The boron-catalyzed polymerization of dimethylsulfoxonium methylide. A living polymethylene synthesis

Article abstract of DOI:10.1021/ja017376c

Trialkyl and aryl organoboranes catalyze the polymerization of dimethylsulfoxonium methylide (1). The product of the polymerization is a tris-polymethylene organoborane. Oxidation affords linear telechelic α-hydroxy polymethylene. The polymer molecular weight was found to be directly proportional to the stoichiometric ratio of ylide/borane, and polydispersities as low as 1.01 - 1.03 have been realized. Although oligomeric polymethylene has been the most frequent synthetic target of this method, polymeric star organoboranes with molecular weights of 1.5 million have been produced. The average turnover frequency at 120 °C in 1,2,4,5-tetrachlorobenzene/toluene is estimated at > 6 x 10⁶ g of polymethylene (mol boron)^-1 h^-1. The mechanism of the polyhomologation reaction involves initial formation of a zwitterionic organoborane·ylide complex which breaks down in a rate-limiting 1,2-alkyl group migration with concomitant expulsion of a molecule of DMSO. The reaction was found to be first order in the borane catalyst and zero order in ylide. DMSO does not interfere with the reaction. The temperature dependence of the reaction rate yielded the following activation energy parameters (toluene, ΔH^? = 23.2 kcal/mol, ΔS^? = 12.6 cal deg/mol, ΔG^? = 19.5 kcal/mol; THF, ΔH^? = 26.5 kcal/mol, ΔS^? = 21.5 cal deg/mol, ΔG^? = 20.1 kcal/mol).

Full text of DOI:10.1021/ja017376c

Published on Web 03/13/2002
The Boron-Catalyzed Polymerization of Dimethylsulfoxonium
Methylide. A Living Polymethylene Synthesis
Brett B. Busch, Manuel M. Paz, Kenneth J. Shea,* Chad L. Staiger,
Jonathan M. Stoddard, James R. Walker, Xian-Zhi Zhou, and Huide Zhu
Contribution from the Department of Chemistry, UniVersity of California IrVine,
IrVine, California 92697-2025
Received October 24, 2001
Abstract: Trialkyl and aryl organoboranes catalyze the polymerization of dimethylsulfoxonium methylide
(1). The product of the polymerization is a tris-polymethylene organoborane. Oxidation affords linear
telechelic R-hydroxy polymethylene. The polymer molecular weight was found to be directly proportional
to the stoichiometric ratio of ylide/borane, and polydispersities as low as 1.01-1.03 have been realized.
Although oligomeric polymethylene has been the most frequent synthetic target of this method, polymeric
star organoboranes with molecular weights of 1.5 million have been produced. The average turnover
6
frequency at 120 °C in 1,2,4,5-tetrachlorobenzene/toluene is estimated at >6 × 10 g of polymethylene
-1
-1
(mol boron)
h . The mechanism of the polyhomologation reaction involves initial formation of a zwitterionic
organoborane‚ylide complex which breaks down in a rate-limiting 1,2-alkyl group migration with concomitant
expulsion of a molecule of DMSO. The reaction was found to be first order in the borane catalyst and zero
order in ylide. DMSO does not interfere with the reaction. The temperature dependence of the reaction
q
q
rate yielded the following activation energy parameters (toluene, ∆H ) 23.2 kcal/mol, ∆S ) 12.6 cal
q
q
q
q
deg/mol, ∆G ) 19.5 kcal/mol; THF, ∆H ) 26.5 kcal/mol, ∆S ) 21.5 cal deg/mol, ∆G ) 20.1 kcal/mol).
Introduction
Carbon backbone polymers comprise one of the world’s
1
largest sources of synthetic materials. They are prepared by
the polymerization of olefins, which are derived from petroleum.
Olefin polymerization reactions build the carbon backbone two-
carbon atoms at a time. Catalysts of exceptional efficiency have
been developed for these purposes, and remarkable control over
many of the key variables that influence physical properties and
2
polymer performance has been achieved. Despite these ad-
Figure 1. Possible disconnections of a simple linear hydrocarbon polymer.
vances, there are still synthetic challenges that remain. For
example, many olefins, particularly the more highly substituted
derivatives, do not polymerize; their polymers are unknown.
methods for their synthesis are needed. Furthermore, despite
significant recent developments, controlled synthesis of co-
4
3
The direct synthesis of many types of polymer architectures,
polymers of the more important commodity polymers such as
5
for example giant macrocyclic rings, cannot be readily achieved
by olefin polymerization. In addition, there are many functional
groups that are not compatible with existing catalysts, so new
poly(ethylene-b-styrene) remains a challenge.
Although olefins are the most obvious and practical synthetic
building blocks for the carbon backbone, alternative methods
for synthesizing carbon chains offer the potential for novel
solutions to some of these aforementioned synthetic challenges.
If one lifts the restriction of the C2 carbon source, new
approaches utilizing C1, C3, C4, or larger building blocks can
be envisioned, providing of course, suitable building blocks and
(
1) (a) Barghoorn, P.; Stebani, U.; Balsam, M. AdV. Mater. 1998, 10, 635. (b)
Morse, P. M. Chem. Eng. News 1999, 77, 11. (c) Younkin, T. R.; Connor,
E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A.
Science 2000, 287, 460. (d) Wilson, E. Chem. Eng. News 2000, 78, 14.
2) (a) Brintzinger, H. H.; Fisher, D.; M u¨ elhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b) Fink, G., M u¨ elhaupt,
R., Brintzinger, H. H., Eds. Ziegler Catalysts: Recent Scientific InnorVations
and Technological ImproVement; Springer-Verlag: Berlin, 1995. (c) Coates,
G. W.; Waymouth, R. M. ComprehensiVe Organometallic Chemistry II;
Pergamon Press: 1995; Vol. 12, p 1193. (d) Britovsek, G. J. P.; Gibson,
V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (e) Coates, G.
W. Chem. ReV. 2000, 100, 1223. (f) Ittel, S. D.; Johnson, L. K.; Brookhart,
M. Chem. ReV. 2000, 100, 1169. (g) Mark, T. J; Chen, E. Y. Chem. ReV.
(
6
catalysts can be found (Figure 1). These novel approaches,
employing completely different chemistries, may not suffer the
same limitations of olefin polymerization.
2
000, 100, 1391. (h) Matyjaszewski, K.; Xia, J. Chem. ReV. 2001, 101,
(4) (a) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479. (b) Hillmyer,
M. Curr. Opin. Solid State Mater. Sci. 1999, 4, 559.
(5) Zhou, X.-Z.; Shea, K. J. Macromolecules 2001, 34, 3114.
(6) Penelle, J. Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Chem.) 1999, 40,
604.
2
921.
(
3) (a) Wagner, C. E.; Shea, K. J. Org. Lett. 2001, 3, 3063. (b) Busch, B. B.;
Paz, M. M.; Shea, K. J. Angew. Chem., Int. Ed. 1998, 37, 1391. (c) Shea,
K. J.; Lee, S. Y.; Busch, B. B. J. Org. Chem. 1998, 63, 5746.
3636
9
J. AM. CHEM. SOC. 2002, 124, 3636-3646
10.1021/ja017376c CCC: $22.00 © 2002 American Chemical Society

Polymerization of Dimethylsulfoxonium Methylide
A R T I C L E S
Scheme 2. Synthesis of Dimethylsulfoxonium Methylide (1)
Scheme 1. Products from the Reaction of Equimolar Amounts of
Ylide 1 and Borane 2 Following Oxidative Cleavage
11
We have been exploring nonolefin routes for the synthesis
7
of carbon backbone polymers. These routes involve repetitive
carbon-carbon bond forming reactions that extend the carbon
chain one carbon at a time. The parent material in this family
of hydrocarbon polymers is polymethylene. The history of this
produced by refluxing a heterogeneous mixture of trimethyl-
sulfoxonium chloride (7) and sodium hydride in THF or toluene
for 4 h. The inorganic salts are filtered to afford a homogeneous
solution of ylide 1 of approximately 0.6 molar. Ylide 1 is stable
and can be stored at -20 °C for greater than 3 weeks. The ylide
concentration is established by quenching an aliquot in water
and titrating with standardized HCl.
8
polymer dates back over 100 years. Bamberger and Tirchner
noted that long standing etheral solutions of diazomethane form
a white precipitate that was analyzed for the formula (CH2)x.
Substantial research has been directed toward the catalyzed
decomposition of diazomethane since this initial observation.
In preliminary studies, triethylborane was added to a solution
of 100 equiv of ylide 1 in THF at 40 °C. The solution became
cloudy, and a white precipitate formed within 10 min. Hydroly-
sis of one drop of the reaction mixture in water containing
phenolphthalein indicated complete consumption of ylide 1. The
organoborane was oxidized with basic hydrogen peroxide to
afford a quantitative yield of R-hydroxypolymethylene (8) (eq
6
9
High molecular weight polymethylene (3.3 × 10 D) is
produced by a number of Lewis acids,10 including copper salts
and BF3. Our efforts have been directed at developing new
methods for the synthesis of simple linear hydrocarbon poly-
mers. This study has led to the discovery of a new, living
polymerization of dimethylsulfoxonium methylide (1). The
chemistry of this reaction is described below.
1
). The NMR and IR spectroscopic properties of this product
were consistent with a linear, terminal alcohol. Interestingly,
analysis of the reaction product by gel permeation chromatog-
raphy (GPC) revealed a broad, polymodal distribution of
polymers. We believe that the turbidity that developed during
the reaction in THF was associated with the aggregation and
precipitation of extended polymethylene chains. Hydrocarbon
chains >30 carbons are not soluble in THF at any temperature.
It is likely that the precipitation of growing polymer chains
resulted in the broad distribution of molecular weights since
heterogeneous polymerizations exhibit varying activities of
catalytic centers brought about by growing polymer chains.13
Results and Discussion
The homologation of organoboranes with dimethylsulfoxo-
nium methylide (1) was first reported by Turfariello and co-
workers (Scheme 1).11 The reaction of equimolar amounts of
ylide 1 and tri-n-heptylborane (2) followed by oxidative cleavage
of the carbon-boron bonds produced three products, heptanol
(3) (69%), octanol (4) (25%), and small amounts of decanol
(5) (6%). The homologated products arise from methylene
insertion into the carbon-boron bond. The formation of a
doubly homologated product 5 was noteworthy and prompted
our investigation of this reaction using a large excess of ylide
(
1) 100 equiv of ylide, 40 °C
1. We speculated that multiple homologations with 1 could result
Et B
8 Et-(CH ) -OH
3
2 n
8
(2) H2O2, NaOH
in polymethylene formation.
Ylide 1 was synthesized according to Scheme 2. Trimethyl-
sulfoxonium iodide (6) was converted to trimethylsulfoxonium
chloride (7) via ion-exchange with benzyltributylammonium
(1)
In an effort to develop homogeneous polymerization condi-
1
2
chloride. The chloride 7 was recrystallized from MeOH.
14
tions, ylide 1 solutions in toluene were prepared. Linear
Alternatively, aqueous solutions of 6 can be passed through an
ion-exchange resin of Dowex-Cl. Both procedures convert the
readily available iodide salt 6 to the chloride salt 7. It is
advantageous to use the chloride salt 7 since the stability and
solubility are higher than those of the iodide 7. The ylide 1 is
polyethylene has significant solubility in toluene at elevated
temperatures. A typical polymerization consisted of injecting
2
1
7 µL of a 1 molar solution of triethylborane (27 µmol) into
4 mL of 0.58 molar ylide 1 (8.1 mmol, theoretical degree of
polymerization (DPth) ) 100) in toluene at 70 °C. The reaction
remained homogeneous. Sampling the reaction mixture after 5
min indicated complete consumption of ylide 1. The toluene
was removed in vacuo, and THF, hydrogen peroxide, and
(
(
(
7) Shea, K. J. Chem.-Eur. J. 2000, 6, 1113.
8) Bamberger, E.; Tirchner, F. Ber. Dtsch. Chem. Ges. 1900, 33, 956.
9) Kantor, S.; Osthoff, R. J. Am. Chem. Soc. 1953, 75, 1931.
(
(
10) Feltzin, J.; Restaino, A.; Mesrobian, R. J. Am. Chem. Soc. 1955, 77, 206.
11) (a) Tufariello, J.; Lee, L. J. Am. Chem. Soc. 1966, 88, 4757. (b) Tufariello,
J.; Wojtkowski, P.; Lee, L. J. Chem. Soc., Chem. Commun. 1967, 505. (c)
Tufariello, J.; Lee, L.; Wotjkowski, P. J. Am. Chem. Soc. 1967, 89, 6804.
12) Corey, E.; Chaykovsky, M. J. Am. Chem. Soc. 1965, 87, 1353.
(13) Floyd, S.; Heiskanen, T.; Taylor, T. W.; Mann, G. E.; Ray, W. H. J. Appl.
Polym. Sci. 1987, 33, 1021.
(14) Soderquist, J.; Najafi, M. J. Org. Chem. 1986, 51, 1330.
(
J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002 3637

A R T I C L E S
Busch et al.
Figure 3. GPC of R-hydroxy-ω-(p-methoxyphenyl) polymethylene (13)
shows a narrow, monodisperse distribution when prepared by oxidation with
trimethylamine-N-oxide (TAO).
Scheme 5. Synthesis of Polymethylene 13 Using
Tris-(4-methoxyphenylethyl) Borane (12)15
Figure 2. Superimposition of GPC traces for R-hydroxypolymethylene (9)
and (10).
Scheme 3. Synthesis of R-Hydroxypolymethylene 9 (DPth ) 100)
and 10 (DPth ) 200)
respondence between stoichiometry and molecular weight in
the preceeding examples is consistent with a rapid initiation
and the absence of termination reactions in the polymerization
of ylide 1.
In the GPC traces (Figure 2), a smaller peak at approximately
twice the molecular weight accounting for up to 5% of the total
area was occasionally observed. The origin of this peak is due
to trace quantities of adventitious oxygen during the oxidation
step with hydrogen peroxide. The details of this reaction will
be described later. Optimum conditions for oxidation were
carried out with trimethylamine-N-oxide dihydrate (TAO) in
toluene. This procedure does not require evaporation of the
Scheme 4. Triethylborane-Initiated Polyhomologation of Ylide 1
Produces an Intermediate 3-Arm Star Polymethylene 11 (Oxidation
Affords Linear R-Hydroxypolymethylene 8)
1
4
solvent or use of THF. On occasion, discrepancies between
the targeted and experimental degree of polymerization can arise
if the concentration or purity of the organoborane is not known
precisely. Because commercial supplies of organoboranes (i.e.,
Et3B) are often contaminated with substantial amounts of
boronic and borinic esters, freshly prepared solutions of tri-
alkylboranes are preferable for use as initiators. For example, a
solution of trialkylborane 12, prepared by hydroboration of
sodium hydroxide were added. The resulting polymer was
isolated by precipitation with acetonitrile and filtration to afford
R-hydroxypolymethylene (9) in 75% yield (Scheme 3).
4
-vinylanisole with BH3‚THF, was used to initiate polyhomolo-
15
gation (Scheme 5).
A representative polyhomologation consists of rapidly adding
220 µL of a 0.15 molar solution of organoborane 12 into 20
mL of 0.5 M solution of ylide 1 (300 equiv, DPth ) 100)
preheated to 70 °C (Scheme 5). The reaction remained
homogeneous, and ylide 1 was consumed within 10 min. The
solution was cooled, 6 equiv of trimethylamine-N-oxide dihy-
drate (TAO) was added, and the solution was heated to 70 °C
for 2 h (Scheme 5). The polymer was isolated by precipitation
with acetonitrile followed by filtration to afford R-hydroxy-ω-
The experiment described above was repeated with one-half
of the borane initiator. The reaction of 13.5 µL of a 1 molar
solution of triethylborane (13.5 µmol) and 14 mL of 0.58 molar
ylide 1 (8.1 mmol, DPth ) 200) was used to afford R-hydroxy-
polymethylene (10) in 78% yield (Scheme 3). GPC analysis
for both 9 (DPexp ) 89, Mn ) 1290, PDI ) 1.02) and 10 (DPexp
)
198, Mn ) 2820, PDI ) 1.02) revealed a narrow, monodis-
perse polymer distribution with an experimental molecular
weight in agreement with the calculated molar ratio of [ylide]/
(
8
)
4-methoxyphenyl) polymethylene (13) in yields ranging from
5 to 95%. A representative GPC of polymethylene 13 (DPexp
106, Mn ) 1639, PDI ) 1.01) shows a narrow, monomodal
distribution (Figure 3).
3
[Et3B] (Figure 2). The stoichiometry of the reaction between
ylide 1 (3n equiv) and triethylborane (1 equiv) is consistent with
the formation of an intermediate 3-arm star polymethylene (DP
)
3n) (Scheme 4). Oxidation affords 3 equiv of R-hydroxy-
(
15) Shea, K.; Walker, J.; Zhu, H.; Paz, M.; Greaves, J. J. Am. Chem. Soc.
polymethylene (9) and (10) with DP ) n. The strict cor-
1997, 119, 9049.
3638 J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002

Polymerization of Dimethylsulfoxonium Methylide
A R T I C L E S
Figure 5. 500 MHz 1H NMR (x: toluene-d8) of R-hydroxyl-ω-(p-
methoxyphenyl) polymethylene (13) (DPexp ) 397) produced from recrys-
tallized ylide 1 and trimethylamine-N-oxide showing an internal methyl
group (h) (0.2% methyl incorporation).
Figure 4. FDMS spectrum of R-hydroxyl-ω-(p-methoxyphenyl) polym-
ethylene (13) (Mn ) 552, DPexp ) 31, PDI ) 1.01) prepared from 90 molar
equiv of dimethylsulfoxonium methylide (1) and tris-(p-methoxyphenethyl)
borane (12). Inset shows an expanded scale revealing isotope patterns with
each main peak separated by 14 m/e.
phenyl) polymethylene (13) (Figure 5) includes a small doublet
at 0.91 ppm (J ) 6.6 Hz) corresponding to a secondary methyl
group located on the polymer backbone. The integration of the
doublet indicates one internal methyl group per 100 methylene
groups (1%). In some samples, as much as 1.5% of the
anomalous methyl group is observed. We attribute the origin
of the internal methyl group to ethylidine incorporation that
arises from a dimethylsulfoxonium ethylide impurity in ylide
a
Table 1. Experimental Degrees of Polymerization (DP) and
b
Polydispersities of R-Hydroxyl-ω-(p-methoxyphenyl)
Polymethylene 13
experimental DP
FDMS
polydispersity
entry
theoretical DP
NMR
GPC
FDMS
GPC
1. We have found that during synthesis of ylide 1, small amounts
1
2
3
4
5
6
7
8
23
30
30
40
40
70
140
228
25
31
35
43
44
1.02
1.01
1.03
1.03
1.02
of dimethylsulfoxonium ethylide (1.3%) byproduct are pro-
35
36
45
47
32
1.02
1
6
duced. On the assumption that ethylidine and methylene
1
7
39
43
75
149
226
1.01
1.03
1.01
1.03
1.04
incorporation occur at competitive rates, a small number of
ethylidine groups will be incorporated in the polymethylene
chain. Ylide 1 can be recrystallized at -50 °C from toluene to
produce a solution containing 0.2% dimethylsulfoxonium eth-
ylide. Polyhomologation with purified ylide 1 produced poly-
130
a
DP is the average number of repeat units based on the Mn. b Polydis-
1
methylene 13 (DP ) 397), whose H NMR spectrum (Figure
persity (PDI) was calculated from Mw/Mn.
5) displays 0.2% of the anomalous signal at 0.91 ppm. The linear
polymer contains fewer than two internal CH3’s per 1000
carbons.
A typical field desorption mass spectrometry (FDMS) spec-
trum for polymethylene 13 (DP ) 31, PDI ) 1.01) is shown in
Figure 4. The distribution consists of peaks separated by 14
amu. It is interesting to compare this spectrum with the mass
spectrum of polyethylene which has peak separations of 28 amu.
Mass spectrometry highlights the distinction between polym-
ethylene and polyethylene. Polymethylene samples contain
polymer chains of integral carbon numbers (n, n + 1, n + 2,
High Molecular Weight Polymethylene. When the poly-
homologation reaction is carried out at 90 °C in toluene,
polymethylene with a DP up to 1000 and low PDI may be
produced. Higher molecular weight polymethylene precipitates
during the polyhomologation under these conditions and results
in broader distributions (PDI > 1.5). To overcome this problem,
the polymerizations were performed in 1,2,4,5-tetrachloroben-
zene (TCB)/toluene. For example, rapid injection of small
amounts of triethylborane into solutions containing a large
excess of ylide 1 in TCB:toluene 2:1 at 120 °C results in rapid
consumption of ylide. The solution remains homogeneous
throughout the reaction. Following oxidation, high molecular
weight polymethylene is produced (Table 2). The control of
high molecular weight is dependent upon the purity of the
initiator and the ability to achieve high stoichiometric ratios
.
..), while polyethylene samples contain polymer chains of
alternating numbers (n, n + 2, n + 4, ...).
Molecular weight analyses of R-hydroxyl-ω-(p-methoxyphe-
1
nyl) polymethylene (13) were performed using H NMR, FDMS,
and GPC. The results are summarized in Table 1. The results
establish an excellent correlation between the theoretical and
observed molecular weights. Entries 2-3 and 4-5 illustrate the
reproducibility of polyhomologation.
Composition of Polymethylene. The polymerization of ylide
1
by trialkyl borane followed by oxidation is expected to produce
(16) A sample of ylide 1 in toluene quenched with aqueous HCl shows 1.3%
ethyldimethylsulfoxonium chloride relative to trimethylsulfoxonium
chloride.
perfectly linear hydroxy-terminated polymethylene. However,
a typical H NMR spectrum of R-hydroxyl-ω-(p-methoxy-
1
(17) Zhou, X.-Z.; Shea, K. J. J. Am. Chem. Soc. 2000, 122, 11515.
J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002 3639

A R T I C L E S
Busch et al.
Table 2. GPC Analysis of High Molecular Weight Polymethylene
Mechanistic Studies. By analogy with known 1,2-rearrange-
20
entry
MW
t
× 103
M
n
× 103
M
w
× 103
PDI
ments of alkylboranes, a plausible mechanism for the reaction
involves the addition of ylide 1 to the Lewis acidic trialkyl-
borane to form a zwitterionic complex. A subsequent 1,2-
migration of one of the three-alkyl groups would afford a
homologated borane. The migration is expected to occur
concurrently with expulsion of dimethyl sulfoxide (DMSO) (eq
2). An alternate mechanism involving rate-limiting decomposi-
tion of ylide 1 to form carbene may also be considered. In this
pathway, methylene insertion may occur through a zwitterionic
complex (eq 3). Carbene intermediates have been proposed in
the reaction of boranes with reactive diazoalkanes.21 However,
we have found that in the absence of Lewis acids, ylide 1 is
stable to temperatures up to 120 °C. Because the homologation
reaction occurs with finite rates at room temperature, it is more
likely, therefore, that the addition-migration mechanism (eq 2)
is operative.
b
b
b
1
2
3
4
14.1
21.2
14.1
21.2
50.0
100
19.6 (15.5 )
20.6 (17.4 )
1.05 (1.12 )
b
b
b
31.4 (27.0 )
33.6 (29.4 )
1.07 (1.09 )
21.4
30.5
62.9
23.7
36.2
92.1
1.11
1.19
a
5
1.47
b
b
1.08b
6
7
105
354
113
523
a
200
1.49
a
Et3B initiator contained substantial impurities from air oxidation.
Light-scattering detector.
b
Figure 6. 11B NMR of (a) tri-n-hexylborane (40 °C), (b) tri-n-hexylborane‚
ylide complex (-15 °C), and (c) trialkylboranes and DMSO product mixture
(40 °C) in toluene. The peak at 48 ppm is a boronic acid impurity (<2%).
with analytical precision. For very high molecular weights, this
is difficult to attain, although reproducibility and control of
relatiVe molecular weights are good (entries 1-4). The repro-
ducibility is established from entries 1-3 and 2-4 which repeat
molecular weight from separate experiments. However, dis-
crepancies between theoretical and observed molecular weights
are found. With commercial samples of triethylborane containing
quantities of boronic and borinic esters, broader, polymodal
distributions are obtained (entries 5 and 7). For polymers
produced from the same batch of ylide 1 with pure triethylbo-
rane, the “theoretical” incremental increase in molecular weight
of 1.5 is noted (1-2; 3-4). GPC analysis of these polymers
reveals a monomodal distribution.
11B NMR was used to acquire evidence for complex forma-
tion taking advantage of a significant chemical shift difference
between tricoordinate and tetracoordinate organoboron species
in noncoordinating solvents. For example, the range of chemical
2
2
shifts of simple trialkyl boranes is 80-90 ppm. Tetraalkyl
borate complexes, on the other hand, have chemical shifts in
2
2
the range of -15 to -20 ppm.
The 11B NMR of tri-n-hexylborane in toluene at 40 °C
exhibits a single resonance at 87.4 ppm (Figure 6). The solution
was cooled to -78 °C, and an equimolar amount of ylide 1 in
1
1
toluene was added. The B NMR of the solution ([R3B] ) 0.5
M, [ylide] ) 0.5 M) at -15 °C exhibits a single resonance (δ
The efficiency of the boron center in mediating the polym-
erization of ylide 1 can be evaluated from the data in entry 7.
The polymer arises from a tris-polymethylene borane with Mn
)
-13.4 ppm). Upon warming this mixture to 40 °C and waiting
1
1
6
for 10 min, the B spectrum was reacquired to reveal a single
>
1.0 × 10 . A Mn of 1.0 million for the star tris-polymethylene
4
resonance at δ ) 82.2 ppm.
borane represents approximately 7.8 × 10 turnovers per boron
11
The B NMR of the 1:1 mixture indicates complete formation
of the zwitterionic intermediate. No evidence was found for
uncomplexed tri-n-hexylborane. If one assumes that as much
as 1% of the uncomplexed tri-n-hexylborane could have escaped
atom. The reaction is complete in 10 min. This corresponds to
6
a turnover frequency of 6 × 10 g of polymethylene (mol
-
1
-1
boron)
h
at 120 °C. The turnover frequency for the boron
catalytic center is comparable to some of the more efficient
homogeneous ethylene polymerization catalysts, such as neutral
4
-1
detection, Keq > 2 × 10 M for the coordination of ylide 1 to
the borane. The zwitterionic complex is indefinitely stable at
-15 °C. 1,2-Migration was induced by warming to 40 °C. The
6
anilinotropone-Ni(II) (8.8 × 10 g of polyethylene (mol
-
1
-1
18
catalyst) h ) (80 °C, 200 psi ethylene), but less than the
homogeneous metallocene catalysts such as (4,4′,5,5′-tetram-
ethyl) bis-(fluorenylidene) (1,2-ethylidene) zirconium dichloride
(
20) Reviews: (a) Matteson, D. S. Tetrahedron 1998, 54, 10555. (b) Brown,
H. C.; Ramachandran, P. V. Pure Appl. Chem. 1994, 66, 201. (c) Negishi,
E.; Idacavage, M. J. Org. React. 1985, 33, 1. (d) Pelter, A. Chem. Soc.
ReV. 1982, 11, 191. (e) Suzuki, A. Acc. Chem. Res. 1982, 15, 178. (f)
Negishi, E. J. Organomet. Chem. 1976, 108, 281.
9
-1 -1
(
2.6 × 10 g of polyethylene (mol catalyst) h ) (60 °C, 145
19
psi ethylene).
(
21) Carbene mechanism: (a) Dorion, G.; Polchlopek, S.; Sheers, E. Angew.
Chem. 1964, 76, 495. Ionic mechanism: (b) Mucha, M.; Wunderlich, B.
J. Polym. Sci. 1974, 12, 1993.
(
18) Hicks, F.; Brookhart, M. Organometallics 2001, 20, 3217.
19) Alt, H. G.; K o¨ ppl, A. Chem. ReV. 2000, 100, 1205.
(
(22) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1988, 20, 61.
3
640 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002
9

Polymerization of Dimethylsulfoxonium Methylide
A R T I C L E S
Table 3. Kinetic Parameters from Arrhenius Plot
parameter
THF
toluene
-
1
Ea kcal mol
27.1 ( 1.5
26.5 ( 1.5
21.5 ( 5.2
20.1 ( 3.0
23.8 ( 1.4
23.2 ( 1.4
12.6 ( 4.7
19.5 ( 2.8
q
-1
∆
∆
∆
H kcal mol
S cal deg mol-1
q
-1
q
-1
G kcal mol (23 °C)
accumulated DMSO does not inhibit the rate of the polyho-
mologation reaction. Figure 7a shows that when ylide 1 is in
large excess, doubling the concentration of ylide 1 does not
change the rate of consumption. However, doubling the
concentration of triethylborane doubled the rate of consumption
of ylide 1. Under these pseudo first-order conditions, the reaction
is first order in organoborane and zero order in ylide 1. Similar
results were obtained in THF. These results are consistent with
the proposed two-step mechanism (eqs 4 and 5), with a rate-
limiting 1,2-migration of the ate complex. The rate expression
is d[product]/dt ) rate ) k2[R3B‚ylide]. Under the reaction
conditions where the ylide 1 concentration is in large excess, a
rapid equilibrium between alkyl borane and ylide 1 will lie far
toward the complex. Thus, the complex concentration will be
close to the initial alkyl borane concentration. The rate expres-
sion can be written as rate ) k2[R3B]0, which is consistent with
the kinetic study.
Figure 7. Kinetic study of the reaction of Et3B with ylide 1 in toluene. (a)
Graph of ylide vs time in toluene at 23 °C. (b) Graph of ln k vs 1/T for
toluene and THF.
data support a preequilibrium between borane and ylide that
strongly favors formation of a zwitterionic complex. This is
followed by a rate-limiting 1,2-migration with concomitant
expulsion of DMSO.
The Arrhenius activation parameters were determined from
the temperature dependence of the rate constants k over a
temperature range of 15-35 °C in toluene and in THF (Figure
The chemical shift and peak shape of the homologated
product differ slightly from those of tri-n-hexylborane. In the
presence of stoichiometric quantities of coordinating solvents
such as DMSO, the chemical shift of trialkyl boranes is shifted
slightly upfield. Furthermore, the 11B chemical shift of trieth-
ylborane in toluene with 1 equiv of DMSO exhibits a noticeable
temperature dependence (1.04 ppm/°C).23 The addition of ylide
to trihexylborane and subsequent warming produces a distribu-
7
b). Uncertainties in the derived activation energy parameters
were evaluated using literature procedures for estimating the
2
4
error propagation from estimates of the uncertainty in tem-
perature ((1 °C) and in the rate constant k. The uncertainty in
k was evaluated from a regression analysis (the method of least
2
5
squares). The results are summarized in Table 3.
At room temperature, the free energy of activation in toluene
and in THF is the same within experimental error. The narrow
temperature range over which the kinetic data was acquired (20
1
1
tion of homologated and unhomologated trialkylboranes. In
addition, 1 equiv of DMSO is also produced. These two factors
contribute to the slight difference in chemical shift and peak
shape between the starting trihexylborane (87.4 ppm) and the
homologated products (82.2 ppm).
°
C) results in a significant uncertainty in the derived activation
entropy. Despite this uncertainty, we believe differences in the
component enthalpy and entropy of activation in the two
solvents have mechanistic significance. The enthalpy of activa-
tion in THF is 3 kcal/mol higher than that in toluene, but the
Additional support for a rate-limiting 1,2-migration step was
obtained from kinetic studies. The rate of trialkylborane-
catalyzed consumption of ylide 1 was monitored by hydrolyzing
aliquots of the reaction mixture in water and titrating with
standardized HCl to the phenolphthalein endpoint. Triethylbo-
rane was reacted with excess ylide 1 (ylide:borane > 21) in
toluene or in THF. Plots of the consumption of ylide 1 versus
time in toluene are linear (Figure 7). This finding indicates that
-
1
-1
corresponding entropy of activation is 9 cal deg mol more
positive. These two factors cancel at 23 °C. The origin of the
effect can be understood in terms of differential solvation of
(
24) (a) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646. (b) Steigel, A.; Sauer, J.; Kleier, D. A.;
Binsch, G. J. Am. Chem. Soc. 1972, 94, 2770.
(
25) Skoog, D. A.; West, D. M.; Holler, F. J. Analytical Chemistry, An
th
(23) Wrackmeyer, B. J. Organomet. Chem. 1976, 117, 313.
Introduction, 5 ed.; Saunders College Publishing: Chicago, 1990; p 60.
J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002 3641

A R T I C L E S
Busch et al.
polymethylene (13). Figure 9a shows an expansion of the
+
spectrum at m/z 726 corresponding to the molecular ion [M]
+
+
for C50H94O2 at m/z 726. The [M + 1] and [M + 2] peaks
have relative intensities (57% and 16%, respectively) as expected
on the basis of the natural isotopic abundance (calculated )
1
-
00:57.1:16.6). In addition, there are significant peaks for [M
2] and [M - 4] ions with relative intensities of 43% and
+
+
1
1% at m/z 724 and 722, respectively. The FDMS spectra of
+
polyethylene commonly produce [M - 2] ions from loss of
H2 with intensities ranging from 10 to 20% relative to the [M]
+
ion dependent on the applied voltages and the molecular
2
8
+
weight. The [M - 4] ion has not been observed previously.
+
We propose that the anomalous intensities of the [M - 2] ion
arise from molecular ions from secondary products aldehyde-
terminated 15 and methyl-terminated polymethylene 16 (Scheme
+
6
). The [M - 4] ion arises from loss of H2 from either 15 or
1
6.
Figure 8. Field desorption mass spectrum (FDMS) of a linear R-hydroxyl-
ω-(p-methoxyphenyl) polymethylene 13 when the oxidation reaction was
carried out with basic hydrogen peroxide in THF. Inset shows an expansion
of isotope patterns with each main peak separated by 14 m/e.
From the high-resolution FMDS (Figure 9b), the mass-
doubled materials can be assigned to di(ω-(p-methoxyphenyl)
polymethylene) ether (17) or a mixture of 17 and R,ω-di(p-
methoxyphenyl) polymethylene (18) (Scheme 6). The isotope
pattern is consistent with the polymethylene ether 17 and
displays an [M - 2] ion which could arise from R,ω-di(p-
methoxyphenyl) polymethylene (18) or the loss of H2 from
the ground and transition states by toluene and THF. The rate-
limiting step involves the fragmentation of a zwitterionic
complex into two neutral molecules. Charge is annihilated in
the reaction. It is likely that the zwitterionic ground state elicits
the greatest differential enthalpy of solvation. In THF, the highly
polar ground state is more strongly solvated (stabilized) as
compared to that in toluene. In the transition state, charge
separation will be dissipated reducing the differential solvation
+
polymer 17.
Support for the presence of these products and their assign-
1
ments can be found in the corresponding H NMR (Figure 10).
The overlapping triplet at 0.89 ppm (J ) 6.0 Hz) is consistent
with a methyl-terminated polymethylene 16. The doublet at 0.91
ppm (J ) 6.6 Hz) is from the internal methyl group. The triplet
at 9.39 ppm (J ) 1.8 Hz) and doublet of triplets at 1.91 ppm (J
enthalpy between THF and toluene. The net effect is a higher
q
∆
H in THF. The compensating positive entropies of activation
result from solvent release in the transition state. In the more
strongly solvating THF, the annihilation of charge produces a
greater release of strongly coordinated solvent molecules than
in the weakly coordinating toluene. The net result is a more
positive entropy of activation in THF than in toluene. These
results are consistent with solvent effects on activation energies
of related charge annihilation reactions.2
)
7.4, 1.8 Hz) correspond to the aldehyde proton and the
adjacent methylene group in the aldehyde-terminated polym-
ethylene 15, respectively. No evidence for olefin protons could
be found. The overlapping small peak at 3.33 ppm may be
tentatively assigned to the methylene group adjacent to the
etheral oxygen in the polymethylene ether 17.
We propose that the origin of these minor products arises
from reaction of oxygen with tris-polymethylene borane. Fol-
lowing consumption of ylide 1, the intermediate tris-polymeth-
ylene borane 14 can react with trace quantities of adventitious
oxygen to produce a mixture of carbon and oxygen centered
6
Reaction of Tris-polymethylene Borane with Oxygen.
Routine processing of tris-polymethylene borane involved
concentration of toluene prior to addition of a THF solution of
basic hydrogen peroxide. These operations can expose the
organoborane intermediate to oxygen. Occasionally, a second
distribution amounting up to 5% of the total area is observed
in the GPC traces of R-hydroxylpolymethylene (9) and (10)
2
9
radicals 19, 20 (Scheme 6). Radicals generated in this way
have been used as a source of macromonomers which can
initiate free radical polymerization of other vinyl monomers for
3
0
(Figure 2) as well as FDMS of R-hydroxyl-ω-(p-methoxyphe-
the synthesis of copolymers. In the absence of added mono-
mers and at low O2 concentration, the radicals 19 and 20 can
undergo dimerization to produce a mixture of mass-doubled
polymethylene 17 and 18. Alternatively, radicals may undergo
disproportionation to form 15 and 16. The pathway to produce
olefin-terminated polymethylene is not observed and may not
be favored since the CdO bond is stronger than the CdC bond.
Additional support for the explanation of the O2 induced
radical byproducts can be found from the fact that the mass-
doubled distribution is eliminated when the intermediate tris-
nyl) polymethylene (13) (Figure 8). In the latter example, the
average molecular weight (Mn ) 1453, PDI ) 1.01) of the minor
distribution is approximately twice that of the major distribution
(Mn ) 725, PDI ) 1.02) of R-hydroxyl-ω-(p-methoxyphenyl)
polymethylene (13). The PDIs of both distributions are very
27
low and could be approximated by a Poisson distribution. The
exact mass from high-resolution FDMS confirms that the major
distribution is composed of R-hydroxyl-ω-(p-methoxyphenyl)
(
26) Reichardt, C. SolVents and SolVent Effects in Organic Chemistry, 2nd ed.;
VCH Verlagsgessellschaft: Weinheim, Fed. Rep. Ger., 1990; pp 136-
(28) (a) Heine, C. E.; Geddes, M. M. Org. Mass Spectrom. 1994, 29, 277. (b)
Evans, W. J.; DeCoster, D. M.; Greaves, J. J. Am. Soc. Mass Spectrom.
1996, 7, 1070.
(29) (a) Brown, C.; Midland, M. Tetrahedron 1987, 40, 4059. (b) Chung, T.
C.; Janvikul, W.; Lu, H. L. J. Am. Chem. Soc. 1996, 118, 705.
(30) (a) Chung, T. C.; Xu, G.; Lu, Y.; Hu, Y. Macromolecules, 2001, 34, 8040.
(b) Chung, T. C.; Xu, G. J. Am. Chem. Soc. 1999, 121, 6763.
1
47.
(
27) The calculated polydispersity of the minor distribution was 1.01. The
theoretical relationship between the major and the minor distribution is
related to the reaction mechanism that links them. The relationship is
considered in the Appendix. Both major and minor distributions are closely
approximated by a Poisson distribution (see Appendix).
3642 J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002

Polymerization of Dimethylsulfoxonium Methylide
A R T I C L E S
Figure 9. (a) Expansion for the molecular ion peak for C50H94O2 of polymethylene 13 at m/z 726 showing a mixture of three polymers: hydroxyl-
terminated 13 (DP ) 41), methyl-terminated 16 (DP ) 42), and aldehyde-terminated 15 (DP ) 41) polymethylene. (b) Expansion of the molecular ion peak
for C102H190O3 in the mass-doubled region showing a possible mixture of two polymers: R,ω-di(p-methoxyphenyl) polymethylene ether (17) (DP ) 84) and
di(ω-(p-methoxyphenyl) polymethylene) (18) (DP ) 85).
polymethylene borane is reacted directly with trimethylamine-
N-oxide dihydrate (TAO) after the ylide 1 is consumed. The
sample handling in the latter case does not require evaporation
of the solvent and introduction of THF, mitigating exposure of
the tris-organoborane to oxygen. Another possible source of
these byproducts is the alkali oxidation with hydrogen peroxide.
Alkane impurities from hydrolytic cleavage31 of boranes have
been reported as byproducts from oxidation with neutral
hydrogen peroxide.32 The TAO oxidation protocol avoids both
of these potential problems.
Ar. All other chemicals were used as received without further
purification. Solutions of borane dimethyl sulfide complex and trieth-
ylborane were obtained from Aldrich. The triethylborane solutions
indicated varying amounts of impurities. The borane dimethyl sulfide
was pure by NMR and titration.33 1H and C NMR spectra were
obtained using either Bruker Omega-500 MHz or General Electric GN-
13
5
00 MHz spectrometers at 500 and 125 MHz, respectively, and
1
1
calibrated with residual undeuterated toluene-d
8
and CDCl
3
. The
B
NMR at 160 MHz was calibrated with an external standard of BF
3
‚
OEt . GPC data were obtained using a Waters 150C Plus GPC using
2
O-xylene as the eluent at 100 °C at 1 mL/min. Samples for chroma-
tography were prepared as 0.5-0.6% solutions in O-xylene. Four
Ultrastyragel (5 µm particle size) were used in series: (500 Å × 2),
Conclusion
(
100 Å × 2). The GPC calibration curve was made with polyethylene
Triorganoboranes mediate the polymerization of dimethyl-
sulfoxonium methylide 1. One mole of DMSO is produced for
each mole of ylide consumed. The product of the polymerization
is a 3-arm star polymethylene borane. Oxidative cleavage of
the tris-star-polymethylene produces a hydroxyl-terminated
polymethylene with molecular weights up to 500 000 D. Typical
polydispersities are <1.1. The reaction involves association of
ylide 1 and trialkylborane to form a zwitterionic complex. The
standards from Polymer Laboratories and from Scientific Polymer
Products. High molecular weight polymethylene samples were analyzed
at Exxon-Mobil. The FDMS spectra were obtained under conditions
28b
previously described. Elemental analyses were performed at Atlanta
Microlab, Inc. IR was obtained on an Analect RFX-40 FTIR spectro-
photometer. Melting points were obtained on a Thomas-Hoover Unimelt
apparatus and are uncorrected.
All hydroboration and polyhomologations were performed in flame-
complex may be directly observed at <-15 °C (Keq > 2 ×
dried glassware under an atmosphere of N
handled under N . The intermediate tris-organoborane polymers are
air sensitive and were oxidized by briefly removing the septum to add
the solid TAO, and continuing the reaction under N . Oxidation with
/NaOH involved incautious exclusion of air during manipulations.
Dimethylsulfoxonium Chloride (7). A biphasic mixture of
CH Cl (325 mL) and H O (440 mL) containing trimethylsulfoxonium
2
. The borane initiators were
4
1
0 ). The activation energy Ea for rate-limiting 1,2-migration
2
was determined in THF (27.1 kcal/mol) and toluene (23.8 kcal/
2
mol). The reported boranes initiate the polymerization of ylide
6
2 2
H O
1
with a turnover frequency of 6 × 10 g of polymethylene
-
1
-1
(mol boron)
h
at 120 °C.
2
2
2
iodide 6 (42.8 g, 194.5 mmol, 1.0 equiv) and benzyltributylammonium
chloride (65.1 g, 208.7 mmol, 1.1 equiv) was vigorously stirred in a
flask protected from light for 17 h. The aqueous layer was separated,
washed with CH Cl (1 × 60 mL), and evaporated in vacuo. The white
Experimental Section
General Methods. Toluene and hexanes were distilled over CaH
under N . THF was passed through an activated alumina column under
2
2
2
2
solid was recrystallized from 95:5 MeOH:toluene, filtered, ground to
(
31) (a) Mikhailov, B. M.; Bezmenov, A. Y.; Vasilev, L. S.; Kiselev, V. Dokl.
Akad. Nauk SSSR 1964, 155, 141. (b) Mikhailov, B.; Aronovich, P. M.;
Kiselev, V. G. IzV. Akad. Nauk SSSR, Ser. Khim. 1968, 146. (c) Zweifel,
G.; Arzoumanian, H. J. Am. Chem. Soc. 1967, 89, 291.
a fine powder, and dried in a vacuum oven (50 °C, 15 mmHg) for
(33) QuantitatiVe Analysis of ActiVe Metals and Metal Hydrides Via Gas Buret;
(32) Bigley, D. B.; Payling, D. W. Chem. Commun. 1968, 16, 938.
Aldrich Technical Information Bulletin No. AL-123.
J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002 3643

A R T I C L E S
Busch et al.
Scheme 6. Possible Products from the Reaction of Oxygen with Tris-polymethylene Borane 14
2
2 h to yield a white powder (24.6 g, 98.4% yield). mp 220.2-221.8
and indicated ylide 1 had been consumed. The reaction was cooled to
room temperature, the septum to the reaction flask was removed to
add trimethylamine-N-oxide dihydrate (156 mg, 1.4 mmol), capped,
34
°C (lit. mp 222-223). IR (KBr): νmax 2968.2, 2885.3, 1411.7, 1342.0,
-
1
1
1
316.2, 1232.9, 1047.4, 961.8, 765.8 cm
.
H NMR (500 MHz,
1
3
DMSO-d
6
): δ 3.91 (s). C NMR (125 MHz, DMSO-d ): δ 38.8.
6
and heated at 60 °C for 2 h under N2. The reaction was cooled to room
Dimethylsulfoxonium Methylide (1). Sodium hydride (60% disper-
sion in oil, 3.40 g, 84.3 mmol) was washed with hexanes (3 × 20 mL)
under nitrogen. Final traces of solvent were removed in vacuo.
Powdered and dry trimethylsulfoxonium chloride (7) (8.34 g, 64.8
mmol) and toluene (75 mL) were transferred to the flask. The
heterogeneous reaction mixture was heated at reflux in anhydrous THF
3
temperature and precipitated with CH CN (200 mL). Filtration, washing
with CH CN (20 mL), acetone (20 mL), and hexane (20 mL), and
3
1
drying afforded a white solid (1.00 g, 100% yield). H NMR (500 MHz,
toluene-d
3H). GPC M
202O: C, 84.55; H, 14.33. Found: C, 84.57; H, 14.34.
Tris-(4-methoxyphenylethyl) Borane (12). A solution of BH
1.0 M in THF, 0.56 mL) was added over 5 min to a solution of
-vinylanisole (0.25 mL, 1.88 mmol) in THF (2.4 mL) at 0 °C. The
8
, 50 °C): 3.37 (t, J ) 6.4 Hz, 2H), 1.35 (s, 203H), 0.93 (m,
1
n
) 1437, M ) 1477, PDI ) 1.028. Anal. Calcd for
w
100
C H
or toluene until evolution of H had stopped (2-4 h). The contents
2
3
‚THF
were cooled to room temperature and filtered under nitrogen through
predried Celite 545 to afford a colorless solution of ylide 1 (0.76 M in
toluene, 88.0% yield). The solution was stored at -20 °C. An aliquot
(
4
reaction was allowed to warm to room temperature over 2 h. The
initiator (0.19 M in THF) was used immediately without further
2
of the solution (0.2 mL) was added to H O (5 mL) and titrated with
standardized HCl before use. Solutions of ylide 1 in toluene can be
recrystallized under nitrogen by cooling the solution to -50 °C,
decanting the supernatant from the colorless needles with a syringe,
and adding an equal volume of toluene.
purification. Oxidation of a small aliquot of the solution with H
and NaOH indicated a 94:6 ratio of expected regioisomers.
2 2
O
r-Hydroxy-ω-(4-Methoxyphenyl) Polymethylene (13). Tris-(4-
methoxyphenylethyl) borane (12) (0.24 M in THF, 0.75 mL, 0.15 mmol)
was rapidly injected via syringe under N into a solution of ylide 1
2
(0.58 M in toluene, 31 mL, 18 mmol) at 55 °C. After 7 min a drop of
the reaction was added to water containing phenolphthalein. The neutral
solution indicated ylide 1 was consumed. The reaction was cooled to
room temperature, toluene was removed in vacuo, THF (5 mL), NaOH
Optimized Conditions for Polyhomologation. r-Hydroxypolym-
ethylene. Borane‚SMe
was rapidly added via syringe to a solution of ylide 1 (0.68 M in toluene,
03.5 mL, 70.4 mmol) at 75 °C under N . After 10 min, a drop of the
reaction mixture was added to H O (3 mL) containing phenolphthalein
2
(1.0 M in CH
2
Cl
2
, 0.235 mL, 0.235 mmol)
1
2
2
(34) Braendstroem, A.; Lamm, B. Acta Chem. Scand., Ser. B 1974, 28, 590.
2 2
(6 M, 0.2 mL, 1.2 mmol), and H O (30%, 0.2 mL, 1.2 mmol) were
3
644 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002
9

Polymerization of Dimethylsulfoxonium Methylide
A R T I C L E S
1
Figure 10. 500 MHz H NMR of R-hydroxyl-ω-(p-methoxyphenyl) polymethylene (13) produced by oxidation with H2O2 and NaOH.
r-Hydroxypolymethylene (8) (High Molecular Weight). Ylide 1
(0.66 M in toluene, 10 mL, 6.6 mmol) was added to a melt of degassed
1
,2,4,5-tetrachlorobenzene (20 g) at 55 °C. The temperature was raised
to 125 °C. Triethylborane (0.01 M in hexanes, 31 µL, 0.31 µmol) was
rapidly added via syringe, and the reaction was stirred under N . After
0 min, a drop of the reaction mixture was added to water containing
phenolphthalein and indicated that ylide 1 had been consumed. Sodium
hydroxide (1 M, 1 mL, 5 mmol) and H (30%, 1 mL, 5 mmol) were
2
1
2 2
O
added, and the solution was stirred for 2 h. The solution was
concentrated in vacuo (25 mmHg) at 150 °C, cooled to room
temperature, and CH CN (50 mL) was added. The precipitate was
3
filtered and dried in vacuo to afford a white solid (87 mg, 89% yield).
1
H NMR (500 MHz, toluene-d
8
, 80 °C): δ 3.35 (t, J ) 6.4 Hz), 1.40-
, 80
1
°
M
.25 (m), 0.91 (d, J ) 6.6 Hz). 13C NMR (125 MHz, toluene-d
8
C): δ 30.1. IR (KBr): νmax 3480, 2919, 2850 cm-1. GPC analysis:
3
3
w
) 104 × 10 , M
n
) 100 × 10 , PDI ) 1.04. T
m
) 126.8 °C. Anal.
Calcd for C5500H11000O: C, 85.60; H, 14.38. Found: C, 85.68; H, 14.47.
Low-Temperature 11B NMR Studies. Tri-n-hexylborane. Borane‚
SMe (2.0 M in CH Cl , 10.3 mL, 20.6 mmol) was added over 5 min
to a solution of 1-hexene (8.0 mL, 63.6 mmol) in CH Cl (20 mL) at
°C. The solution was allowed to warm to room temperature over 2
2
2
2
2
2
0
h. The mixture was purified by removing all volatiles in vacuo (0.01
mmHg) at 50 °C for 2 h. The material was kept in a glovebox and
1
Figure 11. Simulation of distribution of R-hydroxyl-ω-(p-methoxyphenyl)
polymethylene 13 with 2% of dimer.
used immediately. H (500 MHz, C
D
6
): δ 1.49 (m, 2H), 1.33 (m,
6
13
6
3
8
H), 1.26 (m, 2H), 0.93 (t, J ) 7.0 Hz, 3H). C (125 MHz, C
6
D
6
): δ
3.6, 32.7, 29.1 (br), 25.3, 23.5, 14.8. 11B (160 MHz, C
D , 40 °C): δ
6
6
7.4. IR (NaCl): νmax 2940, 1458, 1344 cm-
1
.
added at 0 °C, and stirred at room temperature for 4 h in a flask vented
with a syringe needle. Addition of CH
3
CN (40 mL), filtration of the
Tri-n-hexylborane‚ylide Complex. An NMR tube containing tri-
precipitate, and drying in vacuo afforded a white solid (290 mg, 92%
n-hexylborane (94 mg, 0.35 mmol) was cooled to -78 °C. A solution
of ylide 1 (0.605 M in toluene, 0.58 mL, 0.35 mmol) at -20 °C was
1
yield). H NMR (500 MHz, toluene-d
8
, 50 °C): δ 6.76 (d, 2H, J ) 8.4
1
1
Hz), 3.40 (s, 3H), 3.35 (t, 2H, J ) 5.8 Hz), 2.49 (t, 2H, J ) 7.6 Hz),
added. The mixture was shaken and kept below -40 °C. B NMR
(160 MHz, toluene, -15 °C): δ -13.4. The mixture was warmed for
1
3
1
.40-1.25 (s, 100H), 0.91 (m, 3H), DPexp ) 50. C NMR (125 MHz,
toluene-d , 50 °C): δ 129.4, 114.5, 62.9, 55.0, 37.8, 35.6, 33.5, 32.1,
0.7, 30.5, 30.3, 30.2, 30.1, 27.7. IR (KBr): υmax 3448, 2919, 2850
1
0 min at 40 °C. 11B NMR (160 MHz, toluene, 40 °C): δ 82.2.
8
3
Kinetics. General for THF or Toluene. A solution of ylide 1 (50
-
1
cm . FDMS analysis: M
) 703, PDI ) 1.01. Anal. Calcd for C64
Found: C, 83.63; H, 13.34.
p
) 768.6, PDI ) 1.02. GPC: M
n
) 687,
mL) in either THF or toluene was stirred at the desired temperature
((0.1 °C) in a water bath. A measured amount of Et B (1 M in THF)
was rapidly injected, and the reaction was stirred under N . Aliquots
M
w
122
H O
2
: C, 83.33; H, 13.32.
3
2
J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002 3645

A R T I C L E S
Busch et al.
(
(
5.00 mL) were withdrawn at different time intervals, added to H
50 mL), and titrated with 0.1 N HCl to the phenolphthalein endpoint.
2
O
possible reactions that form (i + j)-mer are shown in eqs 7-12.
Ri+j-1 + R f P
(7)
(8)
1
i+j
Acknowledgment. We thank the Chemistry Division of the
Ri+j-2 + R f P
2
i+j
National Science Foundation for financial support of this work
and Dr. John Greaves for performing FDMS analysis and
interpretation.
.
.
. . . . . . . . . . .
(9)
Ri+j-m + R f P
(10)
m
i+j
Appendix
. . . . . . . . . . .
R + R f Pi+j
(11)
(12)
The distribution function of polymer chains in a living
polymerization is given by a Poisson distribution.35 The poly-
homologation of ylide 1 with R3B produces a polymer distribu-
tion that closely approaches this function. The reaction of this
product with O2 will give a distribution of radicals. What is the
expected distribution of dimers? The following analysis was
performed to establish the nature of the new distribution. The
distribution of the polymeric radicals generated from the reaction
is a Poisson distribution (eq 6)
1
i+j-1
The number fraction of (i + j)-mer can then be expressed by
3
6
eq 13.
i+j-1
i+j-m-1e
-ν
m-1e-ν
ν
ν
Xi+j
)
*
)
∑
m)1
(i + j - m - 1)! (m - 1)!
(2ν)i+j-2e-2ν
i+j-1
i+j-2e
-2ν
ν
m-1
i+j-2
C
*
)
(13)
∑
m)1
(i + j - 2)! (i + j - 2)!
i-1e-ν
i - 1)!
The form of the expression Xi+j is still a Poisson function. This
indicates that the random combination of a Poisson distribution
of radicals should produce a Poisson distribution of dimers at
twice the mass with a very narrow molecular weight distribution
with PDI values close to unity (PDI ) 1.01 with DP ) 85). A
plot of the calculated distributions with 2% of dimers is shown
in Figure 11.
ν
(
Xi )
(6)
where Xi is the number fraction of i-mer radical (denoted by
Ri), and ν is the number average chain length.
To obtain an expression of Xi+j we need to write down all
the ways in which (i + j)-mer (denoted by P(i+j)) can be formed
and then sum the number fractions of these processes. The
JA017376C
(
36) Allcock, H. R.; Lampe, F. W. Contemporary Polymer Chemistry; Prentice-
(35) Flory, P. J. J. Am. Chem. Soc. 1940, 62, 1561.
Hall: New Jersey, 1981; pp 286-289.
3646 J. AM. CHEM. SOC.
9
VOL. 124, NO. 14, 2002