Mechanism of N-h bond cleavage of aniline by a dearomatized PNP-pincer type phosphaalkene complex of Iridium(I)

Article abstract of DOI:10.1021/om401053j

Detailed mechanistic investigations using kinetic and theoretical methods have been conducted for deprotonative N-H bond cleavage of p-YC ₆H₄NH₂ (Y = H, MeO, Me, Cl, Br, NO₂) by [K(18-crown-6)][Ir(Cl)(PPEP*)] (1a) bearing a dearomatized PNP-pincer type phosphaalkene ligand (PPEP*) to afford [Ir(NHC₆H ₄Y)(PPEP)] (2) with an aromatized ligand (PPEP). While 1a is in equilibrium with [K(18-crown-6)]Cl (3) and [Ir(PPEP*)] (4) in solution, the N-H bond cleavage proceeds via association of 1a with aniline, where the coordination of aniline to iridium is insignificant; instead, aniline is associated with PPEP* by hydrogen bonding. In contrast, the N-H bond cleavage of ammonia proceeds via the pentacoordinate intermediate [Ir(Cl)(NH₃)(PPEP*)]. The difference between the N-H bond cleavage processes of aniline and ammonia is examined by DFT calculations.

Full text of DOI:10.1021/om401053j

Article
pubs.acs.org/Organometallics
Mechanism of N−H Bond Cleavage of Aniline by a Dearomatized
PNP-Pincer Type Phosphaalkene Complex of Iridium(I)
Yung-Hung Chang,† Yumiko Nakajima,†,§ Hiromasa Tanaka,‡ Kazunari Yoshizawa,*,‡
and Fumiyuki Ozawa*,†
†International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji,
Kyoto 611-0011, Japan
‡Institute for Materials Chemistry and Engineering, International Research Center for Molecular Systems, Kyushu University,
Nishi-ku, Fukuoka 819-0395, Japan
S
* Supporting Information
ABSTRACT: Detailed mechanistic investigations using kinetic
and theoretical methods have been conducted for deprotona-
tive N−H bond cleavage of p-YC6H4NH2 (Y = H, MeO, Me,
Cl, Br, NO2) by [K(18-crown-6)][Ir(Cl)(PPEP*)] (1a)
bearing a dearomatized PNP-pincer type phosphaalkene
ligand (PPEP*) to afford [Ir(NHC6H4Y)(PPEP)] (2) with
an aromatized ligand (PPEP). While 1a is in equilibrium with
[K(18-crown-6)]Cl (3) and [Ir(PPEP*)] (4) in solution, the
N−H bond cleavage proceeds via association of 1a with aniline,
where the coordination of aniline to iridium is insignificant;
instead, aniline is associated with PPEP* by hydrogen bonding.
In contrast, the N−H bond cleavage of ammonia proceeds via
the pentacoordinate intermediate [Ir(Cl)(NH3)(PPEP*)]. The
difference between the N−H bond cleavage processes of aniline and ammonia is examined by DFT calculations.
Scheme 1. N−H Bond Cleavage of Ammonia and Amines by
a Dearomatized PNP-Pincer Type Phosphaalkene Complex
of Iridium
INTRODUCTION
■
Phosphaalkenes with a PC double bond possess an extremely
low lying π* orbital around the phosphorus atom and thus
serve as strong π acceptors toward transition metals.1 Recently,
we have reported that this particular ligand property remarkably
enhances the reactivity of a pyridine-based PNP-pincer complex
of iridium toward deprotonative N−H bond cleavage of amines
via metal−ligand cooperation.2,3 As shown in Scheme 1,
K[Ir(Cl)(PPEP*)] (1), having a dearomatized PNP-pincer
type phosphaalkene ligand (PPEP*), readily reacts with
ammonia and amines (RNH2; R = H, n-C6H13, Ph) at room
temperature to afford amido complexes 2a−c in quantitative
yields, along with regeneration of the aromatic pyridine ring.4−6
The observed reactivity is clearly higher than that reported
for [Ru(H)(CO)(PNP*)] and [Rh(L)(PNP*)], having a
dearomatized PNP-pincer type phosphine ligand (PNP*).3a,b
DFT calculations for the reaction of ammonia have revealed
that N−H bond cleavage proceeds via the pentacoordinate
intermediate [Ir(Cl)(NH3)(PPEP*)]−, which undergoes a
proton shift from nitrogen to the vinylic carbon of PPEP*,
and elimination of Cl− yields [Ir(NH2)(PPEP)] (2a). This
process involves a remarkable increase in the electron density
of iridium, which significantly destabilizes intermediate species.
However, due to the strong π-accepting ability of the
phosphaalkene unit, the electron density is effectively reduced
by π back-donation, and therefore the N−H bond cleavage
proceeds under very mild conditions.
This paper deals with the mechanism of N−H bond cleavage
of aniline. Particular interest has been focused on the co-
ordination behavior of 1. As mentioned above, DFT calcula-
tions have indicated an associative mechanism involving a
Received: October 29, 2013
Published: January 24, 2014
© 2014 American Chemical Society
715
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
pentacoordinate intermediate. A similar mechanism has been
proposed by Milstein et al. for the reaction of [Rh(L)(PNP*)]
with aniline.3b In both cases, the starting complex is a 16-electron
species with a d8 metal center, which is often very prone to
undergo ligand exchange with nucleophilic amines to form amine
adducts instead of amido complexes. This tendency is considered
to be the primary cause of the difficulty of N−H bond activa-
tion by late transition metals.7 Thus, we have conducted
detailed mechanistic investigations using 1a that can be isolated
(Scheme 1).8 Herein, we present the first kinetic observations on
the associative mechanism. DFT calculations reveal that the
association of aniline is induced by hydrogen bonding and the
coordination to iridium is insignificant even in the transition state
of N−H bond cleavage.
Table 1. Effects of [K(18-crown-6)]Cl (3) on the Reaction of
1a with Aniline
a
b
c
entry
[3]add (M)
104kobsd (s−1
)
r
1
2
3
4
0.017
0.034
0.051
0.085
2.90(9)
3.63(6)
3.89(7)
4.23(14)
0.995
0.999
0.999
0.997
a
Reaction conditions: [1a]0 = 0.0169 M, [PhNH2]0 = 0.169 M, in
b
THF, at 5.0 °C. Concentration of [K(18-crown-6)]Cl (3) added to
the system. Correlation coefficient for least-squares calculations in
c
linear regression analysis.
the reaction rate increases with increasing amounts of 3 but
tends to be saturated at high concentrations of 3. A plot of
1/kobsd against 1/[3]add exhibited a good linear correlation:
1/kobsd = 22.4(5) × (1/[3]add) + 2113(19) (Figure 2).
RESULTS AND DISCUSSION
■
Reactions of [K(18-crown-6)][Ir(Cl)(PPEP*)] (1a) with
Para-Substituted Anilines. Reactions of 1a with aniline
derivatives proceeded at room temperature to afford anilido
complexes 2c−h in quantitative yields, along with the byproduct
[K(18-crown-6)]Cl (3). Complexes 2c−h were isolated from
the reaction systems using 1 instead of 1a8 and were
characterized by NMR spectroscopy and elemental analysis.
Kinetic Examinations. Complex 1a (0.0169 M) was
treated with aniline (0.169 M) in THF at 5.0 °C, and the
conversion of 1a was followed at intervals by 31P{1H} NMR
spectroscopy using a toluene-d8 solution of PPh3 sealed in a
capillary tube as an internal standard for peak integration. Two
sets of doublets arising from 1a (δ 234.6 and 18.9, 2JPP = 463 Hz)
gradually decreased, to be replaced by the signals of anilido
2
complex 2c (δ 206.0 and 24.3, JPP = 458 Hz), where no other
signals were detected. Figure 1 (plot a) shows a pseudo-first-order
Figure 2. Plot of 1/kobsd against 1/[3]add for the reaction of 1a (0.0169 M)
with aniline (0.169 M) in THF at 5.0 °C.
On the other hand, the reaction rate was linearly correlated
with the concentration of aniline. Figure 3 presents a plot of log
kobsd against log [PhNH2] in the concentration range 0.169−
0.422 M (10−25 equiv/1a), showing the following relation: log
Figure 1. First-order plots for the conversion of 1a (0.0169 M) in the
reaction with aniline (0.169 M) in THF at 5.0 °C in the absence (plot a)
or presence (plots b and c) of added [K(18-crown-6)]Cl (3).
plot for the conversion of 1a. The plot deviates from a straight
line, indicating a gradual increase in the reaction rate (see also
Figure S1 in the Supporting Information). This is probably
due to the byproduct [K(18-crown-6)]Cl (3). Indeed, addition of
3 to the system significantly accelerated the reaction (Figure 1,
plots b and c).
Table 1 gives the rate constants observed at four different
concentrations of added 3. The kobsd values were estimated by
linear regression analysis of the first-order plots. It is seen that
Figure 3. Plot of log kobsd against log [PhNH2] for the reaction of 1a
(0.0169 M) with aniline in THF in the presence of added 3 (0.051 M)
at 0.0 °C.
716
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
1
kobsd
K
1
=
+
k[PhNH2][3]
k[PhNH2]
(2)
k = 2.80 × 10−3 s−1 M−1, K = 0.0106 M. The negative entropy
(ΔS⧧ = −14(3) eu) is consistent with an ordered transition state
(i.e., TSNH in Scheme 2).
Effects of Para Substituents. Next, we compared the
reactivity of para-substituted anilines toward 1a at −10.0 °C.
Table 2 summarizes the results. Electron-withdrawing substituents
Table 2. Pseudo-First-Order Rates for the Reactions of 1a
a
with p-Substituted Anilines in THF at −10.0 °C
b
c
entry
p-YC6H4NH2
σp−(Y)
pKa
104kobs (s−1
)
1
2
3
4
5
6
p-MeOC6H4NH2
p-MeC6H4NH2
PhNH2
−0.26
−0.17
0.00
32.5
31.7
30.6
29.4
29.1
20.9
0.0754(6)
0.137(1)
0.426(11)
9.47(12)
14.3(1)
Figure 4. Eyring plot for the reaction of 1a (0.0169 M) with aniline
(0.169 M) in THF.
p-ClC6H4NH2
p-BrC6H4NH2
p-O2NC6H4NH2
0.19
0.25
1.27
rapid
kobsd = 1.04(5) × log [PhNH2] − 2.84(3). Thus, the reaction is
first order in the concentration of aniline.
a
Reaction conditions: [1a]0 = 0.0169 M, [aniline]0 = 0.169 M, in
THF, at −10.0 °C. Data taken from ref 9. Data taken from ref 10.
b
c
The Eyring plot for the rate constants observed at four dif-
ferent temperatures exhibited a good linear correlation (Figure 4),
providing the following kinetic parameters: ΔH⧧ = 17.1(8)
kcal mol−1, ΔS⧧ = −14(3) eu, and ΔG⧧ = 20.9 kcal mol−1 at
273 K. Moreover, a small deuterium isotope effect was observed
with PhND2: kH/kD = 1.56 at 5.0 °C.
These kinetic observations are consistent with the reaction
process given in Scheme 2. Complex 1a is in equilibrium with
[Ir(PPEP*)] (4) and 3 in solution. On the other hand, associa-
tion of 1a with aniline causes N−H bond cleavage across the
iridium and vinylic carbon atoms, giving 2c together with 3.
When the interconversion between 1a and 4 + 3 is a rapid
process, and the N−H bond cleavage serves as the rate-
determining step, the reaction rate is expressed by eq 1, where
remarkably accelerate the formation of anilido complexes.
p-Nitroaniline is particularly reactive, and its reaction was
completed in a few minutes even at −50 °C (entry 6).
Figure 5 shows a plot of log (kY/kH) against the pKa values
of aniline derivatives. It is known that the pKa values are
proportional to the σp− values of para substituents.9,10 Although the
number of data are limited, the plot may be divided into two
regions. When aniline derivatives are acidic, the reactivity appears to
depend simply on the pKa values. On the other hand, the reactivity
of basic anilines (i.e., p-MeC6H4NH2 and p-MeOC6H4NH2)
deviates from this tendency: i.e., the reactivity is higher than that
expected from the pKa values.
DFT Calculations. The mechanism of N−H bond cleavage
of aniline by 1a was investigated by DFT calculations using the
B3LYP-D functional.11 Geometry optimization and vibra-
tional analysis were performed with the SDD and 6-31G(d)
basis sets for iridium and the other atoms, respectively.12
Energy changes were evaluated by single-point calculations at
the optimized geometries using the 6-311+G(d,p) basis set
instead of the 6-31G(d) basis set. Solvation effects (THF) were
taken into account using the polarizable continuum model
(PCM).13
k[PhNH2][3]
K + [3]
d[2c]
dt
= k[PhNH2][1a] =
[Ir]total
(1)
[Ir]total = [1a] + [4] at time t, K = [3][4]/[1a], and k stands
for the rate constant for the conversion of 1a to 2c. Thus, the
1/kobsd values are correlated with the 1/[3] values by eq 2.
Applying the slope and intercept values of Figure 2 to eq 2
results in the following rate and equilibrium constants at 5.0 °C:
Scheme 2. Proposed Mechanism for the Reaction of 1a with Aniline
717
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
state (TS1a/5). Thereafter, the PhNH group of aniline gradually
approaches iridium to yield 5.
In step ii, elongation of the Ir−Cl bond in 5 induces the
migration of the PhNH group from the apical position to the
equatorial position. Complex 2c thus produced adopts a square-
planar configuration around iridium, and [K(18-crown-6)]Cl (3)
is significantly distant from 2c (4.571 Å). Accordingly, 3 is
completely eliminated from iridium. The transition state of step ii
(TS5/2c) is located at E = 15.3 kcal mol−1, the value of which is
lower than that of step i (TS1a/5, E = 16.8 kcal mol−1). Hence,
the N−H bond cleavage is assigned to the rate-determining step,
in accordance with the kinetic observations. The theoretical value
of activation energy (Ea = 16.8 kcal mol−1) is in good agree-
ment with the experimental value (ΔH⧧ = 17.1(8) kcal mol−1).
Comparison of N−H Bond Cleavage Processes of
PhNH2 and NH3. As described above, the coordination of
aniline is not crucial for N−H bond cleavage. In contrast,
ammonia is initially coordinated to iridium and then undergoes
N−H bond cleavage via metal−ligand cooperation.2 Next, we
examined the difference between these reaction systems using
the Mayer bond order.
Table 3 presents changes in the selected bond orders that are
directly concerned with the N−H bond cleavage process. For
both systems, a continuous loss of the N−H bond accompanied
by the formation of a C−H bond is clearly demonstrated. On the
other hand, the Ir−N bond orders are significantly different in the
two systems. For the reaction with ammonia, a relatively large
value (0.43) of the pentacoordinate intermediate [Ir(Cl)(NH3)-
(PPEP*)]− (6) corroborates the presence of a distinct bonding
interaction between iridium and ammonia. The bond order of
the Ir−N bond increases in the N−H bond cleavage process:
0.43 (6) → 0.69 (TS6/7) → 1.13 (7). The considerable change
between 6 and TS6/7 (0.26) also supports the importance of the
precoordination of ammonia in the N−H bond cleavage process.
In contrast, for the reaction with aniline, the Ir−N bond
order increases only by 0.06 from the precursor complex to the
Figure 5. Plot of log (kY/kH) against pKa values of para-substituted
anilines. The data are taken from entries 1−5 in Table 2.
Figure 6 shows an energy diagram obtained for the whole
reaction, which consists of two reaction steps: (i) deprotonative
N−H bond cleavage across the iridium and vinylic carbon
atoms to form the pentacoordinate amido intermediate
[K(18-crown-6)][IrCl(NHPh)(PPEP)] (5) and (ii) elimination
of [K(18-crown-6)]Cl (3) from 5 to give 2c. The most
interesting finding is the absence of distinct coordination of
aniline to iridium prior to N−H bond cleavage. Instead, aniline
is associated with 1a by hydrogen bonding between the N−H
bond and the vinylic carbon of PPEP*. The interatomic distance
between C and H, which is 2.458 Å in the precursor complex
(1a-PhNH2), is reduced to 1.279 Å in the transition state
(TS1a/5), showing the occurrence of N···H···C type hydrogen
bonding. At the same time, the N−H bond length is extended
from 1.020 to 1.483 Å. On the other hand, the nitrogen atom of
aniline remains far from iridium (3.432 Å) even in the transition
Figure 6. Energy profile and optimized structures for the reaction of 1a with aniline to afford 2c via deprotonative N−H bond cleavage. The given
energies are relative to the value of 1a−PhNH2 in kcal mol−1.
718
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
for ammonia. The Lewis acidity of the iridium center of 1a is
significantly enhanced by π back-donation to the phosphaalkene
part of the PPEP* ligand,2 and therefore the coordination
effectively facilitates the deprotonation of amines. As a result,
deprotonative N−H bond cleavage takes place even with basic
amines such n-hexylamine and ammonia (pKa = 41) under very
mild conditions.
Table 3. Mayer Bond Orders of Selected Bonds in the N−H
a
Bond Cleavage of PhNH2 and NH3
description
N−H
PhNH2
C−H
Ir−N
1a-PhNH2
TS1a/5
5
0.77
0.33
0.01
0.06
0.53
0.87
0.14
0.20
0.80
NH3
EXPERIMENTAL SECTION
■
6
0.74
0.34
0.00
0.05
0.47
0.87
0.43
0.69
1.13
General Considerations. All manipulations were carried out
under a nitrogen atmosphere using standard Schlenk techniques and
a glovebox. Nitrogen gas was dried by passing through a P2O5 column
(Merck, SICAPENT). Toluene (Kanto, dehydrated), hexane, and
Et2O (Wako, dehydrated) were used as received. THF and CH3CN were
dried over sodium/benzophenone and calcium hydride, respectively,
distilled, and stored over activated MS4A. [K(18-crown-6)][IrCl-
(PPEP*)] (1a)2 and [K(18-crown-6)]Cl (3)15 were prepared according
to the literature. Other chemicals were purchased from commercial
sources and used without purification. NMR spectra were recorded on a
Bruker AVANCE 400 spectrometer (1H NMR, 400.13 MHz; 13C NMR,
100.62 MHz; 31P NMR, 161.98 MHz). Chemical shifts are reported in δ
(ppm), referenced to 1H (residual) and 13C signals of deuterated solvents
as internal standards or to the 31P signal of 85% H3PO4 as an external
standard. Elemental analysis was performed by ICR Analytical
Laboratory, Kyoto University.
TS6/7
7
a
Structures for aniline are given in Figure 6, whereas those for
ammonia are shown below. The substituents on phosphorus atoms
and the countercation are omitted for simplicity.
transition state: 0.14 (1a-PhNH2) → 0.20 (TS1a/5). This data
indicates that an acid−base interaction between the N−H bond
and the vinylic carbon is predominant even in the transition
state. Hence, the N−H bond cleavage of aniline can be regarded
as a simple deprotonation process, rather than the metal−ligand
cooperative activation of an N−H bond. The iridium center
serves as an acceptor of the negatively charged PhNH group.
The relatively high acidity of aniline (pKa = 30.6) could be the
prime reason for this reaction process.
Preparation and Identification of [Ir(NHC6H4-p-Y)(PPEP)]
(2d−h). The title compounds were prepared from K[IrCl(PPEP*)]
instead of 1a8 according to the synthesis of 2c.2 A typical procedure is
described for the p-chloroanilido complex 2f. A dark green crystalline
solid of K[IrCl(PPEP*)], derived from [IrCl(PPEP)] (34 mg, 0.038
t
mmol) and BuOK in Et2O, was placed in a 25 mL Schlenk tube and
dissolved in THF (3 mL). A solution of p-chloroaniline (0.038 mmol) in
THF (1 mL) was added, and the mixture was stirred for 2 h at room
temperature. The solution instantly changed from dark green to brown,
and a white solid of KCl gradually precipitated. Volatiles were removed
under vacuum, and the residue was dissolved in hexane (1 mL) and
the solution filtered through a Celite pad to remove KCl. The filtrate
was evaporated under vacuum to give a dark brown solid, which
was recrystallized from CH3CN to afford analytically pure 2f (25 mg,
0.026 mmol, 68%). Complexes 2d,e,g,h were similarly prepared using
hexane (2d,e) or MeCN (2g,h) as a recrystallization solvent.
Identification data are as follows.
On the other hand, ammonia (pKa = 41),14 which is much
less acidic than aniline, would be incapable of undergoing a
simple deprotonation process. In this case, the coordination
to iridium, whose Lewis acidity is enhanced by π back-donation
to PPEP*, should facilitate the deprotonation of ammonia,
thereby enabling the N−H bond cleavage via metal−ligand
cooperation. A similar mechanism is probably operative for
basic anilines such as p-MeC6H4NH2 and p-MeOC6H4NH2;
their reactivities are higher than those expected from the pKa
values (Figure 5).
[Ir(NHC6H4-p-OMe)(PPEP)] (2d). 1H NMR (THF-d8, 25 °C): δ 8.43
(dd, JPH = 9.1 Hz, JPH = 3.5 Hz, 1H, PyCHP), 7.73 (td, JHH = 7.3
Hz, JPH = 3.1 Hz, 1H, Py), 7.63 (s, 1H, Ar), 7.55 (s, 1H, Ar), 7.53 (dd,
JPH = 4.6 Hz, JPH = 1.7 Hz, 1H, Ar), 7.31 (m, 2H, Ar + NH), 6.85 (d,
JHH = 8.2 Hz, 2H, Py), 6.77 (d, JHH = 7.0 Hz, 1H, Py), 5.98 (d, JHH
8.9 Hz, 2H, Ar), 5.89 (d, JHH = 8.9 Hz, 2H, Ar), 4.18 (dd, JHH = 18.4
CONCLUSIONS
■
We have reported detailed examinations of the mechanism of
N−H bond cleavage of aniline by 1a bearing a dearomatized
PNP-pincer type phosphaalkene ligand (PPEP*). The kinetic
data clearly indicate an associative reaction process. However,
the coordination of aniline to iridium is unremarkable even in
the transition state of N−H bond cleavage (TS1a/5). Instead,
aniline is associated with 1a by hydrogen bonding between the
N−H bond and the vinylic carbon of PPEP*. Thus, the N−H
bond cleavage process of aniline is best described as a simple
deprotonation process followed by the coordination of an
anionic PhNH group to iridium. We consider that the relatively
high acidity of aniline (pKa = 30.6) is the primary cause of
this type of reaction process. Actually, the reactivity of
acidic anilines, including p-O2NC6H4NH2 (pKa = 20.9),
p-BrC6H4NH2 (pKa = 29.1), p-ClC6H4NH2 (pKa = 29.4),
and PhNH2 (pKa = 30.6), depends simply on the pKa values
(Figure 5). It is noteworthy that the synthesis of transition-metal
amido complexes from dearomatized pincer complexes has so
far been successful only with such relatively acidic amines.3a−c
On the other hand, the N−H bond cleavage of less acidic
amines probably requires precoordination to iridium, as evidenced
=
Hz, JPH = 10.3 Hz, 1H, PyCH2P), 4.13 (dd, JHH = 18.4 Hz, JPH = 9.9
Hz, 1H, PyCH2P), 3.45 (s, ArOCH3), 2.34 (dd, JHH = 14.9 Hz, JPH
=
3.3 Hz, 1H, PCH2), 2.22 (dt, JHH = 14.9 Hz, JPH = 3.8 Hz, 1H, PCH2),
1.80 (s, 9H, CH3), 1.66 (s, 9H, CH3), 1.45 (s, 12H, CH3), 1.41 (s, 9H,
CH3), 1.40 (s, 9H, CH3), 1.23 (s, 3H, CH3). 13C NMR (THF-d8,
25 °C): δ 165.1 (d, JPC = 5 Hz), 163.2 (dd, JPC = 6 and 3 Hz), 159.1
(dd, JPC = 14 and 5 Hz), 156.0 (d, JPC = 2 Hz), 155.8 (s), 154.5 (d,
JPC = 2 Hz), 153.9 (s), 153.7 (d, JPC = 10 Hz), 152.7 (d, JPC = 2 Hz),
152.2 (d, JPC = 3 Hz), 137.4 (d, JPC = 47 Hz, PyCHP), 132.5 (dd,
JPC = 18 and 3 Hz), 130.7 (dd, JPC = 34 and 6 Hz), 125.9 (s), 123.8 (d,
JPC = 8 Hz), 123.0 (d, JPC = 7 Hz), 122.8 (d, JPC = 7 Hz), 122.7 (d,
JPC = 26 Hz), 122.1 (s), 120.3 (d, JPC = 8 Hz), 114.5 (dd, JPC = 12 and
6 Hz), 112.9 (s), 55.9 (s), 50.7 (d, JPC = 29 Hz, PyCH2P), 44.6 (t,
JPC = 4 Hz), 40.3 (d, JPC = 34 Hz), 39.9 (s), 39.8 (s), 38.3 (s), 36.1 (s),
36.0 (s), 34.7 (s), 34.3 (s), 33.6 (s), 32.9 (s), 31.9 (s), 31.8 (s), 31.1
(d, JPC = 9 Hz). 31P{1H} NMR (THF-d8, 25 °C): δ 196.6 (d, JPP = 459
Hz), 22.9 (d, JPP = 459 Hz). Anal. Calcd for C50H71IrN2OP2·0.5C6H14:
C, 62.82; H, 7.76; N, 2.76. Found: C, 62.70; H, 7.97; N, 2.75.
1
[Ir(NHC6H4-p-Me)(PPEP)] (2e). H NMR (THF-d8, 25 °C): δ 8.46
(dd, JPH = 9.4 Hz, JPH = 3.5 Hz, 1H, PyCHP), 7.75 (td, JHH
=
7.4 Hz, JPH = 3.0 Hz, 1H, Py), 7.63 (s, 1H, Ar), 7.55 (s, 1H, Ar),
719
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
7.52 (dd, JPH = 4.6 Hz, JPH = 1.7 Hz, 1H, Ar), 7.36 (br d, JPH = 5.9 Hz,
1H, NH), 7.31 (d, JPH = 1.5 Hz, 1H, Ar), 6.86 (d, JHH = 8.1 Hz, 1H,
Py), 6.78 (d, JHH = 7.0 Hz, 1H, Py), 6.17 (d, JHH = 8.2 Hz, 2H, Ar),
5.86 (d, JHH = 8.2 Hz, 2H, Ar), 4.18 (dd, JHH = 18.1 Hz, JPH = 10.2 Hz,
1H, PyCH2P), 4.12 (dd, JHH = 18.1 Hz, JPH = 10.2 Hz, 1H, PyCH2P),
2.34 (dd, JHH = 14.8 Hz, JPH = 3.4 Hz, 1H, PCH2), 2.28 (dt, JHH = 14.8
Hz, JPH = 3.5 Hz, 1H, PCH2), 2.16 (s, 3H, ArCH3), 1.80 (s, 9H, CH3),
1.66 (s, 9H, CH3), 1.46 (s, 3H, CH3), 1.45 (s, 9H, CH3), 1.42 (s, 9H,
CH3), 1.41 (s, 9H, CH3), 1.23 (s, 3H, CH3). 13C NMR (THF-d8,
25 °C): δ 165.2 (d, JPC = 5 Hz), 163.6 (dd, JPC = 6 and 3 Hz), 159.0
(dd, JPC = 14 and 5 Hz), 156.1 (d, JPC = 2 Hz), 155.9 (s), 155.8 (d,
JPC = 3 Hz), 154.5 (d, JPC = 2 Hz), 153.7 (d, JPC = 10 Hz), 152.7 (d,
JPC = 2 Hz), 137.8 (d, JPC = 47 Hz, PyCHP), 132.3 (dd, JPC = 18
and 3 Hz), 130.7 (dd, JPC = 34 and 6 Hz), 127.8 (s), 126.3 (s), 126.0
(d, JPC = 1 Hz), 123.8 (d, JPC = 9 Hz), 123.0 (d, JPC = 7 Hz), 122.9 (d,
JPC = 7 Hz), 122.7 (d, JPC = 26 Hz), 121.3 (s), 120.1 (d, JPC = 8 Hz),
114.7 (dd, JPC = 12 and 6 Hz), 50.9 (d, JPC = 29 Hz, PyCH2P), 44.6 (t,
JPC = 4 Hz), 40.4 (d, JPC = 34 Hz), 39.9 (s), 39.8 (s), 38.3 (s), 36.1 (s),
36.0 (s), 34.7 (s), 34.3 (s), 33.6 (s), 32.9 (s), 31.9 (s), 31.8 (s), 30.9
(d, JPC = 9 Hz), 20.1 (s). 31P{1H} NMR (THF-d8, 25 °C): δ 199.9 (d,
JPP = 458 Hz), 22.6 (d, JPP = 458 Hz). Anal. Calcd for C50H71IrN2P2:
C, 62.93; H, 7.50; N, 2.94. Found: C, 62.82; H, 7.64; N, 2.90.
the crystallization solvent. Anal. Calcd for C49H68BrIrN2P2·0.5C2H3N:
C, 57.76; H, 6.74; N, 3.37. Found: C, 57.78; H, 6.84; N, 3.30.
[Ir(NHC6H4-p-NO2)(PPEP)] (2h). 1H NMR (THF-d8, 25 °C): δ 8.69
(dd, JPH = 12.4 Hz, JPH = 3.8 Hz, 1H, PyCHP), 7.86 (td, JHH = 7.9
Hz, JPH = 2.6 Hz, 1H, Py), 7.65 (s, 1H, Ar), 7.58 (s, 1H, Ar), 7.57 (s,
1H, Ar), 7.34 (s, 1H, Ar), 7.30 (br d, JPH = 6.0 Hz, 1H, NH), 7.19 (d,
JHH = 8.7 Hz, 2H, Ar), 7.07 (d, JHH = 7.0 Hz, 1H, Py), 7.00 (d, JHH
=
7.9 Hz, 1H, Py), 5.87 (d, JHH = 8.7 Hz, 2H, Ar), 4.23 (dd, JHH = 18.4
Hz, JPH = 10.5 Hz, 1H, PyCH2P), 4.15 (dd, JHH = 18.4 Hz, JPH = 9.7
Hz, 1H, PyCH2P), 2.42 (dd, JHH = 15.0 Hz, JPH = 3.5 Hz, 1H, PCH2),
2.27 (dt, JHH = 15.0 Hz, JPH = 3.3 Hz, 1H, PCH2), 1.76 (s, 9H, CH3),
1.69 (s, 9H, CH3), 1.46 (s, 12H, CH3), 1.42 (s, 9H, CH3), 1.39 (s, 9H,
CH3), 1.27 (s, 3H, CH3). 13C NMR (THF-d8, 25 °C): δ 167.1 (d,
JPC = 5 Hz), 166.7 (dd, JPC = 6 and 3 Hz), 165.5 (s), 159.3 (dd, JPC
=
15 and 4 Hz), 156.8 (s), 156.5 (s), 155.5 (d, JPC = 2 Hz), 153.8 (d,
JPC = 10 Hz), 153.4 (d, JPC = 2 Hz), 143.4 (d, JPC = 50 Hz, PyCHP),
135.0 (s), 131.5 (s), 130.3 (dd, JPC = 18 and 5 Hz), 130.1 (dd, JPC = 36
and 7 Hz), 125.3 (s), 124.4 (d, JPC = 9 Hz), 123.5 (d, JPC = 7 Hz),
123.1 (d, JPC = 7 Hz), 121.5 (d, JPC = 26 Hz), 120.6 (d, JPC = 9 Hz),
117.4 (dd, JPC = 12 and 8 Hz), 117.3 (s), 50.9 (d, JPC = 28 Hz,
PyCH2P), 44.7 (t, JPC = 4 Hz), 42.0 (d, JPC = 33 Hz), 39.6 (s), 38.1
(s), 36.1 (s), 36.0 (s), 34.4 (s), 34.0 (s), 33.8 (d, JPC = 2 Hz), 33.1 (s),
31.7 (s), 31.6 (s), 31.1 (d, JPC = 9 Hz). 31P{1H} NMR (THF-d8,
25 °C): δ 233.6 (d, JPP = 448 Hz), 23.0 (d, JPP = 448 Hz). Anal. Calcd
for C49H68IrN3O2P2: C, 59.73; H, 6.96; N, 4.26. Found: C, 59.58; H,
6.87; N, 4.39.
1
[Ir(NHC6H4-p-Cl)(PPEP)] (2f). H NMR (THF-d8, 25 °C): δ 8.55
(dd, JPH = 10.2 Hz, JPH = 3.6 Hz, 1H, PyCHP), 7.81 (td, JHH = 7.4
Hz, JPH = 2.8 Hz, 1H, Py), 7.65 (s, 1H, Ar), 7.57 (s, 1H, Ar), 7.53 (dd,
JPH = 4.7 Hz, JPH = 1.6 Hz, 1H, Ar), 7.34 (s, 1H, Ar), 7.09 (br d, JPH
=
Kinetic Experiments. A typical procedure is as follows. A solution
of [K(18-crown-6)][IrCl(PPEP*)] (1a; 10.0 mg, 0.00843 mmol) and
[K(18-crown-6)]Cl (3; 2.9 mg, 0.0084 mmol) in THF (0.3 mL) was
introduced into a screw cap NMR tube, and a capillary filled with a
toluene-d8 solution of PPh3 (0.17 M) was inserted. A THF solution
of aniline (10 μL, 8.43 M, 0.00843 mmol) was charged at −78 °C,
and the total volume was adjusted to 0.50 mL with additional THF.
The sample tube was placed in an NMR sample probe controlled to
5.0 0.1 °C, and the conversion of 1a was monitored at intervals by
31P{1H} NMR spectroscopy using the following marker signals: 1a, δ
234.6 and 18.9; PPh3, δ −4.7.
DFT Calculations. Intermediates and transition structures on
potential energy surfaces were searched by using the Gaussian 09
program.16 The PPEP* ligand and [K(18-crown-6)] were treated
without any simplification. As a result, the whole system is neutral and
the electronic ground state is the closed-shell singlet throughout the
reaction. We adopted the B3LYP-D functional, which is the B3LYP
hybrid functional11a−d combined with an empirical dispersion correction
developed by Grimme.11e For optimization the SDD and 6-31G(d) basis
sets were chosen for Ir and the other atoms, respectively.12 Systematic
vibrational analyses were carried out for all reaction species to
characterize stationary-point structures. An appropriate connection
between a reactant and a product for each reaction step was confirmed
by intrinsic reaction coordinate (IRC) calculations.17 Zero-point energy
corrections were applied for energy changes (E) and activation energies
(Ea) calculated for each reaction step.
6.2 Hz, 1H, NH), 6.89 (d, JHH = 7.9 Hz, 1H, Py), 6.85 (d, JHH = 7.0
Hz, 1H, Py), 6.24 (d, JHH = 8.7 Hz, 2H, Ar), 5.90 (d, JHH = 8.7 Hz, 2H,
Ar), 4.20 (dd, JHH = 16.6 Hz, JPH = 10.4 Hz, 1H, PyCH2P), 4.14 (dd,
JHH = 16.6 Hz, JPH = 10.2 Hz, 1H, PyCH2P), 2.41 (dd, JHH = 14.9 Hz,
JPH = 3.3 Hz, 1H, PCH2), 2.28 (dt, JHH = 14.9 Hz, JPH = 2.6 Hz, 1H,
PCH2), 1.78 (s, 9H, CH3), 1.66 (s, 9H, CH3), 1.47 (s, 3H, CH3), 1.44
(s, 9H, CH3), 1.42 (s, 9H, CH3), 1.41 (s, 9H, CH3), 1.29 (s, 3H,
CH3). 13C NMR (THF-d8, 25 °C): δ 165.5 (d, JPC = 5 Hz), 164.4 (dd,
JPC = 6 and 3 Hz), 159.2 (dd, JPC = 14 and 5 Hz), 157.3 (s), 156.2 (s),
156.1 (s), 154.9 (d, JPC = 2 Hz), 153.8 (d, JPC = 10 Hz), 153.0 (d, JPC
=
2 Hz), 139.1 (d, JPC = 48 Hz, PyCHP), 131.9 (dd, JPC = 18 and 3
Hz), 130.4 (dd, JPC = 35 and 7 Hz), 127.6 (s), 127.0 (s), 124.0 (d,
JPC = 8 Hz), 123.2 (d, JPC = 7 Hz), 123.1 (d, JPC = 7 Hz), 122.5 (d,
JPC = 26 Hz), 121.5 (s), 120.6 (s), 120.3 (d, JPC = 8 Hz), 115.5 (dd,
JPC = 12 and 6 Hz), 50.8 (d, JPC = 29 Hz, PyCH2P), 44.6 (t, JPC
=
4 Hz), 40.9 (d, JPC = 34 Hz), 39.9 (s), 39.8 (s), 38.3 (s), 36.2 (s), 36.0
(s), 34.5 (s), 34.3 (s), 33.6 (d, JPC = 1 Hz), 32.9 (s), 31.8 (s), 31.7 (s),
31.0 (d, JPC = 9 Hz). 31P{1H} NMR (THF-d8, 25 °C): δ 209.0 (d,
JPP = 453 Hz), 22.5 (d, JPP = 453 Hz). Anal. Calcd for C49H68ClIrN2P2:
C, 60.38; H, 7.03; N, 2.87. Found: C, 60.44; H, 7.06; N, 2.99.
1
[Ir(NHC6H4-p-Br)(PPEP)] (2g). H NMR (THF-d8, 25 °C): δ 8.56
(dd, JPH = 10.2 Hz, JPH = 3.6 Hz, 1H, PyCHP), 7.81 (td, JHH = 7.6
Hz, JPH = 2.4 Hz, 1H, Py), 7.65 (s, 1H, Ar), 7.57 (s, 1H, Ar), 7.54 (dd,
JPH = 4.6 Hz, JPH = 1.7 Hz, 1H, Ar), 7.34 (s, 1H, Ar), 7.09 (br d, JPH
=
7.0 Hz, 1H, NH), 6.90 (d, JHH = 8.0 Hz, 1H, Py), 6.86 (d, JHH = 7.2
Hz, 1H, Py), 6.35 (d, JHH = 8.8 Hz, 2H, Ar), 5.87 (d, JHH = 8.8 Hz, 2H,
Ar), 4.21 (dd, JHH = 17.2 Hz, JPH = 10.8 Hz, 1H, PyCH2P), 4.14 (dd,
JHH = 17.2 Hz, JPH = 10.0 Hz, 1H, PyCH2P), 2.41 (dd, JHH = 14.8 Hz,
JPH = 3.2 Hz, 1H, PCH2), 2.27 (dt, JHH = 14.8 Hz, JPH = 3.3 Hz, 1H,
PCH2), 1.79 (s, 9H, CH3), 1.67 (s, 9H, CH3), 1.47 (s, 3H, CH3), 1.45
(s, 9H, CH3), 1.42 (s, 9H, CH3), 1.41 (s, 9H, CH3), 1.29 (s, 3H,
CH3). 13C NMR (THF-d8, 25 °C): δ 165.6 (d, JPC = 5 Hz), 164.5 (dd,
JPC = 6 and 3 Hz), 159.1 (dd, JPC = 14 and 5 Hz), 157.8 (s), 156.2 (s),
156.1 (s), 154.9 (d, JPC = 2 Hz), 153.8 (d, JPC = 10 Hz), 153.0 (s),
139.2 (d, JPC = 48 Hz, PyCHP), 131.8 (dd, JPC = 18 and 3 Hz),
130.5 (dd, JPC = 35 and 7 Hz), 129.9 (s), 127.7 (s), 124.0 (d, JPC = 9
Hz), 123.2 (d, JPC = 7 Hz), 123.0 (d, JPC = 7 Hz), 122.5 (d, JPC = 26
Hz), 122.1 (s), 120.3 (d, JPC = 8 Hz), 115.6 (dd, JPC = 12 and 6 Hz),
107.6 (s), 50.8 (d, JPC = 29 Hz, PyCH2P), 44.6 (t, JPC = 4 Hz), 40.9 (d,
JPC = 34 Hz), 39.9 (s), 39.8 (s), 38.3 (s), 36.2 (s), 36.0 (s), 34.5 (s),
34.3 (s), 33.6 (s), 32.9 (s), 31.9 (s), 31.8 (s), 31.0 (d, JPC = 9 Hz).
31P{1H} NMR (THF-d8, 25 °C): δ 210.0 (d, JPP = 454 Hz), 22.8 (d,
JPP = 454 Hz). This complex contained 0.5 of a molecule of MeCN as
ASSOCIATED CONTENT
■
S
* Supporting Information
Cartesian coordinates of the optimized intermediates and
transition structures. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: F.O., ozawa@scl.kyoto-u.ac.jp; K.Y., kazunari@ms.
ifoc.kyushu-u.ac.jp.
Present Address
§National Institute of Advanced Industrial Science and
Technology (AIST), Tsukuba 305-8565, Japan.
720
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721

Organometallics
Article
(8) Isolated complex 1a was employed in kinetic runs to clarify the
reaction stoichiometry. On the other hand, the use of 1, which
was prepared in situ from [IrCl(PPEP)] and BuOK, was crucial
Notes
The authors declare no competing financial interest.
t
for the isolation of 2c−g because of the difficulty of separation of
ACKNOWLEDGMENTS
[K(18-crown-6)]Cl (3) from anilido complexes.2
■
This work was supported by a MEXT Grant-in-Aid for Scientific
Research on Innovative Areas “Stimuli-responsive Chemical
Species” (Nos. 24109014 (K.Y.) and 24109010 (F.O.)), a JSPS
Grant-in-Aid for JSPS Fellows (No. 24·3950 (Y.C.)), and the
MEXT Project of “Integrated Research on Chemical Synthesis”.
(9) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 97, 165.
(10) Bordwell, F. G.; Zhang, X.-M.; Cheng, J.-P. J. Org. Chem. 1993,
58, 6410.
(11) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Becke, A. D. J.
Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys.
Rev. B 1988, 37, 785. (d) Stephens, P. J.; Devlin, F. J.; Chabalowski, C.
F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623. (e) Grimme, S. J.
Comput. Chem. 2006, 27, 1782.
(12) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971,
54, 724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys.
1972, 56, 2257. (c) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta
1973, 28, 213. (d) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.;
Schleyer, P. v. R. J. Comput. Chem. 1983, 4, 294. (e) Francl, M. M.;
Petro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.;
Pople, J. A. J. Chem. Phys. 1982, 77, 3654. (f) Andrae, D.;
REFERENCES
■
(1) (a) Dugal-Tessier, J.; Conrad, E. D.; Dake, G. R.; Gates, D. P. In
Phosphorus(III) Ligands in Homogeneous Catalysis: Design and Synthesis;
Kamer, P. C. J., van Leeuwen, P. W. N. M., Eds.; Wiley: Chichester,
U.K., 2012; Chapter 10. (b) Le Floch, P. Coord. Chem. Rev. 2006, 250,
627. (c) Ozawa, F.; Yoshifuji, M. Dalton Trans. 2006, 4987.
(d) Weber, L. Coord. Chem. Rev. 2005, 249, 741. (e) Mathey, F.
Angew. Chem., Int. Ed. 2003, 42, 1578.
(2) Chang, Y.-H.; Nakajima, Y.; Tanaka, H.; Yoshizawa, K.; Ozawa, F.
J. Am. Chem. Soc. 2013, 135, 11791.
Haußermann, U.; Dolg, M.; Stoll, H.; Preuß, H. Theor. Chim. Acta
̈
1990, 77, 123.
(3) For pioneering works on deprotonative N−H bond cleavage of
amines via metal−ligand cooperation, see: (a) Khaskin, E.; Iron, M. A.;
Shimon, L. J. W.; Zhang, J.; Milstein, D. J. Am. Chem. Soc. 2010, 132,
8542. (b) Feller, M.; Diskin-Posner, Y.; Shimon, L. J. W.; Ben-Ari, E.;
Milstein, D. Organometallics 2012, 31, 4083. (c) de Boer, S. Y.;
Gloaguen, Y.; Reek, J. N. H.; Lutz, M.; van der Vlugt, J. I. Dalton Trans.
2012, 41, 11276. (d) Myers, T. W.; Berben, L. A. J. Am. Chem. Soc.
2013, 135, 9988. (e) Kimura, T.; Koiso, N.; Ishiwata, K.; Kuwata, S.;
Ikariya, T. J. Am. Chem. Soc. 2011, 133, 8880.
(4) For reviews on noninnocent behavior of PNP-pincer complexes,
see: (a) Gunanathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588.
(b) Milstein, D. Top. Catal. 2010, 53, 915. (c) van der Vlugt, J. I.;
Reek, J. N. H. Angew. Chem., Int. Ed. 2009, 48, 8832.
(5) For recent studies by Milstein et al. on Y−H bond cleavage (Y =
H, C, O) by PNP-pincer complexes, see: (a) Ben-Ari, E.; Leitus, G.;
Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2006, 128, 15390.
(b) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Diskin-Posner,
Y.; Leitus, G.; Shimon, L. J. W.; Milstein, D. Organometallics 2010, 29,
3817. (c) Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew.
Chem., Int. Ed. 2011, 50, 2120. (d) Gnanaprakasam, B.; Balaraman, E.;
Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2011, 50, 12240.
(e) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Ben-Ari, E.;
Milstein, D. Organometallics 2011, 30, 2721. (f) Montag, M.; Zhang, J.;
Milstein, D. J. Am. Chem. Soc. 2012, 134, 10325. (g) Langer, R.; Iron,
M. A.; Konstantinovski, L.; Diskin-Posner, Y.; Leitus, G.; Ben-David,
Y.; Milstein, D. Chem. Eur. J. 2012, 18, 7196. (h) Langer, R.; Fuchs, I.;
Vogt, M.; Balaraman, E.; Diskin-Posner, Y.; Shimon, L. J. W.; Ben-
David, Y.; Milstein, D. Chem. Eur. J. 2013, 19, 3407. (i) Vogt, M.;
Rivada-Wheelaghan, O.; Iron, M. A.; Leitus, G.; Diskin-Posner, Y.;
Simon, L. J. W.; Ben-David, Y.; Milstein, D. Organometallics 2013, 32,
300.
(13) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999.
(14) Bordwell, F. G.; Drucker, G. E.; Fried, H. E. J. Org. Chem. 1981,
46, 632.
(15) Song, Y.; Jing, H.; Li, B.; Bai, D. Chem. Eur. J. 2011, 17, 8731.
(16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.;
Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision C.01; Gaussian, Inc., Wallingford, CT, 2010.
(17) (a) Fukui, K. J. Phys. Chem. 1970, 74, 4161. (b) Fukui, K. Acc.
Chem. Res. 1981, 14, 363. (c) Gonzalez, C.; Schlegel, H. B. J. Phys.
Chem. 1990, 94, 5523.
(6) For related studies on Y−H bond cleavage by pincer complexes,
see: (a) Li, J.; Shiota, Y.; Yoshizawa, K. J. Am. Chem. Soc. 2009, 131,
13584. (b) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc.
2009, 131, 14168. (c) van der Vlugt, J. I.; Lutz, M.; Pidko, E. A.; Vogt,
D.; Spek, A. L. Dalton Trans. 2009, 6, 1016. (d) Staubitz, A.; Sloan, M.
E.; Robertson, A. P. M.; Friedrich, A.; Schneider, S.; Gates, P. J.;
Schmedt auf der Gunne, J.; Manners, I. J. Am. Chem. Soc. 2010, 132,
13332. (e) Huff, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133,
18122. (f) Sun, Y.; Koehler, C.; Tan, R.; Annibale, V. T.; Song, D.
Chem. Commun. 2011, 47, 8349. (g) del Pozo, C.; Iglesias, M.;
Sanchez, F. Organometallics 2011, 30, 2180. (h) Li, J.; Yoshizawa, K.
́
Bull. Chem. Soc. Jpn. 2011, 84, 1039. (i) Scharf, A.; Goldberg, K. I.;
Vigalok, A. J. Am. Chem. Soc. 2013, 135, 967.
(7) (a) Klinkenberg, J. L.; Hartwig, J. F. Angew. Chem., Int. Ed. 2011,
50, 86. (b) van der Vlugt, J. I. Chem. Soc. Rev. 2010, 39, 2302.
(c) Aubin, Y.; Fischmeister, C.; Thomas, C. M.; Renaud, J.-L. Chem.
Soc. Rev. 2010, 39, 4130.
721
dx.doi.org/10.1021/om401053j | Organometallics 2014, 33, 715−721