Reactions of Ir(CO)(H)(P(p-tolyl)3)3 with SO2 and O2 Mixtures and with H2SO4, Formation of a Sulfate-Bridged Dimer, and Crystal and Molecular Structure of Ir(CO)(H)(SO2)(P(p-toly

Article abstract of DOI:10.1021/ic951249y

Reactions of HIr(CO)(P(p-tolyl)₃)₃ with SO₂, O₂, mixtures of SO₂ and O₂, and H₂SO₄ are described. Reactions with mixtures of SO₂/O₂. and with H

Full text of DOI:10.1021/ic951249y

Inorg. Chem. 1996, 35, 3683-3686
3683
Reactions of Ir(CO)(H)(P(p-tolyl)3)3 with SO2 and O2 Mixtures and with H2SO4, Formation
of a Sulfate-Bridged Dimer, and Crystal and Molecular Structure of
Ir(CO)(H)(SO2)(P(p-tolyl)3)2
Cynthia A. Miller, Thomas S. Janik, Melvyn Rowen Churchill, and Jim D. Atwood*
Department of Chemistry, University at Buffalo, State University of New York,
Buffalo, New York 14260-3000
ReceiVed September 26, 1995X
Reactions of HIr(CO)(P(p-tolyl)3)3 with SO2, O2, mixtures of SO2 and O2, and H2SO4 are described. Reactions
with mixtures of SO2/O2 and with H2SO4 lead to a common product, Ir2H4(µ-SO4)(P(p-tolyl)3)6, where a bidentate
SO42- bridges the iridium centers. The complex HIr(CO)(P(p-tolyl)3)3 is stable toward O2 but reacts readily with
SO2 to give HIr(CO)(SO2)(P(p-tolyl)3)2, which was characterized by a crystal structure determination. The species
Ir(CO)(H)(SO2)(P(p-tolyl)3)2 crystallizes in the centrosymmetric triclinic space group P1h with a ) 10.675(1) Å,
b ) 10.882(1) Å, c ) 17.740(2) Å, R ) 84.626(10)°, â ) 83.432(10)°, γ ) 87.043(10)°, V ) 2036.6(3) Å3, and
Z ) 2. Diffraction data (Mo KR, 2θ ) 4.5-45.0°) were collected on a Siemens R3m/V diffractometer, and the
structure was refined to R ) 3.00% for 4218 independent reflections with Fo > 6σ(Fo). The five-coordinate
iridium(I) center has a distorted environment (closer to trigonal bipyramidal than to square pyramidal) with H(1)-
Ir(1)-S(1) ) 171.4(23)°. Bond lengths are Ir-P ) 2.303(2) and 2.320(2) Å, Ir-SO2 ) 2.372(2) Å, Ir-CO )
1.906(8) Å, and Ir-H ) 1.65(7) Å. The SO2 ligand has bond distances of S(1)-O(1) ) 1.442(7) and S(1)-O(2)
) 1.441(7) Å, with O(1)-S(1)-O(2) ) 113.1(4)°.
tetrahydrofuran were all dried by refluxing over CaH2, distilling onto
Na/benzophenone, refluxing over Na/benzophenone, and distilling into
an air-free container. The purified solvents were stored in an argon-
filled inert-atmosphere glovebox. Infrared spectra of KBr pellets and
solutions were measured on a Mattson Polaris FTIR instrument in the
2200-400 cm-1 region. NMR spectra were recorded on a Varian VXR
400 spectrometer and were referenced to the deuterated solvent for 1H
spectra or to H3PO4 for 31P spectra.
Reactions of hydride complexes are fundamental for orga-
nometallic chemistry and for homogeneous catalysis.1,2 Rela-
tively few studies have focused on reactions of metal hydrides
with species such as O2, SO2, or H2SO4 because strong oxidants
and a metal hydride are inherently reactive. A dispute3
regarding the reaction of SO2 with Ir(CO)(H)(PPh3)3 was
recently resolved.4c
Preparation of Ir(CO)(H)(P(p-tolyl)3)3. In an argon atmosphere,
trans-Ir(CO)(Cl)(P(p-tolyl)3)2 (101 mg, 0.117 mmol) and P(p-tolyl)3
5
Ir(CO)(H)(PPh3)3 + SO2 f Ir(CO)(H)(SO2)(PPh3)2 +
PPh3 a Ir(CO)(SO2H)(PPh3)2 + PPh3
(177 mg) were placed in a Schlenk flask equipped with a gas adapter.
The reaction vessel was sealed and transferred to a hood, where 30
mL of dearated ethanol was added with a positive N2 pressure. The
solution was brought to reflux, and a dearated solution of NaBH4 (100
mg) in absolute ethanol (25 mL) was added to the flask. The solution
was allowed to reflux for a further 15 min under a nitrogen atmosphere.
The reaction mixture was cooled under N2 and allowed to stir overnight
with a reduced volume of ethanol (40 mL total remaining). After 15
h, a light yellow powder had precipitated. The solid was filtered off
(109 mg, 0.0906 mmol, 82.1% yield) and transferred to an argon
atmosphere glovebox. The product was characterized by IR spectros-
copy [νCO (KBr) 1925 (vs) cm-1, νIr-H 2050 (s) cm-1] and NMR
spectroscopy [31P NMR (CDCl3) 12.2 ppm; 1H NMR resonances -10.7
(q) [J ) 20 Hz], 2.4 (s), 7.0-7.2 (m) ppm]. The characterization data
are similar to those previously reported.6
The insertion product, Ir(CO)(SO2H)(PPh3)2, is similar to the
insertion products we have observed for various hydroxide and
alkoxide complexes.4 Changing from PPh3 to P(p-tolyl)3
frequently improves solubility to allow better characterization
of reaction products. As a part of our continuing studies4 of
reactions of sulfur dioxide with iridium complexes, we examined
the reactions of Ir(CO)(H)(P(p-tolyl)3)3 with SO2, O2, mixtures
of SO2 and O2, and H2SO4.
Experimental Section
IrCl3‚xH2O was purchased from Johnson Matthey. Tri-p-tolylphos-
phine was purchased from Strem Chemical Co. SO2 (anhydrous) and
O2 (CP grade) were purchased from Matheson. Benzene, toluene, and
Preparation of Ir(CO)(H)(SO2)(P(p-tolyl)3)2. In an argon atmo-
sphere, Ir(CO)(H)(P(p-tolyl)3)3 was suspended in hexanes in a Schlenk
flask equipped with a gas adapter. The reaction vessel was sealed and
transferred to a hood where 1 atm of SO2 was passed over the solution
for 20 min, turning the yellow solution orange. The orange precipitate
was filtered off in the hood and transferred into the drybox. An infrared
spectrum in KBr showed νCO 2064 (vs) cm-1, νIr-H 1965 (s) cm-1, and
X Abstract published in AdVance ACS Abstracts, May 1, 1996.
(1) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1987.
(2) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; Wiley:
New York, 1992.
ν
SO 1037, 1177 cm-1. NMR: 1H, -2.8 (t) ppm; 31P, 16.8 ppm (-7.4
(3) (a) Levison, J. J.; Robinson, S. D. J. Chem. Soc., Dalton Trans. 1972,
2013. (b) Bell, L. K.; Mingos, D. M. P. J. Chem. Soc., Dalton Trans.
1982, 673.
(4) (a) Randall, S. L.; Thompson, J. S.; Buttrey, L. A.; Ziller, J. W.;
Churchill, M. R.; Atwood, J. D. Organometallics 1991, 10, 683. (b)
Randall, S. L.; Miller, C. A.; See, R. F.; Churchill, M. R.; Janik, T.
S.; Lake, C. H.; Atwood, J. D. Organometallics 1994, 13, 5088. (c)
Randall, S. L.; See, R. F.; Churchill, M. R.; Miller, C. A.; Atwood, J.
D. Organometallics 1994, 13, 141.
ppm for free P(p-tolyl)3). On the basis of the data, the product is
assigned as Ir(CO)H(P(p-tolyl)3)2(SO2). This is consistent with the
previously reported Ir(CO)H(PPh3)2(SO2) complex [νCO 2050 (vs), νIr-H
1
1965 (s), νSO 1037, 1175 cm-1).3 NMR: 31P, 16.7 ppm; H, -2.8 (t)
(5) Lawson, H. J.; Atwood, J. D. J. Am. Chem. Soc. 1989, 111, 6223.
(6) (a) Bath, S. S.; Vaska, L. J. Am. Chem. Soc. 1963, 85, 3500. (b)
Yagupsky, G.; Wilkinson, G. J. Chem. Soc. A 1969, 725.
S0020-1669(95)01249-3 CCC: $12.00 © 1996 American Chemical Society

3684 Inorganic Chemistry, Vol. 35, No. 12, 1996
Miller et al.
Table 1. Crystallographic Data for Ir(CO)(H)(SO2)(P(p-tolyl)3)2
ppm, JP-H ) 18.0 Hz]. A saturated solution of the SO2 complex in
benzene was placed in one side of a H-tube, and hexanes were placed
in the other. After 5 days, crystals suitable for X-ray crystallography
formed.
empirical formula C43H43IrO3P2S
a ) 10.675(1) Å
b ) 10.882(1) Å
c ) 17.740(2) Å
R ) 84.626(10)°
â ) 83.432(10)°
γ ) 87.043(10)°
V ) 2036.6(3) Å3
Z ) 2
fw ) 894.0
space group ) P1h (No. 2)
T ) 297 K
Preparation of Ir2(µ-SO4)(H)4(P(p-tolyl)3)6. Ir(CO)H(P(p-tolyl)3)3
(0.152 g) was dissolved in 30 mL of THF in an argon atmosphere.
The Schlenk flask was sealed and transferred to a hood, where 5 drops
of dearated H2SO4 were added under a positive N2 pressure. The
resulting solution was stirred for 1 h (less time may result in the
presence of starting material in the reaction products), after which the
volume of THF was reduced (15 mL), followed by the addition of
dearated distilled water to precipitate a yellow-white solid (0.121 g).
Attempts to recrystallize this product were unsuccessful (benzene/
hexane; THF/hexane; slow evaporation of benzene; CD2Cl2 in a freezer).
Reaction of SO2 and O2 with Ir(CO)(H)(P(p-tolyl)3)3 or O2 with
Ir(CO)(H)(SO2)(P(p-tolyl)3)2. These two reactions are similar in
producing a major product in a mixture. For reaction of Ir(CO)(H)-
(P(p-tolyl)3)3 with SO2 and O2, a saturated solution of Ir(CO)H(P(p-
tolyl)3)3 in CD2Cl2 was prepared under an argon atmosphere. An NMR
tube equipped with a vacuum adapter was transferred to the high-
vacuum line, where 50 Torr of SO2 was added to the frozen solution
and the solution was thawed. Next the solution was refrozen, and 50
Torr of O2 was added. The NMR tube was sealed, the contents were
thawed, and an NMR spectrum was recorded. 1H NMR: -11 (dtd),
-9.6 (qd), -7.3 (m), -2.8 (t), 2.3-2.4 (m), 6.8-7.9 (m) ppm. The
-2.8 (t) ppm signal is assigned to the previously prepared Ir(CO)H-
(SO2)(P(p-tolyl)3)2 complex. The 31P NMR spectrum resulted in several
resonances as well: -7.4 (br), -5, -0.4, 16.8, 28 ppm. The -7.4
ppm resonance is assigned to free phosphine, the 16.8 ppm resonance
to Ir(CO)H(SO2)(P(p-tolyl)3)2, and the 28 ppm resonance to phosphine
oxide. The solution was allowed to remain in the NMR tube for 3
days, and another NMR spectrum was recorded. The -11 (dtd) ppm
resonance [J ) 100, 18, 3.6 Hz] and the -9.6 (qd) ppm resonance
λ ) 0.710 73 Å
F
calc ) 1.458 Mg/m3
µ ) 3.426 mm-1
R(Fo)a ) 3.00%
Rw(Fo) ) 3.94%
a The R values are for observed data.
with Z ) 2.8 This choice was confirmed by the successful solution
and refinement of the structure in this higher-symmetry space group.
All reflections were corrected for Lorentz and polarization effects and
for absorption.
Solution and Refinement of the Structure. All calculations were
performed with the Siemens SHELXTL PLUS program package.9 The
analytical scattering factors for the neutral atoms were corrected for
both the real (∆f ′) and imaginary (i∆f ′′) components of anomalous
dispersion.10 The structure was solved by a combination of Patterson,
difference-Fourier, and least-squares refinement methods. Convergence
was reached with R(F) ) 3.00% and Rw(F) ) 3.94% for those 4218
reflections with Fo > 6σ(Fo). Anisotropic thermal parameters were
applied to all non-hydrogen atoms. The hydride ligand (H(1)) was
located and refined, while the remaining organic hydrogen atoms were
placed in optimized locations with d(C-H) ) 0.96 Å.11 Final
coordinates are collected in the Supporting Information.
Results and Discussion
Reaction with SO2. The hydride, Ir(CO)(H)(P(p-tolyl)3)3,
readily reacted with SO2 to form Ir(CO)(H)(SO2)(P(p-tolyl)3)2.
This complex is characterized by IR and 31P and 1H NMR data
as the hydride. The data are completely consistent with those
previously reported for Ir(CO)(H)(SO2)(PPh3)2.3,4 For the
synthesis as a suspension in hexane, no evidence is seen for
the inserted complex, Ir(CO)(SO2H)(P(p-tolyl)3)2; the expected
1H resonance at ∼4.5 ppm and the 31P signal at ∼20 ppm were
absent. To confirm the structural assignment of this complex
and the previous assignments of the PPh3 analogue, we
determined the structure of Ir(CO)(H)(SO2)(P(p-tolyl)3)2.
Description of the Molecular Structure of Ir(CO)(H)(SO2)-
(P(p-tolyl)3)2. The crystal consists of ordered molecular units
of Ir(CO)(H)(SO2)(P(p-tolyl)3)2, separated by normal van der
Waals distances. There are no abnormally short intermolecular
contacts. The overall molecular geometry and labeling of atoms
are depicted in Figure 1; selected interatomic distances and
angles are collected in Table 2.
The central iridium(I) atom has an irregular coordination
environment (local symmetry m or Cs) almost midway between
trigonal bipyramidal (with the H and SO2 ligands in axial sites)
and square pyramidal (with the CO ligand in the unique axial
site). There are two particularly large interligand angles, H(1)-
Ir(1)-S(1) ) 171.4(23)° and P(1)-Ir(1)-P(2) ) 153.9(4)°,
which might be taken as indicative of trans-basal angles in a
square pyramidal geometry. However, one would then expect
the P-Ir-P angle (which is associated with the most bulky
ligands) to be more obtuse than the H-Ir-S angle; this is not
the case. Furthermore, the apical-basal angle C(11)-Ir(1)-
H(1) is acute (79.1(24)°), rather than obtuse. We therefore
1
[16.4, 3.6] remained in the H NMR spectrum. The hydride peaks at
-11 (dtd) and -9.6 (qd) ppm were in a ratio of 1:1. Two triplets at
-19.5 and -5.3 ppm were present in smaller, variable amounts. The
solvent was removed, and an IR (KBr) spectrum was recorded giving
rise to two absorbances in the Ir-H stretching region of 2002 and 2050
(sh) and multiple absorbances in the SO region of 448, 568, 657, 729,
910, 1115, and 1176 cm-1 but no indication of a CtO stretch.
Reaction of Ir(CO)(H)(SO2)(P(p-tolyl)3)2 with O2 proceeded simi-
larly.
(a) In an argon atmosphere, a dilute solution of Ir(CO)H(SO2)(P(p-
tolyl)3)2 in toluene was prepared. The sealed Schlenk flask was
transferred to a hood and O2 was passed over the solution with stirring
for 2 h. An IR spectrum was recorded giving rise to two absorbances
at 2036 (s) and 2070 (sh) cm-1
.
(b) An NMR spectroscopic study of the same reaction as in part a
was performed. In an argon atmosphere, a saturated solution of Ir-
(CO)H(SO2)(P(p-tolyl)3)2 in CD2Cl2 was prepared. The NMR tube was
removed from the box, and O2 was bubbled into the solution for 5
min. The solution remained under an O2 atmosphere for 24 h before
an NMR spectrum was recorded. The resonances in the 31P NMR
spectrum are as follows: -19.4, -3.5, -3.4, -1.6, -0.4, 6.4, 6.9,
and 28 ppm, with the major resonances being at 28 and -3.4 ppm.
The 28 ppm resonance is attributed to phosphine oxide.
Collection of X-ray Diffraction Data for Ir(CO)(H)(SO2)(P(p-
tolyl)3)2. A single crystal, with approximate dimensions of 0.2 × 0.2
× 0.3 mm, was selected for the diffraction study. It was sealed in a
thin-walled glass capillary and aligned on a Siemens R3m/V diffrac-
tometer with its extended direction close to collinear with the φ axis.
Crystal alignment, determination of cell dimensions, and data collection
(coupled θ(crystal)-2θ(counter) mode) were carried out as described
previously;7 details are provided in Table 1.
The crystal belongs to the triclinic system (1h or Ci symmetry of
diffraction only), possible space groups being the noncentrosymmetric
P1 (C11; No. 1) and the centrosymmetric P1h (C1i ; No. 2). The latter,
centrosymmetric, possibility was selected on the basis of (i) intensity
statistics and (ii) its far greater frequency of occurrence, particularly
(8) Nowacki, W.; Matsumoto, T.; Edenharter, A. Acta Crystallogr. 1967,
22, 935.
(9) Sheldrick, G. M. SHELXTL PLUS (Release 4.11 VMS); Siemens
Analytical Instruments, Inc.: Madison, WI, 1990. (See also Siemens
SHELXTL PLUS Manual, 2nd ed., 1990).
(10) International Tables for X-Ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. 4, pp 99-101, 149-150.
(11) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.
(7) Churchill, M. R.; Lashewycz, R. A.; Rotella, F. J. Inorg. Chem. 1977,
16, 265.

Reactions of Ir(CO)(H)(P(p-tolyl)3)3
Inorganic Chemistry, Vol. 35, No. 12, 1996 3685
gand (Ir(1)-S(1) ) 2.372(2) Å). The equatorial sites are
occupied by two tri-p-tolylphosphine ligands (Ir(1)-P(1) )
2.303(2) Å and Ir(1)-P(2) ) 2.320(2) Å) and a carbonyl li-
gand (Ir(1)-C(11) ) 1.906(8) Å, with C(11)-O(11) ) 1.129-
(10) Å and Ir(1)-C(11)-O(11) ) 175.3(7)°). The angle
between the apical ligands (H(1)-Ir(1)-S(1) ) 171.4(23)°) is
close to 180°, but is of limited precision. The diequatorial
angles are irregular (P(1)-Ir(1)-P(2) ) 153.9(1)°, P(2)-Ir-
(1)-C(11) ) 101.2(3)°, and P(1)-Ir(1)-C(11) ) 95.9(3)°). The
iridium atom lies +0.328 Å from the P(1)‚‚‚P(2)‚‚‚C(11)
plane, with other relevant displacements of atoms being
+2.671 Å for S(1) and -1.32 Å for H(1). Clearly, the
equatorial ligands are displaced so as to encroach on the cone
angle normally occupied by an axial ligand more substantial
than a hydride ligand; thus we have H(1)-Ir(1)-P(1) ) 78.2-
(27)°, H(1)-Ir(1)-C(11) ) 79.1(24)°, and H(1)-Ir(1)-P(2)
) 85.8(27)°. This observation is in keeping with studies on
12
Rh(H)(PPh3)4 and Rh(H)(AsPh3)(PPh3)3,13 in which the ar-
rangement of triphenylpnictogen ligands is such as to produce
an essentially tetrahedral RhP4 or RhAsP3 moiety, with the
hydride ligand appearing to have no obvious stereochemical
effect on the geometry.
The sulfur dioxide ligand is S-bonded to the iridium(I) center
and has equivalent sulfur-oxygen bond lengths (S(1)-O(1) )
1.442(7) Å and S(1)-O(2) ) 1.441(7) Å). The sulfur atom
has a pyramidal geometry with bond angles of O(1)-S(1)-
O(1) ) 113.1(4)°, Ir(1)-S(1)-O(1) ) 107.2(2)°, and Ir(1)-
S(1)-O(2) ) 107.2(2)°.
The tri-p-tolylphosphine ligands have the expected P-C(ipso)
distances, ranging from 1.816(7) to 1.831(7) Å and averaging
1.821 Å. The internal angles at the ipso carbon atoms are all
less than 120° (ranging from C(32)-C(31)-C(36) ) 117.2-
(6)° to C(62)-C(61)-C(66) ) 118.3(6)° and averaging 117.7°;
this distortion of the carbocyclic ring from D6h to C2V symmetry
is well established14 and is the result of the electronegative
phosphorus atom at the ipso position.15 One unexpected result
is the large range of Ir-P-C(ipso) angles (from Ir(1)-P(1)-
C(61) ) 101.6(2) to 121.9(2)°). In most triphenylphosphine
complexes these angles are greater than the regular sp3 angle
of 109.5°, with the C-P-C angles typically being less than
109.5°. In the present structural study, the anomalous angles
are Ir(1)-P(1)-C(61) ) 101.6(2)° and Ir(1)-P(2)-C(31) )
108.9(2)°; in each case, these small angles result from the phenyl
group being displaced from its regular position into the cavity
around the axial hydride ligand.
All other distances and angles are self-consistent and are
within accepted norms. This structural study provides the first
example of an iridium complex containing both hydride and
SO2 ligands. It also provides the first example of a five-
coordinate SO2 adduct that is trigonal bipyramidal rather than
square planar.4 In this complex, the SO2 is pyramidal as in the
previous examples.4,16
Figure 1. Molecular geometry and labeling of atoms for Ir(CO)(H)-
(SO2)(P(p-tolyl)3)2 shown by an ORTEP2 diagram with 20% prob-
ability contours for the atomic vibration ellipsoids. Hydrogen atoms
(other than the hydride ligand, H(1)) have been omitted for the sake of
clarity.
Table 2. Selected Interatomic Distances (Å) and Angles (deg) for
Ir(CO)(H)(SO2)(P(p-tolyl)3)2
(A) Iridium-Ligand Distances
Ir(1)-H(1)
Ir(1)-P(2)
Ir(1)-C(11)
1.648(69)
2.320(2)
1.906(8)
Ir(1)-P(1)
Ir(1)-S(1)
2.303(2)
2.372(2)
(B) Phosphorus-Carbon Distances
P(1)-C(51)
P(1)-C(61)
P(1)-C(71)
1.822(7)
1.821(7)
1.816(7)
P(2)-C(21)
P(2)-C(31)
P(2)-C(41)
1.831(7)
1.818(7)
1.820(7)
(C) Sulfur-Oxygen and Carbon-Oxygen Distances
S(1)-O(1)
S(1)-O(2)
1.442(7)
1.441(7)
C(11)-O(11)
1.129(10)
(D) Angles around Iridium Atom
78.2(27) H(1)-Ir(1)-P(2)
153.9(1) H(1)-Ir(1)-S(1)
103.7(1) P(2)-Ir(1)-S(1)
H(1)-Ir(1)-P(1)
P(1)-Ir(1)-P(2)
P(1)-Ir(1)-S(1)
H(1)-Ir(1)-C(11)
P(2)-Ir(1)-C(11)
85.8(27)
171.4(23)
95.2(1)
95.9(3)
92.3(2)
79.1(24) P(1)-Ir(1)-C(11)
101.2(3) S(1)-Ir(1)-C(11)
(E) Angles around Phosphorus Atoms
Ir(1)-P(1)-C(51)
118.1(2) C(51)-P(1)-C(61)
101.6(2) C(51)-P(1)-C(71)
121.9(2) C(61)-P(1)-C(71)
118.3(2) C(21)-P(2)-C(31)
108.9(2) C(21)-P(2)-C(41)
115.0(2) C(31)-P(2)-C(41)
106.6(3)
102.3(3)
104.8(3)
103.9(3)
105.4(3)
104.0(3)
Ir(1)-P(1)-C(61)
Ir(1)-P(1)-C(71)
Ir(1)-P(2)-C(21)
Ir(1)-P(2)-C(31)
Ir(1)-P(2)-C(41)
(F) Angles within Ir-SO2 and Ir-C-O Systems
Ir(1)-S(1)-O(1) 107.2(2) Ir(1)-S(1)-O(2)
O(1)-S(1)-O(2)
107.2(2)
113.1(4) Ir(1)-C(11)-O(11) 175.3(7)
(G) P-C(ipso)-C(ortho) Angles
P(2)-C(21)-C(22)
P(2)-C(31)-C(32)
P(2)-C(41)-C(42)
P(1)-C(51)-C(52)
P(1)-C(61)-C(62)
P(1)-C(71)-C(72)
119.7(6) P(2)-C(21)-C(26)
122.4(5) P(2)-C(31)-C(36)
119.4(5) P(2)-C(41)-C(46)
120.6(5) P(1)-C(51)-C(56)
118.3(5) P(1)-C(61)-C(66)
122.3(5) P(1)-C(71)-C(76)
123.1(5)
120.4(5)
123.0(5)
121.0(5)
123.1(5)
120.0(5)
Reaction of Ir(CO)(H)(P(p-tolyl)3)3 with SO2 and O2.
Reaction of Ir(CO)(H)(P(p-tolyl)3)3 with O2 in solution (CDCl3
or CH2Cl2) results in a small amount of a product consistent
with the equilibrium.
(H) C-C(ipso)-C Angles
(12) Baker, R. W.; Pauling, P. J. Chem. Soc., Chem. Commun. 1969,
1495.
(13) Baker, R. W.; Ilmaier, B.; Pauling, P. J.; Nyholm, R. S. J. Chem.
Soc., Chem. Commun. 1970, 1077.
(14) Churchill, M. R.; DeBoer, B. G. Inorg. Chem. 1975, 14, 2630.
(15) Dominicano, A.; Vaciago, A.; Coulson, C. A. Acta Crystallogr., Sect.
B. 1975, B31, 1630.
(16) La Placa, S. J.; Ibers, J. A. Inorg. Chem. 1966, 5, 405.
(17) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 3rd ed.; John Wiley and Sons: New York, 1978;
p 239.
C(22)-C(21)-C(26) 117.2(7) C(52)-C(51)-C(56) 118.3(7)
C(32)-C(31)-C(36) 117.2(6) C(62)-C(61)-C(66) 118.3(6)
C(42)-C(41)-C(46) 117.6(6) C(72)-C(71)-C(76) 117.7(6)
choose to discuss the molecule within the framework of the
trigonal bipyramidal description.
The axial sites are then occupied by a hydride ligand (with
Ir(1)-H(1) ) 1.65(7) Å) and an S-bonded sulfur dioxide li-

3686 Inorganic Chemistry, Vol. 35, No. 12, 1996
Ir(CO)(H)(P(p-tolyl)3)3 + O2 a
Miller et al.
Ir(CO)(H)(O2)(P(p-tolyl)3)2 + P(p-tolyl)3
1
The H NMR characterization (-11.0 (t) ppm, JP-H ) 7.6) is
consistent with a small amount of Ir(CO)(H)(O2)(P(p-tolyl)3)2
being formed, although the amount was less than 5% after 3
days. Basically, Ir(CO)(H)(P(p-tolyl)3)3 can be considered stable
to oxygen.
Figure 2. Geometry of the sulfate-bridged dimer, Ir2(H)4(µ-SO4)L6
(L ) P(p-tolyl)3), showing the inequivalent phosphorus and hydrogen
atoms.
Reaction of Ir(CO)(H)(P(p-tolyl)3)3 with SO2 and O2 produces
a number of products; the same mixture is obtained from Ir-
(CO)(H)(SO2)(P(p-tolyl)3)2 reacting with O2 and from Ir(CO)-
(H)(P(p-tolyl)3)3 reacting with mixtures of SO2 and O2. Since
Ir(CO)(H)(SO2)(P(p-tolyl)3)2 is observed when Ir(CO)(H)(P(p-
tolyl)3)3 reacts with SO2 and O2, it is likely the common
intermediate. Both free P(p-tolyl)3 and OP(p-tolyl)3 indicate
phosphine lability in the system. A major iridium-containing
product (described fully below) and two minor products are
apparent. The minor products contain two equivalent P(p-tolyl)3
ligands and a hydride (triplets at -19.5 and -5.3 ppm).
Conversion of SO2 and O2 to sulfate is commonly observed on
iridium(I) centers,4,18 and it is likely that all of the products are
iridium(III) sulfates. The minor products could have the sulfate
group as bidentate on one iridium or µ-η4 bridging two iri-
dium centers, but the amounts are too low for definitive
characterization.
Table 3. Infrared Data in the Sulfate Region for
Ir2H4(µ-SO4)(P(p-tolyl)3)6 Compared to Those for
Co2(NH3)8(µ-NH2)(µ-SO4)3+ 17
ν1
ν2
ν3
ν4
Ir2H4(µ-SO4)(P(p-tolyl)3)6
910 (br)
448 (br)
1034 (m)
1178 (sh)
1115 (s)
729 (s)
657 (s)
568 (m)
Co2(NH3)8(µ-NH2)(µ-SO4)3+
995 (m)
462 (m)
1050-1060 (m)
641 (s)
610 (s)
571 (m)
1170 (s)
1105 (s)
formation of Ir2H4(µ-SO4)(P(p-tolyl)3)6 from two very different
routes also supports this formulation. The reaction of Ir(CO)-
(H)(P(p-tolyl)3)3 with H2SO4 provides the cleanest route.
Reaction of Ir(CO)(H)(P(p-tolyl)3)3 with H2SO4. To pro-
vide further information on the possible products from reactions
of Ir(CO)(H)(P(p-tolyl)3)3 with SO2 and O2, the iridium hydride
complex was reacted with sulfuric acid. A saturated solution
of Ir(CO)H(P(p-tolyl)3)3 in CD2Cl2 was prepared in an NMR
tube in the inert-atmosphere glovebox. The NMR tube was
transferred to a hood, and a drop of dearated H2SO4 was added,
2Ir(CO)(H)(P(p-tolyl)3)3 + H2SO4 f
Ir2H4(µ-SO4)(P(p-tolyl)3)6 + 2CO
Reaction of Ir(CO)(H)(P(p-tolyl)3)3 with SO2/O2 also provides
a route, though other species are also formed and hydrogen must
be scavenged. Conversion of SO2 and O2 to sulfate by Ir(I)
complexes is commonly observed.4,19 The minor products from
reaction of SO2/O2 with Ir(CO)(H)(P(p-tolyl)3)3 show triplets
for the hydrides and likely involve P(p-tolyl)3 dissociation (OP-
(p-tolyl)3 is observed), perhaps to give sulfate as bidentate on
one iridium or µ-η4, but the amounts observed are too low for
definitive characterization.
causing the formation of a gray suspension.
A
1H NMR
spectrum of the resulting solution was recorded giving rise to
two hydride resonances at -15.2 (dtd) [J ) 113.6, 18.4, 3.6
Hz] and -13.3 (qd) ppm [J ) 16.8, 3.6 Hz] in a ratio of 1:1.
The 31P NMR spectrum only combined two resonances as well;
-3.3 (t) [J ) 14.6 Hz] and -0.3 (d) ppm [J ) 14.6 Hz] in a
ratio of 2:1. This reaction was also performed as a synthetic
reaction (see Experimental Section); unfortunately, all efforts
to crystallize the product failed.
Conclusion
In this paper we have reported the first crystal structure of
an iridium complex containing both hydride and pyramidally
coordinated SO2. Reaction of this complex with O2 produces
a new complex containing a sulfate bridging two iridium centers.
The same complex is prepared in better yield from reaction of
H2SO4 with Ir(CO)(H)(P(p-tolyl)3)3.
Nature of the Primary Product. Even in the absence of
crystallographic or analytical data, the spectroscopic data
unambiguously allow assignment of the structure of the common
product as Ir2H4(µ-SO4)(P(p-tolyl)3)6. The required structure
is shown in Figure 2. The hydride portion of the NMR spectrum
consists of two resonances in a 1:1 ratio. The resonance for
Ha is a doublet (JP -H ) 100 Hz) of triplets (JP -H ) 18 Hz)
a
b
a
of doublets (JH -H ) a3.6 Hz) at -11.6 ppm as required for the
Acknowledgment. Purchase of the Siemens R3m/V diffrac-
tometer was made possible by Grant 89-13733 from the
Chemical Instrumentation Program of the National Science
Foundation. The Varian VXR-400 NMR instrument was
purchased through a grant from the Department of Education
(2-2-01011). T.S.J. acknowledges support from the Research
Corp. (Grant C2971RR).
b
a
structure shown in Figure 2. The resonance for Hb is a quartet
(JP-H ) 16.4 Hz) of doublets (JH -H ) 3.6 Hz) at -9.7 ppm.
b
a
b
The three cis phosphorus atoms must appear equivalent to give
the quartet. The 31P spectrum, proton decoupled, shows a
doublet (JP-P ) 14.6 Hz) at -0.5 ppm and a triplet (JP-P
)
14.6 Hz) at -3.3 ppm in a 2:1 ratio. These NMR data require
the geometry shown in Figure 2. The infrared data are also
consistent with this structure. Two Ir-H stretches are observed
at 2050 (sh) and 2002 (s) cm-1. The bridging sulfate is also
confirmed by the infrared spectral data in Table 3, where a
comparison is made to a known complex with sulfate bridging
two metals.17 Reaction of H2SO4 with a cobalt complex
produced a very similar µ-SO4 complex.18
Supporting Information Available: Listings of crystal data, atomic
coordinates, complete interatomic distances and angles, anisotropic
thermal parameters, and calculated positions of hydrogen atoms for
the structural study of Ir(CO)(H)(SO2)(P(p-tolyl)3)2 (6 pages). Ordering
information is given on any current masthead page.
IC951249Y
1
The spectroscopic data, H and 31P NMR and IR, are in
(19) (a) Kubas G. J. Inorg. Chem. 1979, 18, 182. (b) Valentine, J.;
Valentine, D., Jr.; Collman, J. P. Inorg. Chem. 1971, 10, 219. (c) Ryan,
R. R.; Kubas, G. J. Inorg. Chem. 1978, 17, 894. (d) Fettinger, J. C.;
Churchill, M. R.; Bernard, K. A.; Atwood, J. D. J. Organomet. Chem.
1988, 340, 377.
excellent agreement with the suggested structure (Figure 2). The
(18) Sykes, A. G.; Mast, R. D. J. Chem. Soc. A 1967, 784.