A straightforward synthesis of unsymmetrical secondary phosphine boranes

Article abstract of DOI:10.1039/b920324a

A one-pot procedure for the synthesis of unsymmetrical alkyl-substituted secondary phosphine oxides is described. The sequential addition of N-benzylaniline to a solution of dichlorophenylphosphine and 1-methylimidazole in methylcyclohexane, separating of the protic ionic liquid formed, addition of Grignard reagent followed by hydrolysis gave unsymmetrical secondary phosphine oxides (SPOs) in high yield. The use of ionic liquids in the first step is essential and streamlined the synthesis. Unsymmetrical SPOs could be quantitatively reduced to secondary phosphine using a catalytic amount of Ti(OiPr)₄ and tetramethyldisiloxane (TMDS) under mild reaction conditions.

Full text of DOI:10.1039/b920324a

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www.rsc.org/greenchem | Green Chemistry
A straightforward synthesis of unsymmetrical secondary
phosphine boranes†
Christelle Petit,a Alain Favre-Re´guillon,*a,b Ge´rard Mignanic and Marc Lemaire*a
Received 29th September 2009, Accepted 11th November 2009
First published as an Advance Article on the web 14th January 2010
DOI: 10.1039/b920324a
A one-pot procedure for the synthesis of unsymmetrical alkyl-substituted secondary phosphine
oxides is described. The sequential addition of N-benzylaniline to a solution of
dichlorophenylphosphine and 1-methylimidazole in methylcyclohexane, separating of the protic
ionic liquid formed, addition of Grignard reagent followed by hydrolysis gave unsymmetrical
secondary phosphine oxides (SPOs) in high yield. The use of ionic liquids in the first step is
essential and streamlined the synthesis. Unsymmetrical SPOs could be quantitatively reduced to
secondary phosphine using a catalytic amount of Ti(OiPr)4 and tetramethyldisiloxane (TMDS)
under mild reaction conditions.
Dichloro-
and
dibromoarylphosphine
are
easily
Introduction
accessible7,16–18 and the one-pot synthesis of unsymmetrical SPOs
by reaction of Grignard reagents with dichlorophenylphosphine
followed by hydrolysis has been studied.19–20 However, due to
the highly electrophilic character of the chlorophosphine, the
yields are often low, with the exception of the bulky tBu.19–20
Thus, a two-step procedure21–22 and solid phase synthesis have
been studied.23–25
As the price of petrochemicals and the cost of waste disposal
increases, the chemical industry is striving to minimize waste
and negative environmental impact.1–2 A key objective is to
eliminate the adverse environmental effects of chemical syn-
thesis. Toward this end, progress has been made using safer
reagents, eliminating the generation of dangerous and toxic
byproducts and reducing the amount of waste produced. To
minimize waste, several options should be considered: working
under more concentrated conditions, selecting different starting
materials and designing new routes that require fewer steps. For
the latter, smaller quantities of starting materials, solvent and
reagents will be used and thus reduce the cost for waste disposal.
Recent interest in air and moisture-stable SPOs has led to
the identification of efficient transition metal catalyzed C–
C, C–N and C–S bond forming reactions.3–5 Furthermore,
SPOs are effective building blocks for the preparation of
tertiary phosphines3 and P-chirogenic tertiary phosphines.6–9
The synthesis of unsymmetrical SPOs via substitution of organo-
lithium or Grignard reagents with H-phosphinate according to
the methods of Emmick10–13 is well-known, and recently the
conversion of optically pure H-phosphinates to optically-active
P-stereogenic SPOs has been described.14–15 However, a limited
number of H-phosphinates has been described and alternative
starting material and methods have to be studied.
The development of an efficient strategy to synthesize un-
symmetrical alkyl-substituted SPOs is in high demand. In
this paper, we report a very efficient and versatile one-pot,
homogeneous liquid phase synthesis of unsymmetrical sec-
ondary phosphine oxides (SPOs). Furthermore, we have found
that these SPOs could be quantitatively reduced at 60 ◦C
using tetramethyldisiloxane (TMDS) in the presence of 10% of
titanium tetraisopropoxide (Ti(OiPr)4).26
Results and discussion
Synthesis of unsymmetrical alkyl-substituted SPOs
When N-benzylaniline was reacted with PhPCl2 in THF at 0 ◦C
in the presence of Et3N (Scheme 1), the 31P NMR showed that
aminophoshine 1 was obtained in high purity. However, the
separation of triethylamine hydrochloride from the reaction
mixture was not straightforward. The ease of formation of
aminophoshine 1 prompted us to further optimize this step.
Neither the change of base (2,6 lutidine, DIPEA, pyridine) or
solvent (toluene, THF, methylcyclohexane (MCH)) improved
the separation or the selectivity.
Recently, the BASIL process was developed and is operated
by BASF. This process, which involves ionic liquids (ILs), uses
1-methylimidazole as an acid scavenger of the HCl produced
during the synthesis of alkoxyphenylphosphine.27 The protic ILs
(PILs)28 formed could be easily separated from the product and
the Brønsted base 1-methylimidazole is easily regenerated by
distillation.27–28 These results prompted us to examine whether
aLaboratoire de Catalyse et de Synthe`se Organique, UMR 5246,
ICBMS, Universite´ Claude Bernard Lyon 1, CPE Bat. 308, 43, bd du 11
Novembre 1918, 69622, Villeurbanne, Cedex, France.
E-mail: marc.lemaire@univ lyon1.fr
bLaboratoire de Transformations Chimiques et Pharmaceutiques,
Conservatoire National des Arts et Me´tiers, 2 rue Conte´, 75003, Paris,
France. E-mail: alain.favre-reguillon@univ-lyon1.fr
cRhodia, Lyon Research Center, 85, avenue des Fre`res Perret, BP 62,
69192, Saint-Fons, Cedex, France
1
† Electronic supplementary information (ESI) available: Copies of H,
13C and 31P NMR of the compounds listed in Tables 1 and 2. See DOI:
10.1039/b920324a
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Table 1 One-pot synthesis of unsymmetrical SPOs
Entry
1
R-MgCl
CH3–
SPOs
Isolated yielda (%)
40b
71
85
2
3
C2H5–
nC5H11–
4
Cyclohexane–
73
5
6
iPr–
80
72
Scheme 1 One-pot synthesis of cyclohexylphenylphosphine oxide 4
with protic ILs.
4-MeO-Ph–
PILs could be used to synthesize unsymmetrical secondary
phosphine oxides (Scheme 1).
The addition of N-benzylaniline to
a
mixture of
dichlorophenylphosphine and 1-methylimidazole at 0 ◦C in
THF gave aminophoshine 1 but the problem of the separation
of the ammonium salt remained. However, using MCH as
solvent, the reaction mixture gave a biphasic reaction media.
The lower phase consists of protic ILs, i.e. 1-methylimidazolium
hydrochloride 2, and the upper phase of aminochlorophosphine
1 in MCH. The use of MCH is essential to minimize the
solubility of the PILs in the upper phase. The lower phase was
discarded and the crude upper phase was diluted with THF (1 :
3, v/v). Then, a stoichiometric amount of cyclohexylmagnesium
chloride solution in THF was added at 0 ◦C. A single product,
3, was detected by 31P NMR.
After 1 h at room temperature, the mixture was quenched
with HCl in diethylether at 0 ◦C and then with water. The
reaction mixture was then extracted with ethyl acetate and
cyclohexylphenylphosphine oxide 4 was obtained with a 31P
NMR purity of 95%. The pure compound, as ascertained by
1H, 13C and 31P NMR spectroscopy, could be obtained after
chromatography on neutral alumina using cyclohexane/ethyl
acetate as eluent.
The procedure was straightforward and reaction of the
aminophoshine 1 with a stoichiometric amount of a variety
of organomagnesium chlorides led to complete substitution of
the P–Cl bonds. After hydrolysis, unsymmetrical SPOs could be
obtained in good yield and the results are summarized in Table 1.
Entries 1–5 in Table 1 illustrate substitutions with Grignard
compounds in order to obtain electron-rich SPOs. However,
a low yield was obtained with methylmagnesium chloride
(Entry 1). The substitution of aminophosphine 1 by methyl-
magnesium chloride gave the methylphenylphosphinamide with
31P NMR purity higher than 98%. However, during hydroly-
sis, several by-products are formed. Under those conditions,
only 65% of methylphenylphosphinamide is transformed into
methylphenylphosphine oxide as ascertained by 31P NMR
(Table 1). Thus, alternative hydrolysis procedures were
evaluated,21 but in that particular case, we were not able to limit
a All compounds were isolated after chromatography on alumina. b The
conversion was 65% as determined by 31P NMR of the crude.
the formation of by-products. The methylphenylphosphine ox-
ide was isolated in moderate yield (40%, entry 1) when compared
to the yield obtained with two-step synthetic procedure starting
from methyl- or phenylphosphinate ethyl esters.13,29 However,
for ethyl- and other alkylmagnesium chlorides (entries 2–5), the
hydrolysis reaction proceeded well and SPOs were obtained in
good yield. Entry 6 shows a clean and complete substitution
of the chloride by an aryl group. Thus, we can conclude that
this methodology represents a versatile and general protocol for
the synthesis of unsymmetrical SPOs, which can be prepared in
one-pot starting from dichlorophenylphosphine using PILs.
Reduction of unsymmetrical SPOs to unsymmetrical secondary
phosphines
The reduction of these unsymmetrical SPOs to unsymmetrical
secondary phosphines was then studied. The reduction of SPOs
is generally obtained using silanes such as diphenylsilane30 or
trichlorosilane in the presence of an amine base.31 However,
reductions using silane are performed at temperature far from
their boiling point.30,31 Thus, alternative process have been
studied using borane32 or DIBAL-H.33 Industries involved in
phosphorus chemistry have successfully developed processes
using these reagents. Nevertheless, due to new regulations and
safety requirements, new, safer and cleaner reduction reagents
compatible with sustainable chemistry are needed for the
reduction of phosphine oxides on a large scale. Recently, we
have shown that using a catalytic amount of Ti(OiPr)4 and
tetramethyldisiloxane (TMDS), as the hydride source, various
tertiary phosphine oxides and secondary phosphine oxides could
be effectively reduced.26 However, a temperature of 100 ◦C was
needed to quantitatively reduce tertiary phosphine oxides in 5 h
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=
Table 2 SPOs reduction and protection as borane complex
using 10 mol% catalyst and a Si–H : P O ratio of 2.5. As the
boiling point of TMDS is 70 ◦C, the reaction has to be done in
a sealed tube.
Entry
1
SPOs
SPs-BH3
Isolated yield (%)
90
However, there are several advantages in using
TMDS/Ti(OiPr)4 system as an alternative reduction system.
TMDS is
a liquid compound soluble in most organic
solvents and inert to air and moisture. Furthermore, the
work up was straightforward and the by-products are inert
TiO2 and oligomeric siloxanes. Thus, we decided to further
investigate this catalytic system for the reduction of SPOs using
diphenylphosphine oxide (Scheme 2).
2
88
3
4
99
85
Scheme
2 Reduction of diphenylphosphine oxide using the
TMDS/Ti(OiPr)4 system.
5
6
90
89
We began our investigation with the reduction of
diphenylphosphine oxide in toluene at 60 ◦C with 2.5 mol of
TMDS and a stoichiometric amount of Ti(OiPr)4. The reaction
was monitored by 31P NMR and we were pleased to see that
diphenylphosphine oxide was reduced under those conditions
even though the reaction proceeded slowly: 24 h at 60 ◦C are
necessary for complete conversion. We next looked at making the
reaction catalytic in Ti(OiPr)4. Again the reaction with 10 mol%
Ti(OiPr)4 worked nearly as well as the stoichiometric variant.
However, no conversion was observed for lower amounts of
Ti(OiPr)4. The amount of TMDS was also decreased down
to 1.25 mol and under those conditions the reduction was
quantitative.
Thus, we have studied the reduction with the unsymmetrical
alkyl-substituted secondary phosphine oxides previously syn-
thesized (Table 1) under those conditions. In these experiments,
the products were isolated as air-stable borane adducts by
treatment of the reaction mixture with BH3/THF complex. The
results are summarized in Table 2. Various secondary phosphine
oxides including electron-rich ones were effectively reduced in
high yield. Aromatic SPOs (entries 1 and 2) were reduced in
high isolated yield under the standard conditions. Electron-
rich alkyl(phenyl)phosphine oxides were also effectively reduced.
Table 2 illustrates the wide substrate scope of this process
and these mild reduction conditions offer several advantages
compared to previously methods of reduction.30–33 Moreover,
given that TMDS is a hydride source inert to air and moisture
and Ti(OiPr)4 was used as an activating agent, these conditions
may be attractive as a general way to reduce SPOs.
phosphine borane in high yield by the use of catalytic amount
of air-stable Ti(OiPr)4 and tetramethyldisiloxane (TMDS) as an
hydride source inert to air and moisture. The reaction can be
performed at temperature below the boiling point of TMDS
and provides secondary phosphines in high yields.
Experimental
General
Tetramethyldisiloxane (TMDS), Ti(OiPr)4 were obtained from
Alfa Aesar, 1-methylimidazole and methylcyclohexane from
Acros and dichlorophenylphosphine, HCl in Et2O and organo-
magnesium were obtained from Aldrich. All compounds were
used without further purification. NMR spectra were recorded
on a Bruker DRX 300 and ALS 300. Chemical shifts are given
in ppm using tetramethylsilane as the external standard for 1H
and 13C NMR spectra, and 31P NMR from 85% H3PO4.
General procedure A: synthesis of secondary phosphine oxide
An oven-dried three-necked round-bottomed flask under an
argon atmosphere was charged with N-benzylphenylamine
(0.9 mg, 5 mmol) and 1-methylimidazole (0.50 mL, 6 mmol)
followed by methylcyclohexane (35 mL). Dichlorophenylphos-
phine (0.75 mL, 5 mmol) was added at room temperature. After
1 h, a biphasic solution was obtained. The crude methylcyclo-
hexane upper phase was removed by syringe through the septum
and added to an oven-dried three-necked round-bottomed flask
under an argon atmosphere. 10 mL of anhydrous THF was
added with a syringe and the homogenous reaction mixture was
Conclusion
In conclusion, we have developed a mild, one-pot synthesis
of unsymmetrical secondary phosphine oxides (SPOs) using
protic ionic liquids (PILs). The use of methylcyclohexane, that
effectively separates the protic ionic liquid formed and the
product, allows the one-pot synthesis of these SPOs. The use of
methylcyclohexane as solvent is essential to minimize the solu-
bility of the PILs. Furthermore, we have shown that these SPOs
could be readily converted into the corresponding secondary
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cooled to 0 ◦C. Alkyl magnesium bromide (6 mmol, solution
in THF) was then added and the reaction mixture is stirred at
room temperature. After 1 h, 31P NMR analysis of an aliquot
indicates the formation of a single product. The flask was then
cooled to 0 ◦C and the reaction mixture was quenched with HCl
1M in diethylether. The reaction mixture was diluted by ethyl
acetate then washed with NaHCO3 and brine. The organic phase
was dried over MgSO4, filtered and concentrated under reduced
pressure. The crude residue was dissolved in cyclohexane and
deposited on a neutral aluminium oxide column. Cyclohexane
was first used as eluent to removed N-benzylphenylamine
hydrochloride. The desired secondary phosphine oxide was then
obtained ethyl acetate–methanol as eluent (100 : 0 to 90 :
10, v/v).
NMR (300 MHz, CDCl3) 8.20 (1 H, d, J = 519 Hz), 7.85–7.66
(3 H, m), 7.57–7.38 (4 H, m), 7.14–7.06 (1 H, m), 6.90 (1 H, dd,
J = 8.3, 5.7 Hz), 3.77 (s, 3 H). 13C NMR (75 MHz, CDCl3): d =
160. 82 (d, J = 2.7 Hz), 134.62 (d, J = 1.9 Hz), 133.22 (d, J =
7.0 Hz), 132.32 (d, J = 78.0 Hz), 132.21 (d, J = 2.9 Hz), 131.68,
130.65 (2 C, d, J = 11.8 Hz), 128.71 (2 C, d, J = 13.1 Hz), 121.32
(d, J = 12.1 Hz), 119.56 (d, J = 75.2 Hz), 110.99 (d, J = 6.0 Hz),
55.72. 31P NMR (81 MHz, CDCl3) 15.7.
General procedure B: reduction of secondary phosphine oxides
At room temperature and under an argon atmosphere was
added Ti(OiPr)4 (0.05 mL, 0.14 mmol) and TMDS (0.38 mL,
2.0 mmol) to a stirred solution of secondary phosphine oxide
(1.4 mmol) with toluene (3 mL). The reaction mixture was then
◦
heated to 60 C. After cooling for 24 h, 31P NMR analysis of
Methyl(phenyl)phosphine oxide. Prepared by general proce-
dure A to give the product (40%) as a colourless oil. 1H NMR
(300 MHz, CDCl3): 7.55 (1 H, d, J = 567 Hz) 7.78–7.52 (2 H,
m), 7.47–7.32 (3 H, m), 4.16–1.55 (3 H, m). 31P NMR (81 MHz,
CDCl3) 23.
an aliquot indicates that conversion was complete. The reaction
mixture was then cooled to 0 ◦C and BH3/THF (3 mmol) was
added. After 1 h at room temperature, 31P NMR analysis of
an aliquot indicates complete conversion to phosphine borane
adduct. Silica gel was then carrefully added to the flask and
the reaction mixture was filtered through a Buchner funnel
and then washed with ethyl acetate. The resulting mixture was
concentrated under reduced pressure. The residue was purified
by flash chromatography on silica gel with cyclohexane/ethyl
acetate as eluent (100 : 0 to 80 : 20, v/v) to give secondary
phosphine borane.
Ethyl(phenyl)phosphine oxide. Prepared by general proce-
1
dure A to give the product (71%) as colourless oil. H NMR
(300 MHz, CDCl3) 7.68–7.61 (2 H, m), 7.52–7.46 (3 H, m), 7.39
(1 H, dt, J = 463, 7.4 Hz) 2.01–1.94 (2 H, m), 1.09 (3 H, dt, J =
20, 7.7 Hz). 13C NMR (75 MHz, CDCl3) 132.8 (d, J = 2.5 Hz),
131.0 (d, J = 96.1 Hz), 130.3 (2C, d, J = 10.6 Hz), 129.3 (2C,
d, J = 12.4 Hz), 23.6 (d, J = 68.2 Hz), 5.8 (d, J = 3.7 Hz). 31
P
NMR (81 MHz, CDCl3) 32.
Diphenylphosphine borane. Prepared by general procedure B
to give the product (90%) as a colourless oil. 1H NMR (300 MHz,
CDCl3) 7.50–7.47 (m, 4 H), 7.14–7.12 (m, 6 H), 5.32 (d, J =
215 Hz, 1 H). 13C NMR (75 MHz, CDCl3) 133.1 (d, J = 9.2 Hz),
131.7 (d, J = 2.5 Hz), 129.2 (d, J = 9.8 Hz), 127.2 (d, J =
177 Hz). 31P NMR (81 MHz, CDCl3) 2.4 (m).
Pentyl(phenyl)phosphine oxide. Prepared by general proce-
dure A to give the product (85%) as a colourless oil. 1H-NMR
(300 MHz, CDCl3) 7.64–7.50 (2 H, m), 7.48–7.29 (3 H, m), 7.35
(1 H, d, J = 464 Hz) 1.88–1.8 (2 H, m), 1.59–1.40 (2 H, m), 1.34–
1.15 (4 H, m), 0.8–0.64 (3 H, m). 13C-NMR (75 MHz, CDCl3) d
132.2 (d, J = 2.9 Hz), 130.9 (d, J = 96.2 Hz), 129.7 (2C, d, J =
10.7 Hz), 128.7 (2C, d, J = 12.4 Hz), 32.5 (d, J = 14.3 Hz), 30.0
(d, J = 67.9 Hz), 21.0 (d, J = 3.7 Hz), 20.78, 12.6. 31P-NMR
(81 MHz, CDCl3) 29.
Ethyl(phenyl)phosphine borane. Prepared by general proce-
1
dure B to give the product (99%) as a colourless oil. H NMR
(300 MHz, CDCl3) 7.79–7.59 (2 H, m), 7.57–7.36 (3 H, m), 5.38
(1 H, ddd, J = 367.9, 12.3, 6.1 Hz), 2.06–1.81 (2 H, m), 1.13
(3 H, dtd, J = 8.0, 7.5, 2.3 Hz), 0.17–0.04 (m, 3 H). 13C NMR
(75 MHz, CDCl3): 132.9 (2 CH, d, J = 8.6 Hz), 131.8 (d, J =
2.6 Hz), 129.1 (2 CH, d, J = 9.9 Hz), 125.4 (d, J = 55.2 Hz),
17.0 (d, J = 36.6 Hz), 8.6 (d, J = 3.6 Hz). 31P NMR (81 MHz,
CDCl3): 2.32 (dd, J = 95.9, 41.6 Hz).
Cyclohexyl(phenyl)phosphine oxide. Prepared by general
1
procedure A to give the product (73%) as a colourless oil. H
NMR (300 MHz, CDCl3): d = 7.65-7.45 (5 H, m), 7.91 (1 H, d,
J = 456 Hz), 1.87–1.66 (6 H, m), 1.20–1.17 (5 H, m). 13C NMR
(75 MHz, CDCl3): d = 132.68 (d, J = 1.9 Hz), 130.64 (2C, d, J =
10.3 Hz), 130.0 (d, J = 92.7 Hz), 129.05 (2C, d, J = 11.9 Hz),
38.87 (d, J = 70.1 Hz), 26.37 (d, J = 3.0 Hz), 26.18 (d, J =
2.6 Hz), 26.1 (d, J = 1.2 Hz), 25.6 (d, J = 1.1 Hz), 24.9 (d, J =
2.3 Hz). 31P NMR (81 MHz, CDCl3) 38.
Pentyl(phenyl)phosphine borane. Prepared by general proce-
1
dure B to give the product (85%) as a colourless oil. H NMR
(300 MHz, CDCl3) 7.72–7.66 (2 H, m), 7.53–7.46 (3 H, m), 5.42
(dm, 1 H, J = 368 Hz), 1.98–1.79 (3 H, m), 1.50–1.57 (2 H, m),
1.36–1.29 (3 H, m), 0.88–0.85 (6 H, m). 13C NMR (75 MHz,
CDCl3) 132.9 (2 CH, d, J = 8.1 Hz), 131.7 (d, J = 2.2 Hz),
129.13 (2 CH, d, J = 10 Hz), 129.08 (d, J = 63 Hz), 33.4 (d,
J = 13.2 Hz), 32.8 (d, J = 12.5 Hz), 25.7 (d, J = 35,9 Hz), 24.0
(d, J = 27.9 Hz), 23.1 (d, J = 86,5 Hz). 31P NMR (81 MHz,
CDCl3): -1.87 (d, J = 41.3 Hz).
Isopropyl(phenyl)phosphine oxide. Prepared by general pro-
1
cedure A to give the product (80%) as a yellow oil. H NMR
(300 MHz, CDCl3): d = 7.4 (1 H, dd, J = 458, 2.4 Hz), 7.65–7.53
(2 H, ddd, J = 12.6, 6.9, 1.3 Hz), 7.53–7.34 (3 H, m), 2.14–1.97
(1 H, m), 1.19–1.00 (6 H, m). 13C NMR (75 MHz, CDCl3) d =
132.66 (d, J = 3.0 Hz), 130.47 (2 CH, d, J = 10.1 Hz), 129.38
(2 CH, d, J = 93.2 Hz), 128.90 (d, J = 12.2 Hz), 28.64 (d,
J = 69.0 Hz), 14.94 (2 CH3, dd, J = 38.1, 1.4 Hz). 31P NMR
(81 MHz, CDCl3) 41.
Cyclohexyl(phenyl)phosphine borane. Prepared by general
1
procedure B to give the product (90%) as a colourless oil. H
NMR (300 MHz, CDCl3): d = 7.70–7.57 (2 H, m), 7.56–7.39
(3 H, m), 5.23 (1 H, dm, J = 367 Hz) 2.00–1.54 (7 H, m),
1.41 (5 H, s). 13C NMR (75 MHz, CDCl3) 133.80 (2 CH, d,
(2-methoxyphenyl)(phenyl)phosphine oxide. Prepared by
general procedure A to give the product (72%) as a yellow oil. 1H
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J = 7.9 Hz), 131.90 (d, J = 2.4 Hz), 129.20 (2 CH, d, J =
9.6 Hz), 125 (d, J = 50 Hz), 33.4 (d, J = 25.8 Hz), 28.3 (d, J =
1.4 Hz), 27.2 (d, J = 92 Hz), 26.47 (d, J = 5.5 Hz), 26.39, 25.68
(d, J = 1.1 Hz). 31P NMR (81 MHz, CDCl3) 13.6–11.8 (dd, J =
57.4, 5.4).
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Isopropyl(phenyl)phosphine borane. Prepared by general
1
procedure B to give the product (83%) as a colourless oil. H
NMR (300 MHz, CDCl3) 7.68–7.45 (5 H, m), 5.86–4.63 (1 H,
dm, J = 363 Hz), 6.67–3.63 (1 H, m), 1.22–1.15 (6 H, m). 13C
NMR (75 MHz, CDCl3) 133.6 (2 CH, d, J = 8.0 Hz), 131.8 (d,
J = 2.5 Hz), 129.0 (2 CH, d, J = 9.9 Hz), 125.0 (d, J = 53.0 Hz),
23.9 (d, J = 35.1 Hz), 17.9 (2CH3 d, J = 17.9 Hz). 31P NMR
(81 MHz, CDCl3) 16.65 (d, J = 50.9 Hz).
(2-Methoxyphenyl)(phenyl)phosphine borane. Prepared by
general procedure B to give the product (88%) as a colourless
oil. 1H NMR (300 MHz, CDCl3) 7.62 (3 H, dddd, J = 21.7, 11.9,
7.8, 1.7 Hz), 7.49–7.20 (4 H, m), 6.98 (1 H, ddd, J = 14.9, 7.4,
1.3 Hz), 6.84 (1 H, dd, J = 8.2, 3.4 Hz), 6.44 (1 H, qd, J = 395,
6.9 Hz), 3.74 (3 H, s). 13C NMR (75 MHz, CDCl3) 160.63 (d, J =
1.2 Hz), 134.94 (d, J = 13.7 Hz), 133.92, 132.83 (2 CH, d, J =
9.8 Hz), 131.13 (d, J = 2.5 Hz), 128.72 (2 CH, d, J = 10.4 Hz),
126.96 (d, J = 57.9 Hz), 121.38 (d, J = 12.3 Hz), 114.63 (d, J =
55.5 Hz), 110.81 (d, J = 4.2 Hz), 55.79. 31P NMR (81 MHz,
CDCl3) -15.28 (d, J = 65.1 Hz).
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