Monophosphine-o-carborane sulfide as a noninnocent ligand for C,S, S,S′, and B,S,S′ coordination modes of half-sandwich iridium and rhodium complexes

Article abstract of DOI:10.1021/om200528q

Half-sandwich iridium and rhodium complexes with three different coordination modes were successfully synthesized by using the monophosphine-o-carborane sulfide 1-SPPh₂-1,2-closo-C ₂B₁₀H₁₁ (1) as the ligand. Tre

Full text of DOI:10.1021/om200528q

ARTICLE
pubs.acs.org/Organometallics
Monophosphine-o-Carborane Sulfide as a Noninnocent Ligand for C,
S, S,S0, and B,S,S0 Coordination Modes of Half-Sandwich Iridium and
Rhodium Complexes
Zi-Jian Yao and Guo-Xin Jin*
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University,
Shanghai 200433, People's Republic of China
S Supporting Information
b
ABSTRACT: Half-sandwich iridium and rhodium complexes with
three different coordination modes were successfully synthesized by
using the monophosphine-o-carborane sulfide 1-SPPh2-1,2-closo-
C2B10H11 (1) as the ligand. Treatments of the dimeric metal com-
plexes [Cp*M(μ-Cl)Cl]2 (M = Ir, Rh; Cp* = η5-C5Me5) with the
lithium salt of monophosphine-o-carborane sulfide generate the C,S-
coordinated complexes [Cp*IrCl(CabC,S)] (2) and [Cp*RhCl(CabC,S)]
(3) (CabC,S = (1-SPPh2-1,2-closo- C2B10H10)ꢀ), respectively. Com-
pound 1 can be modified to give the corresponding thiol 1-SH-2-
SPPh2-1,2-closo-C2B10H10 (4). The unexpected B,S,S0 coordination
0
0
mode product [Cp*Ir(CabB,S,S )] (5) (CabB,S,S = (η1-S0)(η1-SPPh2)-
(η1-1,2-closo-C2B10H9)) through BꢀH activation was obtained by the
reaction of [Cp*Ir(μ-Cl)Cl]2 with the lithium salt of 4. However,
0
0
[Cp*Rh(μ-Cl)Cl]2 gave the product [Cp*RhCl(CabS,S )] (6) (CabS,S = (1-S0-2-SPPh2-1,2-closo- C2B10H10)ꢀ) with the S,S0 mode
under the same conditions. When it was heated in CH3OH, complex 6 gradually transformed from a closo-carborane complex to the
zwitterionic nido-carborane complex [Cp*Rh(7-S0-8-(SPPh2)-7,8-C2B9H10)] (7). They represent the first examples of half-
sandwich complexes incorporating a monophosphine-o-carborane sulfide ligand. In addition, the iridium complex 2 exhibits
catalytic activity up to 1.40 ꢁ 106 g of PNB (mol of Ir)ꢀ1 hꢀ1 for the polymerization of norbornene in the presence of
methylaluminoxane (MAO) as cocatalyst. All complexes were fully characterized by elemental analysis and IR and NMR
spectroscopy. The structures of 1, 2, and 5ꢀ7 were further confirmed by single-crystal X-ray diffraction.
’ INTRODUCTION
nuclear waste,10 and chalcogen-exchange reactions.11 Despite the
well-known affinity of phosphines for chalcogens and destruc-
tion of the transition-metal catalysts through oxidation of the
phosphorus-containing ligands, there are still very few studies on
the reactivity of carboranyl-based phosphorus oxide13aꢀd and
chalcogenide.13e,f Up to October 2010, only one crystal structure
for a carboranyl phosphine sulfide was given in the Cambridge
Crystallographic Database.12 Additionally, our previous studies
proved that a carboranyl-based half-sandwich complex is an
important model to form a variety of useful transition-metal com-
plexes.14 These complexes have advantages in solubility, thermal
stability, and flexible fine-tuning processes of half-sandwich
units,15 as well as applications in catalysis.14 Thus, the unexplored
reactivity of half-sandwich transition-metal complexes with mono-
phosphine-o-carborane chalcogenide has greatly encouraged us
to conduct the present study.
Since the discovery of 1,2-dicarba-closo-dodecaborane in the 1960s,
research interest in carboranyl- and carbollide-based transition-
metal complexes has greatly increased due to their high thermal
and chemical stabilities.1 Their various applications in the fields
of BNCT (boronꢀneutron capture therapy),2 catalysis,3 nuclear-
waste remediation,4 and ion-selective electrodes5 have also been
developed. The CꢀH bonds in this cage are moderately acidic
and can be deprotonated with strong bases; thus, the negatively
charged carbon atoms can be subsequently functionalized with
electrophilic reagents. Among these functionalized carboranyl deri-
vatives, monophosphine-o-carborane (1-PR2-1,2-closo-C2B10H11)
is one of the most attractive starting precursors.6 It has a high
tendency to coordinate to metal centers with its lone pair,7 and it
has one arylphosphine group that can satisfactorily stabilize the
metal ion by bulky steric effects.
Generally, tertiary phosphines are sensitive species that are
easily oxidized to produce more weakly basic oxidative products.
Among these compounds, phosphine chalcogenides have at-
tracted considerable attention because of their use for the
preparation of metal chalcogenide nanoparticles,8 the synthesis
of complexes with PꢀE (E = S, Se) ligands,9 the remediation of
Our previous systematic study exhibited the versatile coordi-
nation modes of monophosphine-o-carborane and their diverse
reactivities.16 We herein report some pioneering examples of
Received: June 27, 2011
Published: September 19, 2011
r
2011 American Chemical Society
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Organometallics
ARTICLE
unique half-sandwich transition-metal complexes using mono-
phosphine-o-carborane sulfide (1-SPR2-1,2-closo-C2B10H11) and
its thiolate derivative ((1-S-2-SPR2-1,2-closo-C2B10H10)ꢀ) as
noninnocent ligands. A series of Ir and Rh complexes containing
versatile coordination modes (C,S, S,S0, and B,S,S0) have been
conveniently obtained. The norbornene polymerization beha-
vior of some of these complexes has also been investigated. All
complexes were fully characterized by elemental analysis and IR
and NMR spectroscopy.
for X-ray diffraction analyses were obtained by the slow diffusion
of hexane into a saturated solution of 1 in dichloromethane. The
molecular structure of 1 and selected bond lengths and angles are
given in Figure 1.
Synthesis of C,S Coordination Mode Complexes 2 and 3.
The reaction of the lithium salt of a monophosphine-o-carborane
sulfide 1-Li-2-SPPh2-1,2-closo-C2B10H11 with 0.5 equiv of dimeric
metal complexes [(Cp*MCl2)2] (M = Ir, Rh) gave, after workup,
the half-sandwich C,S-chelated complexes [Cp*MCl(CabC,S)]
in good yields (Scheme 1) (M = Ir (2), 68%; M = Rh (3),
63%; CabC,S = 1-SPPh2-1,2-closo-C2B10H10). Despite the exis-
tence of a metalꢀcarbon bond, these complexes remain very
stable in the solid state in air. The reason for this can be attri-
buted to the formation of a five-membered chelate ring. They
are soluble in CH2Cl2 and THF and slightly soluble in hexane
and diethyl ether.
’ RESULTS AND DISCUSSION
In comparison with ordinary phosphines, monophosphine-o-
carborane shows high stability because of the bulky carborane
unit. The oxidation of these stable phosphines was studied by
Vin~as et al. very recently.13f However, the yields of 1-SPR2-2-R0-
1,2-closo-C2B10H10 were not very high, even when the reaction
mixture was refluxed in toluene for several days. In our present
study, we found that addition of a small amount of base such as
NEt3 could largely prompt the oxidation process. Under mild
reaction conditions, the target product 1-SPPh2-1,2-closo-
C2B10H11 (1) was obtained with a high isolated yield of 81%
after column chromatography. The detailed synthesis procedure
as well as 1H, 13C, 31P, and 11B NMR spectral data are presented
in the Experimental Section. The sharp signal at δ 51.33 ppm in
the 31P NMR spectrum shows obvious evidence for the oxidation
of the phosphorus atom, which falls in the range expected for
compounds that contain P(S) moieties.13f Single crystals suitable
Complexes 2 and 3 were characterized by various spectro-
scopic data and elemental analyses. For complex 2, the 1H NMR
spectrum in CDCl3 shows a sharp peak at δ 1.49 and several
groups of signals in the range of 8.33ꢀ7.47 ppm, which can be
assigned to the methyl groups of Cp* and protons in aromatic
rings, respectively. In the 13C NMR spectrum of 2, the resonance
of the Cp* ring carbon atoms was found at δ 91.3 ppm and those
of the methyl groups at δ 8.8 ppm. The 11B NMR spectrum
exhibits resonances at δ 2.18 (2B), ꢀ5.47 (4B), and ꢀ8.64 (4B),
while that of 3 shows a similar pattern. In the 31P NMR spectrum,
only one resonance at about δ 60.79 ppm was observed, which
was shifted downfield in comparison to that of 1. The IR
spectrum displays a typical strong and broad characteristic
BꢀH absorption at approximately 2565 cmꢀ1, and the absorp-
tion at 625 cmꢀ1 is ascribed to PdS bond vibrations. A detailed
analysis of the spectroscopic data (IR and 1H, 13C, 11B, and 31
P
NMR spectroscopy) indicates that the structure of 3 is identical
with that of 2, which was also confirmed by elemental analysis.
Single crystals suitable for X-ray diffraction analyses were
obtained by the slow diffusion of hexane into a saturated solution
of 2 in dichloromethane. Complex 2 crystallized in the mono-
clinic space group P21/c. The crystallographic data of 2 are
summarized in Table 1. Figure 2 shows the molecular structure of
2 together with selected bond lengths and angles. The molecular
structure shows that the geometry at the iridium(III) center is
that of a three-legged piano stool with the iridium atom
coordinated by the η5-Cp* and the C and S atoms, as well as
one chloride ligand. The metal center has a distorted-octahedral
environment, assuming that the η5-Cp* group occupies three fac
coordination sides. The of Ir(1)ꢀC(1) and Ir(1)ꢀCl(1) bond
distances are approximately 2.111(3) and 2.4161(6) Å, respec-
tively, which are both within the range of known values for these
bonds in analogous complexes.14 The P(1)ꢀS(1) bond length of
2 is greater than that of 1, probably due to the coordinative
Figure 1. Molecular structure of 1 with thermal ellipsoids drawn at the
30% level. Selected bond lengths (Å) and angles (deg): P(1)ꢀC(1),
1.883(3); P(1)ꢀS(1), 1.9397(10); C(1)ꢀC(2), 1.643(3); C(2)ꢀC(1)ꢀ
P(1), 114.84(17); C(1)ꢀP(1)ꢀS(1), 109.82(8); C(3)ꢀP(1)ꢀC(9),
110.27(12).
Scheme 1. Synthesis of C,S Coordination Mode Complexes 2 and 3
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ARTICLE
Table 1. Crystallographic Data and Structure Refinement Parameters for 1, 2, and 5ꢀ7
1
2
5
6
7
chem formula
C
14H21B10PS
C24H35B10ClIrPS
722.30
C24H34B10IrPS2
717.90
C24H34B10ClRhPS2
665.07
C24H35B9PRhS2
618.81
fw
360.44
T/K
293(2)
173(2)
296(2)
296(2)
173(2)
λ/Å
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
P21/c
0.710 73
triclinic
0.710 73
triclinic
0.710 73
triclinic
cryst syst
space group
P1
P1
P1
a/Å
30.126(11)
9.913(4)
14.001(5)
90
10.1268(7)
11.9506(8)
24.0726(16)
90
11.9243(13)
12.0239(14)
12.8524(14)
84.482(2)
62.969(2)
84.006(2)
1630.0(3)
2
11.596(5)
12.077(5)
12.949(6)
78.644(7)
87.963(7)
77.167(6)
1733.3(13)
2
11.6277(8)
11.8557(15)
12.0237(8)
99.3110(10)
112.3500(10)
99.7310(10)
1463.7(2)
2
b/Å
c/Å
α/deg
β/deg
111.102(5)
90
91.4750(10)
90
γ/deg
V/Å3
3901(2)
8
2912.3(3)
4
Z
F/Mg mꢀ3
μ/mmꢀ1
1.227
1.647
1.463
1.274
1.404
0.242
4.819
4.287
0.751
0.795
F(000)
1488
1416
704
676
632
θ range/deg
no. of rflns collected
completeness to θ/%
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
1.45ꢀ25.01
5870
1.69ꢀ27.89
21 504
1.71ꢀ27.56
11 900
1.76ꢀ27.01
12 106
1.80ꢀ28.24
11 368
95.9
99.5
98.1
98.2
98.3
3299/1/249
0.960
6926/0/358
1.068
7378/2/364
1.091
9865/48/722
1.033
7117/2/355
1.204
R1 = 0.0482,
wR2 = 0.1211
0.345, ꢀ0.236
R1 = 0.0194,
wR2 = 0.0541
1.039, ꢀ0.670
R1 = 0.0485,
wR2 = 0.1505
1.739, ꢀ1.567
R1 = 0.0619,
wR2 = 0.1862
0.781, ꢀ1.175
R1 = 0.0279,
wR2 = 0.0871
0.900, ꢀ0.999
largest diff peak, hole/e Åꢀ3
Synthesis of B,S,S0 and S,S0 Coordination Mode Com-
plexes 5 and 6. In view of another untouched CꢀH bond in
the carborane cage of 1, it is a natural extension for us to do the
stepwise modification of 1 after successful preparation of the C,S-
chelated complexes 2 and 3. Therefore, a thiolate-bridged model
was constructed on the basis of our previous systematic studies of
the 16-electron “pseudo-aromatic” Cp*MS2(C2B10H10) (M =
Co, Rh, Ir) complexes.17
As shown in Scheme 2, the half-sandwich complexes 5 and 6
were prepared in a one-pot reaction by the in situ formation of
the S-lithium salt of 1, followed by the addition of the dimeric metal
complex [Cp*MCl2]2 (M = Ir, Rh) in THF at room temperature.
0
Two different products, [Cp*IrCl(CabB,S,S )] (5) and [Cp*RhCl-
0
0
(CabS,S )] (6) (CabB,S,S =(η1-S0)(η1-SPPh2)(η1-1,2-closo-C2B10H9),
0
CabS,S = [1-S0-2-SPPh2-1,2-closo-C2B10H10]ꢀ), were obtained in
yields of 72% and 65%, respectively. Aside from this method, the
corresponding thiol 1-SH-2-SPPh2-1,2-closo-C2B10H10 (4) was
isolated with a good yield of 85%. Using NaH as a base, the
following reaction of 4 with [Cp*MCl2]2 (M = Ir, Rh) occurred
smoothly. For 5, the 1H NMR spectrum shows a sharp signal at δ
1.96 ppm for the Cp* resonance and several groups of signals in
the range of δ 8.32ꢀ7.38 ppm for the protons of the phenyl ring.
The 11B NMR spectrum shows overlapping signals at δꢀ0.60(3B),
ꢀ6.30 (3B), ꢀ9.39 (1B), and ꢀ12.58 (3B) ppm, whereas a
2:2:3:3 pattern is observed for 6. The 31P NMR spectra show
signals at δ 62.80 and 49.28 ppm for 5 and 6, respectively, which
further proved that the structures of these two complexes are
different. To our surprise, the iridium and rhodium complexes
exhibit different reactivities in this reaction. The iridium complex
Figure 2. Molecular structure of 2 with thermal ellipsoids drawn at the
30% level. All hydrogen atoms are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ir(1)ꢀC(1), 2.111(3); Ir(1)ꢀS(1), 2.3829(7);
Ir(1)ꢀCl(1), 2.4161(6); S(1)ꢀP(1), 1.9993(10); C(1)ꢀC(2), 1.768(4);
C(2)ꢀC(1)ꢀIr(1) 119.59(16); C(1)ꢀC(2)ꢀP(1), 111.86(16); P(1)ꢀ
S(1)ꢀIr(1), 105.65(3); C(2)ꢀP(1)ꢀS(1), 108.04(9).
interaction between the S atom and the metal center. The C(2)ꢀ
C(1)ꢀIr(1) angle of 119.59(16)° in 2 within the five-membered
ring is slightly larger than the expected 108°.
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ARTICLE
Scheme 2. Synthesis Procedure of B,S,S0 and S,S0 Coordination Mode Complexes 5 and 6
Figure 3. Molecular structures of 5 and 6 with thermal ellipsoids drawn at the 30% level. All hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg) are as follows. 5: Ir(1)ꢀS(1), 2.366(2); Ir(1)ꢀS(2), 2.431(2); S(2)ꢀC(2), 1.785(9); Ir(1)ꢀB(3), 2.116(10);
S(1)ꢀP(1), 1.990(3); C(1)ꢀC(2), 1.654(12); C(2)ꢀC(1)ꢀP(1), 119.8(6); S(1)ꢀIr(1)ꢀS(2), 91.12(9); Ir(1)ꢀS(2)ꢀC(2), 88.8(3); P(1)ꢀ
S(1)ꢀIr(1), 104.02(11); C(2)ꢀB(3)ꢀIr(1), 99.8(7); C(1)ꢀP(1)ꢀS(1), 107.9(3). 6: Rh(1)ꢀS(1), 2.385(3); Rh(1)ꢀS(2), 2.401(3); S(1)ꢀC(1),
1.750(14); S(2)ꢀP(1), 2.010(4); Rh(1)ꢀCl(1), 2.409(3); C(1)ꢀC(2), 1.775(18); S(1)ꢀRh(1)ꢀS(2), 92.75(10); C(1)ꢀS(1)ꢀRh(1), 112.1(4).
5 shows an unexpected B,S,S0 coordination mode via BꢀH
activation, whereas the rhodium complex 6 shows a normal S,
S0 mode. To the best of our knowledge, this carboranyl BꢀH
bond activation of ligand 1 induced by a metal complex has been
reported for the first time. A similar intramolecular oxidative
addition process involving a BꢀH bond was originally reported
by Hawthorne18 and other groups.19,20 The possible reason for
BꢀH bond activation may be due to the existence of a sulfur
bridge, which caused the electron-deficient metal center to be
located very close to the BꢀH vertices.
The distances of the MꢀS(C) bonds are 2.431(2) and 2.385(3)
Å for 5 and 6, respectively. These values are close to the
corresponding values for MꢀS bonds in analogous complexes17e
but are much longer than those in the 16-electron complexes
Cp*MS2[C2B10H10].21 This discrepancy may be ascribed to the
fact that the p-type interaction between the metal center and
sulfur atom was destroyed in the 18-electron complexes.22a,b
Additionally, the MꢀS distances of coordinatively unsaturated
complexes are generally shorter than those of the electronically
saturated complexes.22cꢀi For complex 5, the four-membered
ring C(2)ꢀB(3)ꢀIr(1)ꢀS(2), the five-membered ring B(3)ꢀ
C(1)ꢀP(1)ꢀS(1)ꢀIr(1), and the six-membered ring C(2)ꢀ
C(1)ꢀP(1)ꢀS(1)ꢀRh(1)ꢀS(2) were simultaneously formed
due to the insertion of the sulfur bridge. The IrꢀB bond length
(2.116(10) Å) is similar to reported values (Figure 4),17e,23 but
Complexes 5 and 6 crystallized in the triclinic space group P1
and the triclinic space group P1, respectively. The crystallo-
graphic data of 5 and 6 are summarized in Table 1. As shown in
Figure 3, complexes 5 and 6 adopt a three-legged piano-stool
geometry with a distorted-octahedral coordination environment.
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Figure 4. IrꢀB bond lengths of the analogous complexes (Å).
Scheme 3. Synthesis of the Nido S,S0 Coordination Mode
Zwitterionic Complex 7
and C(8)ꢀC(7)ꢀS(2). The Rh(1)ꢀS(1) (2.3248(7) Å) and
Rh(1)ꢀS(2) bond distances (2.2728(6) Å) are both shorter than
the corresponding bond of complex 6, respectively (Chart 1). On
the basis of the molecular framework of 7 (Figure 5), the four
atoms Rh(1), P(1), S(1), and S(2) are arranged on one side and
can be regarded as constituting the handle of a spoon-shaped
nido-carborane complex.
Norbornene Polymerization. On the basis of previous
work,14 we decided to investigate the use of the iridium complex
2 in homogeneous catalysis. Fortunately, complex 2 shows a
good catalytic activity in the polymerization of norbornene.
When the Al/Ir molar ratio was 2000, the catalytic activity of 2
was up to 1.40ꢁ 106 g of PNB (mol of Ir)ꢀ1 hꢀ1 (Table 2, entry 2).
However, when the Al/Ir ratio was further increased, the activity
appeared to decrease (Table 2, entries 3 and 4).
this bond is longer than those of an ordinary iridium boryl
complex (1.971ꢀ2.048 Å).24 The possible reason for the differ-
ence can be ascribed to the carborane cage. The electron density
of the boron atom was reduced because of the presence of the
electron-deficient carborane cage. For complex 6, the Rh(1)ꢀ
S(1) bond (2.385(3) Å) is shorter than the Rh(1)ꢀS(2)
coordinative bond (2.401(3) Å), which indicates a stronger
interaction between Rh and S(1). The dihedral angle between
S(1)ꢀRh(1)ꢀS(2) and S(2)ꢀP(1)ꢀC(2)ꢀC(1)ꢀS(1) is 4.7°
Synthesis of Zwitterionic Nido S,S0 Coordination Mode
Complex 7. Strong Lewis bases, such as alkoxides, amines, and
fluoride, are known to induce the deboronation of closo-carbor-
anes. Upon heating in CH3OH, the solution of 6 clearly changed
from dark red to dark green, and the clear solution turned turbid.
This result indicated that the neutral complex 6 readily loses one
boron atom and was gradually converted to the zwitterionic
complex [Cp*Rh(7-S0-8-(SPPh2)2-7,8-C2B9H10)] (7) (Scheme 3).
To explore the reactivity of this process, different weak bases
such as NaOAc, NaHCO3, and Na2CO3 were added to the
reaction solution. However, the products were all the same with
more or less different yields. In addition, the strong base CH3ONa
greatly prompted this reaction and complex 7 was obtained in
83% yield at ambient temperature.
The solubility of the nido-carborane complex 7 is much less
than that of the closo-carborane complex 6 because of the
destruction of a symmetric structure. X-ray-quality single crystals
of 7 were obtained by slow diffusion of n-hexane into a con-
centrated solution of the complex in CH2Cl2. The crystallographic
data of 7 are summarized in Table 1. The molecular structure of 7
with selected bond lengths and angles are given in Figure 5. The
coordination of the bidentate ligand 7-S0-8-(SPPh2)2-7,8-C2B9H10
to the Rh atom results in a six-membered RhPS2C2 ring. The four
atoms C(7), C(8), P(1), and S(2) nearly form a plane, with a
dihedral angle of 1.51° between the planes of S(2)ꢀP(1)ꢀC(7)
The microstructure of the obtained polynorbornenes were
1
characterized by H NMR and 13C NMR spectroscopy. The
polynorbornenes had similar 1H NMR and 13C NMR spectra. No
resonance was displayed at about δ 5.1 and 5.3 ppm in the 1H NMR
spectrum of the polynorbornene assigned to the cis and trans forms
of the double bond,25 which generally indicates the presence of the
ring-opening metathesis polymerization (ROMP) structure. The
13C NMR spectrum shows the four main groups of resonances δ
49.5, 49.1, 48.4, 47.1, 46.3, δ 38.2, δ 37.2, 34.8, 33.8, and δ 30.2,
29.0 ppm, attributed to carbons 2 and 3, carbons 1 and 4, carbon
7, and carbons 5 and 6, respectively (Scheme 4).26 The 13C NMR
spectrum is similar to that reported by Wu et al.25b and Patil
et al.27 These data indicate that the polynorbornene obtained
with the aforementioned catalysts is a vinyl-type (2,3-linked)
addition product: i.e., no ROMP was observed. Furthermore, the
13C NMR spectrum shows that the polymer is exo enchained. The
spectrum did not exhibit resonances in the δ 20ꢀ24 ppm region.
The presence of such resonances has been taken as evidence of
endo enchainment on the basis of mode studies.25 The multi-
plicity of the peaks suggested that the insertion of monomer units
took place in more than one stereospecific way. Therefore, the
obtained polynorbornenes were atactic.28 Indeed, all polynor-
bornenes are soluble at room temperature in chlorobenzene and
cyclohexane, which indicates low stereoregularity.25
along the S S vector.
3 3 3
All polynorbornenes obtained show similar IR spectra. The IR
spectra reveal the characteristic signals of polynorbornenes at about
943 cmꢀ1. Also, there are no absorptions at 1680ꢀ1620 cmꢀ1
,
especially at about 960 and 735 cmꢀ1, assigned to the trans and
cis forms of double bonds, respectively, which are characteristic
of the ROMP structure of polynorbornenes.25 These absorption
peaks at about 943 cmꢀ1 can be assigned to the ring system of
bicyclo[2.2.1]heptane, as Kennedy noted.29
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ARTICLE
Figure 5. (left) Molecular structure of 7 with thermal ellipsoids drawn at the 30% level. All hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Rh(1)ꢀS(1), 2.3248(7); Rh(1)ꢀS(2), 2.2728(6); S(2)ꢀC(8), 1.794(2); S(2)ꢀP(1), 2.0154(8); C(7)ꢀC(8), 1.584(3);
S(1)ꢀRh(1)ꢀS(2), 100.86(2); C(8)ꢀS(2)ꢀRh(1), 115.83(8); C(8)ꢀC(7)ꢀP(1), 116.49(16). (right) Framework of the structure.
Chart 1. Geometrical Details (Å and Deg) of the Metal
Center in Complexes 5ꢀ7
Scheme 4. Schematic Representation of the Three Different
Types of Polymerization for Norbornene
Table 2. Norbornene Polymerization for the Ir/MAO Cata-
lytic Systema
c
entry
cat.
Al/Ir
yield/mg
activityb
Mw
1
2
3
4
2
2
2
2
1000
2000
3000
4000
189
349
272
210
0.76
1.40
1.09
0.84
4.95
5.17
5.19
5.13
closo-carborane complex 6 to the zwitterionic nido-carborane
complex 7 was also investigated. In addition, a preliminary study
showed that the novel half-sandwich Ir complex 2 exhibited good
catalytic activity in the polymerization of norbornene in the pre-
sence of methylaluminoxane as the cocatalyst. Further studies on
the reactivity of monophosphine-m-carborane and diphosphine-
m-carborane sulfides are currently underway in our laboratory.
a Polymerization conditions: [NB] = 1.00 g; Vtotal = 10 mL; catalyst
iridium complex 2, 0.5 μmol; reaction time 30 min, T = 30 °C, solvent
chlorobenzene. b In units of 106 g of PNB (mol of Ir)ꢀ1 hꢀ1. c In units
of 106 g molꢀ1, measured in chlorobenzene at 25 oC using the Markꢀ
Houwink coefficients.
’ EXPERIMENTAL SECTION
General Data. All manipulations were performed under an atmo-
sphere of nitrogen using standard Schlenk techniques. CH2Cl2 was dried
over CaH2, chlorobenzene was dried over MgSO4 and CaCl2, and THF,
diethyl ether, hexane, and toluene were dried over Na and then distilled
under a nitrogen atmosphere immediately prior to use. Methylalumi-
noxane (MAO), n-butyllithium (1.6 M in n-hexane, Acros), o-carborane,
and other chemicals were used as commercial products without further
purification. [Cp*MCl2]2 (M = Ir, Rh)30 was synthesized according to
’ CONCLUSIONS
In summary, the monophosphine-o-carborane sulfide 1 was used
as a noninnocent ligand to form a series of half-sandwich iridium and
rhodium complexes with versatile coordination modes. The two C,S
coordination mode complexes 2 and 3 were successfully synthe-
sized by the treatment of [Cp*MCl2]2 (M = Ir, Rh) with the
lithium salt of 1. Interestingly, the reactivities of S,S0 bifunctional
derivative 4 with dimeric iridium and rhodium complexes were
different. The unexpected B,S,S0 coordination mode product 5 via
BꢀH activation and the normal S,S0 coordination mode product
6 were obtained, respectively. The formation of 5 may be due to
the electron-deficient metal center located in close proximity to
the BꢀH vertices. The deboronation reaction from the neutral
1
the literature. H NMR (400 MHz), 13C NMR (100 MHz), and 31P
NMR (162 MHz) spectra were measured with a VAVCE DMX-400
spectrometer. 11B NMR (160 MHz) spectra were recorded with a
Bruker DMX-500 spectrometer. Elemental analysis was performed on
an Elementar vario EL III analyzer. IR (KBr) spectra were measured with
a Nicolet FT-IR spectrophotometer.
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Synthesis of 1-SPPh2-1,2-closo-C2B10H11 (1). Sulfur powder
(32 mg, 1 mmol) was added to a solution of 1-PPh2-1,2-closo-C2B10H11
(328 mg, 1 mmol) in toluene (20 mL) at room temperature, and then
NEt3 (1 mL) was added to the solution after the sulfur was completely
dissolved. The mixture was stirred for 12 h at 80 °C. After removal of the
solvent under vacuum, the residue was purified by column chromatog-
raphy on silica gel. Elution with petroleum ether/CH2Cl2 (8/1) gave 1
(266 mg, 81%) as a slightly yellow solid. 1H NMR (400 MHz, CDCl3,
25 °C): δ 8.29ꢀ8.23 (m, 4H, Ph), 7.67ꢀ7.63 (m, 2H, Ph), 7.60ꢀ7.55
(BꢀH), 643 (PdS) cmꢀ1. Anal. Calcd for C14H21B10PS2: C, 42.84; H,
5.39. Found: C, 42.86; H, 5.63.
0
Synthesis of [Cp*Ir(CabB,S,S )] (5). n-BuLi in hexane (1.6 M,
0.25 mL, 0.4 mmol) was added to a solution of LPS (144 mg, 0.4 mmol)
1
in THF (10 mL). The mixture was stirred at 0 °C for /2 h and for
another 1 h at room temperature. Sulfur powder was added to the above
solution and stirred for 2 h, and then [Cp*IrCl2]2 (160 mg, 0.2 mmol)
was added as a solid to the solution and continuously reacted for 8 h at
room temperature. After removal of the solvent under vacuum, the
residue was purified by column chromatography on silica gel. Elution
with petroleum ether/CH2Cl2 (2/1) gave 5 (207 mg, 72%) as a light red
solid. A suitable single crystal of 5 was obtained by slow diffusion of n-
hexane into its concentrated dichloromethane solution. 1H NMR (400
MHz, CDCl3, 25 °C): δ 8.32ꢀ8.27 (m, 2H, Ph), 8.19ꢀ8.14 (m, 2H,
Ph), 7.64ꢀ7.56 (m, 4H, Ph), 7.38 (br, 2H, Ph), 1.96 ppm (s, 15H, Cp*).
13C NMR (400 MHz, CDCl3, 25 °C): δ 135.5 (d, J(C,P) = 9.8 Hz, Ph),
134.9 (d, J(C,P) = 9.6 Hz, Ph), 133.0, 132.7 (dd, J(C,P) = 3.0 Hz, 3.1 Hz,
Ph), 128.2 (d, J(C,P) = 12.4 Hz, Ph), 127.7 (d, J(C,P) = 13.2 Hz, Ph),
100.8 (s, CcageꢀS), 88.1 (d, J(C,P) = 72.8 Hz, CcageꢀP), 90.3 (C5Me5),
9.3 ppm (C5Me5). 11B NMR (160 MHz, CDCl3, 25 °C): δ ꢀ0.60 (3B),
ꢀ6.30 (3B), ꢀ9.39 (1B), ꢀ12.58 (3B) ppm. 31P NMR (162 MHz,
CDCl3, H3PO4, 25 °C): δ 62.80 (s, PdS) ppm. IR (KBr, disk): ν 2562
(BꢀH), 630 (PdS) cmꢀ1. Anal. Calcd for C24H34B10PS2Ir: C, 40.15; H,
(m, 4H, Ph), 4.70 (s, 1H, HCcage), 2.81ꢀ1.73 ppm (br m, 11H, BH). 13
C
NMR (100 MHz, CDCl3, 25 °C): δ 133.5 (d, J(C,P) = 11 Hz, Ph), 133.1
(d, J(C,P) = 3 Hz, Ph), 128.4 (d, J(C,P) = 13 Hz, Ph), 127.4 (d, J(C,P) =
89 Hz, Ph), 72.0 (d, J(C,P) = 34 Hz, CcageꢀP), 63.8 ppm (s, HCcage). 11
B
NMR (160 MHz, CDCl3, 25 °C): δ ꢀ0.08 (1B), ꢀ2.07 (1B), ꢀ6.80
(2B), ꢀ10.53 (2B), ꢀ12.29 (4B) ppm. 31P NMR (162 MHz, CDCl3,
H3PO4, 25 °C): δ 51.33 (s, PdS) ppm. IR (KBr, disk): ν 2626, 2573
(BꢀH), 647 (PdS) cmꢀ1. Anal. Calcd for C14H21B10PS: C, 46.65; H,
5.87. Found: C, 46.78; H, 5.88.
Synthesis of [Cp*IrCl(CabC,S)] (2). n-BuLi (1.6 M in n-hexane,
0.25 mL, 0.4 mmol) was added to a solution of 1 (144 mg, 0.4 mmol) in
THF (10 mL) at ꢀ78 °C, and the mixture was stirred at ꢀ78 °C for 1 h
and at room temperature for another 1 h. Then [Cp*IrCl2]2 (160 mg,
0.2 mmol) was added as a solid to the above mixture and stirred for 8 h at
room temperature. After removal of the solvent under vacuum, the
residue was purified by column chromatography on silica gel. Elution
with petroleum ether/THF (1/1) gave 2 (197 mg, 68%) as a yellow
solid. A suitable single crystal of 2 was obtained by slow diffusion of n-
hexane into its concentrated dichloromethane solution. 1H NMR (400
MHz, CDCl3, 25 °C): δ 8.33ꢀ8.27 (m, 2H, Ph), 7.88ꢀ7.83 (m, 2H,
Ph), 7.68ꢀ7.60 (m, 4H, Ph), 7.47 (br, 2H, Ph), 1.49 ppm (s, 15H, Cp*).
13C NMR (400 MHz, CDCl3, 25 °C): δ 133.8 (d, J(C,P) = 2.8 Hz, Ph),
133.7 (d, J(C,P) = 2.3 Hz, Ph), 128.9 (d, J(C,P) = 3.6 Hz, Ph), 128.7 (d,
J(C,P) = 2.3 Hz, Ph), 91.3 (C5Me5), 8.8 ppm (C5Me5). 11B NMR (160
4.77. Found: C, 40.02; H, 4.80.
0
Synthesis of [Cp*RhCl(CabS,S )] (6). A procedure analogous to
the preparation of 4 was used; [Cp*RhCl2]2 (124 mg, 0.2 mmol) was
added as a solid to the mixture and stirred for 8 h at room temperature.
Yield: 173 mg, 63%; dark red solid. A suitable single crystal of 6 was
obtained by slow diffusion of n-hexane into its concentrated dichlor-
omethane solution. 1H NMR (400 MHz, CDCl3, 25 °C): δ 8.66ꢀ8.61
(m, 2H), 8.10ꢀ8.06 (m, 2H), 7.60ꢀ7.51 (m, 6H), 1.59 ppm (s, 15H,
Cp*). 13C NMR (100 MHz, CDCl3, 25 °C): δ 136.4 (d, J(C,P) = 11.1
Hz, Ph), 133.8, 133.4 (s, Ph), 128.4 (d, J(C,P) = 13.3 Hz, Ph), 128.1 (d,
J(C,P) = 14.0 Hz, Ph), 97.9 (C5Me5), 93.0 (CcageꢀS), 78.1 (d, J(C,P) =
36.2 Hz, CcageꢀP), 9.6 ppm (C5Me5). 11B NMR (160 MHz, CDCl3,
25 °C): δ 2.06 (2B), ꢀ4.04 (2B), ꢀ7.42 (3B), ꢀ10.30 (3B) ppm. 31P
NMR (162 MHz, CDCl3, H3PO4, 25 °C): δ 49.28 (s, PdS) ppm. IR
(KBr, disk): ν 2571 (BꢀH), 629 (PdS) cmꢀ1. Anal. Calcd for
C24H35B10ClPS2Rh: C, 43.34; H, 5.30. Found: C, 43.56; H, 5.38.
Synthesis of [Cp*Rh(7-S0)-(8-SPPh2)-7,8-C2B9H10] (7). Com-
plex 5 (0.2 mmol, 132 mg) was added to CH3OH (20 mL), followed by
the addition of a small amount of CH3ONa, and then the mixture was
stirred at 50 °C for 8 h. After removal of the solvent under vacuum, the
residue was purified by column chromatography on silica gel. Elution
with CH2Cl2 gave 7 (103 mg, 83%) as a dark green solid. A suitable single
crystal of 7 was obtained by slow diffusion of n-hexane into its concentrated
MHz, CDCl3, 25 °C): δ 2.18 (2B), ꢀ5.47 (4B), ꢀ8.64 (4B) ppm. 31
P
NMR (162 MHz, CDCl3, H3PO4, 25 °C): δ 60.79 (s, PdS) ppm. IR
(KBr, disk): ν 2601, 2548 (BꢀH), 625 (PdS) cmꢀ1. Anal. Calcd for
C24H35B10PSClIr: C, 39.91; H, 4.88. Found: C, 39.63; H, 4.91.
Synthesis of [Cp*RhCl(CabC,S)] (3). A procedure analogous to
the preparation of 2 was used; [Cp*RhCl2]2 (124 mg, 0.2 mmol) was
added as a solid to the mixture and stirred for 8 h at room temperature.
Yield: 160 mg, 63%; orange solid. 1H NMR (400 MHz, CDCl3, 25 °C):
δ 8.35ꢀ8.26 (m, 2H, Ph), 7.91ꢀ7.87 (m, 2H, Ph), 7.67ꢀ7.60 (m, 4H,
Ph), 7.45 (br, 2H, Ph), 1.53 ppm (s, 15H, Cp*). 13C NMR (400 MHz,
CDCl3, 25 °C): δ 133.3 (d, J(C,P) = 3.0 Hz, Ph), 132.6 (d, J(C,P) = 2.6
Hz, Ph), 128.3 (d, J(C,P) = 3.6 Hz, Ph), 127.9 (d, J(C,P) = 2.8 Hz, Ph),
89.9 (C5Me5), 9.6 ppm (C5Me5). 11B NMR (160 MHz, CDCl3, 25 °C):
δ 2.24 (2B), ꢀ5.33 (4B), ꢀ8.69 (4B) ppm. 31P NMR (162 MHz, CDCl3,
H3PO4, 25 °C): δ 60.88 (s, PdS) ppm. IR (KBr, disk): ν 2612, 2568
(BꢀH), 633 (PdS) cmꢀ1. Anal. Calcd for C24H35B10PSClRh: C, 45.54;
H, 5.57. Found: C, 45.62; H, 5.57.
1
dichloromethane solution. H NMR (400 MHz, CDCl3, 25 °C): δ
7.89ꢀ7.84 (m, 2H), 7.64ꢀ7.50 (m, 6H), 7.40ꢀ7.38 (m, 2H), 1.54 (s,
Cp*). 11B NMR (160 MHz, CDCl3, 25 °C): δ ꢀ6.43 (2B), ꢀ10.09
(2B), ꢀ17.50 (1B), ꢀ21.60 (1B), ꢀ31.66 (3B) ppm. 31P NMR (162
MHz, CDCl3, H3PO4, 25 °C): δ 46.28 (s, PdS) ppm. Anal. Calcd for
C24H35B9PS2Rh: C, 46.58; H, 5.70. Found: C, 46.43; H, 5.68.
Synthesis of [1-SH-2-SPPh2-1,2-closo-C2B10H11] (4). n-BuLi
in hexane (1.6 M, 0.25 mL, 0.4 mmol) was added to a solution of 1
(144 mg, 0.4 mmol) in THF (10 mL). The mixture was stirred at 0 °C
for 1/2 h and for another 1 h at room temperature. Sulfur powder was
added to the above solution and stirred for 2 h, and then a few drops of
water was added to the solution. After removal of the solvent under
vacuum, the residue was purified by columnchromatography on silica gel.
Elution with CH2Cl2 gave 4 (135 mg, 85%) as a yellow solid. 1H NMR
(400 MHz, CDCl3, 25 °C): δ 8.41ꢀ8.36 (q, 4H, Ph), 7.66ꢀ7.56 (m, 6H,
Ph), 5.54 (s, SH), 2.76ꢀ1.76 ppm (br m, 10H, BH). 13C NMR (100 MHz,
CDCl3, 25 °C): δ 134.5 (d, J(C,P) = 9 Hz, Ph), 133.6 (d, J(C,P) = 10 Hz,
Ph), 128.5 (d, J(C,P) = 13 Hz, Ph), 128.2 (d, J(C,P) = 13 Hz, Ph), 72.4
ppm (d, J(C,P) = 34 Hz, CcageꢀP). 31P NMR (162 MHz, CDCl3,
H3PO4, 25 °C): δ 49.35 (s, PdS) ppm. IR (KBr, disk): ν 2619, 2563
Norbornene Polymerization. A 0.5 μmol amount of iridium
complex 2 in 2.0 mL of chlorobenzene, 1.00 g of norbornene in 2 mL of
chlorobenzene, and 6 mL of fresh chlorobenzene were added into a
special polymerization bottle (50 mL) with a stirrer under a nitrogen
atmosphere. After the mixture was kept at 30 °C for 10 min, a certain
amount of MAO was charged into the polymerization system via a
syringe and the reaction was started. After 15 min, acidic ethanol
(Vethanol/Vconc HCl = 20/1) was added to terminate the reaction. The
PNB was isolated by filtration, washed with ethanol, and dried at 80 °C
for 36 h under vacuum. For all polymerization procedures, the total
reaction volume was 10.0 mL, which can be achieved by varying the
amount of chlorobenzene when necessary. The viscosity-average molar
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Organometallics
ARTICLE
masses (Mw) of PNB were obtained in chlorobenzene at 25 °C using
F. M.; Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1997, 536ꢀ
537, 405–412.
MarkꢀHouwink coefficients:31 α = 0.56, K = 5.97 ꢁ 10ꢀ4 dL gꢀ1
.
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Rouquette, H.; Viꢁnas, C.; Seluckꢀy, P.; Rais, J. New J. Chem. 2002,
26, 1519–1527. (b) Pleꢁsek, J.; Gr€uner, B.; Císaꢁrovꢀa, I.; Bꢀaꢁca, J.; Seluckꢀy,
P.; Rais, J. J. Organomet. Chem. 2002, 657, 59–70. (c) Pleꢁsek, J.; Gr€uner,
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Holub, K.; Seluckꢀy, P.; Rais, J.; Císaꢁrovꢀa, I.; Cꢀaslavskꢀy, J. Polyhedron
2002, 21, 975–986.
X-ray Crystallography. Diffraction data of 1, 2, and 5ꢀ7 were
collected on a Bruker Smart APEX CCD system with graphite-mono-
chromated Mo Kα radiation (λ = 0.710 73 Å). All the data were collected
at room temperature, and the structures were solved by direct methods
and subsequently refined on F2 by using full-matrix least-squares
techniques (SHELXL).32 SADABS33 absorption corrections were ap-
plied to the data, all non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were located at calculated positions. All calculations
were performed using the Bruker program Smart. A summary of the
crystallographic data and selected experimental information are given in
Table 1.
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Corresponding Author
*Tel: (+86)-21-65643776. Fax: (+86)-21-65641740. E-mail:
gxjin@fudan.edu.cn.
’ ACKNOWLEDGMENT
This work was supported by the Shanghai Science and Technology
Committee (Nos. 08DZ2270500 and 08J1400103), the Shanghai
Leading Academic Discipline Project (No. B108), and the National
Basic Research Program of China (No. 2009CB825300).
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Dedicated to Herr Professor Dr. Gerhard Erker on the occasion
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