Synthesis of coumarin derivatives by palladium complex catalyzed intramolecular Heck reaction: Preparation of a 1,2-cyclobutadiene-substituted CpCoCb diphosphine chelated palladium complex

Article abstract of DOI:10.1016/j.inoche.2009.04.031

A cobalt-sandwich diphosphine chelated palladium complex 2, [(η⁵-cyclopentadienyl)(η⁴-1,2-diphenyl-3,4-bis(diphenylphosphino-κP)cyclobutadiene)cobalt(I)]palladium(II)dichloride, was prepared from the reaction of a cyclobutadiene-subs

Full text of DOI:10.1016/j.inoche.2009.04.031

Inorganic Chemistry Communications 12 (2009) 596–598
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis of coumarin derivatives by palladium complex catalyzed
intramolecular Heck reaction: Preparation of a 1,2-cyclobutadiene-substituted
CpCoCb diphosphine chelated palladium complex
*
Chin-Pei Chang, Santhanakrishnan V. Pradiuldi, Fung-E. Hong
Department of Chemistry, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung 40227, Taiwan
a r t i c l e i n f o
a b s t r a c t
A cobalt-sandwich diphosphine chelated palladium complex 2, [(g g
5-cyclopentadienyl)( 4-1,2-diphenyl-
Article history:
Received 10 March 2009
Accepted 28 April 2009
Available online 10 May 2009
3,4-bis(diphenylphosphino-
reaction of a cyclobutadiene-substituted CpCoCb diphosphine 1, (
j
P)cyclobutadiene)cobalt(I)]palladium(II)dichloride, was prepared from the
g
5-cyclopentadienyl) ( 4-1,2-diphe-
g
nyl-3,4-bis-diphenylphosphinocyclobutadiene)cobalt(I), with one molar equivalent of Pd(COD)Cl2. Both
compounds were characterized by spectroscopic means as well as single-crystal X-ray diffraction meth-
ods. Application of purified 2 as the catalytic precursor in intramolecular Heck cyclization reaction on 4-
hydroxycoumarin resulted in the formation of several derivatives with intensity enhanced fluorescence
property.
Keywords:
Heck reaction
Palladium complex
Cobalt-containing phosphine
Fluorescence
Ó 2009 Elsevier B.V. All rights reserved.
Coumarin
The palladium complexes catalyzed cross-coupling reactions
are probably the most popular synthetic methods for the formation
of C–X (X: C, N, O etc.) bond in modern chemistry. Remarkable suc-
cess in the application of this strategy has been well-documented
in the synthesis of numerous organic compounds [1–4]. Consider-
able amount of experimental evidences have demonstrated repeat-
edly that a well-chosen ligand is crucial to the performance of a
palladium-catalyzed cross-coupling reaction [5].
For many years, trialkyl- or triarylphosphines and their deriva-
tives have probably been the most favorite selections [6–8]. Never-
theless, only rather limited number of transition metal-containing
phosphines have been reported [9–11]. The bis(diphenylphos-
phino)ferrocene (dppf) and its derivatives are undoubtedly the
most popular metal-containing bidentate phosphine ligands
known so far [12–15]. Lately, we have been involved in the devel-
opment of another sandwich-type phosphine ligands, substituted
CpCoCb diphosphines [16].
characterized by spectroscopic methods as well as single-crystal
X-ray diffraction methods (Scheme 1) [22]. The fact that five cyclo-
pentadienyl protons of 1 are equivalent in 1H NMR spectrum is re-
vealed by a sharp singlet appears at 4.67 ppm. It is 4.14 ppm for
the five corresponding protons in 2. Besides, a single singlet peak
shows up at À17.6 ppm in 31P NMR spectrum indicates an alike
environment of these two phosphorous atoms in 1. It is also true
for 2 with a singlet appeared at 62.6 ppm. The significant down-
fielded shift of 2 from 1 is a common observation for the coordina-
tion of phosphine ligand towards palladium metal. ORTEP diagrams
of 1 and 2 were depicted in Figs. 1 and 2, respectively. As revealed,
two rings of the sandwich, cyclopentadienyl and cyclobutadiene,
are almost paralleled to each other. The dihedral angles calculated
are 1.28° and 2.11° for 1 and 2, respectively. Two phosphino-substit-
uents are located on the neighboring positions in 1 and ready for
chelation towards the targeted palladium metal. In 2, the Pd(1) is al-
most coplanar with the Cb-ring; while, two atoms, P(1) and P(2), are
below the Cb plane. The distances between two phosphorus atoms
of 2 and 1 are 3.172 and 4.085 Å, respectively. As expected, the
distance is shorter for the palladium complexed case. It is also
evidenced by the reduction of angles of \ P(1)-C(6)-C(9) and
\P(2)-C(6)-C(9) from 1 to 2.
Many coumarin derivatives are biologically active species and
also known for their fluorescence emission nature. It is a rather
useful chemical and physical property in terms of molecular imag-
ing technique for biological systems [17–19].
The cobalt-containing diphosphine ligand, [(g g
5-C5H5)Co( 4-1,2-
(PPh2)2C4Ph2)] 1, was prepared according to procedures described
The coumarin derivatives 5a ꢀ c, substituted 4-phenylamino-
chromen-2-one and 4-benzylamino-chromen-2-one, were prepared
from the reaction of 4-hydroxycoumarin 3 with the corresponding
2-bromoaniline or 2-bromobenzylamine 4a–c (Scheme 2) [23].
Then, 8-methyl-[1]benzopyrano[4,3-b]indol-6(11H)-one 6a and
[1]benzopyrano[4,3-b]indol-6(11H)-one 6b were prepared from
the reactions of the corresponding 5a and 5b via the ligands
elsewhere [20]. Further reaction of 1 with one molar equivalent of
Pd(COD)Cl2 gave 1-chelated palladium complex [(
4-1,2-(PPh2)2C4Ph2)-PdCl2] 2 [21]. Both compounds 1 and 2 were
g
5-C5H5)Co
(g
* Corresponding author. Tel.: +886 4 22840411 607; fax: +886 4 22862547.
E-mail address: fehong@dragon.nchu.edu.tw (F.-E. Hong).
1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.04.031

C.-P. Chang et al. / Inorganic Chemistry Communications 12 (2009) 596–598
597
Ph
Ph
Co
Co
+ Pd(COD)Cl2
Ph
Ph
PPh2
Ph
2
P
Cl
Pd
PPh2
Ph2 P
1
2
Cl
Scheme 1.
Fig. 2. ORTEP drawing of 2. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°): Pd(1)–P(1) 2.2446(15); Pd(1)–P(2) 2.2619(15); Pd(1)–
Cl(2) 2.3439(17); Pd(1)–Cl(1) 2.3454(16); P(1)–C(6) 1.779(6); P(2)–C(9) 1.789(6);
P(1)–Pd(1)–P(2) 89.46(5); P(1)–Pd(1)–Cl(2) 174.71(7); P(2)–Pd(1)–Cl(2) 89.33(6);
P(1)–Pd(1)–Cl(1) 88.88(6); P(2)–Pd(1)–Cl(1) 177.07(7); Cl(2)–Pd(1)–Cl(1) 92.11(6);
C(6)–P(1)–Pd(1) 104.73(18); C(9)–P(2)–Pd(1) 104.77(18); C(9)–C(6)–P(1) 119.8(4);
C(6)–C(9)–P(2) 117.8(4).
OH
Fig. 1. ORTEP drawing of 1. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°): P(1)–C(6) 1.814(3); P(2)–C(9) 1.816(3); C(6)–C(7)
1.456(4); C(6)–C(9) 1.485(4); C(7)–C(8) 1.463(4); C(8)–C(9) 1.481(4); C(6)–P(1)–
C(10) 102.57(15); C(6)–P(1)–C(16) 101.72(14); C(10)–P(1)–C(16) 100.08(15); C(9)–
P(2)–C(40) 101.41(14); C(9)–P(2)–C(34) 102.44(14); C(40)–P(2)–C(34) 100.87(14);
C(9)–C(6)–P(1) 139.8(2); C(6)–C(9)–P(2) 131.8(2).
n
H N
2
+
O
O
Br
R
4a: n=0, R=Me
4b: n=0, R=H
4c: n=1, R=H
3
HN
O
n
HN
n
Br
O
assisted palladium complexes catalyzed intramolecular Heck
methods [24]. In this one pot reaction, a cyclization process of an
annulated heterocycle took place.
R
[Pd]/L
R
O
O
For comparison, various combinations of ligand/Pd(OAc)2 sys-
tems in situ or stand-alone palladium complex, 2, were employed
in the intramolecular Heck method for the preparation of 6a (or
6b). In this particular reaction, the newly-made palladium complex
2, apart from other palladium sources, showed exclusive activity in
the process of cyclization via the intramolecular Heck method (Ta-
ble 1). This work also demonstrates that this process is a potential
route for making coumarin derivatives with extended and fused
five membered ring through cyclization on C2, C3-sites of the
molecule.
6a: n=0, R=Me
6b: n=0, R=H
6c: n=1, R=H (Not observed)
5a: n=0, R=Me
5b: n=0, R=H
5c: n=1, R=H
Scheme 2.
the molecule exhibit small blue shift as well as much intense emis-
sion than the non-substituted coumarin. Particularly, the emission
intensity of compound 6a is more than double of 3. It indicates that
the addition of a new annulated heterocyclic ring to coumarin is a
promising way of making compound with useful fluorescence
emission character.
The excitation and emission spectra of some selected coumarins
were recorded and shown in Supplementary Information. Couma-
rin derivatives with annulated heterocycles from the 3,4-sites of
Table 1
Intramolecular Heck reaction for the preparation of 6a & 6b employing various palladium sources.a
Entry
R
Pd source
Ligand
Pd/L ratio
Time (h)
6a (%)b
6b (%)b
1
2
3
4
5
Me
Me
Me
Me
H
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
2
P(tBu)biPhd
PPh3
dppf
1:1
1:2
1:1
12
12
12
12
24
Trace
Trace
30
99(78.7c)
2
99(72.8c)
a
Reaction conditions: 0.5 mmol 5a (or 5b), 1.5 mmol DABCO (0.168 g), 0.0025 mmol palladium source, and 1 mL dioxane, 100 °C, 12 ꢀ 24 h.
b
c
Determined by 1H NMR; average of two runs.
Isolated yield.
d
2-(Di-t-butylphosphino)biphenyl.

598
C.-P. Chang et al. / Inorganic Chemistry Communications 12 (2009) 596–598
ppm): 135.4 (t, JCP = 6.0 Hz, HC = C–PPh2), 127.9–128.7 (m, Ph), 83.9 (s. 5 C,
Acknowledgements
Cp); 31P{1H} NMR (CDCl3, d/ppm): 62.6; Anal. Calc. for C45H35Cl2CoP2Pd: C,
61.84; H, 4.04. Found: C, 63.99; H, 4.36; MS: m/z = 837 [M–Cl]+.
We are grateful to the National Science Council of the ROC
(Grant NSC 95-2113-M-005-015-MY3) for financial support.
[22] X-ray crystallographic studies: Suitable crystals of 1 and 2 were sealed in thin-
walled glass capillaries under nitrogen atmosphere and mounted on a Bruker
AXS SMART 1000 diffractometer. Intensity data were collected in 1350 frames
with increasing
x (width of 0.3° per frame). The space group determination
was based on a check of the Laue symmetry and systematic absences, and was
confirmed using the structure solution. The structure was solved by direct
methods using a SHELXTL package.[25] All non-H atoms were located from
successive Fourier maps and hydrogen atoms were refined using a riding
model. Anisotropic thermal parameters were used for all non-H atoms, and
Appendix A. Supplementary data
CCDC 678963 and 678965 contain the supplementary crystallo-
graphic data for compound 1 and 2, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.inoche.2009.04.031.
fixed isotropic parameters were used for
C45H35CoP2, Mw = 696.60, Triclinic, space group P-1, a = 9.6156(4) Å, b =
10.9795(5) Å, c = 18.8786(8) Å, = 97.378(2)°, b = 92.628(2)°, = 115.703(2)°,
V = 1753.04(13) Å3, Dc = 1.320 Mg/m3, Z = 2, = 0.613 mmÀ1
25111 data
H atoms. Crystal data for 1:
a
c
l
,
collected, 5699 unique data [R(int) = 0.0575], R1 = 0.0455, wR2 = 0.1215,
CCDC 678963. Crystal data for 2: C45H35Cl2CoP2Pdꢁ2CH2Cl2, Mw = 1043.75,
Monoclinic, space group Pc, a = 10.8270(14) Å, b = 12.9825(17) Å, c = 16.734(2)
Å, b = 93.088(3)°, V = 2348.8(5) Å3, Dc = 1.476 Mg/m3, Z = 2,
l ,
= 1.177 mmÀ1
References
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wR2 = 0.1026, CCDC 678965.
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[23] Synthesis and characterization of 5a ꢀ c: Two reactants, 4-hydroxycoumarin
(3.160 g, 20.000 mmol) and 2-bromoaniline (3.440 g, 20.000 mmol), were
placed in 100 mL capacity round flask charged with a magnetic stirrer. The
latter was functioning as solvent also. Without adding other solvent, the
mixture was heated at 200 °C for 45 minutes before completion. The black
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discarded. This process was repeated several times till the color of the solid
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7.6 mmol). The same procedure was followed for the preparations of 5b and
5c. The resulted pale yellow solids of 5b and 5c are in the yields of 40 %
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NMR (CDCl3, d/ppm): 9.33 (s, 1H, NH), 8.23 (dd, Jdd = 1.2 Hz, Jdd = 6.8 Hz, 1H,
Ph), 7.64(m, 2H, Ph), 7.35 ꢀ 7.42 (m, 3H, Ph), 4.57 (s, 1H,@CH); 13C NMR
(CDCl3, d/ppm): 161.28, 153.37, 153.16, 139.70, 133.76, 132.42, 129.85,
123.70, 122.74, 122.06, 117.06, 114.14, 84.54, 20.26; HRMS: m/z = 329.0054
(M+). Anal. Calc. for C15H10BrNO2: C, 56.99; H, 3.19; N, 4.43. Found: C, 59.68; H,
3.74; N, 4.02; 5b: 1H NMR (CDCl3, d/ppm): 9.43 (s, 1H, NH), 8.23 (dd,
Jdd = 1.6 Hz, Jdd = 6.8 Hz, 1H, Ph), 7.83 (dd, Jdd = 1.2 Hz, Jdd = 6.8 Hz, 1H, Ph),
7.65(t, JH–H = 1.2 Hz, 1H, Ph), 7.49 ꢀ 7.54 (m, 2H, Ph), 7.35–7.43(m, 2H, Ph),
4.59 (s, 1H,@CH); 13C NMR (CDCl3, d/ppm): 161.21, 153.37, 152.92, 136.49,
133.64, 132.48, 130.27, 129.68, 129.29, 123.74, 122.74, 122.34, 117.08, 114.11,
84.75; HRMS: m/z = 314.9897 (M+). Anal. Calc. for C16H12BrNO2: C, 58.20; H,
3.66; N, 4.24. Found: C, 57.69; H, 3.51; N, 4.25. 5c: 1H NMR (CDCl3, d/ppm):
8.33 (t, JH–H = 5.2 Hz, 1H, Ph), 8.12 (dd, Jdd = 1.2 Hz, Jdd = 6.8 Hz, 1H, Ph),
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[20] General procedure of the preparation of 1 was as the following: A 100 mL
round-bottomed flask, equipped with a magnetic stir bar and a rubber septum,
was charged with CoCl(PPh3)3 (0.440 g, 0.499 mmol) and 10 mL toluene. To the
resulting suspension, a solution of NaCp in THF (0.25 mL, 2.0 M, 0.50 mmol) was
slowly added. After 30 minutes, a solution of phenylethynyldiphenylphosphine
(0.286 g, 1.000 mmol), which was dissolved in toluene (5 mL), was injected.
Then, the mixture was refluxed for the next 12 h. Subsequently, purification
was carried out using CTLC. From the yellow band, eluted with CH2Cl2/
hexane = 1/1, a mixture of the title compounds with the ratio of 1:1 was isolated
in the yield of 35 % (0.123 g, 0.176 mmol). 1: 1H NMR (CDCl3, d/ppm): 7.00–7.42
(m, 30H, Ph and PPh2), 4.67 (s, 5H, Cp); 13C NMR (CDCl3, d/ppm): 136.9
(d, JC–P = 4.9 Hz), 135.5, 133.5–134.5 (m), 129.7, 129.3–127.3 (m), 126.2, 85.7
(t, 2JC–P = 6.1 Hz, C(2) and C(4) of Cb), 83.1 (s, 5C, Cp); 31P NMR (CDCl3, d/ppm):
À17.8. Anal. Calcd. for C45H35P2Co: C, 77.72; H, 5.04. Found: C, 76.90; H, 5.17.
MS: m/z = 696 [M]+.
7.59 ꢀ 7.67 (m, 2H, Ph), 7.22 ꢀ 7.35 (m, 3H, Ph), 4.91 (s, 1H,@CH), 4.51(d, JH–H
=
6.0 Hz, 2H, CH2); 13C NMR (CDCl3, d/ppm): 161.28, 153.10, 135.75, 132.70,
132.07, 129.34, 128.58, 127.97, 123.48, 122.50, 116.99, 1147.28, 82.62,
46.035; HRMS: m/z = 329.0050 (M+). Anal. Calc. for C16H12BrNO2: C, 58.20;
H, 3.66; N, 4.24. Found: C, 58.49; H, 3.66; N, 4.23.
[24] Synthesis and characterization of 6a ꢀ b: A 20 mL Schlenk tube was charged
with 5a (0.165 g, 0.500 mmol) (or 5b (0.158 g, 0.500 mmol)), DABCO (0.168 g,
1.500 mmol) and 2 (0.021 g, 0.002 mmol) as well as 1 mL dioxane. The mixture
was stirred at 100 °C for 12 or 24 h depending on the conditions executed. The
resulted brown solid residue was washed with CH2Cl2 several times till the
solution was changed to colorless. Then, the gray solid residue was
concentrated in reduced pressure. The isolated yields for 6a and 6b are 78.7
% (0.098 g, 0.393 mmol) and 72.8 % (0.085 g, 0.362 mmol), respectively. 6a: 1H
NMR (CDCl3, d/ppm): 12.90 (s, 1H, NH), 8.17 (dd, Jdd = 1.2 Hz, Jdd = 6.4 Hz, 1H,
Ph), 7.83 (s, 1H, Ph), 7.43 ꢀ 7.62(m, 4H, Ph), 7.23(dd, Jdd = 1.2 Hz, Jdd = 7.2 Hz,
1H, Ph). 13C NMR (CDCl3, d/ppm): 152.67, 141.74, 136.07, 131.51, 130.76,
126.26, 124.61, 124.37, 122.62, 119.98, 117.24, 113.25, 112.16, 99.63, 21.23;
HRMS: m/z = 249.0792 (M+). 6b: 1H NMR (CDCl3, d/ppm): 12.90 (s, 1H, NH),
8.17 (d, JH–H = 8.00 Hz, 1H, Ph), 7.83 (s, 1H, Ph), 7.43–7.62(m, 5H, Ph), 7.21 (d,
JH–H = 1.20 Hz, 1H, Ph); 13C NMR (CDCl3, d/ppm): 157.83, 152.69, 141.81,
137.75, 130.82, 124.75, 124.33, 122.68, 122.34, 120.17, 117.20, 113.11, 112.44,
99.95; HRMS: m/z = 235.0639 (M+).
[21] Synthesis and characterization of 2: The same size of flask and setup as shown
previously was charged with dichloro(1,5-cyclooctadiene)palladium (0.045 g,
0.156 mmol) and (g g
5-C5H5)Co( 4- (PPh2)2C4Ph2) 1 (0.109 g, 0.156 mmol), and
10 ml CH2Cl2 as solvent. The solution was stirred at 25 °C for 1 h before the
solvent was removed in reduced pressure. Subsequently, purification was
carried out using CTLC with mixture solvent (CH2Cl2/EA = 10/1). A band of
yellow-colored compound was isolated and identified as the title compound in
the yield of 74% (0.102 g, 0.117 mmol). 2: 1H NMR (CDCl3, d/ppm): 8.06–8.11
(dt, 4H, Jdd = 4.8 Hz, Jdt = 1.6 Hz, PPh2), 7.67–7.72 (dt, Jdd = 4.0 Hz, Jdt = 1.6 Hz,
4H, PPh2), 7.18–7.53 (m, 22H, Ph, PPh2), 4.14 (s, 5H, Cp); 13C NMR (CDCl3, d/
[25] G.
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