Variable-temperature NMR studies of soluble polymer-supported phosphine-silver complexes

Article abstract of DOI:10.1021/jo902427w

(Chemical Equation Presented) The use of polymers as supports for organometallic catalysts has received wide attention. However, catalyst reactivity is sometimes altered as a consequence of catalyst immobilization by a polymeric ligand and such altered reactivity can complicate such supported catalysts' use. The results in this study show that heptane phase selectively soluble polyisobutylene (PIB)-bound phosphine ligands have essentially identical kinetic behavior when compared to electronically similar isobutyldiphenylphosphine analogues in phosphine coordination and exchange in silver(I) halide complexes. These studies used variable-temperature ³¹P NMR spectroscopy to probe the silver-phosphine exchange processes for both AgI and AgCl complexes of these polymeric and low molecular weight phosphine ligands. The results show that the dynamic behavior of the PIB- and isobutyldiphenylphosphine-AgX complexes is nearly identical based on line-shape analysis of these ³¹P NMR spectra as a function of temperature. Similar studies of more polar poly(ethylene glycol)triarylphosphine-bound AgX complexes and electronically analogous low molecular weight AgX complexes have similar behavior in variable-temperature ³¹P NMR spectroscopy.

Full text of DOI:10.1021/jo902427w

pubs.acs.org/joc
Variable-Temperature NMR Studies of Soluble Polymer-Supported
Phosphine-Silver Complexes
David E. Bergbreiter* and Yun-Chin Yang
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
bergbreiter@tamu.edu
Received November 12, 2009
The use of polymers as supports for organometallic catalysts has received wide attention. However,
catalyst reactivity is sometimes altered as a consequence of catalyst immobilization by a polymeric
ligand and such altered reactivity can complicate such supported catalysts’ use. The results in this
study show that heptane phase selectively soluble polyisobutylene (PIB)-bound phosphine ligands
have essentially identical kinetic behavior when compared to electronically similar isobutyldiphe-
nylphosphine analogues in phosphine coordination and exchange in silver(I) halide complexes. These
3
1
studies used variable-temperature P NMR spectroscopy to probe the silver-phosphine exchange
processes for both AgI and AgCl complexes of these polymeric and low molecular weight phosphine
ligands. The results show that the dynamic behavior of the PIB- and isobutyldiphenylphosphi-
3
1
ne-AgX complexes is nearly identical based on line-shape analysis of these P NMR spectra as a
function of temperature. Similar studies of more polar poly(ethylene glycol)triarylphosphine-bound
AgX complexes and electronically analogous low molecular weight AgX complexes have similar
3
1
behavior in variable-temperature P NMR spectroscopy.
Introduction
group has emphasized the advantages of terminally functio-
nalized nonpolar polyisobutylene (PIB) supports that readily
separate in a liquid/liquid biphasic system after a homoge-
Strategies that use ligands on polymer supports to immo-
bilize and recover homogeneous transition metal catalysts
have attracted attention ever since Merrifield introduced the
4
neous reaction. These supports are analogous to established
more polar end-functionalized poly(ethylene glycol) (PEG)
1
concept of solid phase synthesis. While much of this work
has involved insoluble cross-linked polymer supports, solu-
2b
supports. We and others have argued that these soluble
polymer supports lead to polymer-supported metal catalysts
that have reactivity directly analogous to that of a more
conventional low molecular weight catalyst. This argument
has been substantiated in a number of studies where the
yields of product or product selectivity for reactions of
soluble polymer-bound catalysts have been compared with
2
ble supports have received attention as well. In recent years,
interest in these supports has increased as new procedures
have been developed that facilitate separation of soluble
3
polymer-bound catalysts from products. For example, our
(
1) (a) Lu, J.; Toy, P. H. Chem. Rev. 2009, 109, 815. (b) The Power of
Functional Resins in Organic Synthesis; Tulla-Puche, J., Albericio, F., Eds.;
Wiley-VCH: Weinheim, Germany, 2008. (c) Combinatorial Chemistry on Solid
Supports; Br €a se, S., Ed.; Springer Verlag: New York, 2007.
(4) (a) Bergbreiter, D. E.; Li, J. Chem. Commun. 2004, 42. (b) Bergbreiter,
D. E.; Sung, S. D.; Li, J.; Ortiz, D.; Hamilton, P. N. Org. Process Res. Dev.
2004, 8, 461. (c) Li, J.; Sung, S.; Tian, J.; Bergbreiter, D. E. Tetrahedron 2005,
61, 12081. (d) Hongfa, C.; Tian, J.; Bazzi, H. S.; Bergbreiter, D. E. Org. Lett.
2007, 9, 3259. (e) Bergbreiter, D. E.; Tian, J. Tetrahedron Lett. 2007, 48, 4499.
(f) Bergbreiter, D. E.; Hamilton, P. N.; Koshti, N. M. J. Am. Chem. Soc.
2007, 129, 10666. (g) Hongfa, C.; Tian, J.; Andreatta, J.; Darensbourg, D. J.;
Bergbreiter, D. E. Chem. Commun. 2008, 975. (h) Bergbreiter, D. E.; Ortiz-
Acosta, D. Tetrahedron Lett. 2008, 49, 5608. (i) Hongfa, C.; Su, H.-L.; Bazzi,
H. S.; Bergbreiter, D. E. Org. Lett. 2009, 11, 665.
(
2) (a) Barrett, A. G. M.; Hopkins, B. T.; K o€ bberling, J. Chem. Rev. 2002,
1
1
3
02, 3301. (b) Dickerson, T. J.; Reed, N. N.; Janda, K. D. Chem. Rev. 2002,
02, 3325. (c) Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem. Rev. 2002, 102,
385. (d) Yoshida, J.-I.; Itami, K. Chem. Rev. 2002, 102, 3693. (e) Buchmeiser,
M. R. Chem. Rev. 2009, 109, 303. (f) Trindade, A. F.; Gois, P. M. P.; Afonso,
C. A. M. Chem. Rev. 2009, 109, 418. (g) Ikegami, S.; Hamamoto, H. Chem.
Rev. 2009, 109, 583.
(3) (a) Bergbreiter, D. E. Chem. Rev. 2002, 102, 3345. (b) Bergbreiter,
D. E.; Tian, J.; Hongfa, C. Chem. Rev. 2009, 109, 530.
DOI: 10.1021/jo902427w
r 2010 American Chemical Society
Published on Web 01/11/2010
J. Org. Chem. 2010, 75, 873–878 873

Bergbreiter and Yang
JOCArticle
those of low molecular weight homogeneous catalysts. In
this study, we examined the similarity of low molecular
weight and high molecular weight phosphine ligands by
studying the dynamics of phosphine ligand exchange at an
NMR-active silver metal center.
ligand exchange process can be analyzed by line shape
analysis because the low temperature (-87 °C) doublet of
doublets (Figure 1b) evolves to a singlet (Figure 1a) at higher
temperature (52 °C) due to the rapid exchange of phosphine
6
from one silver to another. The rate of this exchange as a
function of temperature can then be used to determine the
activation energy for this ligand exchange by using the
Eyring equation (eq 1).
SCHEME 1. 1 Polymer- or Alkyldiphenylphosphine Exchange
Processes of AgX and AgX Complexes
07
109
ꢀ
ꢁ
ꢀ
ꢁ
‡
‡
k
ΔS
kB
ΔH 1
R T
ln
¼
þ ln
-
ð1Þ
T
R
h
31
P
The studies reported below use variable-temperature
NMR spectroscopy to study and compare the dynamic
behavior of silver complexes of both terminally functiona-
lized PIB-PPh and PEG-PPh ligated silver complexes with
31
2
2
P NMR spectroscopy is generally useful as a tool to
silver complexes prepared from electronically similar low
molecular weight phosphine ligands. The results of these
studies show that both terminally functionalized soluble
PIB-PPh2 and PEG-PPh2 phosphine ligands behave like
electronically similar low molecular weight phosphine li-
gands in phosphine metal exchange. This similarity of a
soluble polymeric ligand and a low molecular weight ligand
is consistent with the idea that solutions of these homoge-
neous catalysts bound to these soluble ligands will generally
behave like solutions of their low molecular weight analo-
gues in catalytic processes.
study ligand metal interactions in phosphine complexes of
transition metals. Phosphine-silver complexes are particu-
larly useful subjects in this regard because the phosphine
ligand exchange can often be studied by variable-tempera-
5
ture (VT) dynamic NMR spectroscopy. Specifically, at low
3
1
temperature, the P NMR spectrum of a slowly exchanging
phosphine ligand in a silver-phosphine complex is seen as
a doublet of doublets because silver exists as a nearly equally
1
07
109
abundant mixture of
Ag and
nuclear spin quantum number (I) of / . In such cases,
Ag isotopes each with
1
2
07
1
109
exchange of a phosphine ligand from a Ag to a Ag or
1
07
109
of a Ag or Ag from one phosphine to another as shown
in Scheme 1 can then be studied in detail as a function of
temperature. In the case of complexes like Bu PAgI, this
Results and Discussion
3
The PIB-bound alkyldiphenylphosphine ligand (1) and its
complexes with AgI or AgCl (2 and 3, respectively) were
synthesized from PIB-CH Br by using LiPPh following
temperature-dependent ligand exchange can be monitored
3
1
by P NMR spectroscopy (Figure 1). These spectra show a
temperature-dependent chemical shift for the phosphine
ligand. More importantly, the kinetics of the phosphine
2
2
4
chemistry previously reported (Scheme 2). A lower mole-
cular weight electronically similar phosphine (4) was also
synthesized by reaction of isobutylmagnesium bromide with
chlorodiphenylphosphine and similar AgI and AgCl com-
plexes (5 and 6, respectively) were in turn prepared from 4.
Polyisobutyldiphenyl- and isobutyldiphenylphosphine (1
3
1
and 4, respectively) had identical P NMR spectra with a
singlet at -19.5 ppm (Figure 2). The AgI complexes (2 and 5)
had similar more complex NMR spectra at room tempera-
3
1
ture in C D . The P NMR spectra of the AgCl complexes 3
6
6
and 6 were likewise similar in C D at room temperature.
6
6
The AgI complexes 2 and 5 so formed were then dissolved
3
in CD Cl and their P NMR spectra were recorded from
1
2
2
-64 to 30 °C as shown in Figure 3. Because the PIB-PPh2
ligand is soluble at low temperature, high-quality spectra
were obtained even at -64 °C. As shown, these PIB-PPh AgI
2
3
1
FIGURE 1. P NMR spectra of Bu
b) -87 °C.
3
PAgI in THF at (a) 52 and
and isobutyl-PPh AgI complexes have nearly identical
2
(
dynamic NMR behavior with both the changes in line shape
SCHEME 2. Synthetic Route to Polymeric PIB-Bound Ag Complexes and Their Lower Molecular Weight Analogues
8
74 J. Org. Chem. Vol. 75, No. 3, 2010

Bergbreiter and Yang
JOCArticle
31
FIGURE 2. P NMR spectra of phosphines (1 and 4) and corre-
6 6
sponding silver complexes 2, 3, 5, and 6 in C D at room tempera-
ture.
and the temperature-dependent chemical shifts being very
similar.
The variable-temperature NMR spectra for 2 and 5 can
be used to calculate the rate of silver and phosphine ex-
change (Table 1). Below -33 °C, the exchange process is
slow on the NMR time scale and a doublet of doublets
was observed. The coupling constant of 464 Hz of inner
1
07
31
doublet corresponds to Ag- P coupling, and the outer
1
09
31
doublet has a coupling constant of 536 Hz due to Ag- P.
The ratio of these coupling constants is 0.866, which corre-
1
07
109
Ag/ Ag of 0.870.
sponds to a gyromagnetic ratio of
Integration of inner/outer doublets is 52/48, which corre-
1
07
109
Ag/ Ag of 51.8/48.2.
Using line shape analysis, the rate of phosphine ligand
exchange for 2 and 5 was then calculated at each tempera-
ture. These rate constants were then used to calculate the
ΔG for the exchange process at 20 °C, using the Eyring
equation (Table 2).
sponds to the isotopic ratio of
7
31
FIGURE 3. VT P NMR spectra of 2 and 5 in CD
peratures from -64 to 30 °C.
2 2
Cl at tem-
‡
TABLE 1. Calculated Rate Constants for Phosphine Exchange in 2 and
in CD Cl at Various Temperatures
temp, °C
5
2
2
Similar analyses were also carried out in other solvents
to afford a list of activation energies for PIB-PPh AgI (2),
2
5
2
3
2
0
0
9
4331
2598
1352
743
361
163
57
24
9
3
5215
3012
1731
865
510
238
124
56
PIB-PPh AgCl (3), (CH ) CHCH PPh AgI (5), and (CH ) -
2
3 2
2
2
3 2
CHCH PPh AgCl (6) phosphine exchange in various sol-
2
2
vents. Exchange behavior of 2 and 3 was studied in THF,
CD Cl , and heptane. Heptane was not used for 5 or 6
-1
-
11
22
33
43
2
2
-
-
-
because the silver halide complexes have limited solubility
in this solvent. A slightly higher activation energy is seen in
the less polar solvent heptane for both 2 and 3. However, the
differences in activation energy for the PIB- and the iso-
butylphosphine-silver complexes are minimal. While the
observed differences were often within experimental error, in
-54
-64
21
8
‡
most cases the calculated ΔG of the low molecular weight
phosphine complex was consistently less than or equal to the
TABLE 2. Activation Energies (kcal/mol, 20 °C) for PIB- and
a
Isobutylphosphine-Ag(I) Exchange in Various Solvents
‡
2
5
3
6
ΔG of the polymer-bound species.
b
THF
CD Cl
heptane
12.9
12.6
13.4
12.7
12.5
12.3
11.5
13.0
11.9
11.5
2
2
(
5) (a) Muetterties, E. L.; Alegranti, C. W. J. Am. Chem. Soc. 1970, 92,
b
4115. (b) Muetterties, E. L.; Alegranti, C. W. J. Am. Chem. Soc. 1972, 94,
6386. (c) Bergbreiter, D. E.; Lynch, T. J.; Shimazu, S. Organometallics 1983,
2, 1354.
a
Activation energies were derived from at least seven individual rate
b
6 6
constants measured over a range of -64 to 52 °C. 10% C D was added.
(6) Triaryl- and trialkylphosphine silver(I) complexes usually exist in
tetrameric form in both solution and the solid state. VT NMR studies of
these complexes showed that the ligand exchange process occurs intermole-
cularly. (a) Shimazu, S. Ph.D. Dissertation, Texas A&M University, December,
While our recent work has focused on using soluble
nonpolar PIB-bound ligands as catalyst supports, PEG
2b
derivatives are more common as soluble polymer supports.
1
983; Appendix I. (b) Teo, B.-K.; Calabrese, J. C. Inorg. Chem. 1976, 15, 2474.
7) Line-shape simulations were performed with the computer program
WINDNMR: Reich, H. J. J. Chem. Educ., Software 1996, 3D, 2.
(
Thus, we extended our studies of phosphine ligand exchange
J. Org. Chem. Vol. 75, No. 3, 2010 875

Bergbreiter and Yang
JOCArticle
SCHEME 3. Synthesis of PEG-Bound Ag Complexes and Their Lower Molecular Weight Analogues
to include PEG-triarylphosphine-bound silver halide com-
2 2
without further purification unless otherwise specified. CH Cl
3
1
plexes too. These P NMR spectroscopy studies showed
that phosphine silver halide complexes bound to the termi-
nus of a polar polymer, PEG, also have variable-temperature
NMR behavior and exchange kinetics similar to those of an
electronically analogous low molecular weight phosphine
ligand.
was degassed with three freeze-pump-thaw cycles before being
used in the preparation of silver complexes. Isobutylmagnesium
bromide solution was prepared from 2-bromo-2-methylpropane
and magnesium turnings in THF; the concentration was deter-
8
1
mined by titration. H NMR spectra were recorded on Varian
Inova 500 or Inova 300 spectrometers at 499.834 or 299.959
MHz, respectively. C NMR spectra were recorded on Varian
13
In these studies, we first synthesized PEG-supported
phosphine silver halide complexes (Scheme 3). Electronically
similar low molecular weight phosphines and silver com-
plexes were then also prepared. The comparative dynamic
Inova 500 or Inova 300 spectrometers at 125.695 or 75.432
MHz, respectively. H and C NMR chemical shifts are re-
1
13
3
1
ported in ppm and referenced to CDCl , CD Cl , or C D .
3
2
2
6
6
P
NMR spectra were obtained on an Inova 300 spectrometer at
121.425 MHz and chemical shifts were reported in ppm and were
referenced to external 85% H PO at room temperature. When
3
1
variable-temperature P NMR spectra of these polymeric
and low molecular weight silver phosphine complexes were
3
4
3
1
6 6
THF or heptane was used for VT NMR experiments, 10% C D
again found to be very similar (the P NMR spectra are
provided as Supporting Information). The free energies of
activation for phosphine exchange at 20 °C were again
calculated from the rate constants measured by line shape
analysis at various temperatures over a -76 to 30 °C range
was added as internal lock. Coupling constants (J values) were
reported in Hertz (Hz), and spin multiplicities are indicated by
the following symbols: s (singlet), d (doublet), t (triplet), q
(
quartet), and m (multiplet). All reactions were carried out
under nitrogen atmosphere unless otherwise noted. Tempera-
tures recorded for VT-NMR experiments were calibrated with
100% MeOH. High-resolution MS data were collected from
Applied Biosystems Voyager STR MALDI/TOF mass spectro-
meter with 2,4,6-trihydroxyacetophenone (THAP) as matrix.
Melting points were measured by Stanford Research Systems
‡
for 12, 15, 13, and 16. These ΔG values were 12.3, 12.3, 11.1,
and 10.8 kcal/mol, respectively. As was true for the less polar
terminally substituted PIB-phosphines, the PEG-bound
phosphine and low molecular weight phosphine ligands have
similar behavior.
OptiMelt apparatus and uncorrected. PIB-CH
phosphinyl)phenol (9), and Me(OCH CH
,59 5OMs (10) were
prepared according to literature procedures.
Synthesis of PIB-CH PPh (1). Lithium (0.058 g, 8.36 mmol)
2
Br, 4-(diphenyl-
2
2
)
Conclusions
4
Dynamic NMR studies of phosphine exchange in PIB-
bound, PEG-bound, and low molecular weight phosphine
silver halide complexes show that terminal phosphine li-
gands on polar and nonpolar polymers have exchange
behavior that is very similar to that seen with low molecular
weight phosphine ligands. Line shape analyses show that
the rates and activations energies are nearly the same. This
similar dynamic behavior in a ligand exchange process for
either a polymer or a nonpolymer silver complex supports
the assumption that soluble end-functionalized polymer-
supported metal complexes can be used to prepare soluble
polymer-bound organometallic catalysts whose reactivity
and selectivity will be exactly like that of lower molecular
weight analogues.
2
2
was cut and pressed into rods and placed in a 50-mL round-
bottomed flask equipped with a reflux condenser and a magnetic
stir bar. Triphenylphosphine (1.1 g, 4.2 mmol) was dissolved in
THF (10 mL) and introduced into the reaction flask at room
temperature. The reaction flask was immersed in an oil bath
whose temperature was kept at 70 °C. The reaction mixture was
stirred for 4 h and then cooled to room temperature. At this
point tert-butyl chloride was added (0.46 mL, 4.2 mmol). The
reaction mixture was then stirred at room temperature for
10 min before it was transferred by forced siphon with a cannula
to a 100-mL round-bottomed flask containing PIB-CH
6.54 g, 4.7 mmol in 25 mL THF). The resulting reaction mixture
Br
(
was further stirred at room temperature for 14 h. Then saturated
2
aqueous NH Cl (50 mL) and hexanes (50 mL) were added to the
4
reaction mixture and the aqueous phase was separated. The
nonpolar phase was washed with H
2
O (2 ꢀ 50 mL), 90%
Experimental Section
Vinyl-terminated PIB oligomers (Glissopal 1300) were ob-
tained from BASF Co. and had a M of 1300 based on H NMR
end group analysis of the terminal vinyl group. All other
reagents were purchased from commercial sources and used
1
(8) Krasovskiy, A.; Knochel, P. Synthesis 2006, 890.
9) (a) Sieber, F.; Wentworth, P. Jr.; Toker, J. D.; Wentworth, A. D.;
Metz, W. A.; Reed, N. N.; Janda, K. D. J. Org. Chem. 1999, 64, 5188.
(b) K o€ llhofer, A.; Plenio, H. Chem.;Eur. J. 2003, 9, 1416.
n
(
8
76 J. Org. Chem. Vol. 75, No. 3, 2010

Bergbreiter and Yang
JOCArticle
1
mixture to give a white solid (0.10 g, 0.26 mmol, 6% yield). H
NMR (500 MHz, C
aqueous EtOH (3 ꢀ 50 mL), and acetonitrile (7 ꢀ 20 mL), then
dried over anhydrous MgSO
4
. The solvent was evaporated
6 6
D ): δ 0.99 (d, J = 6.6 Hz, 6 H), 1.97 (t, J =
under reduced pressure to afford a crude product that was
purified by silica gel column chromatography with hexane as
eluting solvent to afford a colorless oil (1.84 g, 1.1 mmol, 26%
7.4 Hz, 2 H), 2.22-2.34 (m, 1 H), 6.94-7.04 (m, 6 H), 7.91-7.97
1
3
(m, 4 H). C NMR (125 MHz, C D ): δ 24.8 (d, J31 13 = 10.0
6
6
P- C
Hz), 27.2 (d, J31P-13C = 10.0 Hz), 37.1 (d, J31P-13C = 13.7 Hz),
128.8 (d, J31P-13C = 9.8 Hz), 129.8, 133.9 (d, J31P-13C = 16.7
1
yield). H NMR (300 MHz, C
6
D
6
): δ 0.80-1.90 (m, 183 H),
3
1
1
5
.90-2.00 (dd, J = 13.4, 8.1 Hz, 1 H), 2.06-2.18 (dd, J = 13.4,
Hz), 135.2 (d, J31P-13C = 26.1 Hz). P NMR (121 MHz, C
δ -0.7. Mp 191-193 °C. HRMS calcd for [(C H -
6 6
D ):
13
.5 Hz, 1 H), 7.02-7.13 (m, 6 H), 7.43-7.54 (m, 4 H). C NMR
): δ 14.4, multiple peaks between 20 and 41 and
1
6
19
þ
2
PAg) Cl] 733.0239, found 733.0394.
(
125 MHz, C
6
D
6
5
5-61, 128.4, 128.6 (d, J31P-13C = 6.2 Hz), 128.7 (d, J31P-13C
P-
31P-13
Hz). P NMR (121 MHz, C
=
Synthesis of Poly(ethylene glycol)triarylphosphine (11). This
phosphine was prepared by a literature procedure. The product
9
5
Hz), 140.0 (d, J
.1 Hz), 133.0 (d, J31 13 = 18.5 Hz), 133.6 (d, J
31P-13
= 19.3
= 14.4
C
C
= 15.2 Hz), 140.2 (d, J
31P-13
was precipitated with diethyl ether (500 mL) and was characteri-
zed by H and P NMR spectroscopy. The product was col-
lected by filtration as a white solid and contaminated with 20%
C
C
31
1
31
D
6 6
): δ -19.5.
Synthesis of Polyisobutyldiphenylphosphine Silver Iodide
PIB-CH PPh AgI) (2). The PIB phosphine 1 (0.041 g, 0.03
1
(
phosphine oxide. H NMR (500 MHz, CDCl ): δ 3.32, (s, 3 H),
2
2
3
mmol) and silver iodide (0.013 g, 0.05 mmol) were placed in a
5-mL round-bottomed flask equipped with a magnetic stir bar.
Then CH Cl (3 mL) was added to the flask and the reaction
mixture was stirred at room temperature for 54 h in the dark.
The suspension was filtered and the solvent was evaporated
under reduced pressure to afford a colorless oil (0.048 g, 0.03
3.42-3.83 (m, 218 H), 4.04-4.08 (m, 2H), 6.79-6.85 (m, 2 H),
3
1
2
7.16-7.28 (m, 12 H). P NMR (121 MHz, CDCl ): δ - 6.5.
3
2
2
Poly(ethylene glycol)triarylphosphine Complexes of Silver
Iodide and Silver Chloride (12 and 13, respectively). Complexes
12 and 13 were prepared from the phosphine 11 and AgI or AgCl
with use of a procedure analogous to that used to prepare PIB-
1
mmol, 99% yield). H NMR (300 MHz, C D ): δ 0.77-2.38
PPh complexes of AgI and AgCl. The silver halide complexes so
2
6
6
1
3
1 31
formed were characterized by H and P NMR spectroscopy
(
(
m, 185 H), 7.03-7.25 (m, 6 H), 7.74-8.00 (m, 4 H). C NMR
1
and were contaminated with up to 25% phosphine oxide. 12: H
75 MHz, C
5-60, and 128-136. P NMR (121 MHz, C
Synthesis of Polyisobutyldiphenylphosphine Silver Chloride
PIB-CH PPh AgCl) (3). The same procedure used to prepare
was used substituting AgCl (0.010 g, 0.07 mmol) for AgI. The
D
6 6
): δ 14.4, 15.2, multiple peaks between 24 and 41,
3
1
5
6
6
D ): δ -15.6.
NMR (500 MHz, CD
2 2
Cl ): δ 3.33, (s, 3 H), 3.42-3.86 (m, 218
H), 4.06-4.10 (m, 2H), 6.83-6.88 (m, 2 H), 7.26-7.33 (m, 4 H),
3
1
(
2
2
7.35-7.41 (m, 2 H), 7.43-7.51 (m, 6 H). P NMR (121 MHz,
1
2
CD
2
Cl
2
2 2
): δ - 3.4. 13: H NMR (300 MHz, CD Cl ): δ 3.32, (s,
product was isolated as a colorless oil (0.052 g, 0.03 mmol, 99%
3 H), 3.32-3.84 (m, 218 H), 4.02-4.09 (m, 2 H), 6.80-6.88 (m,
2 H), 7.24-7.50 (m, 12 H). P NMR (121 MHz, CD Cl ): δ 7.7.
1
31
yield). H NMR (300 MHz, C D ): δ 0.70-1.97 (m, 183 H),
6
6
2
2
1
3
2
.00-2.43 (m, 2 H), 6.98-7.14 (m, 6 H), 7.75-8.09 (m, 4 H).
C
Synthesis of (4-Methoxyphenyl)diphenylphosphine (14). To a
250-mL round-bottomed flask equipped with a magnetic stirrer
was added 4-bromoanisole (5.61 g, 30.0 mmol) and THF
(100 mL). The flask was immersed in a dry ice-acetone bath
for 30 min before BuLi (20 mL, 1.6 M in hexanes, 32.0 mmol)
was added. The reaction mixture was stirred at -78 °C for
60 min at which point chlorodiphenylphosphine (7.2 mL,
40 mmol in 20 mL of THF) was added. The reaction mixture
was stirred at -78 °C for 3 h and then warmed to room
temperature and stirred overnight. Then saturated aqueous
NMR (75 MHz, C
5-60, and 128-134. P NMR (121 MHz, C
Synthesis of Isobutyldiphenylphosphine (4). Isobutylmagne-
6 6
D ): δ multiple peaks between 24 and 38,
31
5
6 6
D ): δ -2.0.
sium bromide (30 mL, 1.25 M in THF) was cooled to 0 °C and
chlorodiphenylphosphine (6.9 mL, 37.6 mmol) was added drop-
wise. The reaction mixture was warmed to room temperature
and stirred for 24 h. Then saturated aqueous NH Cl (50 mL)
4
was added to quench the reaction mixture followed by addition
of ethyl acetate (50 mL). The organic layer was separated and
washed with H
anhydrous MgSO
pressure to afford the crude product, which was further purified
by vacuum distillation to give a colorless liquid (4.55 g, 18.8
2
O (50 mL) and brine (50 mL) and dried over
. The solvent was evaporated under reduced
NH
reaction and the organic phase was separated. The organic
phase was washed with H O (50 mL) and brine (50 mL) and
dried over anhydrous MgSO . The solvent was removed under
reduced pressure to afford a crude product that was purified by
silica gel column chromatography with use of hexane and
CH Cl (hexane:CH Cl = 4:1) to afford a colorless oil that
2 2 2 2
turned into a solid on standing. The solid was further recrys-
tallized from ethanol to give colorless prisms (5.04 g, 17.2 mmol,
4 2
Cl (50 mL) and H O (50 mL) were added to quench the
4
2
4
1
mmol, 50% yield). H NMR (300 MHz, C D ): δ 0.98 (d, J =
6
6
6
.3 Hz, 6 H), 1.55-1.77 (m, 1 H), 1.89 (d, J = 7.0 Hz, 2 H),
13
7
.00-7.12 (m, 6 H), 7.39-7.47 (m, 4 H). C NMR (75 MHz,
): δ 24.3 (d, J31P-13C = 9.6 Hz), 26.4 (d, J31P-13C = 14.0
Hz), 38.9 (d, J31P-13C = 13.8 Hz), 128.5, 128.6 (d, J31P-13C
.6 Hz), 133.1 (d, J31P-13C = 18.8 Hz), 140.2 (d, J31P-13C = 14.3
C
D
6 6
=
1
57% yield). H NMR (500 MHz, CDCl
6.89-6.95 (m, 2 H), 7.28-7.43 (m, 12 H). C NMR (75 MHz,
6
3
): δ 3.82, (s, 3 H),
31
13
Hz). P NMR (121 MHz, C
Synthesis of Isobutyldiphenylphosphine Silver Iodide ((CH
CHCH PPh AgI) (5). The same procedure used to prepare 2
D
6 6
): δ -19.5.
)
2
-
CDCl
6.8 Hz), 128.4 (d, J31P-13
19.0 Hz), 135.6 (d, J31P-13
3
): δ 55.1, 114.2 (d, J P-
3
1
13C=8.1 Hz), 127.3 (d, J
31P-13
31P-13
C
C
=
=
3
C
= 6.8 Hz), 128.5, 133.4 (d, J
2
2
C
= 21.3 Hz), 137.6 (d, J
31P-13
C
= 9.3
was used. The product was recrystallized from a mixture of
EtOH and CH Cl to give a white solid (0.51 g, 1.1 mmol, 27%
yield). H NMR (500 MHz, C ): δ 1.02 (dd, J = 6.7, 0.5 Hz, 6
3
1
Hz), 160.4. P NMR (121 MHz, CDCl ): δ -6.5. Mp 65-66 °C
3
2
2
1
10
D
6 6
(lit. mp 64.5-65.5 °C).
H), 2.15 (t, J = 7.0 Hz, 2 H), 2.31-2.46 (m, 1 H), 7.01-7.06
(4-Methoxyphenyl)diphenylphosphine Silver Iodide and Silver
Chloride (15 and 16). 15 and 16 were prepared from (4-meth-
oxyphenyl)diphenylphosphine and AgI or AgCl. The product
1
3
(
(
J
J
J
m, 2 H), 7.06-7.12 (m, 4 H), 7.81-7.88 (m, 4 H). C NMR
125 MHz, C
): δ 25.2 (d, J31P-13C = 9.2 Hz), 26.9 (d,
31P-13C = 9.2 Hz), 31.9 (d, J31P-13C = 8.9 Hz), 128.7 (d,
= 9.2 Hz), 129.6 (d, J = 1.5 Hz), 133.9 (d,
6 6
D
CH
H NMR (300 MHz, CD
OC
H
PPh
AgI was isolated as white needles in 80% yield.
Cl ): δ 3.80 (s, 3 H), 6.86-6.93 (m,
3
6
4
2
1
31P-13
31P-13
C
2
2
C
31
31P-13C = 15.3 Hz), 135.3 (d, J31P-13C = 20.1 Hz). P NMR
2 H), 7.31-7.39(m, 4 H), 7.40-7.47 (m, 2 H), 7.54-7.64 (m, 6 H).
13
C NMR (75 MHz, CD
= 28.7 Hz), 129.1 (d, J
Cl
): δ 55.8, 114.8 (d, J P-
31
13 = 10.8
= 9.5 Hz),
(
[
121 MHz, C
(C H PAg) I] 824.9595, found 824.9785.
6
D
6
): δ -15.3. Mp 260-264 °C. HRMS calcd for
2
2
C
þ
Hz), 123.3 (d, J31P-13
31P-13
16
19
2
C
C
Synthesis of Isobutyldiphenylphosphine Silver Chloride
(CH CHCH PPh AgCl) (6). The same procedure used to
prepare 5 was used substituting AgCl (0.72 g, 5.0 mmol) for
(
3
)
2
2
2
(
10) McEwen, W. E.; Shiau, W.-I.; Yeh, Y.-I.; Schulz, D. N.; Pagilagan,
R. U.; Levy, J. B.; Symmes, C. Jr.; Nelson, G. O.; Granoth, I. J. Am. Chem.
Soc. 1975, 97, 1787.
AgI. The product was recrystallized from an EtOH/CH Cl
2
2
J. Org. Chem. Vol. 75, No. 3, 2010 877

Bergbreiter and Yang
= 16.5 Hz), 136.5 (d, J = 18.5 Hz),
JOCArticle
1
1
1
30.3 (d, J
31P-13
= 1.6 Hz), 133.8 (d, J
31P-13
= 24.9 Hz),
134.2 (d, J
31P-13
31P-13
C
C
C
C
3
1
34.5 (d, J31P-13C = 15.7 Hz), 136.7 (d, J31P-13C = 17.6 Hz),
61.9 (d, J31P-13C = 1.5 Hz). P NMR (121 MHz, CD
161.9 (d, J31P-13C = 1.4 Hz). P NMR (121 MHz, CD
Cl
): δ
2
2
3
1
þ
2
-
6.5. Mp 97-100 °C. HRMS calcd for [(C19
832.9824, found 833.0092.
H17OPAg) Cl]
2
Cl ): δ -6.5. Mp 188-189 °C. HRMS calcd for [(C H -
2
19 17
þ
OPAg)
H
2
I] 924.9181, found 924.8835. The product CH
AgCl was isolated as a white solid in 73% yield. H
Cl ): δ 3.75 (s, 3 H), 6.81-6.88 (m, 2 H),
3 6
OC -
1
4
PPh
2
Acknowledgment. Support from the Robert A. Welch
Foundation (A-635) is gratefully acknowledged.
NMR (300 MHz, CD
2
2
1
3
7
.27-7.35 (m, 4 H), 7.36-7.44 (m, 2 H), 7.50-7.62 (m, 6 H). C
NMR (75 MHz, CD
2
Cl
2
): δ 55.7, 114.9 (d, J31P-13C = 11.2 Hz),
Supporting Information Available: NMR spectra and struc-
tures with peak assignments. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
1
23.1 (d, J31P-13C = 32.6 Hz), 129.2 (d, J31P-13C = 9.8 Hz),
30.4 (d, J = 1.7 Hz), 133.6 (d, J = 28.7 Hz),
31P-13
31P-13
C
C
8
78 J. Org. Chem. Vol. 75, No. 3, 2010