Phosphine functionalized polyphosphazenes: soluble and re-usable polymeric reagents for highly efficient halogenations under Appel conditions

Article abstract of DOI:10.1007/s00706-016-1791-x

In this paper we present the preparation and application of a novel soluble phosphine functionalized polyphosphazene (poly[3-(diphenylphosphino)propylamino]phosphazene) and investigate its application as a polymeric reagent. Upon chlorination of the pendant phosphine groups, the polymer was found to facilitate the rapid and efficient transformation of alcohols to the corresponding chlorides and bromides under Appel-type conditions. Reaction times followed by ³¹P NMR spectroscopy are shown to be rapid (several minutes) and the yields for the transformation of alcohols to the corresponding halides are in the range 80–99?%. The facile recovery of the oxidized polymeric agent by precipitation is also described, offering a significant advantage over notoriously difficult to remove small molecule phosphine oxide by-products. Furthermore the regeneration of the reactive phosphine chloride pendant groups is demonstrated, which could be efficiently re-used in a further chlorination reaction. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1791-x

Monatsh Chem
DOI 10.1007/s00706-016-1791-x
ORIGINAL PAPER
Phosphine functionalized polyphosphazenes: soluble and re-usable
polymeric reagents for highly efficient halogenations under Appel
conditions
1
1
1
1
Michael K o¨ nig
•
Anne Linhardt
•
Oliver Br u¨ ggemann
•
Ian Teasdale
Received: 14 March 2016 / Accepted: 23 May 2016
Ó Springer-Verlag Wien 2016
Abstract In this paper we present the preparation and appli-
novel soluble phosphine functionalized
(poly[3-(diphenylphosphino)propyl-
Keywords Polyphosphazenes Á Inorganic polymers Á
Polymeric reagents Á Chlorination Á
cation of
a
polyphosphazene
Phosphorus compounds Á Phosphine reagents
amino]phosphazene) and investigate its application as a
polymeric reagent. Upon chlorination of the pendant phosphine
groups, the polymer was found to facilitate the rapid and effi-
cient transformation of alcohols to the corresponding chlorides
and bromides under Appel-type conditions. Reaction times
Introduction
Phosphines play an important role in today’s synthetic
organic chemistry [1]. They are employed as reagents
[2–4], as complex-ligands for transition-metal catalysts or
act as organo-catalysts [5–7]. The use of phosphines as
reagents, in particular triphenylphosphine, enables a vast
number of synthetic transformations including Appel-type
halogenations [8], Staudinger [9], Mitsunobu [10–12], and
Wittig reactions [13, 14], as well as amidations [15] and the
reduction of sulfonyl chlorides and sulfoxides to thiols and
sulfides [16, 17]. Although this wide variety of possible
applications make phosphine reagents a valuable tool for
the synthetic organic chemist, all of these examples suffer
from two major drawbacks. Firstly, the formation of the
corresponding phosphine oxide by-products which are
often difficult to remove, even by chromatographic meth-
ods. This latter issue has been addressed by various groups
using modified phosphines which either give water-soluble
phosphine oxides after reaction for removal via aqueous
extraction [18], or by polymer-supported phosphines
3
1
followed by P NMR spectroscopy are shown to be rapid
several minutes) and the yields for the transformation of
(
alcohols to the corresponding halides are in the range 80–99 %.
The facile recovery of the oxidized polymeric agent by pre-
cipitation is also described, offering a significant advantage
over notoriously difficult to remove small molecule phosphine
oxide by-products. Furthermore the regeneration of the reactive
phosphine chloride pendant groups is demonstrated, which
could be efficiently re-used in a further chlorination reaction.
Graphical abstract
[
19–21] which can be more easily removed by filtration.
Secondly, atom efficiency has also been a concern, and
improvements in this regard have recently gained increas-
ing attention. The two basic approaches here are the
recovery of the initial phosphine by reductive methods
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1791-x) contains supplementary
material, which is available to authorized users.
&
Ian Teasdale
ian.teasdale@jku.at
[
22], which often requires hazardous reagents and is not
always efficient or the direct re-use of the phosphine oxides
as reagents or catalysts [23–27].
1
Institute of Polymer Chemistry, Johannes Kepler University,
Linz, Austria
123

M. K o¨ nig et al.
Polyphosphazenes are an attractive class macromolec-
ular carriers of reactive functionalities as they display a
number of inherent features such as high functionality, with
two functional groups per repeat unit, and the possibility of
facile and variable post-polymerization chemical func-
tionalization. The unusually high flexibility of the chemical
backbone [28] and thus conformational flexibility further
makes them ideally suited as solution state polymeric
reagents in organic synthesis. Furthermore, the potential
for chirality [29–31] renders them highly interesting as
polymer supports [32–35].
by the loss of the NMR signal at -16 ppm and the
appearance of a new signal at 79 ppm corresponding to the
chlorophosphonium chloride salt [42] (Fig. 1).
Upon addition of one equivalent of 3,5-dimethoxyben-
zyl alcohol, and stirring for 10 min, a complete shift in the
3
1
1 31
P{ H} NMR spectrum was observed. P NMR signal of
the reaction mixture to 34 ppm is observed, corresponding
to complete formation of the phosphine oxide polymer 5.
These high reaction rates achieved in comparison to other
polymer-supported alkyl diphenyl phosphines [43] can be
explained by the polyphosphazenes exhibiting very open
conformations in solution (assisted by the chain flexibility)
that facilitate the accessibility of the reactive site groups.
After completion of the reaction, the two products, phos-
phine oxide polymer and benzyl chloride were separated by
precipitating a concentrated chloroform solution of the
crude reaction mixture into cyclohexane. Excess hex-
achloroethane and the by-product, tetrachloroethylene were
removed by a co-evaporation step with chloroform and
drying under high vacuum. The oxidized polymer 5 was
recovered in a 96 % yield (calculated from 3) after filtra-
tion and washing with cyclohexane, while the product
benzyl chloride was obtained in 80 % yield from the
combined filtrates via simple evaporation.
Polyphosphazene supported phosphines have been syn-
thesized and used as macromolecular ligands for transition-
metal catalysts over recent decades [36–38] but, to the best
of the authors knowledge, the use of pendant phosphines
themselves as macromolecular reagents has not been
investigated previously. Herein, we present the synthesis of
a novel soluble phosphine functionalized polyphosphazene
and investigate its use in the transformation of a series of
alcohols to the corresponding chlorides and bromides,
followed by recovery of the polymeric reagent by simple
precipitation. Furthermore, the regeneration of the oxidized
polymer and its re-application in such Appel-type reactions
is investigated.
To evaluate the scope of the reaction, a series of alco-
hols, chosen to represent alcohols with widely differing
properties, were reacted under similar conditions (Table 1).
Among these examples were the electron-poor 4-ni-
trobenzyl alcohol, the highly electron-rich 2,4-
Results and discussion
The polymeric reagent poly[3-(diphenylphosphino)propyl-
0
amino]phosphazene
macromolecular substitution of poly(dichloro)phosphazene
PNCl ] (2) [39, 40] with 3-(diphenylphosphino)propyl-
(3)
was
synthesized
by
dimethoxybenzyl alcohol, a secondary 4,4 -dichlorobenz-
hydrol as well as the aliphatic 1-hexadecanol and
2-hexadecanol. These alcohols were transformed into the
corresponding chlorides within 15 min in good to very high
yields (80–99 %), thus demonstrating the applicability of
the polymeric reagents for a range of primary and sec-
ondary substrates. However, the reaction with 4-phenyl-2-
methyl-2-butanol (11a) did not yield the desired product,
instead the starting alcohol was quantitatively recovered.
Further expansion of the scope to more polar products
which are insoluble in hydrocarbons could be possible due
to the fact that the polymer also precipitates efficiently
from toluene and diethyl ether.
[
2
n
amine. The precursor [PNCl ] was prepared via living
2
n
cationic polymerization of trichlorophosphoranimine with
triphenylchlorophosphonium chloride as initiator, previ-
ously prepared in situ by the reaction of triphenylphosphine
with hexachloroethane [41]. The resulting [PNCl ] was
2
n
converted to the polymeric phosphine reagent 3 by
macromolecular substitution with 3-(diphenylphos-
phino)propylamine (Scheme 1), to give a soluble polymer
3
1
1
with two-phosphine groups per repeat unit. P{ H}-NMR
spectroscopy was used to follow progress of the macro-
molecular
-(diphenylphosphino)propylamine to give the fully sub-
stituted product 3 [NPR ] (details of this reaction and full
substitution
of
[NPCl2]n
with
Since the polymer proved to be successful for use in
chlorination reactions, the bromination of alcohols was also
investigated. For this purpose, eight equivalents of CBr4
were reacted with a solution of the polymer in CH Cl . The
3
2
n
spectra are given in the supplementary material, Fig. S2).
After purification, polymer 3 then underwent chlorina-
tion of the pendant phosphine ligands to give the
chlorophosphonium chloride salt (polymer 4, Scheme 2).
The chlorination of the polymer-bound phosphine is rapid,
2
2
work-up of the reaction was performed in the same fashion
as for the chlorination. However, the bromination reaction
1
resulted in a mixture of substances as indicated by H
NMR spectroscopy. The major product with 70 % was the
anticipated benzyl bromide but the mixture also contained
some unreacted alcohol (25 %) and curiously also 5 % of
the benzyl chloride (Fig. 2c). To clarify this, we repeated
3
1
1
as observed in P{ H} NMR measurements. Upon reac-
tion with four equivalents of hexachloroethane in CD Cl ,
2
2
the initial phosphine is consumed within 5 min indicated
1
23

Phosphine functionalized polyphosphazenes: soluble and re-usable polymeric reagents for…
Scheme 1
Scheme 2
3
the reaction in CD Cl as a solvent and measured P{ H}
1
1
in MeCN as this solvent and avoiding chlorinated solvents
in the work-up and characterisation. MeCN is known to
have a similar stabilizing effect as dichloromethane on the
salt-like structure of R PX -type compounds [42, 44] a
2
2
NMR spectra at the various reaction stages. First, a shift in
3
1
1
the P{ H} NMR spectrum from -16 to 32 ppm was
observed confirming the reaction of the phosphine to the
bromophosphonium salt. Interestingly, a minor signal at
3
2
prerequisite for the rapid transformation of alcohols to
halides. Acetonitrile proved to be a more effective reagent
for the bromination reagent giving 99 % yield of a mixture
containing 75 % of the corresponding benzyl bromide and
25 % of unreacted alcohol (Fig. 2d).
7
9 ppm could also be observed, which is identical to the
signal for the chlorophosphonium chloride in the chlori-
nation reaction described above. Upon addition of one
equivalent of 3,5-dimethoxybenzyl alcohol, both signals
disappeared within 10 min and a new signal at 34 ppm
representing the phosphine oxide could be observed. To
rule out the participation of a possible C Cl impurity we
Although the chlorination reactions described above are
very rapid and highly efficient, they still suffer from the
low atom economy that is distinct for non-catalytic phos-
phine mediated reactions. To address this issue, we also
experimented with the re-use of the phosphine oxide
polymer 5 of the chlorination reactions. Chlorination
reactions with both small molecule, and polymer-supported
phosphine oxides, were recently reported by the group of
Denton [23–26]. In a similar approach, we reacted the
phosphine oxide polymer 5 with 4.4 equivalents of oxalyl
chloride in CH Cl under an argon atmosphere for 12 h
2
6
also prepared the reagent from commercially available
triphenyl-chlorophosphonium chloride and compared the
bromination reaction of 3,5-dimethoxybenzyl alcohol with
both polymers, however, no influence of the polymer
synthesis route on the composition of the crude bromina-
tion product was observed. Another suspected source for
the chloride impurity was a non-innocent behavior of the
solvent CH Cl . Therefore, we also performed the reaction
2
2
2
2
123

M. K o¨ nig et al.
3
1
1
Fig. 1 P{ H} NMR spectra in CD
over the course of the reaction a free phosphine polymer (3)
-16.0 ppm); b polymer after chlorination (4) (78.5 ppm); c phos-
phine oxide polymer (5) after reaction (34.4 ppm). The signals at
2
Cl
2
of the polymeric reagent
around 5 and 12 ppm correspond to the phosphorus nuclei in the
backbone and the end groups, respectively (see supplementary
material)
(
(
Scheme 3). The successful conversion of the phosphine
Conclusion
oxide to the chlorophosphonium chloride (4) was con-
3
1
1
firmed by the shift of the P{ H} NMR signal from 35 to
7 ppm. After removal of the solvent and excess oxalyl
The successful synthesis of a novel polyphosphazene-based
phosphine reagent is reported and its employment as a
polymeric reagent in the Appel-type chlorination of alco-
hols demonstrated on a range of alcohol substrates with
broad spectrum of properties. The reactions were observed
to be high yielding and fast for every example tested, with
yields in the range of 80–99 % within 15 min reaction
time. The polymeric reagent also proved to be convenient
to handle, since it can be easily removed from the reaction
mixture by simple precipitation in [95 % recovery. Fur-
thermore, it is demonstrated that the phosphine-based
polymer could be regenerated and re-used with similar
efficiency a further reaction, although this activity was
diminished upon further cycles. The polymeric reagent
could also be used in the transformation of alcohols to the
corresponding bromides, although this reaction proved to
have inferior efficiency compared to the chlorination
7
chloride in vacuo, the regenerated polymer 4 could be
directly employed in the chlorination of alcohols under
inert conditions. In an example reaction, 4-nitrobenzyl
chloride (6b) could be obtained in excellent 97 % yield in
1
h reaction time.
The longer reaction time necessary for the full conver-
sion of the alcohol is due to the film morphology of the re-
chlorinated polymer which requires longer to fully dis-
solve. The solution only becomes clear as the reaction
proceeds and the chlorophosphonium salt is consumed. A
re-precipitation of the polymer film to regain a powdered
form would be highly inconvenient due to the moisture
sensitivity of the intermediate. Repeated re-use (2–3
cycles) showed decreased activity (see supplementary
material Table S1 and Fig. S3).
1
23

Phosphine functionalized polyphosphazenes: soluble and re-usable polymeric reagents for…
Table 1 Scope of the
Producta
Yield /%
b
Ref.
[45]
Entry
Starting material
chlorination reaction
1
99
99
5
6
a
a
5b
2
3
[46]
[47]
6b
80
96
7
a
7b
4
[48]
8
9
a
a
8b
9b
5
6
99
98
[
49]
c
1
0a
1a
10b
11b
7
-
1
Complementary characterization of all products is provided in the supplementary material
a
Conditions: 2 eq. of 3, 4 eq. C
2 6
Cl , r.t., 15 min
b
1
Isolated yield. Product purity exceeded 95 % in every case according to H NMR
spectroscopy
c
No literature NMR spectra found for this compound
reactions. Overall, this polymer represents an interesting
new polymeric reagent, due to its excellent reactivity
combined with its simple recovery and efficient re-
usability.
Alfa Aesar and stored under Argon, all other solvents were
from VWR and used without further purification unless
otherwise noted. The polymer synthesis and halogenation
reactions were carried out in a glove box (MBRAUN)
1
13
under argon. Proton ( H NMR) and carbon ( C NMR)
spectra were recorded on a Bruker Ultra Shield 300 device
at 300 and 75 MHz, respectively. Chemical shifts are given
as parts per million (ppm) on the delta (d) scale and ref-
erenced to the ‘‘solvent residual signal’’ at 7.26 and
Experimental
3
-(Diphenylphosphino)propylamine was purchased from
3
1
1
ABCR Chemicals, other chemical from Sigma Aldrich, or
TCI Chemicals. Anhydrous solvents were purchased from
77.16 ppm for CDCl [37]. Phosphorus ( P{ H} NMR)
3
were recorded on a Bruker Ultra Shield 300 device at
123

M. K o¨ nig et al.
1
Fig. 2 H NMR (CDCl
bromination in MeCN
3
) spectra of the benzylic CH
2
group a alcohol; b after chlorination; c after bromination in CH
2
Cl
2
, and d after
Scheme 3
eluted with DMF containing 10 mM LiBr at a flow rate of
3
0
.75 cm /min at 60 °C. The molecular weight was esti-
mated by multi-detector calibration (refractive index, right
angle light scattering, low angle light scattering and vis-
cosity detector) using a linear polystyrene standard.
Polyphosphazene reagent synthesis
Triphenylphosphine (7.5 mg, 28.6 lmol) was reacted with
3
7
.4 mg C Cl (31.5 lmol) in 1 cm CH Cl for 24 h at
2
6
2
2
room temperature to yield dichlorotriphenylphosphorane.
Then 320.9 mg N-(trimethylsilyl)-trichlorophosphoran-
imine (1.43 mmol) was added and stirred over night at
room temperature to yield poly(dichloro)phosphazene. For
1
21.4 MHz or on a Bruker DRX 500 device at 202.4 MHz,
using 85 % phosphoric acid as an external standard. ATR-
IR-spectra were recorded on a PerkinElmer Spectrum 100
Series. Gel permeation chromatography (GPC) was mea-
sured with a Viscothek GPCmax instrument equipped with
macromolecular substitution 869.6 mg 3-(diphenylphos-
3
phino)propylamine (3.57 mmol) and 0.5 cm
Et N
3
3
361.7 mg, 3.57 mmol) were dissolved in 5 cm anhydrous
(
THF and added to the reaction mixture. The reaction was
stirred for 16 h at room temperature. After filtration, the
solvent was concentrated and the polymer precipitated
a
PFG column from PSS (Mainz, Germany;
3
00 mm 9 8 mm, 5 lm particle size). The samples were
1
23

Phosphine functionalized polyphosphazenes: soluble and re-usable polymeric reagents for…
three times in heptane and three times in methanol to yield
1
90 mg of the product as colourless solid in 64 % yield. H
References
4
1
. Allen DW (2016) In: Allen DW, Loakes D, Tebby JC (eds)
Organophosphorus Chemistry, vol 45. Royal Society of Chem-
istry, Cambridge, p 1
. Honaker M, Hovland J, Nicholas Salvatore R (2007) Curr Org
Chem 4:31
NMR (300 MHz, CDCl ): d = 1.42 (br, 3H, NH and –
3
CH -PPh ), 1.83 (br, 2H, –CH –CH –CH –), 2.81 (br, 2H,
2
2
2
2
2
1
3
–
NH–CH –), 7.75–6.99 (m, 10H, Ph-H) ppm; C NMR
2
2
(
75.432 MHz, CDCl ): d = 138.8, 132.7, 130.9, 128.4,
2.3, 28.3, 20.1 ppm; P{ H} NMR (121.4 MHz, CDCl ):
3
3
3
1
1
3
4
5
. Valentine Jr DH, Hillhouse JH (2003) Synthesis 317
. Xu S, He Z (2013) RSC Adv 3:16885
4
d = -17.13 (–PPh ), 3.49 ([NPR] ), 10.43 (a-end group)
2
2
. Chan JW, Hoyle CE, Lowe AB, Bowman M (2010) Macro-
molecules 43:6381
6. Lu X, Zhang C, Xu Z (2001) Acc Chem Res 34:535
ppm; SEC (multidetector calibration): M = 35,000 -
n
-
g mol , Ð: 1.1.
1
7
8
. Methot JL, Roush WR (2004) Adv Synth Catal 346:1035
. Appel R (1975) Angew Chem Int Ed 14:801
General procedure for the chlorination of alcohols
3
In a 10 cm flask, 50 mg of phosphine-polyphosphazene
9. Staudinger H, Meyer J (1919) Helv Chim Acta 2:635
10. Mitsunobu O (1981) Synthesis 1
1. Kumara Swamy KC, Bhuvan Kumar NN, Balaraman E, Pavan
Kumar KVP (2009) Chem Rev 109:2551
12. Fletcher S (2015) Org Chem Front 2:739
3
0.094 mmol) was dissolved in 3 cm anhydrous CH Cl
(
2
2
1
under an argon atmosphere. The resulting solution was
3
cooled to 0 °C and a solution of 0.384 mmol C Cl in 1 cm
2
6
anhydrous CH Cl was added followed by 0.094 mmol of
13. Wittig G, Geissler G (1953) Justus Liebigs Ann Chem 580:44
2
2
1
4. Wittig G, Sch o¨ llkopf U (1954) Chem Ber 87:1318
15. Frøyen P (1995) Synth Commun 25:959
16. Jang Y, Kim KT, Jeon HB (2013) J Org Chem 78:6328
the alcohol after 5 min. After further stirring for 15 min the
solvent was removed, the residue was taken up in a minimum
amount of CHCl and the oxidized polymer was precipitated
3
17. Bellale E, Chaudhari M, Akamanchi K (2009) Synthesis 3211
18. Smith CD, Baxendale IR, Tranmer GK, Baumann M, Smith SC,
Lewthwaite RA, Ley SV (2007) Org Biomol Chem 5:1562
in an appropriate solvent. The polymer was removed by
filtration, and washed with the precipitation solvent. The
combined filtrates were evaporated to dryness and dried
under high vacuum to yield the corresponding alkyl or
benzyl chlorides.
1
9. Ley SV, Baxendale IR, Bream RN, Jackson PS, Leach AG,
Longbottom DA, Nesi M, Scott JS, Storer RI, Taylor SJ (2000) J
Chem Soc Perkin Trans 1:3815
20. Dickerson TJ, Reed NN, Janda KD (2002) Chem Rev 102:3325
1. Guin o´ M, Hii KK (2007) Chem Soc Rev 36:608
22. H e´ rault D, Nguyen DH, Nuel D, Buono G (2015) Chem Soc Rev
4:2508
2
General procedure for the re-use of the oxidized polymer
3
In a 25 cm two-neck round bottom flask equipped with an
4
2
2
2
3. Tang X, An J, Denton RM (2014) Tetrahedron Lett 55:799
4. Denton RM, An J, Adeniran B (2010) Chem Commun 46:3025
5. Denton RM, An J, Adeniran B, Blake AJ, Lewis W, Poulton AM
(2011) J Org Chem 76:6749
6. An J, Tang X, Moore J, Lewis W, Denton RM (2013) Tetrahe-
dron 69:8769
argon inlet and a magnetic stirring bar were placed 56 mg of
the phosphine oxide polymer (0.1 mmol) and dissolved in
3
cm dry CH Cl under an Argon atmosphere. After cooling
4
2
2
3
2
2
the solution to 0 °C in an ice-bath 37 mm oxalyl chloride
0.44 mmol) were added. After gas evolution (!care CO
(
7. van Kalkeren HA, Leenders SHAM, Hommersom CRA, Rutjes
FPJT, van Delft FL (2011) Chem Eur J 17:11290
28. Sun H (1997) J Am Chem Soc 119:3611
formation!) had ceased, the ice-bath was removed and the
mixture stirred at room temperature for 12 h after which the
solvent and excess reagent were removed in vacuo. The
2
9. Carriedo GA, Garc ´ı a Alonso FJ, Presa Soto A (2006) Macro-
molecules 39:4704
0. Carriedo GA, Garc ´ı a Alonso FJ, Presa-Soto A (2003) Eur J Inorg
Chem 4341
3
resulting residue was re-dissolved in 3 cm dry CH Cl and a
2
2
3
3
solution of 0.1 mmol alcohol in 1 cm CH Cl was added.
2
2
The reaction was stirred for 1 h, the solvent was removed, the
31. Maeda K, Kuroyanagi K, Sakurai S, Yamanaka T, Yashima E
2011) Macromolecules 44:2457
(
residue was taken up in a minimum amount of CHCl and the
3
3
3
3
3
2. Carriedo GA, L o´ pez S, Su a´ rez-Su a´ rez S, Presa-Soto D, Presa-
Soto A (2011) Eur J Inorg Chem 1442
3. Carriedo GA, Crochet P, Alonso FJG, Gimeno J, Presa-Soto A
(2004) Eur J Inorg Chem 3668
4. Cuetos A, Valenzuela ML, Lavandera I, Gotor V, Carriedo GA
oxidized polymer was precipitated in an appropriate solvent.
The polymer was removed by filtration, and washed with the
precipitation solvent. The combined filtrates were evaporated
to dryness and dried under high vacuum to yield the
corresponding alkyl or benzyl chlorides. It is important to
maintain inert conditions throughout the full regeneration and
re-use procedure, as contact with moisture in the air instan-
taneously converts the polymer back to the phosphine oxide.
(
2010) Biomacromolecules 11:1291
5. D ´ı az C, Valenzuela ML, Carriedo GG, Garc ´ı a Alonso FJ, Presa A
2006) Polym Bull 57:913
36. Carriedo GA, Garc ´ı a Alonso FJ, Gonz a´ lez PA, G o´ mez-Elipe P
1999) Polyhedron 18:2853
(
(
3
3
3
7. Dubois RA, Garrou PE, Lavin KD, Allcock HR (1986) Organo-
metallics 5:460
8. Allcock HR, Lavin KD, Tollefson NM, Evans TL (1983) Orga-
nometallics 2:267
9. Tian Z, Zhang Y, Liu X, Chen C, Guiltinan MJ, Allcock HR
Acknowledgments We thank Dr. Wolfgang Schoefberger for his
help with the NMR measurements and Wolfgang Gnong for his
assistance with the GC–MS measurements. A.L. thanks the Springer
¨
Verlag, the Austrian Academy of Sciences (OAW) and the Gesell-
(
2013) Polym Chem 4:1826
¨
¨
schaft Osterreichischer Chemiker (GOCH) for Chemical Monthly
Fellowship for 3 months research abroad.
123

M. K o¨ nig et al.
4
4
4
4
4
0. Henke H, Wilfert S, Iturmendi A, Br u¨ ggemann O, Teasdale I
2013) J Polym Sci A Polym Chem 51:4467
1. Wilfert S, Henke H, Schoefberger W, Br u¨ ggemann O, Teasdale I
2014) Macromol Rapid Commun 35:1135
2. Godfrey SM, McAuliffe CA, Sheffield JM (1998) Chem Com-
mun 921
3. Bergbreiter DE, Blanton JR (1985) J Chem Soc Chem Commun
45. Nicoletti TM, Raston CL, Sargent MV (1990) J Chem Soc Perkin
Trans 1:133
46. Yasuda M, Yamasaki S, Onishi Y, Baba A (2004) J Am Chem
Soc 126:7186
47. Weist S, Kittel C, Bischoff D, Bister B, Pfeifer V, Nicholson GJ,
Wohlleben W, S u¨ ssmuth RD (2004) J Am Chem Soc 126:5942
48. He S, Xiao J, Dulcey AE, Lin B, Rolt A (2016) J Med Chem
59:841
49. Dubey A, Upadhyay AK, Kumar P (2010) Tetrahedron Lett
51:744
(
(
3
37
4. Yin Q, Ye Y, Tang G, Zhao Y (2006) Spectrochim Acta A Mol
Biomol Spectrosc 63:192
1
23