltammetry at platinum electrodes in THF at
room temperature using 0.2 M TBAP as the supporting electrolyte.
The CV of 3 when examined at a scan rate of 250 mV/s over the po-
tential range of 1.5 to ꢀ1.5 V revealed a diffusion-controlled irre-
versible oxidation at Eap ¼ 1:42 V [33]. The nature of the orbital
associated with this oxidation wave in 3 was established by MO
analysis of the model complex CpIr(l-Cl)3Re(CO)3 at the extended
Hückel level. The energy level of the HOMO in 3 was computed to
be ꢀ11.52 eV by extended Hückel MO calculations, and the HOMO
is best described as an antibonding Re–Ir orbital that is largely irid-
ium based and formed from the overlap of metal dz2 and chlorine
pz orbitals, as depicted below.3 The general orbital composition of
the HOMO in 3 is similar to the a2” HOMO reported by Hoffmann
and co-workers for a series of homobimetallic L3M(l-X)3ML3 com-
the homometallic products [Cp*Ir(l l-
-SR)3IrCp*]+ and [(OC)3Re(
pounds [25,34]. Finally, the computed Mulliken reduced overlap
population (ROP) of ꢀ0.095 between the two metal centers in 3 rein-
forces the absence of any net bonding between the two metal
centers.
SR)3Re(CO)3]ꢀ is not an important manifold in the reaction involv-
ing 3 with added thiol [28].
3.3. Reaction of 3 with tertiary phosphines
The reactivity of 3 with various phosphines was next ex-
plored by NMR spectroscopy, with the synthesis of ligand-substi-
CO
tuted derivatives possessing an intact heterobimetallic Ir(l-
HOMO (-11.52 eV)
CO
Cl)3Re core as our targeted goal. To our knowledge, no reports
exist for the reaction of such halide-bridged mixed-metal sys-
tems and phosphine donor ligands. 3 reacts rapidly with a slight
excess of added PPh3 (ca. 3.1 equiv. per 3 employed), leading to
the disruption of the starting chloride-bridged dimer and forma-
CO
Cl
Cl
Cp*
PPh3
PPh3
PPh3
Cp*Ir
ð3Þ
Re
Re
Cl
Ir
Cl
Cl
Ph3P
Cl
tion of the known mononuclear compounds fac-ClRe(CO)3(PPh3)2
and Cp*IrCl2(PPh3), as depicted in Eq. (3) [29]. Similar reactivity
was found when an excess of P(OMe)3 was employed in the
reaction with 3, with the corresponding compounds fac-ClRe-
(CO)3[P(OMe)3]2 and Cp*IrCl2 [P(OMe)3] observed by NMR
spectroscopy.
3
The HOMO in the model compound CpIr(l-Cl)3Re(CO)3 consists of significant
atomic contributions from the iridium (84%) and rhenium (4%) centers, and the three
bridging chlorines (collectively 8%). Here the three in-phase linear combination of pz
chlorine orbitals are situated antisymmetric relative to a twofold rotation axis defined
by the metal atoms.

X. Wang et al. / Polyhedron 28 (2009) 2294–2300
2299
deposit@ccdc.cam.ac.uk.
Acknowledgment
Generous and continued financial support from the Robert A.
Welch Foundation (Grant B-1093-MGR) is much appreciated.
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l

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