A convenient one-pot synthesis of Di-t-butylphosphinic chloride

Article abstract of DOI:10.1080/10426500801967781

A convenient one-pot synthesis of (t-Bu)2P(O)Cl (1) from m-chloroperbenzoic acid and (t-Bu)2PCl is described. The byproduct m-chlorobenzoic acid is neutralized by addition of Et3N. Complex 1 crystallizes in the monoclinic space group P21/c (No. 14), with a = 5.9637(2) , b = 11.4734(4) , c = 16.2400(5) and = 107.7160(14).

Full text of DOI:10.1080/10426500801967781

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A Convenient One-
Pot Synthesis of Di-t-
butylphosphinic Chloride
a
a
Daniel F. Brayton , Karen I. Goldberg , Werner
a
a
Kaminsky & D. Michael Heinekey
a
Department of Chemistry , University of
Washington , Seattle, Washington, USA
Published online: 26 Sep 2008.
To cite this article: Daniel F. Brayton , Karen I. Goldberg , Werner Kaminsky & D.
Michael Heinekey (2008) A Convenient One-Pot Synthesis of Di-t-butylphosphinic
Chloride, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:10,
2534-2540, DOI: 10.1080/10426500801967781
To link to this article: http://dx.doi.org/10.1080/10426500801967781
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Phosphorus, Sulfur, and Silicon, 183:2534–2540, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500801967781
A Convenient One-Pot Synthesis of Di-t-butylphosphinic
Chloride
Daniel F. Brayton, Karen I. Goldberg, Werner Kaminsky,
and D. Michael Heinekey
Department of Chemistry, University of Washington, Seattle,
Washington, USA
A convenient one-pot synthesis of (t-Bu)2 P(O)Cl (1) from m-chloroperbenzoic acid
and (t-Bu)2 PCl is described. The byproduct m-chlorobenzoic acid is neutralized by
addition of Et3 N. Complex 1 crystallizes in the monoclinic space group P21 /c (No.
˚
˚
˚
1
4), with a = 5.9637(2) A, b = 11.4734(4) A, c = 16.2400(5) A and β = 107.7160(14).
Keywords Chemical synthesis; crystal structure; phosphinic chloride
INTRODUCTION
Organophosphorus compounds have extensive applications in the field
of chemistry, especially in the area of catalysis. Trivalent phosphorous
compounds are widely employed as ligands in several important homo-
geneously catalyzed processes.1 Phosphine oxides can also be useful
ligands to metal centers, particularly in combination with phosphines.3
Mixed phosphines, with various combinations of alkyl groups, are of-
ten prepared from dialkylphosphines or the corresponding phosphides.
These, in turn, can be derived from the corresponding dialkylphosphine
halides by various reduction procedures. The P Cl bonds in trivalent
phosphorous compounds such as dialkylphosphine chlorides are very
,2
4
sensitive to hydrolysis. To clarify the structure and nomenclature,
relevant phosphorus compounds are shown in Scheme 1. Oxidation
affords the dialkyl phosphinic chlorides, which are much more sta-
ble with respect to hydrolysis. Dialkylphosphinic chlorides, specifically
the dimethyl compound (Me)2P(O)Cl have proven to be useful acid
stable protecting groups for the side chain phenol moiety of tyrosine
in peptide synthesis.5
–7
Received 24 October 2007; accepted 15 January 2008.
We thank the DOE Center of Excellence for Chemical Hydrogen Storage for funding.
Address correspondence to Prof. D. Michael Heinekey, Department of Chemistry,
University of Washington, Seattle, WA 98195-1700, USA. E-mail: heinekey@chem.
washington.edu
2534

One-Pot Synthesis of Di-t-butylphosphinic Chloride
2535
SCHEME 1
In recent years, the use of sterically demanding alkyl phosphine
ligands in homogeneous catalysis has increased. Various aryl(di-t-
butyl)phosphine ligands have found numerous applications, especially
6
–8
for Pd mediated cross-coupling reactions.
In our own research,
we have employed pincer ligands containing a di-t-butylphosphinite
9
–11
moiety.
[
In particular, we found that a (POCOP)Ir(H)2 (POCOP =
3
κ -1,3-(OP(t-Bu)2)2C6H3]) complex is an exceptionally active catalyst
for the dehydrogenation of NH3BH3.
1
1
Synthesis of tertiary butyl phosphine derivatives often requires the
use of reagents such as (t-Bu)2PCl, (t-Bu)2PH, and the corresponding
phosphide anion. These are very reactive species, with restrictions on
4
air transport due to facile oxidation and hydrolysis reactions. However,
the oxy-chloride analogue, (t-Bu)2P(O)Cl is an air stable compound. We
report herein a simple, high-yield synthesis and purification method for
di-t-butylphosphinic chloride, 1, (t-Bu)2P(O)Cl). This phosphinic chlo-
ride is indefinitely stable on the benchtop and can be converted to useful
reagents such as the phosphine (t-Bu)2PH or back to the chlorophos-
phine by well established methods.1
2–14
RESULTS AND DISCUSSION
While several syntheses have been reported for the title compound,
we found them to suffer from low yields and difficult purifica-
tion procedures.1
5–19
One such report describes the synthesis of 1
from di-t-butylchlorophosphine using aqueous hydrogen peroxide as
1
5
the oxidant. This is surprising, since dialkylchlorophosphines are
well known to rapidly hydrolyze to give HCl and the corresponding

2536
D. F. Brayton et al.
4
phosphine oxide. In our hands, we found that reaction of (t-Bu)2PCl
with aqueous hydrogen peroxide affords a complex mixture of prod-
ucts, with the major product being di-t-butylchlorophosphine oxide (t-
1
31
Bu)2P(O)H, which is readily identified by H and P NMR spectroscopy
(
2
0
δ P-H, 5.82 ppm, JPH = 422 Hz and δ (P) = 63.5 ppm). The oxide was
also observed if glassware used in reactions of (t-Bu)2PCl was not rig-
orously dried.
Another synthetic method described the vigorous bubbling of O2
1
5
through a refluxing xylene solution of (t-Bu)2PCl. We found this reac-
tion to give only partial oxidation, affording (t-Bu)2PCl, (t-Bu)2P(O)Cl,
and (t-Bu)2P(O)H in the ratio 80:15:5.
A four-step synthesis has also been reported in which the chlorophos-
phine is hydrolyzed to the oxide, oxidized to the phosphinic acid,
followed by chlorination with thionyl chloride to the give the title com-
1
6,17
pound 1.
However, we found that the oxidation step proceeded in
low yield; therefore, we did not pursue this pathway.
The method outlined below in Scheme 2 starts with the commer-
◦
cially available (t-Bu)2PCl. Reaction with m−CPBA at 0 C generates
1
in along with byproduct meta-chlorobenzoic acid. An excess of tri-
ethylamine is then added to deprotonate the benzoic acid. The entire
reaction mixture is eluted down a silica plug (2 grams) with methylene
chloride/hexanes (2:1). The volatiles (solvent and excess NEt3) are re-
moved, leaving behind colorless crystalline compound 1 in ∼95% yield.
SCHEME 2
Structure of 1
Crystals of 1 suitable for X-ray diffraction were grown by concentration
of a methylene chloride solution. A clear prism of dimensions 0.59 ×
0
.29 × 0.12 mm was mounted on a glass capillary with oil. Data was
collected at 130 K. Crystal-to-detector distance was 30 mm and expo-
sure time was 20 s per degree for all sets. The scan width was 2 . Data
◦

One-Pot Synthesis of Di-t-butylphosphinic Chloride
2537
TABLE I Crystallographic Data for (t-Bu)
2
P(O)Cl
Empirical formula
Formula weight
Temperature
C8H18ClOP
196.66
130 K
Crystal system
Space group
Unit cell dimensions
Monoclinic
P21/c
˚
˚
˚
◦
a = 5.9637(2) A
α = 90 .
◦
b = 11.4734(4) A
β = 107.7160(14) .
◦
c = 16.2400(5) A
γ = 90 .
˚
3
Volume
Crystal size
Index ranges
Reflections collected
Independent reflections
Refinement method
R final
1058.51 A
3
0.59 × 0.29 × 0.12 mm
–7 ≤ h ≤ 7, –14 ≤ k ≤ 15, –21 ≤ l ≤ 21
22448
2522 [R(int) = 0.0824]
2
Full-matrix least-squares on F
0.0484
0.984
2
Goodness-of-fit on F
◦
◦
collection was 96% complete to 28.3 and 98.2% complete to 25 in ϑ. A
total of 22,448 partial and complete reflections were collected covering
the indices, h = –7 to 7, k = –14 to 15, l = –21 to 21. 2522 reflec-
tions were symmetry independent. Indexing and unit cell refinement
indicated a monoclinic P lattice. The space group was P21/c (No. 14).
The data was integrated and scaled using hkl-SCALEPACK. Solu-
tion by direct methods (SIR97) produced a complete heavy atom phas-
ing model consistent with the proposed structure. All hydrogen atoms
FIGURE 1 ORTEP diagram of [(t-Bu)
2
P(O)Cl]. 50% thermal ellipsoids are
shown. Hydrogen atoms are omitted for clarity. CCDC deposit number 673,938.

2538
D. F. Brayton et al.
˚
2
TABLE II Selected Bond Lengths (A) for R P(O)Cl Derivatives
◦
Reference (compound)
P O
P Cl
P C1
P C2
C P C Angle ( )
2
2
2
2
2
1 (2)
2 (3)
3 (4)
4 (5)
5 (6)
1.477
1.483
1.486
1.463
1.504
1.473
2.031
2.056
2.051
2.061
2.048
2.068
1.828
1.834
1.822
1.841
1.840
1.836
1.837
1.843
1.821
1.872
1.850
1.839
104.1
85.9
110.2
116.8
103.8
117.7
This work (1)
SCHEME 3
were located using a riding model. All non-hydrogen atoms were re-
fined anisotropically by full-matrix least-squares. The crystallographic
data for 1 are tabulated in Table I.
The structure of 1 exhibits some distortions from idealized tetrahe-
dral angles around the central P atom. The ORTEP diagram for 1 is
shown in Figure 1. The largest distortion arises from the steric bulk of
◦
the t-Bu groups, which leads to a C1-P-C5 bond angle of 117.7(3) . The
relevant bond distances are listed in Table II. The bond lengths for this
2
1–25
structure fall well within the range of previously reported values.
CONCLUSION
Although several methods have been reported for the preparation of
, none of the existing procedures is satisfactory. The method reported
1
here provides a simple one-pot synthesis and isolation procedure that
should be general for a wide variety of R groups.

One-Pot Synthesis of Di-t-butylphosphinic Chloride
2539
EXPERIMENTAL
General Procedures
Benzene was distilled from CaH2. All other solvents were reagent grade
and were used as received. Di-t-butylchlorophosphine and all other
reagents were supplied by Aldrich. Glove-box and standard Schlenk
techniques were used as required. NMR spectra were obtained at am-
bient temperature on Bruker AV300 and AV500 spectrometers, with
3
1
chemical shifts (δ) reported in ppm downfield of tetramethylsilane.
P
NMR spectra were referenced externally to 85% H3PO4. Elemental
analyses were performed by Desert Analytics, Phoenix, AZ.
Abbreviations
Di-t-butylphosphinic chloride = (t-Bu)2P(O)Cl; PMHS = polymethyl-
hydrosilane; m-CPBA = meta-chloroperbenzoic acid.
Synthesis of Di-t-butylphosphinic Chloride (t−Bu) P(O)Cl
2
A Schlenk flask was charged with m-CPBA (707 mg, 4.11 mmol) dis-
solved in CH2Cl2 (20 mL). Di-t-butylchlorophosphine (0.410 mL, 2.18
◦
mmol) was added dropwise at 0 C. The resulting solution was vigor-
ously stirred for 1 h at room temperature. Neat triethylamine (∼1 mL,
7
2
.2 mmol) was added dropwise, and the solution was allowed to stir for
0 min. The entire reaction mixture was chromatographed on a silica
plug (2 grams), eluting with methylene chloride. Evaporation of the sol-
vent gave 0.402 g of a white crystalline solid. (94% yield) Anal. calcd.
1
for POClC8H18: C, 48.85; H, 9.22. Found: C, 48.84; H, 8.79. H NMR
1
3
(
500 MHz, C6D6): 1.37 (d, 18 H, -CH3,J = 17 Hz). C NMR: 41.74 (d,
31
P-C-(CH3)3, J = 62 Hz), 26.9 (s, -CH3). P NMR: δ(P) = 96.2 (s).
Supplementary Material
Crystallographic data for the structural analysis of compound 1 has
been deposited at the Cambridge Crystallographic Data Center (CCDC
number 673938). Copies of the information may be obtained free of
charge from The Director, CCDC, 12 Union Road, Cambridge CB2
1
EZ, UK (Fax: + 44-1223-336033; email: deposit@ccdc.cam.ac.uk or
www.ccdc.cam.ac.uk).

2540
D. F. Brayton et al.
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