Synthesis and characterizations of bismuth-bridged triiridium carbonyl complexes containing germyl/germylene and stannyl/stannylene ligands

Article abstract of DOI:10.1021/om300813t

The reaction of Ir₃(CO)₉(μ₃-Bi) with Ph₃GeH yielded the compound Ir₃(CO)₆(GePh ₃)₃(μ₃-Bi)(μ-H)₃ (1). When 1 was heated to reflux in hexane, it wa

Full text of DOI:10.1021/om300813t

Article
pubs.acs.org/Organometallics
Synthesis and Characterizations of Bismuth-Bridged Triiridium
Carbonyl Complexes Containing Germyl/Germylene and Stannyl/
Stannylene Ligands
Richard D. Adams,* Mingwei Chen, Gaya Elpitiya, and Qiang Zhang
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
S
* Supporting Information
ABSTRACT: The reaction of Ir3(CO)9(μ3-Bi) with Ph3GeH
yielded the compound Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 (1).
When 1 was heated to reflux in hexane, it was transformed into
the compound Ir3(CO)6(μ-GePh2)3(μ3-Bi) (2), which contains
three bridging GePh2 ligands by loss of 3 equiv of benzene. The
reaction of Ir3(CO)9(μ3-Bi) with Ph3SnH yielded the com-
pounds Ir3(CO)6(SnPh3)3(μ3-Bi)(μ-H)3 (3) and Ir3(CO)6-
(μ-SnPh2)3(μ3-Bi) (4), respectively. Compounds 1−4 were char-
acterized crystallographically. Compounds 1 and 3 each have
three terminally coordinated EPh3 (E = Ge, Sn) ligands in equa-
torial coordination sites, one on each of the iridium atoms. In
solution compounds 1 and 3 exist as two isomers. The major isomer has the structure found in the solid state. The two
isomers interconvert rapidly on the NMR time scale by tripodal, trigonal-twist rearrangement mechanisms: for 1, ΔH⧧ =
66.6 kJ/mol and ΔS⧧ = 1.58 J/(K mol), and for 3, ΔH⧧ = 65.6 kJ/mol and ΔS⧧ = −1.4 J/(K mol). The molecular orbitals
and UV−vis spectra of 2 were calculated and analyzed by ADF DFT computational treatments. The visible spectrum is
dominated by transitions from the Ir−Bi bonding orbitals HOMO-3 and HOMO-4 to an Ir−Ir antibonding orbital, the
LUMO, in the Ir3 core of the complex.
INTRODUCTION
■
Germanium1 and tin2 are well-known to be valuable modi-
fiers for heterogeneous transition-metal catalysts. Studies
have shown that mixed-metal cluster complexes can serve as
precursors to valuable bi- and multimetallic supported het-
erogeneous catalysts.3 In recent studies we have synthesized
a variety of transition-metal carbonyl complexes containing
germanium and tin ligands. Triphenylgermane, Ph3GeH,4
and triphenylstannane, Ph3SnH,5 react with polynuclear metal
carbonyl complexes to yield cluster complexes containing
bridging germylene/stannylene ligands A and/or bridging
germylyne/stannylyne ligands B and C (E = Ge, Sn): e.g.,
eqs 1 and 2, where CO ligands are shown only as lines from
the metal atoms and M = second- or third-row transition-
metal atom.
These reactions invariably proceed through intermediates
containing triphenylgermyl or triphenylstannyl ligands
EPh3 (D; E = Ge, Sn). The bridging germylene/stannylene
and bridging germylyne/stannylyne ligands are formed by
the cleavage of phenyl group(s) from the triphenylgermyl
and triphenylstannyl ligands. If hydride ligands are pres-
ent in the complex, the phenyl groups are often eliminated
from the complex in the form of benzene: e.g., eqs 34c,5b
and 4.6
It has recently been shown by a computational analysis that
the α cleavage of a phenyl group from a GePh3 ligand in the
transformation of the triiridium complex Ir3(CO)6(μ-CO)
Received: August 23, 2012
Published: October 9, 2012
© 2012 American Chemical Society
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silica gel 60 Å F254 glass plates. Dynamic NMR simulations for
compounds 1 and 3 were performed by using the SpinWorks pro-
gram.11 The exchange rates were determined at seven different tem-
peratures in the temperature range −20 to +60 °C. The activation
parameters were determined from a least-squares Erying plot by using
the program Microsoft Excel 2007.
Synthesis of Ir3(CO)9(μ3-Bi). Ir3(CO)9(μ3-Bi) was prepared by a
modified procedure of the method published by Schmid and co-
workers.9 In a typical experiment, 100.0 mg (0.1187 mmol) of
[PPN][Ir(CO)4] was dissolved in 25 mL of THF in an ice bath for
5 min. Then 21.0 mg (0.0432 mmol) of Bi(NO3)3·5H2O was added to
the above solution and the mixture was stirred in an ice bath for 1 h.
The solvent was removed in vacuo, and the product was then isolated
by TLC using a 3/1 hexane/methylene chloride solvent mixture. A
25.2 mg amount (61% yield) of yellow Ir3(CO)9(μ3-Bi) was obtained.
Synthesis of Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 (1). A 18.1 mg
portion (0.0516 mmol) of Ph3GeH was added to 13.9 mg (0.0134
mmol) of Ir3(CO)9(μ3-Bi) in 15 mL of methylene chloride. The
reaction mixture was heated to reflux for 7 h. The solvent was removed
in vacuo, and the product was then isolated in a pure form by TLC by
using a 4/1 hexane/methylene chloride solvent mixture. An 8.0 mg
amount (31% yield) of Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 (1) was
obtained. Spectral data for 1 are as follows. IR νCO (cm−1 in CH2Cl2):
1
2058 (s), 2025 (s), 2074 (w). H NMR (at −20 °C, in CDCl3): δ
(μ-GePh2)2(GePh3)3 into the complex Ir3(CO)6(η1-Ph)-
(μ-GePh2)3(GePh3)2 (eq 5) occurs at a single iridium atom.7
7.20−7.41 (m, 45H, Ph), −17.63 (s, 3H, Ir−H, isomer A), −17.14
(d, JH−H = 2.4 Hz, 1H, Ir−H, isomer B), −17.25 (s, JH−H = 2.4 Hz, 1H,
Ir−H, isomer B), −17.55 (s, 1H, Ir−H, isomer B). 1H NMR (at 25 °C,
in CD2Cl2): δ 7.25−7.49 (m, 45H, Ph), −17.24 (s, 1H, Ir−H, isomer B),
−17.33 (s, 1H, Ir−H, isomer B), −17.57 (s, 1H, Ir−H, isomer B),
1
−17.68 (s, 3H, Ir−H, isomer A). H NMR (at 60 °C, in CDCl3):
δ 7.26−7.39 (m, 45H, Ph), −17.55 (s, broad, 3H, Ir−H). The ratio
of A to B was 7/3 at room temperature. Mass spectrum (ES−): m/z
1867 (M − H−). UV−vis in CH2Cl2: λmax 559 nm, ε559 = 952 L mol−1
cm−1; λmax 494 nm, ε494 = 2085 L mol−1 cm−1; λmax 426 nm, ε426
=
9305 L mol−1 cm−1.
Conversion of 1 to Ir3(CO)6(GePh2)3(μ3-Bi) (2). A 10.20 mg
portion (0.005 274 mmol) of 1 was added to 10 mL of hexane. The
reaction mixture was heated to reflux for 4.5 h. The solvent was
removed in vacuo, and the product was then isolated by TLC using a
4/1 hexane/methylene chloride solvent mixture. A 7.60 mg amount
(87% yield) of 2 was obtained. Spectral data for 2 are as follows. IR
We have recently shown that rhenium−bismuth and
rhenium−antimony carbonyl complexes can serve as precursors
to excellent catalysts for the ammoxidation of 3-picoline.8 In
the present work, we have investigated the reactions of
Ir3(CO)9(μ3-Bi),9 the only previously known bismuth-contain-
ing iridium carbonyl cluster complex, with Ph3GeH and
Ph3SnH. The results of these studies are reported herein.
1
νCO (cm−1 in CH2Cl2): 2018 (s), 1996 (m), 2044 (w). H NMR
(CDCl3, in ppm): δ 7.28−7.54 (m, 30H, Ph). Mass spectrum (ES−):
m/z 1679 (M + CO2H−).
Reaction of Ir3(CO)9(μ3-Bi) with Ph3SnH. A 23.3 mg portion
(0.0663 mmol) of Ph3SnH was added to 17.2 mg (0.0166 mmol) of
Ir3(CO)9(μ3-Bi) in 15 mL of hexane. The reaction mixture was heated
to reflux for 4 h. The solvent was removed in vacuo, and the product
was then isolated by TLC by using a 4/1 hexane/methylene chloride
solvent mixture. A 6.20 mg amount (21% yield) of Ir3(CO)6-
(μ-SnPh2)3(μ3-Bi) (4) and 1.00 mg (3% yield) of Ir3(CO)6(SnPh3)3-
(μ-H)3(μ3-Bi) (3) were obtained. Spectral data for 3 are as follows. IR
1
νCO (cm−1 in CH2Cl2): 2053 (s), 2020 (s), 2068 (w). H NMR (at
25 °C in CDCl3): δ 7.30−6.84 (m, 45H, Ph), −17.10 (s, 1H, Ir−H,
EXPERIMENTAL SECTION
isomer B), −17.50 (s, 1H, Ir−H, isomer B), −18.42 (s, 1H, Ir−H,
■
1
isomer B), −17.99 (s, 3H, Ir−H, isomer A). H NMR (at −15 °C in
General Data. Reagent grade solvents were dried by the standard
procedures and were freshly distilled prior to use. Infrared spectra were
recorded on a Thermo Nicolet Avatar 360 FT-IR spectrophoto-
meter. Room-temperature 1H NMR spectra were recorded on a
Varian Mercury 300 spectrometer operating at 300.1 MHz. Variable-
CDCl3): δ 7.15−7.55 (m, 45H, Ph), −17.10 (s, 1H, Ir−H, isomer B),
−17.52 (s, 1H, Ir−H, isomer B), −18.44 (s, 1H, Ir−H, isomer B),
−18.01 (s, 3H, Ir−H, 2JSn−H1 = 25.2 Hz, 2JSn−H2 = 92.9 Hz, isomer A).
The ratio of A to B was 7/3 at room temperature. Mass spectrum
(ES−): m/z 2005 (M − H−). Spectral data for 4 are as follows. IR νCO
(cm−1 in CH2Cl2): 2006 (s), 1984 (m), 2032 (w), 1970 (w). 1H NMR
(CDCl3, in ppm): δ 7.74−7.12 (m, 30H, Ph). Mass spectrum (ES−):
m/z 1817 (M + CO2H−).
1
temperature H NMR spectra for compounds 1 and 3 were recorded
on a Varian Mercury 400 spectrometer operating at 400 MHz.
Positive/negative ion mass spectra were recorded on a Micromass
Q-TOF instrument by using electrospray (ES) ionization. Ir4(CO)12 and
BiNO3·5H2O were obtained from Strem, and Ph3GeH and Ph3SnH
were obtained from Gelest and Aldrich, respectively, and were used
Crystallographic Analyses. Orange single crystals of 1 suitable
for X-ray diffraction analyses were obtained by slow evaporation of
solvent from a hexane/methylene chloride solvent mixture at −25 °C.
Red single crystals of 2 suitable for X-ray diffraction analyses were
obtained by slow evaporation of hexane at −25 °C. Yellow single
crystals of 3 suitable for X-ray diffraction analyses were obtained by
10
without further purification. [PPN]Ir(CO)4 was prepared according
to the previously reported procedures. Ir3(CO)9(μ3-Bi) was prepared
by a modification of the previously reported procedure9 (see below).
Product separations were performed by TLC in air on Analtech 0.25
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Table 1. Crystallographic Data for Compounds 1−4
1
2
3
4
empirical formula
formula wt
cryst syst
Ir3BiGe3O6C60H48·C6
1934.39
Ir3BiGe3O6C42H30 .1/4CH2Cl2
1/3[Ir3BiSn3O6C60H48]
1/3[Ir3BiSn3O6C42H30]
1655.24
668.88
590.77
monoclinic
monoclinic
trigonal
trigonal
lattice params
a (Å)
25.6331(17)
15.4787(11)
30.772(2)
90.00
33.584(17)
14.609(6)
37.282(16)
90.00
15.4057(2)
15.4057(2)
30.9537(7)
90.00
12.4372(3)
12.4372(3)
38.7624(19)
90.00
b (Å)
c (Å)
α (deg)
β (deg)
97.328(2)
90.00
98.623(14)
90.00
90.00
90.00
γ (deg)
120.00
120.00
V (Å3)
12 109.7(14)
C2/c (15)
8
18 084(14)
C2/c (15)
16
6362.18(19)
P31c (159)
12
5192.6(3)
P31c (159)
12
space group (No.)
Z
ρcalcd (g/cm3)
μ(Mo Kα) (mm−1
temp (K)
2θmax (deg)
2.122
2.432
2.095
2.267
)
10.981
14.712
10.207
12.489
293(2)
294(2)
293(2)
294(2)
50.40
52.80
43.66
50.04
no. of obsd rflns (I > 2σ(I))
6818
9287
6986
6166
no. of params
684
967
368
238
a
goodness of fit (GOF)
1.068
1.037
1.075
1.090
Max. shift final cycle
0.006
0.001
0.000
0.001
a
residuals: R1; wR2
0.0586; 0.1351
multiscan 1.000/0.485
1.58
0.0637; 0.1345
multiscan 1.000/0.375
0.0363; 0.0877
multiscan 1.000/0.479
1.52
0.0450; 0.1055
multiscan 1.000/0.570
0.82
abs cor, max/min
largest peak in final diff map (e/Å3)
2.07
a
2
R1 = ∑hkl(||Fo| − |Fc||)/∑hkl|Fo|; wR2 = [∑hklw(|Fo| − |Fc|)2/∑hklwFo ]1/2; w = 1/σ2(Fo); GOF = [∑hklw(|Fo| − |Fc|)2/(ndata − nvari)]1/2
.
slow evaporation of heptane at −5 °C. Red single crystals of 4 suitable
for X-ray diffraction analyses were obtained by slow evaporation of
solvent from a hexane/methylene chloride solvent mixture at −25 °C.
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-
based diffractometer using Mo Kα radiation (λ = 0.710 73 Å). The raw
data frames were integrated with the SAINT+ program by using a
narrow-frame integration algorithm.12 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 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.13 All non-hydrogen atoms
were refined with anisotropic displacement parameters. The hydride
ligands H1 and H3 in 1 were located and refined. The hydride ligand
H2 was located and refined with the constraint Ir−H = 1.80 Å. All
other hydrogen atoms were calculated and placed in geometrically
idealized positions and included as standard riding atoms during the
final cycles of least-squares refinement. Crystal data, data collection
parameters, and results of the analyses are listed in Table 1.
Compounds 1 and 2 crystallized in the monoclinic crystal system.
The space group C2/c was indicated by the systematic absences in the
data and confirmed by the successful solutions and refinements for
both structures. One molecule of hexane was cocrystallized with 1 in
the asymmetric crystal unit. The carbon atoms of the hexane were
refined with constraints, C−C = 1.44 Å, and hydrogen atoms on the
hexane molecule were ignored. Half of a molecule of methylene
chloride was cocrystallized with two molecules of 2 in the asymmetric
crystal unit. Compounds 3 and 4 both crystallized in the trigonal
crystal system. The space group P31c was indicated on the basis of
the systematic absences in the data and confirmed by the successful
solutions and refinements of both structures. For compound 3, two
phenyl rings on Sn2 (C5−C10 and C17−C22) were disordered over
two sites with 50% populations each. The disorder is a rotation about
the Sn−C(ipso) bond. Each of the four half-occupied rings was refined
as a regular hexagon with C−C bonds constrained to 1.39 Å, and the
carbon atoms were refined with a single isotropic thermal parameter
for both of the two disordered rings. For compound 3, the unit cell
contains several solvent molecules (total potential solvent accessible
void volume is 128.2 Å3 and electron count/cell is 11) which have
been treated as a diffuse contribution to the overall scattering without
specific atom positions by SQUEEZE/PLATON.14 The crystal of 4
was also refined as an inversion twin on the basis of the absolute
structure (Flack) parameter near the end of the refinement. The
fraction of the minor twin domain refined to 0.11(1). The unit cell of
4 contains solvent molecules (total potential aolvent accessible void
volume is 1020.0 Å3 and electron count/cell is 373) which was treated
as a diffuse contribution to the overall scattering without specific atom
positions by SQUEEZE/PLATON.
Computational Details. All density functional theory (DFT)
calculations were performed with the Amsterdam Density Functional
(ADF) suite of programs15a by using the PBEsol functional15b with
valence quadruple-ζ + 4 polarization function, relativistically optimized
(QZ4P) basis sets for iridium, bismuth, and germanium atoms, and
double-ζ (DZ) basis sets for carbon, oxygen, and hydrogen atoms with no
frozen cores. The molecular orbitals and their energies were determined
by a single point calculation based on the structure as established by the
crystal structure analysis. The time-dependent DFT (TDDFT)
calculation was performed at the same theory level. The transitions to
triplet and higher order multiplet excited states from the ground state are
forbidden because the ground states of the species in this study are
singlets. Calculations of the oscillator strengths f for the singlet to triplet
transitions are all effectively zero; see the Supporting Information.
RESULTS AND DISCUSSION
■
The new compound Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 (1) was
obtained in 31% yield from the reaction of Ir3(CO)9(μ3-Bi)
with Ph3GeH in a solution in methylene chloride solvent at
reflux for 7 h. Compound 1 was characterized by a combination
1
of IR and H NMR spectroscopy, mass spectrometry, and a
single-crystal X-ray diffraction analysis. An ORTEP diagram
of the molecular structure of 1 is shown in Figure 1. Like its
parent Ir3(CO)9(μ3-Bi), compound 1 consists of a triangular
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Scheme 1
Figure 1. ORTEP diagram of the molecular structure of
Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 (1) showing 30% probability thermal
ellipsoids. Selected interatomic bond distances (Å) and angles (deg)
are as follows: Ir(1)−Ir(2) = 3.0094(8), Ir(2)−Ir(3) = 3.0073(9),
Ir(3)−Ir(1) = 3.0071(8), Ir(1)−Bi(1) = 2.7610(9), Ir(2)−Bi(1) =
2.7597(9), Ir(3)−Bi(1) = 2.7668(9), Ir(1)−Ge(1) = 2.5032(18),
Ir(2)−Ge(2) = 2.5054(16), Ir(3)−Ge(3) = 2.5046(18), Ir(1)−H(2) =
1.75(2), Ir(1)−H(3) = 1.8(2), Ir(2)−H(1) = 1.7(2), Ir(2)−H(3) =
1.8(2), Ir(3)−H(2) = 1.76(2), Ir(3)−H(1) = 1.6(2), Ir(3)−H(2) =
1.76(2); Ge(1)−Ir(1)−Bi(1) = 93.79(5), Ge(1)−Ir(1)−Ir(3) =
150.33(5), Bi(1)−Ir(1)−Ir(3) = 57.13(2), Ge(1)−Ir(1)−Ir(2) =
100.91(4), Ir(3)−Ir(1)−Ir(2) = 59.97(2).
Figure 3. ORTEP diagram of the molecular structure of Ir3(CO)6-
(μ-GePh2)3(μ3-Bi) (2) showing 30% probability thermal ellipsoids.
Selected interatomic bond distances (Å) and angles (deg) are as
follows: Ir(1)−Ir(2) = 2.8356(14), Ir(2)−Ir(3) = 2.8383(15), Ir(1)−
Ir(3) = 2.8568(15) Ir(1)−Bi(1) = 2.7651(12), Ir(2)−Bi(1) =
2.7678(13), Ir(3)−Bi(1) = 2.7751(12), Ir(1)−Ge(1) = 2.516(2),
Ir(2)−Ge(1) = 2.477(2), Ir(2)−Ge(2) = 2.509(2), Ir(3)−Ge(2) =
2.487(2), Ir(3)−Ge(3) = 2.506(2), Ir(1)−Ge(3) = 2.498(2); Ge(3)−
Ir(1)−Ge(1) = 165.95(7), Ge(3)−Ir(1)−Bi(1) = 82.38(5), Ge(3)−
Ir(1)−Ir(2) = 114.81(6), Ge(1)−Ir(1)−Ir(2) = 54.74(6), Bi(1)−
Ir(1)−Ir(2) = 59.22(3), Ir(2)−Ir(1)−Ir(3) = 59.82(3).
in 1 (Ir(1)−Ir(2) = 3.0094(8) Å, Ir(1)−Ir(3) = 3.0071(8) Å, and
Ir(2)−Ir(3) = 3.0073(9) Å) are significantly longer than those
found in Ir3(CO)9(μ3-Bi) (average 2.759(2) Å).9 This is prob-
ably due to the presence of three bridging hydride ligands16
but may also be due in part to steric effects produced by the
bulky GePh3 ligands. The Ir−Bi distances in 1 (Ir(1)−Bi(1) =
2.7610(9) Å, Ir(2)−Bi(1) = 2.7597(9) Å, and Ir(3)−Bi(1) =
2.7668(9) Å) are quite similar to the Ir−Bi distances in
Ir3(CO)9(μ3-Bi) (average 2.734(2) Å). The Ir−Ge distances in
1 (Ir(1)−Ge(1) = 2.5032(18) Å, Ir(2)−Ge(2) = 2.5054(16) Å,
and Ir(3)−Ge(3) = 2.5046(18) Å) are shorter than the Ir−
GePh3 distances found in the triiridium complexes Ir3(CO)6-
Figure 2. Stacked plot of 1H NMR spectra for compound 1 at various
temperatures in CDCl3 solution.
7
(μ-CO)(μ-GePh2)2(GePh3)3 (2.5098(14), 2.5155(16), and
2.5401(15) Å), Ir3(CO)6(η1-Ph)(μ-GePh2)3(GePh3)27 (2.551(2)
and 2.5519(19) Å), and Ir3(CO)6(μ-GePh2)3(GePh3)3
(2.5754(7), 2.5959(7), and 2.5534(8) Å).17 The metal atoms in
compound 1 contain a total of 48 electrons; thus, each metal atom
formally has an 18-electron configuration.
cluster of three iridium atoms with a triply bridging bismuth
atom. Each Ir atom contains one GePh3 ligand that lies ap-
proximately in the plane of the Ir3 triangle. Each Ir atom also
contains two terminal CO ligands: one lies in the plane of the
Ir3 triangle, and the other lies approximately perpendicular to
the plane of the Ir3 triangle. Overall the Ir3BiGe3 portion of the
molecule has approximate C3 symmetry. There are three bridg-
ing hydride ligands, one across each Ir−Ir bond. They lie approxi-
mately on the plane of the Ir3 triangle. The Ir−Ir bond distances
1
The H NMR spectrum of 1 can be interpreted only by the
presence of two isomers in solution. The major isomer A shows
a single resonance at δ −17.67. This resonance can be attri-
buted to the structure of 1 as found in the solid state. Three
additional hydride resonances observed at δ −17.24, −17.33,
and −17.57, each of intensity 1, can be attributed to the less
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Scheme 2
Figure 5. ORTEP diagram of the molecular structure of Ir3(CO)6-
(μ-SnPh2)3(μ3-Bi) (4) showing 30% probability thermal ellipsoids.
Selected interatomic bond distances (Å) and angles (deg) are as
follows: Ir(1)−Ir(1) = 2.8697(13) Å, Ir(1)−Bi(1) = 2.7505(12),
Ir(1)−Sn(1) = 2.6347(16), Ir(1′)−Sn(1) = 2.6437(16); Sn(1)−
Ir(1)−Sn(1) = 171.16(6), Sn(1)−Ir(1)−Bi(1) = 85.69(4), Sn(1)−
Ir(1)−Ir(1) = 57.22(4), Sn(1)−Ir(1)−Ir(1) = 116.81(4), Bi(1)−
Ir(1)−Ir(1) = 58.556(18), Ir(1)−Bi(1)−Ir(1) = 62.89(4).
Figure 4. ORTEP diagram of the molecular structure of
Ir3(CO)6(SnPh3)3(μ-H)3(μ3-Bi) (3) showing 30% probability thermal
ellipsoids. Selected interatomic bond distances (Å) and angles (deg)
are as follows: Ir(1)−Ir(1) = 2.9969(8), Ir(1)−Bi(1) = 2.7702(9),
Ir(1)−Sn(1) = 2.660(1); Ir(1) −Bi(1)−Ir(1) = 65.49(3), Sn(1)−
Ir(1)−Bi(1) = 88.47(3), Sn(1)−Ir(1)−Ir(1) = 96.71(3), Bi(1)−
Ir(1)−Ir(1) = 57.254(13), Sn(1) −Ir(1)−Ir(1) = 144.88(3).
symmetric isomer B. The ratio of A to B was 7/3 at room
temperature. The structure proposed for isomer 1B is shown
below. This isomer is preferred over other possibilities because
the GePh3 ligands all lie in the Ir3 plane as found in isomer A.
Isomer B has C1 symmetry, and thus the three hydride ligands
are inequivalent. The resonances of both isomers are broad at
room temperature, which is indicative of a dynamic exchange
Figure 6. UV−vis absorption spectrum of 2 in methylene chloride
solution.
metal carbonyl cluster complexes,18 is proposed to explain the
isomerization of isomers 1A and 1B (see Scheme 1). Line
shape analyses provided rates which provided the following
activation parameters for the process: ΔH⧧ = 66.6 kJ/mol and
ΔS⧧ = 1.58 J/(K mol).
When a solution of 1 was heated to reflux in hexane solvent
for 4.5 h, it was converted into compound 2 in 87% yield.
Compound 2 was also characterized by a single-crystal X-ray
diffraction analysis, and an ORTEP diagram of the molecular
structure of 2 is shown in Figure 3.
1
process that is rapid on the H NMR time scale. This process
was confirmed by variable-temperature NMR measurements.
Compound 2 consists of an Ir3 triangular cluster with a triply
bridging bismuth atom. There are three bridging GePh2 ligands,
one across each Ir−Ir bond and two terminal CO ligands on
each Ir atom. One CO ligand lies approximately in the plane of
the Ir3 triangle; the other is approximately perpendicular to it.
The Ir−Ir bond distances in 2 (Ir(1)−Ir(2) = 2.8356(14) Å,
Ir(2)−Ir(3) = 2.8383(15) Å, and Ir(1)−Ir(3) = 2.8568(15)
Å) are significantly shorter than those in 1 but longer than
those in Ir3(CO)9(μ3-Bi).9 The Ir−Bi distances in 2 (Ir(1)−
Bi(1) = 2.7651(12) Å, Ir(2)−Bi(1) = 2.7678(13) Å, and
The resonances sharpen at lower temperature and broaden
and merge into a broad average resonance at δ −17.55 when
the temperature is raised to 60 °C. A stacked plot of the
hydride spectra at various temperatures is shown in Figure 2. A
polytopal trigonal-twist mechanism, as has been observed for
M(CO)3 groups and phosphine-substituted M(CO)3 groups in
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Figure 7. Selected molecular orbitals for compound 2.
Ir(3)−Bi(1) = 2.7751(12) Å) are virtually the same as those in
1. The Ir−Ge distances to the bridging GePh2 ligands (Ir(1)−
Ge(1) = 2.516(2) Å, Ir(2)−Ge(1) = 2.477(2) Å, Ir(2)−Ge(2) =
2.509(2) Å, Ir(3)−Ge(2) = 2.487(2) Å, Ir(3)−Ge(3) = 2.506(2) Å,
and Ir(1)−Ge(3) = 2.498(2) Å) are very similar to the Ir−Ge
distances to the terminal GePh3 ligands in 1. The transforma-
tion of 1 to 2 involves the cleavage of a phenyl ring from
each of the GePh3 ligands in 1 and their elimination from the
molecule together with the hydride ligands, presumably in
the form of benzene (Scheme 2). Like 1, the metal atoms in
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compound 2 contain a total of 48 electrons, and each metal
atom formally has an 18-electron configuration.
(2) 486 nm, which is a combination of the two transitions
HOMO-3 to LUMO (f = 0.040) and HOMO-4 to LUMO
(f = 0.022), and (3) 404 nm, which involves transitions from
the phenyl rings to the LUMO and LUMO+1. Calculated
transition 1 corresponds to the observed transition at 559 nm.
Calculated transition 2 corresponds to the observed transition
at 496 nm. Calculated transition 3 corresponds to the observed
transition at 426 nm. The excitations for the absorptions in the
visible region, 559 and 494 nm, are due to electronic transitions
from the Ir−Bi bonding orbitals to the antibonding Ir−Ir
LUMO (see Figure 7).
The reaction of Ir3(CO)9(μ3-Bi) with Ph3SnH is similar to
the reaction of Ir3(CO)9(μ3-Bi) with Ph3GeH, except that both
products Ir3(CO)6(SnPh3)3(μ-H)3(μ3-Bi) (3, 3% yield; 4, 21%
yield) are obtained together. The yield of 3 is very low and
could not be improved by doing the reaction at lower tem-
perature. Compounds 3 and 4 were both characterized cry-
stallographically. ORTEP diagrams of the molecular structures
of 3 and 4 are shown in Figures 4 and 5, respectively. The
structures of 3 and 4 are analogous to those of 1 and 2, with the
replacement of the GePh3 ligands with SnPh3 ligands and
GePh2 ligands with SnPh2 ligands. Compounds 3 and 4 both
crystallized in the space group P31c and have crystallographi-
cally imposed C3 symmetry. Due to the large number of heavy
atoms, it was not possible to locate the hydride ligands in the
structural analysis of 3. The Ir−Ir and Ir−Bi distances are simi-
lar to those in 1 and 2, respectively. The Ir−Sn distances (Ir−
SnPh3 = 2.660(1) Å and Ir−SnPh2 = 2.6347(16) and 2.6437(16) Å)
are similar to those found in Ir3(CO)6(SnPh3)3(μ-SnPh2)3.5c
SUMMARY
■
The tris-EPh3 complexes 1 and 3 (E = Ge, Sn) were obtained
from the reactions of Ir3(CO)9(μ3-Bi) with the compounds
Ph3EH. They can be converted into the tris-EPh2 complexes 2
and 4 (E = Ge, Sn) thermally by cleavage and elimination of a
phenyl ring from each EPh3 ligand together with the elimina-
tion of the three hydride ligands. These transformations are
similar to the transformations of the compounds Ru3(CO)9-
(EPh3)3(μ-H)3 (E = Ge, Sn) into the compounds Ru3(CO)9-
(μ-EPh2)3 (see eq 3),4c,5b further demonstrating the scope and
viability of these phenyl cleavage reactions for the synthesis of
new transition-metal complexes containing bridging germylene
and bridging stannylene ligands. It is anticipated that these
complexes will be able to serve as precursors to new stoichio-
metrically precise supported Ge- and Sn-containing multimetal-
lic heterogeneous catalysts by thermal removal of the CO
ligands and phenyl rings.3
1
The H NMR spectrum of 3 shows that it also exists in
solution as a mixture of the two isomers A and B in a 7/3 ratio
at room temperature: δ −17.10 (s, 1H, isomer B), −17.50
(s, 1H, isomer B), −18.42 (s, 1H, isomer B), and −17.99 (s, 3H,
isomer A). Like 1, these isomers are also in a dynamic equilibrium.
Line shape analyses of the spectra recorded at different tem-
peratures provided the following activation parameters: ΔH⧧=
65.6 kJ/mol and ΔS⧧ = −1.4 J/(K mol).
Compounds 2 and 4 are a dark red, indicating that they have
significant absorptions in the visible region of the spectrum.
Since they are both electronically saturated, we decided to
investigate the spectrum of 2 in detail. A UV−vis absorption
spectrum of 2 is shown in Figure 6. There are three absorp-
tions: λmax 559 nm, ε559 = 952 L mol−1 cm−1; λmax 494 nm,
ε494 = 2085 L mol−1 cm−1; λmax 426 nm, ε426 = 9305 L mol−1
cm−1. The broad absorption at 494 nm is responsible for the
observed red color of the compound. In order to understand
the bonding and electronic transitions in 2, DFT and TD-DFT
molecular orbital calculations were performed by using the
PBsol functional of the Amsterdam Density Functional
program library. Selected important molecular orbitals for 2
are shown in Figure 7. The MOs HOMO through HOMO-4
are dominated by bonding between the bismuth atom and the
iridium atoms. The LUMO is Ir−Ir antibonding across the Ir3
triangle. The UV−vis absorption spectrum for 2 was calculated
by using a time-dependent PBEsol calculation, as shown in
Figure 8. The calculated absorptions are as follows: (1) 556 nm,
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files, figures, and tables giving crystallographic data for the
1
structural analyses, H NMR and mass spectra for compounds
1−4, and results of the calculations of the energies of electronic
transitions with oscillator strengths. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Adamsrd@mailbox.sc.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the National Science
Foundation (Grant CHE-1111496). We thank Dr. Mark
Smith for assistance in the solution and refinements of the
structures in the trigonal space group.
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