σ-bond metathesis between M-X and RC(O)X′ (M = Pt, Pd; X, X′ = Cl, Br, I): Facile determination of the relative Δ G values of the oxidative additions of RC(O)X to an M(0) complex, evidence by density functional theory calculations, and synthetic applications

Article abstract of DOI:10.1021/om400157a

The novel utility of the ligand exchange reaction between M-X and RC(O)X′ (X, X′ = halogen; R = aryl, alkyl) is described. The relative ΔGs (ΔΔGs) of the oxidative additions of acid halides RC(O)X to M(PPh₃)₂L_n (M = Pt, Pd) were determined using the halogen-exchange reactions between X of trans-M(X)[C(O)R](PPh₃)₂ and X′ of RC(O)X′. Experimental thermodynamics data are reasonably consistent with those obtained by density functional theory (DFT) calculations. Activation parameters obtained by experiments as well as a systematic DFT study supported the fact that reactions occurred through slightly distorted quadrangular pentacoordinated σ-bond metatheses, in which the Cl atom underwent a more indirect course than the Br atom. Moreover, exchange reactions were employed as the accessible prototype for the conversion of halogen ligands of nickel triad complexes into heavier halogen ligands.

Full text of DOI:10.1021/om400157a

Article
pubs.acs.org/Organometallics
σ‑Bond Metathesis between M−X and RC(O)X′ (M = Pt, Pd; X, X′ = Cl,
Br, I): Facile Determination of the Relative ΔG Values of the Oxidative
Additions of RC(O)X to an M(0) Complex, Evidence by Density
Functional Theory Calculations, and Synthetic Applications
Hitoshi Kuniyasu,*,† Atsushi Sanagawa,† Daisuke Nakane,† Takanori Iwasaki,† Nobuaki Kambe,*,†
Karan Bobuatong,‡ Yunpeng Lu,§,‡ and Masahiro Ehara*,‡
†Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
‡Institute for Molecular Science, Nishigo-Naka 38, Myodaiji, Okazaki 444-8585, Japan
§Division of Chemistry and Biochemistry, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore
S
* Supporting Information
ABSTRACT: The novel utility of the ligand exchange reaction
between M−X and RC(O)X′ (X, X′ = halogen; R = aryl, alkyl) is
described. The relative ΔGs (ΔΔGs) of the oxidative additions of
acid halides RC(O)X to M(PPh3)2Ln (M = Pt, Pd) were determined
using the halogen-exchange reactions between X of trans-M(X)[C-
(O)R](PPh3)2 and X′ of RC(O)X′. Experimental thermodynamics
data are reasonably consistent with those obtained by density
functional theory (DFT) calculations. Activation parameters
obtained by experiments as well as a systematic DFT study
supported the fact that reactions occurred through slightly distorted
quadrangular pentacoordinated σ-bond metatheses, in which the Cl
atom underwent a more indirect course than the Br atom. Moreover,
exchange reactions were employed as the accessible prototype for the
conversion of halogen ligands of nickel triad complexes into heavier halogen ligands.
between M1−X (M1 = transition metal) and M2−R (M2 =
INTRODUCTION
■
metals such as Mg, Zn, and B; R = carbon or heteroatom
functional group) is also widely employed in many catalytic
reactions such as cross-coupling (eq 3).3 For reactions
represented by eq 4, Tanaka and co-workers briefly reported
the ligand-exchange reaction of PhTe of trans-Pd(TePh)(Ph)-
(PEt3)2 with I of PhI to afford trans-Pd(I)(Ph)(PEt3)2.4a
However, the general significance of ligand-exchange reactions
between M−X and R−X′ has not been completely recognized.4
Herein, we wish to demonstrate the following: (1) the utility
of such ligand-exchange reactions for determining the relative
ΔGs of the oxidative addition of acid halides RC(O)X (1, X =
Cl; 2, X = Br; 3, X = I) to M(PPh3)2Ln (4, M = Pt; 5, M = Pd),
producing trans-M(X)[C(O)R](PPh3)2 (6, M = Pt, X = Cl; 7,
M = Pt, X = Br; 8, M = Pt, X = I; 9, M = Pd, X = Cl; 10, M =
Pd, X = Br; 11, M = Pd, X = I) and nL (eq 5), (2) its reaction
mechanism by density functional theory (DFT) methods, and
(3) synthetic application of the method for the conversion of
M−X bonds into M−X′ bonds with heavier halogens.
Ligand-exchange reactions are fundamental transformations in
organometallic chemistry, and their representative reaction
types are shown in Scheme 1.1 Equation 1 represents an
Scheme 1. Representative Reaction Types of Ligand-
a
Exchange Reactions ( )
a
Legend: L, neutral ligand; X, X′, halogen or pseudo-halogen.
exchange between neutral compounds L1 and L2, a process
involved in a number of transition-metal-catalyzed reactions for
incorporating organic substrates into the metal catalyst and
liberating products from the coordination site. Exchange of
M1−X (X = anionic element or functionality) with a different
low-valent metal complex (M2) is known as redox trans-
metalation (eq 2).2 Transmetalation that involves an exchange
Received: February 27, 2013
Published: March 13, 2013
© 2013 American Chemical Society
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ΔGExc‑I‑Br of this ligand exchange reaction, it can be concluded
that the addition of 3a to Pt(PPh3)2Ln (4) producing trans-8a
and nL is −10.9
0.4 kJ/mol (ΔΔGOA‑I‑Br) more favorable
than that of 2a to 4, yielding trans-7a and nL. A similar
treatment of trans-Pt(Cl)[C(O)Ph](PPh3)2 (trans-6a) with
PhC(O)I (3a) gave both trans-Pt(I)[C(O)Ph](PPh3)2 (trans-
8a) and PhC(O)Cl (1a) exclusively within 25 min at 20 °C.
Although ΔΔGOA‑I‑Cl cannot be directly calculated from these
experimental data, it is quantitatively evaluated by assuming a
system comprising 1 equiv of 1a, 2a, 3a, and 4 (F (C + 3a)).
Consider the addition reactions of 1a, 2a, and 3a to 4 to
produce G (trans-6a + 2a + 3a + nL = D + 3a), H (trans-7a +
1a + 3a + nL = E + 3a), and I (trans-8a + 1a + 2a + nL)
accompanied by ΔGOA‑Cl, ΔGOA‑Br, and ΔGOA‑I, respectively.
The value of ΔΔGOA‑I‑Cl is clearly the gap between G and I: i.e.,
RESULTS AND DISCUSSION
■
During the course of our studies to clarify the reactivity of C−X
bonds of RC(O)X toward M(0) (M = Pt, Pd),5−8 we found
that the type 4 ligand-exchange reaction between trans-
M(X)[C(O)R](PPh3)2 and RC(O)X′ occurred successfully.
For instance, the solution of trans-Pt(Cl)[C(O)Ph](PPh3)2
(trans-6a; 0.02 mmol, δ 20.4, JPt−P = 3360 Hz by 31P NMR
spectrum) and PhC(O)Br (2a; 0.02 mmol) in benzene-d6 (0.7
mL) at 35 °C produced an equilibrium mixture of trans-6a + 2a
(system A) and trans-Pt(Br)[C(O)Ph](PPh3)2 (trans-7a δ 19.8,
JPt−P = 3340 Hz) + PhC(O)Cl (1a) (system B) within 24 h
(Scheme 2, eq 6); in this reaction, Cl of trans-6a was exchanged
with Br of 2a. Neither the intermediate nor the cis isomer was
detected during the reaction.
the sum of ΔΔGOA‑Br‑Cl and ΔΔGOA‑I‑Br (−26.1
0.8 kJ/
mol).12,13 Moreover, ΔΔG can be calculated more simply by
eliminating the isolated trans-Pt(X)[C(O)Ph](PPh3)2 by the
reaction starting with 1a, 2a, and Pt(PPh3)2(C2H4) (4a),
resulting in the formation of an equilibrium mixture with a K
value identical with that determined from the result of the
reaction of eq 6. Similarly, the reactions between the
corresponding palladium complexes trans-Pd(Cl)[C(O)Ph]-
(PPh3)2 (trans-9a) and PhC(O)Br (2a) afforded an equilibrium
mixture of trans-9a + 2a and trans-Pd(Br)[C(O)Ph](PPh3)2
(trans-10a) + 1a within 60 min at 20 °C: the ΔΔGOA‑Br‑Cl value
was −14.6 0.1 kJ/mol. From the reaction of trans-10a with
3a producing an equilibrium mixture of trans-Pd(Br)[C(O)-
Ph](PPh3)2 (trans-10a) + 3a and trans-Pd(I)[C(O)Ph](PPh3)2
(trans-11a) + 2a, ΔΔGOA‑I‑Br was determined to be −6.9 0.1
kJ/mol. Accordingly, ΔΔGOA‑I‑Cl was calculated to be −21.5
0.2 kJ/mol. These results are summarized in Tables 1 and 2.
Scheme 2. ΔGExc‑Br‑Cl Calculation by the Halogen-Exchange
Reaction
Table 1. ΔΔGOA‑X′‑X by Experiment and ΔΔGOA‑X′‑X‑t by DFT
Calculation (kJ/mol) (M = Pt)
theor
X′
X
exptl ΔΔGOA‑X′‑X
ΔGOA‑X‑t
ΔΔGOA‑X′‑X‑t
By applying the equilibrium constants K to the equation ΔG
= −RT ln K, the energy gap between A and B (ΔGExc‑Br‑Cl) was
calculated as −15.2 0.7 kJ/mol (Scheme 2).9 Considering a
reaction system consisting of 1 equiv of PhC(O)Cl (1a),
PhC(O)Br (2a), and Pt(PPh3)2Ln (4) (Scheme 3, C), the
Br
I
Cl
Br
Cl
−15.2 0.7
−10.9 0.4
−26.1 0.8
−38.3
−55.7
−67.2
−17.3
−11.5
−28.9
I
Table 2. ΔΔGOA‑X′‑X by Experiment and ΔΔGOA‑X′‑X‑t by DFT
Calculation (kJ/mol) (M = Pd)
Scheme 3. Evaluation of ΔΔGOA‑Br‑Cl
theor
X′
X
exptl ΔΔGOA‑X′‑X
ΔGOA‑X‑t
ΔΔGOA‑X′‑X‑t
Br
I
Cl
Br
Cl
−14.6 0.1
−6.9 0.1
−21.5 0.2
−15.7
−36.2
−49.2
−20.5
−13.0
−33.5
I
Next, ΔGOA values for the addition of PhC(O)X to
M(PPh3)2Ln (M = Pt, Pd) were theoretically evaluated using
M(PH3)2(C2H4) (4a′, M = Pt; 5a′, M = Pd) as model
compounds. The value of ΔGOA‑Cl‑t (t = theoretical) for the
formation of trans-Pt(Cl)[C(O)Ph](PH3)2 (trans-6a′) and
C2H4 from PhC(O)C (1a) and 4a′ was found to be −38.3
kJ/mol by DFT calculations with the TPSS functional.14,15
Similarly, ΔGOA‑Br‑t and ΔGOA‑I‑t were calculated as −55.7 and
−67.2 kJ/mol, respectively (the fourth column of Table 1).
Therefore, ΔΔGOA‑Br‑Cl‑t, ΔΔGOA‑I‑Br‑t, and ΔΔGOA‑I‑Cl‑t were
−17.3, −11.5, and −28.9 kJ/mol, respectively (the fifth column
of Table 1). The data for the corresponding palladium
oxidative addition of 1a to 4 gives D (trans-6a + 2a + nL = A +
nL) with free energy change ΔGOA‑Cl, whereas the reaction of
2a with 4 gives E (trans-7a + 1a + nL = B + nL), accompanied
by ΔGOA‑Br
.
Accordingly, ΔGExc‑Br‑Cl obtained from eq 6 is equal to the
free energy gap between ΔGOA‑Br and ΔGOA‑Cl (ΔGExc‑Br‑Cl
=
ΔΔGOA‑Br‑Cl).10,11
Similarly, a solution of trans-7a and PhC(O)I (3a) produced
an equilibrium mixture of trans-7a + 3a and trans-Pt(I)[C(O)-
Ph](PPh3)2 (trans-8a) + PhC(O)Br (2a); therefore, from
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complexes are also summarized in Table 2. ΔGOA‑Cl‑t, ΔGOA‑Br‑t
,
ΔΔG of the oxidative addition of acid halides to Pt(PPh3)2Ln
(4) can be determined from the present ligand-exchange
reaction; however, the process itself is not involved in the
transformation. This fact also demonstrated that the formation
of Pt(IV) intermediates can be ruled out when the geometrical
analogy between the advancing pathway and the backward
pathway is considered.18 Moreover, to obtain information
about the effect of the polarity of the solvent, the reaction of
trans-6a with 2a in CD2Cl2 was monitored by 31P NMR
spectroscopy, and the reaction rate was compared with that of
benzene-d6. As a result, there was no remarkable difference
observed in reaction rate. In addition, the rate of the ligand-
exchange reaction was hardly influenced by the addition of free
PPh3, TEMPO, or galvinoxyl, which suggests that participation
of both the cationic complex {Pt[C(O)Ph](PPh3)3}+X− and
radical species was improbable. To obtain additional
information about the reaction mechanism, the activation
parameters of the reaction of trans-6a (0.01 mmol) with an
excess of 2a (0.2 mmol) to afford trans-7a and 1a were
calculated by measuring the temperature dependence of
reaction rate (−10 to +20 °C). The values of ΔH⧧ and ΔS⧧
were successfully measured to be 44 3 and −148 9 J/(K
mol), respectively.
and ΔGOA‑I‑t were −15.7, −36.2, and −49.2 kJ/mol,
respectively (the fourth column of Table 2). Therefore,
ΔΔGOA‑Br‑Cl‑t, ΔΔGOA‑I‑Br‑t, and ΔΔGOA‑I‑Cl‑t were −20.5,
−13.0, and −33.5 kJ/mol, respectively (the fifth column of
Table 2). These results demonstrate that ΔΔG values obtained
from the experiment are relatively consistent with those of the
theoretical calculations, indicating the reliability of the ΔΔG
calculations.
The methodology of ΔΔG calculation is not limited to the
reaction using benzoyl halides. The values of ΔΔGOA‑X′‑X for
the oxidative addition of t-BuCH2C(O)X (1b, X = Cl; 2b, X =
Br; 3b, X = I) to Pt(PPh3)2Ln (4) can be determined by a
similar procedure (Table 3).
Table 3. ΔΔGOA‑X′‑X of the Oxidative Addition of t-
BuCH2C(O)X to Pt(PPh3)2Ln (4) (kJ/mol)
Next, the mechanisms of the σ-bond metatheses shown in
Scheme 5, a direct route from trans-6a-1 (mechanism 1) and
The result showed that the values of ΔΔGOA‑Br‑Cl and
ΔΔGOA‑I‑Br are comparable to those of the oxidative addition of
benzoyl halides: ΔΔGOA‑Br‑Cl and ΔΔGOA‑I‑Br were −15.4 0.6
and −7.2 0.2 kJ/mol, respectively, showing that ΔΔGOA‑Br‑Cl
Scheme 5. Possible σ-Bond Metathesis Mechanisms via
Pentacoordinated Complexes
is slightly greater than ΔΔGOA‑I‑Br
.
To gain insight into the mechanism of the present halogen
exchange, the reaction of trans-Pt(Cl)[C(O)Ph](PPh3)2 (trans-
6a) with p-MeC6H4C(O)Br (2c) was examined (eq 7).
The reaction selectively afforded a mixture of trans-6a and
trans-Pt(Br)[C(O)Ph](PPh3)2 (trans-7a) in a ratio of 2:98.
Neither trans-Pt(Cl)[C(O)C6H4Me-p](PPh3)2 (trans-6c) nor
trans-Pt(Br)[C(O)C6H4Me-p](PPh3)2 (trans-7c) was observed,
suggesting that the reaction of trans-Pt(Cl)[C(O)Ph]1(PPh3)2
(trans-6a-1) with [PhC(O)]2Br (2a-2) provides trans-Pt(Br)-
[C(O)Ph]1(PPh3)2 (trans-7a-1) and [PhC(O)]2Cl (1a-2)
(Scheme 4).16,17 The mechanism involving reductive elimi-
nation of PhC(O)Cl (1a) from trans-6a to give coordinatively
unsaturated Pt(PPh3)2, followed by the oxidative addition of
PhC(O)Br (2a), to form trans-Pt(Br)[C(O)Ph](PPh3)2 (trans-
7a) for the reaction shown in eq 6 is ruled out.
metathesis after trans-to-cis isomerization (mechanism 2), were
theoretically examined with the M06 functional.19 The
transition state TS1 was successfully located for mechanism
1, and the energy diagram of the reaction coordinate and two
different views of the structure of TS1 are shown in Figures 1
and 2, respectively.20
Scheme 4. Retention of Benzoyl Ligand by Halogen
Exchange
Figure 1. Reaction coordinate of pentaoordinated σ-bond metathesis
from trans-6a-1 (mechanism 1).
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Figure 3. Selected bond distances (Å) of the optimized structures of
reactants, TS1, and products.
roundabout route than the Br atom during the course of σ-bond
metathesis. The CO bond length of C2 of TS1 is 1.185 Å,
which is barely different from that of free 2a-2 and 1a-2 (1.190
Å).
The structure of the transition state TS2 during the σ-bond
metathesis via cis-6a-1 was also found. The reaction coordinate
and structure of the transition state TS2 are shown in Figures 4
Figure 2. Structure of TS1 of the Pt complex via pentacoordinated σ-
bond metathesis from trans-6a-1 (two different views).
TS1 is 48.1 kJ/mol energetically higher than the reactants
(trans-6a-1 + 2a-2). The value is relatively consistent with ΔH⧧
obtained from the experimental data. Moreover, the value of
ΔS⧧ calculated theoretically was −137.9 J/(K mol), which is
also consistent with the experimental data.21 The selected bond
distances of the optimized structures of reactants, transition
state, and products involved in the reaction mechanism are
summarized in Table 4 and Figure 3. When the Pt−Cl bond of
Figure 4. Reaction coordinate of pentacoordinated σ-bond metathesis
from cis-6a-1.
and 5, respectively. The activation energy required to form TS2
from cis-6a-1 is 69.5 kJ/mol, which is slightly greater than that
required to form TS1 from trans-6a-1. However, the energy of
Table 4. Selected Bond Distances (Å) of the Optimized
Structures of Reactants, Transition State, and Products of
the Reaction Mechanism through Pentacoordinated σ-Bond
Metathesis from trans-6a-1 to trans-7a-1
trans-6a-1
TS1
trans-7a-1
1a-2
2a-2
RPt−Br
RPt−Cl
RC−Br
RC−Cl
RC−O
2.82
2.97
2.13
2.38
1.185
2.63
2.55
2.01
1.84
1.221
1.221
1.190
1.190
trans-6a-1 (2.55 Å) is compared with that of TS1 (2.97 Å), the
bond is stretched by 0.42 Å. On the other hand, the C−Br
bond elongation difference between 2a-2 (2.01 Å) and TS1
(2.13 Å) is only 0.12 Å. The bond length difference of C−Cl
between TS1 (2.38 Å) and 1a-2 (1.84 Å) is 0.54 Å, whereas the
Pt−Br bond in TS1 (2.82 Å) shrinks by 0.19 Å with respect to
that in trans-7a-1a (2.63 Å). Therefore, both Pt−Cl and C−Cl
bonds undergo more dynamic bond changes than do C−Br and
Pt−Br bonds. In other words, the Cl atom takes a more
Figure 5. Structure of TS2 of the Pt complex via pentaoordinated σ-
bond metathesis.
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cis-6a-1 is higher than that of trans-6a-1 by 53.6 kJ/mol. Hence,
the mechanism through TS2 is less probable.22
The transition state of the pentacoordinated σ-bond
metathesis was also located for the reaction of the
corresponding palladium complex, trans-9a-1, with [PhC-
(O)]2Br (2a-2). The reaction coordinate and structure of the
transition state TS3 are shown in Figures 6 and 7, respectively.
The selected interatomic distances of reactants, transition
state, and the products of the reaction are summarized in Table
5 and Figure 8.
Table 5. Selected Bond Distances (Å) of the Optimized
Structures of Reactants, Transition State, and Products of
the Reaction Mechanism through Pentacoordinated σ-Bond
Metathesis from trans-9a-1 to trans-10a-1
trans-9a-1
TS3
trans-10a-1
1a-2
2a-2
RPd−Br
RPd−Cl
RC−Br
RC−Cl
RC−O
2.68
3.25
2.30
2.26
1.180
2.58
2.49
2.01
1.84
1.215
1.215
1.190
1.190
Figure 6. Reaction coordinate of pentacoordinated σ-bond metathesis
from trans-9a-1.
Figure 8. Selected bond distances (Å) of the optimized structures of
reactants, TS8, and products.
When the bond of Pd−Cl of trans-9a-1 is compared with that
of TS3 (2.49 Å vs 3.25 Å), the gap is 0.76 Å. The difference in
the bond lengths of C−Br between 2a-2 (2.01 Å) and TS3
(2.30 Å) is 0.29 Å. On the other hand, the difference in the
bond lengths of C−Cl between TS3 (2.26 Å) and 1a-2 (1.84
Å) and that in the bond length of Pd−Br between TS3 (2.68
Å) and trans-10a-1 (2.58 Å) are 0.42 and 0.10 Å, respectively.
Again, these results indicated that the Cl atom takes a more
circuitous route than the Br atom during σ-bond metathesis.
On the basis of the aforementioned discussions, we conclude
that pentacoordinated σ-bond metathesis of trans-M(X)[C-
(O)R]2(PPh3)2 and RC(O)X′ is the most probable mechanism
for the present halogen-exchange reaction.
Because it became evident that only halogen atoms were
exchanged, the utility of this transformation as a halogen-
exchange prototype was examined as follows: after the reaction
of 1.0 mmol of cis-[Pt(Cl)2(PPh3)2] (12) with 4.0 mmol of
MeC(O)(Br) (2d) in CH2Cl2 (50 mL) at 20 °C for 30 min, the
solvent, excess 2d (bp 75 °C−77 °C), and byproduct of
MeC(O)(Cl) (1d) (bp 52 °C) were removed by subjecting the
reaction mixture to reduced pressure to produce the analytically
pure cis-[Pt(Br)2(PPh3)2] quantitatively.23 The removal of salt
by filtration, washing with water, drying with desiccant, and
recrystallization, which are generally required by the conven-
tional Cl-to-Br exchange reaction with a typical element metal
salt such as LiBr and NaBr, was not required.24 Moreover, the
corresponding iodide was isolated similarly by the treatment of
12 with CH3C(O)I (3d; bp 108 °C) and subsequent
evaporation. Similarly, the reaction of trans-[Pd(Cl)2(PPh3)2]
with 2d and 3d afforded trans-[Pd(Br)2(PPh3)2] and trans-
[Pd(I)2(PPh3)2], respectively.25 This methodology of the
halogen-exchange reaction was also applicable to complexes
with alkyl phosphine or nickel complexes. The conversions of
trans-[Pd(Cl)2(PEt3)2] and [Ni(Cl)2(dppe)] into trans-[Pd-
Figure 7. Structure of TS3 of the Pd complex formed from trans-9a-1
via pentacoordinated σ-bond metathesis (two different views).
The energy of TS3 is only 15.5 kJ/mol higher than that of the
reactant (trans-9a-1 + 2a-2), which is consistent with the fact
that the reaction of trans-9a with 2a occurred more quickly
than that using the corresponding platinum complex trans-6a.
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Yamamoto, Y. J. Chem. Soc., Chem. Commun. 1986, 442. (c) Martinezí-
(X)2(PEt3)2] and [Ni(X)2(dppe)] (X = Br, I) were easily
achieved.26,27
́
́
Prieto, L. M.; Melero, C.; Río, D.; Palma, P.; Campora, J.; Alvarez, E.
Organometallics 2012, 31, 1425. (d) Yamamoto, T.; Kohara, T.;
Osakada, K.; Yamamoto, A. Bull. Chem. Soc. Jpn. 1983, 56, 2147.
(e) Yamamoto, T.; Kohara, T.; Yamamoto, A. Bull. Chem. Soc. Jpn.
1981, 54, 2010.
CONCLUSION
■
The significance of the present study is summarized as follows:
(1) the reactions of trans-M(X)[C(O)R](PPh3) with RC(O)X′
produced clean equilibrium mixtures of trans-M(X)[C(O)R]-
(PPh3)/RC(O)X′ and trans-M(X′)[C(O)R](PPh3)/RC(O)X,
(2) ΔG values were equal to the relative ΔGs of the oxidative
additions of RC(O)X/ RC(O)X′ to M(PPh3)2Ln, which was
clearly supported by DFT calculations, (3) both experimental
and computational studies substantiated that the reaction
occurred via pentacoordinated σ-bond metathesis, in which
significant behavioral disparity was suggested between Cl and
Br atoms, and (4) the ligand-exchange reaction can be utilized
as a simple prototype to convert chloro ligands into heavier
halogen ligands of nickel triad complexes. We believe that the
present study demonstrates the unappreciated utility of the type
4 ligand-exchange reaction, shown in Scheme 1. Further studies
to elucidate the scope and limitations of the present
methodology are in progress.
(5) For reviews: (a) Kuniyasu, H. In Catalytic Heterofunctionalization;
Togni, A., Grutzmacher, H., Eds.; Wiley-VCH: Weinheim, Germany,
̈
2001; p 217. (b) Kuniyasu, H.; Kambe, N. Chem. Lett. 2006, 35, 1320.
(c) Kuniyasu, H.; Kurosawa, H. Chem. Eur. J. 2002, 8, 2660.
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2006, 24, 2949.
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(9) The value was obtained as an average of ΔGs obtained from
several experiments. The standard error was calculated by using a
statistical method equipped in Excel for expressing the margin of error
(http://en.wikipedia.org/wiki/Standard_error_(statistics)).
(10) The oxidative additions of acid halides to Pt(PPh3)n have been
well-documented. See: (a) Cook, C. D.; Jauhal, G. S. Can. J. Chem.
1967, 45, 301. (b) Baird, M. C.; Wilkinson, G. J. Chem. Soc. A. 1967,
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Chem. 1975, 97, 307.
(11) For catalytic reactions triggered by the oxidative addition of acid
halides to low-valent transition-metal complexes, see: (a) Iwai, T.;
Fujiwara, T.; Terao, J.; Tsuji, Y. J. Am. Chem. Soc. 2010, 132, 9602.
(b) Iwai, T.; Fujiwara, T.; Terao, J.; Tsuji, Y. J. Am. Chem. Soc. 2009,
131, 6668. (c) Zhao, X.; Yu, Z. J. Am. Chem. Soc. 2008, 130, 8136.
(d) Kashiwabara, T.; Fuse, K.; Hua, R.; Tanaka, M. Org. Lett. 2008, 10,
5469. (e) Kashiwabara, T.; Kataoka, K.; Hua, R.; Shimada, S.; Tanaka,
M. Org. Lett. 2005, 7, 2241. (f) Sugihara, T.; Satoh, T.; Miura, M.
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(12) Because the reactions of 1a, 2a, and 3a with Pt(PPh3)2(C2H4)
(4a) and Pt(PPh3)4 (4b) both quantitatively produce trans-6a, trans-
7a, and trans-8a, respectively, nL can be either C2H4 or 2PPh3.
(13) The error was calculated using the law of error propagation
(http://en.wikipedia.org/wiki/Propagation_of_uncertainty).
(14) (a) Frisch, M. J. et al. GAUSSIAN09, Revision B.01; Gaussian,
Inc., Wallingford, CT, 2010. (b) Tao, J. M.; Perdew, J. P.; Staroerov, V.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Text, figures, and tables giving experimental procedures as well
as energy diagrams, structures, and coordinates by DFT studies.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: kuni@chem.eng.osaka-u.ac.jp (H.K.); kambe@chem.
eng.osaka-u.ac.jp (N.K.); ehara@ims.ac.jp (M.E.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study was partially supported financially by a grant from
the Ministry of Education, Culture, Sports, Science and
Technology of Japan. M.E. acknowledges the support from a
Grant-in-Aid for Scientific Research from the JSPS (No.
22000009) and JENESYS programs. The computations were
partially performed at the Research Center for Computational
Science, Okazaki, Japan.
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Organometallics
Article
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