Use of the imine-enamine equilibrium in cooperative ligand design

Article abstract of DOI:10.1021/om400688v

The imine-phosphine ligands Ph₂PC₅H₇NAr, where Ar = 2,6-Prⁱ₂C₆H₃, 2,6-Me ₂C₆H₃, were deprotonated using KH to generate the corresponding potassium salts, which were reacted with [(COD)IrCl] ₂ to generate the enamidophosphine derivatives (COD)Ir(Ph ₂PC₅H₆NAr) (Ar = 2,6-Prⁱ ₂C₆H₃, 4a; Ar = 2,6-Me₂C ₆H₃, 4b). These complexes were exposed to alcohols, H ₂, and CO to generate a series of products, some of which involve protonation of the enamido unit to generate the imine tautomer. The reaction of 4a with isopropyl alcohol or H₂ generates the dinuclear hexahydride [(Ph₂PC₅H₇N-2,6-Prⁱ ₂C₆H₃)IrH₂]₂(μ-H) ₂ (5a), while the reaction with primary alcohols generates the dicarbonyl enamidophosphine complex (CO)₂Ir(Ph₂PC ₅H₆NAr) (6a). The reaction of the hexahydride 5a with CO generates 6a, for which a mechanism is proposed on the basis of monitoring this reaction as a function of time by NMR spectroscopy. On the basis of these experiments, cooperative ligand effects can be replicated by imine-phosphine ligands by proton transfer to and from the ligand backbone.

Full text of DOI:10.1021/om400688v

Article
pubs.acs.org/Organometallics
Use of the Imine−Enamine Equilibrium in Cooperative Ligand Design
Truman C. Wambach, Jun Myun Ahn, Brian O. Patrick, and Michael D. Fryzuk*
Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
S
* Supporting Information
ABSTRACT: The imine−phosphine ligands Ph2PC5H7NAr, where
Ar = 2,6-Pri2C6H3, 2,6-Me2C6H3, were deprotonated using KH to
generate the corresponding potassium salts, which were reacted with
[(COD)IrCl]2 to generate the enamidophosphine derivatives
(COD)Ir(Ph2PC5H6NAr) (Ar = 2,6-Pri2C6H3, 4a; Ar = 2,6-
Me2C6H3, 4b). These complexes were exposed to alcohols, H2,
and CO to generate a series of products, some of which involve
protonation of the enamido unit to generate the imine tautomer.
The reaction of 4a with isopropyl alcohol or H2 generates the
dinuclear hexahydride [(Ph2PC5H7N-2,6-Pri2C6H3)IrH2]2(μ-H)2
(5a), while the reaction with primary alcohols generates the
dicarbonyl enamidophosphine complex (CO)2Ir(Ph2PC5H6NAr)
(6a). The reaction of the hexahydride 5a with CO generates 6a, for
which a mechanism is proposed on the basis of monitoring this reaction as a function of time by NMR spectroscopy. On the
basis of these experiments, cooperative ligand effects can be replicated by imine−phosphine ligands by proton transfer to and
from the ligand backbone.
We noticed that the equilibrium described in eq 1 could also
be compared to the related equilibrium between complexes A
and B in Scheme 1, in which the ligand scaffold is simplified to
INTRODUCTION
■
When one designs a new ancillary ligand system to be used in
concert with metal ions to generate potential catalyst
precursors, a modular system wherein steric and electronic
effects can be systematically varied has been de rigueur for
decades. In addition, it has been assumed that the ancillary
ligand should remain innocent and not participate in any of the
elementary steps of the transformation of interest. However,
recently a new paradigm has appeared in which it is desirable
that the ligand system be able to cooperate during the
transformation via a redox type reaction,1−4 proton transfer
steps,5−26 or perhaps both. These cooperative ligand systems
have shown remarkable results in a variety of processes, for
example, the conversion of alcohols and amines to esters6 and
amides,9 and even in the reverse reaction, in the hydrogenation
of carbonyl functionalities.7
Scheme 1
a bidentate metal imine−phosphine fragment A that could be in
equilibrium with the metal-enamido moiety B and dihydrogen.
We reasoned that these two species could be superficially
related to the equilibrium between an imine and an enamine, as
shown in C and D in Scheme 1. What becomes evident is that
this kind of cooperativity between A and B does not necessarily
require dearomatization/aromatization, as shown explicitly for
1 in eq 1; instead, one can also invoke participation of the
linker between an imine and another donor such as a
phosphine.11,13−16,27−29
A particularly important example is the tridentate pyridine-
based ligand system 1 in eq 1. In this case, it is the involvement
In this report we examine the deprotonation and
coordination chemistry of a simple imine−phosphine ligand
with iridium(I) and its reactivity with small molecules in an
of a hydrogen from the ligand backbone with a ruthenium
hydride that acts cooperatively to lose dihydrogen (H2) and
generate the dearomatized ligand framework that has been
proposed to be involved in the catalytic dehydrogenation of
reactions.6,9
Received: July 13, 2013
© XXXX American Chemical Society
A
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attempt to replicate transformations that would be consistent
with ligand cooperativity.
X-ray-quality crystals of 3b were obtained from THF by the
addition of hexanes. The solid-state molecular structure is given
in Figure 1 along with selected bond lengths and bond angles.
RESULTS AND DISCUSSION
■
We chose to examine the known arylimine phosphine ligand
systems 2a,b, which were prepared according to modifications
of literature procedures as shown in Scheme 2.30,31 The short-
Scheme 2
Figure 1. ORTEP drawing of the solid-state molecular structure of 3b,
with probability ellipsoids at the 50% level. The carbon atoms of both
molecules of THF were excluded for clarity, as were all of the
hydrogen atoms. Selected bond lengths (Å) and angles (deg): K1−O1
= 2.7050(18), K1−N1 = 2.9829(17), K1−N1* = 2.8222(17), K1−
C12 = 3.066(2), K1−C17 = 3.216(2), K1−C24 = 3.280(3), K1−P1 =
3.4141(10), K1−K1* = 3.5045(13), N1−C1 = 1.347(2), C1−C2 =
1.347(2); N1−C1−C2 = 127.26(16), C1−C2−P1 = 120.46(10).
Overall, the structure is dimeric with the amido nitrogens of the
enamido units bridging the two potassium ions, with one
coordinated THF also bound to each potassium. One notable
feature is that one of the phenyl rings attached to the
phosphorus of the ligand participates in an η3 interaction with
the K+. Due to this interaction the two phenyl rings attached to
the phosphorus are not equivalent, and overall the compound is
Ci symmetric in the solid state. As mentioned above, the
observed inequivalent P-phenyl groups in the solid state are not
maintained in solution.
form descriptors we use are CY5[NP]DIPPH (2a) and
CY5[NP]DMPH (2b), in which CY5 represents the cyclo-
pentylidene linker and DIPP and DMP are 2,6-diisopropyl-
phenyl and 2,6-dimethylphenyl, respectively, which are the
imine N-aryl substituents. In solution both 2a,b exist
predominantly in the imine form, with the enamine tautomer
evident by a small upfield peak in the 31P{1H} NMR spectrum.
Addition of excess KH in THF to solutions of 2a,b results in
the formation of the corresponding potassium salts 3a,b, which
can be isolated as solids in 68−78% yield. In solution, these
species display singlets in the 31P{1H} NMR spectra at δ −22.7
and −19.1 for 3a,b, respectively. The 1H NMR spectra of both
compounds are quite simple and show resonances that indicate
that the alkyl substituents in the ortho positions of the N-aryl
moiety are equivalent, as are the phenyl groups attached to the
phosphine. A 13C HSQC experiment displays a carbon signal at
δ 69.2 with 1JPC = 14.8 Hz for 3a that does not correlate to any
Synthesis and Reactivity of Iridium Enamido Com-
plexes. The reaction of the potassium derivatives 3a,b with
[(COD)IrCl]2 at room temperature in toluene results in an
immediate color change to produce a bright red solution along
with the formation of potassium chloride. After workup, the
pure iridium enamido complexes CY5[NP]DIPPIr(COD) (4a)
and CY5[NP]DMPIr(COD) (4b) could be obtained in good
yields. Similar bidentate ligands have been installed on iridium
using salt methathesis.32 Diagnostic of these complexes are the
upfield-shifted singlets in the 31P{1H} NMR spectra, in
comparison to the precursor potassium salts; for example, for
4a, this resonance is observed at δ 12.1, whereas the signal for
3a is found at δ −22.7.
1
resonance in the H NMR spectrum, which is consistent with
the α-carbon next to the PPh2 unit in the deprotonated
enamido structure; similar features in the NMR spectra are
evident for 3b. In the 1H NMR spectrum of 3a the resonances
for the β-CH2 protons of the coordinated THF are partially
obscured by a doublet assigned to the methyl protons of the
isopropyl groups of the N-aryl moiety at δ 1.4. Close inspection
of the 13C HSQC and 13C APT spectra show a correlation with
a CH2 resonance in the carbon-13 spectrum at 24.7 ppm. The
α-CH2 protons of coordinated THF are clearly visible at 3.4
Monitoring the reaction by 31P{1H} NMR spectroscopy
shows that the formation of 4a,b is quantitative and virtually
instantaneous at the time of mixing. 1H and 13C NMR data and
elemental analyses are consistent with the square-planar
enamido complexes shown in eq 2.
X-ray-quality crystals of 4a were obtained by allowing a
hexanes solution of the complex to slowly evaporate or by
cooling a concentrated hexanes solution to −35 °C. The
1
ppm in the H NMR spectrum of 3a. It is possible to remove
the coordinated THF under high vacuum (see the Supporting
Information).
B
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molecular structure is shown in Figure 2 along with selected
bond lengths and bond angles.
overnight also forms 5a. If a J. Young tube is charged with 0.033
g of 4a, 0.5 mL of C6H6, and 0.5 mL of isopropyl alcohol, clear,
yellow, X-ray-quality crystals form upon heating overnight,
which correspond to 5a (Figure 3). Generally if the reaction is
performed on a larger scale, a fine yellow powder is recovered
in moderate yield.
Figure 2. ORTEP drawing of the solid-state molecular structure of 4a
with probability ellipsoids at the 50% level. Selected bond lengths (Å)
and angles (deg): Ir1−N1 = 2.061(2), Ir1−P1 = 2.3047(7), Ir1−C31
= 2.200(3), Ir1−C30 = 2.201(3), Ir1−C31 = 2.200(3), Ir1−C34 =
2.117(3), Ir1−C35 = 2.131(3), N1−C1 = 1.365(3), C1−C2 =
1.360(4), C2−P1 = 1.747(3), C30−C31 = 1.384(4), C34−C35 =
1.414(4); N1−C1−C2 = 124.6(3), C1−C2−P1 = 113.5(2), N1−Ir1−
P1 = 81.12(6), C34−Ir1−P1 = 93.00(7), C35−Ir1−P1 = 96.55(8),
N1−Ir1−C30 = 94.93(10), N1−Ir1−C31 = 97.86(10).
Figure 3. ORTEP drawing of the solid-state molecular structure of 5a
with probability ellipsoids at the 50% level. All of the hydrogen atoms
except α-protons and hydrides have been excluded for clarity. One P1-
phenyl has been removed for clarity. Three hydrides, H1, H2, and H3,
were located from the difference map; their isotropic thermal
parameters (Ueq) were coupled to Ir2, and their coordinates were
freely refined. The X-ray data did not allow the remaining three
hydrides to be located with any certainty. Selected bond lengths (Å)
and angles (deg): Ir1−N1 = 2.238(9), Ir1−P1 = 2.210(3), Ir2−N2 =
2.236(8), Ir2−P2 = 2.196(3), Ir1−Ir2 = 2.7089(4), N1−C1 =
1.288(12), C1−C2 = 1.522(13), N2−C30 = 1.286(12), C30−C31 =
1.509(13); N1−C1−C2 = 120.9(9), P1−C2−C1 = 108.1(6), P1−
Ir1−N1 = 81.3(2), P2−Ir2−N2 = 81.2(2).
The geometry around iridium is square planar as expected,
with the N1−C1−C2-P1 plane relatively flat and coplanar with
the P1−Ir1−N1 plane. The Ir1−N1 bond length of 2.061(2) Å
is similar to those in other iridium amido derivatives, and the
Ir1−P1 distance of 2.3047(7) Å is typical. In addition the COD
unit is bound normally, with the two double bonds
perpendicular to the square plane of the complex.
In an effort to replicate typical transformations proposed for
cooperative ligands, we examined the reactivity of the iridium
enamido complexes with dihydrogen and with alcohols.
Exposing 4a to 4 atm of H2 in pentane causes the solution to
darken to a deep red-orange and is accompanied by the
formation of a light yellow precipitate, which can be identified
as the hexahydride dimer 5a. A similar result occurs if the
reaction of H2 with 4a is repeated in C6D6 in a J. Young NMR
tube. Monitoring the reaction by 31P{1H} NMR spectroscopy
shows that the reaction pathway is complex, as a number of
unidentified intermediates are observed. Over a period of 12 h,
the 1,5-cyclooctadiene ligand is completely hydrogenated to
cyclooctane, as monitored by 1H NMR spectroscopy (eq 3). In
addition to a singlet due to 5a at δ 32.7, two other unidentified
signals are observed at δ 11.3 and −7.4. 5a is easily separated
from this mixture by washing with hexanes. Attempts to extend
these results with 4b resulted in intractable mixtures of
products.
Because 5a is sparingly soluble in benzene, toluene, and
other nonpolar organic solvents, acquiring multinuclear NMR
spectra proved difficult. However, meaningful spectra could be
obtained in CD2Cl2 even though the complex slowly
decomposes in this solvent. Of particular importance to
confirm the solid-state structure (Figure 3) was identification
of the proton on the ancillary ligand for the imine tautomeric
1
form of the ligand. The H NMR spectrum taken at 600 MHz
in CD2Cl2 shows a resonance at δ 3.7, which with 13C APT and
HSQC experiments indicates that this signal correlates to a CH
1
carbon signal δ 62.8 (d, JPC = 33.1 Hz) strongly coupled to
phosphorus, thus confirming that protonation at carbon has
1
occurred. In the H NMR spectrum all of the signals assigned
to the various CH2 groups of the cyclopentylidene linker appear
as well-resolved diastereotopic multiplets, each integrating to
one proton per iridium center. Additional information about
the structure of 5a was gleaned from the three unique signals in
the hydride region of the spectrum, one of which is a triplet at δ
Treating a benzene solution of 4a with excess isopropyl
alcohol in a sealed reaction vessel and heating to 90 °C
C
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−20.0, which results from coupling to two equivalent
phosphorus-31 nuclei and denotes that a dimeric structure
exists in solution. When the 31P nucleus is decoupled, the signal
collapses into a broad singlet. We observe no H−H coupling
between any of the three unique hydride signals. In solution,
the overall symmetry of the dimer is Ci symmetric, which is
identical with the symmetry observed in the solid state.
The solid-state molecular structure is shown in Figure 3,
along with selected bond lengths and angles. All of the metrical
parameters of the ligand are unremarkable and confirm
protonation of the ligand at carbon. The iridium−iridium
distance is 2.7089(4) Å, which is shorter than the sum of the
van der Waals radius of the two atoms.33 A similar compound
with a tridentate ligand and a hemilabile arm has an iridium−
iridium distance of 2.7325(7) Å and has been assigned as an
iridium−iridium double bond.34 Cationic iridium polyhydride
clusters have been previously investigated, and their formation
usually indicates catalyst deactivation during hydrogenation
type processes.35−39 Consistent with this is the fact that
hexahydride 5a does not react further with dihydrogen, with
additional isopropyl alcohol, or even with primary alcohols such
as benzyl alchohol (vide infra).
Scheme 4
31P{1H} NMR spectroscopy shows clean conversion of the
singlet at δ 12.1 (4a) to a new signal at δ 21.3 that is assigned as
the dicarbonyl complex 6a. Removing the volatiles under
vacuum gives a red oil that can be dissolved into C6D6 for
characterization by multinuclear NMR spectroscopy.
1
The H NMR spectrum of the red oil shows that the COD
ligand has been lost; furthermore, no resonance diagnostic of
protonation of the ligand can be found. 13C APT and HSQC
definitively establish that the ligand is in the enamido form,
since the resonance for the carbon atom of the linker directly
attached to phosphorus occurs at δ 83.5 (d, 1JPC = 64.4 Hz) and
While speculative, one can propose a mechanism for the
formation of this hexahydride dimer 5a by reaction of 4a with
isopropyl alcohol, as shown in Scheme 3. The first step is
1
does not correlate with any signal in the H NMR spectrum.
No resonance attributable to an NH proton is observed. The
CH2 protons of the linker appear as three signals with the
expected splitting patterns each integrating to two protons.
Overall, the data point to a molecule with Cs symmetry in
solution.
Scheme 3
Confirmation of the presence of two different carbonyl
ligands was given by ATR FTIR spectroscopy of a crystalline
sample of the complex (Supporting Information). Two distinct
CO stretches occur at 1966 and 2041 cm−1.
Further evidence for the proposed structure was achieved by
independently synthesizing 6a by treating the COD complex 4a
with 1 atm of CO. Monitoring the reaction by 31P{1H} NMR
spectroscopy shows that it quickly goes to completion, giving
the expected singlet at δ 21.3; 1H NMR spectroscopy confirms
loss of the COD ligand. The reaction mixture was taken to
dryness and subsequently dissolved in a minimal amount of
hexanes. X-ray-quality crystals formed by slowly evaporating the
hexanes from a loosely sealed vial overnight in a glovebox or by
cooling a concentrated solution to −35 °C.
The solid-state molecular structure is shown in Figure 4,
along with selected bond lengths and bond angles. As is clearly
evident, 6a is square planar as expected and matches the COD
starting complex 4a in terms of bond lengths and angles.
Solution data and the solid-state molecular structure are
consistent with each another. The oxidation of primary
alcohols, followed by decarbonylation of the resulting
aldehydes, has been documented for several late-transition-
metal coordination compounds.40−46 While we have not
investigated the mechanism here, it is possibly very similar to
that shown in Scheme 3, except that upon β-elimination of the
primary alkoxy group the aldehyde produced can be oxidatively
added and decarbonylated. At some stage, elimination of H2
from an intermediate, perhaps cooperatively from the imine
phosphine ligand and an iridium hydride, generates the
enamido dicarbonyl derivative 6a.
protonation of the enamido ligand to generate an imine
phosphine derivative with a coordinated isopropoxy unit;
subsequent β-elimination results in the formation of acetone
and an Ir(I) hydride intermediate. Further reaction with more
isopropyl alcohol in a multistep process results in the
hydrogenation of the 1,5-cyclooctadiene and the formation of
the imine−phosphine iridium(III) trihydride (Scheme 3).
When primary alcohols such as ethanol and benzyl alcohol
are used in place of isopropyl alcohol, entirely different
reactivity is observed (Scheme 4). Heating the iridium enamido
compound 4a dissolved in toluene in either an open reflux
under nitrogen or a sealed reaction vessel results in the
formation of a light red solution. Monitoring the reaction by
As shown by the reaction of alcohols with the iridium
enamide derivative 4a, different outcomes are observed
depending on whether a primary versus a secondary alcohol
D
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phosphorus and more complex but analyzable multiplets for the
inequivalent cis hydrides. As shown in Scheme 5, a reasonable
pathway for the formation of BB is addition of 1 equiv of CO to
cleave the hydride dimer 5a and generate the trihydride
monocarbonyl AA (not observed), which upon dissociation of
the bulky imine donor can be subsequently trapped by CO to
generate BB.
The next observed intermediate is identified as DD, a square-
planar, monohydride iridium(I) complex with the imine unit
coordinated and only one carbonyl ligand. Its 31P{1H}
resonance (δ 1.6, s) was assigned on the basis of correlations
observed by 31P HMBC as well as 1H and 1H{31P} spectra. The
hydride resonance for DD in the 1H NMR spectrum (δ −11.6,
d, 2JPH = 52.2 Hz) as well as the α-CH of the linker (δ 4.2, v dt,
Figure 4. ORTEP drawing of the solid-state molecular structure of 6a
with probability ellipsoids at the 50% level. All of the hydrogen atoms
have been removed for clarity. Selected bond lengths (Å) and angles
(deg): Ir1−N1 = 2.047(2), Ir1−P1 = 2.3373(12), Ir1−C31 =
1.859(3), Ir1−C30 = 1.905(3), N1−C1 = 1.367(4), C1−C2 =
1.358(4), C2−P1 = 1.752(3); N1−C1−C2 = 125.0(2), C1−C2−P1 =
113.8(2), N1−Ir1−P1 = 82.26(7), C30−Ir1−N1 = 90.06(10), C31−
Ir1−P1 = 90.05(8).
2
2JHH = 7.7 Hz, JPH = 13.5 Hz) both show cross peaks to the
31P{1H} signal; interestingly, no coupling of the hydride to the
cis 13CO could be resolved. However, the 13C HMBC spectrum
confirms the presence of a CO ligand (δ 176.9, s) by
correlation of this signal to the hydride resonance. The
formation of DD could result via reductive elimination of H2
from BB to form the dicarbonyl monohydride species CC (not
observed), which upon associative binding of the imine
followed by CO dissociation, or the reverse, results in the
formation of DD.
is used. As discussed above, we observe both the enamido and
imine forms of the ligand in various complexes, which clearly
indicates that the ligand is noninnocent in these trans-
formations and is perhaps acting in a cooperative manner. To
probe this further, we examined the reaction of the iridium(III)
hexahydride dimer 5a with CO and found that we could also
generate the enamido dicarbonyl 6a (eq 4).
The third hydride intermediate detected is FF, which
corresponds to the 31P{1H} NMR singlet resonance at δ
30.6. The 31P HMBC of the reaction using 13C-labeled CO
correlates this resonance to an NH resonance (6.0, s) and a
hydride signal (δ −12.1, dq, 2JPH = 80.3 Hz, 2JCH = 5.3 Hz); the
quartet pattern for the hydride is a result of coupling to three
equivalent 13CO ligands, which correspond to a resonance
2
located in the 13C APT NMR spectrum (δ 176.5, d, JPC = 8.5
Hz), and is confirmed by the 13C HMBC data. The most
important feature of FF is that the ligand is in the enamine
form, bound only through the phosphine unit. We suggest that
FF forms via the unobserved dicarbonyl CC by an imine-to-
enamine tautomerism, followed by trapping with CO. We
believe that this tautomerization (conversion of CC to EE) is a
key step by which these imine−phosphine ligands can replicate
cooperative ligand processes, as it provides a simple way for a
proton from the ligand backbone to combine with a metal
hydride. This is expanded on below.
As shown in eq 4 and detailed in Scheme 5, the CO-induced
conversion of hexahydride 5a to dicarbonyl 6a requires loss of 2
equiv of H2 per iridium center, where three of the hydrogen
atoms come from the iridium hydrides and one hydrogen
originates from the backbone of the ligand; it is worth noting
that the starting imine unit in 5a is converted to the enamido
form in 6a. We are unable to determine how the hydrogen from
the ligand actually combines with a metal hydride by the
experiments reported here, nevertheless, we can speculate on
some of the possibilities, particularly as they relate to
cooperativity.
The observation of DD and FF on the way to 6a suggests
that the imine must tautomerize to the enamine, and we
suggest that the equilibrium between CC and EE in Scheme 5
can account for this, but it should be emphasized that, during
the CO addition reaction to the hexahydride 5a, no other
intermediates after FF are observed. We were able to run the
reaction backward by addition of H2 to the dicarbonyl 6a,
whereupon a new intermediate can be observed that is not
present during the excess CO reaction. This new species is
identified as the dihydride dicarbonyl GG in Scheme 5, which
This is a slow reaction that takes a few days under 1 atm of
CO and at 25 °C. As a result, we could observe intermediates
by monitoring this process as a function of time by multinuclear
NMR spectroscopy using natural-abundance CO and carbon-
13 labeled CO. Suspending 5a in d8-THF in a J. Young or a
flame-sealed NMR tube under slightly less than 1 atm of carbon
monoxide resulted in the observation of three hydride
intermediates, in varying amounts, on the way to 6a.
Interestingly, the same hydride complexes could be identified
when more forcing conditions were used: for example, addition
of 4 atm of CO at 60 °C. On the basis of the observation of
these species, we propose the mechanism shown in Scheme 5,
which tries to incorporate these observed species with other
plausible intermediates on the basis of simple elementary
reactions such oxidative addition and reductive elimination.
The first observed hydride intermediate is identified as BB, in
which the imine donor is dissociated. The NMR data (see the
Supporting Information) are consistent with this species
containing three inequivalent hydrides, two inequivalent
CO’s, and one coordinated phosphine unit; the inequivalent
hydrides are a result of the geometry as well as the presence of
the chiral center on the imine backbone. With unlabeled CO,
the hydrides appear as two overlapping doublets at δ −10.9 and
−10.8 due to cis coupling to phosphorus-31 and a doublet at δ
−11.2 with a large trans coupling to phosphorus-31. Use of
13CO results in a doublet of triplets for the hydride trans to
E
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Scheme 5
forms via cis oxidative addition of H2 to 6a. Particularly
diagnostic of GG are the two doublet hydride resonances, one
the iridium to ultimately form H2. While the potentially
bidentate imine−phosphine ligand coordinated to iridium
examined here allows these steps to be inferred, it is clear
that in relation to tridentate and even tetradentate systems that
involve imines, pyridine, and phosphines, these bidentate
systems would be less stable, especially under more harsh
conditions typically found in catalytic processes that involve
dehydrogenation. As we will report in due course, our bidentate
systems can be made catalytic but their thermal instability
makes them less efficient in comparison to the tridentate
Milstein systems or the tetradentate Morris complexes.
of which shows a large trans coupling to phosphorus (2JPH
=
123.0 Hz) and the other shows a smaller coupling indicative of
being cis to the phosphine (2JPH = 12.0 Hz); confirmation that
GG has two carbonyl ligands is obtained by addition of H2 to
the 13CO-labeled isotopologue of 6a, which results in further
multiplicities consistent with one CO trans to one of the
hydrides and one CO cis to both hydrides (see the Supporting
Information). Furthermore, running the reaction backward
under excess H2 for longer periods results in the depletion of
GG and observation of BB, the imine trihydride, formed in the
CO addition process discussed above. It is worth noting that
the conversion of GG to BB also results in transfer of a
hydrogen atom from the iridium center to the ligand.
EXPERIMENTAL PROCEDURES
■
General Considerations. All procedures and manipulations were
performed under an atmosphere of dry, oxygen-free dinitrogen or
argon by means of standard Schlenk or glovebox techniques. Argon
and dinitrogen were dried and deoxygenated by passing the gases
through a column containing molecular sieves and MnO. Hexanes,
toluene, THF, and diethyl ether were purchased from Aldrich, dried by
passage through a tower of alumina, and degassed by passage through
a tower of Q-5 catalyst under positive pressure of nitrogen. 13CO was
purchased from Cambridge Isotope Laboratories in 1 L glass bulbs.
Deuterated toluene, benzene, and THF were refluxed over sodium/
benzophenone, trap-to-trap distilled, and freeze−pump−thaw de-
gassed three times. Deuterated dichloromethane was purchased in
ampules from Aldrich and used as received. ATR (attenuated total
reflectance) FTIR (Fourier transform infrared spectroscopy) spectra
were recorded on a Perkin-Elmer Frontier FTIR spectrometer. NMR
(nuclear magnetic resonance) spectra were recorded on Bruker
AvanceII 300 MHz and Bruker Avance 400 MHz spectrometers unless
otherwise noted. Chemical shifts for 31P nuclei were referenced to 85%
CONCLUSIONS
■
The identification of ligand-based processes that might
combine with fundamental steps in catalysis, namely oxidative
addition and reductive elimination, is the subject of this study,
which involves a simple bidentate imine−phosphine ligand and
its coordination chemistry and reactivity with iridium. While
none of the alcohol dehydrogenations reported herein are
catalytic, by examination of some simple reactions we find
evidence to support that a hydrogen atom from the ligand
backbone can combine with an iridium hydride to generate
dihydrogen, and conversely a hydride on iridium can be
transferred to the ligand. How this occurs is still a matter of
conjecture, although it has been examined computationally for
Ir, Ru, and Fe systems.28,47−53 In our study we suggest without
proof that this process results via oxidative addition of a
dissociated enamine to generate an enamido hydride, shown in
Scheme 5 as the equilibrium between EE and GG, respectively,
which provides the key connection to relay the ligand proton to
1
H3PO4 in H2O (0 ppm). H nuclei were referenced to resonances of
the residual protonated solvents relative to tetramethylsilane (0 ppm),
and 13C spectra were referenced to the solvent carbon resonance(s).
Elemental analysis was performed at the facilities of the Chemistry
Department of the University of British Columbia.
F
dx.doi.org/10.1021/om400688v | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
Caution! All reactions that resulted in a pressure of 1.5 atm or
greater within a sealed vessel upon warming to room temperature were
performed with great care and were always manipulated behind a blast
shield. Pressurized NMR tubes were warmed to room temperature in a
(d, 6H, JHH = 6.9 Hz, N-PriCH3), 1.5 (m, 2H, COD-CH2), 1.7 (m,
2H, COD-CH2), 2.1 (m, 8H, γ-CH2, 2 × COD-CH2, β-CH2), 2.4 (t,
2H, 3JHH = 6.5 Hz, δ-CH2), 3.3 (br. d, 2H, JHH = 2.7 Hz, trans-N-COD-
CH), 4.0 (m, 2H, N-PriCH), 4.1 (m, 2H, trans-P-COD-CH), 7.0−7.1
(m, 2H, P-p-ArCH), 7.1−7.2 (m, 5H, N-p/P-m-ArCH), 7.2 (m, 2H, N-
m-ArCH), 7.8 (m, 4H, P-o-ArCH). 13C APT NMR (C6D6, 100.6 MHz,
298 K): δ 24.5 (s, N-PriCH3), 25.6 (s, δ-CH2), 25.6 (s, N-PriCH3),
27.8 (s, N-PriCH), 28.7 (d, 2JPC = 8.7 Hz, β-CH2), 30.1 (d, 3JPC = 1.2
Hz, COD-CH2), 32.1 (d, 3JPC = 16.8 Hz, γ-CH2), 33.0 (d, JPC = 3.2 Hz,
COD-CH2), 53.9 (s, trans-N-COD-CH), 87.7 (d, 1JPC = 61.0 Hz, α-C),
90.2 (d, JPC = 12.8 Hz, trans-P-COD-CH), 123.6 (s, N-m-ArCH), 125.7
safe location and used normally after.
54
[(COD)IrCl]2
and 2a,b were synthesized via literature
procedures.30,31 Isopropyl alcohol was dried over sodium and distilled
into a Kontes-sealed thick-walled flask under nitrogen. Absolute
ethanol and benzyl alcohol were degassed by purging with nitrogen.
Potassium hydride was purchased from Aldrich as a suspension in oil.
Using standard Schlenk techniques, the solid was collected on a glass
frit, washed with hexanes, and dried under vacuum.
(s, N-p-ArCH), 128.7 (d, 3JPC = 10.0 Hz, P-m-ArCH), 129.9 (d, 3JPC
=
Synthesis of [CY5(NP)DIPPK(THF)]2 (3a). In a Schlenk flask 2a
(8.83 g, 20.7 mmol) was added to excess potassium hydride (1.86 g,
46.4 mmol). THF (100 mL) was added, and the suspension was
stirred overnight. During this time the solution became bright yellow.
Small bubbles were observed. The reaction mixture was filtered
through Celite. The solvent was removed by vacuum, which produced
a yellow oil. It was triturated with pentane or hexanes. A pure yellow
powder was collected by filtration through a glass frit (8.73 g, 78.6%).
2
1.8 Hz, P-p-ArCH), 133.0 (d, JPC = 11.0 Hz, P-o-ArCH), 134.5 (d,
2JPC = 52.5 Hz, N-Cenamide), 145.2 (s, N-ArCPri), 147.9 (s, N-CAr),
1
189.9 (d, JPC = 32.3 Hz, P-CAr). Anal. Calcd for C37H46IrNP: C,
61.05; H, 6.34; N, 1.92. Found: C, 61.24; H, 6.15; N, 1.91.
Synthesis of CY5(NP)DMPIr(COD) (4b). See the procedure for 4a
(performed on a variety of scales, 57.0%). 31P{1H} NMR (C6D6, 161.9
1
MHz, 298 K): δ 11.5 (s). H NMR (C6D6, 400 MHz, 298 K): δ 1.6
(m, 2H, COD-CH2), 1.8 (m, 2H COD-CH2), 2.0 (m, 2H, β-CH2), 2.1
(m, 2H, COD-CH2), 2.2 (m, 2H, COD-CH2), 2.3 (m, 2H, γ-CH2), 2.5
(t, 2H, 3JHH = 6.7 Hz, δ-CH2), 2.7 (s, 6H, N-CH3), 3.4 (dd, 2H, J = 2.7
Hz, J = 5.6 Hz, trans-N-COD-CH), 4.1 (dd, 2H, J = 2.6 Hz, J = 6.2 Hz,
trans-P-COD-CH), 7.1 (t, 1H, 3JHH = 7.5 Hz, N-p-ArCH), 7.2 (m, 2H,
P-p-ArCH), 7.2−7.3 (m, 6H, N-m-/P-m-ArCH), 7.9 (ddd, 4H, J = 1.1
Hz, J = 8.0 Hz, J = 9.6 Hz, P-o-ArCH). 13C APT NMR (C6D6, 100.6
MHz, 298 K): δ 19.1 (s, N-CH3), 25.4 (s, δ-CH2), 28.2 (d, 3JPC = 9.1
Hz, γ-CH2), 30.5 (d, JPC = 2.0 Hz, COD-CH2), 30.9 (d, 2JPC = 17.2 Hz,
β-CH2), 33.1 (d, JPC = 3.4 Hz, COD-CH2), 54.0 (s, trans-N-COD-CH),
1
31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ −19.1 (s). H NMR
3
(C6D6, 400.0 MHz, 298 K): δ 1.1 (d, 6H, JHH = 6.9 Hz, N-PriCH3),
1.4 (m, 4H, THF-CH2), 1.4 (d, 6H, 3JHH = 6.8 Hz, N-PriCH3), 1.9 (m,
2H, γ-CH2), 2.3 (t, 2H, 3JHH = 7.3 Hz, β-CH2), 2.7 (t, 2H, 3JHH = 6.6
Hz, δ-CH2), 3.4 (m, 4H, THF-CH2), 3.5 (m, 2H, N-PriCH) 7.0 (t, 1H,
3JHH = 7.5 Hz, N-p-ArCH), 7.1 (m, 4H, N-m/P-p-ArCH), 7.2 (v.t, 4H,
J = 7.3 Hz, P-m-ArCH), 7.7 (v t, 4H, J = 7.2 Hz, P-o-ArCH). 13C APT
NMR (C6D6, 100.6 MHz, 298 K): δ 24.3 (s, N-PriCH3), 24.6 (s, γ-
CH2), 24.7 (s, N-PriCH), 25.7 (s, THF-CH2), 27.8 (s, N- PriCH3),
32.2 (d, 2JPC = 4.6, β-CH2), 35.8 (d, 3JPC = 9.0, δ-CH2), 67.8 (s, THF-
1
87.5 (d, JPC = 60.8 Hz, α-C), 90.0 (d, JPC = 12.8 Hz, trans-P-COD-
1
3
CH2), 69.2 (d, JPC = 14.8 Hz, α-C), 120.1 (s, N-p-ArCH), 123.2 (s,
CH), 124.7 (s, N-p-ArCH), 128.1 (s, N-m-ArCH), 128.8 (d, JPC
=
3
4
N-m-ArCH), 127.1 (s, P-p-ArCH), 128.4 (d, JPC = 6.1 Hz, P-m-
10.0 Hz, P-m-ArCH), 129.0 (d, JPC = 2.2 Hz, P-p-ArCH), 133.0 (d,
2
ArCH), 133.2 (d, JPC = 16.4 Hz, P-o-ArCH) 142.2 (s, N-ArCPri),
2JPC = 11.1 Hz, P-o-ArCH), 134.4 (d, 2JPC = 52.0 Hz, N-Cenamide), 135.2
142.4 (d, 2JPC = 3.1 Hz, N-Cenamide), 154.4 (s, N-CAr), 175.8 (d, 1JPC
=
1
(s, N-ArMe), 150.6 (s, N-CAr), 188.6 (d, JPC = 32.6 Hz, P-CAr).
32.7 Hz, P-CAr). Anal. Calcd for C33H41KNOP: C, 73.70; H, 7.68; N,
2.60. Found: C, 73.64; H, 7.92; N, 2.99.
Synthesis of [{CY5(NP)DIPP}Ir(H)3]2 (5a). 4a (0.405 g, 0.557 mmol)
was dissolved in toluene (30 mL) in a Kontes sealed reaction flask.
Isopropyl alcohol (30 mL) was added; the bomb (80 mL) was sealed
and heated to 100 °C overnight. A yellow precipitate formed. The
precipitate was allowed to settle, and the reaction mixture was
decanted. It was washed with hexanes and taken to dryness to give a
yellow solid (0.192 g, 55.2%). Alternatively, a J. Young tube was
charged with 4a (0.033 g), C6H6 (0.5 mL), and isopropyl alcohol (0.5
mL); clear, yellow, X-ray-quality crystals formed upon heating to 90
°C overnight. Alternatively, a Kontes sealed vessel charged with 4a and
toluene was freeze−pump−thaw degassed three times and back-filled
with H2 at −196 °C. The flask was sealed and warmed to room
temperature under 4 atm of H2. After the mixture was stirred
overnight, the H2 pressure was released and the mixture was taken to
dryness. Addition of pentane, followed by filtration of the resulting
suspension, allowed for the isolation of the desired product as a yellow
Synthesis of [CY5(NP)DMPK(THF)]2 (3b). See the procedure for 3a.
After the yellow product was collected by filtration, the solution was
concentrated and treated with hexanes. X-ray-quality crystals grew
(performed on a variety of scales, yield 68.0%). The coordinated THF
can be removed under high vacuum; see the Supporting Information
for the relevant spectra. The THF adduct is described here. 31P{1H}
NMR (C6D6, 161.9 MHz, 298 K): δ −22.1 (s). 1H NMR (C6D6, 400.0
MHz, 298 K): δ 1.4 (m, 4H, THF-CH2), 1.9 (m, 2H, γ-CH2), 2.0 (s,
6H, N-CH3), 2.2 (t, 2H, 3JHH = 7.5 Hz, δ-CH2), 2.6 (t, 2H, 3JHH = 6.7
3
Hz, β-CH2), 3.5 (m, 4H, THF-CH2), 6.9 (t, 1H, JHH = 7.4 Hz, N-p-
ArCH), 7.1 (d, 2H, 3JHH = 7.4 Hz, N-m-ArCH), 7.2 (t, 2H, 3JHH = 7.3
Hz, P-p-ArCH), 7.3 (v.t, 4H, J = 7.2 Hz, P-m-ArCH), 7.5 (v.t, 4H, J =
7.3 Hz, P-o-ArCH). 13C APT NMR (C6D6, 100.6 MHz, 298 K): δ 20.0
2
(s, N-CH3), 24.2 (d, JPC = 4.4 Hz, γ-CH2), 25.7 (s, THF-CH2), 32.5
3
3
(d, JPC = 4.8 Hz, δ-CH2), 36.1 (d, JPC = 7.9 Hz, γ-CH2), 67.8 (s,
solid. 31P{1H} NMR (d2-DCM, 161 MHz, 298 K): δ 32.7 (s). H
1
1
THF-CH2), 69.9 (d, JPC = 9.8 Hz, α-C), 120.0 (s, N-p-ArCH), 127.3
(s, P-p-ArCH), 128.4 (d, JPC = 6.4 Hz, P-m-ArCH), 128.7 (s, N-m-
NMR (d2-DCM, 400 MHz, 298 K): δ −23.2 (v.dd, 2JPH = 8.6 Hz, 2JHH
= 3.7 Hz, 2H, trans-H-Ir-H), −20.0 (t, 2JPH = 28.6 Hz, 2H, bridging-Ir-
H), −8.6 (d, 2JPH = 82.9 Hz, 2H, trans-N-Ir-H), 0.81 (d, 6H, 3JHH = 6.7
3
2
ArCH), 131.6 (s, N-ArCMe), 133.4 (d, JPC = 16.9 Hz, P-o-ArCH),
141.6 (d, 2JPC = 3.3 Hz, N-Cenamide), 156.9 (s, N-CAr), 175.9 (d, 1JPC
=
Hz, N-PriCH3), 0.9 (d, 6H, JHH = 8.5 Hz, N-PriCH3), 0.9(2) (d, 6H,
3
32.4 Hz, P-CAr). Anal. Calcd for C29H33KNOP: C, 72.23; H, 6.91; N,
2.91. Found: C, 71.43; H, 6.53; N, 3.76. Despite many attempts,
satisfactory microanalyses could not be obtained.
3JHH = 7.1 Hz, N-PriCH3), 1.3 (m, 2H, δ-CH2), 1.5 (d, 6H, 3JHH = 6.5
Hz, N-PriCH3), 1.7 (m, 2H, γ-CH2), 1.8 (m, 2H, γ-CH2), 1.9 (m, 2H,
β-CH2), 2.0 (m, 2H, β-CH2), 2.3 (m, 2H, δ-CH2), 2.8 (m, 2H, 3JHH
=
Synthesis of CY5(NP)DIPPIr(COD) (4a). [(COD)IrCl]2 (0.881 g,
1.31 mmol) was combined with 3a (1.41 g, 1.31 mmol) in toluene (50
mL), and the mixture was stirred for about 20 min. The solution
became an intense red, and a white precipitate (potassium chloride)
formed, which was removed by Celite filtration. The solvent was
removed, and the product was dried under vacuum to give a bright red
solid. Recrystallization by slowly evaporating hexanes or cooling a
concentrated hexanes solution to −35 °C gave X-ray-quality crystals
(1.29 g, 67.5%). This reaction was performed on various scales.
6.5 Hz, N-PriCH), 3.4 (m, 2H, 3JHH = 6.7 Hz, N-PriCH), 3.7 (v.dt, 2H
3JPH = 9.5 Hz, 3JHH = 11.3 Hz, α-CH), 6.9 (d, 2H, 3JHH = 7.2 Hz, N-m-
3
3
ArCH), 7.1 (t, 2H, JHH = 7.5 Hz, N-p-ArCH), 7.2 (d, 2H, JHH = 6.1
Hz, N-m-ArCH), 7.3 (m, 6H, P-m/p-ArCH), 7.4 (br.s, 6H, P-m/p-
ArCH), 7.5 (br.m, 4H, P-o-ArCH), 7.8 (m, 4H, P-o-ArCH). 13C APT
NMR (d2-DCM, 241.7 MHz, 298 K): δ 23.2 (s, N-PriCH3), 24.6 (s, N-
PriCH3), 24.7 (s, N-PriCH3), 25.2 (s, N-PriCH3), 27.6 (d, JPC = 7.4
2
Hz, β-CH2), 27.9 (s, N-PriCH), 28.1 (s, N-PriCH), 28.2 (d, 3JPC = 5.6
Hz, δ-CH2), 31.2 (d, 3JPC = 6.3 Hz, γ-CH2), 62.8 (d, 1JPC = 33.1 Hz, α-
CH), 123.6 (s, N-m-ArCH), 123.7 (s, N-m-ArCH), 125.2 (s, N-p-
ArCH), 127.8 (d, 3JPC = 9.7 Hz, P-m-ArCH), 128.1 (d, 3JPC = 10.4 Hz,
1
Conversion is quantitative by 31P{1H} and H NMR spectroscopy.
31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ 12.1 (s). 1H NMR
(C6D6, 400 MHz, 298 K): δ 1.3 (d, 6H, 3JHH = 6.8 Hz, N-PriCH3), 1.5
G
dx.doi.org/10.1021/om400688v | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
P-m-ArCH), 129.6(7) (d, 4JPC = 1.3 Hz, P-p-ArCH), 129.7(2) (d, 4JPC
= 1.2 Hz, P-p-ArCH), 131.0 (d, 1JPC = 34.0 Hz, P-CAr), 133.7 (d, 2JPC
= 11.4 Hz, P-o-ArCH), 134.5 (d, 2JPC = 13.1 Hz, P-o-ArCH), 138.6 (d,
1JPC = 61.3 Hz, P-ArC), 139.1 (s, N-ArCPri), 140.0, (s, N-ArCPri),
149.6 (s, N-Ar). A peak corresponding to Cenamide could not be
identified from −20 to 200 ppm in the 13C APT spectrum. Anal. Calcd
for C29H37IrNP: C, 55.93; H, 5.99; N, 2.25. Found: C, 56.05; H, 5.93;
N, 2.63.
(8) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2006, 128, 15390.
(9) Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007, 317,
790.
(10) Iron, M. A.; Ben-Ari, E.; Cohen, R.; Milstein, D. Dalton Trans.
2009, 9433.
(11) Friedrich, A.; Ghosh, R.; Kolb, R.; Herdtweck, E.; Schneider, S.
Organometallics 2009, 28, 708.
Synthesis of CY5(NP)DIPPIr(CO)2 (6a). 4a (0.250 g, 0.344 mmol)
was dissolved in hexanes (30 mL) and transferred to a Kontes sealed
vessel. The mixture was degassed with three freeze−pump−thaw
cycles and warmed to room temperature under vacuum. CO was back-
filled into the evacuated vessel. The solution instantly lightened. After
the mixture was stirred for approximately 30 min, it was taken to
dryness. The mixture was then dissolved in a minimal amount of
hexanes and left to crystallize at −35 °C. X-ray-quality crystals formed
(0.145 g, 63.0%). 31P{1H} NMR (C6D6, 161.9 MHz, 298 K): δ −21.3
(s). 1H NMR (C6D6, 400.0 MHz, 298 K): δ 1.2 (d, 6H, 3JHH = 6.9 Hz,
(12) Schwartsburd, L.; Iron, M. a.; Konstantinovski, L.; Diskin-
Posner, Y.; Leitus, G.; Shimon, L. J. W.; Milstein, D. Organometallics
2010, 29, 3817.
(13) Friedrich, A.; Drees, M.; Schmedt auf der Gunne, J.; Schneider,
̈
S. J. Am. Chem. Soc. 2009, 131, 17552.
(14) Askevold, B.; Khusniyarov, M. M.; Herdtweck, E.; Meyer, K.;
Schneider, S. Angew. Chem. Int. Ed. 2010, 49, 7566.
(15) Friedrich, A.; Drees, M.; Kass, M.; Herdtweck, E.; Schneider, S.
Inorg. Chem. 2010, 49, 5482.
(16) Meiners, J.; Schiebel, M. G.; Lemee-Cailleau, M.-H.; Mason, S.
A.; Boeddinghaus, B.; Fassler, T. F.; Herdtweck, E.; Khusniyarov, M.
M.; Schneider, S. Angew. Chem., Int. Ed. 2011, 50, 8184.
(17) Feller, M.; Diskin-Posner, Y.; Shimon, L. J. W.; Ben-Ari, E.;
Milstein, D. Organometallics 2012, 31, 4083.
(18) Askevold, B.; Nieto, J. T.; Tussupbayev, S.; Diefenbach, M.;
Herdtweck, E.; Holthausen, M. C.; Schneider, S. Nat. Chem. 2011, 3,
532.
(19) Scheibel, M. G.; Askevold, B.; Heinemann, F. W.; Reijerse, E. J.;
Bruin, B. D.; Schneider, S. Science 2012, 4, 552.
(20) Fryzuk, M. D.; MacNeil, P. A. Organometallics 1983, 2, 682.
(21) Fryzuk, M. D.; MacNeil, P. A. Organometallics 1983, 2, 355.
(22) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. Organometallics 1985,
4, 1145.
3
3
N-PriCH3), 1.4 (d, 6H, JHH = 6.8 Hz, N-PriCH3), 2.0 (t, 2H, JHH
=
3
7.3 Hz, γ-CH2), 2.2 (m, 2H, δ-CH2), 2.4 (t, 2H, JHH = 6.6 Hz, β-
CH2), 3.9 (hept, 2H, JHH = 6.8 Hz, N-PriCH), 7.0−7.1(m, 9H,
3
3
3
4
ArCH), 7.8 (ddd, JPC = 12.2 Hz, JHH = 7.7 Hz, JHH = 1.7 Hz, P-o-
ArCH). 13C APT NMR (C6D6, 100.6 MHz, 298 K): δ 24.2 (s,
PriCH3), 24.3(s, PriCH3), 26.4 (s, β-CH2), 28.2 (s, PriCH), 29.6 (d,
3JPC = 9.2 Hz, δ-CH2), 31.3 (d, 3JPC = 17.7 Hz, γ-CH2), 83.5 (d, 1JPC
=
64.4 Hz, α-C), 123.4 (s, N-m-ArCH), 126.4 (s, N-p-ArCH), 129.2 (d,
3JPC = 11.0 Hz, P-m-Ar−CH), 130.9 (s, P-p-ArCH), 132.5 (s, N-
ArCenamide), 133.0 (d, 2JPC = 11.6 Hz, P-o-ArCH), 144.0 (s, N-CArPri),
152.5 (s, N-CAr), 180.1(d, 2JPC = 11.1 Hz, trans-N-CO), 181.5 (d, 2JPC
1
= 103.5 Hz, trans-P-CO), 189.3 (d, JPC = 32.5 Hz, P-CAr). Anal.
Calcd for C31H34IrNO2P: C, 55.10; H, 5.07; N, 2.07. Found: C, 54.35;
H, 4.89; N, 2.33. ATR FTIR: CO stretches occur at 1966 and 2041
cm−1.
(23) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. Organometallics 1986,
5, 2469.
(24) Fryzuk, M. D.; MacNeil, P. a.; Rettig, S. J. J. Am. Chem. Soc.
1987, 109, 2803.
(25) Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics
ASSOCIATED CONTENT
■
S
* Supporting Information
1991, 10, 467.
Text, tables, figures, and CIF files giving crystallographic data
and details of the X-ray structure refinement, pictures and full
assignment of all the relevant multinuclear NMR spectra, and
additional experimental details. This material is available free of
charge via the Internet at http://pubs.acs.org.
(26) Maire, P.; Buttner, T.; Breher, F.; Le Floch, P.; Grutzmacher, H.
̈
̈
Angew. Chem., Int. Ed. 2005, 44, 6318.
(27) Mikhailine, A. A.; Maishan, M. I.; Lough, A. J.; Morris, R. H. J.
Am. Chem. Soc. 2012, 134, 12266.
(28) Prokopchuk, D. E.; Morris, R. H. Organometallics 2012, 31,
7375.
(29) Sonnenberg, J. F.; Coombs, N.; Dube, P. A.; Morris, R. H. J. Am.
Chem. Soc. 2012, 134, 5893.
(30) Guan, Z.; Marshall, W. J. Organometallics 2002, 21, 3580.
(31) Keim, W.; Killat, S.; Nobile, C. F.; Paolo, G.; Englert, U.; Wang,
R.; Mecking, S.; Schroder, D. L. J. Organomet. Chem. 2002, 662, 150.
AUTHOR INFORMATION
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(32) Dahlenburg, L.; Gotz, R. Eur. J. Inorg. Chem. 2004, 2004, 888.
̈
■
(33) Batsanov, S. S. Inorg. Mater. 2001, 37, 871.
(34) Choualeb, A.; Lough, A. J.; Gusev, D. G. Organometallics 2007,
26, 5224.
We thank the NSERC of Canada for funding (Discovery Grant
to M.D.F.). We also thank Nathan Halcovitch, Fraser Pick, and
Dr. Brian O. Patrick for help with the X-ray structures.
(35) Smidt, S. P.; Pfaltz, A.; Martínez-Viviente, E.; Pregosin, P. S.;
Albinati, A. Organometallics 2003, 22, 1000.
REFERENCES
(36) Wang, H. H.; Pignolet, L. H. Inorg. Chem. 1980, 19, 1470.
(37) Chodosh, D. F.; Crabtree, R. H.; Felkin, H.; Morehouse, S.;
Morris, G. E. Inorg. Chem. 1982, 21, 1307.
(38) Xu, Y.; Celik, M. A.; Thompson, A. L.; Cai, H.; Yurtsever, M.;
Odell, B.; Green, J. C.; Mingos, D. M. P.; Brown, J. M. Angew. Chem.,
Int. Ed. 2009, 48, 582.
■
(1) Bart, S. C.; Chłopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky,
E.; Neese, F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128,
13901.
(2) Bouwkamp, M. W.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J. J.
Am. Chem. Soc. 2006, 128, 13340.
(39) Crabtree, R. H.; Felkin, H.; Morris, G. E. J. Organomet. Chem.
1977, 141, 205.
(40) Ohno, K.; Tsuji, J. J. Am. Chem. Soc. 1968, 90, 99.
(41) Doughty, D. H.; Pignolet, L. H. J. Am. Chem. Soc. 1978, 100,
7083.
(3) Sylvester, K. T.; Chirik, P. J. J. Am. Chem. Soc. 2009, 131, 8772.
(4) Russel, S. K.; Milsmann, C.; Lobkovsky, E.; Weyhermuller, T.;
Chirik, P. J. Inorg. Chem. 2011, 50, 3159.
(5) Zhang, J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.;
Milstein, D. Organometallics 2004, 23, 4026.
(42) Saunders, M.; Kates, M. R. J. Am. Chem. Soc. 1978, 100, 7083.
(43) Anderson, M. P.; Casalnuovo, A. L.; Johnson, B. J.; Mattson, B.
M.; Mueting, A. M.; Pignolet, L. H. Inorg. Chem. 1988, 27, 1649.
(44) Iwai, T.; Fujihara, T.; Tsuji, Y. Chem. Commun. 2008, 6215.
(6) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem. Soc.
2005, 127, 10840.
(7) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew. Chem.,
Int. Ed. 2006, 45, 1113.
H
dx.doi.org/10.1021/om400688v | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(45) Roa, A. E.; Salazar, V.; Lopez-Serrano, J.; Onate, E.; Paneque, M.
Organometallics 2012, 31, 716.
(46) Ho, H.-A.; Manna, K.; Sadow, A. D. Angew. Chem., Int. Ed. 2012,
51, 8607.
(47) Yang, X.; Hall, M. B. J. Am. Chem. Soc. 2010, 132, 120.
(48) Zeng, G.; Li, S. Inorg. Chem. 2011, 50, 10572.
(49) Li, H.; Wang, X.; Huang, F.; Lu, G.; Jiang, J.; Wang, Z.-X.
Organometallics 2011, 30, 5233.
(50) Sandhya, K. S.; Suresh, C. H. Organometallics 2011, 30, 3888.
(51) Yang, X. ACS Catal. 2012, 2, 964.
(52) Ma, C.; Piccinin, S.; Fabris, S. ACS Catal. 2012, 2, 1500.
(53) Li, H.; Wen, M.; Wang, Z.-X. Inorg. Chem. 2012, 51, 5716.
(54) Herde, J. L.; Lambet, J. C.; Senoff, C. V. Inorg. Synth. 1974, 15,
18.
I
dx.doi.org/10.1021/om400688v | Organometallics XXXX, XXX, XXX−XXX