Aqueous organometallic chemistry of mer -Ir(H)2(PMe 3)3X complexes

Article abstract of DOI:10.1021/om300140f

A series of Ir(H)₂(PMe₃)₃X compounds where X = various anionic ligands has been synthesized. The most studied of this group with X = Cl has been characterized fully, including by X-ray crystallography. For X = Cl, PhCO₂^-, dissolution in water results in the establishment of the equilibrium Ir(H)₂(PMe ₃)₃X + H₂O ? [Ir(H)₂(PMe ₃)₃(H₂O)]⁺X^-, which is responsible for the reaction of these compounds with unsaturated organic compounds. Reactions between the dihydrides and alkynes in water as well as the thermodynamics of the aqueous equilibrium are discussed.

Full text of DOI:10.1021/om300140f

Article
pubs.acs.org/Organometallics
Aqueous Organometallic Chemistry of mer-Ir(H)2(PMe3)3X Complexes
Joseph S. Merola,* Trang Le Husebo, and Kelly E. Matthews
Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24016, United States
S
* Supporting Information
ABSTRACT: A series of Ir(H)2(PMe3)3X compounds where
X = various anionic ligands has been synthesized. The most
studied of this group with X = Cl has been characterized fully,
−
including by X-ray crystallography. For X = Cl, PhCO2 ,
dissolution in water results in the establishment of the
equilibrium Ir(H)2 (PMe3 )3 X
+ H2 O ⇌ [Ir-
(H)2(PMe3)3(H2O)]+X−, which is responsible for the reaction
of these compounds with unsaturated organic compounds.
Reactions between the dihydrides and alkynes in water as well as the thermodynamics of the aqueous equilibrium are discussed.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
The aqueous chemistry of metal complexes for organic catalysis
has received significant attention, in the main because water is
more benign than many organic solvents currently in use and
because it may allow for easier separation of organic products.
In addition, water has been found to activate certain metal
complexes for catalytic activity and accelerate reactions that
proceed more slowly or not at all in organic solvents.1−5 For
some time, we have been investigating the oxidative addition
chemistry of [Ir(COD)(PMe3)3]Cl (1; COD = 1,5-cyclo-
ctadiene) with a variety of E−H bonds where E has been a
variety of elements, including boron, carbon, nitrogen, and
oxygen as well as hydrogen.6−15
Mer-Ir(H)2(PMe3)3Cl (2) is synthesized in high yield via the
reaction between [Ir(COD)(PMe3)3]Cl (1; COD = 1,5-
cyclooctadiene)24 and H2 at 80 °C (eq 2). Spectroscopy
indicates that, as we have seen in almost all of the oxidative
addition reactions we have explored, the product is exclusively
the meridional isomer with cis hydrides. Compound 2 is a
textbook system for exploring geometries by NMR spectros-
1
1
copy, given the presence of both H and 31P nuclei. The H
NMR spectrum shows a doublet for the methyl protons of the
central PMe3 ligand and the outer set of PMe3 ligands appears
as a virtual triplet.25 Two different types of hydride ligands are
indicated by resonances at δ −11.2 and −24.1 ppm. The
resonance at δ −11.2 ppm is attributable to the hydride trans to
one PMe3 ligand, cis to two PMe3 ligands, and also cis to a
hydride. The net result of a strong coupling (135 Hz) to the
trans phosphorus and smaller couplings to the cis phosphines
and the cis hydride is a doublet of triplet of doublets pattern.
The resonance at δ −24.1 ppm arises from the hydride trans to
chlorine and cis to three phosphorus atoms and one hydrogen.
This hydride displays a complicated pattern best described as a
closely spaced quartet of doublets. The proton-decoupled 31P
spectrum is also consistent with the meridional structure,
showing a doublet and a triplet from the two different
phosphorus environments as well as P−P coupling.
The product obtained when E = hydrogen (i.e., from the
oxidative addition of H2) is a very water-soluble iridium
dihydride complex. It is soluble to the extent of 40 mg of solid/
mL of water, equivalent to 40 g/L. Previously, we published a
communication on the aqueous chemistry of this dihydride
Ir(H)2(PMe3)3Cl (2), which reacts with unsaturated organic
compounds only in aqueous solution.11 In this paper we
present our detailed studies on the aqueous chemistry of
Ir(H)2(PMe3)3X compounds, where X = various 1− charged
ligands, and on their reactions with unsaturated compounds.
The work discussed in this current paper is distinct from a body
of work that utilizes water-soluble phosphine ligands to impart
water solubility such as sulfonated triphenylphosphine16−20 or
1,3,5-triaza-7-phosphaadamantane (PTA).21−23 In this work,
the water solubility is derived solely by ian nteraction between
water and the metal center, resulting in the dissociation of
appropriate anionic ligands.
A single-crystal X-ray structure was obtained for 2, and the
resulting structure is displayed as a thermal ellipsoid plot in
Figure 1. The structure confirms that already deduced by
various spectroscopic measurements, and crystal data for 2 are
Received: February 20, 2012
Published: May 9, 2012
© 2012 American Chemical Society
3920
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
Table 1. Experimental Details for X-ray Crystallographic
Analyses
param
2
4d
9
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
C9H29ClIrP3
457.9
C15H35ClIrP3
535.99
C22H44IrO2P3
624.7
293(2)
293(2)
293(2)
0.710 73
monoclinic
P21/n
0.710 73
0.710 73
triclinic
orthorhombic
P212121
P1
̅
12.507(3)
10.265(2)
14.000(3)
90
11.827(3)
12.535(3)
14.506(3)
90
8.489(7)
11.995(5)
14.916(7)
84.08(4)
76.51(5)
71.39(5)
1399(1)
1.483
b (Å)
c (Å)
α (deg)
β (deg)
102.64(3)
90
90
γ (deg)
V (Å3), Z
90
1753.8(6), 4
1.780
2150.5(9), 4
1.655
calcd density (g/
Figure 1. Solid-state structure of the dihydride 2. Methyl hydrogens
have been omitted for clarity. Select bond distances (Å): Ir1−P1,
2.2872(16); Ir1−P2, 2.3187(17); Ir1−P3, 2.2895(16); Ir1−Cl1,
2.5003(16); Ir−H1, 1.50(7); Ir−H2, 1.66(8) Select bond angles
(deg): P1−Ir1−P2, 98.76(7); P1−Ir1−P3, 163.33(6); P2−Ir1−P3,
97.88(6); Cl1−Ir1−P2, 96.13(7); Cl1−Ir1−P1, 88.89(6); Cl1−Ir1−
P3, 88.22(6); H2−Ir−H1, 78(4).
cm3)
abs coeff (mm−1
F(000)
)
8.015
960
6.58
4.936
626
1056
cryst size (mm)
θ range for data
collection (deg)
0.4 × 0.2 × 0.2 0.4 × 0.4 × 0.3 0.3 × 0.2 × 0.2
1.98−27.5
2.15−25
1.75−25°
limiting indices
0 ≤ h ≤ 16
0 ≤ k ≤ 12
−18 ≤ l ≤ 17
4100
0 ≤ h ≤ 14
0 ≤ k ≤ 14
0 ≤ l ≤ 17
2156
0 ≤ h ≤ 10
−13 ≤ k ≤ 14
−17 ≤ l ≤ 17
5289
given in Table 1, while important bond lengths and angles are
indicated in the figure caption. Forming a tris-phosphine
compound with two hydrides and a chloride ligand requires a
balance of the steric constraints of the phosphine ligands.
Analogous compounds with PR3 = PPhMe2,26−28 mixture of
P(i-Pr)3 and PPhMe2,29 PTA21 have been reported. Their
reactivities have not been explored in depth, and for our
purposes, the presence of phenyl groups invites ortho
metalation side reactions that would hamper further stud-
ies.30−32 In addition, the extra organic bulk of many of the
phosphine ligands previously reported would greatly reduce or
eliminate water solubility.
no. of rflns
collected
no. of indep rflns
(Rint)
3925 (0.0640)
2156
4913 (0.0246)
completeness to θ 97.6 (θ = 27.5°) 100 (θ = 25°)
(%)
99.8 (θ = 25°)
refinement method
full-matrix least squares on F2
no. of data/
restraints/params
3925/0/136
2156/0/182
4913/0/254
goodness of fit on 1.040
1.038
1.005
F2
final R indices (I > R1 = 0.0387;
2θ(I))
R1 = 0.0292;
wR2 = 0.0648
R1 = 0.0495;
wR2 = 0.0936
wR2 = 0.0953
As discussed above, 2 is very water-soluble and the aqueous
1
R indices (all data) R1 = 0.0473;
R1 = 0.0364;
wR2 = 0.0674
R1 = 0.0882;
wR2 = 0.0994
chemistry is interesting in a number of ways. First, H NMR
wR2 = 0.1005
spectroscopy shows that two different species exist in H2O or
D2O solution. The splitting patterns evident in both 1H and 31
P
absolute structure
param
n/a
−0.024(14)
n/a
spectra are consistent with both species maintaining a
meridional arrangement of phosphines as well as a cis
arrangement of the two hydrides. Therefore, two sets of closely
extinction coeff
0.0042(3)
n/a
n/a
largest diff peak/
2.904/−1.360
0.974/−0.778
1.272/−0.664
hole (e Å−3
)
1
spaced quartets of doublets are observed in the H NMR
spectrum at −25.3 ppm (minor) and −21.8 ppm (major) and
two sets of a doublet of triplets pattern at −8.8 ppm (major)
and −8.0 ppm (minor). The 31P NMR spectrum appears as a
set of triplets at −49.6 ppm (major) and −44.5 ppm (minor) as
well as doublets at −44.7 ppm (major) and −40.2 ppm
(minor). Given that five of the six coordination sites of the
octahedron must be the same to explain the spectroscopic data,
these two species in water can only differ in the sixth
coordination site. The NMR data led us to postulate the
equilibrium shown in eq 3.
greatly reduces the resonance from 2a and increases the
intensity of the resonance from 2. In addition, calculations of
1
equilibrium constants using either H or 31P spectroscopy and
variable concentrations of 2 in solution could only be modeled
satisfactorily with the simple equilibrium indicated in eq 3 (see
the Supporting Information.) Attempts to isolate 2a were
unsuccessful, even though we had been able to isolate and
characterize a number of other noble-metal aqua species in
other systems.33,34
The lability of chloride in water compared with the lability in
organic solvents was probed. The addition of PMe3 to a
solution of 2 in dichloromethane resulted in no observable
reaction. It is possible to force chloride removal with the use of
Tl[PF6] in the presence of PMe3 to yield [IrH2(PMe3)4][PF6].
This is in contrast with the catecholboryliridium hydride
complex we synthesized, which reacts without the need for a
chloride scavenger.7 In that case, the catecholboryl ligand is
One observation in support of this equilibrium is that
addition of chloride (as NaCl) to an aqueous solution of 2/2a
3921
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
trans to the chloride (as opposed to trans to H in this case),
which may be responsible for the increased lability of the
chloride ligand. On the other hand, Tl+ is not needed in water
and addition of PMe3 to an aqueous solution of 2 led to the
fully protio vinyl compound, the resonance at δ 5.2 disappears
and the resonance at δ 6.6 loses H−H coupling, all indicating
that the deuteride ligand is the migrating group, consistent with
the alkyne initially replacing the aqua ligand and being cis to the
deuteride (eq 7).
35
+
clean formation of IrH2(PMe3)4
4).
as the chloride salt 3 (eq
The exact driving force for the final product geometry of
having hydride trans to chloride is not known, but the reaction
proceeding through a five-coordinate intermediate gives a low-
energy pathway to rearrangement to the more thermodynami-
cally favored product. Having the vinyl group cis to two PMe3
groups rather than all three lowers unfavorable nonbonded
interactions and is the most likely driving force for the
geometry of the isolated product. The only exception observed
was found for 4b, where an 80/20 mixture of products with the
vinyl group cis to chloride/trans to chloride was observed. Of
all of the vinyl compounds, suitable crystals were obtained for
4d and Table 1 contains a condensed listing of experimental
parameters. The thermal ellipsoid plot for 4d can be found in
Figure 2, and select bond lengths and angles may be found in
the figure caption.
The reactivity of 2 in aqueous solution with carbon−carbon
multiple bonds, especially alkynes, was investigated. Alkynes
were particularly chosen because previous work in our
group6,7,10,11 showed that vinyl complexes could readily be
isolated, if formed, and therefore studied in greater detail.
Reactions between 2 and alkynes in CD2Cl2 at room
temperature were monitored for 2 weeks with no indication
of any reaction. On the other hand, reaction between 2 and
various alkynes in water led to complete reaction from insertion
of the alkyne into an Ir−H bond. 1H NMR tube-scale
experiments indicated that most alkyne reactions were
complete within a few minutes.
In preparative studies, reactions took place upon addition of
the alkyne to aqueous solutions of 2 with immediate
1
precipitation of product (eq 5). The H and 31P NMR spectra
for the tert-butylvinyl product 4a are illustrative of all
complexes. Both spectra indicated that the meridional arrange-
ment of phosphines persists. The remaining hydride signal is
observed at δ −23.9 ppm, a chemical shift indicative of a
placement trans to chloride (see the discussion on Chemical
Shift Relationships), and is a quartet with JP−H = 16.9 Hz from
splitting by three cis PMe3 ligands. The vinyl protons both
display H−H coupling to each other as well as long-range P−H
coupling to all three PMe3 groups.
Figure 2. Solid-state structure of vinyl hydride complex 4d. Hydrogen
atoms ae omitted for clarity. Select bond distances (Å): Ir−H1,
1.499(8); Ir1−P1, 2.314(3); Ir1−P2, 2.540(3); Ir1−P3, 2.320(3);
Ir1−C3, 2.143(9); C3−C2, 1.334(15); C2−C1, 1.505(15); C3−C4,
1.424(15); C4−C5, 1.204(15); C5−C6, 1.447(15). Select bond angles
(deg): P1−Ir1−P2, 94.1(1); P1−Ir1−P3, 168.4(1); P2−Ir1−P3,
93.2(1); Cl1−Ir1−P1, 9.4(1); Cl1−Ir1−P2, 86.8(1); Cl1−Ir1−P3,
94.04(9); Cl1−Ir1−C3, 93.2(3); C1−C2−C3, 127.0(1); C2−C3−Ir1,
123.5(8); C2−C3−C4, 118.2(9); Ir1−C3−C4, 118.3(7); C3−C4−
C5, 179.2(1).
Observation of the 1H NMR spectrum of the hydride region
of 2 in D2O showed that H/D exchange occurs between the
hydride ligands and solvent over time, albeit at very different
rates. The hydride ligand cis to the chloride (or aqua group)
exchanges quickly, the reaction being complete in approx-
imately 30 min. The hydride ligand trans to chloride (or water)
shows appreciable exchange only after 24 h (eq 6).
An unusual reaction with ethynylpyridine led to the
formation of a product where a metallacycle composed of
three alkynes formed; we have already reported on this
reaction.36
We took advantage of this H/D exchange to probe the
insertion reaction in more depth. Complex 2 was dissolved in
D2O, and the H/D exchange was allowed to proceed for 60
min to ensure complete exchange of the hydride cis to chlorine
with minimal exchange of the trans hydride. tert-Butylacetylene
was added to the solution to form the tert-butylvinyl complex
Equilibrium Studies. Further studies on the nature of the
aqueous equilibrium between 2 and 2a through a variable-
temperature 31P NMR study was undertaken to examine the
thermodynamics of this system. 31P NMR spectroscopy was
chosen because the H/D exchange discussed above precluded
using the hydrides as the probe with 1H NMR spectroscopy. By
measurement of the 31P integrals, the equilibrium constants at
1
and the H NMR spectrum recorded. In comparison with the
3922
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
the various temperatures were calculated and the resulting van’t
Hoff plot is shown in Figure 3. The data is a reasonable linear
[Ir(COD)X]2 compounds with the bridging groups X =
PhCO2 , MeCO2 , F3CCO2 . The carboxylates are drawn as η2
bridging on the basis of previous work on rhodium chemistry
that supported this bonding mode.38 In addition, Finke39
recently reported the crystal structure of an iridium COD dimer
bridged by 2-ethylhexanoate which clearly shows the η2
bonding. It is interesting to note that one of the earliest
reports on bridging carboxylates indicated that the Ir COD
acetate dimer was unstable in solution and could not be made
with silver acetate,38 but that is not our experience at all.
Addition of PMe3 to 6a−c yielded tris-PMe3 COD iridium
complexes with the appropriate carboxylate counterion (eq 10).
−
−
−
Figure 3. van’t Hoff plot for the equilibrium between 2 and 2a in
aqueous solution as depicted in eq 3. Details are provided in the
Supporting Information.
fit (R2 = 0.996) allowing for calculation of enthalpic and
entropic parameters, yielding ΔH and ΔS values of 34 3 kJ/
mol and 68 10 J/(K mol), respectively. While little can be
concluded from the exact values of these numbers, the signs
and relative magnitudes make sense. All other factors being
more or less equal, the ΔH value represents the difference
between the Ir−Cl bond energy and the Ir−O bond energy, a
value that would be expected to favor the Ir−Cl bond. The
positive value of ΔS is also to be expected in a dissociative
equilibrium such as this.
Other Anionic Groups. We investigated other anionic
leaving groups in the Ir(H)2(PMe3)3X system. While we were
interested in studying a broad range of X groups, the actual
number we were able to make was limited by synthetic
methodologies. Simple replacement of X in 2 with other
anionic ligands was successful for some, but not for all
variations of X. Addition of NaI or NaBr to an aqueous solution
of 2 resulted in the immediate precipitation of Ir(H)2(PMe3)3I
or Ir(H)2(PMe3)3Br (eq 8). This is not an unexpected
The final step in this sequence, the synthesis of the dihydrido
iridium complex 8, was only completely successful for R = Ph
(eq 11). For acetate and trifluoroacetate, NMR spectroscopy
indicated that some of the desired product was formed among a
complicated mixture of products. We are not able to explain
these results at this time, but it is clear that the counterion plays
a critical role at some stage in the H2 addition reaction. We will
be investigating the role the counterion plays in the mechanism
of the oxidative addition reactions of the [Ir(COD)(PMe3)3]+
cation as part of our continuing studies on this system.
Given the excellent yield of the benzoate compound, further
studies were carried out on it. Ir(H)2(PMe3)3(O2CPh) (8) is as
water-soluble as 2 and, in some respects, more reactive. One
indication of the increased reactivity is that both hydrides
exchange with D2O within the time required for mixing and
1
acquiring a H NMR spectrum (eq 12).
outcome, given that I− and Br− are not as strongly solvated
by water as Cl− and a simple hard/soft acid/base view would
argue that I− and Br− would bind more strongly to the iridium
to yield insoluble complexes. 1H, 31P, and 13C NMR spectra are
all consistent with the meridional phosphine, cisdihydride
structure shown in eq 8. Attempted replacement of chloride
with fluoride led to decomposition with no isolable products.
Syntheses of the heavier transition-metal fluoride complexes in
general and iridium fluoride compounds specifically have
proven to be a challenge.37
Given the difference in H/D exchange rates between
compounds 2 and 8, some discussion on the nature of the
H/D exchange reaction seems warranted. While no specific
studies were aimed at probing the mechanism of the exchange
reaction directly, it would seem reasonable that the exchange
occurs via a mechanism similar to one already described in the
For carboxylate ligands, a synthetic scheme introducing the
carboxylate at the COD dimer stage proved to be the most
successful. The method shown in eq 9 was used to prepare
3923
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
literature.22 Since the first H to exchange with D is the one cis
to the putative aqua group, an intramolecular mechanism seems
appropriate to postulate wherein D from the coordinated D2O
“protonates” the Ir−H bond, forming a transient iridium
dihydrogen complex. The reverse of that reaction regenerates
the hydride with a 50% probability of the formation of Ir-D.
Continued steps as well as aqua exchange result in complete
deuteration. Ultimate deuteration of both hydrides likely stems
from a five-coordinate intermediate that has a low barrier to
rearrangement, allowing for the interchange between the two
hydride positions. Figure 4 sketches this hypothetical exchange
mechanism.
Figure 5. Solid-state structure of the vinyl hydride benzoate complex
9. Phosphorus methyl groups and hydrogen atoms other than the
hydride and vinyl hydrogens are omitted for clarity. Select bond
distances (Å): Ir1−C1, 2.094(9); Ir1−O1, 2.193(6); Ir1−P1,
2.321(3); Ir1−P2, 2,317(3); Ir1−P3, 2.304(3). Select bond angles
(deg): Ir1−C1−C2, 131.1(8); P1−Ir1−P2, 99.6(1); P2−Ir1−P3,
94.5(1); P1−Ir1−P3, 165.8(1); O1−Ir1−C1, 89.2(3); O2−C7−O1,
125.8(8).
between the chemical shift of the trans hydride versus the
electronegativity of the trans ligand atom bonded to the iridium
center. The H NMR chemical shift data and the electro-
Figure 4. Hypothetical mechanism for H/D exchange between iridium
hydrides and D2O.
1
negativity data are given in Table 2, and a plot of chemical shift
31P NMR spectroscopy revealed a single set of resonances,
indicating that only one species was present in solution, with
spectral properties identical with those observed for the aqua
complex 2a. Addition of varying amounts of NaCl establishes
the same two species in equilibrium observed upon dissolution
of 2 in water. This indicates that the benzoate ligand is
completely dissociated in water, a result in keeping with our
findings from the equilibrium involving 2 and 2a, where the
positive ΔH value is in the main responsible for the unfavorable
Keq value. For the benzoate complex the exchange of one
oxygen ligand (benzoate) for another (aqua) has ostensibly a
ΔH value close to zero and the favorable entropic changes
drives the equilibrium completely to the aqua complex.
The reaction of 8 with alkynes is complete within a few
minutes in aqueous solution (monitoring by 1H NMR
spectroscopy), leading to the formation of a vinyl iridium
hydride compound 9, analogous in all respects to the chloride
compounds reported above except for benzoate in place of
chloride in the sixth coordination site (eq 13). Suitable crystals
1
Table 2. H Chemical Shifts of Ir(H)2(PMe3)3X in CD2Cl2
X
electronegativity40
H(trans) (ppm)
O
2.82
2.76
2.6
−26.4
−24.0
−23.0
−20.8
−19.4
−13.6
Cl
Br
I
N15
P
2.45
2.28
1.84
vs electronegativity is shown in Figure 6. Specifically, the plot of
Mulliken−Jaffee “p” electronegativity values40 vs chemical shifts
of the trans hydrides yielded a very good linear relationship.
The use of the “p” values is justified in that the highest
occupied molecular orbital on each atom involved in the
bonding to iridium has nearly 100% p character. (See the
of 9 were obtained, and a single-crystal X-ray structure analysis
was performed. Table 1 contains a concise tabulation of
experimental data for the structure of 9. The overall structure is
presented as a thermal ellipsoid plot in Figure 5 with selected
bond lengths and angles given in the figure caption.
Chemical Shift Relationships. While we were reviewing
1H NMR data, a trend was observed in the chemical shifts of
the hydrides. The doublet of triplet of doublets due to the
hydride trans to the phosphine group shifted upfield as the
ligand in the sixth coordination site was changed from I to Br to
Cl. Examination of the data found a significant relationship
Figure 6. Plot of hydride chemical shifts vs Mulliken−Jaffee p
electronegativity of Ir(H)2(PMe3)3X in CD2Cl2. Data are given in
Table 2.
3924
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
XHydex and were placed in indicated positions without further
refinement.44 The program JMP was used for statistical analyses.45
Synthesis of Ir(H)2(PMe3)3Cl (2). A 50.0 mL three-necked flask
equipped with a magnetic stir bar and a septum was charged with 2.78
g of [Ir(COD)(PMe3)3]Cl (1) under nitrogen in a drybox. The flask
was then connected to a double-manifold (vacuum/nitrogen) Schlenk
line, and 20.0 mL of mesitylene was added by syringe. The flask was
then fitted with a reflux column equipped with a nitrogen inlet and
connected to the Schlenk line. H2 was bubbled through the mixture at
a very slow rate, and the suspension was stirred by magnetic stirrer and
heated to about 100 °C. Upon heating, the white solids dissolved, and
after 3 h of heating, a light yellow solution was observed. The solvent
was removed under reduced pressure, and the resulting solids were
washed three times with copious amounts of pentane to give whitish
yellow solids. The white solids were dried in vacuo to give 2.13 g of 2
(4.65 mmol, 94.3% yield).
Anal. Calcd (found) for C9H29IrClP3: C, 23.60 (23.38); H, 6.40
(6.12). 1H NMR (CD2Cl2): δ −24.1 (m, JHP = 11 Hz, JHH = 5.56 Hz,
1H), −11.2 (dtd, JHPtrans = 135 Hz, JHPcis = 22.2 Hz, JHH = 5.56 Hz,
1H), 1.63 (t, JHP = 4.8 Hz, 18H of trans PMe3), 1.55 (d, JHP = 11.1 Hz,
9 Hz of cis PMe3). 31P NMR (CD2Cl2): δ −48.44 (t, JPP = 54.57 Hz,
1P of cis PMe3), −42.6 (d, JPP = 54.2 Hz, 2P of trans PMe3). 13C NMR
(CD2Cl2): δ 22.48 (t, JCP = 66.31 Hz, 6C of trans PMe3), 20.09 (d, JCP
= 104.22 Hz, 3C of cis PMe3).
Crystals suitable for X-ray diffraction were grown by slow
evaporation of a diethyl ether solution of 1 under nitrogen.
Synthesis of [Ir(H)2(PMe3)4][PF6] (3a). A 25.0 mL one-necked
side-armed flask equipped with a magnetic stir bar and a septum was
charged with 0.10 g (0.22 mmol) of Ir(H)2(PMe3)3Cl and 0.08 g (0.22
mmol) of Tl[PF6] under nitrogen in a drybox. The flask was then
connected to a double-manifold Schlenk line, and 5.00 mL of
methylene chloride was added by syringe followed by 0.023 mL (4.36
mmol) of trimethylphosphine. The reaction mixture was stirred
magnetically. A white precipitate formed in a clear solution. The
precipitate was removed by filtration, and the methylene chloride
solution was stripped under reduced pressure to give white solids,
which were dried in vacuo to give 0.060 g of 3a (0.110 mol, 51.5%
yield).
Supporting Information for the results of Gaussian calculations
of molecular orbitals using the WebMO interface.) As the
ligand X becomes more electronegative, the chemical shifts of
the hydride cis to the ligand X and the phosphines all shift
downfield, corresponding to a greater withdrawal of electron
density from the metal center onto the more electronegative
ligand, thus deshielding these ligands. However, the chemical
shift of the hydride trans to X displays an opposite effect. This
cannot be explained in terms of electronegativity; otherwise, a
downfield shift similar to the cis hydride and the phosphines
would be expected. The chemical shift behavior of the trans
hydride can be rationalized as a “trans effect”, with the H being
pulled closer to the metal, thus embedding it further in the
metal electron density.
In 1971 Birnbaum described similar results in a study of the
hydride shifts of monohydrido halo transition-metal complexes.
He observed that the chemical shift of a hydride trans to the
halide decreased in the order Cl− > Br− > I−, while the chemical
shifts of the hydride cis to the halide increased in the order Cl−
< Br− < I− . These experimental results were exactly the
opposite of the trends theoretically predicted by Buckingham
and Stevens in 1964. Birnbaum attributed this to an increase in
the covalent character of the complexes in the order Cl− < Br−
< I−.
Specific chemical shift data on a different iridium complex
were found in the research of Eisenberg et al. on iridium
dihydrides formed by hydrogenation of Ir(CO)(dppe)X (X =
Cl, Br, I).41
It is obvious from the plot of chemical shifts versus
electronegativity of ligand X in Eisenberg’s complexes and
from Birnbaum’s studies that this is not an isolated
phenomenon.
CONCLUSIONS
■
Anal. Calcd (found) for C12H37P5IrF6: C, 22.40 (22.47); H, 5.95
mer-Ir(H)2(PMe3)3Cl and mer-Ir(H)2(PMe3)3O2CPh are both
very water-soluble hydride complexes and have proven to have
very interesting aqueous chemistry. The loss of an anionic
ligand provides a facile route in water to open a coordination
site to allow for reaction chemistry, and the migratory insertion
of hydride into carbon−carbon multiple bonds shows the
potential for these complexes to catalyze organic reactions in
aqueous solutions. Future work will elaborate on the expansion
of the anionic leaving groups as well as investigate the reactivity
of monohydrido systems in water, including their catalytic
activity for hydrogenation and terminal alkyne dimerization.
(5.92). 1H NMR (acetone-d): δ −13.7 (dt, JHPtrans = 115.0 Hz, JHPcis
23.2 Hz, 2H), 1.0 (t, JHP = 7.7 Hz, 18H of trans PMe3), 1.4 (d, JHP
13.8 Hz, 18 H of cis PMe3).
=
=
Synthesis of [Ir(H)2(PMe3)4][Cl] (3b). A 10.0 mL one-necked
side-armed flask equipped with a magnetic stir bar and a septum was
charged with 0.030 g (0.066 mmol) of Ir(H)2(PMe3)3Cl under
nitrogen in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 2.00 mL of distilled water was added by
syringe followed by 7.20 μL of trimethylphosphine. The solution was
stirred magnetically at room temperature for 2 h. At completion, a
clear solution was observed. The water solution was stripped under
reduced pressure to give white solids, which were dried in vacuo at
room temperature to give 0.025 g of 3b (0.045 mol, 70.0% yield) (C,
−
EXPERIMENTAL SECTION
H analysis obtained only for the PF6 complex).
■
1H NMR (CD2Cl2): δ −12.95 (dt, JHPtrans = 115.0 Hz, JHPcis = 22.0
Hz, 2H), 1.65 (d, JHP = 8.1 Hz, 18 H of cis PMe3), 1.73 (t, JHP = 3.2
Hz, 18 H of trans PMe3). 31P NMR (CD2Cl2): δ −59.82 (t, JPP = 20.2
Hz, 2P of cis PMe3), −53.6 (t, JPP = 19.4 Hz, 2P of trans PMe3).
Synthesis of Ir(H)(C(H)C(H)CMe3)(PMe3)3Cl (4a). A 250.0 mL
one-necked side-armed flask equipped with a magnetic stir bar and a
septum was charged with 0.400 g (0.090 mmol) of Ir(H)2(PMe3)3Cl
under nitrogen in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 14.0 mL of distilled water was added by
syringe followed by 244 mL (1.98 mmol) of tert-butylacetylene. A
milky solution formed, and white solids were observed immediately.
The solution was stirred magnetically at room temperature for 3 h.
The water was stripped under reduced pressure to give white solids,
which were dried in vacuo to give 0.380 g of 4 (7.02 mmol, 78.0%
yield).
General Methods. All reactions were performed under an inert
atmosphere of purified nitrogen. Standard glassware and Schlenk line
techniques were used. [Ir(COD)(PMe3)3]Cl (1) was synthesized by a
previously reported procedure.24 All other chemicals were reagent
grade and were used without further purification. Unless otherwise
noted, solvents used were of reagent grade and were dried by the
appropriate technique before use. Water was deionized with a reverse
osmosis system. The proton and carbon NMR spectra were obtained
on a Bruker WP270SY or WP200SY instrument. The 31P NMR
spectra were obtained on a Bruker WP200SY instrument operating at
81 MHz and referenced using an internal standard of 85% H3PO4. All
elemental analyses were performed by Atlantic Microlab, Inc.,
Norcross, GA. X-ray crystal structures were obtained using a
Siemens/Bruker R3m/v diffractometer and Mo Kα (λ = 0.710 71 Å)
radiation at 303 K, and solution and refinement was carried out with
the SHELX42 suite of programs. ORTEP plots were generated using
the program Olex2.43 Hydrides were located using the program
Anal. Calcd (found) for C15H39P3ClIr: C, 33.36 (32.82); H, 7.28
1
(7.35). H NMR (CD2Cl2): δ −23.9 (q, JHP = 16.9 Hz, 1H), 0.95 (s,
3925
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
9H, CMe3), 1.45 (t, JHP = 4.3 Hz, 18H of trans PMe3), 1.52 (d, JHP
=
ether solution was filtered off, and the solids were dried in vacuo to
yield 0.300 g of 7 (0.560 mmol, 85.5% yield).
7.6 Hz, 9H of cis PMe3), 6.7(ddt, JHH = 17.5 Hz, JHPtrans = 3.5 Hz, JHPcis
= 3.5 Hz, 1H, vinyl IrCH), 5.33 (ddt, JHH = 17.5 Hz, JHPtrans = 7.0 Hz,
JHPcis = 2.7 Hz, 1H, vinyl Me3CCH). 31P NMR (CD2Cl2): δ −42.34 (d,
JPP = 65.1 Hz, 1P of cis PMe3), −51.38 (t, JPP = 65.1 Hz, 2P of trans
PMe3). 13C NMR (CD2Cl2): δ 16.62 (t, JCP = 74.9 Hz, 6C of trans
PMe3), 21.5 (d, JCP = 108.22 Hz, 3C of cis PMe3), 29.86 (s, 3 C of
CMe3), 37.3(s, 1C of CMe3), 128.27 (t, JCP = 15.0 Hz, 1C of vinyl
C(H)CMe3), 148.95 (s, 1C of vinyl CH).
Anal. Calcd (found) for C14H41IrP3Cl: C, 31.72 (32.17); H, 7.79
1
(8.09). H NMR (CD2Cl2): δ −23.7 (q, JHP = 12.0 Hz, 1H), 1.45 (t,
JHP= 4.9 Hz, 18H of trans PMe3), 1.52 (d, JHP = 8.2 Hz, 9H of cis
PMe3), 1.6−1.8 (m, 3H of CMe), 2.0 (s, 3H of CCCMe), 6.25 (m,
1H of vinyl CH). 31P NMR (CD2Cl2): δ −51.30 (t, JPP = 49.8 Hz, 2P
of trans PMe3), −40.72 (d, JPP = 29.8 Hz, 1P of cis PMe3).
Crystals suitable for X-ray diffraction were grown by slow vapor
diffusion of diethyl ether into a dichloromethane solution of 4d.
Synthesis of Ir(H)2(PMe3)3Br (5a). A side-arm flask equipped with
septa and stirrer was charged with 1 (0.25 g, 0.55 mmol) under
nitrogen. A 10.0 mL portion of H2O was added by syringe and the
solution stirred until homogeneous. Excess KBr (0.65 g, 5.5 mmol)
was added, and a white precipitate immediately formed, while the
solution was stirred for 1 h. The solvent was removed under reduced
pressure and the residue extracted with 2 × 5 mL of CH2Cl2 to give
pure 6 (0.23 g, 85%) as a white powder.
Synthesis of Ir(H)(C(H)C(H)(SiMe3)(PMe3)3Cl (4b). A 250.0
mL one-necked side-armed flask equipped with a magnetic stir bar and
a septum was charged with 0.200 g (0.440 mol) of Ir(H)2(PMe3)3Cl
under N2 in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 5.00 mL of distilled water was added by
syringe. Next, 67.9 μL (0.480 mol) of trimethylsilylacetylene was
added by syringe. Light yellow solids were formed. The reaction
mixture was stirred overnight. The light yellow solids were collected by
filtration, and the solids were dried in vacuo to yield a product mixture
1
of 6 with two different isomers, which were identified by H NMR
Anal. Calcd (found) for C9H29IrP3Br: C, 21.80 (21.5); H, 5.81
1
spectroscopy. C,H analysis was not obtained for this mixture; other
compounds in this family have been characterized.
(5.87). H NMR (CD2Cl2): δ −23.0 (m, 1 H), −11.3 (dtd, JHPtrans
=
134 Hz, JHPcis = 22.3 Hz, JHHcis =5.1 Hz, 1 H), 1.50 (d, JHP = 7.3 Hz, 9
Major isomer: 1H NMR (CD2Cl2) δ −23.45 (q, JHP = 16.9 Hz, 1H),
1.44 (t, JHP = 3.4 Hz, 18H of trans PMe3), 1.49 (d, JHP = 7.6 Hz, 9H of
H of cis PMe3), 1.65 (t, JHP = 5.7 Hz, 18 H of trans PMe3). 31P NMR
(CD2Cl2): δ −53.7 ppm (t, JPP = 62.1 Hz, cis PMe3), −46.7 (d, JPP
=
cis PMe3), −0.03 (s, 9H of SiMe3), 6.15 (ddt, JHH = 20.2 Hz, JHPtrans
=
54.1 Hz, trans PMe3). 31P NMR (H2O): major species δ −53.4 (t, JPP
= 48.1 Hz, cis PMe3), −47.3 (d, JPP = 55.0 Hz, trans PMe3); minor
species δ −44.0 (t, cis PMe3), −39.5 (d, JPP = 54.4 Hz, trans PMe3).
Synthesis of Ir(H)2(PMe3)3I (5b). A 100.0 mL one-necked side-
armed flask equipped with a magnetic stir bar and a septum was
charged with 0.300 g (0.660 mmol) of 2 under nitrogen in a drybox.
The flask was then connected to a double-manifold Schlenk line, and
14.0 mL of distilled water was added by syringe. The mixture was
stirred magnetically at room temperature. Next, 0.130 g (0.790 mmol)
of potassium iodide was added quickly. White solids precipitated out
immediately. After 24 h, the precipitate was filtered. The white solids
were washed three times with excess distilled water and dried in vacuo
to give 0.250 g of Ir(H)2(PMe3)3I (0.230 mmol, 70.0% yield).
Anal. Calcd (found): I, 25.2 (25.12). 1H NMR (methylene-d
chloride): δ −20.7 (m, JHP = 11.2 Hz, JHH = 5.2 Hz), −12.0 (dtd,
11.2 Hz, JHPcis ≤ 3 Hz, 1H of vinyl C(H)(SiMe3)), 8.3 (ddt, JHH = 20.2
1
Hz, JHPtrans = 5.9 Hz, JHPcis = 3.7 Hz, H of vinyl IrC(H)).
Minor isomer: 1H NMR (CD2Cl2) δ −10.75 (dt, JHPtrans = 135.0 Hz,
JHPcis = 16.9 Hz, 1H), 1.49 (d, JHP = 7.6 Hz, 18H of trans PMe3), 1.6
(t, JHP = 3.4 Hz, 9H of cis PMe3), −0.003 (s, 9H of SiMe3), 7.9 (dtd,
JHH = 20.2 Hz, JHPtrans = 11.2 Hz, JHPcis ≤ 3 Hz, 1H of vinyl
C(H)(SiMe3)), signal for vinyl IrC(H) was not seen.
Attempts to separate the two isomers led to decomposition of the
material, and complete spectral characterization was not obtained.
However, the 1H NMR spectra of the hydride region (both the
chemical shift and the splitting patterns) clearly indicate the presence
of the two indicated isomers.
Synthesis of Ir(H)(C(H)C(H)(Ph))(PMe3)3Cl (4c). A 250.0 mL
one-necked side-armed flask equipped with a magnetic stir bar and a
septum was charged with 0.500 g (1.09 mmol) of Ir(H)2(PMe3)3Cl
under nitrogen in a drybox. The flask was then connected to a double-
manifold (Schlenk line, and 14 mL of distilled water was added by
syringe. Next, 132 μL (1.20 mmol) of phenylacetylene was added by
syringe. A milky white solution formed, and white solids precipitated
immediately. The water was stripped off under reduced pressure to
give white solids, which were dried in vacuo to give 0.400 g of 5 (0.714
mmol, 66.0% yield).
JHPtrans = 132.2 Hz, JHPcis = 22.0 Hz, JHH = 5.9 Hz, 1H), 1.58 (d, JHP
=
7.79 Hz, 9H of cis PMe3), 1.72 (t, JHP = 3.28 Hz, 18H of trans PMe3).
31P NMR (methylene-d chloride): δ −61.0 (t, JPP = 54.46 Hz, 1P of cis
PMe3), −51.6 (d, JPP = 52.3 Hz, 2P of trans PMe3). 13C NMR
(methylene-d chloride): δ 22.0 (JCP = 110.0 Hz, 3C of cis PMe3), 24.4
(t, JCP = 67.1 Hz, 6C of trans PMe3).
Synthesis of [Ir(COD)(O2CCH3)]2 (6a). A 250 mL one-necked
side-armed flask equipped with a magnetic stir bar and a septum was
charged with 1.00 g (1.49 mmol) of [Ir(COD)Cl]2 under nitrogen in a
drybox. The flask was then connected to a double-manifold Schlenk
line, and 25.0 mL of toluene was added by syringe. A 0.550 g portion
(3.27 mmol) of Ag[O2CCH3] was added quickly and the flask covered
to protect it from light. The reaction mixture was stirred magnetically
at room temperature for 2 days. The reddish purple solution was
filtered away from the white AgCl salt. A 100 mL portion of toluene
was used to wash the white solid AgCl salt. The solutions were all
combined, and the solvent was removed under reduced pressure to
give reddish purple solids. The reddish purple solids were dried in
vacuo to give 0.890 g of [Ir(COD)(O2CCH3)]2 (1.24 mol, 83.0%
yield).
Anal. Calcd (found) for C17H35ClP3Ir: C, 36.46 (36.55); H, 6.30
1
(6.25). H NMR (CD2Cl2): δ −23.2 (q, JHP = 17.0 Hz, 1H), 1.45 (t,
JHP = 5.4 Hz, 18H of trans PMe3), 1.57 (d, JHP = 10.5 Hz, 9H of cis
PMe3), 6.55 (ddt, JHH = 22.0 Hz, JHPtrans = 9.2 Hz, JHPcis = 3.7 Hz, 1H,
vinyl PhCCH), 8.25 (ddt, JHH = 19.24 Hz, JHPtrans = 4.2 Hz, JHPcis ≤ 3.0
Hz, 1H, vinyl IrCH), 7.0−7.4 (m, 5H of phenyl). 31P NMR (CD2Cl2):
d-40.85 ppm (d, JPP = 53.38 Hz, 2P of trans PMe3), −51.77 (t, JPP
=
=
52.52 Hz, 1P of cis PMe3). 13C NMR (CD2Cl2): δ 16.96 ppm (t, JCP
15 Hz, 6C of trans PMe3), 21.34 (d, JCP = 18.5 Hz, 3C of cis PMe3),
146.1 (t, JCP = 15.0 Hz, 1C of vinyl C(H)(Ph), 138.51 (s, 1C of vinyl
IrC(H)), 124.38 (s, 1C, para carbons of phenyl), 124.74 (s, 2C, ortho
carbons of phenyl), 128.63 (s, 2C, meta carbons of phenyl).
Anal. Calcd (found) for C20H30IrO4: C, 45.6 (45.9); H, 5.74 (6.13).
1H NMR (CDCl3): δ 4.06 (br s, 2H of COD olefinic), 3.86 (br s, 2H
of COD olefinic), 2.52 (br s, 2H of COD aliphatic), 2.30 (br m, 2H of
COD aliphatic), 1.45 (br m, 4 H of COD aliphatic), 1.89 (s, 3H of
CH3).
Synthesis of [Ir(COD)(O2CPh)]2 (6b). A 500 mL one-necked side-
armed flask equipped with a stir bar and a septum was charged with
3.50 g (5.21 mmol) of [Ir(COD)Cl]2 under nitrogen in a drybox. The
flask was then connected to a double-manifold Schlenk line, and 100
mL of toluene was added by syringe. Next, 2.63 g (11.5 mmol) of
Ag[O2CPh] was added quickly and the flask covered to protect it from
light. The suspension was stirred magnetically at room temperature for
Synthesis of Ir(H)(Me3CC(H)CMe)(PMe3)3Cl (4d). A 250.0
mL one-necked side-armed flask equipped with a magnetic stir bar and
a septum was charged with 0.300 g (0.655 mmol) of Ir(H)2(PMe3)3Cl
under N2 in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 14.0 mL of distilled water was added by
syringe. Next, 0.050 g (0.655 mmol) of 2,4-hexadiyne was charged
quickly. A milky white solution was formed, and white solids were
observed immediately. The reaction mixture was stirred magnetically
at room temperature. After 4 h, the water was stripped under reduced
pressure to give light whitish brown solids. The solids were dissolved
in 0.500 mL of methylene chloride, and 5.00 mL of diethyl ether was
used to recrystallize the compound. The methylene chloride/diethyl
3926
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
3 days. The reddish purple solution was filtered away from the white
AgCl salt. A 300 mL portion of toluene was used to wash the white
AgCl salt. All of the reddish purple solution was concentrated by
evaporating at reduced pressure to give reddish purple solids. The
reddish purple solids were dried in vacuo to give 3.30 g of
[Ir(COD)(OCOPh)]2 (3.93 mmol, 75.4% yield).
Anal. Calcd (found) for C30H34O4Ir: C, 42.74 (42.52): H, 4.07
(4.03). 1H NMR (CDCl3): δ 4.25 (br s, 2H of COD olefinic), 3.96 (br
s, 2H of COD olefinic), 2.57 (br m, 2H of COD aliphatic), 2.43 (br m,
2H of COD aliphatic), 1.50 (br m, 4H of COD), 7.94 (m, 2H of
C6H5), 7.4−7.2 (m, 3 H of C6H5). 13C NMR (CDCl3): δ 32.07 (s, 4C
of COD), 56.5 (s, 4C of COD), 127.75 (s, 2C, meta carbons, phenyl
ring), 129.92 (s, 2C, ortho carbons, phenyl ring), 131.84 (s, 1C, para
carbon, phenyl ring).
phenyl ring), 69.20 (s, 4C of COD), 34.37 (s, 4C of COD), 20.02−
20.54 (m, 9C of PMe3).
Synthesis of ]Ir(COD)(PMe3)3][O2CCF3] (7c). A 250 mL one-
necked side-armed flask equipped with a magnetic stir bar and a
septum was charged with 0.600 g (0.726 mmol) of [Ir(COD)-
(O2CCF3)]2 (6c) under nitrogen in a drybox. The flask was then
connected to a double-manifold Schlenk line, and 50.0 mL of toluene
was added by syringe. Next, 47.0 μL (4.57 mmol) of trimethylphos-
phine was added slowly by syringe. White solids precipitated
immediately. The suspension was stirred at room temperature for 1
day. The solid was then collected by filtration. The white solids were
washed three times with pentane and tetrahydrofuran and dried in
vacuo to give 0.760 g of [Ir(COD)(PMe3)3][O2CCF3] (1.20 mmol,
82.1% yield).
Anal. Calcd (found) for C19H39O2F3Ir: C, 35.57 (35.82); H, 6.13
Synthesis of [Ir(COD)(O2CCF3)]2 (6c). A 250 mL one-necked
side-armed flask equipped with a stir bar and a septum was charged
with 1.00 g (1.49 mmol) of [Ir(COD)Cl]2 under nitrogen in a drybox.
The flask was then connected to a double-manifold Schlenk line, and
25.0 mL of toluene was added by syringe. A 0.720 g portion (3.27
mmol) of Ag[O2CCF3] was added quickly, and the flask was covered
to protect the solution from light. The reaction mixture was stirred
magnetically at room temperature for 2 days. The reddish orange
solution was filtered away from the white AgCl salt. A 100 mL portion
of toluene was used to wash the AgCl salt. All of the reddish orange
solution was concentrated by removing toluene under reduced
pressure to give reddish orange solids. The reddish orange solids
were dried in vacuo to give 1.11 g of [Ir(COD)(OCOCF3)]2 (1.35
mmol, 90.3% yield).
1
(6.01). H NMR (CD2Cl2): δ 3.3 (br s, 4H of COD olefinic), 2.5 (br
s, 4H of COD aliphatic), 2.2 (br s, 4H of COD aliphatic), 1.5 (virtual
t, 27H of 3 PMe3).
Synthesis of Ir(H)2(PMe3)3(O2CPh) (8). A 50.0 mL three-necked
flask equipped with a magnetic stir bar and septa was charged with
1.37 g (2.08 mmol) of [Ir(COD)(PMe3)3][O2CPh] (7b) under
nitrogen in a drybox. The flask was then connected to a double-
manifold (vacuum, nitrogen) Schlenk line, and 20.0 mL of dried
mesitylene was added by syringe. The flask was then fitted with a reflux
column equipped with a nitrogen inlet and connected to the Schlenk
line. H2 was bubbled through the solution at a very slow rate. The
suspension was stirred magnetically and heated to about 100 °C. Upon
heating, the white solids dissolved to give a light yellow solution. After
3 h of heating, all of the solids had dissolved to yield a light yellow
solution. The solution was concentrated under reduced pressure,
yielding white solids which were washed three times with copious
amounts of pentane. The solids were dried in vacuo to give 1.08 g of
Ir(H)2(PMe3)3(O2CPh) (1.98 mmol, 95.2% yield).
1H NMR (CD2Cl2): δ 4.5 (br s, 2H of COD olefinic), 4.15 (br s,
2H of COD olefinic), 2.6 (br s, 2H of COD aliphatic), 2.3 (br s, 2H of
COD aliphatic), 1.7 (br s, 4H of COD aliphatic).
Synthesis of [Ir(COD)(PMe3)3][O2CCH3] (7a). A 250 mL one-
necked side-armed flask equipped with a magnetic stir bar and a
septum was charged with 0.630 g (8.76 mmol) of [Ir(COD)-
(O2CCH3)]2 (6a) under nitrogen in a drybox. The flask was
connected to a double-manifold Schlenk line, and 40.0 mL of toluene
was added by syringe. Next, 0.550 mL (5.34 mmol) of
trimethylphosphine was added slowly by syringe. White solids
precipitated immediately. The suspension was stirred magnetically at
room temperature for 1 day, and the solids were collected by filtration.
The solids were washed three times each with an excess of pentane
and tetrahydrofuran and dried in vacuo to give 0.700 g of
[Ir(COD)(PMe3)3][O2CCH3] (1.20 mmol, 68.0% yield).
Anal. Calcd (found) for C16H34O2P3Ir: C, 35.36 (35.61); H, 6.30
(6.24). 1H NMR (CD2Cl2): δ −26.3 (m, JHP = 12.5 Hz, JHH = 5.4 Hz,
1H), −10.52 (dtd, JHPtrans= 134.1 hz, JHPcis = 23.9 Hz, JHH = 6.06 Hz,
1H), 1.55 (d, JHP = 8.3 Hz, 9H of cis PMe3), 1.6 (t, JHP = 4.2 Hz, 18 H
of trans PMe3), 7.1−7.3 (m, 3H of phenyl ring), 7.85−7.9 (m, 2H of
phenyl ring). 31P NMR (CD2Cl2): δ −42.45 (t, JPP = 52.94 Hz, 1P of
cis PMe3), −38.31 (d, JPP = 52.76 Hz, 2P of trans PMe3). 13C NMR
(CD2Cl2): δ 21.34 (d, JCP = 105.3 Hz, 3C of cis PMe3), 23.02 (t, JCP
=
66.34 Hz, 6C of cis PMe3), 127.72 (s, 2C, meta carbons of phenyl
ring), 129.45 (s, 1C, para carbons of phenyl ring), 129.95 (s, 2C, ortho
carbons of phenyl ring).
Anal. Calcd (found) for C19H42IrP3O2: C, 40.1 (39.76); H, 4.25
Oxidative Addition of H2 to [Ir(COD)(PMe3)3][O2CCF3]. A 250
mL three-necked flask equipped with a magnetic stir bar and septa was
charged with 1.95 g (3.04 mmol) of [Ir(COD)(PMe3)3][O2CCF3]
under nitrogen in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 20.0 mL of dried mesitylene was added by
syringe. The flask was then fitted with a reflux column equipped with a
nitrogen inlet and connected to the Schlenk line. H2 was bubbled
through the solution at a very slow rate. The suspension was stirred
magnetically and heated slowly to about 100 °C. Upon heating, the
white solids dissolved to give a light yellow solution. After 3 h of
heating, a light yellow solution was observed. The solution was
concentrated under reduced pressure to give a light yellow oily crude
product. Methylene chloride/ether was used to recrystallize the oily
crude product. Yellow solids were obtained upon recrystallization and
dried in vacuo to give a very low yield of [Ir(H)2(PMe3)4][OC(O)-
CF3].
1
(4.01). H NMR (CDCl3): δ 3.1 (broad s, 4H of COD olefinic), 2.3
(broad s, 4H of COD aliphatic), 2.1 (br s, 4H of COD aliphatic), 1.8
(s, 3H of CH3), 1.62 (virtual t, 27H of 3 PMe3). 31P NMR (CDCl3): δ
−53.15 (s, 3P of 3 PMe3).
Synthesis of [Ir(COD)(PMe3)3][O2CPh] (7b). A 250 mL one-
necked side-armed flask equipped with a magnetic stir bar and a
septum was charged with 0.500 g (0.593 mmol) of [Ir(COD)-
(OOCPh)]2 (6b) under nitrogen in a drybox. The flask was then
connected to a double-manifold (vacuum, nitrogen) Schlenk line, and
30.0 mL of toluene was added by syringe. Next, 0.400 mL (3.80
mmol) of trimethylphosphine was added slowly also by syringe. White
solids precipitated immediately. The suspension was stirred at room
temperature overnight. The light pink liquid solution was filtered off
from the white solid product. Three 15.0 mL portions of pentane were
used to wash the white solids. Three 15.0 mL portions of
tetrahydrofuran were also used to wash the white solids. The white
solids were then dried in vacuo to give 0.580 g of [Ir(COD)-
(PMe3)3][O2CPh] (0.883 mmol, 74.5% yield).
1
Anal. Calcd (found): C, 27.5 (27.28); H, 6.26 (6.13). H NMR
(CD2Cl2): δ −12.9 (dt, JHPtrans = 113.16 Hz, JHPcis = 24.79 Hz, 1H),
1.63 (d, JHP = 7.63 Hz, 18H of cis PMe3), 1.71 (t, JHP = 3.5 Hz, 18H of
trans PMe3). 31P NMR (CD2Cl2): δ −59.95 (t, JPP = 51.4 Hz, 2P of cis
PMe3), −53.69 (t, JPP = 52.04 Hz, 2P of trans PMe3).
Oxidative Addition of H2 to [Ir(COD)(PMe3)3][O2CCH3]. A 250
mL three-necked flask equipped with a magnetic stir bar and septa was
charged with 0.500 g (0.779 mmol) of [Ir(COD)(PMe3)3][O2CCH3]
under nitrogen in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 20.0 mL of mesitylene was connected to
Anal. Calcd (found) for C24H44O2P3Ir: C, 44.32 (44.23); H, 6.92
(6.95). 1H NMR (CDCl3): δ 8.15 (m, 2H of phenyl ring), 7.2 (m, 3H
of phenyl ring), 3.1 (br s, 4H of COD olefinic), 2.35 (br s, 4H of COD
aliphatic), 2.19 (br s, 4H of COD aliphatic), 1.52 (t, J = 2.77 Hz, 27H
of 3 PMe3). 31P NMR (CDCl3): δ −53.27 (s, 3P of 3 PMe3), 13C
NMR (CD2Cl2): δ 128.92 (s, 2C, meta carbons, phenyl ring), 130.21
(s, 2C, ortho carbons, phenyl ring), 133.99 (s, 1C, para carbons,
3927
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
the Schlenk line. H2 was bubbled through the solution at a very slow
rate. The suspension was magnetically stirred and heated slowly up to
about 100 °C. Upon heating, the white solids dissolved to give a light
yellow solution. After 3 h of heating, a light yellow solution was
observed. The solution was concentrated under reduced pressure and
washed three times with copious amounts of pentane to give a light
charging a septum bottle equipped with a magnetic stir bar with 0.088
g (0.162 mmol) of IrH2(PMe3)3(O2CPh), sealing under nitrogen in a
glovebox, and adding 3.0 mL of H2O by syringe. The mixture was
stirred until the solution became homogeneous to give a pale yellow
solution. Sample NMR tubes were flushed and sealed under argon
with a septum. A 0.486 M aqueous NaCl solution was prepared by
dissolving 0.0852 g of NaCl in 3.0 mL of H2O. The samples were
prepared by adding appropriate aliquots of the standard solution of 8
followed by NaCl. 31P NMR spectra were acquired and integration
values determined.
1
yellow oily crude product. H NMR spectroscopy indicated that the
crude product was a mixture of at least two products: Ir-
(H)2(PMe3)3(O2CCH3) and [Ir(H)2(PMe3)4][O2CCH3]. Recrystalli-
zation and separation by methylene chloride/ether was not successful.
No further work was carried out.
Reaction of PMe3 with 20 in Water. A 25.0 mL one-necked side-
armed flask equipped with a magnetic stir bar and a septum was
charged with 0.050 g (0.092 mmol) of Ir(H)2(PMe3)3(O2CPh) (20)
under nitrogen in a drybox. The flask was then connected to a double-
manifold Schlenk line, and 5.00 mL of distilled water was added. Next,
19.1 μL (0.184 mmol) of trimethylphosphine was added by syringe.
The solution was magnetically stirred for 1 day. Water was stripped off
under reduced pressure to yield white solids. The white solids were
dried in vacuo to yield Ir(H)2(PMe3)4][O2CPh]. 1H NMR (CD2Cl2):
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving full crystallographic information for compounds
2, 4d, and 9, text, tables, and figures describing the detailed
analysis used to determine and compute the aqueous
equilibrium involving 2 and 2a, and figures and tables showing
the Gaussian calculations used in support of the use of Mulliken
“p” electronegativities in Table 2 and in constructing Figure 6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
δ −12.98 (dt, JHPtrans = 100.52, JHPcis = 21.74 Hz, 1H), 1.62 (d, JHP
=
7.52 Hz, 18H of cis PMe3), 1.70 (t, JHP = 3.24 Hz, 18H of trans PMe3),
7.23 (t, 3H of phenyl ring), 8.0 (q, 2H of phenyl ring). 31P NMR
(CD2Cl2): δ-59.84 (t, JPP = 50.48 Hz, 2P of cis PMe3), −53.62 (t, JPP
=
AUTHOR INFORMATION
50.34 Hz, 2P of trans PMe3).
■
Synthesis of Ir(H)(C(H)C(H)(CMe3)(PMe3)3(O2CPh) (9). A 250
mL one-necked side-armed flask equipped with a magnetic stirrer and
a septum was charged with 0.215 g (0.400 mmol) of 8 under nitrogen
in a drybox. The flask was connected to a double-manifold Schlenk
line, and 10.0 mL of distilled water was added by syringe. Next, 53.6
μL (0.435 mmol) of tert-butylacetylene was added also by syringe. A
milky solution and white solids were observed immediately. The
solution was magnetically stirred at room temperature for 4 h. The
water was then stripped under reduced pressure to give white solids,
which were dried in vacuo to give 0.226 g of Ir(H)(C(H)
C(H)(CMe3)(PMe3)3(O2CPh) (0.361 mmol, 91.2% yield).
Corresponding Author
*Tel: 540-231-4510. Fax: 540-231-3255. E-mail: jmerola@vt.
edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge support of this work by the
National Science Foundation (Grant No. CHE-9214027).
Support for the server upon which Gaussian is run (see the
Supporting Information) came from NSF Grant No. CHE-
0741927.
1
Anal. Calcd (found): C, 42.23 (41.33); H, 7.09 (6.98). H NMR
(CD2Cl2): δ −26.1 (q, JHP = 15.14 Hz, 1H), 0.96 (s, 9H of CMe3),
1.45 (t, JHP = 3.46 Hz, 18H of trans PMe3), 1.5 (d, JHP = 8.03 Hz, 9H
of cis PMe3), 5.45 (dtd, JHH = 17.2 Hz, JHPtrans= 7.68 Hz, JHPcis < 3.0
Hz, 1H of vinyl C(H)(CMe3)), 6.66 (dtd, JHH = 17.2 Hz, JHPtrans = 3.64
REFERENCES
1
■
Hz, JHPcis < 3.0 Hz, H of vinyl C(H)), 7.24−7.33 (m, 3H of phenyl
ring), 7.98−8.03 (m, 2H of phenyl ring). 31P NMR (CDCl3): δ
−47.08 (t, JPP = 49.4 Hz, 1P of cis PMe3), −40.1 (d, JPP = 50.8 Hz, 2P
of trans PMe3). 13C NMR (CDCl3): δ 17.14 (t, JCP= 74.8 Hz, 6C of
trans PMe3), 22.88 (d, JCP = 109.28 Hz, 3C of cis PMe3), 29.7 (s, 3C
of CMe3), 137.0 (s, 1C of vinyl C(H)(CMe3)), 148.0 (s, 1C of vinyl
C(H)), 127.4 (s, 2C, meta carbons of phenyl ring), 129.2 (s, 1C, para
carbon of phenyl ring), 129.4 (s, 2C, ortho carbon of phenyl ring).
Crystals suitable for X-ray diffraction were grown by slow
evaporation of a diethyl ether solution of 9 under nitrogen.
(1) Cornils, B., Herrmann, W. A., Eds. Aqueous Phase Organometallic
Catalysis, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2004.
(2) Santos, A. M.; Kuehn, F. E. In Catalysts for an Aqueous Biphasic
Catalysis: Central Atoms; Wiley-VCH: Weinheim, Germany, 2005; pp
55−65.
(3) Breno, K. L.; Ahmed, T. J.; Pluth, M. D.; Balzarek, C.; Tyler, D.
R. Coord. Chem. Rev. 2006, 250, 1141−1151.
(4) Genet, J.-P.; Darses, S.; Michelet, V. Pure Appl. Chem. 2008, 80,
831−844.
Variable-Temperature 31P NMR of IrH2(PMe3)3Cl (2) in H2O.
(5) Hapiot, F.; Ponchel, A.; Tilloy, S.; Monflier, E. C. R. Chim. 2011,
31P NMR spectra were acquired over the temperature range 280−310
14, 149−166.
(6) Merola, J. S. Organometallics 1989, 8 (12), 2975−2977.
K and integration values determined; 310 K was not exceeded to avoid
decomposition. The first spectrum was acquired at 300 K and used as a
reference spectrum. The temperature was incrementally lowered by 5
K, the temperature of the sample was allowed to equilibrate, and then
data were acquired; and the whole process was repeated down 280 K.
The probe was then slowly warmed to 300 K, the sample was allowed
to equilibrate, and then data were acquired. This spectrum was
checked against the reference spectrum to ensure that no
decomposition had occurred. The temperature was then incrementally
increased by 5 K, the temperature of the sample was allowed to
equilibrate, and then data were acquired; the whole process was
repeated until 310 K. The probe was slowly cooled to 300 K, the
sample was allowed to equilibrate, and then data were acquired. This
spectrum was again checked against the reference spectrum, which
indicated no decomposition had occurred.
(7) Knorr, J. R.; Merola, J. S. Organometallics 1990, 9 (12), 3008−
3010.
(8) Ladipo, F. T.; Merola, J. S. Inorg. Chem. 1990, 29 (21), 4172−
4173.
(9) Ladipo, F. T.; Kooti, M.; Merola, J. S. Inorg. Chem. 1993, 32 (9),
1681−1688.
(10) Ladipo, F. T.; Merola, J. S. Inorg. Chem. 1993, 32 (23), 5201−
5205.
(11) Le, T. X.; Merola, J. S. Organometallics 1993, 12 (10), 3798−
3799.
(12) Selnau, H. E.; Merola, J. S. Organometallics 1993, 12 (10),
3800−3801.
(13) Selnau, H. E.; Merola, J. S. Organometallics 1993, 12 (5), 1583−
1591.
Variable-Concentration 31P NMR of IrH2(PMe3)3(O2CPh) (8)
and Chloride Ion in H2O. A 0.054 M solution of 8 was prepared by
(14) Kooti, M.; Merola, J. S. Iran. J. Chem. Chem. Eng. 1997, 16 (1),
4−7.
3928
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929

Organometallics
Article
(15) Roy, C. P.; Huff, L. A.; Barker, N. A.; Berg, M. A. G.; Merola, J.
S. J. Organomet. Chem. 2006, 691 (10), 2270−2276.
(16) Joo, F.; Toth, Z. J. Mol. Catal. 1980, 8, 369−383.
(17) Bakos, J. NATO ASI Ser., Ser. 3 1995, 5, 231−244.
(18) Pierre, G. J.; Savignac, M. J. Organomet. Chem. 1999, 576, 305−
317.
(19) Joo, F.; Kovacs, J.; Benyei, A. C.; Nadasdi, L.; Laurenczy, G.
Chemistry 2001, 7 (1), 193−199.
(20) Papp, G.; Horvath, H.; Katho, A.; Joo, F. Helv. Chim. Acta 2005,
88 (3), 566−573.
(21) Krogstad, D. A.; Halfen, J. A.; Terry, T. J.; Young, V. G. Inorg.
Chem. 2000, 40 (3), 463−471.
(22) Kovacs, G.; Nadasdi, L.; Laurenczy, G.; Joo, F. Green Chem.
2003, 5 (2), 213−217.
(23) Frost, B. J.; Mebi, C. A. Organometallics 2004, 23 (22), 5317−
5323.
(24) Frazier, J. F.; Merola, J. S. Polyhedron 1992, 11 (22), 2917−
2927.
(25) Musher, J. I.; Corey, E. J. Tetrahedron 1962, 18 (6), 791−809.
(26) Robertson, G. B.; Tucker, P. A. J. Am. Chem. Soc. 1982, 104 (1),
317−318.
(27) Robertson, G. B.; Tucker, P. A. Aust. J. Chem. 1988, 41 (5),
641−650.
(28) Robertson, G. B.; Tucker, P. A. Aust. J. Chem. 1988, 41 (3),
283−291.
(29) Ditzel, E. J.; Robertson, G. B. Aust. J. Chem. 1995, 48 (6), 1183−
1191.
(30) Brym, M.; Jones, C. Transition Met. Chem. (Dordrecht, Neth.)
2003, 28, 595−599.
(31) Del, P. G.; Perego, G.; Zazzetta, A.; Cesari, M. Cryst. Struct.
Commun. 1974, 3, 725−9.
(32) Hasnip, S. K.; Colebrooke, S. A.; Sleigh, C. J.; Duckett, S. B.;
Taylor, D. R.; Barlow, G. K.; Taylor, M. J. Dalton Trans. 2002, 743−
751.
(33) Bergmeister, J. J.; Hanson, B. E.; Merola, J. S. Inorg. Chem. 1990,
29 (23), 4831−4833.
(34) Boyer, P. M.; Roy, C. P.; Bielski, J. M.; Merola, J. S. Inorg. Chim.
Acta 1996, 245, 7−15.
(35) Behr, A.; Herdtweck, E.; Herrmann, W. A.; Keim, W.;
Kipshagen, W. Organometallics 1987, 6 (11), 2307−2313.
(36) Le, T. X.; Selnau, H. E.; Merola, J. S. J. Organomet. Chem. 1994,
468 (1−2), 257−264.
(37) Gorol, M.; Mosch-Zanetti, N. C.; Roesky, H. W.; Noltemeyer,
̈
M.; Schmidt, H.-G. Eur. J. Inorg. Chem. 2004, 2004 (13), 2678−2682.
(38) Haszeldine, R. N.; Lunt, R. J.; Parish, R. V. J. Chem. Soc. A 1971,
3696−3698.
̈
(39) Alley, W. M.; Girard, C. W.; Ozkar, S.; Finke, R. G. Inorg. Chem.
2009, 48 (3), 1114−1121.
(40) Bratsch, S. G. J. Chem. Educ. 1988, 65 (1), 34.
(41) Johnson, C. E.; Eisenberg, R. J. Am. Chem. Soc. 1985, 107,
3148−3160.
(42) Sheldrick, G. Acta Crystallogr., Sect. A 2008, 64 (1), 112−122.
(43) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42 (2), 339−341.
(44) Orpen, A. G. J. Chem. Soc., Dalton Trans. 1980, 2509.
(45) JMP, Version 9; SAS Institute Inc., Cary, NC, 1989−2011.
3929
dx.doi.org/10.1021/om300140f | Organometallics 2012, 31, 3920−3929