Transmetalation reactions yield new tetra- and pentairidium carbonyl complexes containing σ-bonded phenyl rings

Article abstract of DOI:10.1021/om2007198

The new air-stable σ-phenyl tetrairidium carbonyl salt [Et ₄N][Ir₄(CO)11Ph], 1, has been obtained by transmetalation reactions between [Et₄N][Ir₄(CO)₁₁Br] and SnPh₃OH in 45% yield or SnPh₄ in 36% yield. Compound 1 reacts with PPh₃ to yield the complex [Et₄N][Ir ₄(CO)₁₁(PPh₂C₆H₄)], 2, which contains an ortho-metalated bridging PPh2C6H4 ligand across an edge of a tetrahedral cluster of four iridium atoms. Compound 2 reacts with Ir(CO)(PPh₃)₂Cl by halide displacement to yield the two new uncharged pentairidium complexes Ir₅(CO)₁₂(Ph) (PPh₃), 3, and Ir₅(CO)₁₁(PPh ₃)(PPh₂C₆H₄), 4. Compounds 3 and 4 both contain trigonal-bipyramidal clusters of iridium atoms. Compound 3 contains a σ-phenyl ligand coordinated to one of the apical iridium atoms. Compound 4 contains an ortho-metalated PPh₂C₆H₄ ligand that bridges an apical-equatorial edge of the trigonal-pyramidal cluster of metal atoms. Compound 4 was also obtained from 3 by reaction with PPh ₃.

Full text of DOI:10.1021/om2007198

ARTICLE
pubs.acs.org/Organometallics
Transmetalation Reactions Yield New Tetra- and Pentairidium
Carbonyl Complexes Containing σ-Bonded Phenyl Rings
Richard D. Adams* and Mingwei Chen
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
S Supporting Information
b
ABSTRACT: The new air-stable σ-phenyl tetrairidium carbonyl salt [Et4N][Ir4(CO)11Ph], 1,
has been obtained by transmetalation reactions between [Et4N][Ir4(CO)11Br] and SnPh3OH in
45% yield or SnPh4 in 36% yield. Compound 1 reacts with PPh3 to yield the complex
[Et4N][Ir4(CO)11(PPh2C6H4)], 2, which contains an ortho-metalated bridging PPh2C6H4
ligand across an edge of a tetrahedral cluster of four iridium atoms. Compound 2 reacts with
Ir(CO)(PPh3)2Cl by halide displacement to yield the two new uncharged pentairidium
complexes Ir5(CO)12(Ph)(PPh3), 3, and Ir5(CO)11(PPh3)(PPh2C6H4), 4. Compounds 3 and
4 both contain trigonal-bipyramidal clusters of iridium atoms. Compound 3 contains a σ-phenyl
ligand coordinated to one of the apical iridium atoms. Compound 4 contains an ortho-metalated
PPh2C6H4 ligand that bridges an apical-equatorial edge of the trigonal-pyramidal cluster of metal
atoms. Compound 4 was also obtained from 3 by reaction with PPh3.
’ INTRODUCTION
Ir4(CO)12 and Ir4(CO)11(PPh3) with SnPh3OH in the presence
of [OH]ꢀ, eq 2.11
Applications of iridium in catalysis have developed slowly
compared to those of other metals from the precious metals
group.1 Most catalytic applications are of a homogeneous type.2
Today iridium is the catalyst of choice for the synthesis of acetic
acid by the carbonylation of methanol.3 Sinfelt showed that the
addition of iridium greatly improved the activity of platinum for
the catalytic reforming of petroleum.4 Gates has shown that
iridium carbonyl cluster complexes are precursors to catalysts
that exhibit good activity for hydrogenation of aromatics.5 Tin
has been shown to be a valuable modifier of homogeneous
transition metal catalysts.6 We have recently been investigating
the synthesis and reactivity of polynuclear transition metal
carbonyl complexes containing organotin ligands.7,8 To date,
there have been very few examples of iridium carbonyl cluster
complexes that contain tin ligands. Garlaschelli et al. have
obtained a number of tetra- and hexairidium carbonyl complexes
containing bridging SnX3 ligands, X = Cl and Br, from reaction of
the complex anion [Ir4(CO)11Br]ꢀ and Ir6(CO)16 with SnCl2,
SnBr2, and the anion [SnCl3]ꢀ.9 The triiridium complex Ir3-
(CO)6(SnPh3)3(μ-SnPh2)3 was obtained from the reaction of
Ir4(CO)12 with an excess of HSnPh3 at 125 °C, eq 1.10
We have now investigated the reaction of the anion
[Ir4(CO)11Br]ꢀ with SnPh3OH and SnPh4. Interestingly,
the iridium-containing product from these reactions, [Et4N]-
[Ir4(CO)11Ph], 1, does not contain a tin ligand, but instead
contains a terminally coordinated σ-phenyl ligand. SnPh4 has
been shown to be useful as a source of phenyl for palladium-
catalyzed Stille coupling reactions.12 Tilley has reported that
hafnium complexes containing the SnPh3 ligand can eliminate
a SnPh2 group to form complexes containing a σ-phenyl group,
e.g., eq 3.13
We have recently obtained some new tetrairidium carbonyl
complexes containing SnPh3 ligands from the reactions of
Received: August 2, 2011
Published: October 11, 2011
r
2011 American Chemical Society
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Organometallics
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Table 1. Crystallographic Data for Compounds 1ꢀ4
1
2
3
4
empirical formula
fw
Ir4NC25H25O11
1284.33
Ir4PNC36H34O10
1440.49
Ir5PC36H20O12
1636.59
Ir5P2C47H29O11
1792.75
cryst syst
lattice params
a (Å)
monoclinic
monoclinic
monoclinic
monoclinic
15.6537(8)
13.4349(7)
16.4958(9)
90
33.565(4)
13.5442(18)
19.622(3)
90
18.5348(4)
13.0734(3)
15.9317(4)
90
16.2096(8)
19.9166(10)
16.9894(8)
90
b (Å)
c (Å)
α (deg)
β (deg)
113.836(1)
90
103.262(3)
90
103.922(1)
90
108.529(1)
90
γ (deg)
V (Å3)
3173.3(3)
P21/n, 14
4
8683(2)
C2/c, 15
8
3747.05(15)
P21/c, 14
4
5200.5(4)
P21/n, 14
4
space group, No.
Z value
F
calc (g/cm3)
2.688
2.270
2.901
2.448
μ(Mo Kα) (mmꢀ1
temperature (K)
2Θmax (deg)
)
16.775
12.312
17.798
12.971
294(2)
294(2)
56.68
294(2)
294(2)
48.88
56.58
56.78
no. obsd (I > 2σ(I))
no. params
6457
7679
6609
7459
332
474
487
529
goodness of fit (GOF)
1.085
1.059
0.999
1.097
max. shift in cycle
0.001
0.001
0.001
0.001
residuals:a R1; wR2
0.0477; 0.1266
multiscan 1.000/0.417
2.70
0.0432; 0.1261
multiscan 1.000/0.531
2.08
0.0453; 0.1339
multiscan 1.000/0.540
1.15
0.0622; 0.2054
multiscan 1.000/0.426
2.38
absorp corr, max./min.
largest peak in final diff map (eꢀ/Å3)
a R = ∑hkl(||Fobs| ꢀ |Fcalc||)/∑hkl|Fobs|; Rw = [∑hklw(|Fobs| ꢀ |Fcalc|)2/∑hklwF2
]
1/2; w = 1/σ2(Fobs); GOF = [∑hklw(|Fobs| ꢀ |Fcalc|)2/(ndata ꢀ nvari)]1/2
.
obs
solvent was then removed in vacuo, and the product was isolated
by TLC by eluting with methylene chloride solvent to yield light
yellow [Et4N][Ir4(CO)11Ph], 1, 13.5 mg (45% yield). Spectral
data for 1: IR νCO (cmꢀ1 in CH2Cl2): 2067(m), 2028(vs),
1991(s), 1821(m), 1801(m). 1H NMR (CDCl3, in ppm):
δ 6.65ꢀ6.69 (m, 5H, σ-Ph), 0.95ꢀ0.98 (t, 12H, CH3),
1.182ꢀ1.452 (m, 8H, CH2). MS ES (negative ion) for 1:
m/z = 1155 (MH). The isotope distribution pattern was con-
sistent with the presence of four iridium atoms.
The use of aryl tin reagents may serve a convenient and
effective method for preparing polynuclear metal carbonyl com-
plexes containing σ-phenyl ligands from metal carbonyl com-
plexes containing halide ligands.
(b) A 30.0 mg (0.076 mmol) amount of SnPh4 was added to 25.0 mg
(0.019 mmol) of [Et4N][Ir4(CO)11Br] in 25 mL of methanol.
The reaction mixture was stirred at room temperature for 16 h.
The solvent was then removed in vacuo. A119Sn NMR spectrum
of the entire reaction mixture in CD2Cl2 solvent showed only two
resonances, δ = ꢀ60.48 (SnPh3Br)15 and ꢀ129.79 (unreacted
SnPh4, confirmed by recording a spectrum of a sample of the SnPh4
from the reagent bottle). The product 1 was isolated by TLC by
eluting with a 6:1 methylene chloride/hexane solvent mixture to
yield 10.9 mg (yield 36.4%).
’ EXPERIMENTAL SECTION
General Data. Reagent grade solvents were dried by the standard
procedures and were freshly distilled under nitrogen prior to use.
Infrared spectra were recorded on a Thermo Nicolet Avatar 360 FT-
1
IR spectrophotometer. H NMR spectra were recorded on a Varian
Mercury 300 spectrometer operating at 300.1 MHz. Mass spectrometric
(MS) measurements performed by a direct-exposure probe using
electron impact ionization (EI) and electrospray ionization (ESI) were
made on a VG 70S instrument. SnPh3OH and Ir(CO)(PPh3)2Cl were
obtained from Strem and were used without further purification. SnPh4
was purchased from Gelest. [Et4N][Ir4(CO)11Br] was prepared accord-
ing to the published procedure.14 Product separations were performed
by TLC in air on Analtech 0.25 and 0.5 mm silica gel 60 Å F254 glass
plates.
Reaction of 1 with PPh3 at 80 °C. A 2.0 mg (0.0076 mmol)
amount of PPh3 was added to 7.5 mg (0.0058 mmol) of 1 dissolved in
20 mL of benzene. The reaction solution was then heated to reflux for
1 h. After cooling, the solvent was removed in vacuo, and the product was
isolated by TLC by eluting with a 3:1 hexane/methylene chloride
solvent mixture to yield 5.0 mg of [Et4N][Ir4(CO)10(PPh2C6H4)], 2
(60% yield). Spectral data for 2: IR νCO (cmꢀ1 in CH2Cl2): 2044(s),
1
2012(vs), 1978(vs), 1800(m), 1761(m). H NMR (CDCl3, in ppm):
δ 7.19ꢀ7.32 (m, 14H, Ph), 0.91ꢀ0.97 (t, 12H, CH3), 1.15ꢀ1.48
(m, 8H, CH2). MS ES (negative ion) for 2: m/z = 1311 (MH). The
isotope distribution pattern was consistent with the presence of four
iridium atoms.
Synthesis of [Et4N][Ir4(CO)11Ph], 1
(a) A 25.0 mg (0.068 mmol) amount of SnPh3OH was added to 30.0
mg (0.023 mmol) of [Et4N][Ir4(CO)11Br] in 25 mL of metha-
nol. The reaction was stirred at room temperature for 12 h. The
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Reaction of 2 with HBF4 under CO. A 0.06 mL amount of HBF4
(51% in diethyl ether) was added to 14.0 mg (0.0097 mmol) of
[Et4N][Ir4(CO)11(PPh2C6H4)] dissolved in 20 mL of methanol. The
reaction was stirred under an atmosphere of CO for 1 h. The solvent was
removed in vacuo, and the product was then isolated by TLC by eluting
with a 3:1 hexane/methylene chloride solvent mixture to yield 11.4 mg
of the known compound Ir4(CO)11(PPh3)16 (81%) and 1.0 mg of
Ir4(CO)12.
Reaction of [Et4N][Ir4(CO)11Ph], 1, with Ir(CO)(PPh3)2Cl. A
9.20 mg (0.0118 mmol) amount of Ir(CO)(PPh3)2Cl was added to
14.4 mg (0.0112 mmol) of [Et4N][Ir4(CO)11Ph] that was dissolved in
25 mL of benzene. The reaction solution was heated to reflux for 2 h.
The solvent was then removed in vacuo, and the product was isolated by
TLC by eluting with a 3:1 hexane/methylene chloride solvent mixture.
This yielded in order of elution 1.56 mg of brown Ir5(CO)12Ph(PPh3), 3
(11% yield), 3.50 mg of brown Ir5(CO)11(PPh3)(PPh2C6H4), 4 (22%
yield), 6.02 mg of yellow 2 (37% yield), and 1.21 mg of Ir4(CO)11-
(PPh3)16 (8% yield). The yield of 4 was increased to 40% at the expense
of 3 (only a trace) and 2 (17%) when the reflux period was increased to
5 h. Spectral data for 3: IR νCO (cmꢀ1 in CH2Cl2): 2080(w), 2053(vs),
2045(vs), 2018(s), 1841(m), 1813(m). 1H NMR (CDCl3, in ppm): δ
7.19ꢀ7.41 (m, 15H, Ph), 6.67ꢀ6.72 (m, 5H, σ-Ph). MS ES (negative
ion) for 3: m/z = 1635 (MH). The isotope distribution pattern was
consistent with the presence of five iridium atoms. Spectral data for 4: IR
νCO (cmꢀ1 in CH2Cl2): 2061(s), 2038(vs), 2022(s), 2007(s), 1990(m),
1850(m), 1816(m), 1787(m). 1H NMR (CDCl3, in ppm): δ 7.19ꢀ7.42
(m, 29H, Ph). MS ES (positive ion) for 4: m/z = 1794 (M+), 1831(M +
K+). The isotope distribution pattern was consistent with the presence
of five iridium atoms.
Figure 1. ORTEP diagram of the molecular structure of the complex
anion [Ir4(CO)11Ph]ꢀ of 1 showing 30% thermal ellipsoid probability.
The hydrogen atoms on the phenyl ring are not shown for clarity.
Selected interatomic bond distances (Å) and angles (deg) are as follows:
Ir1ꢀIr2 = 2.7494(7), Ir1ꢀIr3 = 2.7393(7), Ir1ꢀIr4 = 2.7515(7),
Ir2ꢀIr3 = 2.7015(7), Ir2ꢀIr4 = 2.7235(7), Ir3ꢀIr4 = 2.7317(7),
Ir1ꢀC44 = 2.125(13); C44ꢀIr1ꢀIr2 = 104.4(4), Ir4ꢀIr1ꢀC44 =
160.0(4).
Synthesis of 4 by the Reaction of 2 with Ir(CO)(PPh3)2Cl. A
7.3 mg (0.0094 mmol) sample of Ir(CO)(PPh3)2Cl was added to 13 mg
(0.0090 mmol) of 4 dissolved in 25 mL of benzene. The reaction was
heated to reflux for 5 h. The solvent was removed in vacuo, and the
product was then isolated by TLC by eluting with a 3:1 hexane/
methylene chloride solvent mixture. Yield: 1.78 mg of 4 (11%).
Synthesis of 4 by the Reaction of 3 with PPh3. A 1.2 mg
(0.0046 mmol) amount of PPh3 was added to 5.6 mg (0.0042 mmol) of
3 dissolved in 20 mL of benzene. The reaction was heated to reflux for
1.5 h. The solvent was then removed in vacuo, and the product was
isolated by TLC by eluting with a 3:1 hexane/methylene chloride
solvent mixture. Yield: 2.66 mg of 4 (43% yield).
Crystallographic Analyses. Single crystals of 1 (yellow), 2
(yellow), and 3 (brown) suitable for X-ray diffraction analyses were
obtained by slow evaporation of solvent from hexane/methylene
chloride solvent mixtures at ꢀ25 °C. Single crystals of compound 4
were grown from a benzene/methylene chloride solvent mixture by slow
evaporation of solvent at room temperature. Each data crystal was glued
onto the end of a thin glass fiber. X-ray intensity data were measured by
using a Bruker SMART APEX CCD-area detection diffractometer by
using Mo Kα radiation (λ = 0.71073 Å). The raw data frames were
integrated with the SAINT+ program by using a narrow-frame integra-
tion algorithm.17 Corrections for Lorentz and polarization effects were
also applied with SAINT+. An empirical absorption correction based on
the multiple measurement of equivalent reflections was applied in each
analysis by using the program SADABS. All structures were solved by a
combination of direct methods and difference Fourier syntheses and
refined by full-matrix least-squares on F2, using the SHELXTL software
package.18 All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were placed in geometrically
idealized positions and included as standard riding atoms during the
least-squares refinements. Crystal data, data collection parameters, and
results of the analyses are listed in Table 1. Compounds 1, 2, 3, and 4 all
crystallized in the monoclinic crystal system. The space group P21/n was
indicated by the systematic absences in the intensity data for compounds
1 and 4 and was confirmed by the successful solutions and refinements of
those structures. There is one symmetry-independent molecule in the
asymmetric unit in the crystal structures of 1 and of 4. The systematic
absences in the intensity data for compound 2 were consistent with the
space groups Cc and C2/c. The centrosymmetric space group C2/c was
selected and confirmed by the successful solution and refinement of the
structure. There is one symmetry-independent molecule of 2 in the
asymmetric crystal unit. The crystal of 2 also contains a half-molecule of
hexane from the crystallization solvent that was cocrystallized with the
complex. The space group P21/c was identified uniquely on the basis of
the systematic absences in the intensity data for compound 3. There is
one molecule of methylene chloride and a half-molecule of benzene
from the crystallization solvent cocrystallized with 4 in the asymmetric
crystal unit. The solvent molecules were satisfactorily refined with
isotropic thermal parameters.
’ RESULTS AND DISCUSSION
The new air-stable tetrairidium anion [Ir4(CO)11(σ-Ph]ꢀ, 1,
was isolated as the [Et4N]+ salt in 45% yield from the reaction of
[Et4N][Ir4(CO)11Br] with SnPh3OH. [Et4N]1 was character-
1
ized by a combination of IR, H NMR, MS, and single-crystal
X-ray diffraction analyses. An ORTEP diagram of the tetrair-
idium anion 1 is shown in Figure 1. The structure of the anion 1 is
similar to that of the complex anion [Ir4(CO)11Br]ꢀ from which
it was made.19 The anion 1 consists of a tetrahedral Ir4 cluster
with 11 carbonyl ligands distributed as shown in the figure. There
are three bridging carbonyl ligands. All of the other CO ligands are
terminally coordinated. The IrꢀIr bond distances are similar to
those found in the anion [Ir4(CO)11Br]ꢀ.19 The anion 1
contains one σ-phenyl ligand that is terminally coordinated to
iridium atom Ir(1). The IrꢀC bond distance to the phenyl
ligand, Ir(1)ꢀC(44) = 2.125(13) Å, is slightly longer than the
IrꢀC distances to the σ-phenyl ligands in the previously reported
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Figure 3. ORTEP diagram of the molecular structure of Ir5(CO)12Ph-
(PPh3), 3, showing 30% thermal ellipsoid probability. Hydrogen atoms
are not shown for clarity. Selected interatomic bond distances (Å) and
angles (deg) are as follows: Ir1ꢀIr2 = 2.7303(8), Ir1ꢀIr3 = 2.8268(8),
Ir1ꢀIr4 = 2.7215(8), Ir2ꢀIr3 = 2.6848(8), Ir2ꢀIr4 = 2.7988(8),
Ir2ꢀIr5 = 2.7765(8), Ir3ꢀIr4 = 2.7021(8), Ir3ꢀIr5 = 2.7629(8),
Ir4ꢀIr5 = 2.7912(8), Ir5ꢀC4 = 2.116(16), Ir1ꢀP1 = 2.311(4);
P1ꢀIr1ꢀIr2 = 115.81(9), P1ꢀIr1ꢀIr3 = 171.83(9), C4ꢀIr5ꢀIr2 =
102.1(4), C4ꢀIr5ꢀIr4 = 160.3(4), Ir1ꢀIr3ꢀIr5 = 108.93(2).
Figure 2. ORTEP diagram of the molecular structure of the complex
anion [Ir4(CO)10(PPh2C6H4)]ꢀ of 2 showing 30% thermal ellipsoid
probability. Hydrogen atoms are not shown for clarity. Selected intera-
tomic bond distances (Å) and angles (deg) are as follow: Ir1ꢀIr2 =
2.7367(6), Ir1ꢀIr3 = 2.6633(6), Ir1ꢀIr4 = 2.7434(7), Ir2ꢀIr3 =
2.7383(7), Ir2ꢀIr4 = 2.7183(7), Ir3ꢀIr4 = 2.7728(7), Ir3ꢀC56 =
2.096(12), Ir1ꢀP1 = 2.286(3); P1ꢀIr1ꢀIr2 = 97.57(7), P1ꢀIr1ꢀIr3 =
90.32(8), P1ꢀIr1ꢀIr4 = 149.50(7), C56ꢀIr3ꢀIr1 = 93.3(3).
Ir3, Ir4, and Ir8 complexes: Ir3(CO)9(Ph)(μ3-PPh)(μ-dppm),
2.084(16) Å,20 Ir4(CO)8(σ-Ph)[μ4-η3-PhPC(H)CPh](μ-PPh2),
2.09(1) Å,21 and Ir8(CO)16(σ-Ph)(μ-PPh2)(μ4-PPh), 2.06(4) Å.22
Compound 1 was also obtained in 36.4% yield from the
reaction of SnPh4 with [Et4N][Ir4(CO)11Br] in methanol sol-
vent over a 16 h period. An analysis of a reaction mixture by 119Sn
NMR spectroscopy revealed a resonance at δ = ꢀ60.48, which is
consistent with the formation of the tin compound SnPh3Br.15
This observation confirms that the formation of 1 by the reaction
with SnPh4 occurs by Br for Ph transmetalation, eq 4.
coordinated. The most interesting ligand is an edge-bridging
PPh2C6H4 group derived from the PPh3 reagent that became
ortho-metalated to one of the Ir atoms. The aryl group is σ-bonded
to Ir(3). The IrꢀC bond, Ir3ꢀC56 = 2.096(12) Å, is similar in
length to that of the σ-bonded phenyl group in anion 1. The
shortest IrꢀIr bond in the cluster is the one bridged by the
PPh2C6H4 ligand, Ir1ꢀIr3 = 2.6633(6) Å. The longest IrꢀIr bond
is the one trans to the σ-bonded aryl group, Ir3ꢀIr4 = 2.7728(7) Å.
This may be due to a strong trans-structural effect of the σ-bonded
aryl group.26 The fate of the phenyl group that was eliminated from
1 in the reaction and that of the hydrogen atom that was cleaved
from the ortho-position of the metalated phenyl ring in 2 has not
been established. It is presumed that they have been combined to
form benzene.
Interestingly, when anion 2 was treated with HBF4 under an
atmosphere of CO for 1 h, the anion was neutralized by the
addition of H+. The H+ was added to the carbon atom of the
metalated phenyl ring. A CO ligand was added to the complex,
and the known compound Ir4(CO)11(PPh3)16 was obtained in
81% yield together with a trace of Ir4(CO)12.
Compounds 2 (37% yield) and Ir4(CO)11(PPh3) (8% yield)
together with two new pentairidium compounds, Ir5(CO)12Ph-
(PPh3), 3 (11% yield), and Ir5(CO)11(PPh3)(PPh2C6H4), 4
(22% yield), were obtained from the reaction of 1 with Ir(CO)-
(PPh3)2Cl in a benzene at reflux. The yield of 4 was increased to
40% at the expense of the formation of 3 by increasing the
reaction time to 5 h, probably because 3 reacts with PPh3 to yield
4; see below. Compounds 3 and 4 were both characterized by
single-crystal X-ray diffraction analysis. An ORTEP diagram of
the molecular structure of 3 is shown in Figure 3. The compound
contains a trigonal-bipyramidal cluster of five iridium atoms. The
apical iridium atom Ir(1) contains a PPh3 ligand, and apical
½Ir4ðCOÞ Brꢁꢀ þ SnPh4 f ½Ir4ðCOÞ Phꢁꢀ þ SnPh3Br
11
11
ð4Þ
Transmetalation reactions between aryltin compounds and
metal halide complexes of platinum23 and palladium24 have been
known for some years. Recently, aryltin compounds have been
used to transfer aryl groups to gold(I) halides.25 Tin compounds
also form the basis for the important transmetalation step in the
well-known Stille coupling reactions.12 Although SnPh3OH
reacts with Ir4(CO)12 in the presence of base to yield Ir4Sn
complexes, eq 2, we think the reaction with the bromo complex
[Ir4(CO)11Br]ꢀ reported to yield 1 here in the absence of base
proceeds instead by a transmetalation process.
When compound 1 was allowed to react with PPh3 in benzene
solvent at reflux for 1 h, the new compound [Et4N][Ir4(CO)10-
(PPh2C6H4)], 2, was obtained and isolated in 60% yield. Com-
pound 2, a salt, was characterized by a combination of IR, 1H NMR,
MS, and single-crystal X-ray diffraction analyses. An ORTEP
diagram of the tetrairidium anion of 2 is shown in Figure 2. The
anion of 2 consists of a tetrahedral Ir4 cluster with 10 carbonyl
ligands. Three of the CO ligands are bridging ligands about the
Ir(1)ꢀIr(2)ꢀIr(3) triangle. The other CO ligands are terminally
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iridum atom Ir(5) contains a terminally coordinated σ-phenyl
ligand. The IrꢀIr bond distances span a considerable range,
2.6848(4)ꢀ2.8269(8) Å. The two longest IrꢀIr bonds lie trans
to the phosphine and σ-phenyl ligands, Ir(1)ꢀIr(3) = 2.8269(8)
Å and Ir(4)ꢀIr(5) = 2.7912(8) Å, respectively. The IrꢀC bond
to the σ-phenyl ligand is similar in length to that found in 1,
Ir5ꢀC4 = 2.116(16) Å. Compound 3 has four bridging carbonyl
ligands with two bridging to each of the apical Ir atoms of the cluster.
An ORTEP diagram of the molecular structure of 4 is shown
in Figure 4. This compound also consists of a trigonal-pyramidal
cluster of five iridium atoms. As in 3, the apical iridium atom Ir(1)
also contains a PPh3 ligand. There is a bridging PPh2C6H4 ligand
similarto that foundin2 withthe phosphorus atom coordinatedto
Ir(5) and the metalated phenyl ring coordinated to the equatorial
Ir atom, Ir(2), Ir2ꢀC70 = 2.14(2) Å. The PPh2C6H4-bridged
bond Ir(2)ꢀIr(5) is the shortest in the molecule, 2.6891(8) Å,
and the Ir(1)ꢀIr(3) bond that lies trans to the PPh3 ligand is the
longest in the molecule, 2.8269(8) Å, as found in 3. Anion 2 was
found to react with Ir(CO)(PPh3)2Cl to give compound 4 in
11% yield, and 3 was transformed into 4 in 43% yield in a CO
ligand substitution reaction with PPh3 that also results in metal-
lation of one of the PPh3 rings and the elimination of benzene.
A summary of the reactions described in this report is shown in
Scheme 1. The new air-stable anionic tetrairidium complex 1
containing a terminally coordinated ligand was obtained via a
phenyl for Br exchange (transmetalation) reaction between
[Ir4(CO)11Br]ꢀ and the tin reagents SnPh3OH and SnPh4.
Anion 1 reacts with PPh3 to yield the tetrairidium anion 2 by
the addition of one PPh3 ligand, loss of one CO ligand, and an
ortho-metalation of one of the phenyl rings of the PPh3 ligand.
The original phenyl ligand in 1 and the hydrogen atom that was
cleaved from the metalated phenyl ring were eliminated from the
complex in this reaction; presumably they were combined to
form benzene. When 2 was treated with H+ in the presence of
CO, the ortho-metalation was reversed presumably via proton-
ation at one of the metal atoms followed by CꢀH reductive
elimination of the metalated phenyl ring and the addition of CO
to that site. Treatment of 1 with Ir(CO)(PPh3)2Cl also yielded
some 2, possibly by a simple competing reaction of 1 with some
PPh3 released from the Ir(CO)(PPh3)2Cl. In addition the two
new pentairidium complexes 3 and 4 were obtained from this
reaction. Complex 3 was formed by an addition of one equivalent
of Ir(CO)(PPh3)2Cl to 1 accompanied by the loss of one PPh3
Figure 4. ORTEP diagram of the molecular structure of Ir5(CO)11-
(PPh3)(PPh2C6H4), 4, showing 30% thermal ellipsoid probability.
Hydrogen atoms are not shown for clarity. Selected interatomic bond
distances (Å) and angles (deg) are as follows: Ir1ꢀIr2 = 2.7555(12),
Ir1ꢀIr3 = 2.7932(12), Ir1ꢀIr4 = 2.7047(13), Ir2ꢀIr5 = 2.6891(12),
Ir3ꢀIr5 = 2.6948(12), Ir4ꢀIr5 = 2.7607(14), Ir2ꢀC70 = 2.14(2),
Ir1ꢀP1 = 2.317(6), Ir5ꢀP2 = 2.289(7); P1ꢀIr1ꢀIr2 = 109.66(14),
P1ꢀIr1ꢀIr3 = 170.05(15), P2ꢀIr5ꢀIr2 = 93.34(16), P2ꢀIr5ꢀIr3 =
104.09(16), P2ꢀIr5ꢀIr4 = 154.95(16), Ir1ꢀIr2ꢀIr5 = 108.71(4),
Ir3ꢀIr2ꢀC70 = 103.8(6), Ir1ꢀIr2ꢀC70 = 138.1(5), Ir5ꢀIr2ꢀC70 =
90.1(5).
Scheme 1
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dx.doi.org/10.1021/om2007198 |Organometallics 2011, 30, 5867–5872

Organometallics
ARTICLE
ligand and Clꢀ. Compound 4 was formed by an addition of one
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one CO ligand and Clꢀ. Interestingly, compound 4 was also
obtained by the reaction of 2 with one equivalent of Ir(CO)-
(PPh3)2Cl that was accompanied by the loss of one PPh3 ligand
and Clꢀ and also by reaction of 3 with PPh3 that was accom-
panied by a loss of CO and the elimination of the σ-phenyl ligand
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’ CONCLUSIONS
Phenyl-substituted tin compounds are active for the synthesis
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by halide displacement to yield uncharged pentairidium com-
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’ ASSOCIATED CONTENT
S
Supporting Information. CIF files for the structural
b
analyses are available. This material is available free of charge
via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: Adams@mail.chem.sc.edu.
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’ ACKNOWLEDGMENT
(25) (a) Meyer, N.; Sivanathan, S.; Mohr, F. J. Organomet. Chem.
2011, 696, 1244–1247. (b) Meyer, N.; Lehmann, C. W.; Lee, T. K. M.;
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(c) Bojan, R. V.; Lꢀopez-de-Luzuriaga, J. M.; Monge, M.; Olmos, M. E.
J. Organomet. Chem. 2010, 696, 2385–2393.
This research was supported by the National Science Founda-
tion under grant no. CHE-1111496. We thank the USC Nano-
Center for financial support of this work and Mr. Qiang Zhang
for assistance with the structural analyses.
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