Neutral and zwitterionic half-sandwich Ir, Rh complexes supported by P,S-substituted o-carboranyl ligands: Synthesis, characterization and reactivity

Article abstract of DOI:10.1039/b918272a

The neutral Cp*M(Cl)(1-PPh₂-2-S-1,2-C₂B ₁₀H₁₀) and zwitterionic Cp*M(3-OCH ₃-7-PPh₂-8-S-7,8-C₂B₉H₉) (Cp* = η⁵-C₅Me₅, M = Ir, Rh, 1-PPh₂-2-S-1,2-C₂B₁₀H₁₀ = [1-(diphenylphosphino)-2-thiolato)-1,2-dicarba-closo-carborane], 3-OCH ₃-7-PPh₂-8-S-7,8-C₂B₉H₉ = [3-(methoxyl)-7-(diphenylphosphino)-8-(thiolato)-7,8-dicarba-nido-carborane] ^-) were synthesized and fully characterized. The 18-electron neutral closo-carborane complexes Cp*M(Cl)(1-PPh₂-2-S-1,2-C ₂B₁₀H₁₀) (M = Ir (1a), Rh (1b)) can be easily deboronated to result in the formation of reactive 16-electron zwitterionic nido-carborane complexes [Cp*M(3-OCH₃-7-PPh₂-8-S-7, 8-C₂B₉H₉)] (M = Ir (2a), Rh(2b)). The oxidation of 2b with O₂ gas afforded the corresponding sulfone complex 3b in high yields. Utilization of its unsaturated feature in 16-electron zwitterionic nido-carborane complexes offers a potential strategy to synthesize new types of organometallic complexes.

Full text of DOI:10.1039/b918272a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Neutral and zwitterionic half-sandwich Ir, Rh complexes supported by
P,S-substituted o-carboranyl ligands: Synthesis, characterization and
reactivity†‡
Xian-Kuan Huo, Ge Su and Guo-Xin Jin*
Received 3rd September 2009, Accepted 19th November 2009
First published as an Advance Article on the web 5th January 2010
DOI: 10.1039/b918272a
The neutral Cp*M(Cl)(1-PPh2-2-S-1,2-C2B10H10) and zwitterionic Cp*M(3-OCH3-7-PPh2-8-
5
S-7,8-C2B9H9) (Cp* = h -C5Me5, M = Ir, Rh, 1-PPh2-2-S-1,2-C2B10H10 = [1-(diphenylphosphino)-
2-thiolato)-1,2-dicarba-closo-carborane], 3-OCH3-7-PPh2-8-S-7,8-C2B9H9 = [3-(methoxyl)-7-
(diphenylphosphino)-8-(thiolato)-7,8-dicarba-nido-carborane]-) were synthesized and fully
characterized. The 18-electron neutral closo-carborane complexes Cp*M(Cl)(1-PPh2-2-S-1,2-C2B10H10)
(M = Ir (1a), Rh (1b)) can be easily deboronated to result in the formation of reactive 16-electron
zwitterionic nido-carborane complexes [Cp*M(3-OCH3-7-PPh2-8-S-7,8-C2B9H9)] (M = Ir (2a),
Rh(2b)). The oxidation of 2b with O2 gas afforded the corresponding sulfone complex 3b in high yields.
Utilization of its unsaturated feature in 16-electron zwitterionic nido-carborane complexes offers a
potential strategy to synthesize new types of organometallic complexes.
application of this kind of chemistry on reproducing the mech-
Introduction
anism of [NiFe] hydrogenase and the development of selective
new stoichiometric and catalytic substrate activation chemistry;9
During the past decade, considerable attention has been devoted
to 1, 2-dicarba-closo-dodecaborane and its metal complex deriva-
tives, which are highly versatile molecules featuring the symmetry
of the icosahedral carborane cage and high thermal and chemical
stability.1 They can be converted into the closo-C2B10H102-, nido-
2
(iv) [Cp*M(k -P, S)] (M = Ir, Rh) complexes bearing o-carborane
ligands and their applications are scantly reported which also
urged us to investigate.
With the aim of synthesizing new half-sandwich complexes
containing bifunctional carborane groups and comparing the
difference between the bifunctional carborane (1-PPh2-2-LiS-1,2-
C2B10H10 or [3-OCH3-7-PPh2-8-LiS-7,8-C2B9H9]-) and the carbo-
rane 1,2-(LiS)2-1,2-C2B10H10 on forming 16-electron unsaturated
complexes, herein, we present seven new compounds containing
the unit of Cp*M(Cl)(1-PPh2-2- S-1,2-C2B10H10) or Cp*M(3-
OCH3-7-PPh2-8- S-7,8-C2B9H9) (M = Ir, Rh). It is interesting
to note that two of those compounds are neutral Cp*M(Cl)
(1-PPh2-2- S-1,2-C2B10H10) (M = Ir, Rh) and the other five are
zwitterions Cp*M(3-OCH3-7-PPh2-8- S-7,8-C2B9H9) (M = Ir,
Rh), which are the first reported to the best of our knowledge
about this sort of complex to date, and the neutral complexes can
C2B9H12-, nido-C2B9H112-, and even arachno-C2B10H12 under
4-
suitable conditions,2 which has led to its use as a desirable
building unit with many promising applications.1-3 It is well known
that ligand modifications have played very important roles in
developing new materials as well as their properties,4 especially the
ligands containing bifunctional groups often offer complexes some
additional advantage.5 Based on our recent systematic studies of
16-electron Cp*MS2[C2B10H10] (M = Co, Rh, Ir) a wide range of
direct metal–metal bonds complexes or multinuclear complexes
and their applications on ethylene polymerization or some others
were revealed,6,3d the bifunctional P,S-o-carborane ligand seized
our attention for the following reasons:7 (i) The arylphosphine can
stabilize the metal ion; (ii) Coordinating sulfur atom may be readily
used as a bridged atom by an incoming low oxidation state metal
fragment (such as Mo(CO)3(Py)3 Co2(CO)8, [(COD)IrCl]2) to
form directed metal–metal bonds or other binuclear complexes;6a,8
2
(iii) The analogous complexes Cp*M (k -P, S) (M = Ir, Rh) bearing
2,6-dimesitylphenyl thiolate or indene which were just reported
by K. Tatsumi and M. Stradiotto, have widely broadened the
Shanghai Key Laboratory of Molecular Catalysis and Innovative Material,
Department of Chemistry, Advanced Materials Laboratory, Fudan Univer-
sity, 200433, Shanghai, P. R. China. E-mail: gxjin@fudan.edu.cn; Fax: +86-
21-65641740; Tel: +86-21-65643776
† Dedicated to Professor Seyferth on the occasion of his 80th birthday.
‡ CCDC reference numbers 746417 (1a), 746418 (2a), 746419 (3b), and
746420 (4·2a). For crystallographic data in CIF or other electronic format
see DOI: 10.1039/b918272a
Chart 1
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undergo a facial deboronation reaction in polar solvent to afford
the corresponding nido-carborane zwitterions easily10 (Chart 1).
Utilizing its unsaturated feature, the 16-electron zwitterionic nido-
carborane complexes reacted with two electron donor ligands CO
and PPh3 to give the corresponding 18-electron products.
(Scheme 1). The complexes were obtained in higher yields from
recrystallization in the form of air-stable and orange transparent
prismatic crystals when the low temperature was applied. For
complex 1a, the IR spectra shows a strong band for the B–H
vibration at approximately 2570 cm-1, the formation of 1a is
1
also confirmed by the appearance of the H signals at d 1.59,
7.45–7.59, 7.93–7.95 ppm, which can be ascribed to the Cp*
and phenyl, respectively. 11B NMR spectra exhibit resonances
at d -2.19, -3.13, -5.29, -6.19, -8.98, -9.97, -11.38, -14.45,
-15.52 ppm. The 31P NMR spectra exhibit a sharp signal at d
57.81 ppm, corresponding to the -PPh2 group of the 1-PPh2-2-S-
1,2-C2B10H10 ligand. These spectroscopic data and the combustion
analyses for H and C indicate the formation of a new complex
Cp*Ir(Cl)(1-PPh2-2-S-1,2-C2B10H10), which was further confirmed
by X-ray crystallography. For complex 1b, a detailed analysis of
Results and discussion
Synthesis of 1-PPh2-1,2-C2B10H10 and 1-PPh2-2-LiS-1,2-C2B10H10
Some works has been done on synthesizing the mono-substituted
o-carborane derivatives in aromatic solvent, but the conversion
was found to be too low for further development of this kind of
compound.11a The preparation of them was improved by C. Vina˜s
and co-authors utilizing DME as solvent and the monosubsti-
tuted o-carborane derivatives (for example 1-SH-1,2-C2B10H11 and
1-PPh2-1,2-C2B10H11) can be obtained in high yields.11b But the
product was impure which contained disubstituted compounds
and unreacted staring materials. So a modified synthesis◦method
was applied in this work. Firstly, low temperature (-15 C) was
applied when o-carborane was reacted with BunLi (1 : 1) in DME;
secondly, the reflux time was lengthened to 4 h when l-Li-1,2-
C2B10H11 was reacted with equivalent ClPPh2; thirdly, the DME
solvent was removed in vacuo and the residue extracted with
n-hexane, giving a white solid from evaporation of the filtrate.
The target mono-substituted compound was isolated by column
chromatography on silica gel (71% yield).
1
the spectroscopic data (IR, H NMR, 11B NMR and 31P NMR)
shows the structure is the same as 1a, which was also confirmed
by elemental analyses.
Suitable crystals for X-ray crystallography of 1a were obtained
by slow diffusion of hexane into a concentrated solution of
the complex in dichloromethane. The crystallographic data for
complex 1a are summarized in Table 1; An ORTEP drawing
of complex 1a and selected bonds and angles are shown in
Fig. 1. The molecular structure reveals that the geometry at the
iridium(III) center is a three-legged piano-stool with the iridium
5
2
atom coordinated by the h -Cp*, k -1-PPh2-2-S-1,2-C2B10H10, and
chloride atom, consequently it can be described as a pseudo-
5
octahedron in which h -Cp* group occupies three fac coordination
The 1-PPh2-2-LiS-1,2-C2B10H10 was obtained by reaction be-
tween the 1-PPh2-1,2-C2B10H10, BunLi (1 : 1) and the powdered
sides. The coordination of the bidentate ligand 1-PPh2-2- S-1,2-
C2B10H10 anion to the central metal Ir atom results in a five-
membered IrPSC2 ring which is puckered at the Ir atom and the
remaining four atoms [C(1),C(2),S(1),P(1)] almost form a plane
◦
◦
sulfur in Et2O at -10 C. If low temperature (-78 C) is applied
in Et2O or THF, some by-products besides 1-PPh2-2-LiS-1,2-
C2B10H10 were isolated. Following the literature procedure,8c the
same by-products were also isolated in low yields. So we think
diethyl ether is a better choice of solvent when a second lithiation
occurs on the mono-substituted carborane compound, which
agreed with the literature.11b
˚
(with a maximum deviation of 0.13 A). The distances of Ir(1)–S(1)
˚
˚
(2.3529(12) A) and Ir(1)–P(1) (2.3016(10) A) are shorter than that
˚
of Ir(1)–Cl(1) (2.4210(11) A), which are all within the range of
known values for them in analogous complexes.9,12a
Synthesis of neutral complexes 1a and 1b
Pursuit of the coordinatively unsaturated zwitterion 2a and 2b
The neutral P,S-chelated metal complexes [Cp*M(Cl))(1-PPh2-
2- S-1,2-C2B10H10)] (M = Ir, Rh) were prepared by the reaction
between the corresponding dimeric metal complexes [Cp*MCl2]2
(M = Ir, Rh) and 2 equiv of compound 1-PPh2-2-LiS-1,2-C2B10H10
Having successfully prepared the new saturated neutral Ir and Rh
complexes, we turned our focus to the synthesis of structurally
related unsaturated zwitterions 2a and 2b (Scheme 2) which may
act as a precursor just like our reported reactive 16-electron
Scheme 1 Synthesis of the neutral complexes 1a and 1b.
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Table 1 Crystallographic data and structure refinement parameters for 1a, 2a, 3b·CH2Cl2 and 4·2a
1a
2a
3b·CH2Cl2
4·2a
empirical formula
Formula weight
C24H35B10ClPSIr
722.30
C25H37B9OPSIr
706.07
C26H39B9Cl2O3PSRh
733.70
C51H74B18Ir2O3P2S2
1440.14
Crystal syst., space group
Monoclinic, P21/n
12.230(4)
11.756(4)
21.071(6)
90
98.154(4)
90
2998.9(16), 4
1.600
4.680
Monoclinic, P21/n
10.231(3)
16.911(5)
17.352(5)
Monoclinic, P21/n
14.934(12)
11.386(9)
22.427(18)
90
100.797(13)
90
3746(5), 4
1.301
Monoclinic, P21/c
24.198(7)
12.368(4)
22.609(6)
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
90
90
103.047(4)
90
2924.6(15), 4
1.604
4.711
1392
1.70–27.00
-13,10;-17,21;-20,21
13726/6225[0.0298]
27.00 (97.4%)
6225/0/370
0.908
114.066(3)
90
6178(3), 4
1.548
4.463
2840
1.81–25.01
-18,28;-14,14;-26,26
25157/10908[0.046]
25.01 (100%)
10908/12/728
1.017
3
˚
volume/A , Z
Dc/g cm-3
m(Mo-Ka)/mm-1
F(000)
0.723
1496
1416
q range (deg)
limited indices
1.82–26.01
-11,15;-12,14;-26,12
13304/5784[0.0336]
26.01 (98.3%)
5784/0/358
0.870
1.39–25.01
-17,14;-13,12;-26,26
15207/6590[0.1377]
25.01 (99.8%)
6590 0 406
0.818
Reflections/unique [R(int)]
completeness to q/deg
data/restraints/parameters
Goodness-of-fit on F2
R1a, wR2a[I > 2s(I)]
R1, wR2(all data)
0.0242, 0.0440
0.0353, 0.0456
0.0267, 0.0537
0.0421, 0.0568
0.0820, 0.1844
0.1844, 0.2090
0.0665, 0.1782
0.0967, 0.1933
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ (based on reflections with Fo > 2sF2). wR2 = [ [w(Fo - Fc2)2]/ [w(Fo2)2]]1/2; w = 1/[s (Fo2)+(0.095P)2]; P = [max(Fo2, 0) +
2
2
2
2
2Fc2]/3 (also with Fo > 2sF2).
Fig.
1
ORTEP drawing of 1a with thermal ellipsoids drawn at
the 30% level, all hydrogen atoms were omitted for clarity. Selected
Scheme 2 Synthesis of the zwitterionic complexes 2a and 2b.
˚
bond lengths (A) and angles (deg): Ir(1)–P(1) 2.3016(10), Ir(1)–S(1)
2.3529(12), Ir(1)–Cl(1) 2.4210(11), Ir(1)–C(18) 2.206(3), Ir(1)–C(15)
2.211(3), Ir(1)–C(17) 2.222(3), P(1)–Ir(1)–Cl(1) 93.41(4), S(1)–Ir(1)–Cl(1)
89.08(4), P(1)–Ir(1)–S(1) 89.02(4).
confirmed by the appearance of the 1H signals at 1.59, 3.17, 7.45–
7.79 ppm (in the ratio 15 : 3 : 10), which can be ascribed to the
Cp*, -OCH3 and phenyl, and 11B NMR spectra exhibit resonances
at d -2.77, -4.27, -6.82, -9.70, -10.78, -11.22, -12.90, -20.02,
-35.63 ppm, which indicated that closo-carborane was changed
to nido-carborane.12 The 31P NMR spectra exhibits a sharp
signal at d 68.32 ppm, corresponding to the -PPh2 group of the
3-OCH3-7-PPh2-8- S-7,8-C2B9H9 ligand. Elemental analytical and
spectroscopic data support the formulation of 2a as a mononuclear
16-electron Ir(III) phosphinothiolato-nido-o-carborane complex.
Another method (Method 2 in the Experimental section) was
also applied and the targeted product was obtained in moderate
yields from the crude residue following purification by column
chromatography. It should be noted that the pyrazine in those
precursor Cp*MS2[C2B10H10] (M = Co, Rh, Ir).6 Treatment of
1a with AgOTf in CH3OH solution, yielded a blue solid [Cp*Ir
(1-PPh2-2- S-1,2-C2B10H10)]+[OTf]-, then 1 equiv of pyrazine was
added and a purple solid (2a) [Cp*Ir (3-OCH3-7-PPh2-8- S-7,8-
C2B9H9)] was obtained after stirring for 48 h at room temperature.
The complex is soluble in THF, CH2Cl2 and toluene, and is
insoluble in CH3OH. 2a was obtained in moderate yields from
recrystallization in the form of air-stable, purple, transparent
crystals. For 2a, the IR spectra shows a strong band for the B–H
vibration at approximately 2573 cm-1, the formation of 2a is also
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two reactions plays the role of base and different equiv. (2, 5, 10
equiv.) of pyrazine were also used to test the influence on the yield
of targeted compound; but the yields did not differ much. Many
efforts were also made to prepare 2a and 2b via reaction between
1-PPh2-2-LiS-1,2-C2B10H10 and dimeric complexes [Cp*MCl2]2
(M = Ir, Rh) in polar solvent and in the presence of a weak
base such as Et3N and K2CO3 or a very weak nucleophile such as
the fluoride ion,13 but the isolated compounds were not soluble in
general organic solvents such as toluene, THF, CH2Cl2, CH3OH,
CH3CN even DMSO, so they were not the targeted complexes.
Suitable crystals for X-ray crystallography of 2a were obtained
by slow diffusion of hexane into a concentrated solution of 2a in
THF. The crystallographic data for complex 2a are summarized
in Table 1; An ORTEP drawing of complex 2a and selected bonds
and angles are shown in Fig. 2. The molecular structure shows
the Ir(III) atom is unsaturated five coordinated by one S atom,
one P atom from 3-OCH3-7-PPh2-8-S-7,8-C2B9H9 ligand and one
Cp* ligand functioned as a three-coordinated ligand, forming a
two-legged piano-stool geometry. The five-membered ring formed
by the Ir(1), S(1), P(1), C(7), C(8) atoms is almost on a plane with
the dihedral angle of 8.16◦ between the plane [Ir(1), S(1), P(1)]
and the plane [S(1), P(1), C(7), C(8)]. The dihedral angle between
the Cp* plane and the plane [Ir(1), S(1), P(1)] is 83.07◦, which is
close to perpendicular. Compared with analogous complexes,9,12
a good precursor for other addition reactions because of its higher
degree of coordinative unsaturation.
Compared with 1a, there are two phenomena occurring in the
carborane cage in 2a, (i) the hydrogen bond with B(3) has been
substituted by a methoxyl group; (ii) one boron atom (original
B(6) atom in 1a) has been removed from the mother cage, which
has made the closo-carborane into nido-carborane anion and
enables the anionic charge to be delocalized onto the pendant
ring (C2B3) and consequently 2a has become a zwitterion with
2
[Cp*Ir (k -P, S)]+.
As discussed above, the 16-electron complex 2a is an air-stable
complex due to the p-type interaction between the metal center
and the pp orbital on the sulfur atom. So we wondered whether the
complex would change if the p-type interaction was removed by
force. According to the 18-electron rule, the 16-electron complex
may be more unstable and reactive, and will be easily coordinated
with other two electron donor ligands. In an effort to remove the
p-type interaction between the metal center and the pp orbital
on the sulfur atom, the sulfur atom was oxidized into sulfone by
treatment of 2a and 2b with pure O2 gas in the mixture solution
of ethyl acetate and methanol in high yields (Scheme 3). Suitable
crystals for X-ray crystallography of 3b were obtained by slow
diffusion of hexane into a concentrated solution of the complex
in dichloromethane. The crystallographic data for complex 3b are
summarized in Table 1 and selected bonds and angles are shown in
Fig. 3. As illustrated in Fig. 3, what differs from 2a is that the sulfur
atom is oxidized into sulfone and the Rh atom was coordinated by
the methoxyl group forming an 18-electron complex. The Rh–S,
Rh–P bond distances are all within the range of known values for
them in analogous complexes.9a,16 The dihedral angle along the
P ◊ ◊ ◊ S in the metallocycle is 132.26◦ which is much deviated from
the plane. The molecular structure of 3b was also confirmed by
˚
the Ir(1)–P(1) bond distance (2.2880(10) A) is normal but the
˚
Ir(1)–S(1) bond length (2.1971(11) A) is sharply shorter than that
˚
in the analogous complex 1a (2.35 A) and even shorter than that
14
˚
of the pseudo-aromatic Cp*IrS2[C2B10H10] in which it is 2.257 A.
The reason can be interpreted by p-type interactions; in order
to alleviate coordinative unsaturation around the Ir atom, the
electron donation from the pp orbital on the sulfur atom occurs to
stabilize the coordinatively unsaturated Ir center.15,14 So 2a may be
Fig. 2 ORTEP drawing of 2a with thermal ellipsoids drawn at the 30%
level, all hydrogen atoms were omitted for clarity. Selected bond lengths (A)
Fig. 3 ORTEP drawing of 3b with thermal ellipsoids drawn at the
30% level, all hydrogen atoms and solvent molecules were omitted for
˚
˚
and angles (deg): Ir(1)–P(1) 2.2880(10), Ir(1)–S(1) 2.1971(11), Ir(1)–C(16)
2.158(4), Ir(1)–C(18) 2.193(4), Ir(1)–C(20) 2.210(4), S(1)–Ir(1)–P(1)
87.63(4), S(1)–Ir(1)–C(17) 169.60(11), C(17)–Ir(1)–P(1) 101.65(11),
C(18)–Ir(1)–S(1) 140.16(12), C(18)–Ir(1)–P(1) 120.19(12).
clarity. Selected bond lengths (A) and angles (deg): Rh(1)–S(1) 2.269(3),
Rh(1)–P(1) 2.302(3), Rh(1)–O(1) 2.243(6), O(1)–Rh(1)–S(1) 81.74(19),
O(1)–Rh(1)–P(1) 78.73(19), S(1)–Rh(1)–P(1) 83.59(11), C(20)–Rh(1)–S(1)
108.3(3), C(20)–Rh(1)–P(1) 107.9(3), C(18)–Rh(1)–O(1) 104.9(3).
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Scheme 3 Synthesis of 3b by oxidation of 2b with O2 gas.
detailed analysis of the spectroscopic data (1H NMR, 11B NMR,
31P NMR and IR spectra).
Synthesis and characterization of complexes
Cp*Ir(3-OCH3-7-PPh2-8- S-7,8-C2B9H9)L (4-5) (L = CO, PPh3)
To explore the reactivity of complex 2a, we investigated the
reaction with Mo(CO)3(CH3CN)3 at room temperature in toluene
for direct formation of metal–metal bonds. The reaction was
stirred for two days at room temperature but there was no obvious
phenomena to observe. Then the reaction was stirred for one
more day at high temperature and the color changed from purple
to dark red. Complex 4 was obtained by recrystallization from
CH2Cl2–hexane and characterized by IR and NMR (1H, 11B, 31P)
spectroscopies. The IR spectrum exhibits one intense carbonyl
stretch at 2029 mm-1. Compared with complex 2a, the 1H NMR
and 11B NMR and 31P NMR suffer only minor changes.
Scheme 4
Fig. 4 ORTEP drawing of 4 with thermal ellipsoids drawn at the
30% level, all hydrogen atoms were omitted for clarity. Selected bond
˚
lengths (A) and angles (deg): Ir(1)–P(1) 2.316(3), Ir(1)–S(1) 2.377(3),
Ir(1)–C(16) 1.865(16), P(1)–Ir(1)–S(1) 82.84(10), C(16)–Ir(1)–S(1) 96.3(4),
C(16)–Ir(1)–P(1) 94.4(4).
coordinated by CO molecules on the basis of 2a and unfortunately
the formation of direct metal–metal bonds did not occur in 4. The
Ir(III) atom environment is transformed from a two-legged piano-
stool geometry in 2a to a three-legged version in 4. The Ir(1)–P(1)
˚
bond length (2.317 A) is a little longer than that of 2a while the
˚
Ir(1)–S(1) bond length (2.377 A) is much longer than that of 2a
˚
(2.1971(11) A), and all of them are comparable to those reported
Scheme 4 Reaction of 2a with CO and PPh3.
for the Ir(III) complexes with P,S-ligands.9,12 The Ir(1)–S(1) bond
length in 4 became normal and the reason may be due to the fact
that complex 4 is an 18-electron saturated complex and the p-type
interaction between the metal center and the pp orbital on the
sulfur atom in the 2a complex disappeared. The distance for the
Suitable crystals for X-ray crystallography of 4 were obtained
by slow diffusion of hexane into a concentrated solution of 4 in
THF. The crystallographic data for complex 4 are summarized in
Table 1; An ORTEP drawing of complex 4 and selected bonds and
angles are shown in Fig. 4. The molecular structure shows complex
4 is an 18-electron zwitterion whose central atom Ir(III) is further
˚
Ir(1)–C(16) carbonyl bond of 1.865 A and the nearly linear Ir(1)–
C(16)–O(1) bond angle of 165.08◦ in 4 are in excellent agreement
with the analogous lengths and angles reported for other iridium
1958 | Dalton Trans., 2010, 39, 1954–1961
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carbonyl complexes.18,19 The Cp* ring undergoes tilting of about
31.71◦ relative to the plane [Ir(1), S(1), P(1)] when 2a was converted
to 4. In the five-membered ring, the plane [Ir(1), S(1), P(1)] also
undergoes tilting of about 17.05◦ relative to the plane [S(1), P(1),
C(7), C(8)] when 2a was converted to 4. This complex is air- and
moisture-stable and soluble in common organic solvents such as
THF, CH2Cl2, toluene, and CH3CN. It should be noted that there
is one molecule of complex 4 and one surplus molecule of the
starting material 2a in the unit of this crystal.
vario EL III analyzer. IR (KBr) spectra were recorded on a
Nicolet FT-IR spectrophotometer.
The modified synthesis of 1-PPh2-1,2-C2B10H10
n-BuLi in hexane (1.6 m, 1.25 mL, 2 mmol) was added to a solution
of ortho-carborane (288 mg, 2 mmol) in DME (20 mL) at -15 ◦C,
and the reaction mixture was stirred for 1 h at this temperature, and
stirred at room temperature for the same period, then cooled again
to -15 ◦C and diphenylphosphino chloride (441.2 mg, 2 mmol)
was added slowly and the stirred reaction mixture was allowed
to warm to room temperature for 1 h, then refluxed for 4 h. The
DME was removed in vacuo and the residue extracted with n-
hexane. Evaporation of the filtrate gave a white solid. The target
compound was obtained by column chromatography on silica gel
eluted with CH2Cl2–hexane (1 : 5). Yield: 464 mg, 71%, 1H NMR
(400 MHz, CDCl3, ppm): d 3.47(s, 1H, Ccage–H), 7.22–7.79 (m,
10H, Phenyl). 31P NMR (162 MHz, CDCl3, H3PO4, ppm): d 75.33
(s, PPh2). About 7% of 1, 2-bis(diphenylphosphino)-o-carborane
was also obtained.
Complex 4 can be isolated quantitatively if CO was bubbled
through the solution of 2a in toluene for 1 h, which was confirmed
by IR, 1H NMR and elemental analyses.
We have also investigated the reaction of 2a with PPh3 in toluene.
The 1H NMR spectra exhibited two signals for the phenyl group
at d 7.35–7.45 and 7.62–7.66 ppm, a methoxyl group signal at d
3.36 ppm and a Cp* signal at d 1.50 ppm. The 31P NMR spectra
exhibited two signals for -PPh2 and -PPh3 at d 55.10, 114.26 ppm,
which indicated that the Ir atom was further coordinated by PPh3.
These spectroscopic data and the elemental analyses for H and C
indicate the formation of a new complex Cp*Ir(3-OCH3-7-PPh2-
8- S-7,8-C2B9H9)(PPh3). In 5, it is not hard to see that the PPh3
ligand is coordinated to the iridium(III) atom and the geometry at
the iridium(III) center is a three-legged piano-stool.
Synthesis of 1-PPh2-2-LiS-1,2-C2B10H10
n-BuLi in hexane (1.6 m, 1.25 mL, 2 mmol) was added to a solution
of 1-PPh2-1,2-C2B10H10 (164 mg, 0.5 mmol) in Et2O (15 mL)
at -10 ◦C, and the reaction mixture was stirred for 1 h at this
temperature, and the stirred reaction mixture was allowed to warm
Conclusion
In summary, 18-electron neutral Cp*M(Cl)(1-PPh2-2-S-1,2-
C2B10H10) (M = Ir, Rh) complexes have been synthesized and fully
characterized. The neutral closo-carborane can be deboronated
easily to result in the reactive 16-electron zwitterionic nido-
carborane Cp*M(3-OCH3-7-PPh2-8- S-7,8-C2B9H9) (M = Ir, Rh)
at very mild temperatures under the conditions of a polar solvent
(methanol) and a very weak base (pyrazine). An interesting
investigation of this deboronation reaction from neutral closo-
carborane complexes to zwitterionic nido-carborane complexes
was carried out. The p-type interaction of the M–S bond in
the zwitterion and the reactivity of the 16-electron unsaturated
complex were also investigated initially. Building on these results
and encouraged by our reported 16-electron Cp*MS2[C2B10H10]
(M = Co, Rh, Ir) and a great quantity of their derivatives,
utilizing its unsaturated attributes, much effort has been made
to synthesize novel complexes bearing direct metal–metal bonds
bridged by a mono sulfur atom and the results of these and related
investigations will be reported in the near future.
◦
to room temperature for 10 h, then cooled again to -10 C and
sulfur powder was added and stirred for 3 h at room temperature,
yielding a light yellow solution. The Et2O was removed in vacuo
and the residue was washed by n-hexane (5 mL) twice. Yield: 97%
(177.5 mg, 0.49 mmol). 1H NMR (400 MHz, CDCl3, ppm): 7.35–
7.79 (m, 10H, Phenyl).
Synthesis of complex 1a
[Cp*IrCl(m-Cl)]2 (197 mg, 0.25 mmol) was added to a THF
(10 mL) solution of 1-PPh2-2-LiS-1,2-C2B10H10 (183 mg, 0.5 mmol)
at -78 ◦C. This temperature was maintained for 0.5 h, then
the solution was stirred for 24 h at room temperature. The
solution gradually turned dark red suggesting the formation of
the Cp*Ir(Cl)(1-PPh2-2- S-1,2-C2B10H10) complex. The solvent
was removed in vacuo, and the residue was red in color and
washed with hexane twice. Fine red crystals of 1a (486 mg, 67.4%)
were obtained through recrystallization from CH2Cl2–hexane at
-18 ◦C. Anal. Calcd for C24H35B10ClPSIr: C, 39.9%; H, 4.88%.
Found: C, 40.3%; H, 4.95%. IR (KBr, disk): u, 2570 cm-1(B–H),
Experimental
1
1378 cm-1. H NMR(400 MHz, CDCl3, ppm): d 1.59 (s, 15H,
Cp*), 7.45–7.59 (m, 8H, Phenyl), 7.93–7.95 (m, 2H, Phenyl). 11B
NMR (160 MHz, CDCl3, ppm) d -2.19, -3.13, -5.29, -6.19, -8.98,
-9.97, -11.38, -14.45, -15.52, (in the ratio 1 : 1 : 1 : 1 : 1 : 1 : 2 : 1 : 1).
31P NMR (162 MHz, CDCl3, H3PO4, ppm): d 57.81 (s, PPh2).
All manipulations were carried out under
a
nitrogen
atmosphere using standard Schlenk techniques, unless
otherwise stated. Solvents were distilled under nitrogen
from sodium benzophenone (hexane, diethyl ether, THF,
dimethoxyethane (CH3OCH2CH2OCH3, DME)) or calcium
hydride (dichloromethane) and methanol was distilled over
Mg/I2. The starting material [Cp*MCl(m-Cl)](M = Ir, Rh)
was synthesized according to a literature procedure.17 Other
chemical reagents were obtained from commercial sources and
Synthesis of complex 1b
A procedure analogous to the preparation of 1a was used,
[Cp*RhCl(m-Cl)]2 (154.5 mg, 0.25 mmol) was added to a THF
(10 mL) solution of 1-PPh2-2-LiS-1,2-C2B10H10 (183 mg, 0.5 mmol)
at -78 ◦C. This temperature was maintained for 0.5 h, and
then the solution was stirred for 24 h at room temperature.
1
used without further purification. H NMR (400 MHz) and 11B
NMR (160 MHz) spectra were obtained on a VAVCE DMX-400
spectrometer. Elemental analysis was performed on an Elementar
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1
The solution gradually turned purple suggesting the formation
of phosphionothiolato the Cp*Rh(Cl)(1-PPh2-2-S-1,2-C2B10H10)
complex. Yield: 66% (417.8 mg, 0.33 mmol). Anal. Calcd for
C24H35B10ClPSRh: C, 45.5%; H, 5.57%. Found: C, 44.9%; H,
5.65%. IR (KBr, disk): u, 2557 cm-1(B–H), 1383 cm-1. 1H
NMR(400 MHz, CDCl3, ppm): d 1.59 (s, 15H, Cp*), 7.45–7.95 (m,
10H, Phenyl). 11B NMR (160 MHz, CDCl3, ppm): d -2.16, -3.15,
-6.65, -8.68, -9.97, -11.15, -14.45, (in the ratio 1 : 1 : 1 : 2 : 2 : 3).
31P NMR (162 MHz, CDCl3, H3PO4, ppm): d 70.62 (s, PPh2).
5.83%. IR (KBr): u(B–H, disk) 2545 cm-1. H NMR(400 MHz,
CDCl3, ppm): d 1.53 (s, 15H, Cp*), 3.36 (s, 3H, -OCH3), 7.43–7.83
(m, 10H, Phenyl). 11B NMR (160 MHz, CDCl3, ppm): d -2.19,
1
-4.37, -6.74, -10.54, -12.07, -15.78, -20.23, -22.72, -36.21. P
NMR (162 MHz, CDCl3, H3PO4, ppm): d 57.89 (s, PPh2).
Synthesis of complex 4
Method 1. Mo(CO)3(CH3CN)3 (15.2 mg, 0.05 mmol) was
added to the purple solution of 2a (36 mg, 0.05 mmol) in toluene,
and the mixture was refluxed for 12 h. The color changed gradually
from purple to dark red, then the solvent was removed in vacuo.
4 was isolated by recrystallisation from CH2Cl2–hexane at -18 ◦C
affording dark red crystals. Yield: 25.3 mg, 35%. Anal. Calcd for
C51H74B18Ir2O3P2S2: C, 42.53%; H, 5.18%. Found: C, 42.62%; H,
Synthesis of complex 2a
Method 1. AgOTf (36.0 mg, 0.14 mmol) was added to a
solution of 1a (91.5 mg, 0.125 mmol) in CH3OH at room
temperature and stirred for 4 h, and followed by filtration to
remove the insoluble compounds. Pyrazine (10.0 mg, 0.125 mmol)
was added to the above filtrate and stirred for 24 h, during this
period, a lot of purple insoluble compound was found and washed
by hexane twice and fine purple crystals of 2a were obtained
through recrystallization from CH2Cl2–hexane (46.4 mg, 52.6%).
Anal. Calcd for C25H37B9OPSIr: C, 42.5%; H, 5.28%. Found:
C, 43.1%; H, 5.22%. IR (KBr, disk): u(B–H) 2557 cm-1. 1H
NMR(400 MHz, d6-DMSO, ppm): d 1.57 (s, 15H, Cp*), 3.17 (s,
3H, -OCH3), 7.45–7.79 (m, 10H, Phenyl). 11B NMR (160 MHz, d6-
DMSO, ppm) d -2.77, -4.27, -6.82, -9.70, -10.78, -11.22, -12.90,
-20.02, -35.63. 31P NMR (162 MHz, d6-DMSO, H3PO4, ppm): d
68.32 (s, PPh2).
5.23%. IR (KBr): u(B–H, disk) 2526 cm-1, u(CO) 2029 cm-1. H
1
NMR(400 MHz, CDCl3, ppm): d 1.54 (s, 15H, Cp*), 1.24(s, 15H,
Cp*), 3.32 (s, 3H, -OCH3), 3.15(s, 3H, -OCH3), 7.34–7.73 (m, 20H,
Phenyl). 31P NMR (162 MHz, CDCl3, H3PO4, ppm): d 58.79 (d,
J(P–P) = 73, PPh2).
Method 2. A solution of complex 2a (36 mg, 0.05 mmol) in
toluene was treated with excess CO gas for 1 h at room temperature.
The purple color of the solution faded quickly to give a dark
red solution. The volatile substances were then removed in vacuo,
and the resulting solid was extracted with CH2Cl2. Addition of
hexane to the concentrated extract gave complex 4 as dark red
crystals. Yield: 33.3 mg, 91%. Anal. Calcd for C26H37B9O2PSIr:
C, 42.54%; H, 5.08%. Found: C, 42.50%; H, 5.12%. IR (KBr):
Method 2. AgOTf (282 mg, 1.1 mmol) was added to a
suspension of [Cp*IrCl(m-Cl)]2 (197 mg, 0.25 mmol) in CH3OH
at room temperature and stirred for 4 h, followed by filtration
to remove the insoluble compounds. The filtrate was added to a
solution of freshly prepared 1-PPh2-2-LiS-1,2-C2B10H10 (183 mg,
0.5 mmol). At the same time, pyrazine (20 mg, 0.25 mmol) was
added to the mixture, and stirred for 48 h, during this period, the
deposited purple solid of 2a was also obtained (341 mg, 48.3%).
1
u(B–H, disk) 2528 cm-1, u(CO) 2033 cm-1. H NMR(400 MHz,
CDCl3, ppm): d 1.73 (s, 15H, Cp*), 3.33(s, 3H, -OCH3), 7.42–7.78
(m, 10H, Phenyl). 11B NMR (160 MHz, CDCl3, ppm): d -2.17,
-4.57, -6.52, -9.35, -10.48, -11.72, -13.79, -20.67, -34.98. 31P
NMR (162 MHz, CDCl3, H3PO4, ppm): d 58.62 (s, PPh2).
Synthesis of 5
PPh3 (13.2 mg, 0.05 mmol) was added to the purple solution of
2a (36 mg, 0.05 mmol) in CH2Cl2 and the mixture was stirred
for 12 h, The color changed from purple to dark red, then the
solvent was removed in vacuo. 5 was isolated by recrystallisation
from CH2Cl2–hexane at -18 ◦C affording dark red crystals. Yield:
48.3 mg, 87%. Anal. Calcd for C43H52B9OP2SIr: C, 53.33%; H,
5.41%. Found: C, 53.41%; H, 5.47%. IR (KBr): u(B–H, disk)
Synthesis of complex 2b
A procedure analogous to the preparation of 2a was used, but
[Cp*RhCl(m-Cl)]2 (154 mg, 0.25 mmol), the deposited dark red
solid of 2b was obtained (376 mg, 61.1%). The red complex was
obtained through recrystallization from CH2Cl2–hexane. Anal.
Calcd for C25H37B9OPSRh: C, 48.7%; H, 6.05%. Found: C, 49.2%;
H, 5.97%. IR (KBr, disk): u(B–H) 2569 cm-1. 1H NMR (400 MHz,
CDCl3, ppm): d 1.85 (s, 15H, Cp*), 3.48 (s, 3H, -OCH3), 7.45–7.73
(m, 10H, Phenyl). 11B NMR (160 MHz, CDCl3, ppm): d -0.15,
1
2543 cm-1. H NMR (400 MHz, CDCl3, ppm): d 1.50 (s, 15H,
Cp*), 3.36 (s, 3H, -OCH3), 7.35–7.45 (m, 20H, Phenyl), 7.62–7.66
(m, 5H, Phenyl). 11B NMR (160 MHz, CDCl3, ppm): d -2.66,
-5.03, -6.81, -7.89, -10.54, -12.02, -12.56, -19.95, -35.23. 31P
NMR (162 MHz, CDCl3, H3PO4, ppm): d 55.10 (s, PPh2), 114.26
(s, PPh3).
-6.24, -13.54, -14.04, -15.73, -19.91, -22.21, -23.92, -35.57. 31
NMR (162 MHz, CDCl3, H3PO4, ppm): d 66.63 (s, PPh2).
P
Synthesis of complex 3b
X-Ray crystallography
A solution of complex 2b (30.8 mg, 0.05 mmol) in 5 mL ethyl
acetate and 5 mL methanol was treated with an excess of O2
gas for 1 h at room temperature. The red color of the solution
faded quickly to give an orange solution. The volatile substances
were then removed in vacuo, and the resulting solid was extracted
with CH2Cl2. Addition of hexane to the concentrated extract
gave complex 3b (25.9 mg, 80%) as red crystals. Anal. Calcd for
C25H37B9O3PSRh: C, 46.28%; H, 5.75%. Found: C, 46.53%; H,
Diffraction data of 1a, 2a, and 3b and 4 were collected on a Bruker
Smart APEX CCD diffractometer with graphite-monochromated
˚
Mo Ka radiation (l = 0.71073 A). 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),20 SADABS21 absorption
corrections were applied to the data. All the non-hydrogen atoms
1960 | Dalton Trans., 2010, 39, 1954–1961
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were refined anisotropically, and hydrogen atoms were located
at calculated positions. There are disordered solvent molecules
in the crystal of 3b, which can not be solved properly. Hence
the SQUEEZE algorithm was used to omit them and the crystal
data was refined to convergence. A summary of the crystallo-
graphic data and selected experimental information are given in
Table 1.
Zhu, A. T. Peng, K. Carpenter, J. A. Maguire, N. S. Hosmane and
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Acknowledgements
This work was supported by the National Science Foundation
of China (20531020, 20721063, 20771028), Shanghai Science and
Technology Committee (08DZ2270500, 08DJ1400103), Shanghai
Leading Academic Discipline Project (B108) and the National
Basic Research Program of China (2009CB825300).
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 1954–1961 | 1961
©