Vinyl- and dienylpalladium complexes formed via insertion of alkyne into sterically hindered Pd-aryl bonds

Article abstract of DOI:10.1246/bcsj.74.1435

[PdI(C₆H₃Me₂-2,6)(bpy)] reacts with excess amounts of dimethyl acetylenedicarboxylate to produce [PdI{CZ=CZ-(C₆H₃Me₂-2,6)}(bpy)] (2, Z = COOMe) and [PdI{CZ=CZ-CZ=CZ(C₆H₃Me₂-2,6)}(bpy)] (3). Crystallographic study revealed the molecular structures of 2 and 3 the latter of which has an s-trans dienyl ligand.

Full text of DOI:10.1246/bcsj.74.1435

c. Jpn.
Bull. Chem. Soc. Jpn., 74, 1435–1436 (2001) 1435
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Short Articles
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CZ(C6H3Me2-2,6)}(bpy)] (2, Z = COOMe) and [PdI{CZwCZ–
CZwCZ(C6H3Me2-2,6)}(bpy)] (3), as shown in Scheme 1.
Complexes 2 and 3 were isolated from recrystallization of the
products of the reactions (i) and (ii), respectively. Extremely
low solubility of 3 in acetone helped its isolation from the re-
action mixture containing the three Pd complexes. 1H NMR
analyses of the reaction mixture of DMAD (0.32 M) with 1
(0.043 M) in acetone-d6 over 2 weeks revealed initial forma-
tion of 2 and its gradual conversion into 3. The reaction (i) re-
quires more severe conditions than insertion of a DMAD mol-
ecule into Pd–Ar bond of [PdI(C6H3Me2-3,5)(bpy)] (24 h at
room temperature or a few hours at 50 °C). The reaction (ii)
produces the dienylpalladium complex in 68% isolated yield
after 9 d, whereas a similar reaction of DMAD with
[PdI(C6H3Me2-3,5)(bpy)] at 50 °C gives the corresponding die-
nylpalladium complex in less than 20% yield after 6 days.
Figure 1 depicts molecular structures of 1–3 determined by
X-ray crystallography. The 4-aryl-1,3-dienyl ligand of 3 has
an s-trans structure as shown in Fig. 1c. It contrasts with the
Vinyl- and Dienylpalladium
Complexes Formed via Insertion of
Alkyne into Sterically Hindered Pd–
Aryl Bonds
01
35
36
SJA8
09-2673
1002
T. Yagyu et al.
Takeyoshi Yagyu and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technol-
ogy, 4259 Nagatsuta,Midori-ku, Yokohama 226-8503
(Received February 27, 2001)
01
01
[PdI(C6H3Me2-2,6)(bpy)] reacts with excess amounts of
dimethyl acetylenedicarboxylate to produce [PdI{CZwCZ-
(C6H3Me2-2,6)}(bpy)] (2, Z = COOMe) and [PdI{CZwCZ–
CZwCZ(C6H3Me2-2,6)}(bpy)] (3). Crystallographic study re-
vealed the molecular structures of 2 and 3 the latter of which
has an s-trans dienyl ligand.
recently
reported
[Pd{CZwCZ–CZwCZ(C6H3Me2-3,5)}-
(MeCN)(bpy)]+ whose crystallographic study revealed an s-cis
structure of the ligand and the presence of π–π interaction be-
tween the aryl group and the bpy ligand. The dihedral angle
between aryl plane and the C–C double bond plane of 3 is
large (114°), due to a steric repulsion between the ortho meth-
yl and COOMe groups of the ligand.
Insertion of a carbon–carbon triple bond into a transition
metal–carbon bond is important since it is often involved as a
crucial step in the transition metal complex catalyzed synthetic
organic reactions and polymerization of the unsaturated mole-
cules. Recently we reported the reaction of dimethyl acety-
lenedicarboxylate (DMAD) with Pd complexes having a 3,5-
dimethylphenyl ligand, which led to insertion of one, two, or
three molecules into the Pd–Ar bond depending on the reaction
conditions.1 Late transition metal complexes with a 2,6-dime-
thylphenyl ligand have attracted current attention owing to the
stable metal–carbon bond and unique reactivity.2 In this paper
we report the reactions of DMAD with a 2,6-dimethylphe-
nylpalladium(Ⅱ) complex with a bipyridine ligand and the
structures of the products.
1
Table 1 summarizes the H and 13C{1H} NMR data of the
complexes. The 1H NMR spectrum of 3 exhibits the signals of
aryl hydrogens of the 4-aryl-1,3-dienyl ligand at positions
close to those of 1 and 2. On the other hand, peak positions of
the aryl hydrogens of [Pd{CZwCZ–CZwCZ(C6H3Me2-3,5)}-
(MeCN)(bpy)]+, having a π–π interaction between the bpy and
Results and Discussion
The iodo arylpalladium(Ⅱ) complex [PdI(C6H3Me2-2,6)-
(bpy)] (1), prepared from the literature method,3,4 reacts with
excess amounts of DMAD at 50 °C and produces [PdI{CZw
Scheme 1.
Fig. 1. ORTEP drawing of (a) 1, (b) 2, and (c) 3 (50% probability). Atoms except Pd and I of 3 are refined isotropically due to in-
sufficient collected data/parameter ratio. Selected bond distances (Å) are summarized below. 1: Pd–I 2.5718(8), Pd–N1 2.145(5),
Pd–N2 2.064(5), Pd–C1 1.997(6). 2: Pd–I 2.5577(7), Pd–N1 2.124(4), Pd–N2 2.084(4), Pd–C1 2.007(4). 3: Pd–I 2.573(5), Pd–
N1 2.16(3), Pd–N2 2.00(4), Pd–C1 1.95(4).

1436 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
© 2001 The Chemical Society of Japan
Table 1. 1H and 13C{1H} NMR Data in CDCl3
1Ha)
13C{1H}
Ar
bpy
OCH3
meta
para
CH3
2.63
H3, H3ꢀ
H4, H4ꢀ
H5, H5ꢀ
H6, H6ꢀ
1
2
6.8(m)
6.8(m)
8.05*
8.05*
7.97(m) 7.53(m)
7.95(m) 7.28(m)
7.94(d, 8) 8.03(m) 7.58(m)
9.61(d, 5)
7.41(d, 6)
9.36(d, 6)
6.8(m)
7.0(m)
7.0(m)
1.97
2.41
3.62,
3.85
174.2, 162.8, 158.2, 155.4,
154.1, 154.0, 153.7,
139.4, 139.1, 138.9, 135.5,
133.9, 127.7, 126.8,
7.90(d, 7) 7.86(m) 7.24(m)
9.43(d, 5)
126.7, 126.5, 126.2, 121.7,
121.6, 51.9, 22.3, 21.6
173.0, 168.7, 168.3, 163.5,
160.6, 154.7, 153.9, 152.9
139.6, 139.1, 138.8, 137.8,
136.8, 133.4,133.3, 128.3
127.6, 126.8, 126.7, 121.7,
121.3,52.4, 51.9, 51.9
51.5, 21.9, 21.1
3 6.64(d, 7)
6.87
(dd, 7, 7)
2.16
2.46
8.0*
8.0*
8.0*
8.0*
7.49(m)
7.49(m)
9.81(d, 5)
8.58(d, 5)
3.16, 3.46
3.61, 3.64
6.94(d, 7)
a) Positions of the peaks with asterisks are not precise due to overlapping with other signals.
-7R automated four-cycle diffractometers by using Mo-Kα radia-
tion (λ = 0.71069 Å) and ω-2θ scan method, and an empirical ab-
sorption correction (ψ scan) was applied. Calculations were car-
aryl group, and those of [Pd{CZwCZ(C6H3Me2-3,5)}(MeCN)-
(bpy)]+ differ by ca. 0.4 ppm.1 The above contrast of the NMR
data suggests that the dienyl ligand of 3 prefers the s-trans
structure and is free from the π–π interaction with the bpy
ligand in solution.
The palladium complex with a sterically demanding aryl
ligand, 1, undergoes insertion of one or two DMAD molecules,
although it requires heating at 50 °C for a long time. The pres-
ence of ortho methyl groups influences the reaction rate of the
first and second insertion as well as structure of the insertion
product.
ried out using a program package TEXSAN for Windows.
1
(C18H17IN2Pd): 1.03 × 0.70 × 0.15 mm, Mr = 494.65, monoclin-
ic, P21/n, a = 9.583(1), b = 12.148(1), c = 15.074(2) Å, β =
95.39(1)°, V = 1747.1(3) Å3, Z = 4, Dcalcd = 1.880 g cm−3, µ =
2.828 mm−1, F(000) = 952, R(Rw) = 0.038(0.038) for 2744 re-
flections with I > 3σ(I). 2 (C24H23IN2O4Pd): 0.55 × 0.43 × 0.25
mm, Mr = 636.76, monoclinic, P21/n, a = 10.172(2), b =
15.527(2), c = 15.454(3) Å, β = 100.86(2)°, V = 2397.0(9) Å3, Z
= 4, Dcalcd = 1.764 g cm−3, µ = 2.095 mm−1, F(000) = 1248,
R(Rw) = 0.034(0.024) for 3645 reflections with I > 3σ(I).
3
Experimental
(C30H29IN2O8Pd): 0.24 × 0.18 × 0.11 mm, Mr = 778.87, triclinic,
P1, a = 11.154(7), b = 17.39(1), c = 8.650(6) Å, α = 99.62(5), β
= 96.75(6), γ = 71.91(6)°, V = 1569(2) Å3, Z = 2, Dcalcd = 1.649
g cm−3, µ = 1.627 mm−1, F(000) = 772, R(Rw) = 0.123(0.127)
for 1920 reflections with I > 3σ(I).
All the data of the crystallographic study except Fo-Fc tables
are deposited as Document No. 74044 at the Office of the Editor
of Bull. Chem. Soc. Jpn. Crystallographic data are deposited also
at the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and cop-
ies can be obtained on request, free of charge, by quoting the pub-
lication citation and the deposition numbers 163005 and 163006.
Complex 1 was prepared from the reaction of 2,6-dimeth-
yliodobenzene with [Pd(dba)2]3 (dba = dibenzylideneacetone) in
the presence of 2,2ꢀ-bipyridine and recrystallized from CH2Cl2–
hexane (1.47 g, 41%).4 Anal. Calcd for C18H17IN2Pd: C, 43.71; H,
3.46; N, 5.66; I, 25.65%. Found: C, 43.67; H, 3.42; N, 5.73; I,
25.54%.
Preparation of 2. A mixture of [PdI(C6H3Me2-2,6)(bpy)]
(197 mg, 0.398 mmol) and DMAD (0.60 cm3, 4.9 mmol) in 6 cm3
of dry CH3CN was stirred for 1 day at 50 °C. Cooling the reaction
mixture at room temperature caused separation of a yellow solid
which was collected by filtration and recrystallized from CH2Cl2–
hexane to give 2 (125 mg, 49%). Anal. Calcd for C24H23IN2O4Pd:
C, 45.27; H, 3.64; N, 4.40; I, 19.93%. Found: C, 45.41; H, 3.64;
N, 4.31; I, 19.65%.
T. Y. is grateful for a fellowship from JSPS (Japan Society
for Promotion of Science).
Preparation of 3. A mixture of [PdI(C6H3Me2-2,6)(bpy)]
(390 mg, 0.788 mmol) and DMAD (0.65 cm3, 5.3 mmol) in 10
cm3 of dry acetone was stirred for 9 days at 50 °C. Cooling the re-
action mixture at room temperature caused separation of a yellow
solid which was collected by filtration and recrystallized from
CH2Cl2–hexane to give 3 (414 mg, 68%). Anal. Calcd for
C30H29IN2O8Pd: C, 46.26; H, 3.75; N, 3.60; I, 16.29%. Found: C,
46.34; H, 3.75; N, 3.60; I, 16.33%.
References
1
T. Yagyu, M. Hamada, K. Osakada, and T. Yamamoto, Or-
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2
3
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4
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