Unsymmetrical bidentate ligands of α-aminoaldimines leading to sterically controlled selectivity of geometrical isomerism in square planar coordination

Article abstract of DOI:10.1039/b805674a

New α-aminoaldimines with the formula of Et₂NCMe ₂CHNR (R = ⁱPr, ^tBu, Ph) and their dichloro or diacetato complexes of Ni, Pd, Pt are prepared and structurally characterized. A nickel complex is in a distorted tetrahedral configuration, and the Pd and Pt complexes (4-6) are of square planar form. The α-aminoaldimines can chelate to the metal in a C₂-unsymmetric bidentate motif through the hetero functionalities of amine and imine, which show comparable trans influence. Square planar organometallic palladium derivatives bearing α-aminoaldimines, including Pd-methyl, Pd-acetyl, and Pd- (η²-acetylnorboryl) (7-10), are also synthesized. The latter two species are a result of CO-insertion into Pd-methyl complexes and ensuing norbornene-insertion, respectively. The geometrical isomerism is found in the trans configuration in most studied cases. Such a stereoselectivity results from the thermodynamic stability governed predominantly by steric control. The stereoselectivity is also supported by DFT calculations.

Full text of DOI:10.1039/b805674a

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www.rsc.org/dalton | Dalton Transactions
Unsymmetrical bidentate ligands of a-aminoaldimines leading to sterically
controlled selectivity of geometrical isomerism in square planar coordination†
Jen-Jeh Lee, Feng-Zhao Yang, Ya-Fan Lin, Ya-Chun Chang, Kuo-Hsuan Yu, Mu-Chieh Chang,
Gene-Hsiang Lee, Yi-Hung Liu, Yu Wang, Shiuh-Tzung Liu and Jwu-Ting Chen*
Received 4th April 2008, Accepted 18th July 2008
First published as an Advance Article on the web 16th September 2008
DOI: 10.1039/b805674a
i
t
=
New a-aminoaldimines with the formula of Et2NCMe2CH NR (R = Pr, Bu, Ph) and their dichloro or
diacetato complexes of Ni, Pd, Pt are prepared and structurally characterized. A nickel complex is in a
distorted tetrahedral configuration, and the Pd and Pt complexes (4–6) are of square planar form. The
a-aminoaldimines can chelate to the metal in a C2-unsymmetric bidentate motif through the hetero
functionalities of amine and imine, which show comparable trans influence. Square planar
organometallic palladium derivatives bearing a-aminoaldimines, including Pd–methyl, Pd–acetyl, and
2
Pd–(h -acetylnorboryl) (7–10), are also synthesized. The latter two species are a result of CO-insertion
into Pd–methyl complexes and ensuing norbornene-insertion, respectively. The geometrical isomerism
is found in the trans configuration in most studied cases. Such a stereoselectivity results from the
thermodynamic stability governed predominantly by steric control. The stereoselectivity is also
supported by DFT calculations.
Introduction
New auxiliary ligands often bring new chemical features to
coordination chemistry. The bidentate ligands with hybrid hard
and soft donors have been acquiring enormous attention, because
Chart 1 Square planar configuration with a-aminoaldimines.
they are anticipated to confer different electronic and steric effects
to the metal center as well as reactivity of the complexes.1 Some
unsymmetrical bidentate ligands contain the same donor atom
in hybrid functionalities.2 Among them, those that coordinate
through the functionalities of amine and imine are rarely studied.3
Still, a few cases have proved to be useful for catalysis.4 Others
are found to be important to bio-functions.5 Amino acids which
can coordinate with metal through two hard groups of amine
and carboxylate simultaneously can serve as natural unsymmet-
rical bidentate ligands.6 The a-aminoaldimines, which are imino
derivatives of amino acids, may be expected to provide chelation
of non-C2-symmetry through the two nitrogen donor atoms of the
hetero functionalities of amine and imine. Such ligands might be
suitable candidates for the examination of the individual power
of electronic and steric influences in their coordination chemistry,
particularly in the square planar mode.
There are at least several distinguishable aspects between amine
and imine that are worthy of note. Amine is a typical s-base
containing a nitrogen donor atom of sp3 configuration, often with
bond angles of less than 110◦. On the other hand, imine has
both s-donating and p-accepting character and has a nitrogen
donor atom of sp2 configuration, and gives significantly larger
bond angles of around 120◦ with the adjacent ligand. In the square
planar coordinating motif as shown in Chart 1, a-aminoaldimines
constitute a non-planar five-membered ring with the metal ion.
The amine holds two substituents, but the imine may only have
one. The imino substituent can rotate along the N–C bond which
lies in the molecular plane.7 In contrast, the amino substituents
are in tetrahedral fashion that directs out of molecular plane and
potentially can provide an asymmetric environment.8 Therefore,
the coordination sites of A and B are expected to experience
individual influence from the amine and imine functionalities.
In this article we report the synthesis and structures of the
dichloro, diacetato, and some organometallic complexes of group
10 transition metals that bear new ligands of a-aminoaldimines.
In the dichloro and diacetato species, the functionalities of
amine and imine demonstrate comparable trans influence. In the
organometallic derivatives, these unsymmetrical auxiliary ligands
lead to geometrical stereoselectivity and geometrical isomerism
that are attributed to the sterically controlled thermodynamic
stability.
Results and discussion
Synthesis and spectroscopic characterization
The starting material, 2-bromo-2-methylpropanal (1),9 was pre-
pared by a reaction of bromine-1,4-dioxane and 2-methylpropanal
in diethyl ether. The reaction slurry was constantly stirred till
the disappearance of the orange color. The reaction solution was
stirred for another 10 min, then extracted with ice-cold water. The
resulting solution was dried with MgSO4, and ether was removed
Department of Chemistry, National Taiwan University, No 1, Section 4, Roo-
sevelt Road, Taipei, 106, Taiwan. E-mail: jtchen@ntu.edu.tw; Fax: +886-2-
2363-6359; Tel: +886-2-3366-1659
† CCDC reference numbers 682281, 683783–683791 (3c, 4a, 4c, 5b, 5c, 6c,
7a, 7c, 8c and 10c). For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b805674a
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on a rotary evaporator. The brominated derivative 1 was usually
ready for immediate use in the ensuing reaction.
tetrahedral configuration in the coordinating mode of amine.11
Treating 4a or 4c with double molar amounts of silver acetate
There are two potential electrophilic sites in 2-bromo-2-
methylpropanal (1). The reaction of 1 with secondary amine
only leads to the substitution of bromine, presumably by
gives rise to the formation of diacetato complexes in the form of
i
=
=
[Et2NCMe2CH NR]Pd(OAc)2 (R = Pr (6a), Ph (6c)). The C O
stretching frequencies below 1700 cm-1 appear to be lower than
the free acetates, and comparable to the coordinating fashion.12
The C2-unsymmetrical ligand results in the differentiation for
the two acetato ligands. The two acetyloxy methyl groups in 6a
have close resonances in the1H NMR spectrum, implying small
electronic difference between the amine and imine functionalities.
For 6c, there is only one carbonyl carbon identified in the 13C
NMR spectrum. However, two acetyloxy methyl signals in the1H
and 13C NMR spectra are observed. One is particularly upfield,
presumably due to the ring current from the phenyl group on the
cis imine.
radical-nucleophilic substitution, SRN1, mechanism.10 The new
i
=
a-aminoaldimines in the form of Et2NCMe2CH NR (R = Pr
t
(2a), Bu (2b), Ph (2c)) are synthesized first by substitution of
diethylamine for bromine in 1, and followed by condensation using
primary amine or aniline, respectively, as shown in Scheme 1. The
products are collected as viscous colorless liquids in good yields
by means of distillation under reduced pressure. The structures of
the new derivatives of a-aminoaldimines are mainly determined
by spectroscopic methods.
Neutral organometallic complexes in the formula of
i
=
[Et2NCMe2CH NR]Pd(Me)Cl (R = Pr (7a), Ph (7c)) could be
prepared either by substitution of a-aminoaldimines for COD
(1,4-cyclooctadiene) in (COD)Pd(Me)Cl,13 or by transmetallation
using an organotin reagent14 with [Et2NCMe2CH NR]PdCl2
=
(Scheme 3). The NMR data indicate that a single geometrical
isomer is formed selectively. The Pd-bound methyl group of 7c
appears substantially upfield than that of 7a, d 0.46 vs. 0.73,
implicating that methyl is likely cis to imine, and thus influenced by
the ring current from the imino phenyl group. Chloride abstraction
Scheme 1 Synthesis of a-aminoaldimines.
Compounds 2a, 2b or 2c can serve as bidentate ligands with
hybrid donor functionalities of amine and imine. The substitution
reactions of 2a, 2b or 2c with (PhCN)2MCl2 (M = Pd, Pt)
from 7a or 7c by silver triflate in acetonitrile results in the cationic
i
=
species {[Et2NCMe2CH NR]PdMe(NCMe)}OTf (R = Pr (8a),
Ph (8c)). The stereochemistry of the trans isomerism is considered
to be retained, since the Pd-bound methyl group in the NMR
spectra for 8a and 8c resemble those for 7a and 7c, respectively.
leads to the neutral amine–imine complexes in the form of
i
=
[Et2NCMe2CH NR]MCl2 (M = Pd, R = Pr (4a), Ph (4c); M =
t
Pt, R= Bu (5b), Ph (5c)), as shown in Scheme 2. The yields for the
palladium complexes are excellent, but relatively poor for the plat-
inum complexes. Similar reaction of 2c and (DME)NiCl2 (DME =
=
1,2-dimethoxyethane) generate [Et2NCMe2CH NPh]NiCl2 (3c).
Recrystallization of the violet inorganic product from CH2Cl2–
Et2O gives 62% yields and single crystals. The broadened NMR
spectra of 3c implicates a paramagnetic electronic configuration
and tetrahedral molecular geometry.
Scheme 3 Synthesis of methylpalladium complexes.
Allowing CO to bubble through the solution of 7a or 7c readily
results in a single product of neutral acetylpalladium complex 9a
or 9c, respectively. A characteristic acyl CH3 signal is at d 2.44
1
in the H NMR; and an acyl carbonyl is at d 226.4 in the 13C
NMR for 9a. For 9c, the corresponding data are d 2.10 and d
223.0, respectively. Chloride abstraction from 8a or 8c using silver
triflate in acetonitrile with the presence of norbornene leads to
olefin insertion, yielding cationic acetylnorbornyl complexes 10a
or 10c, respectively. Complexes 10a and 10c may alternatively be
achieved from 8a and 8c, respectively ,with the presence of carbon
monoxide and norbornene together, as illustrated in Scheme 4. The
carbonyl stretching signals of low infrared frequencies, 1608 cm-1
for 10a and 1605 cm-1 for 10c, suggest that a coordinating mode
Scheme 2 Synthesis of dichloro and diacetato complexes of Ni, Pd,
or Pt.
The distinct shift of the imino hydrogen signals in the 1H
NMR spectra and the imino carbon in the 13C NMR spectra for
the palladium and platinum complexes indicate the coordination
mode of the ligand. The diastereotopic hydrogens of the amino
methylene group, shown by the 1H NMR, also support the
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Scheme 4 CO and norbornene insertion of methylpalladium complexes.
through acyl oxygen might occur, as observed in many analogous
prior cases.15 It is noted again that some NMR resonances
corresponding to the norbornyl hydrogen in 10c are in the upfield
region compared to 10a. It is thus thought that the norbornyl
group is cis to the imino functionality.
X-Ray structural analysis
Single crystals of 3c, 4a, 4c, 5b, 5c, 6c, 7a, 7c, 8c and 10c that
are suitable for X-ray diffractions have been obtained. Crystallo-
graphic analyses provide unequivocal evidence for the molecular
structures of these complexes which bear unsymmetrical amine–
imine bidentates. The crystal data are listed in Table 1, and the
selected bond lengths and bond angles are collected in Table 2.
In Fig. 1, the ORTEP drawing of complex 3c is in a dis-
torted tetrahedral configuration which explains its paramagnetism
suggested by the broadened NMR signals. The amine–imine
complexes of dichloropalladium, dichloroplatinum, and diac-
etatopalladium are all square planar. The representative ORTEP
drawings of 4a, 4c, 5b and 6c are shown in Fig. 2 and 3; 8c and
10c are in Fig. 4 and 5, respectively.
i
=
Fig. 2 ORTEP drawings of (a) [Et2NCMe2CH N Pr]PdCl2 (4a), and
=
(b) [Et2NCMe2CH NPh]PdCl2 (4c). All hydrogen atoms are omitted for
clarity.
˚
1.979 A); and the distance of the amino C2–N2 bond is longer
˚
˚
than the imino C1–N1 bond (1.520 A vs. 1.297 A), as expected. The
N1–Ni–N2 angle is 83.5(1)◦, nearly the same as that in Brookhart’s
diimine catalysts.16 The Cl1–Ni–Cl2 angle is 115.65(5)◦. In other
Pd or Pt complexes of square planar geometry, the differences
between the Pd–N1 bond and Pd–N2 bond are slightly larger
˚
˚
than that in 3c (about 0.1 A vs. 0.07 A). The imino C1–N1 bonds
˚
˚
are generally shorter (about 1.27 A vs. 1.30 A) and the N1–M–N2
angles are generally smaller (about 80◦ vs. 84◦) in 4a, 4c, 5b, 5c
and 6c than in 3c. It is noted that in the square planar complexes
of 4a, 4c, 5b, 5c, and 6c the distances of two M–Cl or of two
Pd–O bonds are all rather comparable, with the difference being
˚
less than about 0.01 A. In the general sense, this phenomenon
indicates that the amino group and the imino group hardly show
significant difference in trans influence.17
The structures of organometallic species 7a, 7c, 8c and 10c are
all in the trans configuration, i.e. the metal–carbon bond is trans
to the amino nitrogen, no matter if the substituent on the imino
nitrogen is isopropyl or the phenyl group. Complex 10c indicates
that the norbornene insertion into the Pd–acyl bond takes place
in the sole syn/exo-fashion.18
Further looking into the bond parameters as summarized in
=
Table 3, a few trends may be noticed. The Pd–N2 bonds in the
Fig. 1 ORTEP drawing of [Et2NCMe2CH NPh]NiCl2 (3c). All hydrogen
atoms are omitted for clarity.
˚
organometallic derivatives are substantially longer (>0.1 A) than
those in the dichloro derivatives. And, the differences between
the Pd–N1 and Pd–N2 bonds are larger in the organometallic
By viewing the data of 3c in Table 2, the distance of the Ni–
N2(sp ) bond is longer than the Ni–N1(sp ) bond (2.045 A vs.
3
2
˚
˚
˚
complexes than in the dichloro complexes (0.2 A vs. 0.1 A). This
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5948 | Dalton Trans., 2008, 5945–5956
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◦
˚
Table 2 Selected bond distances (A) and angles ( )
=
[Et2NCMe2CH NPh]NiCl2 (3c)
Ni–N1
1.979(3)
1.297(8)
1.482(6)
83.5(1)
Ni–N2
N2–C2
N2–C7
Cl1–Ni–Cl2
N1–C1–C2
C7–N2–Ni
2.045(2)
1.520(5)
1.531(6)
115.65(5)
120.4(6)
107.2(3)
Ni–Cl1
C1–C2
2.217(1)
1.498(9)
Ni–Cl2
N1–C21
2.206(1)
1.428(4)
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
112.8(4)
107.4(4)
125.6(2)
106.5(2)
112.6(3)
i
=
[Et2NCMe2CH N Pr]PdCl2 (4a)
Pd–N1
2.028(3)
1.263(6)
1.493(7)
79.78(1)
100.9(2)
115.9(3)
Pd–N2
N2–C2
N2–C7
Cl1–Pd–Cl2
N1–C1–C2
C7–N2–Pd
2.126(4)
1.534(6)
1.510(6)
89.31(6)
120.9(4)
107.6(3)
Pd–Cl1
C1–C2
2.314(1)
1.493(6)
Pd–Cl2
N1–C9
2.297(1)
1.477(6)
N1–C1
N2–C5
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
Pd–N1–C1
N2–C2–C1
C9–N1–Pd
111.8(3)
105.2(3)
124.8(3)
=
[Et2NCMe2CH NPh]PdCl2 (4c)
Pd–N1
2.026(2)
1.268(3)
1.505(3)
80.03(8)
103.0(2)
112.58(2)
Pd–N2
N2–C2
N2–C7
Cl1–Pd–Cl2
N1–C1–C2
C7–N2–Pd
2.115(2)
1.528(3)
1.517(4)
88.61(3)
120.4(2)
106.5(2)
Pd–Cl1
C1–C2
2.2822(7)
1.507(3)
Pd–Cl2
N1–C21
2.2947(8)
1.435(3)
N1–C1
N2–C5
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
112.9(2)
105.4(2)
127.2(2)
t
=
[Et2NCMe2CH N Bu]PtCl2 (5b)
Pt–N1
2.03(1)
1.31(2)
1.51(2)
80.1(5)
103(7)
Pt–N2
N2–C2
N2–C7
Cl1–Pt–Cl2
N1–C1–C2
C7–N2–Pt
2.12(1)
1.54(2)
1.52(2)
84.8(2)
121(1)
Pt–Cl1
C1–C2
2.310(4)
1.47(2)
Pt–Cl2
N1–C9
2.304(4)
1.50(2)
N1–C1
N2–C5
N1–Pt–N2
Pt–N2–C2
C5–N2–Pt
Pt–N1–C1
N2–C2–C1
C9–N1–Pt
112(1)
106(1)
128.6(8)
111.3(8)
109(1)
=
[Et2NCMe2CH NPh]PtCl2 (5c)
Pt–N1
2.016(3)
1.281(5)
1.522(6)
80.3(1)
Pt–N2
N2–C2
N2–C7
Cl1–Pt–Cl2
N1–C1–C2
C7–N2–Pt
2.119(3)
1.537(5)
1.524(6)
88.04(4)
120.1(3)
107.5(3)
Pt–Cl1
C1–C2
2.303(1)
1.504(5)
Pt–Cl2
N1–C21
2.311(1)
1.447(5)
N1–C1
N2–C5
N1–Pt–N2
Pt–N2–C2
C5–N2–Pt
Pt–N1–C1
N2–C2–C1
C21–N1–Pt
114.0(3)
105.7(3)
126.7(2)
104.1(2)
111.3(3)
=
[Et2NCMe2CH NPh]Pd(OAc)2 (6c)
Pd–N1
1.996(4)
1.271(6)
1.491(6)
81.0(2)
Pd–N2
N2–C2
N2–C7
O1–Pd–O3
N1–C1–C2
C7–N2–Pd
2.075(4)
1.520(6)
1.524(5)
85.8(1)
118.2(5)
107.4(3)
Pd–O1
C1–C2
2.012(3)
1.502(6)
Pd–O3
N1–C21
2.012(3)
1.437(6)
N1–C1
N2–C5
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
114.6(3)
105.7(4)
125.8(3)
104.3(3)
109.7(3)
i
=
[Et2NCMe2CH N Pr]Pd(Me)Cl (7a)
Pd–N1
2.046(3)
1.282(6)
1.500(5)
78.3(1)
Pd–N2
N2–C2
N2–C7
Cl1–Pd–C9
N1–C1–C2
C7–N2–Pd
2.250(3)
1.531(5)
1.485(5)
88.2(1)
122.7(3)
107.3(2)
Pd–C9
C1–C2
2.022(4)
1.478(8)
Pd–Cl1
N1–C21
2.306(1)
1.485(7)
N1–C1
N2–C5
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
112.8(3)
106.1(3)
125.1(3)
100.5(2)
111.9(2)
=
[Et2NCMe2CH NPh]Pd(Me)Cl (7c)
Pd–N1
2.040(3)
1.268(5)
1.494(5)
78.3(1)
Pd–N2
N2–C2
N2–C7
Cl1–Pd–C9
N1–C1–C2
C7–N2–Pd
2.270(3)
1.520(5)
1.485(5)
87.5(1)
122.9(3)
106.4(2)
Pd–C9
C1–C2
2.018(4)
1.498(8)
Pd–Cl1
N1–C21
2.310(2)
1.444(5)
N1–C1
N2–C5
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
115.1(3)
107.0(3)
126.9(2)
103.2(2)
110.7(2)
=
{[Et2NCMe2CH NPh]Pd(Me)(NCMe)}OTf (8c)
Pd–N1
2.027(3)
1.266(5)
1.501(5)
79.1(1)
Pd–N2
2.230(3)
1.509(5)
1.505(5)
86.9(2)
122.6(4)
108.1(2)
Pd–C9
C1–C2
N3–C10
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
2.007(4)
1.490(5)
1.123(5)
113.3(3)
107.1(3)
127.0(2)
Pd–N3
N1–C21
2.001(4)
1.437(5)
N1–C1
N2–C5
N2–C2
N2–C7
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
C10–N3–Pd
N3–Pd–C9
N1–C1–C2
C7–N2–Pd
101.6(2)
109.9(2)
174.3(4)
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Table 2 (Contd.)
=
{[Et2NCMe2CH NPh]Pd[C(O)Me(C7H10)]}OTf (10c)
Pd–N1
2.019(3)
1.280(5)
1.481(5)
79.2(1)
Pd–N2
2.227(3)
1.513(5)
1.488(5)
83.6(2)
121.4(4)
109.4(2)
115.2(3)
Pd–C9
C1–C2
O1–C16
Pd–N1–C1
N2–C2–C1
C21–N1–Pd
2.008(4)
1.501(6)
1.240(6)
113.7(3)
106.2(3)
126.7(3)
Pd–O1
N1–C21
2.045(3)
1.438(5)
N1–C1
N2–C5
N2–C2
N2–C7
N1–Pd–N2
Pd–N2–C2
C5–N2–Pd
C14–C9–Pd
O1–Pd–C9
N1–C1–C2
C7–N2–Pd
C16–O1–Pd
101.5(2)
107.9(3)
109.0(3)
=
Fig. 4 ORTEP drawing of {[Et2NCMe2CH NPh]Pd(Me)(NCMe)}-
OTf (8c). All hydrogen atoms are omitted for clarity, thermal ellipsoids
drawn at the 30% probability level.
t
=
Fig. 3 ORTEP drawings of (a) [Et2NCMe2CH N Bu]PtCl2 (5b), and
=
Fig. 5 ORTEP drawing of {[Et2NCMe2CH NPh]Pd[C(O)Me(C7H10)]}-
=
(b) [Et2NCMe2CH NPh]Pd(OAc)2 (6c). All hydrogen atoms are omitted
for clarity.
OTf (10c). All hydrogen atoms are omitted for clarity, thermal ellipsoids
drawn at the 30% probability level.
is attributed to the large trans influence of the Pd-bound methyl.
Despite the slight lengthening of the Pd–N1 and Pd–N2 bonds
in the organometallic complexes, the bite-angles of N1–Pd–N2 in
7a and 7c are smaller (1–2◦) than in the corresponding dichloro
complexes 4a and 4c, respectively; however, they are slightly larger
than in the methylchloro analogues of the diimino complexes.19
even the products from the reaction of CO or olefin insertion
as illustrated in Scheme 4. The stereo-retention of CO insertion
and norbornene insertion may be explained either by a pathway
involving a five-coordinate intermediacy,20 or isomerization via
amine dissociation and re-coordination.21
In complexes 7a and 7c, the trans isomerism appears to be not
affected by the isopropyl or phenyl group on the imine. Such
a stereoselectivity is attributed to steric hindrance between the
methyl ligand in 7 or 8, acetyl in 9 or norbornyl in 10 and the
ethyl substituents of amine functionality that could destabilize the
Geometrical isomerism
All the prepared organometallic derivatives with the title ligands
show a single geometrical isomer of the trans configuration,
5950 | Dalton Trans., 2008, 5945–5956
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kcal mol-1. For 10c, the trans-syn/exo, trans-syn/endo, and the
cis-syn/exo configurations have been compared. The cis-exo form
is 5.51 kcal mol-1, while the trans-endo form is 1.47 kcal mol-1 less
stable than the trans-exo form that is the sole isomer observed by
X-ray diffractions.
Table 3 Selected bond parameters from crystallographic analysis
◦
˚ ˚
Complex
Pd–N1 (A) Pd–N2 (A) N1–Pd–N2 (◦) L1–Pd–L2a ( )
4a
2.028(3)
2.026(2)
2.046(3)
2.040(3)
2.027(3)
2.126(4)
2.115(2)
2.250(3)
2.270(3)
2.230(3)
2.227(3)
79.8(1)
80.03(8)
78.3(1)
78.3(1)
79.1(1)
79.2(1)
89.31(6)
88.61(3)
88.2(1)
87.5(1)
86.9(2)
83.6(2)
4c
trans-7a
trans-7c
trans-8c
The structural parameters from the theoretical approach are
listed in Table 5. It is shown that all of the biting angles of
N1–Pd–N2 are about 3◦ smaller than the data from X-Ray analy-
sis. But the angles of L1–Pd–L2 are matched well. Comparing the
theoretical structures for the geometrical isomers of 7a, 7c, 8c and
9c, the larger bond lengths between Pd–N1 and Pd–N2 in the trans
species rather than in cis could be attributed to the trans influence.
However, it is difficult to ascribe the favorable stability of the trans
form to electronic or steric effect according to these data.
In the case of 10c, the bond parameters of trans-exo derivative
between the calculated and the experimental data are rather
comparable. In the trans-endo form, the hindrance appears to be
mainly resulting from a methyl on the a-carbon of the bidentate
ligand and the H of nobornyl bridge. The closest H ◊ ◊ ◊ H distance
trans-exo-10c 2.019(3)
a L1: the donor atom trans to imine; L2: the donor atom trans to amine.
cis form.22 The two methyl substituents on the a-carbon (C2) of
aminoaldimines might enhance this hindrance. On the other hand,
the imino functionality in which the trigonal planar disposition
around the N(sp2) is supposed to be more tolerable to the steric
strain than the N(sp3). Besides, teriary amines are known to be
hemi-labile.23 It is reasonable to assume that the trans isomerism
is a thermodynamic result of isomerization via amine dissociation
and re-coordination.
˚
˚
is 2.313 A (whilst 3.025 A in trans-exo), as shown in Fig. 6(a)
and 6(b). In the cis-exo form, multiple H ◊ ◊ ◊ H hindrances likely
result from the interaction between the amino ethyl groups and the
norbornyl group. In Fig. 6(c), three sets of H ◊ ◊ ◊ H distance within
Calculational analysis
In order to seek theoretical support for the stereoselectivity to
the trans geometrical isomers, DFT calculations of the energy
differences between the trans and cis isomers of 7a, 7c, 8c, 9c and
the trans/cis-exo/endo forms for 10c have been carried out.
The results regarding the calculated relative stability between
the isomers are consistent with the experimental observations. As
the data listed in Table 4 shows, the neutral complexes of trans-7a,
trans-7c, and trans-9c are more stable than their corresponding cis
isomers by 4.08, 5.21, and 4.78 kcal mol-1, respectively. For the
cationic complex 8c, the trans form is more favorable by only 2.62
˚
2.3 A are found. It indicates that the respective steric effects from
Table 4 DFT calculations for the relative stability of organopalladium
stereoisomers
Complex
trans (kcal mol-1)
cis (kcal mol-1)
7a
0
0
0
0
4.08
5.21
2.62
4.78
5.51
—
7c
8c
9c
10c-exo
10c-endo
0
1.47a
Fig. 6 Calculated steric hindrance in 10c of (a) trans-exo, (b) trans-endo,
(c) cis-exo.
a Relative to 10c-trans-exo.
Table 5 Selected bond parameters from calculations
N1–Pd–N2 (◦)
L1–Pd–L2 (◦)
a
b
˚
˚
˚
˚
˚
=
Complex
Pd–N1 (A)
Pd–N2 (A)
C1 N1 (A)
Pd–L1 (A)
Pd–L2 (A)
cis-7a
trans-7a
cis-7c
trans-7c
cis-8c
trans-8c
cis-9c
trans-9c
cis-exo-10c
trans-endo-10c
trans-exo-10c
2.201
2.138
2.273
2.131
2.223
2.105
2.318
2.197
2.115
2.224
2.113
2.337
2.416
2.335
2.421
2.260
2.371
2.432
2.500
2.334
2.279
2.334
1.259
1.268
1.269
1.275
1.265
1.273
1.265
1.271
1.269
1.275
1.274
2.072(L1 = C9)
2.071(L1 = C9)
2.077(L1 = C9)
2.073(L1 = C9)
2.080(L1 = C9)
2.083(L1 = C9)
1.986(L1 = C9)
1.995(L1 = C9)
2.079(L1 = C9)
2.089(L1 = C9)
2.073(L1 = C9)
2.369(L2 = Cl1)
2.366(L2 = Cl1)
2.369(L2 = Cl1)
2.369(L2 = Cl1)
2.064(L2 = N3)
2.065(L2 = N3)
2.420(L2 = Cl1)
2.400(L2 = Cl1)
2.146(L2 = O1)
2.133(L2 = O1)
2.123(L2 = O1)
74.99
74.99
74.39
75.15
76.15
76.23
73.18
73.66
76.06
74.73
76.74
88.07
88.16
85.12
88.22
87.27
86.76
83.67
88.07
81.46
80.81
81.52
a L1: the donor atom trans to imine. b L2: the donor atom trans to amine.
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the amino and imino functionalities of such aldimines are crucial
to the geometrical isomerism in the square planar configuration.
C(CH3)2), 1.02 (t, JH–H = 7.1 Hz, 6H, NCH2CH3); 13C NMR
(CDCl3): d 205.5 (CHO), 66.7 (C(CH3)2), 43.4 (NCH2CH3), 18.9
(C(CH3)2), 16.0 (NCH2CH3); MS (FAB, m/z): 143 (M+).
i
Concluding remarks
=
Et2NCMe2CH N Pr (2a). In a round-bottom flask was placed
Et2NCMe2CHO (4.33 g, 30.3 mmol) and isopropylamine (1.9 g,
New unsymmetric bidentate ligands of a-aminoaldimines in the
formula of Et2NCMe2CH NR are synthesized. A tetrahedral
˚
32.8 mmol) in 100 mL of benzene. The solution was stirred with 4 A
=
molecular sieves at 25 ◦C. Distillation under vacuum gave colorless
dichloronickel(II) complex and square planar dichloro and diac-
etato complexes of palladium or platinum are synthesized. The
amine and imine functionalities show comparable trans influence.
Square planar organometallic complexes of palladium with selec-
tive geometrical isomerism favored by the trans configuration are
acquired. Such a stereoselectivity is a result of the thermodynamic
option governed predominantly by the steric control from the
hetero-donating functionalities of the ligand. In more specific
words, the bulkier ligands prefer to coordinate cis to the imine
group rather than amine group in the studied cases, so that the
steric hindrance could be minimized.
liquid product in 49% yield (2.7 g). IR (KBr): nCN 1666 cm-1; 1H
=
NMR (CDCl3) d 7.51 (s, 1H, CH N), 3.27 (h, JH–H = 6.8 Hz,
1H, NCH(CH3)2), 2.50 (q, JH–H = 7.2 Hz, 4H, NCH2CH3), 1.12
(s, 6H, C(CH3)2), 1.10 (d, JH–H = 6.8 Hz, 6H, NCH(CH3)2), 1.00
(t, JH–H = 7.2 Hz, 6H, NCH2CH3);13C NMR (CDCl3): d 168.3
=
(C N), 61.1 (C(CH3)2), 61.0 (NCH(CH3)2), 43.2 (NCH2CH3),
23.9 (C(CH3)2), 22.0 (NCH(CH3)2), 16.4 (NCH2CH3); MS (FAB,
m/z): 185.2 (M+ + 1).
t
t
=
Et2NCMe2CH N Bu (2b). Using BuNH2 and following the
similar procedure as the preparation for 2a gave the product of
1
=
2b in a yield of 76%. H NMR (CDCl3): d 7.48 (s, 1H, CH N),
2.51 (q, JH–H = 7.1 Hz, 4H, NCH2CH3), 1.13 (s, 9H, C(CH3)3),
Experimental section
1.12 (s, 6H, C(CH3)2), 1.02 (t, JH–H = 7.1 Hz, 6H, NCH2CH3);
13
=
Synthesis and spectral characterization
C NMR (CDCl3): d 165.0 (CH N), 61.44 (C(CH3)3), 56.16
(C(CH3)2), 43.30 (NCH2CH3), 29.63 (C(CH3)3), 21.73 (C(CH3)2),
16.40 (NCH2CH3).
General procedures. Commercially available reagents were
purchased and used without further purification unless otherwise
indicated. Organic solvents were dried from purple solutions of
benzophenone ketyl or over P2O5 under nitrogen, and distilled
immediately prior to use. Air-sensitive material was manipulated
under a nitrogen atmosphere in a glove box or by standard Schlenk
techniques. The IR spectra were recorded on a Bio-Rad FTS-40
spectrophotometer. The NMR spectra were measured on Bruker
AC-200, AC-300, or AC-400 spectrometer. The corresponding
frequencies for 13C NMR spectra were 50.324 and 75.469 MHz,
=
Et2NCMe2CH NPh (2c). In a round-bottom flask was added
Et2NCMe2CHO (7.0 g, 49 mmol) and then aniline (7.6 g, 82 mmol)
in 150 mL of benzene. The solution was refluxed under nitrogen
with Dean–Stark set-up. The product was isolated as a viscous
colorless liquid by distillation under vacuum. The yield was 66%
1
(11.8 g). IR (KBr): nCN 1648 cm-1; H NMR (CDCl3): d 7.75 (s,
=
1H, CH N), 7.35–6.99 (m, 5H, phenyl-H), 2.61 (q, JH–H = 7.0 Hz,
4H, NCH2CH3), 1.28 (s, 6H, C(CH3)2), 1.06 (t, JH–H = 7.0 Hz, 6H,
1
or 100.625 MHz respectively. Values upfield of H and 13C data
13
=
NCH2CH3); C NMR (CDCl3): d 172.6 (C N), 151.8, 130–112
are given in d relative to tetramethylsilane (d 0.00) in CDCl3
or to benzene in d6-benzene (7.15, C6H6; 128.7, C6H6). Mass
spectrometric analyses were collected on a Finnigan TSQ-46C
or JEOL SX-102A spectrometer. Elemental analysis was done on
a Perkin-Elmer 2400 CHN analyzer.
(phenyl-C), 63.0 (C(CH3)2), 43.8 (NCH2CH3), 21.8 (C(CH3)2),
15.8 (NCH2CH3); MS (FAB, m/z): 219.2 (M+ + 1). Anal. calcd
for C14H22N2: C, 77.01; H, 10.16; N, 12.83%. Found: C, 76.43; H,
10.01; N, 12.32%.
=
[Et2NCMe2CH NPh]NiCl2 (3c). (DME)NiCl2 (300 mg, 1
BrCMe2CHO (1). Orange bromine–1,4-dioxane adduct
(32.7 g, 0.132 mol) was added in several aliquots to 2-
methylpropanal (10 g, 0.139 mol) in 50 mL of diethyl ether
at 5 ◦C. The orange slurry was continuously stirred until the
disappearance of the color. The resulting solution was stirred for
10 min more, and then extracted three times with ice-cold water.
The solution was dried with MgSO4 and ether was removed on a
rotary evaporator. The yield was 70%. IR (KBr): nCO 1733 cm-1;
1H NMR (CDCl3): d 9.34 (s, 1H, CHO), 1.77 (s, 6H, CH3); 13C
NMR (CDCl3): d 192.8 (CHO), 63.8 (CMe2Br), 26.5 (CH3); MS
(FAB, m/z): 151 (M+).
mmol) and 2c (327 mg, 1.5 mmol) were placed in a round-bottom
flask under nitrogen. Predried CH2Cl2 (15 mL) was transferred
under vacuum. The orange solution turned to violet within 10 min.
The reaction was allowed to complete at 25 ◦C. After removal
of the supernatant solid, the reaction solution was concentrated.
Addition of dry Et2O resulted in the solid product, and the yield
of 1a was 62% (270 mg) after recrystallization from CH2Cl2–Et2O.
i
=
[Et2NCMe2CH N Pr]PdCl2 (4a). To a 20 mL CH2Cl2 solution
containing (PhCN)2PdCl2 (547 mg, 1.428 mmol) was added the
ligand 2a (270 mg, 1.467 mmol). The solution was stirred at
25 ◦C for 45 min, then was concentrated. Addition of diethyl ether
gave the yellow precipitate in 93% yield (480 mg). Single crystals
suitable for X-ray analysis were obtained by recrystallization from
CH2Cl2–Et2O. IR (KBr pellet): nCN 1655 cm-1; 1H NMR (CD3CN):
Et2NCMe2CHO. In
a round-bottom flask was placed
BrCMe2CHO (14 g, 92 mmol) in 30 mL of diethyl ether. The
solution was first cooled to 0 ◦C. Et2NH (17 g, 233 mmol) was
added dropwise. The mixture was then stirred for 4 h to allow the
reaction to complete. After the removal of amine salt, the solution
was distilled to give a viscous yellow liquid product in 88% yield
=
d 7.36 (s, 1H, CH N), 4.54 (h, JH–H = 6.6 Hz, 1H, NCH(CH3)2),
3.13, 2.99 (m, JH–H = 7.2, 14.6 Hz, 4H, NCH2CH3), 1.82 (s,
6H, C(CH3)2), 1.49 (t, JH–H = 7.2 Hz, 6H, NCH2CH3), 1.31 (d,
JH–H = 6.6 Hz, 6H, NCH(CH3)2);13C NMR (CD3CN): d 176.8
1
(11.7 g). IR (KBr): nCO 1739 cm-1; H NMR (CDCl3): d 9.39 (s,
=
1H, CHO), 2.50 (q, JH–H = 7.1 Hz, 4H, NCH2CH3), 1.07 (s, 6H,
(C N), 75.0 (C(CH3)2), 56.7 (NCH(CH3)2), 49.2 (NCH2CH3),
5952 | Dalton Trans., 2008, 5945–5956
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23.3 (C(CH3)2), 21.9 (NCH(CH3)2), 13.1 (NCH2CH3); MS (FAB,
m/z): 327.0 (M+ + 1 - Cl). Anal. calcd for C11H24Cl2N2Pd: C,
36.53; H, 6.69; N, 7.75%. Found: C, 35.74; H, 6.57; N, 7.62%.
C), 74.4 (C(CH3)2), 47.7 (NCH2CH3), 23.3 (C(CH3)2), 22.7, 22.3
(C(O)CH3), 12.2 (NCH2CH3); MS (FAB, m/z): 382.1 (M+ - OAc).
i
=
[Et2NCMe2CH N Pr]Pd(Me)Cl (7a). To a 15 mL CH2Cl2
solution containing (COD)Pd(Me)Cl (241.6 mg, 0.911 mmol)
was added 2a (176 mg, 0.957 mmol). The solution was stirred
at 25 ◦C for 1 h, then concentrated. Addition of diethyl ether
gave the yellow precipitate in 83% yield (258 mg). Single crystals
suitable for X-ray analysis were obtained by recrystallization from
CH2Cl2–Et2O. IR (KBr pellet): nCN 1646 cm-1; 1H NMR (CDCl3):
=
[Et2NCMe2CH NPh]PdCl2 (4c). Using similar procedures as
for 4a, the reaction of (PhCN)2PdCl2 (395 mg, 0.969 mmol) and
ligand 2c (235 mg, 1.078 mmol) gave the yellow precipitate of 4c in
95% yield (389 mg). Single crystals were grown from CH2Cl2–Et2O
cosolvents. IR (KBr): nCN 1627 cm-1; 1H NMR (CDCl3): d 7.57 (s,
=
1H, CH N), 7.48–7.20 (m, 5H, phenyl-H), 3.22, 3.07 (br, JH–H
=
=
=
d 7.53 (s, 1H, CH N), 3.88 (h, JH–H = 6.6 Hz, 1H, NCH(CH3)2),
7.1 Hz, 2H, 2H, NCH2CH3), 1.88 (s, 6H, C(CH3)2), 1.54 (t, JH–H
13
2.91, 2.86 (m, JH–H = 7.4, 16.8 Hz, 4H, NCH2CH3), 1.56 (s, 6H,
C(CH3)2), 1.26 (dd, JH–H = 7.4, 7.4 Hz, 6H, NCH2CH3), 1.24 (d,
JH–H = 6.6 Hz, 6H, NCH(CH3)2), 0.73 (s, 3H, PdCH3); 13C NMR
=
7.1 Hz, 6H, NCH2CH3); C NMR (CDCl3): d 183.1 (C N), 128.7,
128.6, 123.2 (phenyl-C), 74.7 (C(CH3)2), 49.5 (NCH2CH3), 23.1
(C(CH3)2), 13.3 (NCH2CH3); MS (FAB, m/z): 323.1 (M+ - 2Cl),
359 (M+ - Cl). Anal. calcd for C14H22Cl2N2Pd: C, 42.50; H, 5.60;
N, 7.08%. Found: C, 41.66; H, 5.09; N, 6.91%.
=
(CDCl3): d 176.6 (C N), 66.6 (C(CH3)2), 55.0 (NCH(CH3)2), 43.8
(NCH2CH3), 23.4 (C(CH3)2), 22.2 (CH(CH3)2), 11.9 (NCH2CH3),
-4.48 (PdCH3); MS (FAB, m/z): 307.1 (M+ - Cl). Anal. calcd for
C12H27ClN2Pd: C, 42.24; H, 8.21; N, 7.98%. Found: C, 42.22; H,
8.25; N, 8.07%.
t
=
[Et2NCMe2CH N Bu]PtCl2 (5b). A similar procedure as the
preparation for 5c gave the product in a yield of 42%. Single crys-
tals suitable for X-ray analysis were obtained by recrystallization
from CH2Cl2–Et2O. IR (KBr): nCN 1633 cm-1; 1H NMR (CDCl3):
=
[Et2NCMe2CH NPh]Pd(Me)Cl (7c). Using similar proce-
dures as for 7a, the reaction of (COD)Pd(Me)Cl (200 mg, 0.75
mmol) and 2c (173 mg, 0.79 mmol) gave the yellow precipitate of 7c
in 68% yield (620 mg). Alternatively, a reaction of 4c (86 mg, 0.217
mmol) and SnMe4 (46 mg, 0.257 mmol) was carried out in CH2Cl2
at 25 ◦C for 13 h. After filtration with Celite the reaction solution
was concentrated. Addition of diethyl ether gave the yellow solid
product in 68% yield (56 mg). Single crystals were grown from
CH2Cl2–Et2O co-solvents. IR (KBr pellet): nCN 1625 cm-1; 1H
=
d 7.84 (s, 1H, CH N), 3.19, 3.12 (m, JH–H = 7.0 Hz, 2H, 2H,
NCH2CH3), 1.83 (s, 6H, C(CH3)2), 1.58 (s, 9H, C(CH3)3), 1.43
(t, JH–H = 7.0 Hz, 6H, NCH2CH3); 13C NMR (CDCl3): d 177.0
=
(CH N), 76.2 (C(CH3)2), 50.2 (NCH2CH3), 30.1 (C(CH3)3), 29.6
(C(CH3)3), 22.1 (C(CH3)2), 12.9 (NCH2CH3); MS (FAB, m/z):
464.1 (M+ - Cl).
=
[Et2NCMe2CH NPh]PtCl2 (5c). To a 20 mL benzene solution
containing (PhCN)2PtCl2 (50 mg, 0.1 mmol) was added the ligand
2c (125 mg, 0.57 mmol). The solution was refluxed for 24 h,
then was concentrated. Addition of diethyl ether gave the yellow
precipitate in 20% yield (10 mg). Single crystals suitable for X-ray
analysis were obtained by recrystallization from CH2Cl2–Et2O. 1H
=
NMR (CDCl3): d 7.74 (s, 1H, CH N), 7.38–7.24, 7.02–6.97 (m,
m, 3H, 2H, C6H5), 3.01, 3.02 (q, JH–H = 7.3 Hz, 2H, NCH2CH3),
1.68 (s, 6H, C(CH3)2), 1.33 (t, JH–H = 7.3 Hz, 6H, NCH2CH3),
13
=
0.46 (s, 3H, PdCH3); C NMR (CDCl3): d 182.9 (C N), 147.8,
129.0, 127.8, 122.1 (phenyl-C), 66.7 (C(CH3)2), 44.1 (NCH2CH3),
23.3 (C(CH3)2), 12.0 (NCH2CH3), 0.80 (PdCH3); MS (FAB, m/z):
323. (M+ - Cl - CH3). Anal. calcd for C15H25ClN2Pd: C, 48.01; H,
6.71; N, 7.47%. Found: C, 47.84; H, 6.57; N, 7.75%.
=
NMR (CDCl3): d 8.13 (s, 1H, CH N), 7.37–7.08 (m, 5H, phenyl-
H), 3.46, 3.28 (m, JH–H = 7.1 Hz, 2H, 2H, NCH2CH3), 1.81 (s, 6H,
C(CH3)2), 1.52 (t, JH–H = 7.1 Hz, 6H, NCH2CH3).
i
i
=
[Et2NCMe2CH N Pr]Pd(OAc)2 (6a). Treating a solution of 4a
=
{[Et2NCMe2CH N Pr]Pd(Me)(NCMe)}OTf (8a). 7a (50 mg,
(144 mg, 0.398 mmol) in 15 mL CH2Cl2 with AgOAc (133 mg,
0.797 mmol) under N2 atmosphere. The solution was stirred at
25 ◦C for 50 min, then was concentrated after the removal of
AgCl precipitates. Addition of diethyl ether gave the yellow solid
product in 78% yield (127 mg). IR (KBr): nCO, nCN 1658, 1626,
0.147 mmol) was treated with AgOTf (38 mg, 0.148 mmol) in
CH3CN for 15 min, then AgCl precipitate was filtered off. The
1
residue was a dark brown oil. H NMR (CDCl3): d 7.72 (s, 1H,
=
CH N), 3.70 (h, JH–H = 6.6 Hz, 1H, CH(CH3)2), 2.97, 2.65 (m,
JH–H = 7.0 Hz, Jgem = 14.1 Hz, 2H, 2H, NCH2CH3), 2.38 (s,
-1
1
=
1596 cm ; H NMR (CD3CN, 200 MHz): d 7.16 (s, 1H, CH N),
3H, NCCH3), 1.58 (s, 6H, C(CH3)2), 1.27 (t, JH–H = 7.0 Hz, 6H,
3.61 (h, JH–H = 6.6 Hz, 1H, CH(CH3)2), 2.97, 2.72 (qd, qd, JH–H
=
NCH2CH3), 1.19 (d, JH–H = 6.6 Hz, 6H, CH(CH3)2), 0.63 (s, 3H,
13
7.3 Hz, Jgem = 12.6 Hz, 2H, 2H, NCH2CH3), 1.87, 1.84 (s, s, 3H,
3H, C(O)CH3), 1.83 (s, 6H, C(CH3)2), 1.52 (t, JH–H = 7.1 Hz, 6H,
NCH2CH3), 1.24 (d, JH–H = 6.6 Hz, 6H, CH(CH3)2); MS (FAB,
m/z): 349.1 (M+ - OAc).
=
PdCH3); C NMR (CD3CN): d 181.2 (C N), 121 (C∫N), 67.9
(CCH3), 55.9 (CH(CH3)2), 44.2 (NCH2CH3), 23.1 (C(CH3)2), 21.7
(CH(CH3)2), 11.7 (NCH2CH3), 3.2 (NCCH3), -0.7 (PdCH3); MS
(FAB, m/z): 346.1 (M+ - OTf).
=
=
[Et2NCMe2CH NPh]Pd(OAc)2 (6c). Using similar proce-
{[Et2NCMe2CH NPh]Pd(Me)(NCMe)}OTf
(8c). 7c
dures as for 6a, the reaction of 4c (141.7 mg, 0.358 mmol) and
AgOAc (119.6 mg, 0.717 mmol) gave the yellow precipitate of 6c
in 95% yield (150 mg). Single crystals were grown from n-hexane–
MeOH co-solvents. IR (KBr): nCO, nCN 1631, 1605, 1579 cm-1; 1H
(166 mg, 0.44 mmol) was treated with AgOTf (114 mg, 0.444
mmol) in CH3CN for 15 min. The solution was filtered to remove
the precipitate of AgCl and was concentrated. Addition of diethyl
ether gave the yellow solid of 8c in 93% yield (201 mg). Single
crystals were grown from CH2Cl2–Et2O co-solvents. IR (KBr
=
NMR (CD3CN): d 7.41 (s, 1H, CH N), 7.29 (br, s, 5H, phenyl-
-1
1
=
H), 3.13, 2.87 (qd, qd, JH–H = 7.2 Hz, Jgem = 13.0 Hz, 2H, 2H,
NCH2CH3), 1.97 (s, 6H, C(CH3)2), 1.91 (s, 3H, C(O)CH3), 1.63 (t,
JH–H = 7.2 Hz, 6H, NCH2CH3), 1.45 (s, 3H, C(O)CH3); 13C NMR
pellet): nCN 1633 cm ; H NMR (CDCl3): d 7.97 (s, 1H, CH N),
7.40–7.28, 7.05–7.01 (m, m, 3H, 2H, C6H5), 3.13, 2.87 (m, m,
JH–H = 7.1 Hz, JH–H = 7.1 Hz, 2H, NCH2CH3), 2.44 (s, 3H,
NCCH3), 1.74 (s, 6H, C(CH3)2), 1.37 (t, JH–H = 7.1 Hz, 6H,
=
=
(CDCl3): d 179.5 (C O), 177.8 (C N), 145.2, 128.9, 122.5 (phenyl-
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©

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NCH2CH3), 0.44 (s, 3H, PdCH3); 13C NMR (CDCl3): d 187.2
(C N), 146.5, 129.3, 128.5, 122.3 (phenyl-C), 68.1 (C(CH3)2), 44.7
(NCH2CH3), 23.2 (C(CH3)2), 12.1 (NCH2CH3), 3.8 (PdCH3), 3.5
(NCCH3); MS (FAB, m/z): 380.1 (M+ - OTf). Anal. calcd for
C18H28F3N3O3SPd: C, 40.80; H, 5.33; N, 7.93%. Found: C, 40.71;
H, 5.26; N, 7.70%.
1.92, 1.64 (s, s, 3H, 3H, C(CH3)2), 1.52, 1,25 (t, t, JH–H = 7.3 Hz,
JH–H = 7.3 Hz, 3H, 3H, NCH2CH3), 1.44 (tt, JH–H = 12.4, 4.6 Hz,
1H, nbe), 1.33 (d, JH–H = 3.7 Hz, 1H, nbe), 1.12 (m, 2H, nbe), 0.85
(tt, JH–H = 12.4, 4.6 Hz, 1H, nbe), 0.37 (m, 1H, nbe); 13C NMR
=
=
=
(CDCl3): d 238.8 (C O), 186.4 (C N), 146.9, 129.1, 128.4, 122.5
(phenyl-C), 70.7, 68.2, 53.3, 44.9, 43.9, 43.2, 42.1, 36.5, 29.2, 28.0,
27.3, 25.0, 21.1, 12.9, 11.2.
i
=
[Et2NCMe2CH N Pr]PdC(O)MeCl (9a). A 1 mL solution of
CDCl3 containing 7a (31 mg, 0.091 mmol) was bubbled with
X-Ray crystallographic analysis
CO for 15 min. The yellowish green solution was monitored
1
=
with H NMR: d 7.52 (s, 1H, CH N), 3.66 (h, JH-H = 6.4 Hz,
Diffraction data were measured on
SmartCCD, or Nonius KappaCCD diffractometer with graphite-
a Nonius CAD-4,
1H, NCH(CH3)2), 2.78, 2.64 (m, JH-H = 7.2, 14.5 Hz, 2H, 2H,
˚
NCH2CH3), 2.44 (s, 3H, PdC(O)CH3), 1.53 (s, 6H, C(CH3)2), 1.20
monochromatized Mo Ka radiation (l = 0.7103 A). No signif-
(t, JH–H = 7.2 Hz, 6H, NCH2CH3), 1.15 (d, JH–H = 6.4 Hz, 6H,
icant decay was observed during the data collection. The data
were processed on a PC using the SHELXTL refinement software
package.24 The structures were solved using the direct method and
refined by full-matrix least-squares on the F2 value.
13
=
=
NCH(CH3)2); C NMR (CDCl3): d 226.4 (C O), 176.8 (C N),
65.5 (C(CH3)2), 59.0 (NCH(CH3)2), 42.9 (NCH2CH3), 36.0
(C(O)CH3), 23.6 (C(CH3)2), 22.1 (CH(CH3)2), 11.8 (NCH2CH3);
MS (FAB, m/z): 333.0 (M+ - Cl).
All the non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were identified by calculation and refined using a
riding mode, and their contributions to structure factors were
included. Atomic scattering factors were taken from the Inter-
national Tables of Crystallographic Data, Vol IV.25 Computing
programs are from the NRC VAX package. Crystallographic data
and selected atomic coordinates and bond parameters are collected
in Tables 1–3. The rest of the data are supplied in the ESI.†
=
[Et2NCMe2CH NPh]PdC(O)MeCl (9c). To a 20 mL CH2Cl2
containing 7c (254 mg, 0.677 mmol), was bubbled with CO for
20 min. The solution was concentrated. Addition of diethyl ether
gave the yellow precipitate of 9c in 83% yield (226 mg). IR (KBr):
1
nCN 1638 cm-1, nCO 1716 cm-1; H NMR (CDCl3): d 7.68 (s, 1H,
=
CH N), 7.31–7.23, 7.07–7.02 (m, m, 3H, 2H, C6H5), 2.93–2.81 (m,
JH–H = 7.3 Hz, 4H, NCH2CH3), 2.10 (s, 3H, PdC(O)CH3), 1.66 (s,
6H, C(CH3)2), 1.35 (t, JH-H = 7.3 Hz, 6H, NCH2CH3); 13C NMR
Computational details
=
=
(CDCl3): d 223.0 (C O), 182.3 (C N), 149.1, 129.1, 128.0, 121.4
(phenyl-C), 65.7 (C(CH3)2), 43.4 (NCH2CH3), 33.6 (PdC(O)CH3),
23.5 (C(CH3)2), 12.1 (NCH2CH3); MS (FAB, m/z): 367.1
(M+ - Cl).
All configurations were optimized by first using molecular me-
chanics MM+ (ArgusLab 4.01) and then with Amsterdam Density
Functional (ADF 2004.01) without any restriction to symmetry
and restrains. For the structures with crystallographic data, direct
optimization was applied. The Vosko–Wilk–Nusair (VWN) pa-
rameterization of the electron gas for local density approximation
(LDA) and exchange–correlation functionals from Becke–Lee–
Yang–Parr (BLYP) for the generalized gradient approximation
(GGA) were used. Relativistic zero-order regular approximation
(ZORA) was applied.
For palladium, a standard triple-zeta Slater-type orbitals
(STOs) basis set with one set of polarization functions was applied
as implemented in the ADF basis set library (ADF database
ZORA/TZP). The 1s–4p electrons were treated with the frozen
core approximation. For main-group elements (C, N, O, H) a
standard double-zeta Slater-type orbitals (STOs) basis set with
one set of polarization functions was applied as implemented in
the ADF basis set library (ADF database ZORA/DZP). The
1s electrons were treated with frozen core approximation. All
structures shown correspond to minimum points on the potential
surface. No symmetry constraints were used.
i
=
{[Et2NCMe2CH N Pr]Pd[C(O)Me(C7H10)]}OTf
(10a).
Complex 9a was first prepared from 7a (113.6 mg, 0.333 mmol)
and CO in situ at 0 ◦C. The reaction solution was flushed by
nitrogen for 15 min, followed by 2 mL CH3CN, norbornene
(nbe) (31.5 mg, 0.335 mmol), and AgOTf (86 mg, 0.335 mmol) in
sequence. The solution was stirred at 0 ◦C for 3 h. After removal
of AgCl precipitate, the solution was concentrated. Addition of
diethyl ether gave the whitish precipitate in 75% yield (137 mg).
1
IR (KBr): nCN 1643 cm-1, nCO 1608 cm-1; H NMR (CDCl3): d
=
7.87 (s, 1H, CH N), 3.62 (m, 1H, NCH(CH3)2), 3.15, 3.04, 2.85
(m, 1H, 1H, 1H, NCH2CH3 + nbe), 2.68 (br, 1H, nbe), 2.47 (br,
2H, nbe), 2.33 (m, 4H, nbe and C(O)CH3), 1.96 (br, 1H, nbe),
1.82 (s, 6H, C(CH3)2), 1.53 (br, 3H, NCH2CH3 + nbe), 1.40 (br,
3H, NCH2CH3), 1.34 (br, 8H, NCH(CH3)2 + nbe), 1.16 (br, 4H,
NCH2CH3 + nbe);13C NMR (CDCl3): d 238, 180.9, 103.4, 70.5,
68.3, 57.8, 49.5, 44.6, 43.3, 43.2, 36.8, 29.5, 29.1, 27.3, 25.6, 24.0,
20.8, 20.6, 12.8, 10.7; MS (FAB, m/z): 427.1 (M+ - OTf). Anal.
calcd for C21H37F3N2O4SPd: C, 43.71; H, 6.46; N, 4.85%. Found:
C, 42.71; H, 6.28; N, 4.92%.
Acknowledgements
=
{[Et2NCMe2CH NPh]Pd[C(O)Me(C7H10)]}OTf (10c). Us-
We thank the National Science Council, Taiwan, ROC, and the
NSC-NWO joint project for the financial support.
ing similar procedures as for 10a, reaction of 7c (101 mg, 0.269
mmol) gave the white solid 10c in 67% yield (111 mg). The single
crystals were grown by evaporating off CHCl3. IR (KBr): nCN
1624 cm-1, nCO 1605 cm-1; 1H NMR (CDCl3): d 8.02 (s, 1H,
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