Hydrogen bonding behavior of amide-functionalized α-diimine palladium complexes

Article abstract of DOI:10.1021/om500978n

A class of (N,N′-diaryl-α-diimine)Pd complexes bearing amide substituents on the N-aryl rings is described. Hydrogen bonding interactions involving the amide groups influence the structures, isomer distributions, and ligand coordination behavior of these compounds. The amide-functionalized α-diimine ligands (2,6-ⁱPr₂-Ph)N=CMeCMe=N(2-C(=O)NMe₂-6-ⁱPr-Ph) (4a), (2,6-ⁱPr₂-Ph)N=CMeCMe=N(2,6-(C(=O)NMe₂)₂-Ph) (4b), and (2-C(=O)NMe₂-6-ⁱPr-Ph)N=CMeCMe=N(2-C(=O)NMe₂-6-ⁱPr-Ph) (4c) were prepared by condensation reactions of 2,3-butanedione and the appropriate anilines. The attempted preparation of (2,6-ⁱPr₂-Ph)N=CMeCMe=N(2-C(=O)NHMe-6-ⁱPr-Ph) (4d) yielded the corresponding 1,2-dihydroquinazolinone derivative 4d′ formed by nucleophilic attack of the amide nitrogen at the proximal imine carbon. 4a and 4b react with (cod)PdMeCl to yield square planar (α-diimine)PdMeCl complexes 5a,a′ and 5b,b′, respectively, which exist as two isomers that differ in the orientation (trans/cis) of the Pd-Me ligand and the amide-substituted arylimine unit. 4c reacts with (MeCN)₂PdCl₂ and (cod)PdMeCl to yield (4c)PdCl₂ (6c-anti,syn) and (4c)PdMeCl (5c-anti,syn), which exhibit anti/syn isomerism due to hindered rotation of the C_aryl-N bonds. In the solid state, the amide oxygen atoms in 6c-anti and 5c-syn engage in hydrogen bonding with cocrystallized CH₂Cl₂ solvent molecules. 4d′ reacts with (MeCN)₂PdCl₂ via ring-opening metalation to afford the α-diimine complex (4d)PdCl₂ (6d). Transmetalation of 6d with SnMe₄ yields (4d)PdMeCl (5d,d′) as a mixture of trans and cis isomers. The reaction of 5d,d′ with AgOAc yields (4d)PdMe(OAc) (7d) as a single isomer in which the Pd-Me group is trans to the amide-functionalized arylimine unit. 5d, 6d, and 7d exhibit intramolecular N-H···Cl and N-H···O hydrogen bonding interactions involving the amide NH units. The reactions of 5a,a′, 5c-anti, and 5d,d′ with AgSbF₆ in the presence of pyrazole yield the corresponding (α-diimine)PdMe(pz)⁺SbF₆^- salts (8a,c,d; pz = pyrazole), which exhibit an intramolecular hydrogen bond between the amide oxygen and the pyrazole NH unit. 8a,c,d undergo partial dissociation of pyrazole in CD₃CN solution to generate the corresponding CD₃CN complexes 9a,c,d. The non-hydrogen-bonded complex {(2,6-ⁱPr₂-Ph)N=CMeCMe=N(2,6-ⁱPr₂-Ph)}PdMe(pz)⁺SbF₆^- (8e) and its pyrazole dissociation product {(2,6-ⁱPr₂-Ph)N=CMeCMe=N(2,6-ⁱPr₂-Ph)}PdMe(CD₃CN)⁺SbF₆^- (9e) were generated in a similar fashion. The pyrazole dissociation constants, K_eq = [(α-diimine)PdMe(CD₃CN)⁺] × [pz] × [(α-diimine)PdMe(pz)⁺]^-1, vary in the order 8e > 8d > 8a > 8c, span more than 2 orders of magnitude, and reflect the enhancement of pyrazole binding in 8a,c,d by amide-pyrazole hydrogen bonding. The intramolecular hydrogen bonding in 8c strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔG = 2.8(1) kcal mol^-1) relative to the case of 8e.

Full text of DOI:10.1021/om500978n

Article
pubs.acs.org/Organometallics
Hydrogen Bonding Behavior of Amide-Functionalized α‑Diimine
Palladium Complexes
Feng Zhai and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
S
* Supporting Information
ABSTRACT: A class of (N,N′-diaryl-α-diimine)Pd complexes
bearing amide substituents on the N-aryl rings is described.
Hydrogen bonding interactions involving the amide groups
influence the structures, isomer distributions, and ligand
coordination behavior of these compounds. The amide-
functionalized α-diimine ligands (2,6-iPr2-Ph)N
CMeCMeN(2-C(O)NMe2-6-iPr-Ph) (4a), (2,6-iPr2-
Ph)NCMeCMeN(2,6-(C(O)NMe2)2-Ph) (4b), and
(2-C(O)NMe2-6-iPr-Ph)NCMeCMeN(2-C(
O)NMe2-6-iPr-Ph) (4c) were prepared by condensation
reactions of 2,3-butanedione and the appropriate anilines.
The attempted preparation of (2,6-iPr2-Ph)NCMeCMeN(2-C(O)NHMe-6-iPr-Ph) (4d) yielded the corresponding 1,2-
dihydroquinazolinone derivative 4d′ formed by nucleophilic attack of the amide nitrogen at the proximal imine carbon. 4a and
4b react with (cod)PdMeCl to yield square planar (α-diimine)PdMeCl complexes 5a,a′ and 5b,b′, respectively, which exist as
two isomers that differ in the orientation (trans/cis) of the Pd−Me ligand and the amide-substituted arylimine unit. 4c reacts
with (MeCN)2PdCl2 and (cod)PdMeCl to yield (4c)PdCl2 (6c-anti,syn) and (4c)PdMeCl (5c-anti,syn), which exhibit anti/syn
isomerism due to hindered rotation of the Caryl−N bonds. In the solid state, the amide oxygen atoms in 6c-anti and 5c-syn
engage in hydrogen bonding with cocrystallized CH2Cl2 solvent molecules. 4d′ reacts with (MeCN)2PdCl2 via ring-opening
metalation to afford the α-diimine complex (4d)PdCl2 (6d). Transmetalation of 6d with SnMe4 yields (4d)PdMeCl (5d,d′) as a
mixture of trans and cis isomers. The reaction of 5d,d′ with AgOAc yields (4d)PdMe(OAc) (7d) as a single isomer in which the
Pd−Me group is trans to the amide-functionalized arylimine unit. 5d, 6d, and 7d exhibit intramolecular N−H···Cl and N−H···O
hydrogen bonding interactions involving the amide NH units. The reactions of 5a,a′, 5c-anti, and 5d,d′ with AgSbF6 in the
−
presence of pyrazole yield the corresponding (α-diimine)PdMe(pz)+SbF6 salts (8a,c,d; pz = pyrazole), which exhibit an
intramolecular hydrogen bond between the amide oxygen and the pyrazole NH unit. 8a,c,d undergo partial dissociation of
pyrazole in CD3CN solution to generate the corresponding CD3CN complexes 9a,c,d. The non-hydrogen-bonded complex
−
{(2,6-iPr2-Ph)NCMeCMeN(2,6-iPr2-Ph)}PdMe(pz)+SbF6 (8e) and its pyrazole dissociation product {(2,6-iPr2-Ph)N
CMeCMeN(2,6-iPr2-Ph)}PdMe(CD3CN)+SbF6 (9e) were generated in a similar fashion. The pyrazole dissociation
−
constants, Keq = [(α-diimine)PdMe(CD3CN)+] × [pz] × [(α-diimine)PdMe(pz)+]−1, vary in the order 8e > 8d > 8a > 8c, span
more than 2 orders of magnitude, and reflect the enhancement of pyrazole binding in 8a,c,d by amide−pyrazole hydrogen
bonding. The intramolecular hydrogen bonding in 8c strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔG = 2.8(1) kcal
mol−1) relative to the case of 8e.
epoxidation,8 alkene hydroformylation,4d,9 and allylation of
INTRODUCTION
Hydrogen bonding interactions1 can strongly influence the
■
indoles.10 Second-sphere hydrogen bond donor groups play an
important role in substrate activation in the catalytic hydro-
structures and ligand-binding preferences of coordination and
genation and transfer hydrogenation of carbonyl compounds,
organometallic compounds and provide a potentially versatile
imines, and nitriles4c,11 and the hydrogenation of CO2.12
tool for controlling their reactivity. The incorporation of
Hydrogen bonding groups also provide critical proton relay
hydrogen bonding units in the ancillary ligands of metal
pathways in electrocatalytic H2 oxidation and production,13 O2
reduction,14 and CO2 reduction.15
complexes provides a means to stabilize high-energy species,2
control molecular recognition,3 activate chemical bonds,
mediate proton transfer, enable new reactivity modes, and
influence selectivity in catalytic reactions.4 For example,
molecular recognition through hydrogen bonding in the second
coordination sphere enables highly regio- and/or stereo-
selective catalytic organic transformations, including sp3 C−H
oxidation,5 C−H amination,6 sulfoxidation of sulfides,7 alkene
Pd complexes that contain ancillary α-diimine ligands have
been used as catalysts for olefin polymerization,16 copoly-
merization of olefins with polar comonomers,17 olefin/CO
Received: September 25, 2014
© XXXX American Chemical Society
A
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copolymerization,18 cationic polymerization of vinyl ethers,19
dimerization of vinyl ethers to acetals,20 oligomerization and
functionalization of alkynes,21 selective hydrogenation of
alkynes to Z-alkenes,22 and other reactions.23 (α-Diimine)Pd
complexes have also been used in the stoichiometric activation
of aliphatic,24 aryl,25 and indenyl C−H bonds26 and the C−N
bond in nitromethane.27
Many structural modifications of α-diimine ligands have been
explored to manipulate their electronic and steric properties.
Additionally, multifunctional α-diimine ligands have been
designed to enable hemilabile coordination of pendant donors,
external control of reactivity, and modulation of selectivity
through secondary interactions. Representative examples of
multifunctional (α-diimine)Pd species are shown in Chart 1.
pyridyl units enabled coordination of zinc(II) salphen
complexes in trinuclear species F, and the (α-diimine)PdMe+
cation derived from F yielded high-MW syndiotactic copolymer
in catalytic CO/4-tert-butylstyrene copolymerization.32
Here we describe the syntheses, structures, and dynamics of
several (α-diimine)PdRX and (α-diimine)PdRL+ complexes
that contain amide functional groups in the α-diimine ligand.
The amide carbonyl group behaves as a hydrogen bond
acceptor, and the (secondary) amide NH unit behaves as a
hydrogen bond donor. Intramolecular hydrogen bonding in the
second coordination sphere is an important feature of these
complexes and strongly influences their structures and ligand-
binding affinities.
RESULTS AND DISCUSSION
■
Chart 1. Representative Multifunctional (α-Diimine)Pd
Complexes
Tertiary Amide-Functionalized α-Diimine Ligands.
The monoamide-functionalized α-diimine (2,6-iPr2-Ph)N
CMeCMeN(2-C(O)NMe2-6-iPr-Ph) (4a) was synthe-
sized by the route in Scheme 1 starting from 3-isopropylan-
Scheme 1
thranilic acid (1).33 The reaction of 1 with thionyl chloride to
generate the corresponding acyl chloride in situ, followed by
reaction with aqueous dimethylamine, afforded o-amino-
benzamide 2a. Acid-catalyzed condensation of 2a and α-
ketaimine 3 yielded 4a.34 The 1H NMR spectrum of 4a at room
temperature contains three sets of isopropyl resonances, which
implies that rotation around the Caryl−N bonds is slow on the
1
NMR time scale. The H NMR spectrum also contains two
NMe resonances, consistent with the expected slow rotation
around the amide OC−NMe2 bond.
The unsymmetrical bisamide-functionalized α-diimine
(2,6-iPr2-Ph)NCMeCMeN(2,6-(C(O)NMe2)2-Ph)
(4b), which contains two dimethylamide groups on the same
aryl ring, was prepared by condensation of aniline 2b35 and α-
1
ketaimine 3 (Scheme 2). The room-temperature H NMR
spectrum of 4b is consistent with the expected Cs symmetry.
Scheme 2
Coordination of the pendant ether and thiophene units was
observed in A and B.24,28 A cyclophane-type (α-diimine)Pd
catalyst with a trans-azobenzene unit (C) exhibited excellent
activity and stereoselectivity in the polymerization of
diallylmalonate, whereas photoisomerization to the cis-
azobenzene isomer significantly diminished both properties.29
Hemilabile F···Pd interactions in D30 and binding of Al
cocatalysts to the pyridine unit of E31 are believed to strongly
influence the molecular weights (MWs) and branching
densities in polyethylene produced by these catalysts. The m-
B
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i
The spectrum contains two Pr doublets, corresponding to the
i
inequivalent Me groups within each Pr unit, and two singlets
for the −NMe2 groups due to restricted rotation around the
amide OC−NMe2 bonds. Warming the sample to 70 °C results
in coalescence of two NMe signals (Supporting Information).
The free energy barrier for amide NMe exchange is ΔG⧧ =
16.5(4) kcal mol−1, which is within the normal range for N,N-
dialkylamides.36
The isomeric bisamide-functionalized α-diimine (2-C(
O)NMe2-6-iPr-Ph)NCMeCMeN(2-C(O)NMe2-6-iPr-
Ph) (4c), which contains one amide group on each N-aryl unit,
was prepared by condensation of 2,3-butanedione with 2 equiv
1
of aniline 2a (Scheme 3). The H NMR spectra of 4c in
Scheme 3
Figure 1. Molecular structure of 4c-anti. Hydrogen atoms are omitted.
Selected bond lengths (Å) and angles (deg): C13−N2 1.273(3),
C13−C13#1 1.489(5), C9−N2 1.407(3), C10−O1 1.229(3), C10−
N1 1.329(3); N2−C13−C13#1 115.7(3), C13−N2−C9 121.6(2),
O1−C10−N1 121.4(2), C10−N1−C12 119.7(2).
8.7:1 mixture of isomers by crystallization from CH2Cl2/
hexanes at −40 °C; this mixture equilibrates to a 4.5:1 mixture
in CD2Cl2 at room temperature. Similarly, 5b,b′ was isolated as
a 6.5:1 isomer mixture, which equilibrates to a 17:1 mixture at
room temperature. For these square planar (α-diimine)PdMeCl
complexes, two isomers that differ in the orientation (trans/cis)
of the Pd−Me ligand and the amide-substituted arylimine unit
are possible.38 The NOESY spectrum of 5a,a′ exhibits
correlations between the Pd−Me resonance of the major
isomer 5a and two isopropyl methyl resonances, which
establishes that the Pd−Me group of this isomer is cis to the
N-(2,6-iPr2-Ph) imine unit and trans to the amide-substituted
arylimine unit. The NOESY spectrum of 5b,b′ exhibits Pd−
Me/iPr correlations for the major isomer 5b, which establishes
that the Pd−Me ligand is also cis to the N-2,6-iPr2-Ph imine
unit and trans to the amide-substituted arylimine unit. The
equilibrium isomer ratios reflect the preference for the strong
donor Pd−Me group to be positioned trans to the imine unit
that is the weaker donor.
CDCl3, CD2Cl2, and toluene-d8 at room temperature contain
two complete sets of resonances, indicating the presence of two
C2-symmetric isomers in a ca. 1.4:1 ratio. The two species were
assigned to be the syn and anti isomers that result from
restricted rotation around the Caryl−N bonds.37 4c-anti was
isolated by crystallization from a CH2Cl2/hexanes solution of
the 4c-anti/4c-syn mixture and characterized by X-ray
diffraction (Figure 1). The NCMeCMeN unit is planar
and adopts an s-trans conformation. The N-aryl groups are
nearly perpendicular to the NCMeCMeN plane (dihedral
angle C8−C9−N2−C13 = −74.2(3)°), and the amide groups
are rotated ca. 65° out of the plane of the adjacent aryl ring
(dihedral angle C9−C8−C10−O1 = 114.5(3)°).
Pd Complexes of 4c. The reaction of 4c (1.4:1 anti/syn
mixture) with (MeCN)2PdCl2 in CH2Cl2 at room temperature
yields a 1:1.7 mixture of isomeric (α-diimine)PdCl2 complexes
6c-anti and 6c-syn (Scheme 5). Heating a CDCl2CDCl2
solution of the product mixture at 110 °C for 1 h produces a
5.7:1 equilibrium mixture of 6c-anti/6c-syn. The thermody-
namically more stable isomer 6c-anti was selectively crystallized
as the solvate 6c-anti·3CH2Cl2 from CH2Cl2/hexanes and
identified by X-ray diffraction. The solid-state structure of 6c-
anti·3CH2Cl2 is shown in Figure 3. The Pd center exhibits
square planar geometry, and the two N-aryl groups are
perpendicular to the Pd plane. The amide oxygen atoms (O1,
O2) are directed toward the α-diimine side of the molecule and
do not interact with Pd (O1···Pd1, O2···Pd1 distances >4 Å).
However, each oxygen atom forms a hydrogen bond with a
CH2Cl2 molecule.39 The two N-aryl units show noticeable
bowing to the side of O1, as quantified by the deviations of the
C1 (0.264(6) Å) and C17 (0.186(6) Å) atoms from the N1−
Pd1−N3 least-squares plane.
Two dynamic processes are observed for 4c in solution by
1H NMR spectroscopy in the temperature range 20 to 90 °C:
rotation around the Caryl−N bonds, which interconverts 4c-syn
and 4c-anti, and rotation around the amide OC−NMe2 bonds,
which permutes the two NMe groups within a given amide
unit. With reference to the labeling scheme for the methyl
groups in Scheme 3, 4c-anti/4c-syn interconversion results in
a/a′, b/b′, and c/c′ exchange, while amide OC−NMe2 bond
rotation results in b/c and b′/c′ exchange. Free energies of
activation for these processes were determined by total line
shape analysis (Figure 2); ΔG⧧
= 16.4(11) kcal
syn→anti,20 °C
mol−1; ΔG⧧
= 18.0(11) kcal mol−1, ΔG⧧
=
b/c,20 °C
b′/c′,20 °C
17.6(8) kcal mol−1.
Pd Complexes of 4a and 4b. The reaction of α-diimine
ligands 4a and 4b with (cod)PdMeCl in Et2O yields the
corresponding square planar (α-diimine)PdMeCl complexes
5a,a′ and 5b,b′ (Scheme 4). Complex 5a,a′ was isolated as an
1H NMR analysis of pure 6c-anti enabled assignment of the
NMR spectra of both isomers. The kinetically favored isomer
6c-syn was isolated in pure form by recrystallization of the 1:1.7
C
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Figure 2. Variable-temperature 1H NMR spectra of 4c in toluene-d8 (10 to 90 °C, 500 MHz). The δ 3.05−2.00 region is shown. Left: Experimental
spectra. Right: Simulated spectra (gNMR). The labeling scheme is given in Scheme 3. First-order rate constants (s−1) determined by simulation are
shown for each temperature.
Scheme 4
Scheme 5
kinetic anti/syn isomer mixture. The barrier for isomerization
of 6c-syn to 6c-anti is ΔG⧧ = 29.1(3) kcal mol−1 at 80(1) °C
(Supporting Information).
The reaction of 4c (1.4:1 anti/syn mixture) with (cod)-
PdMeCl in Et2O yields a 5.2:1 mixture of isomeric (α-
diimine)PdMeCl complexes 5c-anti and 5c-syn (Scheme 6). In
CD2Cl2, anti/syn isomerization produces a 4.6:1 equilibrium
mixture of 5c-anti and 5c-syn in a few hours at room
temperature. Crystallization of a 5.2:1 isomer mixture at −40
°C from CH2Cl2/hexanes yields crystals of the bis-CH2Cl2
solvate of the minor isomer, 5c-syn·2CH2Cl2, which was
characterized by X-ray diffraction (Figure 4). The Pd1−N2
bond is ca. 0.11 Å longer than the Pd1−N1 bond, which is
attributed to the stronger trans influence of the Pd−Me ligand
D
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Figure 3. Molecular structure of 6c-anti in 6c-anti·3CH2Cl2. Left: Front view. Hydrogen atoms and solvent molecules are omitted. Right: Side view,
which shows the O1···H30a#1−C30#1 and O2···H31b−C31 hydrogen bonds. The C29 CH2Cl2 molecule is omitted. Selected bond lengths (Å) and
angles (deg): N1−Pd1 1.984(4), N3−Pd1 2.002(4), Cl1−Pd1 2.2565(16), Cl2−Pd1 2.2436(16), C13−N1 1.280(6), C15−N3 1.284(6), C13−C15
1.463(8), C1−N1 1.439(7), C17−N3 1.416(7), C10−O1 1.212(7), C26−O2 1.217(7), C10−N2 1.326(7), C26−N4 1.337(8); N1−Pd1−N3,
79.18(18), N1−Pd1−Cl2 174.71(13), N3−Pd1−Cl2 95.55(13), N1−Pd1−Cl1 95.29(13), N3−Pd1−Cl1 174.47(13), Cl2−Pd1−Cl1 89.98(6),
O1−C10−N2 122.3(6), O2−C26−C22 118.7(6).
feature, was targeted as a ligand for Pd(II) complexes. The
secondary o-aminobenzamide 2-NH2-3-iPr-PhC(O)NHMe
(2d) was prepared analogously to 2a. Acid-catalyzed con-
densation of 2d with α-ketaimine 3 yields 1,2-dihydroquinazo-
linone derivative 4d′ instead of the α-diimine 4d, via imine
condensation to form 4d and subsequent ring closure between
the secondary amide group and the adjacent imine CN unit.
The structure of 4d′ was established by X-ray diffraction and is
shown in Figure 5. Two independent molecules are present in
the asymmetric unit, which are linked by intermolecular N−
H···O hydrogen bonds to form infinite chains (Supporting
Information). The C15−N2 (1.440(5) Å) and C15−N3
(1.445(5) Å) bond lengths establish that both of these bonds
Scheme 6
1
are single bonds. The H NMR spectrum of 4d′ in CDCl3
contains a broad singlet at δ 5.11 for the NH unit and a sharp
singlet at δ 3.28 for the NMe group. The absence of JNH−NMe
coupling shows that 4d′ does not undergo ring opening to form
α-diimine 4d in solution. The 13C NMR resonance for the
aminal carbon C15 appears at δ 76.7. 4d was not observed as an
intermediate or a coproduct in Scheme 7.
The reaction between pro-ligand 4d′ and (MeCN)2PdCl2 in
CD2Cl2 for 3 d at room temperature or 1 d at 40 °C results in
heterocycle opening and formation of the α-diimine complex
(4d)PdCl2 (6d, Scheme 8). This reaction may proceed by
initial κ2-CN,NH-coordination of 4d′ to Pd, which induces
the ring-opening of 4d′. The α-diimine structure of 6d is
stabilized by chelation to Pd(II).43
The structure of 6d was confirmed by X-ray diffraction and is
shown in Figure 6. The secondary amide N−H bond points
toward a chloride ligand, and the associated N3···Cl1 (3.436(3)
Å) and H3N···Cl1 (2.68(6) Å) distances are consistent with an
N−H···Cl hydrogen bonding interaction.44 The Pd1−Cl2 bond
is ca. 0.02 Å shorter than the Pd1−Cl1 bond, which may reflect
the weaker donor ability and trans influence of the N-(2-C(
O)NHMe-6-iPr-Ph) imine unit compared to the N-(2,6-iPr2-
Ph) imine unit. It is also possible that the H3N···Cl1 hydrogen
bond contributes to the lengthening of the Pd1−Cl1 bond.
versus the chloride ligand. One CH2Cl2 molecule is hydrogen
bonded to the O2 atom.40
The interconversion of the anti and syn isomers of 5c and 6c
requires net rotation around one (or both) N−Caryl bond, and
the rate of this process is probably determined by steric
factors.41 The Pd1−N2 bond in 5c-syn, which is trans to the
Pd−Me group, is ca. 0.16 Å longer than the Pd−N bonds in 6c-
anti, due to the trans influence of the Pd−Me ligand. The
C18−C23 aryl group that is bonded to N2 in 5c-syn is thus less
crowded than the aryl groups in 6c-anti and may experience a
lower barrier to rotation, which would explain the faster anti/
syn isomerization of 5c (hours at room temperature) versus 6c
(hours at 80 °C).42
Secondary-Amide-Functionalized (α-Diimine)Pd
Chloride Complexes. The α-diimine (2,6-iPr2-Ph)N
CMeCMeN(2-C(O)NHMe-6-iPr-Ph) (4d, Scheme 7),
which contains a secondary amide group as the key structural
E
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Figure 4. Molecular structure of 5c-syn in 5c-syn·2CH2Cl2. Left: Front view. Hydrogen atoms and solvent molecules are omitted. Right: Side view,
which shows the O2···H31a−C31 hydrogen bond. The C30/C30X CH2Cl2 molecule is omitted. Selected bond lengths (Å) and angles (deg): N1−
Pd1 2.0455(15), N2−Pd1 2.1560(16), Cl1−Pd1 2.2855(5), C1−Pd1 2.0288(18), C14−N1 1.288(2), C16−N2 1.285(2), C14−C16 1.501(3), C2−
N1 1.442(2), C18−N2 1.435(2), C11−O1 1.230(2), C27−O2 1.230(3), C11−N3 1.344(3), C27−N4 1.342(3); N1−Pd1−N2 77.03(6), N1−Pd1−
Cl1 176.04(4), N2−Pd1−Cl1 100.04(4), C1−Pd1−N1 96.42(7), C1−Pd1−N2 173.11(7), C1−Pd1−Cl1 86.60(6), O1−C11−N3 122.72(18),
O2−C27−N4 122.4(2).
Scheme 7
Figure 5. Molecular structure of one independent molecule of 4d′.
The structure of the other independent molecule is similar. Hydrogen
atoms are omitted except H2N. Selected bond lengths (Å) and angles
(deg): C13−N1 1.248(5), C13−C15 1.536(6), C18−O1 1.222(5),
C18−N3 1.342(5), N2−H2N 0.98(3); N1−C13−C15 117.4(5), N2−
1
The H NMR spectrum of 6d in CD2Cl2 contains a doublet
C15−C13 108.9(4), N3−C15−C13 110.8(4), N2−C15−N3
at δ 3.03 (J = 4.9 Hz) for the amide NMe group, which is
coupled to the amide NH resonance (br q, J = 4.9 Hz) at δ
6.75. The solid-state IR spectrum of 6d exhibits a νN−H
stretching band at 3330 cm−1, which is consistent with the
intramolecular N−H···Cl hydrogen bond observed in the
crystal structure.45
107.8(4), O1−C18−N3 121.5(5).
Scheme 8
4d′ does not react with (cod)PdMeCl in Et2O at room
temperature. However, 6d reacts with SnMe4 in CH2Cl2 at
room temperature to yield a 16:1 equilibrium mixture of
(4d)PdMeCl complexes 5d and 5d′, which differ in the relative
positions of the Pd−Me group and the amide-substituted
arylimine unit (5d trans, 5d′ cis, Scheme 9). The major isomer
5d was selectively crystallized from CH2Cl2/hexanes at −40 °C
and identified by X-ray diffraction. Isomer 5d is stable in
CD2Cl2 at −40 °C, but isomerizes to the equilibrium 5d,d′
mixture within 5 min at room temperature.
Å) and H3N···Cl1 (2.53(3) Å) distances are 0.09 and ca. 0.15 Å
shorter, and the N3−H3N···Cl1 angle (172(3)°) is 31° larger,
than the corresponding values for 6d. The Pd1−N2 bond is ca.
0.10 Å longer than the Pd1−N1 bond due to the stronger trans
influence of the Pd−Me ligand compared to chloride.
The structure of 5d is shown in Figure 7. The secondary
amide group is hydrogen bonded to the Pd−Cl ligand in a
manner similar to that observed for 6d. The N3···Cl1 (3.345(4)
The amide 1H NMR NH resonance for 5d in CD2Cl2
solution appears as a broad signal at δ 7.48, which overlaps
an aromatic hydrogen resonance. This assignment was
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Figure 7. Molecular structure of complex 5d. Hydrogen atoms are
omitted except H3N. Selected bond lengths (Å) and angles (deg):
N1−Pd1 2.026(3), N2−Pd1 2.121(3), C17−Pd1 2.021(3), Cl1−Pd1
2.2979(12), N3−H3N 0.82(3); C17−Pd1−N1 95.92(12), C17−
Pd1−N2 173.44(12), N1−Pd1−N2 77.54(10), C17−Pd1−Cl1
90.03(10), N1−Pd1−Cl1 172.83(7), N2−Pd1−Cl1 96.54(8),
H3N···Cl1−Pd1 75.0(7).
Figure 6. Molecular structure of complex 6d. Hydrogen atoms are
omitted except H3N. Selected bond lengths (Å) and angles (deg):
N1−Pd1 2.018(3), N2−Pd1 2.019(3), Cl1−Pd1 2.2929(8), Cl2−Pd1
2.2701(9), N3−H3N 0.91(6); N1−Pd1−N2 79.15(11), N1−Pd1−
Cl2 94.71(8), N2−Pd1−Cl2 173.79(8), N1−Pd1−Cl1 172.56(8),
N2−Pd1−Cl1 94.12(8), Cl2−Pd1−Cl1 92.06(3), N3−H3N···Cl1
141(4), H3N···Cl1−Pd1 82.8(11).
ability of the Pd−Me group of 5d versus the Pd−Cl groups in
6d.
Scheme 9
Secondary-Amide-Functionalized (α-Diimine)Pd Ac-
etate Complex. The salt metathesis reaction of 5d,d′ and
AgOAc yields (4d)PdMe(OAc) (7d, Scheme 10), which exists
Scheme 10
confirmed by the COSY spectrum, which exhibits a correlation
between the amide NH signal and the amide NMe signal at δ
2.92 (d, J = 4.9 Hz). The amide NH signal of 5d′ appears at δ
6.29. The 1.19 ppm downfield shift of the amide NH resonance
of 5d versus 5d′ is due to the intramolecular hydrogen bond in
the former species. The IR spectrum of 5d (thin film) contains
a νN−H stretching band at 3302 cm−1.
The equilibrium 5d/5d′ ratio is significantly greater than the
equilibrium 5a/5a′ ratio despite the similarity in the steric and
electronic properties of the α-diimine ligands in these
compounds. The additional stabilization in 5d by the
intramolecular hydrogen bond is most likely responsible for
this effect.
The structural and spectroscopic data discussed above
establish that 5d has a stronger intramolecular hydrogen
bond than 6d. In particular, the N3···Cl1 distance of 5d is 0.09
Å shorter than that of 6d, the amide 1H NMR NH resonance of
5d is 0.73 ppm downfield versus that of 6d, and the IR νN−H
value for 5d is 28 cm−1 lower than the value for 6d. This
difference is ascribed to higher basicity of the chloride ligand in
5d versus those in 6d, which results from the stronger donor
as a single isomer in CD2Cl2 solution. The structure of 7d was
confirmed by X-ray crystallography (Figure 8). The acetate
ligand is coordinated to Pd in a κ1-fashion, lies perpendicular to
the Pd square plane, and is cis to the amide-functionalized
arylimine donor. The non-Pd-bound acetate oxygen O2 is
directed toward the amide NH unit, and the N3···O2 (2.866(2)
Å) and H3N···O2 (2.06(2) Å) distances are indicative of an
N−H···O hydrogen bond.46
1
The H NMR resonance for the amide NH unit of 7d in
CD2Cl2 solution appears at low field (δ 9.43), and the IR νN−H
stretching band appears at 3213 cm−1 in the solid state. These
data confirm the presence of hydrogen bonding. The IR
spectrum of 7d also exhibits asymmetric and symmetric acetate
νOCO stretching bands at 1590 and 1329 cm−1, which shift to
1557 and 1317 cm−1, respectively, when the carboxyl carbon is
13C-labeled. The difference between the νOCO,asym and νOCO,sym
values (ΔνOCO = 261 cm−1) is characteristic of a highly
unsymmetrically bound acetate ligand.47 The ΔνOCO value for
7d is 32 cm−1 lower than that for the model complex {(2,6-iPr2-
G
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Figure 9 and features an N−H···O hydrogen bond between the
pyrazole ligand and the amide oxygen (N4···O1 2.815(4) Å,
Figure 8. Molecular structure of complex 7d. Hydrogen atoms are
omitted except H3N. Selected bond lengths (Å) and angles (deg):
N1−Pd1 2.0176(14), N2−Pd1 2.1233(14), C1−Pd1 2.0158(17),
O1−Pd1 2.0247(12), C18−O2 1.231(2), C18−O1 1.278(2), C18−
C19 1.512(2), N3−H3N 0.82(2); C1−Pd1−N1 97.43(6), C1−Pd1−
O1 87.24(6), N1−Pd1−O1 173.58(5), C1−Pd1−N2 174.35(6), N1−
Pd1−N2 77.49(5), O1−Pd1−N2 98.02(5), C18−O1−Pd1
120.25(11), O2−C18−O1 125.83(16), O2−C18−C19 120.05(16),
O1−C18−C19 114.11(15), N3−H3N···O2 168(2), H3N···O2−C18
133.5(6).
Figure 9. Molecular structure of 8d. Hydrogen atoms are omitted
except H4N and H5N. The SbF6 anion is omitted. Selected bond
−
lengths (Å) and angles (deg): N1−Pd1 2.029(3), N2−Pd1 2.142(2),
N3−N4 1.348(4), N3−Pd1 2.016(3), C1−Pd1 2.019(3), C14−O1
1.229(4); N3−Pd1−C1 86.94(13), N3−Pd1−N1 172.32(11), C1−
Pd1−N1 96.80(12), N3−Pd1−N2 98.56(10), C1−Pd1−N2
174.42(13), N1−Pd1−N2 77.85(10), H4N···O1−C14 112.6(12).
Ph)NCMeCMeN(2,6-iPr2-Ph)}PdMe(OAc) (7e, ΔνOCO
= 293 cm−1, Scheme 10), which lacks the amide group, due to
the presence of the hydrogen bond. For comparison, the
ΔνOCO value for the intramolecularly N−H···O hydrogen-
bonded Ir(III) κ1-formate compound κ3-P,N,P′-(iPr2P-
(CH2)2NH(CH2)2PiPr2)Ir(H)2(O2CH) reported by Hazari
and Crabtree is 265 cm−1.12a
The isomer of 7d in which the acetate ligand is trans to the
amide-functionalized arylimine unit was not observed and is
likely disfavored relative to 7d because its geometry would
preclude strong intramolecular N−H···O hydrogen bonding.
Amide-Functionalized (α-Diimine)Pd Pyrazole Com-
plexes. The reaction of 5a,a′ or 5d,d′ with AgSbF6 in the
presence of pyrazole yields pyrazole adducts 8a and 8d,
respectively (Scheme 11). Pyrazole adduct 8e derived from α-
diimine complex 5e that lacks an amide group was prepared in
the same manner. Complexes 8a and 8d exist as single isomers
in CD2Cl2 solution. The solid-state structure of 8d is shown in
H4N···O1 2.02(4) Å, N4−H4N···O1 166(4)°). The secondary
amide NH unit does not participate in intramolecular or
intermolecular hydrogen bonding in the solid state.
In the solid state, the pyrazole IR νN−H stretching bands for
8a and 8d appear at 3135 and 3137 cm−1, shifted ca. 230 cm−1
to lower frequency versus the νN−H band for 8e (3364 cm−1)
due to the N−H···O hydrogen bonding in 8a,d. Comparison of
1
the H NMR data for 8a,d,e provides strong evidence that the
pyrazole-amide hydrogen bonding is maintained in CD2Cl2
1
solution for 8a,d. The pyrazole H NMR NH resonances for
8a,d appear at δ > 14, ca. 4 ppm downfield from the pyrazole
NH resonance for 8e.
These (α-diimine)PdMe(pz)+ complexes undergo partial
dissociation of the pyrazole ligand in CD3CN solution (Scheme
12). Complex 8a, which bears the unsymmetrical α-diimine
ligand 4a, reacts in CD3CN to generate an equilibrium mixture
of free pyrazole and isomeric CD3CN adducts (4a)PdMe-
(CD3CN)+SbF6 (9a,a′, equilibrium ratio 1.3:1). Analogously,
−
Scheme 11
the secondary amide-functionalized α-diimine complex 8d
generates isomeric CD3CN adducts 9d,d′ (equilibrium ratio
1.1:1) in CD3CN. The model compound 8e also dissociates
pyrazole to yield 9e in CD3CN.
The equilibrium constants for pyrazole dissociation, Keq
=
[(α-diimine)PdMe(CD3CN)+] × [pz] × [(α-diimine)PdMe-
(pz)+]−1, were measured by 1H NMR and are listed in Table 1.
These values vary in the order 8e > 8d > 8a and span more
than a factor of 50. The lower values of Keq for 8a,d reflect the
intramolecular hydrogen bonding between the pyrazole NH
and amide carbonyl units, which enhances pyrazole binding.
The lower value of Keq for 8a versus 8d reflects the higher
basicity of the tertiary amide in 8a versus the secondary amide
in 8d.
Because 9a,a′ and 9d,d′ exist in two isomeric forms, there is
an extra entropic contribution that favors pyrazole dissociation
from 8a,d that is not present for 8e. To circumvent this issue,
H
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a
Scheme 12
Scheme 13
a
Scheme 14
a
−
Anion = SbF6 .
Table 1. Equilibrium Constants of Pyrazole Dissociation of
(α-Diimine)PdMe(pz)+ Complexes in CD3CN
ab
c
,
reaction
8a ⇌ 9a/9a′ + pz
Keq/M
7.7(3) × 10−5
3.3(4) × 10−5
3.7(1) × 10−4
8c-anti/8c-syn ⇌ 9c-anti/9c-syn + pz
8d ⇌ 9d/9d′ + pz
8e ⇌ 9e + pz
4.1(2) × 10−3
a
b
Conditions: CD3CN solvent, room temperature. Isomer ratios at
equilibrium are as follows: 9a/9a′ = 1.3:1; 8c-anti/8c-syn = 2.0:1; 9c-
c
anti/9c-syn = 1.6:1; 9d/9d′ = 1.1:1. Average values from three
independent measurements.
a
−
Anion = SbF6 .
bonding in 8c strengthens pyrazole binding by a factor of ca.
120 (i.e., ΔΔG = 2.8(1) kcal mol−1) relative to the case of 8e.
pyrazole complexes 8c-anti,syn were studied (Scheme 13). The
reaction of pure 5c-anti with AgSbF6 and pyrazole in CD2Cl2 at
room temperature yields a 13:1 kinetic mixture of isomeric
pyrazole adducts 8c-anti and 8c-syn in 5 min, which
equilibrates to a 1.5:1 isomer mixture within a few hours
(Supporting Information). The pyrazole 1H NMR NH
resonances (δ 14.42, broad singlet, 8c-anti and 8c-syn,
CD2Cl2 solvent) and thin-film IR νN−H stretching band (3131
cm−1) of the 8c-anti/8c-syn mixture establish the presence of
an intramolecular N−H···O hydrogen bond. 8c-anti,syn
undergoes partial pyrazole dissociation in CD3CN to yield a
mixture of CD3CN adduct 9c-anti and 9c-syn (Scheme 14;
equilibrium ratio 1.6:1) and a mixture of 8c-anti and 8c-syn
(equilibrium ratio 2.0:1). The apparent pyrazole dissociation
constant for 8c, Keq = [9c-anti,syn] × [pz] × [8c-anti,syn]−1,
CONCLUSION
■
Hydrogen bonding interactions involving amide substituents on
the N-aryl rings of (N,N′-diaryl-α-diimine)Pd complexes
strongly influence the structures and ligand coordination
behavior of (N,N′-diaryl-α-diimine)PdMeX and (N,N′-diaryl-
α-diimine)PdMeL+ complexes. The tertiary amide −C(
O)NMe2 group is a good hydrogen bond acceptor, whereas
the secondary amide −C(O)NHMe group behaves as an
acceptor or a donor. In the solid state, the amide oxygen atoms
in 6c-anti and 5c-syn engage in hydrogen bonding with
cocrystallized CH2Cl2 solvent molecules. Intramolecular hydro-
gen bonding influences the equilibrium isomer ratios of
unsymmetrical (α-diimine)PdMeX and (α-diimine)PdMeL+
complexes due to selective stabilization of the isomer that can
engage in hydrogen bonding, and leads to the greater ratio for
5d/5d′ versus the non-hydrogen-bonded 5a/5a′ and the
observation of a single isomer for the cases of acetate 7d and
pyrazole complexes 8a,d. The pyrazole dissociation constants in
1
was measured by H NMR (Table 1) and is decreased by a
factor of 2 compared to the Keq value for 8a. The lower value of
Keq for 8c versus 8a reflects the fact that both 8c and its
pyrazole dissociation product 9c exist as two isomers, so that
the entropic factor that contributes to the Keq for pyrazole
dissociation from 8a is absent. The intramolecular hydrogen
I
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CD3CN, Keq = [(α-diimine)PdMe(CD3CN)+] × [pz] × [(α-
diimine)PdMe(pz)+]−1, vary in the order 8e > 8d > 8a > 8c,
span more than 2 orders of magnitude, and reflect the
enhancement of pyrazole binding in 8a,c,d by amide-pyrazole
hydrogen bonding. The intramolecular hydrogen bonding in 8c
strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔG =
2.8(1) kcal mol−1) relative to the case of 8e. Future studies will
explore the influence of hydrogen bonding on the behavior of
amide-functionalized (N,N′-diaryl-α-diimine)Pd complexes in
olefin polymerization and other catalytic reactions.
(126 MHz, CDCl3): δ 171.6 (CO), 142.2, 133.5, 126.4, 125.3,
120.4, 117.2 (Ar), 39.4 (br, amide NMe), 34.9 (br, amide NMe), 27.5
(iPr methine), 22.2 (iPr methyl). IR (cm−1): νN−H, 3459, 3364; νCO
,
1611. HRMS (APCI-TOF, positive ion, m/z): calcd 207.1497 ([M +
H]+), found 207.1497.
2-Amino-N,N,N′,N′-tetramethylisophthalamide (2b).35
N,N,N′,N′-Tetramethyl-2-nitroisophthalamide (5.47 g, 20.6 mmol)
i
and iron powder (4.14 g, 3.6 equiv) were suspended in PrOH (30
mL), and the mixture was heated to reflux under air. An aqueous
NH4Cl solution (1.23 g in 20 mL of water, 1.1 equiv) was added to the
reaction mixture during reflux. The mixture turned rust-colored
instantly and was refluxed for an additional 22.5 h. The mixture was
vacuum-filtered through a Buchner funnel to remove most of the iron
powder. The PrOH were removed on a rotovap. The remaining
̈
EXPERIMENTAL SECTION
i
■
aqueous fraction was then filtered through a pad of Celite to give a
yellow solution. The solution was diluted to 300 mL, treated with
Na2CO3, and extracted with CH2Cl2. The organic phase was washed
with brine, dried with anhydrous MgSO4, filtered, and concentrated to
give white microcrystals (3.21 g, 66%). 1H NMR (500 MHz, CDCl3):
δ 7.12 (d, J = 7.6, 2H, Ar), 6.70 (t, J = 7.6, 1H, Ar), 4.37 (br s, 2H,
NH2), 3.05 (br s, 12H, amide NMe). 13C{1H} NMR (126 MHz,
CDCl3): δ 170.5 (CO), 143.5, 129.4, 122.0, 116.6 (Ar), 39.5 (br,
amide NMe), 35.4 (br, amide NMe). IR (cm−1): νN−H, 3481, 3370;
νCO, 1622. HRMS (ESI-TOF, positive ion, m/z): calcd 236.1399
([M + H]+), found 236.1400.
General Procedures. All manipulations of organometallic
compounds were performed under nitrogen or vacuum using Schlenk
or high-vacuum techniques or in a nitrogen-filled drybox unless
otherwise indicated. Nitrogen was purified by passage through
activated molecular sieves and Q-5 oxygen scavenger. Hexanes,
benzene, and toluene were purified by passage through activated
alumina and BASF R3-11 oxygen scavenger. THF, CH2Cl2, and Et2O
were purified by passage through activated alumina. All workup and
purification procedures for organic compounds were carried out with
reagent grade solvents in air. CDCl3 and CD2Cl2 were distilled from
P2O5 and stored under vacuum. CDCl2CDCl2 was distilled from P2O5
and stored under N2. CD3CN was distilled from CaH2 and stored
under N2. Toluene-d8 was purchased from Cambridge Isotope
Laboratories and used as received. 3-Isopropylanthranilic acid (1),33
N,N,N′,N′-tetramethyl-2-nitroisophthalamide,35 α-ketaimine 3,34
(cod)PdMeCl (cod = 1,5-cyclooctadiene),48 and complex 5e49 were
synthesized by literature procedures or modifications thereof.
2-Amino-3-isopropyl-N-methylbenzamide (2-NH2-3-iPr-
PhC(O)NHMe, 2d). A 500 mL round-bottom flask was charged
with 3-isopropylanthranilic acid (1, 10.0 g, 55.8 mmol), benzene (150
mL), and thionyl chloride (25 mL). The yellow suspension was
refluxed for 2.5 h under air to give an orange solution. The volatiles
were removed under vacuum to yield the crude acyl chloride as a red
oil. The oil was dissolved in dry THF (100 mL) and added dropwise
to a mixture of MeNH2 solution in THF (60 mL, 2.0 M, 2.2 equiv)
and Et3N (16.7 mL, 2.15 equiv) at 0 °C. The mixture was stirred at 0
°C for an additional 10 min and at room temperature for 20 min and
quenched with water (ca. 100 mL). The THF was removed on a
rotovap. The aqueous residue was extracted with EtOAc. The organic
phase was washed with brine, dried with anhydrous MgSO4, filtered,
and concentrated to give an orange oil. The residue was subjected to
flash column chromatography (silica, hexanes/EtOAc/Et3N = 82:14:5
by volume), concentrated, and washed with hexanes to yield pale
NMR spectra were recorded on a Bruker DMX-500 spectrometer in
Teflon-valved tubes at ambient temperature unless otherwise
indicated. H and 13C chemical shifts are reported relative to SiMe4
1
and were determined by reference to the residual H and 13C solvent
1
resonances. 19F NMR spectra were referenced externally to CFCl3 (δ
0). Coupling constants are given in hertz (Hz). NMR assignments
were made with the aid of COSY, NOESY, HMQC, and HMBC
experiments. For all compounds containing N,N-dimethylbenzamide
groups, the 13C NMR resonances at δ ca. 39.5 and 35.0 were assigned
to the amide N−Me groups that are trans and cis to O, respectively.50
Elemental analyses were performed by Robertson Microlit
Laboratories (Ledgewood, NJ, USA) or Columbia Analytical Services
(Tucson, AZ, USA). Infrared spectra were recorded on thin-film solid
samples on NaCl plates using a Nicolet NEXUS 470 FT-IR
spectrometer. Mass spectrometry was performed on an Agilent 6130
LC-mass spectrometer (low resolution) or an Agilent 6224 Tof-mass
spectrometer (high resolution). The listed m/z value corresponds to
the most intense peak in the isotope pattern.
1
yellow needles (7.48 g, 70%). H NMR (500 MHz, CDCl3): δ 7.21
(dd, J = 7.6, 1.1, 1H, Ar), 7.18 (dd, J = 7.8, 1.3, 1H, Ar), 6.67 (t, J =
7.7, 1H, Ar), 6.03 (br s, 1H, amide NH), 5.68 (br s, 2H, NH2), 2.97
(d, J = 4.9, 3H, amide NMe), 2.90 (septet, J = 6.8, 1H, iPr), 1.26 (d, J
i
= 6.8, 6H, Pr). 13C{1H} NMR (126 MHz, CDCl3): δ 170.9 (CO),
145.5, 133.7, 128.1, 124.9, 116.7, 116.4 (Ar), 27.3 (iPr methine), 26.6
(amide NMe), 22.1 (iPr methyl). IR (cm−1): νN−H, 3454, 3348; νCO
,
1610. HRMS (ESI-TOF, positive ion, m/z): calcd 193.1341 ([M +
H]+), found 193.1312.
2-Amino-3-isopropyl-N,N-dimethylbenzamide (2-NH2-3-iPr-
PhC(O)NMe2, 2a). A 500 mL round-bottom flask was charged with
3-isopropylanthranilic acid (1, 9.45 g, 52.7 mmol), benzene (120 mL),
and thionyl chloride (20 mL). The yellow suspension was refluxed for
19 h under air to give an orange solution. The volatiles were removed
under vacuum to form the crude acyl chloride as a red oil. The oil was
dissolved in dry THF (100 mL) and added dropwise to an aqueous
Me2NH solution (28 mL, 40 wt %, 4.2 equiv) at 0 °C. The mixture
was warmed to room temperature, stirred for an additional 40 min,
and quenched with water (ca. 100 mL). The THF was removed on a
rotovap. The aqueous residue was extracted with EtOAc. The organic
phase was washed with aqueous NaHCO3 solution and brine, dried
with anhydrous MgSO4, filtered, and concentrated to give a dark red
oil. The residue was subjected to flash column chromatography (silica,
hexanes/EtOAc/Et3N = 82:14:5 to 71:24:5 by volume) and
concentrated to give an orange oil, which crystallized at −30 °C
after 1 day. The resultant solid was washed with hexanes to yield a pale
(2,6-iPr2-Ph)NCMeCMeN(2-C(O)NMe2-6-iPr-Ph) (4a). A
Schlenk flask was charged with 3 (2.45 g, 10.0 mmol), 2a (2.17 g, 10.5
mmol, 1.05 equiv), a small amount of anhydrous TsOH (ca. 100 mg),
and benzene (100 mL) under nitrogen. The flask was equipped with a
Dean−Stark trap filled with 3 Å molecular sieves and a water
condenser. The mixture was refluxed under nitrogen for 40 h, then
cooled to room temperature, and quenched with Et3N (ca. 5 mL). The
volatiles were removed under vacuum to give a brown oil. The oil was
subjected to flash column chromatography (silica, hexanes/CH2Cl2/
Et3N = 80:20:0.5 by volume) and concentrated to give a yellow oil,
which crystallized at −30 °C to give yellow granular crystals. Yield:
1
1.65 g (53%). H NMR (500 MHz, CD2Cl2): δ 7.37−7.33 (m, 1H,
Ar), 7.16−7.13 (m, 4H, Ar), 7.07 (dd, J = 8.0, 7.3, 1H, Ar), 2.94 (s,
3H, H7), 2.83 (s, 3H, H6), 2.83 (septet, J = 6.8, 1H, iPr methine), 2.67
i
i
(septet, J = 6.8, 1H, Pr methine), 2.62 (septet, J = 6.8, 1H, Pr
methine), 2.07 (s, 3H, H1), 1.96 (s, 3H, H2), 1.22 (d, J = 6.8, 3H, iPr),
1.18 (d, J = 6.8, 3H, iPr), 1.17 (d, J = 6.8, 6H, iPr), 1.14 (d, J = 6.8, 6H,
iPr). 13C{1H} NMR (126 MHz, CD2Cl2): δ 170.3 (C4), 169.9 (C3),
168.1 (C5), 146.5, 145.0, 137.0, 135.40, 135.36, 126.6, 126.5, 125.0,
124.4, 124.2, 123.4, 123.3 (Ar), 38.1 (C6), 34.6 (C7), 29.0, 28.9, 28.7
1
yellow powder (7.04 g, 64%). H NMR (500 MHz, CDCl3): δ 7.16
(dd, J = 7.7, 1.4, 1H, Ar), 6.96 (dd, J = 7.6, 1.5, 1H, Ar), 6.74 (t, J =
7.6, 1H, Ar), 4.38 (br s, 2H, NH2), 3.06 (br s, 6H, amide NMe), 2.90
(septet, J = 6.8, 1H, Pr), 1.27 (d, J = 6.8, 6H, Pr). 13C{1H} NMR
i
i
J
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Organometallics
Article
(iPr methine), 23.4, 23.2, 23.0, 22.8 (2C), 22.7 (iPr methyl), 17.2 (C1),
16.6 (C2). IR (cm−1): νCN+CO, 1645. HRMS (ESI-TOF, positive
ion, m/z): calcd 456.2991 ([M + Na]+), found 456.3014.
8.28; N, 12.11. Found: C, 72.61; H, 7.94; N, 11.76. ESI-MS (1:1
CH2Cl2/MeOH, positive ion scan, m/z): 463.2 ([M + H]+).
(2,6-iPr2-Ph)NCMeCMeN(2,6-(C(O)NMe2)2-Ph) (4b). A
100 mL Schlenk flask was charged with 3 (1.37 g, 55.9 mmol), 2b
(1.43 g, 60.9 mmol, 1.1 equiv), a small amount of TsOH·H2O (ca. 50
mg), and benzene (40 mL) under nitrogen. The flask was equipped
with a Dean−Stark trap containing 3 Å molecular sieves and a water
condenser. The mixture was refluxed under nitrogen for 20 h, then
cooled to room temperature, and quenched with Et3N (ca. 5 mL). The
solvent was removed under vacuum to afford a dark oil. The oil was
subjected to flash column chromatography (silica, hexanes/CH2Cl2/
Et3N = 49:49:1 by volume) and concentrated to give a yellow powder
4d′. A Schlenk flask was charged with 2d (1.99 g, 9.55 mmol), 3
(3.52 g, 14.3 mmol, 1.5 equiv), and TsOH·H2O (99 mg, 0.06 equiv)
under nitrogen. Benzene (50 mL) was added via cannula. The flask
was equipped with a Dean−Stark trap containing 3 Å molecular sieves
and a water condenser. The mixture was refluxed under nitrogen for
19.5 h. The mixture was cooled to room temperature and quenched
with Et3N (ca. 5 mL). The volatiles were removed under vacuum to
give a brown oil. The oil was triturated with acetone (20 mL), leading
to formation of white crystals. The mixture was kept at −30 °C for 2
days and filtered. The crystals were washed with cold acetone and
1
1
(1.69 g, 65%). H NMR (500 MHz, CD2Cl2): δ 7.36 (d, J = 7.6, 2H,
Et2O. Yield: 1.81 g (46%, 2 crops). H NMR (500 MHz, CDCl3): δ
Ar), 7.23 (t, J = 7.6, 1H, Ar), 7.15 (d, J = 7.4, 2H, Ar), 7.08 (dd, J =
7.83 (dd, J = 7.8, 1.1, 1H, Ar), 7.28 (dd, J = 7.6, 1.1, 1H, Ar), 7.03−
6.97 (m, 3H, Ar), 6.90 (t, J = 7.7, 1H, Ar), 5.01 (br, 1H, amine NH),
3.28 (s, 3H, amide NMe), 2.94 (septet, J = 6.8, 1H, iPr methine), 2.27
8.4, 6.9, 1H, Ar), 2.97 (s, 6H, H7), 2.88 (s, 6H, H6), 2.60 (septet, J =
i
6.9, 2H, Pr methine), 2.11 (s, 3H, H1), 1.88 (s, 3H, H2), 1.15 (d, J =
i
i
6.9, 6H, Pr), 1.13 (d, J = 6.8, 6H, Pr). 13C{1H} NMR (126 MHz,
CD2Cl2): δ 171.4 (C3), 169.1 (C5), 167.8 (C4), 146.3, 143.4, 135.3,
128.1, 127.6, 124.7, 124.3, 123.4 (Ar), 38.1 (C6), 34.6 (C7), 28.7 (iPr
i
i
(septet, J = 6.9, 1H, Pr methine), 1.93 (septet, J = 6.9, 1H, Pr
methine), 1.91 (s, 3H, MeCN), 1.68 (s, 3H, CMe(N)(N)), 1.26 (d,
i
i
i
J = 6.8, 3H, Pr), 1.24 (d, J = 6.8, 3H, Pr), 1.01 (d, J = 6.8, 3H, Pr),
0.95 (d, J = 6.9, 3H, iPr), 0.87 (d, J = 6.8, 3H, iPr), 0.81 (d, J = 6.9, 3H,
iPr). 13C{1H NMR (126 MHz, CDCl3): δ 173.4 (CN), 164.7 (C
O), 144.8, 142.8, 136.2, 135.8, 133.3, 129.5, 126.6, 123.9, 123.1, 122.9,
120.0, 117.2 (Ar), 76.7 (CMe(NH)(NMe)), 29.9 (NMe), 28.1, 27.8,
27.1 (iPr methine), 25.3 (CMe(NH)(NMe)), 23.54, 23.45, 23.35, 22.8,
22.6, 22.3 (iPr methyl), 16.9 (MeCN). IR (cm−1): νN−H, 3340;
νCN+CO, 1633. HRMS (ESI-TOF, positive ion, m/z): calcd
420.3015 ([M + H]+), found 420.3012.
methine), 23.3, 22.9 (iPr methyl), 17.5 (C1), 16.6 (C2). Key H−13C
1
HMQC correlations (CD2Cl2): δ/δ 2.97/34.6 (H7/C7), 2.88/38.1
(H6/C6), 2.11/17.5 (H1/C1), 1.88/16.6 (H2/C2). IR (cm−1):
νCN+CO, 1645. HRMS (ESI-TOF, positive ion, m/z): calcd
463.3073 ([M + H]+), found 463.3044.
5a,a′. A Schlenk flask was charged with 4a (98 mg, 0.23 mmol),
(cod)PdMeCl (59 mg, 0.22 mmol, 1.0 equiv), and Et2O (8 mL). The
mixture was stirred at room temperature for 24 h to give an orange
suspension. The yellow solid was collected by vacuum filtration. Yield:
80.0 mg (65%). The equilibrium isomer ratio 5a/5a′ is ca. 4.5:1 in
CD2Cl2 at room temperature based on integration of the Pd−Me
resonances. 5a: 1H NMR (500 MHz, CD2Cl2): δ 7.45 (dd, J = 7.9, 1.1,
1H, Ar), 7.31−7.27 (m, 4H, Ar), 7.11 (dd, J = 7.5, 1.3, 1H, Ar), 3.25
(septet, J = 6.9, 1H, H10), 3.09 (s, 3H, H6), 3.03 (s, 3H, H7), 3.00
(septet, J = 6.9, 1H, H13 or 16), 2.95 (septet, J = 6.9, 1H, H13 or 16), 2.16
(s, 3H, H2), 2.00 (s, 3H, H1), 1.44 (d, J = 6.8, 3H, H8), 1.34 (d, J = 6.8,
(2-C(O)NMe2-6-iPr-Ph)NCMeCMeN(2-C(O)NMe2-
6-iPr-Ph) (4c-anti,syn). A Schlenk flask was charged with 2,3-
butanedione (1.7 mL, 19 mmol), 2a (8.38 g, 40.6 mmol, 2.1 equiv),
TsOH·H2O (250 mg), and benzene (150 mL) under nitrogen. The
flask was equipped with a Dean−Stark trap containing 3 Å molecular
sieves and a water condenser. The mixture was refluxed under nitrogen
for 65 h. The mixture was cooled to room temperature and quenched
with Et3N (ca. 5 mL). The volatiles were removed under vacuum to
give a brown solid. The solid was recrystallized from hexanes/CH2Cl2
to give brownish-yellow microcrystals. The crystals were collected by
vacuum filtration, washed with cold acetone, and dried under vacuum
to give light yellow crystals. Yield: 3.80 g (43%). The equilibrium 4c-
anti/4c-syn ratio in CD2Cl2, CDCl3, and toluene-d8 solution at room
temperature is 1.4:1. 4c-anti: 1H NMR (500 MHz, CD2Cl2): δ 7.34−
7.33 (br m, 2H, Ar), 7.16−7.10 (br m, 4H, Ar), 2.92 (br s, 6H, H5),
2.81 (br s, 6H, H4), 2.77 (septet, J = 6.9, 2H, iPr methine), 2.00 (br s,
3H, H11 or 14), 1.31 (d, J = 6.8, 3H, H11 or 14), 1.18−1.16 (m, 6H, H12
+
H15), 1.14 (d, J = 6.9, 3H, H9), 0.32 (s, 3H, Pd−Me). 13C{1H} NMR
(126 MHz, CD2Cl2): δ 175.6 (C3), 172.9 (C4), 169.1 (C5), 142.0,
141.7, 140.4, 139.1, 138.8, 128.2, 128.0, 126.7, 126.6, 124.4, 124.3,
124.2 (Ar), 40.7 (C6), 34.9 (C7), 29.3 (C10), 28.7 (C13 or 16), 28.4
(C13 or 16), 24.2 (C9 or 12 or 15), 24.1 (C9 or 12 or 15), 24.0 (C9 or 12 or 15),
23.43 (C11 or 14), 23.41 (C11 or 14), 23.1 (C8), 21.9 (C2), 21.4 (C1), 2.2
(Pd−Me). Key 1H−1H NOESY correlations (CD2Cl2): δ/δ 1.34/0.32,
1.31/0.32 (H11/Pd−Me + H14/Pd−Me), 1.18−1.16/2.00 (H12/H1 +
H15/H1), 1.14/2.16 (H9/H2). Key 1H−13C HMQC correlations
(CD2Cl2): δ/δ 3.09/40.7 (H6/C6), 3.03/34.9 (H7/C7). 5a′: 1H
NMR (500 MHz, CD2Cl2): δ 7.50 (dd, J = 8.0, 1.3, 1H, Ar), 7.35 (t, J
= 7.8, 1H, Ar), 7.25−7.21 (m, 3H, Ar), 7.18 (dd, J = 7.5, 1.3, 1H, Ar),
i
i
i
6H, H1), 1.22−1.19 (br m, 6H, Pr), 1.17−1.14 (br m, 6H, Pr).
13C{1H} NMR (126 MHz, CD2Cl2): δ 170.4 (C2), 169.6 (C3), 144.3,
136.7, 126.4, 126.0, 124.8, 124.5 (Ar), 38.1 (C4), 34.7 (C5), 28.5 (iPr
3.19 (septet, J = 6.9, 1H, Pr methine), 3.06 (s, 3H, H7), 2.99 (s, 3H,
H6), 2.13 (s, 3H, H2), 2.00 (s, 3H, H1), 1.37 (d, J = 6.9, 6H, iPr), 1.35
(d, J = 6.9, 3H, iPr), 0.38 (s, 3H, Pd−Me). 13C{1H} NMR (126 MHz,
CD2Cl2): δ 178.4 (C4), 170.8 (C3), 168.2 (C5), 142.4, 142.2, 140.8,
138.7, 138.3, 128.4, 127.4, 127.2, 127.0, 125.3, 123.6, 123.5 (Ar), 39.6
(C6), 35.0 (C7), 29.1, 28.8, 28.7 (iPr methine), 23.9, 23.8, 23.6, 23.2,
20.0 (iPr methyl + MeCN), 1.3 (Pd−Me). The other 1H NMR and
13C{1H} NMR resonances overlap with resonances for 5a and are not
listed. Key 1H−13C HMQC correlations (CD2Cl2): δ/δ 2.99/39.6
1
methine), 22.8, 22.7 (iPr methyl), 17.2 (C1). 4c-syn: H NMR (500
MHz, CD2Cl2): δ 2.99 (br s, 6H, H5), 2.81 (br s, 6H, H4), 2.00 (br s,
6H, H1). 13C{1H} NMR (126 MHz, CD2Cl2): δ 170.2 (C2), 169.6
(C3), 144.7, 136.3, 126.3, 126.2, 124.6, 124.4 (Ar), 38.1 (C4), 34.9
(C5), 28.7 (iPr methine), 23.1, 22.8 (iPr methyl), 17.1 (C1). IR
(cm−1): νCN+CO, 1641. Anal. Calcd for C28H38N4O2: C, 72.69; H,
K
dx.doi.org/10.1021/om500978n | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(H6/C6). IR (cm−1): νCO, 1634. Anal. Calcd for C27H37ClN3OPd: C,
58.98; H, 7.17; N, 7.12. Found: C, 58.80; H, 6.98; N, 6.98. ESI-MS
(1:1 MeOH/H2O, positive ion scan, m/z): 554.2 ([M − Cl]+).
1.12 (d, J = 6.9, 3H, H15), 0.34 (s, 3H, Pd−Me). 1H NMR (500 MHz,
CD2Cl2, −30 °C): δ 7.45 (dd, J = 7.9, 1.2, 1H, Ar), 7.40 (dd, J = 7.9,
1.1, 1H, Ar), 7.32 (t, J = 7.7, 1H, Ar), 7.27 (t, J = 7.7, 1H, Ar), 7.16
(dd, J = 7.5, 1.3, 1H, Ar), 7.08 (dd, J = 7.5, 1.3, 1H, Ar), 3.12 (septet, J
= 6.8, 1H, H16), 3.06 (s, 3H, H9), 3.00 (s, 3H, H7), 3.00 (septet, J =
6.8, 1H, H13), 2.99 (s, 3H, H10), 2.95 (s, 3H, H6), 2.10 (s, 3H, H2),
2.08 (s, 3H, H1), 1.34 (d, J = 6.7, 3H, H14), 1.28 (d, J = 6.8, 3H, H11),
1.10 (d, J = 6.9, 3H, H12), 1.05 (d, J = 6.9, 3H, H15), 0.27 (s, 3H, Pd−
Me). 13C{1H} NMR (126 MHz, CD2Cl2): δ 178.8 (C3), 173.3 (C4),
169.0 (C8), 168.0 (C5), 142.4, 141.7, 140.7, 140.5, 128.3, 128.2, 127.3,
127.1, 126.6, 126.5, 125.1, 124.1 (Ar), 40.8 (C9), 39.7 (C6), 34.94
(C7 or 10), 34.90 (C7 or 10), 29.2 (C16), 28.6 (C13), 24.0 (2C, C12 + C15),
23.1 (2C, C2 + C14), 22.9 (C11), 21.8 (C1), 1.6 (Pd−Me). Key 1H−1H
NOESY correlations (CD2Cl2): δ/δ 1.28/0.27 (H11/Pd−Me), 2.95/
0.27 (H6/Pd−Me), 1.10/2.08 (H12/H1), 1.05/2.10 (H15/H2). Key
1H−13C HMQC correlations (CD2Cl2): δ/δ 3.06/40.8 (H9/C9), 3.00/
5b,b′. A Schlenk tube was charged with (cod)PdMeCl (0.265 g,
1.00 mmol) and 4b (0.449 g, 0.0972 mmol). Et2O (5 mL) was added,
and the mixture was stirred overnight to afford an orange suspension.
The orange solid residue was isolated by cannula filtration and washed
twice with Et2O. The resulting orange powder was recrystallized by
layering hexanes onto a CH2Cl2 solution at room temperature to
afford an orange powder (0.570 g, 95%). The equilibrium isomer ratio
5b/5b′ is ca. 17:1 in CD2Cl2 at room temperature based on
integration of the Pd−Me resonances. 5b: 1H NMR (500 MHz,
CD2Cl2): δ 7.34−7.24 (m, 6H, Ar), 3.18 (s, 6H, H6), 3.05 (s, 6H, H7),
2.95 (septet, J = 6.8, 2H, H10), 2.22 (s, 3H, H2), 1.99 (s, 3H, H1), 1.30
(d, J = 6.8, 6H, H8), 1.16 (d, J = 6.9, 6H, H9), 0.24 (s, 3H, Pd−Me).
13C{1H} NMR (126 MHz, CD2Cl2): δ 175.8 (C3), 175.0 (C4), 167.9
(C5), 143.4, 142.2, 138.9, 129.2, 127.8, 127.4, 125.2, 124.2 (Ar), 40.9
(C6), 35.1 (C7), 28.5 (C10), 24.0 (C9), 23.2 (C8), 22.7 (C2), 21.3 (C1),
1
34.9 (H7/C7), 2.99/34.9 (H10/C10), 2.95/39.7 (H6/C6). Key H−13C
HMBC correlations (CD2Cl2): δ/δ 3.06/169.0 (H9/C8), 3.00/168.0
(H7/C5), 2.99/169.0 (H10/C8), 2.95/168.0 (H6/C5). 5c-syn: 1H NMR
(500 MHz, CD2Cl2): δ 7.50 (dd, J = 7.9, 1.3, 1H, Ar), 7.44 (dd, J =
7.9, 1.3, 1H, Ar), 7.34 (t, J = 7.8, 1H, Ar), 7.29 (t, J = 7.8, 1H, Ar), 7.21
(dd, J = 7.5, 1.4, 1H, Ar), 7.13 (dd, J = 7.5, 1.3, 1H, Ar), 3.48 (septet, J
= 6.9, 1H, H16), 3.21 (septet, J = 6.9, 1H, H13), 3.11 (s, 3H,
or 9
or 9
H6 or 7
H
or 10), 3.082 (s, 3H, H6 or 7
or 10), 3.077 (s, 3H,
6 or 7 or 9 or 10), 2.99 (s, 3H, H6 or 7 or 9 or 10), 2.12 (s, 3H, H2), 2.07
(s, 3H, H1), 1.44 (d, J = 6.8, 3H, H14), 1.37 (d, J = 6.8, 3H, H11), 1.14
(d, J = 7.0, 3H, H12), 1.08 (d, J = 7.0, 3H, H15), 0.37 (s, 3H, Pd−Me).
1H NMR (500 MHz, CD2Cl2, −30 °C): δ 7.48 (d, J = 7.8, 1H, Ar),
7.42 (d, J = 8.0, 1H, Ar), 7.33 (t, J = 7.7, 1H, Ar), 7.29 (t, J = 7.7, 1H,
Ar), 7.19 (d, J = 7.5, 1H, Ar), 7.14 (d, J = 7.6, 1H, Ar), 3.48 (septet, J =
6.9, 1H, H16), 3.08 (septet, J = 6.9, 1H, H13), 3.08 (s, 3H,
1
2.1 (Pd−Me). Key H−1H NOESY correlations (CD2Cl2): δ/δ 1.30/
1
0.24 (H8/Pd−Me), 1.16/1.99 (H9/H1). 5b′: H NMR (500 MHz,
CD2Cl2): δ 3.07 (s, 6H, H6 or 7), 3.06 (s, 6H, H6 or 7), 2.91 (septet, J =
6.8, 2H, H10), 2.20 (s, 3H, H2), 1.99 (s, 3H, H1), 1.34 (d, J = 6.8, 6H,
H8), 1.15 (d, J = 6.8, 6H, H9), 0.37 (s, 3H, Pd−Me). Several 1H NMR
resonances overlap with resonances for 5b and are not listed. IR
(cm−1): νCO, 1636. Anal. Calcd for C29H41ClN4O2Pd: C, 56.22; H,
6,67; N, 9.04. Found: C, 55.97; H, 6.40; N, 8.85. ESI-MS (1:1 MeOH/
H2O, positive ion scan, m/z): 583.1 ([M − Cl]+).
H
6 or 7 or 9 or 10), 3.06 (s, 3H, H6 or 7 or 9 or 10), 3.04 (s, 3H, H6 or 7 or 9 or 10),
2.94 (s, 3H, H6 or 7 or 9 or 10), 2.09 (s, 3H, H2), 2.03 (s, 3H, H1), 1.38 (d,
J = 6.7, 3H, H14), 1.31 (d, J = 6.7, 3H, H11), 1.09 (d, J = 6.8, 3H, H12),
0.99 (d, J = 6.9, 3H, H15), 0.29 (s, 3H, Pd−Me). 13C{1H} NMR (126
MHz, CD2Cl2): δ 178.5 (C3), 172.8 (C4), 169.0 (C8), 167.9 (C5),
142.6, 141.1, 140.7 (2C), 128.5, 127.72, 127.70, 127.0, 126.7, 126.6,
125.8, 124.9 (Ar), 40.7 (C9), 39.8 (C6), 35.4 (C7 or 10), 35.2 (C7 or 10),
29.6 (C16), 28.7 (C13), 24.0, 23.8, 22.93, 22.86, 22.7 (iPr methyl +
MeCN), 1.3 (Pd−Me). One aliphatic carbon signal overlaps with a
resonance of 5c-anti. Key 1H−1H NOESY correlations (CD2Cl2): δ/δ
1.31/0.29 (H11/Pd−Me), 1.09/2.03 (H12/H1). IR (cm−1): νCO
,
1631. Anal. Calcd for C29H41ClN4O2Pd: C, 56.22; H, 6.67; N, 9.04.
Found: C, 55.95; H, 6.62; N, 8.82. ESI-MS (1:1 MeOH/H2O, positive
ion scan, m/z): 583.2 ([M − Cl]+).
5c-anti,syn. A Schlenk flask was charged with α-diimine 4c (231
mg, 0.500 mmol), (cod)PdMeCl (132 mg, 0.500 mmol), and Et2O (10
mL). The mixture was stirred at room temperature for 28 h to give an
orange suspension. The orange solid was collected by vacuum
filtration, washed with Et2O, and dried under vacuum. Yield: 265
mg (85%). This solid is a 5.2:1 mixture of anti and syn isomers, as
determined by 1H NMR at −30 °C based on the integrals of the Pd−
Me resonances. The isomer mixture was recrystallized by layering
hexanes onto a dilute CH2Cl2 solution of the 5.2:1 isomer mixture at
−30 °C to give pure major isomer 5c-anti as orange needles. A similar
recrystallization from a concentrated solution of the isomer mixture
gave a mixture of orange needles and orange granular crystals. A
granular crystal was subjected to X-ray analysis and identified as 5c-
syn·2CH2Cl2. The 1H NMR spectrum of a crystalline sample of 5c-syn·
2CH2Cl2 in CD2Cl2 at −30 °C confirmed that 5c-syn is the minor
isomer in the equilibrium mixture. Anti/syn isomerization affords a
4.6:1 equilibrium 5c-anti/5c-syn mixture within a few hours at room
temperature in CD2Cl2. 5c-anti: 1H NMR (500 MHz, CD2Cl2): δ 7.47
(dd, J = 7.9, 1.2, 1H, Ar), 7.42 (dd, J = 7.9, 1.1, 1H, Ar), 7.37 (t, J =
7.7, 1H, Ar), 7.31 (t, J = 7.8, 1H, Ar), 7.17 (dd, J = 7.5, 1.3, 1H, Ar),
7.09 (dd, J = 7.5, 1.3, 1H, Ar), 3.15 (septet, J = 6.9, 1H, H16), 3.10 (s,
3H, H9), 3.07 (septet, J = 6.9, 1H, H13), 3.04 (s, 3H, H7), 3.02 (s, 3H,
H10), 2.99 (s, 3H, H6), 2.12 (s, 3H, H2), 2.10 (s, 3H, H1), 1.40 (d, J =
6.8, 3H, H14), 1.34 (d, J = 6.8, 3H, H11), 1.16 (d, J = 6.9, 3H, H12),
5d,d′. A glass vial was equipped with a stir bar and charged with 6d
(473 mg, 0.793 mmol), CH2Cl2 (3 mL), and SnMe4 (425 mg, 2.38
mmol, 3.0 equiv, 0.8 M). The vial was covered with foil, and the
mixture was stirred at room temperature for 29 h, giving a dark red
solution and Pd mirror. The solution was filtered through a pad of
Celite, and the filtrate was concentrated under vacuum to 0.5 mL.
Et2O (20 mL) was added in one portion, and orange microcrystals
formed in a few minutes. The crystals were collected by vacuum
filtration, washed with Et2O, and dried under vacuum. The product
was stored in a −40 °C freezer. Yield: 406 mg (89%). The equilibrium
5d/5d′ ratio is ca. 16:1 at room temperature in CD2Cl2 based on the
integration of the Pd−Me resonances. 5d: 1H NMR (500 MHz,
CD2Cl2): δ 7.48 (br, 1H, amide NH), 7.46 (dd, J = 6.9, 2.2, 1H, Ar),
7.35−7.28 (m, 5H, Ar), 3.04 (septet, J = 6.9, 1H, H12 or 15), 2.98
(septet, J = 6.9, 1H, H9), 2.92 (d, J = 4.9, 3H, H6), 2.92 (septet, J = 6.8,
L
dx.doi.org/10.1021/om500978n | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1H, H12 or 15), 2.08 (s, 3H, H2), 2.03 (s, 3H, H1), 1.43 (d, J = 6.8, 3H,
H7), 1.36 (d, J = 6.8, 3H, H10 or 13), 1.30 (d, J = 6.8, 3H, H10 or 13), 1.20
(d, J = 6.8, 3H, H8), 1.19 (d, J = 6.8, 3H, H11 or 14), 1.15 (d, J = 6.9, 3H,
3.12 (s, 6H, H4), 3.09 (s, 6H, H5), 2.18 (s, 6H, H1), 1.48 (d, J = 6.8,
6H, H6), 1.19 (d, J = 6.9, 6H, H7). 13C{1H} NMR (126 MHz,
CD2Cl2): δ 181.9 (C2), 168.1 (C3), 141.4, 141.0, 128.7, 128.1, 127.3,
125.2 (Ar), 40.6 (C4), 35.6 (C5), 29.6 (C8), 23.8 (C7), 23.2 (C6), 22.8
(C1). IR (cm−1): νCO, 1632. Anal. Calcd for C28H38Cl2N4O2Pd: C,
52.55; H, 5.99; N, 8.75. Found: C, 52.39; H, 5.75; N, 8.55. ESI-MS
(1:1 MeOH/H2O, positive ion scan, m/z): 603.2 ([M − Cl]+).
H
11 or 14), 0.40 (s, 3H, Pd−Me). 13C{1H} NMR (126 MHz, CD2Cl2):
δ 175.5 (C3), 171.8 (C4), 168.9 (C5), 141.8, 141.0, 138.9, 138.8, 138.7,
130.1, 128.2, 127.4, 127.2, 125.2, 124.4, 124.3 (Ar), 29.1 (C9), 29.0
(C12 or 15), 28.6 (C12 or 15), 26.2 (C6), 24.1 (C11 or 14), 23.8 (C11 or 14),
23.5 (C10 or 13), 23.4 (C7), 23.2 (C8), 22.9 (C10 or 13), 21.4 (C1), 20.1
1
(C2), 2.8 (Pd−Me). Key H−1H COSY correlations (CD2Cl2): δ/δ
7.48/2.92 (amide NH/H6). Key 1H−1H NOESY correlations
(CD2Cl2): δ/δ 1.36/0.40, 1.30/0.40 (H10/Pd−Me + H13/Pd−Me),
1.19/2.03, 1.15/2.03 (H11/H1 + H14/H1), 1.20/2.08 (H8/H2). 5d′: 1H
NMR (500 MHz, CD2Cl2): δ 7.55 (dd, J = 7.8, 1.4, 1H, Ar), 6.29 (br,
i
1H, amide NH), 3.17 (septet, J = 6.9, 1H, Pr methine), 2.10 (s, 3H,
H2), 2.04 (s, 3H, H1), 1.38 (d, J = 6.8, 6H, iPr), 0.29 (s, 3H, Pd−Me).
1
Several H NMR resonances overlap with resonances for 5d and are
not listed. IR (cm−1): νN−H, 3302; νCO, 1664. Anal. Calcd for
C28H40ClN3OPd: C, 58.33; H, 6.99; N, 7.29. Found: C, 58.19; H,
6.75; N, 7.12. ESI-MS (1:1 MeOH/H2O, positive ion scan, m/z):
524.1 ([M − Cl − CH4]+), 540.2 ([M − Cl]+).
6d. A Schlenk flask was charged with 4d′ (419 mg, 1.00 mmol),
(MeCN)2PdCl2 (265 mg, 1.00 mmol, 1.00 equiv), and CH2Cl2 (30
mL) under nitrogen. The flask was equipped with a water condenser,
and the mixture was stirred at reflux for 20 h to give a red
homogeneous solution. The mixture was cooled to room temperature,
and the volatiles were removed under vacuum. The red solid residue
was dissolved in a minimum volume of CH2Cl2 (ca. 5 mL). Et2O (30
mL) was slowly added, and a red solid precipitated. The solid was
collected by vacuum filtration and washed with Et2O. Yield: 560 mg
1
(94%). H NMR (500 MHz, CD2Cl2): δ 7.51 (dd, J = 7.9, 1.3, 1H,
Ar), 7.44 (t, J = 7.7, 1H, Ar), 7.39 (t, J = 7.8, 1H, Ar), 7.32 (dd, J = 7.4,
1.4, 1H, Ar), 7.28−7.26 (m, 1H, Ar), 7.26−7.25 (m, 1H, Ar), 6.75 (br,
1H, amide NH), 3.11 (septet, J = 6.8, 1H, iPr methine), 3.06 (septet, J
6c-anti. A Schlenk flask was charged with 4c (463 mg, 1.00 mmol),
(MeCN)2PdCl2 (259 mg, 1.00 mmol), and CH2Cl2 (10 mL). The
mixture was stirred at room temperature for 3.5 h to give an orange
solution. The volatiles were removed under vacuum to yield a yellow
powder (603 mg, 94% based on Pd, 6c-anti/6c-syn = 1:1.7). A
Schlenk flask was charged with the isomer mixture and dry 1,2-
dichloroethane (25 mL). The resulting orange solution was refluxed
for 2 h. The solvent was removed under vacuum, and the isomer ratio
was determined to be 6c-anti/6c-syn = 3.6:1 by 1H NMR. This
mixture was recrystallized by layering hexanes onto a CH2Cl2 solution
at −30 °C. Repeating this recrystallization procedure three times
yielded orange needles of pure 6c-anti (270 mg, 42% based on Pd).
1H NMR (500 MHz, CD2Cl2): δ 7.45 (dd, J = 7.9, 1.2, 2H, Ar), 7.38
(t, J = 7.7, 2H, Ar), 7.15 (dd, J = 7.4, 1.3, 2H, Ar), 3.13 (s, 6H, H4),
3.13 (septet, J = 6.9, 2H, H8), 3.10 (s, 6H, H5), 2.18 (s, 6H, H1), 1.44
(d, J = 6.8, 6H, H6), 1.22 (d, J = 6.9, 6H, H7). 13C{1H} NMR (126
MHz, CD2Cl2): δ 182.3 (C2), 168.2 (C3), 141.6, 141.3, 128.6, 128.0,
127.3, 124.7 (Ar), 40.6 (C4), 35.2 (C5), 29.3 (C8), 23.9 (C7), 23.4
(C6), 22.7 (C1). IR (cm−1): νCO, 1629. Anal. Calcd for
C28H38Cl2N4O2Pd: C, 52.55; H, 5.99; N, 8.75. Found: C, 52.31; H,
6.22; N, 8.60. ESI-MS (1:1 MeOH/H2O, positive ion scan, m/z):
603.2 ([M − Cl]+).
i
i
= 6.9, 1H, Pr methine), 3.05 (septet, J = 6.9, 1H, Pr methine), 3.03
(d, J = 4.9, 3H, amide NMe), 2.18 (s, 3H, MeCN), 2.10 (s, 3H,
MeCN), 1.48 (d, J = 6.8, 3H, iPr), 1.46 (d, J = 6.8, 3H, iPr), 1.41 (d,
i
i
i
J = 6.8, 3H, Pr), 1.24 (d, J = 6.9, 3H, Pr), 1.23 (d, J = 6.9, 3H, Pr),
1.20 (d, J = 6.9, 3H, iPr). 13C{1H} NMR (126 MHz, CD2Cl2): δ 180.8,
179.3 (imine CN), 168.5 (CO), 141.0, 140.4, 140.3, 139.8, 139.6,
130.6, 129.2, 129.0, 128.0, 125.0, 124.2, 124.0 (Ar), 29.7, 29.4, 29.3
(iPr methine), 26.7 (amide NMe), 24.0, 23.84, 23.80, 23.6, 23.5, 23.2
(iPr methyl), 21.6, 21.2 (MeCN). IR (cm−1): νN−H, 3330; νCO
,
1658. Anal. Calcd for C27H37Cl2N3OPd: C, 54.33; H, 6.25; N, 7.04.
Found: C, 54.06; H, 5.97; N, 6.91. ESI-MS (1:1 MeOH/H2O, positive
ion scan, m/z): 560.0 ([M − Cl]+).
7d. A solution of 5d,d′ (81.6 mg, 0.142 mmol) in CH2Cl2 (2 mL)
was vigorously stirred at room temperature, and AgOAc (26.4 mg,
0.159 mmol, 1.1 equiv) was added in one portion. The mixture was
stirred at room temperature for 22 min to give a suspension of an off-
white precipitate in a red solution. The suspension was filtered through
a pad of Celite, and the filtrate was concentrated to dryness. The red
solid residue was dissolved in hexanes/CH2Cl2 and kept at −30 °C
overnight to give pure product as red granular crystals (59.4 mg, 70%).
1H NMR (500 MHz, CD2Cl2): δ 9.43 (br q, J = 4.5, 1H, amide NH),
7.43 (dd, J = 7.8, 1.1, 1H, Ar), 7.33−7.27 (m, 5H, Ar), 3.58 (septet, J =
6.9, 1H, iPr methine), 3.09 (septet, J = 6.9, 1H, iPr methine), 2.90 (d, J
i
= 4.6, 3H, amide NMe), 2.90 (septet, J = 6.9, 1H, Pr methine), 2.12
i
(s, 3H, MeCN), 1.96 (s, 3H, MeCN), 1.45 (d, J = 6.8, 3H, Pr),
1.40 (d, J = 6.8, 3H, iPr), 1.36 (s, 3H, CH3CO2), 1.35 (d, J = 6.8, 3H,
i
i
iPr), 1.16 (d, J = 6.8, 3H, Pr), 1.15 (d, J = 6.8, 3H, Pr), 1.05 (d, J =
6.9, 3H, Pr), 0.27 (s, 3H, Pd−Me). 13C{1H} NMR (126 MHz,
i
CD2Cl2): δ 177.6 (MeCO2), 175.8, 170.6 (imine CN), 169.4
(amide CO), 142.4, 140.6, 139.9, 138.8, 138.6, 131.3, 128.1, 127.7,
126.7, 125.8, 124.3 (2C) (Ar), 29.3, 28.9, 28.6 (iPr methine), 26.4
(amide NMe), 24.5, 24.2, 23.8, 23.5, 23.2 (iPr methyl), 22.6 (MeCO2),
6c-syn. A Schlenk flask was charged with 4c (935 mg, 2.02 mmol),
(MeCN)2PdCl2 (519 mg, 2.00 mmol), and CH2Cl2 (10 mL). The
mixture was stirred at room temperature for 2 h to give an orange
solution. The volatiles were removed under vacuum to yield a yellow
powder (1.22 g, 95% based on Pd, 6c-anti/6c-syn = 1:1.8). The
mixture was recrystallized by layering hexanes onto a CH2Cl2 solution
at −30 °C. Repeating the recrystallization procedure four times yielded
1
22.2 (iPr methyl), 21.2, 20.1 (MeCN), 3.2 (Pd−Me). Key H−1H
COSY correlation (CD2Cl2): δ/δ 9.43/2.90 (amide NH/NMe). IR
(cm−1): νN−H, 3211; νCO,amide, 1653; νOCO,asym, 1590; νOCO,sym, 1329.
Anal. Calcd for C30H43N3O3Pd: C, 60.04; H, 7.22; N, 7.00. Found: C,
59.83; H, 6.96; N, 6.93. ESI-MS (1:1 MeOH/H2O, positive ion scan,
m/z): 540.2 ([M − OAc]+), 524.1 ([M − OAc − CH4]+), 581.3 ([M
− H2O]+).
1
orange crystals of pure 6c-syn (420 mg, 33% based on Pd). H NMR
(500 MHz, CD2Cl2): δ 7.46 (dd, J = 7.9, 1.3, 2H, Ar), 7.40 (t, J = 7.7,
7e. A solution of 5e (80.6 mg, 0.143 mmol) in CH2Cl2 (3 mL) was
vigorously stirred at room temperature, and AgOAc (30.1 mg, 0.180
2H, Ar), 7.17 (dd, J = 7.5, 1.3, 2H, Ar), 3.26 (septet, J = 6.9, 2H, H8),
M
dx.doi.org/10.1021/om500978n | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mmol, 1.26 equiv) was added in one portion. The mixture was stirred
at room temperature for 2 h to give a suspension of an off-white
precipitate in a brown solution. The suspension was filtered by pipet
filtration. Hexanes (12 mL) was added to the filtrate in one portion,
and the mixed solution was kept at −40 °C overnight to afford the
product as brown needles that contained 0.63 equiv of CH2Cl2 as
determined by 1H NMR integration (79.0 mg, 87%). Recrystallization
from CH2Cl2/Et2O at −40 °C yielded brown crystals of 7e·CH2Cl2.
1H NMR (500 MHz, CD2Cl2): δ 7.33−7.22 (m, 6H, Ar), 3.11 (septet,
J = 6.8, 2H, iPr methine), 3.09 (septet, J = 6.8, 2H, iPr methine), 2.06
8c-syn mixture within 5 h at room temperature in CD2Cl2 or a 2.0:1
equilibrium 8c-anti/8c-syn mixture within 1 h at room temperature in
CD3CN. 8c-anti: 1H NMR (500 MHz, CD2Cl2): δ 14.42 (br s, 1H, pz
NH), 7.53 (dd, J = 7.9, 1.4, 1H, Ar), 7.41 (t, J = 7.7 Hz, 1H, Ar), 7.31−
7.22 (m, 3H, Ar), 7.19−7.17 (m, 3H, pz H3 + pz H5 + 1 Ar CH), 6.16
(q, J = 2.2, 1H, pz H4), 3.23 (s, 3H, amide NMe), 3.110 (s, 3H, amide
NMe), 3.108 (s, 3H, amide NMe), 3.05 (s, 3H, amide NMe), 3.05
i
i
(septet, J = 6.8, 1H, Pr methine), 2.93 (septet, J = 6.8, 1H, Pr
methine), 2.26 (s, 3H, MeCN), 2.18 (s, 3H, MeCN), 1.35 (d, J =
6.8, 3H, iPr), 1.231 (d, J = 6.9, 3H, iPr), 1.13 (d, J = 6.9, 3H, iPr), 1.04
i
1
i
(d, J = 6.8, 3H, Pr), 0.44 (s, 3H, Pd−Me). H NMR (500 MHz,
CD3CN): δ 14.49 (br s, 1H, pz NH), 6.18 (q, J = 2.3, 1H, pz H4), 0.35
(s, 3H, Pd−Me). 13C{1H} NMR (126 MHz, CD2Cl2): δ 181.8, 173.5
(imine CN), 170.0, 167.8 (CO), 142.1, 140.6 (Ar), 140.46 (pz
C5), 140.2, 140.0 (Ar), 130.7 (pz C3), 128.77, 128.11, 127.95, 127.75,
127.4, 126.6, 125.8, 125.1 (Ar), 106.61 (pz C4), 39.74, 39.4, 35.4, 35.1
(amide NMe), 28.85, 28.6 (iPr methine), 23.89, 23.75, 23.15 (iPr
methyl), 23.11 (MeCN), 23.06 (iPr methyl), 20.3 (MeCN), 5.8
(s, 3H, MeCN), 1.97 (s, 3H, MeCN), 1.41 (d, J = 6.8, 6H, Pr),
1.39 (d, J = 6.8, 6H, iPr), 1.33 (s, 3H, CH3CO2), 1.18 (d, J = 6.9, 6H,
i
iPr), 1.15 (d, J = 6.9, 6H, Pr), 0.30 (s, 3H, Pd−Me). 13C NMR (126
MHz, CD2Cl2): δ 175.2 (MeCO2), 174.9, 169.5 (imine CN), 142.6,
141.7, 138.9, 138.8, 127.9, 127.1, 124.3, 123.6 (Ar), 29.3, 28.8 (iPr
methine), 24.0, 23.9, 23.6, 23.4 (iPr methyl), 23.1 (MeCO2), 21.2, 20.1
(MeCN), 1.6 (Pd−Me). IR (cm−1): νN−H, 3210; νOCO,asym, 1615;
νOCO,sym, 1322. Anal. Calcd for C31H46N2O2Pd·CH2Cl2: C, 57.36; H,
7.22; N, 4.18. Found: C, 57.33; H, 6.84; N, 3.96. ESI-MS (1:1 MeOH/
H2O, positive ion scan, m/z): 566.3 ([M − H2O]+), 509.2 ([M − OAc
− CH4]+).
1
(Pd−Me). 8c-syn: H NMR (500 MHz, CD2Cl2): δ 14.42 (br s, 1H,
pz NH), 7.53 (dd, J = 7.9, 1.4, 1H, Ar), 7.41 (t, J = 7.7 Hz, 1H, Ar),
7.31−7.22 (m, 3H, Ar), 7.22−7.21 (m, 1H, pz H5), 7.19−7.17 (m, 2H,
pz H3 + 1 Ar CH), 6.16 (m, 1H, pz H4), 3.29 (s, 3H, amide NMe),
3.20 (s, 3H, amide NMe), 3.07 (s, 3H, amide NMe), 2.96 (septet, J =
8a. A glass vial was charged with 5a,a′ (54.3 mg, 0.0919 mmol),
AgSbF6 (39.1 mg, 1.24 equiv), and pyrazole (6.3 mg, 1.0 equiv).
CH2Cl2 (2 mL) was added to the reaction mixture, and the vial was
agitated for 20 s to give a suspension of an off-white precipitate in an
orange solution. The suspension was filtered by pipet filtration. The
filtrate was concentrated to 2 mL, layered with hexanes (8 mL), and
kept at −40 °C overnight to give orange needles (73.5 mg, 91%). The
solid contained 0.020 equiv of CH2Cl2 and 0.20 equiv of Et2O as
determined by 1H NMR. 1H NMR (500 MHz, CD2Cl2): δ 14.38 (br s,
1H, pz NH), 7.38−7.26 (m, 5H, Ar), 7.24−7.23 (m, 1H, pz H5),
7.21−7.19 (m, 2H, pz H3 + 1 Ar CH), 6.16 (q, J = 2.3, 1H, pz H4),
3.23 (s, 3H, amide NMe), 3.11 (s, 3H, amide NMe), 3.01 (septet, J =
i
i
6.8, 1H, Pr methine), 2.94 (septet, J = 6.8, 1H, Pr methine), 2.93 (s,
3H, amide NMe), 2.25 (s, 3H, MeCN), 2.17 (s, 3H, MeCN), 1.42
i
i
(d, J = 6.8, 3H, Pr), 1.234 (d, J = 6.9, 3H, Pr), 1.14 (d, J = 6.9, 3H,
i
1
iPr), 1.09 (d, J = 6.8, 3H, Pr), 0.46 (s, 3H, Pd−Me). H NMR (500
MHz, CD3CN): δ 14.54 (br s, 1H, pz NH), 6.16 (m, 1H, pz H4), 0.37
(s, 3H, Pd−Me). 13C{1H} NMR (126 MHz, CD2Cl2): δ 181.4, 173.2
(imine CN), 169.9, 167.5 (CO), 142.0, 140.44, 140.40 (Ar),
140.35 (pz C5), 140.1 (Ar), 130.8 (pz C3), 128.74, 128.03, 127.89,
127.82, 127.6, 126.7, 125.9, 125.0 (Ar), 106.57 (pz C4), 39.72, 39.6,
35.7, 35.5 (amide NMe), 28.92, 28.88 (iPr methine), 23.87, 23.70 (iPr
methyl), 23.21, 23.15, 23.08 (iPr methyl + MeCN), 20.5 (MeC
N), 6.0 (Pd−Me). 19F NMR (470 MHz, CD3CN): δ −123.3; overlay
of 121SbF6 (sextet, JSbF = 1930) and 123SbF6 (octet, JSbF = 1050). IR
(cm−1): νN−H, 3131; νCO, 1630, 1606. Anal. Calcd for
C32H45F6N6O2PdSb: C, 43.29; H, 5.11; N, 9.47. Found: C, 42.73;
H, 5.07; N, 9.15. ESI-MS (1:1 MeOH/H2O, positive ion scan, m/z):
651.3 ([M − SbF6]+). ESI-MS (1:1 MeOH/H2O, negative ion scan,
i
i
6.8, 1H, Pr methine), 2.96 (septet, J = 6.9, 1H, Pr methine), 2.91
(septet, J = 6.9, 1H, iPr methine), 2.24 (s, 3H, MeCN), 2.22 (s, 3H,
MeCN), 1.40 (d, J = 6.8, 3H, iPr), 1.36 (d, J = 6.8, 3H, iPr), 1.23 (d,
i
i
i
J = 6.9, 3H, Pr), 1.22 (d, J = 6.9, 3H, Pr), 1.16 (d, J = 6.9, 3H, Pr),
1.07 (d, J = 6.8, 3H, iPr), 0.42 (s, 3H, Pd−Me). 1H NMR (500 MHz,
CD3CN): δ 14.47 (br s, 1H, pz NH), 6.18 (q, J = 2.3, 1H, pz H4), 0.28
(s, 3H, Pd−Me). 13C{1H} NMR (126 MHz, CD2Cl2): δ 178.8, 173.3
(imine CN), 170.0 (CO), 141.6 (Ar), 140.7 (pz C5), 140.3,
140.1, 139.0, 138.5 (Ar), 130.6 (pz C3), 128.7 (2C), 128.0, 126.8,
125.1, 124.8, 124.5 (Ar), 106.6 (pz C4), 39.4, 35.2 (amide NMe), 29.2,
29.0 (2C) (iPr methine), 23.9, 23.8, 23.6, 23.33, 23.25, 23.21 (iPr
methyl), 21.6, 20.4 (MeCN), 7.1 (Pd−Me). 19F NMR (470 MHz,
CD3CN): δ −123.7; overlay of 121SbF6 (sextet, JSbF = 1940) and
123SbF6 (octet, JSbF = 1050). IR (cm−1): νN−H, 3134; νCO, 1607. ESI-
MS (1:1 MeOH/H2O, positive ion scan, m/z): 622.3 ([M − SbF6]+).
−
m/z): 234.9 (SbF6 ). HRMS (ESI-TOF, positive ion, m/z): calcd
651.2639 ([M − SbF6]+), found 651.2647.
−
ESI-MS (1:1 MeOH/H2O, negative ion scan, m/z): 234.9 (SbF6 ).
HRMS (ESI-TOF, positive ion, m/z): calcd 622.2737 ([M − SbF6]+),
found 622.2752.
8d. A glass vial was charged with 5d,d′ (52.1 mg, 0.0903 mmol),
AgSbF6 (37.3 mg, 1.20 equiv), and pyrazole (6.1 mg, 1.0 equiv).
CH2Cl2 (2 mL) was added to the reaction mixture, and the vial was
agitated for 20 s to give a suspension of an off-white precipitate in an
orange solution. The suspension was filtered by pipet filtration. The
filtrate was concentrated to 1 mL, layered with hexanes (8 mL), and
kept at −40 °C overnight to give orange needles (70.0 mg, 91%). The
solid contained 0.10 equiv of CH2Cl2 and 0.12 equiv of Et2O as
determined by 1H NMR. 1H NMR (500 MHz, CD2Cl2): δ 14.09 (br s,
1H, pz NH), 7.38 (m, 1H, Ar), 7.33−7.28 (m, 5H, Ar), 7.26 (m, 2H,
pz H3 + H5), 6.80 (br q, J = 4.5, 1H, amide NH), 6.18 (q, J = 2.3, 1H,
pz H4), 3.08 (d, J = 4.9, 3H, amide NMe), 3.03 (septet, J = 6.8, 1H, iPr
methine), 2.99 (septet, J = 6.9, 1H, iPr methine), 2.92 (septet, J = 6.9,
8c-anti,syn. A glass vial was charged with pure 5c-anti (63.4 mg,
0.102 mmol), AgSbF6 (37.1 mg, 1.06 equiv), and pyrazole (7.0 mg, 1.0
equiv). CH2Cl2 (3 mL) was added to the reaction mixture, and the vial
was agitated for 10 s to give a suspension of an off-white precipitate in
an orange solution. The suspension was filtered by pipet filtration. The
filtrate was layered with hexanes (10 mL) and kept at −40 °C to give
yellow crystals (76.0 mg, 84%). This solid is a 6.3:1 mixture of 8c-anti
and 8c-syn, as determined by H NMR at room temperature in ca. 5
min after sample preparation based on the integrals of the Pd−Me
resonances. Anti/syn isomerization affords a 1.5:1 equilibrium 8c-anti/
i
i
1H, Pr methine), 2.19 (s, 6H, MeCN), 1.41 (d, J = 6.8, 3H, Pr),
1.36 (d, J = 6.8, 3H, iPr), 1.22 (d, J = 6.9, 6H, iPr), 1.14 (d, J = 6.9, 3H,
1
i
1
iPr), 1.09 (d, J = 6.8, 3H, Pr), 0.42 (s, 3H, Pd−Me). H NMR (500
MHz, CD3CN): δ 14.00 (br s, 1H, pz NH), 6.18 (q, J = 2.3, 1H, pz
N
dx.doi.org/10.1021/om500978n | Organometallics XXXX, XXX, XXX−XXX

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H4), 0.28 (s, 3H, Pd−Me). 13C{1H} NMR (126 MHz, CD2Cl2): δ
178.7, 174.0 (imine CN), 171.1 (CO), 141.5 (Ar), 140.8 (pz C5),
140.4, 139.5, 138.9, 138.6 (Ar), 130.9 (pz C3), 129.3, 128.8, 128.4,
128.3, 125.4, 124.8, 124.5 (Ar), 106.7 (pz C4), 29.2, 29.0 (2C) (iPr
methine), 27.4 (amide NMe), 24.0, 23.9, 23.45, 23.41, 23.3, 23.2 (iPr
methyl), 21.7, 20.0 (MeCN), 6.9 (Pd−Me). 19F NMR (470 MHz,
CD3CN): δ −124.1; overlay of 121SbF6 (sextet, JSbF = 1920) and
123SbF6 (octet, JSbF = 1050). IR (cm−1): νN−H, 3413, 3137; νCO, 1626.
Anal. Calcd for C31H44F6N5OPdSb·0.10CH2Cl2·0.12C4H10O: C,
43.99; H, 5.31; N, 8.12. Found: C, 43.45; H, 5.31; N, 8.12. ESI-MS
(1:1 MeOH/H2O, positive ion scan, m/z): 608.3 ([M − SbF6]+). ESI-
X-ray Crystallography. Data for 4c-anti, 4d′, 5d, and 6c-anti·
3CH2Cl2 were collected on a Bruker SMART APEX diffractometer
using Mo Kα radiation (0.710 73 Å). Data for 5c-syn·2CH2Cl2, 6d, 7d,
and 8d were collected on a Bruker D8 Venture System with CMOS
detector and Mo microsource radiation. All data were collected at 100
K except for 6c-anti·3CH2Cl2, whose data were collected at 200 K.
Direct methods were used to locate many atoms from the E-map.
Repeated difference Fourier maps allowed recognition of all expected
non-hydrogen atoms. Following anisotropic refinement of all non-H
atoms, ideal H atom positions were calculated unless otherwise noted.
Final refinement was anisotropic for all non-H atoms and isotropic-
riding for H atoms. No anomalous bond lengths or thermal parameters
were noted unless otherwise indicated. ORTEP diagrams are drawn
with 50% probability ellipsoids. Specific comments for each structure
follow. 4c-anti: Crystals of 4c-anti were obtained by diffusion of
hexanes into a CH2Cl2 solution of 4c (1.4:1 anti/syn mixture) at 0 °C.
4d′: Crystals of 4d′ were obtained by diffusion of hexanes into a
CH2Cl2 solution at room temperature. Two independent molecules
are present in the asymmetric unit. 5c-syn: See the synthetic procedure
for single-crystal preparation. Two solvent molecules of CH2Cl2 are
present with one found to be disordered over two positions (0.7 to 0.3
relative occupancy). Identical anisotropic thermal parameters were
used for the C atoms of the disordered CH2Cl2 molecule. The
coordinates of H31A and H31B were refined and the thermal
parameters of these atoms were constrained to be 1.2 times those of
C31. 5d: Crystals of 5d were obtained by diffusion of hexanes into a
CH2Cl2 solution at −30 °C. 6c-anti: Crystals of 6c-anti were obtained
by diffusion of hexanes into a CH2Cl2 solution at 0 °C. Initial attempts
to collect data at 100 K proved unsuccessful, probably due to a phase
transformation. Three CH2Cl2 solvent molecules were present with
full occupancy. 6d: Crystals of 6d were obtained by slow evaporation
of a CH2Cl2/Et2O solution at room temperature. 7d: Crystals of 7d
were obtained by layering hexanes onto a CH2Cl2 solution at −30 °C.
8d: Crystals of 8d were obtained by layering hexanes onto a CH2Cl2
solution at −40 °C. The hydrogen atoms on the nitrogens in 4d′, 5d,
6d, 7d, and 8d were located on the difference Fourier maps, and their
positions were refined isotropically.
−
MS (1:1 MeOH/H2O, negative ion scan, m/z): 234.9 (SbF6 ). HRMS
(ESI-TOF, positive ion, m/z): calcd 608.2581 ([M − SbF6]+), found
608.2594.
8e. A glass vial was charged with 5e (51.6 mg, 0.0919 mmol),
AgSbF6 (36.5 mg, 1.16 equiv), and pyrazole (6.3 mg, 1.0 equiv).
CH2Cl2 (2 mL) was added to the reaction mixture, and the vial was
agitated for 20 s to give a suspension of an off-white precipitate in a
yellow solution. The suspension was filtered by pipet filtration, and the
yellow filtrate was concentrated to 1 mL. Formation of yellow crystals
was observed. The mixture was layered with hexanes (8 mL) and kept
at −40 °C overnight to give yellow needles (73.3 mg, 96%). The solid
contained 0.30 equiv of CH2Cl2 and 0.022 equiv of Et2O as
1
1
determined by H NMR. H NMR (500 MHz, CD2Cl2): δ 9.92 (br
s, 1H, pz NH), 7.52−7.51 (m, 1H, Ar, pz H3), 7.42−7.34 (m, 4H, Ar),
7.28 (d, J = 7.8, 2H, Ar), 6.63 (td, J = 2.2, 0.4, 1H, pz H5), 6.14 (q, J =
2.4, 1H, pz H4), 2.99 (septet, J = 6.8, 2H, iPr methine), 2.87 (septet, J
i
= 6.8, 2H, Pr methine), 2.28 (s, 3H, MeCN), 2.26 (s, 3H, MeC
N), 1.38 (d, J = 6.8, 6H, iPr), 1.23 (d, J = 6.9, 6H, iPr), 1.23 (d, J = 6.9,
6H, iPr), 1.14 (d, J = 6.8 Hz, 6H, iPr), 0.52 (s, 3H, Pd−Me). 1H NMR
(500 MHz, CD3CN): δ 11.29 (br s, 1H, pz NH), 6.49 (t, J = 2.1, 1H,
pz H5), 6.07 (q, J = 2.3, 1H, pz H4), 0.28 (s, 3H, Pd−Me). 13C{1H}
NMR (126 MHz, CD2Cl2): δ 179.3, 173.3 (imine CN), 141.5 (pz
C5), 141.38, 141.37, 138.9, 138.2 (Ar), 132.2 (pz C3), 129.0, 128.8,
125.0, 124.8 (Ar), 107.0 (pz C4), 29.5, 29.2 (iPr methine), 24.0, 23.6,
23.3, 23.1 (iPr methyl), 21.9, 20.6 (MeCN), 8.6 (Pd−Me). 19F
NMR (470 MHz, CD3CN): δ −123.7; overlay of 121SbF6 (sextet, JSbF
= 1940) and 123SbF6 (octet, JSbF = 1050). IR (cm−1): νN−H, 3364. Anal.
Calcd for C32H47F6N4PdSb·0.30CH2Cl2·0.022C4H10O: C, 45.39; H,
5.62; N, 6.54. Found: C, 45.25; H, 5.56; N, 6.54. ESI-MS (1:1 MeOH/
H2O, positive ion scan, m/z): 593.3 ([M − SbF6−]+). ESI-MS (1:1
MeOH/H2O, negative ion scan, m/z): 234.9 (SbF6 ).
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis of compounds; details of the dynamics of 4b and the
isomerization behavior of (α-diimine)Pd complexes; deviations
from square planar geometry for (α-diimine)Pd complexes;
details of the hydrogen bonding in the solid-state structures of
4d′, 5c-syn·2CH2Cl2, and 6c-anti·3CH2Cl2; NMR spectra for
new compounds; crystal structure reports; and crystallographic
data in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rfjordan@uchicago.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Ian Steele and Alexander Filatov for assistance with
X-ray crystallography and Naomi Clayman for assistance with
the synthesis of 4b and 5b,b′. This work was supported by the
National Science Foundation (grants CHE-0911180 and CHE-
1048528).
Measurement of Pyrazole Dissociation Constant of (α-
−
diimine)PdMe(pz)+SbF6 in CD3CN. A J. Young NMR tube was
−
charged with (α-diimine)PdMe(pz)+SbF6 (10−20 mg) and CD3CN
(0.5−1.5 mL). The tube was sealed, shaken to yield a yellow
homogeneous solution, and maintained at room temperature, and
NMR spectra were recorded periodically. For 8a,d,e, equilibrium was
reached after 10 min. For 8c-anti,syn, equilibrium was reached after 1
h. The dissociation constants, Keq = [(α-diimine)PdMe(CD3CN)+] ×
[pz] × [(α-diimine)PdMe(pz)+]−1 = [pz]2[(α-diimine)PdMe(pz)+]−1
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■
1
(M), were calculated from H NMR integrations.
O
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