Synthesis of two p-methoxyphenyl substituted phosphines

Article abstract of DOI:10.1080/10426507.2016.1192626

Bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1) and di(n-butyl)(p-methoxy-phenyl)-phosphine (4) were synthesized and characterized by¹H,¹³C, and³¹P NMR spectroscopy and 1 also by single crystal X-ray diffraction. The sy

Full text of DOI:10.1080/10426507.2016.1192626

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Synthesis of Two p-Methoxyphenyl Substituted
Phosphines
Christina Hettstedt, Anna Frank & Konstantin Karaghiosoff
To cite this article: Christina Hettstedt, Anna Frank & Konstantin Karaghiosoff (2016): Synthesis
of Two p-Methoxyphenyl Substituted Phosphines, Phosphorus, Sulfur, and Silicon and the
Related Elements, DOI: 10.1080/10426507.2016.1192626
To link to this article: http://dx.doi.org/10.1080/10426507.2016.1192626
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Published online: 26 May 2016.
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Synthesis of Two p-Methoxyphenyl Substituted Phosphines
Christina Hettstedta, Anna Frankb and Konstantin Karaghiosoffa,*
aLudwig-Maximilians University (LMU), Butenandtstrasse 5-13 (Haus D), 81377 Munich,
Germany. Fax: +49-89-2180-77492, Web: www.cup.uni-muenchen.de
bMax-Planck-Institut fuer Eisenforschung, Max-Planck-Str.1, 40237 Duesseldorf, Germany
Corresponding author E-mail: klk@cup.uni-muenchen.de
Abstract
Bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1) and di(n-butyl)(p-methoxy-phenyl)-
phosphine (4) were synthesized and characterized by 1H, 13C and 31P NMR spectroscopy and 1
also by single crystal X-ray diffraction. The syntheses and analytical data are discussed.
Key words
Methoxyphenyl substituted phosphine; synthesis; phosphorus; crystal structure
Introduction
Arylphosphines like triphenyl phosphine Ph3P are long and well known substances.[1] Variation
of the phosphorus substituents results in a great structural diversity, which provides the basis for
their use in many different applications. In hand with the great structural diversity also a large
number of different synthetic routes to phosphines have been developed.[2] Applications of
phosphines or derivatives thereof include their use as herbicides[3], insecticides, flame retardants
or drugs.[2c,d] In chemical laboratories, phosphines are essential as reagents in reactions like the
Wittig[4] or Appel[5] reaction and as ligands for transition metal catalyzed reactions, e.g. cross
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coupling[6], olifination reactions[2c,d] and hydrogenation reactions[7]. Due to the great variety of
different applications of phosphines there is great need for new representatives with particular
substitution schemes in the organic part.
In the course of our investigations on transition metal complexes with tertiary phosphines
functionalized in the organic backbone we are interested in the synthesis and structural properties
of phosphines with different functionalities in the organic substituent. Of particular interest are
the structural properties in the solid state concerning the steric demand and the electronic
influence of the organic substituents on phosphorus. Here we present the synthesis and structural
characterization of the new phosphine bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1)
and the new synthesis and NMR characterization of the literature[8] known di(n-butyl)(p-
methoxyphenyl)phosphine (4).
Results and Discussion
Synthesis
Bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1) was synthesized by allowing
(p-methoxyphenyl)dichlorophosphine (2)[9] to react with two equivalents of the m-
methoxyphenyl Grignard reagent[9] 3 (Scheme 1). Phosphine 1 was formed quantitatively
31
according to the P NMR spectrum of the crude reaction mixture. It was isolated by multiple
extraction steps with Et2O and toluene as a colorless solid in 51% yield.
Di(n-butyl)(p-methoxyphenyl)phosphine (4) was prepared by direct reaction of two equivalents
of n-BuLi with dichlorophosphine 2 (Scheme 2). Phosphine 4 was formed besides some
unidentified side products. Nevertheless it could be isolated by extraction with pentane and
distillation as a colorless liquid in 34% yield, which is a significant increase compared to the
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reported value (15%)[8b]. Both (p-methoxyphenyl)phosphines are readily soluble in common
aprotic organic solvents.
Molecular and Crystal Structure of Bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1)
Single crystals suitable for X-ray diffractions were obtained by slow evaporation of an acetone
solution. Phosphine 1 crystallizes in the triclinic space group P−1 with two formula units in the
unit cell. The asymmetric unit consists of one molecule 1 (Figure 1). Selected atom distances and
bond angles are compiled in Table 1.
The P--C atom distances in 1 are very similar and two of them (P1--C1, P1--C7) are shorter than
the literature value for a P--C single bond (1.836 Å)[10]. The three P--C bonds in 1 are
comparable to the bond lengths (1.831(2) Å) in the molecular structure of Ph2P(p-OMeC6H5)[11]
as are also the bond angles around the phosphorus atom. The three bond angles are between
101.3 ° and 104.4 ° and smaller than the tetrahedron angle of 109.5 °.
In the crystal the molecules of 1 form chains along the b-axis connected by intermolecular non
classical C--H···π hydrogen bonds (Figure 2).
NMR Data
The phosphorus chemical shift of the mixed p-methoxyphenyl m-methoxyphenyl substituted
phosphine 1 (δP = −5.5) is comparable to the chemical shift of PPh3 (δP = −5.1)[12] and lies
between the chemical shifts of the pure tris(p-methoxyphenyl) phosphine (δP = −9.5)[12] and
tris(m-methoxyphenyl) phosphine (δP = −2.6)[12]. The phosphorus NMR signal of bis(n-butyl)(p-
methoxyphenyl)phosphine (4) is with δP = −25.9 significantly shifted to higher field as compared
to the signal of 1. It is in the region of PhP(nBu)2 (δP = −20.0[13a] or δP = −24.6[13b]). Remarkable
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in the 13C NMR spectrum of 4 is the long range coupling over four bonds (4JPC = 0.6 Hz). The P-
CH2 protons in 4 do not show the expected diastereotopy in the 1H NMR spectrum.
Experimental Section
General information
All chemicals were commercially available and were used as received. NMR spectra were
recorded with a JEOL EX 400 Eclipse instrument operating at 400.128 MHz (1H) and 100.626
MHz (13C). Chemical shifts are referred to Me4Si (1H, 13C) and 85% H3PO4 (31P) as external
standards. All spectra were measured, if not mentioned otherwise, at 25°C. The assignment of
13
1
the signals in the 1H and C NMR spectra is based on 2D (1H,1H-COSY45, H,13C-HMQC and
1H,13C-HMBC) experiments. For the HMBC NMR spectra a sinebell window function and a
zero filling in both directions was applied resulting in a 4k × 4k matrix. Mass spectrometric data
were obtained with a JEOL Mstation JMS 700 spectrometer using the direct EI mode. The
molecular structures in the crystalline state were determined by single crystal X-ray diffraction.
For data collection an Xcalibur3 diffractometer equipped with a Spellman generator (voltage 50
kV, current 40 mA) and a Kappa CCD detector with an X-ray radiation wavelength of 0.71073 Å
was used. The data collection was performed with the CrysAlis CCD software[14] and the data
reduction with the CrysAlis RED software[15]. The structures were solved with SIR-92, refined
with SHELXL-97 and finally checked using PLATON.[16] The absorptions were corrected by
SCALE3 ABSPACK multiscan method.[17] All relevant data and parameters of the X-ray
measurements and refinements are given in Table 2. Crystallographic data (excluding structure
factors) for the structure in this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be
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obtained free of charge on quoting the depository numbers CCDC 1458563 (1). (Fax: +44-1223-
336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac. uk).
Synthetic Procedure
Bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1)
p-Methoxyphenyldichlorophosphine (2) (982.4 mg, 4.7 mmol) was dissolved in 10 mL of dry
THF and cooled to 0°C with an ice bath. m-Methoxyphenyl magnesium bromide (3) (2 eq, 9.4
mmol) which was prepared according to a literature procedure[9], dissolved in THF (20 mL)was
added dropwise while stirring. The reaction mixture was allowed to reach room temperature over
night and the solvent was removed in vacuo. The crude product was extracted two times with 24
mL of dry Et2O and once with dry toluene (24 mL). After every extraction step, the colorless
precipitate was removed by filtration. After removing of the toluene, 1 was obtained as a
colorless solid in 51% yield (4.8 mmol, 1.69 g). It was always accompanied by the
corresponding oxide (<1%, δP = 30 ppm).
HRMS (DEI+): Mcalcd for C21H21O3P: 352.1228; Mfound: 352.1236 (M+, 100%).
1H NMR (400.18 MHz, CDCl3): δ = 7.31 - 7.27 (m, 2H, H2), 7.26 - 7.23 (m, 2H, H8), 6.90 -
6.88 (m, 2H, H9), 6.87 - 6.86 (m, 4H, H3, H7), 6.85 - 6.84 (m, 2H, H11), 3.81 (s, 3H, H5), 3.73
(s, 6H, H12).
13C NMR (100.64 MHz, CDCl3): δ = 160.6 (C4), 159.6 (d, 3JPC = 8.2 Hz, C10), 139.5 (d, 1JPC
=
11.1 Hz, C6), 135.8 (d, 2JPC = 21.5 Hz, C2), 129.6 (d, 3JPC = 7.5 Hz, C8), 127.5 (d, 1JPC = 8.0 Hz,
C1), 125.9 (d, 2JPC = 18.6 Hz, C7), 118.9 (d, 2JPC = 21.0 Hz, C11), 114.4 (d, 3JPC = 8.2 Hz, C3),
113.0 (C9), 55.3 (C5), 55.3 (C12).
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31P NMR (162.0 MHz, CDCl3): δ = −5.5 (septet, 3JPH = 7.5 Hz).
Di(n-butyl)(p-methoxyphenyl)phosphine (4)
(p-Methoxyphenyl)dichlorophosphine (2) (2.1 g, 10.0 mmol) was dissolved in dry THF (20 mL)
and cooled to −78°C with a dry ice/acetone bath. n-BuLi (2 eq, 13.7 mL, 20 mmol, 1.45 M in
hexane) was slowly added dropwise while stirring. The reaction mixture was allowed to reach
room temperature over night and the solvent was removed in vacuo. The crude product was
extracted with dry pentane (24 mL) and the solid was removed by filtration. The solvent was
removed in vacuo and the product bis(n-butyl)(p-methoxyphenyl)phosphine (4) was isolated by
distillation (5.0 · 102 mbar, 112°C, 150°C oilbath) as a colorless liquid in 34% yield (3.47
mmol, 876 mg). It contained an impurity (6%, δP = −32.8 ppm).
3
1H NMR (400.18 MHz, CDCl3): δ = 7.45 (A part of AA’MM’X spectrum, N = 8.8 Hz, JAX
=
3JPH = 6.9 Hz, 2H, H2), 6.90 (M part of AA’MM’X spectrum, N = 8.8 Hz, 2H, H3), 3.81 (s, 3H,
H5), 1.66 - 1.62 (m, 4H, H6), 1.41 - 1.27 (m, 8H, H7, H8), 0.90 - 0.84 (t, 3JHH = 7.1 Hz, 6H, H9).
13C NMR (100.64 MHz, CDCl3): δ = 160.3 (d, 4JCP = 0.6 Hz, C4), 134.0 (d, 2JPC = 20.2 Hz, C2),
1
3
1
129.8 (d, JPC = 12.8 Hz, C1), 114.0 (d, JPC = 7.8 Hz, C3), 55.2 (C5), 28.7 (d, JPC = 10.3 Hz,
C6), 28.3 (d, JPC = 13.7 Hz, C7 or C8), 24.4 (d, JPC = 11.9 Hz, C7 or C8), 13.9 (C9).
31P{1H} NMR (162.0 MHz, CDCl3): δ = −25.9.
Conclusion
The phosphines bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1) and di(n-butyl)(p-
methoxyphenyl)phosphine
(4)
are
readily
prepared
starting
from
(p-
methoxyphenyl)dichlorophosphine (2) by reaction with the m-methoxyphenyl Grignard reagent
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(3) and n-BuLi, respectively. The availability of these phosphines with different electron rich
substituents at phosphorus opens the way for systematic studies of their properties as ligands in
transition metal complexes.
Acknowledgment
Financial support from the Department of Chemistry, Ludwig-Maximilians-University of
Munich is gratefully acknowledged. The authors are thankful to Prof. T.M. Klapötke for the
generous allocation of diffractometer time and his continuous support.
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Table 1 Selected atom distances [Å] and bond angles [°] in the molecular structure of 1.
P1--C1
P1--C7
P1--C13
1.828(6)
1.828(2)
1.836(11)
C1--P1--C7
C1--P1--C13
C7--P1--C13
104.4(5)
102.2(8)
101.3(14)
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Table 2 Structural data of 1.
Empirical formula C21H21O3P
Formula weight 352.35
Cryst. size, [mm³] 0.4 × 0.4 ×
0.35
Cryst. habitus
colorless
block
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [ų]
triclinic
P−1 (No. 2)
9.7682(5)
9.8214(4)
10.4720(5)
68.516(4)
79.172(4)
81.33(7)
914.46(13)
2
Z
T [K]
173(2)
1.280
0.167
372
−9 ≤ h ≤ 12
−8 ≤ k ≤ 12
−19 ≤ l ≤ 17
15365
4502
0.0251
ρcalcd, [gcm--3]
μ(MoKα), [cm--1]
F(000), [e]
hkl range
Refl. Measured
Refl. Unique
Rint
Param. Refined
θ Range [°]
244
4.17 ≤ θ ≤
28.28
R1, wR2 [I > 2σ(I)] 0.0367,
0.0900
R1, wR2 (all data)
0.0452,
0.0958
GooF
1.048
δpmax, δpmin
0.364, −0.211
[e∙nm−3]
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Figure 1 Asymmetric unit of 1. Thermal ellipsoids are drawn at 50% probability level.
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Figure 2 Non classical C--H···π hydrogen bonds in the crystal structure of 1. d(C3···Cg(2)b) =
3.593 Å, C3--H3···Cg(2) = 154 °, d(C19···Cg(3)b) = 3.722 Å, C19--H19A···Cg(3) = 171 °,
d(C21···Cg(1)a) = 3.699 Å, C21--H21A···Cg(1) = 160 °. Cg is the center of gravity of the
aromatic ring, Cg(1) contains C1, Cg(2) contains C7, Cg(3) contains C13. Symmetry codes: a) x,
−1+y, z; b) 1−x, 1−y, 1−z; c) x, 1+y, −1+z. Thermal ellipsoids are drawn at 50% probability
level.
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Figure 3 Numbering of the carbon atoms of the phosphines 1 and 4 for the assignment of the
NMR data.
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Scheme 1 Synthesis of bis(m-methoxyphenyl)(p-methoxyphenyl)phosphine (1)
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Scheme 2 Synthesis of di(n-butyl)(p-methoxyphenyl)phosphine (4) by direct reaction of n-BuLi
with dichlorophosphine 2.
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