2-Aryl-dibenzo-1,2-oxaphosphorine as a ligand in borane and in Pt(II) complexes

Article abstract of DOI:10.1002/hc.20042

Optimum conditions for the synthesis of aryl-dibenzo-oxaphosphorines (2) from the corresponding phosphonous chloride (1) were explored to avoid the formation of by-products (e.g., 4-6). The aryl-dibenzo-oxaphosphorines (2) were converted to the P-oxides (

Full text of DOI:10.1002/hc.20042

Heteroatom Chemistry
Volume 15, Number 6, 2004
2-Aryl-dibenzo-1,2-oxaphosphorine as a
∗
Ligand in Borane and in Pt(II) Complexes
Gyo¨rgy Keglevich,1 Helga Szelke,2 Andrea Kere´nyi,1 T´ımea Imre,3
Krisztina Luda´nyi,3 Jo´zsef Dukai,4 Ferenc Nagy,4 and Pe´ter Ara´nyi4
1Department of Organic Chemical Technology, Budapest University of Technology and Economics,
1521 Budapest, Hungary
2Research Group of the Hungarian Academy of Sciences at the Department of Organic Chemical
Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary
3Hungarian Academy of Sciences, Chemical Research Center, 1525 Budapest, Hungary
4NIKE 2000, 8175 Balatonfu¨ zfo¨, Hungary
Received 8 June 2004; revised 30 June 2004
P-cycles form a special class [1]. The dibenzo-1,2-
ABSTRACT: Optimum conditions for the synthesis
oxaphosphorines with phosphorous function repre-
of aryl-dibenzo-oxaphosphorines (2) from the corre-
sent a group that attracted much attention [2–4]. The
sponding phosphonous chloride (1) were explored to
P-aryl derivatives were not, however, studied in de-
avoid the formation of by-products (e.g., 4–6). The
tail, mainly their oxides were described [5]. For this,
aryl-dibenzo-oxaphosphorines (2) were converted to
we decided to examine the synthesis and complexing
the P-oxides (3), and were utilized in the synthe-
properties of aryl-dibenzo-1,2-oxaphosphorines.
sis of phosphinite-boranes 7 and Pt(II) complexes 8.
The chloro derivative (1) available via the cy-
Depending on the aryl substituent, the Pt(II) com-
clization of ortho-hydroxybiphenyl by phosphorus
plex (8) was formed with cis and trans geome-
trichloride [2] was first reacted with phenylmag-
ꢀ
C
try.
2004 Wiley Periodicals, Inc. Heteroatom Chem
nesium bromide in tetrahydrofuran at 0 → 26◦C
under nitrogen. After the work-up procedure in-
cluding hydrolysis, a mixture of phosphinite 2a
(83%) and 2-diphenylphosphino-2ꢁ-hydroxybiphenyl
4 (17%) formed by ring opening with a second equiv-
alent of Grignard reagent was obtained according
to 31P NMR and mass spectroscopic analysis of the
crude mixture. The two components were obtained
in a pure form as their oxides (3a and 5, respec-
tively) after oxidation and purification by column
chromatography (Scheme 1). A similar side reaction
was also observed in the reaction of the P-oxide of
the chlorodibenzooxaphosphorine with methylmag-
nesium bromide [5]. The substitution was extended
to the preparation of triisopropylphenyl phosphinite
2b (Scheme 1). The product (2b) was formed in a
neat reaction, under the conditions of the hydrolysis
15:459–463, 2004; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20042
INTRODUCTION
The P-ligands are widely applied in transition metal
complexes that may be useful catalysts. The hete-
rocyclic P-ligands including five- and six-membered
∗IUPAC name of 2-aryl-dibenzo-1,2-oxaphosphorine is 1,2-
oxaphosphinine.
Correspondence to: Gyo¨rgy Keglevich; e-mail: gkeglevich@mail.
bme.hu.
Contract grant sponsor: National Research and Development
Project (NKFP).
Contract grant number: 3-35/2002.
c
ꢀ
2004 Wiley Periodicals, Inc.
459

460 Keglevich et al.
SCHEME 1
applying 0.15 M hydrochloric acid; the oxaphospho-
rine ring of 2b was, however, opened up partially
to afford 2-aryl-H-phosphinoxido-2ꢁ-biphenyl 6-2 (as
the predominant component of a tautomeric equi-
librium). According to 31P NMR and MS, the crude
mixture consisted of 80% of phosphinite (2b) and
20% of by-product 6-2. Performing the hydrolysis in
the absence of hydrochloric acid, the ring opening
side reaction could be avoided. It can be seen that
the oxaphosphorine ring of the triisopropylphenyl
compound (2b) is more sensitive under the condi-
tions of acidic hydrolysis than that of the phenyl
derivative (2a) is. At same time, the oxaphosphorine
ring in 2 is more vulnerable toward PhMgBr than
to triiPrC6H2MgBr, as the by-product from double
arylation was formed only in the first case (4).
To prepare a more stable derivative, phosphinite
2b was converted to phosphinate 3b by oxidation
and was isolated in 66% after column chromatogra-
phy (Scheme 1).
Phosphinites 2a and 2b and phosphinates 3a and
3b were characterized by 31P and 13C NMR, as well
as mass spectroscopy, the P-oxides (3a and 3b) also
by 1H NMR spectral data. By-products 4, 5, and 6-1
were identified by 31P NMR and MS.
The P-ligands are usually protected against
oxidation as borane complexes [6]. The aryl-
phosphinites (2a and 2b) were reacted with
dimethylsulfide borane to give the phosphinite-
boranes (7a and 7b, respectively) that were charac-
terized after purification by 31P, 11B, and 13C NMR
spectral parameters (Scheme 2). The phosphinite bo-
ranes (7a and 7b) were of a ca. 95% purity.
Finally, arylphosphinites 2a and 2b were reacted
with dichlorodibenzonitrile platinum in boiling ben-
zene. On cooling, the products were precipitated and
identified as complexes 8a and 8b (Scheme 2).
The 31P NMR spectra of the complexes 8a and 8b
revealed a signal at ꢀ 76.8 with a JPt–P of 4240 Hz and
at ꢀ 84.6 with a JPt–P of 2900 Hz, respectively. Both

2-Aryl-dibenzo-1,2-oxaphosphorine as a Ligand in Borane and in Pt(II) Complexes 461
SCHEME 2
signals were accompanied by a pair of satellites re-
sulting from the presence of the 195Pt isotope. The
cis and trans orientation of the ligands in complexes
8a and 8b, respectively, is in accord with the stere-
ospecific JPt–P couplings detected. It is known that
within a cis and trans diastereomer pair, the larger
coupling belongs to the cis isomer, while the smaller
one to the trans form [7]. The outcome of the com-
plexation can be explained well with the role of steric
factors; with the smaller phenyl group, the orienta-
tion of the ligands in the usual cis, while with the
sterically more demanding triisopropylphenyl sub-
stituent, the ligands are in the more favorable trans
relationship. A similar situation was reported for the
corresponding phospholes [7,8].
H3PO4, F3B · OEt2 or TMS. The coupling constants
are given in Hz. Mass spectrometry was performed
on a ZAB-2SEQ instrument.
The Preparation of Phenyl-oxaphosphorines 2a,
3a, and 7a
To 1.0 g (4.26 mmol) of chlorooxaphosphorine 1
in 10 mL of tetrahydrofuran was added dropwise
5.54 mmol of phenylmagnesium bromide in 10 mL
of diethyl ether (prepared from 0.86 g (5.54 mmol)
of bromobenzene and 0.14 g (5.54 mmol) of magne-
sium in 10 mL of ether) at 0◦C with stirring. After ad-
dition was complete, content of the flask was stirred
at 26◦C for 20 h under nitrogen. Solvent was evap-
orated and the residue taken up in the mixture of
20 mL of chloroform and 5 mL of water. The organic
phase was dried (Na2SO4) and concentrated. 0.82 g
crude product containing 99% of 2a and 1% of 4 was
obtained.
1
Complex 8a was also characterized by H NMR
spectroscopic data. The solubility of complexes 8a
and 8b in chloroform is very poor. Moreover, com-
pound 8b was found to be unstable in CHCl3 (CDCl3)
solution.
In summary, two arylphosphines together with
the corresponding boranes and the two kinds of
platinum complexes based on the dibenzooxaphos-
phorine skeleton were prepared and characterized.
2a: Yield: 70%; 31P NMR (CDCl3) ꢀ 84.6; 13C
NMR (CDCl3) ꢀ 120.8 (CH ), 123.1 (CH ), 124.0
(3 J = 5.8, C1a)a, 124.1 (3 J = 1.5, CH ), 125.0 (CH ),
3
ꢁ
127.5 (CH ), 128.1 ( J = 4.2, C3 ), 129.4 (CH ), 129.6
ꢁ
ꢁ
(CH ), 130.7 (CH ), 130.9 (C2 ), 131.5 (C4 ), 131.9
(1 J = 13.9, C6a)b, 133.5 (C10a) , 138.9 ( J = 30.1, C1 ) ,
151.3 (2 J = 10.8, C4a), a,bmay be reversed; FAB-MS,
277 (M+H); (M+H)+found = 277.0782, C18H14OP re-
quires 277.0755.
a
1
b
ꢁ
EXPERIMENTAL SECTION
1
The 31P, 11B, 13C, and H NMR spectra were taken
on a Bruker DRX-500 spectrometer operating at
202.4, 160.4 125.7, and 500 MHz, respectively. Pos-
itive chemical shifts are downfield relative to 85%
4: 31P NMR (CDCl3) ꢀ–11.8; FAB-MS, 355 (M+H).
The crude product was taken up in 20 mL of chlo-
roform and was treated with 1.3 mL (12.8 mmol)

462 Keglevich et al.
of 30% hydrogen peroxide at 0◦C for 2 h on stir-
ring. The organic phase was washed with 3 × 10 mL
of water and dried (Na2SO4), and finally concen-
trated. The main component was obtained by col-
umn chromatography (silica gel, 3% methanol in
chloroform) to afford 0.69 g (80%) of 3a as a white
solid.
C4 CHMe2), 3.99 (m, 2H, C2 CHMe2), 6.85–8.15
ꢁ
ꢁ
(m, 10H, Ar); FAB-MS, 403 (M+H); (M + H)f+ound
=
403.2124, C27H31OP requires 403.2191.
3b: Yield: 1.11 g (76%); could be separated as a
crystalline compound, m.p. 155–157◦C (acetone); 31
P
NMR (CDCl3) ꢀ 25.6; 13C NMR (CDCl3) ꢀ 23.8, 24.4,
25.3 (CH(CH3)2), 30.4 (3 J = 3.6, C2 CHMe2), 34.6
ꢁ
3a: m.p. 156–158◦C (acetone); 31P NMR (CDCl3)
ꢀ 25.0 (99%); 13C NMR (CDCl3) ꢀ 120.4 (2 J = 6.0, C7)a,
121.8 (3 J = 11.1, C1a)b, 123.5 (3 J = 9.6, C10)a, 124.5
(C3)c, 124.7 (1 J = 128.1, C6a)d, 124.9 (C1)c, 128.1 (3 J =
(C4 CHMe2), 118.7 (1 J = 140.7, Cꢁ)c, 120.9 (2 J =
ꢁ
5.9, C7)a, 121.7 (3 J = 11.3, C1a)d, 123.0 (3 J = 13.4,
3
a
b
b
ꢁ
C3 ), 123.7 ( J = 8.9, C10) , 124.2 (C3) , 125.0 (C1) ,
127.0 (3 J = 14.6, C4)a, 129.1 (1 J = 125.3, C6a)c, 129.4
(3 J = 13.9, C8)a, 130.2 (C2)b, 132.0 (C9)b, 133.8 (2 J =
a
3
e
1
ꢁ
14.1, C4) , 128.4 ( J = 14.2, C3 ) , 129.3 ( J = 143.6,
d
3
a
2
d
2
ꢁ
ꢁ
ꢁ
C1 ) , 130.3 (C4 ), 130.7 ( J = 12.2, C8) , 131.9 ( J =
4.3, C10a) , 148.4 ( J = 8.2, C4a), 153.9 (C4 ), 156.5
e
c
c
2
2
1
11.0, C2 ) , 132.8 (C9) , 132.9 (C2) , 135.5 ( J = 5.3,
( J = 13.3, C2 ), a-dtentative assignment; H NMR
ꢁ
ꢁ
C
10a)b, 148.9 (2 J = 8.5, C4a), a-etentative assignment;
(CDCl3) ꢀ 1.00 (d, 3 JHH = 7.0, 6H, CH(CH3)2), 1.22 (d,
1H NMR (CDCl3) ꢀ 7.27–8.07 (m, 13H, Ar); FAB-MS,
293 (M+H); M+found = 292.0601, C18H14O2P requires
292.0653.
3 JHH = 6.5, 6H, CH(CH3)2), 1.31 (d, JHH = 7.0, 6H,
3
3
ꢁ
CH(CH3)2), 2.96 (sept, JHH = 7.0, 1H, C4 CHMe2),
ꢁ
3.89 (m, 2H, C2 CHMe2), 7.20–8.07 (m, 10H, Ar);
5: 31P NMR (CDCl3) ꢀ 32.7 (1%); 1H NMR (CDCl3)
ꢀ 6.46–8.04 (m, 18H, Ar), 9.03 (s, 1H, OH); FAB-MS,
371 (M+H).
FAB-MS, 419 (M+H); M+found = 418.1982, C27H31O2P
requires 418.2062.
6-2: 31P NMR (CDCl3) ꢀ 15.3; FAB-MS, 420
(M+H)
To the 20 mL dichloromethane solution of
4.26 mmol of phosphine 2a was added 2.6 mL
(5.12 mmol) of 2 M tetrahydrofuran solution of
dimethylsulfide borane at room temperature under
nitrogen and the mixture was stirred for 24 h. Evap-
oration of the volatile components led to 7a as pale
yellow solid. Yield: ∼100%.
7b: Yield: ∼100%; 31P NMR (CDCl3) ꢀ 101.9
(broad); 11B NMR (CDCl3) ꢀ −30.0 (broad); 13C NMR
(CDCl3) ꢀ; 23.9, 24.6, 25.7 (CH(CH3)2), 31.0 (3 J = 6.3,
C2 CHMe2), 34.5 (C4 CHMe2), 120.9 (2 J = 5.4, C7)a,
ꢁ
ꢁ
1
b
3
c
ꢁ
121.5 ( J = 50.5, C1 ) , 123.2 ( J = 9.8, C1a) , 123.4
3
3
a
d
ꢁ
( J = 8.8, C3 ), 124.0 ( J = 6.4, C10) , 124.2 (C3) , 125.1
(C1)d, 128.2 (3 J = 11.7, C4)a, 128.6 (1 J = 55.5, C6a)b,
130.0 (3 J = 14.7, C8)a, 130.6 (C2)d, 131.8 (C9)d, 134.2
7a: 31P NMR (CDCl3) ꢀ 93.7 (broad); 11B NMR
(CDCl3) ꢀ –36.2 (broad); 13C NMR (CDCl3) ꢀ 120.8
2
a
1
b
3
c
2
2
ꢁ
ꢁ
( J = 4.5, C7) , 123.1 ( J = 59.9, C1 ) , 123.4 ( J =
(C10a) , 149.2 ( J = 9.1, C4a), 153.7 (C4 ), 156.1 ( J =
10.0, C1a)c, 124.3 (3 J = 6.0, C10)a, 124.8 (C3)d, 125.4
12.0, C2 ), a-dtentative assignment; H NMR (CDCl3)
1
ꢁ
d
3
e
3
a
(C1) , 128.7 ( J = 10.0, C3 ) , 128.8 ( J = 13.3, C4) ,
ꢀ 1.02 (d, 3 JHH = 6.5, 6H, CH(CH3)2), 1.10 (d, 3 JHH
=
ꢁ
1
b
2
129.8 ( J = 41.0, C6a) , 130.7 (C4 ), 131.3 ( J = 11.5,
7, 6H, CH(CH3)2), 1.23 (d, 3 JHH = 7.0, 6H, CH(CH3)2),
ꢁ
e
3
a
d
d
ꢁ
ꢁ
ꢁ
C2 ) , 131.7 ( J = 18.9, C8) , 132.4 (C9) , 133.3 (C2) ,
135.0 (C10a)c, 149.4 (2 J = 12.6, C4a), a-etentative as-
signment; 1H NMR (CDCl3) ꢀ 7.06–7.96 (m, 13H, Ar);
FAB-MS, 277 (M–BH3+H).
2.87 (m, 1H, C4 CHMe2), 3.82 (m, 2H, C2 CHMe2),
7.08–7.85 (m, 10H, Ar); FAB-MS, 417 (M+H), 403
(M–BH3+H).
The Preparation of Pt-Complexes 8a and 8b
The Preparation of Triisopropylphenyl-
Oxaphosphorines 2b, 3b, and 7b
To 0.21 mmol of phosphinite 2 in 20 mL of ben-
zene, 0.10 g (0.21 mmol) of dichlorodibenzonitrile-
platinum was added and the mixture was stirred at
reflux for 1.5 h under nitrogen. Fractional crystalliza-
tion from the benzene solution furnished 8 as pale
yellow powder-like crystal.
2b, 3b, and 7b were prepared from 1 as described
for the 1→2a→3a→7a transformation.
2b: Yield: 1.4 g (82%); 31P NMR (CDCl3) ꢀ 112.0;
13C NMR (CDCl3) ꢀ 23.3, 23.7, 26.0 (CH(CH3)2), 31.4
ꢁ
ꢁ
(C2 CHMe2), 34.7 (C4 CHMe2), 120.9 (CH ), 122.3
8a: Yield: 60 mg (44%); in a purity of ca. 90%; 31
P
3
ꢁ
(CH ), 122.6 ( J = 3.6, C3 ), 123.2 (CH ), 123.6
NMR (CDCl3) ꢀ 76.8 (JPt-P = 4239); 1H NMR (CDCl3)
ꢀ 6.11–7.97 (m, 18H, Ar).
(CH ), 125.3 (CH ), 125.8 (3 J = 9.7, C1a)a, 128.0
1
b
8b: Yield: 50 mg (31%); in a purity of ca. 75%; 31
P
ꢁ
(CH ), 129.1 (CH ), 129.7 ( J = 31.3, C1 ) , 130.1
(CH ), 134.5 (2 J = 12.6, C10a)a, 138.6 (1 J = 26.4, C6a)b,
NMR (CDCl3) ꢀ 84.6 (JPt-P = 2900); 1H NMR (CDCl3) ꢀ
0.90 (d, 3 JHH = 6.5, 6H, CH(CH3)2), 1.02 (d, 3 JHH = 6.0,
152.5 (C4a), 152.9 (C4 ), 156.5 (C2 ), a,bmay be reversed;
ꢁ
ꢁ
3
1H NMR (CDCl3) ꢀ 1.12 (d, 3 JHH = 6.5, 6H, CH(CH3)2),
6H, CH(CH3)2), 1.15 (d, JHH = 6.5, 6H, CH(CH3)2),
3
3
ꢁ
1.26 (d, JHH = 7.0, 6H, CH(CH3)2), 1.37 (d, JHH
=
2.77 (sept, 3 JHH = 7.0, 1H, C4 CHMe2), 4.28 (m, 2H,
3
ꢁ
7.0, 6H, CH(CH3)2), 2.97 (sept, JHH = 7.0, 1H,
C2 CHMe2), 6.93–8.03 (m, 15H, Ar).

2-Aryl-dibenzo-1,2-oxaphosphorine as a Ligand in Borane and in Pt(II) Complexes 463
Ed 2000, 39, 1640.
[5] Cherynshev, E. A.; Aksenov, V. I.; Ponomarev, V. V.;
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