Palladium-catalyzed arylation of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene- 10-oxide (DOPO) with halogen-substituted phenols

Article abstract of DOI:10.1080/10426500802705420

Phenol functionalized 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives are synthesized via palladium-catalyzed arylation of DOPO with halogen-substituted phenols. 2-,3-, and 4-Substituted halogen phenols are successfully applied to th

Full text of DOI:10.1080/10426500802705420

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Palladium-Catalyzed Arylation
of 9,10-Dihydro-9-oxa-10-
phosphaphenanthrene-10-
oxide (DOPO) with Halogen-
Substituted Phenols
Liancheng Yang a , Longhe Xu a & Zaizhou Tao b
a State Key Laboratory of Fine Chemicals , Dalian
University of Technology , Dalian, China
b Shenyang Research Institute of Chemical Industry ,
Shenyang, China
Published online: 18 Nov 2009.
To cite this article: Liancheng Yang , Longhe Xu & Zaizhou Tao (2009) Palladium-
Catalyzed Arylation of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)
with Halogen-Substituted Phenols, Phosphorus, Sulfur, and Silicon and the Related
Elements, 184:12, 3175-3181, DOI: 10.1080/10426500802705420
To link to this article: http://dx.doi.org/10.1080/10426500802705420
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Phosphorus, Sulfur, and Silicon, 184:3175–3181, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802705420
Palladium-Catalyzed Arylation of
9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide
(DOPO) with Halogen-Substituted Phenols
Liancheng Yang,1 Longhe Xu,1 and Zaizhou Tao2
1State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian, China
2Shenyang Research Institute of Chemical Industry, Shenyang, China
Phenol functionalized 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide
(DOPO) derivatives are synthesized via palladium-catalyzed arylation of DOPO
with halogen-substituted phenols. 2-,3-, and 4-Substituted halogen phenols
are successfully applied to the cross-coupling reactions. This method is mild,
convenient, and leads to high yields (65–95%).
Keywords Arylation; catalysis; cross-coupling; DOPO; palladium
INTRODUCTION
The cyclic organic phosphorus compound, 9,10-dihydro-9-oxa-10-
phospha-phenanthrene-10-oxide (DOPO), has received notable atten-
tion in research due to its attractive properties.1–5 DOPO derivatives
have been widely incorporated into polymers for improving the their
flame retardant properties and thermal stability.6–13 For example, an
aromatic DOPO derivative containing a phenol functional group, 2-(6-
oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-1,4-dihydroxy phenylene
(ODOPB), has been used as a reactive flame retardant.14–18 Owing to
the high content of phosphorus and of aromatic groups, ODOPB exhib-
ited not only better flame retardant properties but also higher thermal
stability and glass transition temperature.14 Moreover, incorporation
of ODOPB into the molecular structure of polymers via phenol groups
brought improved organosolubility to the polymer, and avoided the
molecular migration of flame retardants.15 However, to the best of our
Received 16 October 2008; accepted 16 December 2008.
We thank Shenyang BMD Chemical Co., Ltd. (China) for funding this project.
Address correspondence to Liancheng Yang, Liaoning Petrochemical Vocational Tech-
nology College, Room 213, Petrochemical Department, Jinzhou 121001, China. E-mail:
ylc94@163.com
3175

3176
L. Yang et al.
knowledge, only three phenol derivatives of DOPO have been reported;
they were synthesized by the addition of DOPO to quinones.19–21 In the
present work, we attempt to synthesize phenol functionalized DOPO
derivatives through palladium-catalyzed phosphorus–carbon forma-
tion reactions. Although cross-coupling of P-H compounds with aryl
halides, catalyzed by transition metal catalyst (such as Pd, Ni, Cu),
have been studied in sufficient detail during the last two decades,22–32
far from all the reported procedures are able to be used in the aryla-
tion of DOPO with aryl halides. In particular, triethylamine, which
is usually used as a base in such transformations, turned out to
be insufficiently effective. Although Beletskaya et al.33 examined the
palladium-catalyzed arylation reactions of DOPO with some aryl io-
dides and aryl bromides, no halogen-substituted phenols were used as
coupling partners. In this article, we wish to report a general procedure
for palladium-catalyzed arylation of DOPO with halogen-substituted
phenols.
SCHEME 1
RESULTS AND DISCUSSION
The arylation conditions were optimized using the reactions of DOPO
with 4-iodophenol as examples (Scheme 1). The natures of the base, sol-
vent, and catalyst were varied. The reaction conditions and the yields of
P-phenyl derivative are summarized in Table I. Firstly, PdCl2(Ph3P)2,
an effective catalyst in the palladium catalyzed arylation of DOPO,33
was used as a catalyst. Various bases were added to the reaction mix-
ture, and the reaction was carried out in dioxane at reflux temperature.
Low to good yields of the target products were obtained (entries 2–9)
except entry 6, in which the reaction mainly produced byproducts prob-
ably caused by the addition of P-H to propylene oxide. The best result

Pd-Catalyzed Arylation of DOPO with Halo-Phenols
3177
TABLE I Cross Coupling of DOPO with 4-Iodophenol (Ia)a
Catalyst (5% mol) +
Phase-transfer
Ligand (10% mol) catalyst (20%mol)
Reaction
time, h
Yield,b
%
b
Entry
1
Base
Et3N
—
—
24
No
reaction
2
3
4
5
6
Et3N
Et3N
PdCl2(Ph3P)2
PdCl2(Ph3P)2
—
24
24
24
24
24
8
BTEAC
BTEAC
BTEAC
BTEAC
10
12
45
—
i-Pr2NEtc PdCl2(Ph3P)2
Cy2NMec PdCl2(Ph3P)2
Propylene PdCl2(Ph3P)2
oxide
7
8
9
10
11
12
13
14
15
K2CO3
NaOAc
NaOAc
NaOAc
Et3N
NaOAc
NaOAc
Et3N
PdCl2(Ph3P)2
PdCl2(Ph3P)2
PdCl2(Ph3P)2
Pd(OAc)2+Ph3P
Pd(OAc)2+Ph3P
Pd(Ph3P)4
Pd(Ph3P)4
Pd(Ph3P)4
PdCl2+Ph3P
BTEAC
24
4
4
4
4
4
5
58
67
66
94
83
95
94d
85
72
—
BTEAC
—
—
—
—
—
4
4
Et3N
—
aThe reactions were carried out using DOPO (1 mmol), 4-iodophenol (1 mmol), and
base (2 mmol), in dioxane (3 mL) at 100◦C under nitrogen atmosphere.
bIsolated yield.
ci-Pr2NEt: N,N-diisopropylethylamine; Cy2NMe: N,N-dicyclohexylmethylamine.
dCH3CN (3 mL) was used as the solvent and the reaction was carried out at reflux
temperature.
was obtained using NaOAc as a base (entry 8). The addition of phase-
transfer catalyst (BTEAC) had little effect on the reaction when NaOAc
was used as the base (entries 8 and 9). Moreover, the reaction did not
proceed in the absence of the catalyst (entry 1). Then, effects of other
catalysis system on the cross-coupling reaction were evaluated. It was
found that Pd(OAc)2/Ph3P, Pd(Ph3P)4, and PdCl2/Ph3P could catalyze
the reaction; however, Pd(OAc)2/Ph3P and Pd(Ph3P)4 were more effec-
tive (entries 10–14). The best procedure for the synthesis of Ia was
cross coupling of DOPO with 4-iodophenol in the presence of 2 equiv
of NaOAc, 5% mol of Pd(OAc)2, and 10% mol of Ph3P (method A) [or
5% mol of Pd(Ph3P)4 (method B)], which takes 4 h in boiling dioxane
(entries 10 and 12). A similar result was obtained when CH3CN was
used as a solvent, and the reaction was completed at 80◦C after 5 h
(entry 13).
The two methods were then extended to the synthesis of other
phenol functionalized DOPO derivatives Ib–d (Table II). When iodo-
substituted phenols were applied, compounds Ib–d were obtained in

3178
L. Yang et al.
TABLE II Cross Coupling of DOPO with Various Halogen-Substituted
Phenolsa
Entry Halogen-substituted phenols Product Reaction time, h Yield,%b Methodc
1
Ib
Ic
Id
4
94
A
2
3
4
24
93
10
B
A
4
5
4
12
78
13
B
A
6
7
12
24
65
33
B
B
Ia
Ib
8
24
24
24
28
5
B
B
B
9
Ic
10
Id
25
aThe reactions were carried out using DOPO (1 mmol), halogen-substituted phenol (1
mmol), and NaOAc (2 mmol), in dioxane (3 mL) at 100◦C under nitrogen atmosphere.
bIsolated yield.
cMethod A: Pd(OAc)2 (5% mol), Ph3P (10% mol) were used as catalysts. Method B:
Pd(Ph3P)4 was used as a catalyst.
good to high yields after workup and chromatography on silica gel (elu-
ent 2:98 to 5:95 MeOH/CH2Cl2). Compared with method B, method A
led to lower yields of Ic and Id (Entries 3 and 5). This indicated that a
steric hindrance effect played an important role using a 2-substituted
phenol as coupling partner when Pd(OAc)2/Ph3P was used as catalyst.
However, the yields of Ic and Id were greatly improved when Pd(Ph3P)4
was applied as the catalyst. As to bromo-substituted phenols, low to

Pd-Catalyzed Arylation of DOPO with Halo-Phenols
3179
moderate yields of Ib–d were obtained (entries 7–10). Extending the
reaction times only caused the formation of a considerable amount
(more than 50%) of unidentified byproducts.
EXPERIMENTAL
General
DOPO (BMD Chemical Co., Ltd., Shenyang, China) was purified by
recrystallization from THF. 2-, 3-, and 4-Iodo (or bromo) phenols were
of commercial quality (Aldrich) and used without further purification.
2-Iodobenzene-1,4-diol34 and 2-bromobenzene-1,4-diol35 were prepared
according to the reported procedures. Other reagents and solvents were
commercially available and distilled, recrystallized, or dehydrated thor-
¨
oughly. Melting points were determined on a Buchi melting point ap-
1
paratus and are uncorrected. H NMR spectra were performed on a
Mercury 300 spectrometer (Varian, H: 300 MHz) with DMSO-d6 as
1
the solvent and TMS as the internal standard. 31P NMR spectra were
obtained on the Mercury 300 (Varian, 121 MHz) spectrometer using
H3PO4 as an internal standard. Infrared spectra were recorded with a
PE-983G instrument (Perkin-Elmer). Combustion analyses for C and
H elemental composition were made with a Vario EL III analyzer (Ele-
mentar). Phosphorus content was determined by oxygen flask method.
All reactions were monitored by TLC.
General Procedure for the Arylation of DOPO with
Halogen-Substituted Pphenols
Method A
In a flask containing DOPO (216 mg, 1.0 mmol), palladium acetate
(11 mg, 0.05 mmol, 0.05 eq), Ph3P (26 mg, 0.1 mmol, 0.1 eq), NaOAc
(164 mg, 2.0 mmol), and halogen-substituted phenol (1.0 mmol) under
N2 were added under stirring dry dioxane (3 mL) at room temperature.
The reaction mixture was heated at 100◦C until complete consumption
of the phenol, which was monitored by TLC. After cooling, the reaction
mixture was diluted with ethyl acetate (20 mL), and diluted HCl (1:2,
10 mL) was added, the mixture was stirred, and the aqueous phase
was separated and extracted with ethyl acetate (3 × 20 mL). The ex-
tracts were combined with the organic phase, then washed with water
(3 × 10 mL) and brine (10 mL), and dried over Na2SO4. The crude
solution is concentrated under reduced pressure, affording a solid pu-
rified by column chromatography over silica gel (eluent 2:98 to 5:95
MeOH/CH2Cl2).

3180
L. Yang et al.
Method B
Method B was performed the same as method A, except that
Pd(Ph3P)4 was used as a catalyst.
4-(6-Oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)phenol (1a)
White solid: mp 256–258◦C, IR (KBr): 3451 (Ph-OH); 1600, 1583 (Ph);
1202 (P = O); 1147, 931 (P-O-Ph) cm−1; 1H NMR (300 MHz, DMSO-d6):
δ 6.87 (dd, J = 9.0, 3.6 Hz, 2H, ArH), 7.23–7.34 (m, 2H, ArH), 7.41–7.57
(m, 5H, ArH), 7.71–7.76 (m, 1H, ArH), 8.15–8.22 (m, 2H, ArH), 10.26 (s,
1H, OH); 31P NMR (121 MHz, DMSO-d6, H3PO4): δ 24.18. Anal. Calcd.
for C18H13O3P: C, 70.13; H, 4.25; P, 10.05; found: C, 70.20; H, 4.22; P,
10.13.
3-(6-Oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)phenol (1b)
White solid: mp 235–236◦C, IR (KBr): 3415 (Ph-OH); 1597 (Ph);
1
1189(P = O); 1148, 922 (P-O-Ph) cm−1; H NMR (300 MHz, DMSO-
d6): δ 6.96–7.08 (m, 2H, ArH), 7.14–7.29 (m, 4H, ArH), 7.37–7.56 (m,
3H, ArH), 7.70 (t, J = 7.2, 1H, ArH), 8.07–8.15 (m, 2H, ArH), 9.62 (s,
1H, OH); 31P NMR (121 MHz, DMSO-d6, H3PO4): δ 23.40. Anal. Calcd.
for C18H13O3P: C, 70.13; H, 4.25; P, 10.05; found: C, 70.18; H, 4.27; P,
10.08.
2-(6-Oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)phenol (1c)
White solid: mp 285–287◦C, IR (KBr): 3441 (Ph-OH); 1594 (Ph); 1193
1
(P = O); 1150, 922 (P-O-Ph) cm−1; H NMR (300 MHz, DMSO-d6): δ
6.78–6.83 (m, 1H, ArH), 6.93–6.96 (m, 1H, ArH), 7.22–7.31 (m, 2H,
ArH), 7.40–7.61 (m, 4H, ArH), 7.70–7.75 (m, 2H, ArH), 8.17–8.23 (m,
2H, ArH), 10.12 (s, 1H, OH); 31P NMR (121 MHz, DMSO-d6, H3PO4): δ
25.22. Anal. Calcd. for C18H13O3P: C, 70.13; H, 4.25; P, 10.05; found: C,
70.19; H, 4.22; P, 10.15.
2-(6-Oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-1,4-
dihydroxy Phenylene (1d)
White solid: mp 254–255◦C, IR (KBr): 3175 (Ph-OH); 1593, 1502
(Ph); 1473 (P-Ph); 1182 (P = O); 932 (P-O-Ph) cm−1; 1H NMR (300 MHz,
DMSO-d6): δ 6.63–6.67 (t, 1H, ArH), 6.89–6.92 (d, 1H, ArH), 7.19–7.32
(m, 2H, ArH), 7.43–7.59 (m, 3H, ArH), 7.62–7.75 (t, 1H, ArH), 8.23–8.24
(d, 2H, ArH), 9.19 (s, 1H, OH), 9.48 (s, 1H, OH); 31P NMR (121 MHz,
DMSO-d6, H3PO4): δ 21.92. Anal. Calcd. for C18H13O4P: C, 66.67; H,
4.04; P, 9.55; found: C, 66.47; H, 4.12; P, 9.31.

Pd-Catalyzed Arylation of DOPO with Halo-Phenols
3181
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