Formation of chelated counteranions using lewis acidic diboranes: Relevance to isobutene polymerization

Article abstract of DOI:10.1021/om700672q

The reactions of chelating diboranes with PhCMe₂Cl and related initiators were studied by variabletemperature NMR spectroscopy. Although thermally stable ion-pairs featuring weakly coodinating anions (WCA) are formed, isobutene polymerization is complicated by the tendency of these WCA to act as hindered bases toward Bronsted acidic chain ends.

Full text of DOI:10.1021/om700672q

Organometallics 2007, 26, 5667-5679
5667
Formation of Chelated Counteranions Using Lewis Acidic
Diboranes: Relevance to Isobutene Polymerization
Jianfang Chai,§ Stewart P. Lewis,§,† Scott Collins,*,§ Timo J. J. Sciarone,
Lee D. Henderson, Preston A. Chase, Geoffrey J. Irvine, Warren E. Piers,*,
Mark R. J. Elsegood,|,‡ and William Clegg|
Department of Polymer Science, The UniVersity of Akron, Akron, Ohio 44325-3909, Department of
Chemistry, UniVersity of Calgary, Calgary, Alberta, Canada T2N 1N4, and School of Natural Sciences
(Chemistry), Newcastle UniVersity, Newcastle upon Tyne, NE1 7RU, U.K.
ReceiVed July 4, 2007
The reactions of chelating diboranes with PhCMe2Cl and related initiators were studied by variable-
temperature NMR spectroscopy. Although thermally stable ion-pairs featuring weakly coodinating anions
(WCA) are formed, isobutene polymerization is complicated by the tendency of these WCA to act as
hindered bases toward Brønsted acidic chain ends.
Scheme 1
Introduction
Protic or electrophilic initiators that give rise to weakly
coordinating anions (WCA),1 partnered with propagating car-
bocations in isobutene polymerization,2 is a topic of significant
interest in the context of butyl rubber manufacture at elevated
temperature.3 A variety of initiator systems are effective in neat
monomer, hydrocarbon, or more polar media,4 and generally a
rather weak temperature dependence is observed for the MW
of poly(isobutene) or butyl rubber formed. These polymeriza-
tions are uncontrolled and with MW values in several cases
comparable to those that can be achieved using γ-ray initiation
involving “free” carbocations.5
Several years ago we communicated that chelating diborane
1 (Scheme 1)6 was an effective co-initiator of isobutene
polymerization, initiated by cumyl chloride (CumCl) in the
presence of the sterically hindered pyridine 2,6-di-tert-butyl-
4-methylpyridine (DtBMP).7 Variable-temperature NMR spec-
troscopic experiments established that CumCl and diborane 1
formed an unstable ion-pair, 3a, in CD2Cl2 solution at low
temperature whose structure was inferred from spectroscopic
data on the stable ion-pair 4a formed from triphenylmethyl
chloride and diborane 1 (eq 1)6,7 as well as literature data
reported for the cumyl cation.8
The polymerization experiments were conducted on a vacuum
line using monomer and solvents purified by vacuum transfer
(4) (a) Tse, C. K. W.; Penciu, A.; McInenly, P. J.; Kumar, K. R.; Drewitt,
M. J.; Baird, M. C. Eur. Polym. J. 2004, 40, 2653-2657. (b) Tse, C. K.
W.; Kumar, K. R.; Drewitt, M. J.; Baird, M. C. Macromol. Chem. Phys.
2004, 205, 1439-1444. (c) Cordoneanu, A.; Baird, M. C. Macromolecules
2004, 37, 6744-6747. (d) McInenly, P. J.; Drewitt, M. J.; Baird, M. C.
Macromol. Chem. Phys. 2004, 205, 1707-1712. (e) Kumar, K. R.; Penciu,
A.; Drewitt, M. J.; Baird, M. C. J. Organomet. Chem. 2004, 689, 2900-
2904. (f) Garratt, S.; Carr, A. G.; Langstein, G.; Bochmann, M. Macro-
molecules 2003, 36, 4276-4287. (g) Kumar, K. R.; Hall, C.; Penciu, A.;
Drewitt, M. J.; McInenly, P. J.; Baird, M. C. J. Polym. Sci., Part A: Polym.
Chem. 2002, 40, 3302-3311. (h) Baird, M. C. Chem. ReV. 2000, 100, 1471-
1478. (i) Jacob, S.; Pi, Z.; Kennedy, J. P. In Ionic Polymerizations and
Related Processes; Puskas, J. E., Ed.; Nato Science Series, Ser. E.;
Kluwer: Dordrecht, The Netherlands, 1999; Vol. 359, pp 1-12. (j) Jacob,
S.; Pi, Z.; Kennedy, J. P. Polym. Mater. Sci. Eng. 1999, 80, 495. (k) Jacob,
S.; Pi, Z.; Kennedy, J. P. Polym. Bull. 1998, 41, 503-510. (l) Carr, A. G.;
Dawson, D. M.; Bochmann, M. Macromolecules 1998, 31, 2035-2040.
(m) Carr, A. G.; Dawson, D. M.; Bochmann, M. Macromol. Rapid Commun.
1998, 19, 205-207. (n) Barsan, F.; Karan, A. R.; Parent, M. A.; Baird, M.
C. Macromolecules 1998, 31, 8439-8447. (o) Shaffer, T. D. ACS Symp.
Ser. 1997, 665, 96-105. (p) Shaffer, T. D. ACS Symp. Ser. 1997, 665,
1-11. (q) Shaffer, T. D.; Ashbaugh, J. R. J. Polym. Sci., Part A: Polym.
Chem. 1997, 35, 329-344. (r) Shaffer, T. D.; Ashbaugh, J. R. Polym. Prepr.
1996, 37, 339-40. (s) Bochmann, M.; Dawson, D. M. Angew. Chem., Int.
Ed. Engl. 1996, 35, 2226-2228.
* Corresponding authors. E-mail: collins@uakron.edu.
§ The University of Akron.
† Current address: Stewart’s Technologies LLC, 3154 State St., Suite
2300, Blacksburg, VA 24060, www.stewartstechnologies.com.
University of Calgary.
| Newcastle University.
‡ Current address: Chemistry Department, Loughborough University,
Loughborough, Leicestershire, LE11 3TU, UK.
(1) (a) Reed, C. A. Chem. Commun. 2005, 1669-1677. (b) Reed, C. A.
Acc. Chem. Res. 1998, 31, 133-139. (c) Lupinetti, A. J.; Strauss, S. H.
Chemtracts 1998, 11, 565-595. (d) Strauss, S. H. Chem. ReV. 1993, 93,
927-42.
(2) (a) Cationic Polymerization: Fundamentals and Applications; Faust,
R., Shaffer, T. D., Eds.; ACS Symp. Ser. 665; American Chemical
Society: Washington, DC, 1997; 219 pp. (b) Cationic Polymerizations:
Mechanisms, Synthesis, and Applications; Matyjaszewski, K., Ed.; Dekker
M Press: New York: 1996; 768 pp. (c) Anionic Polymerization to Cationic
Polymerization. In Encyclopedia of Polymer Science and Engineering, Vol.
2, 2nd ed.; Mark, H. F., Ed.; John Wiley and Sons Inc.: New York, 1985;
814 pp. (d) Kennedy, J. P.; Marechal, E. Carbocationic Polymerization;
John Wiley and Sons: New York, 1982; 510 pp.
(5) (a) Kennedy, J. P.; Rengachary, S. AdV. Polym. Sci. 1974, 14, 2-48.
(b) Kennedy, J. P.; Shinkawa, A; Williams, F. J. Polym. Sci. 1971, 9 (A-
1), 1551-1561. (c) Kennedy, J. P.; Milliman, G. E. AdV. Chem. Ser. 1969,
91, 287-305. (d) Kennedy, J. P.; Thomas, R. M. AdV. Chem. Ser. 1962,
34, 111. (e) Kennedy, J. P.; Thomas, R. M. J. Polym. Sci. 1961, 49, 189.
(f) Thomas, R. M.; Sparks, W. J.; Frolich, P. K.; Otto, M.; Mueller-Cunradi,
M. J. Am. Chem. Soc. 1940, 62, 276-280.
(3) Kresge, E. N.; Schatz, R. H.; Wang, H.-C. Isobutylene Polymers. In
Encyclopedia of Polymer Science and Engineering, 2nd ed., Vol. 8; Mark,
H. F., Bikales, N. M., Overberger, C. G., Menges, G., Eds.; Wiley-
Interscience: New York, 1987; pp 423-448.
10.1021/om700672q CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/13/2007

5668 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
methyl ether, or azide (eq 1).6d The µ-Cl ion-pair 4a7 and µ-OMe
ion-pair 4c6a have already been reported in the literature and
have been fully characterized by X-ray crystallography. Here
we compare and contrast the structures of ion-pairs 4e and 4f,
both featuring the µ-N3 anion. Spectroscopic and analytical data
for µ-Cl ion-pair 4b and ion-pairs 4d-f are included in the
Experimental Section. In particular, the 19F NMR spectroscopic
data are diagnostic for these counteranions (Table 1) and assisted
with the characterization of unstable ion-pairs 3a-f to be
described later.
from tri-n-octylaluminum where background impurity levels
were ∼1 ppm expressed as H2O.9 Despite these precautions, a
large excess of DtBMP (ca. 1-10 equiv with respect to diborane
1) had to be used to suppress competing protic initiation in the
absence of CumCl, while polymerizations conducted in the
presence of CumCl and excess DtBMP were characterized by
low conversions (20-40%) but with initiator efficiencies (Ieff)
consistent with chain transfer (i.e., Ieff ≈ 100-300%). A
reduction in the amount of DtBMP led to increases in conversion
(to as high as 95%) and an increase in Ieff (>300%), consistent
with more effective chain transfer. In the absence of CumCl
and DtBMP, polymerizations were quantitative and characterized
by Ieff > 1000%.9
These polymerization reactions are uncontrolled, given the
weakly coordinating nature of the counteranions present. As
will be reported in detail elsewhere, the chain transfer processes
involved in these polymerizations do not involve chain transfer
to monomer on the basis of the shallow temperature dependence
of MW.10
With a view to developing initiator systems that would allow
controlled isobutene polymerizations, we considered the use of
diborane 1 or its more Lewis acidic analogue diborole 2 (Scheme
1)11 with either cumyl methyl ether (CumOMe) or cumyl azide
(CumN3), which would generate more coordinating counteran-
ions and thus initiator systems that might feature reversible
termination as required for a living polymerization.12
In this paper we describe the reactions of diboranes 1 and 2
with these initiators to form inter alia unstable ion-pairs 3a-f,
the characterization of stable ion-pairs 4a-f formed from these
compounds and the corresponding Ph3C-X (eq 1), the X-ray
crystal structures of stable µ-N3 ion-pairs 4e and 4f, and
oligomerization studies using the model monomer 2,4,4-
trimethyl-1-pentene (TMP) and the various initiators in conjunc-
tion with diborane 1.
The structures of compounds 4e and 4f are depicted in Figure
1, while selected crystallographic and refinement data and
selected bond lengths and angles appear in Tables 2 and 3,
respectively. In contrast to the structure of ion-pair 4a, which
features a weak, electrostatic interaction between the trityl
carbocation and the µ-Cl anion,7 there is limited interaction of
this cation with the µ-azido counteranion in these structures. In
particular, the closest contact between the central trityl atom
C31 and the anion in the structure of ion-pair 4f is in excess of
4 Å and involves F29, while for ion-pair 4e an analogous contact
with F30 is 3.428(6) Å; this is still well outside the sum of the
van der Waals radii for C and F. In both structures the trityl
cation has, as expected, a planar configuration for the central C
atom (rms displacement 0.001 Å in each case for the four C
atoms), which has short C-C bonds (1.436-1.450 Å), and a
propeller conformation, the dihedral angles between the phenyl
groups and the central C4 plane being in the range 26.7-41.6°.
In the structure of ion-pair 4f the five-membered ring,
containing the two B atoms, one N atom of the N3 anion, and
C1 and C7 of the perfluorophenylene backbone, is slightly
puckered with a dihedral angle between the mean planes defined
by B1-C1-C6-B2 (rms displacement 0.007 Å) and B1-N1-
B2 of 5.5(1)°. A similar distortion in the case of ion-pair 4e is
observed where the analogous angle is 3.2(1)°. However, in the
latter case the B1-C1-C6-B2 unit is not planar (rms displace-
ment 0.037 Å), with B1 and B2 located significantly above and
below the mean plane, in contrast to the situation in ion-pair
4f.
In the structure of ion-pair 4e, the B-N bond lengths of
1.630(3) and 1.627(3) Å are essentially equivalent, while those
observed in the structure of ion-pair 4f are different at 1.643(3)
and 1.681(3) Å and significantly longer on average [1.662(3)
Å] than those observed in ion-pair 4e. In addition, the endocyclic
angle at N1 is significantly more acute in ion-pair 4f [115.0-
(2)°] than in ion-pair 4e [117.5(2)°], largely as a result of the
longer B-N distances in the former structure.
The C7-B1-C18 and C19-B2-C30 angles in ion-pair 4f
are small, with values of 97.9(2)° and 98.0(2)°, as a consequence
of the strained borole ring, while the angles N1-B1-C1 and
N1-B2-C6 are 96.8(1)° and 96.6(1)°, respectively. In contrast,
in the structure of ion-pair 4e, the corresponding angles within
the central five-membered ring are similar at 95.9(2)° and 95.9-
(2)°, while the exocyclic C19-B2-C25 and C7-B1-C13
angles are much more obtuse at 111.5(2)° and 113.2(2)°,
respectively. In essence, the B atoms in ion-pair 4e can easily
rehybridize so as to allow closer approach of the azide ion in
contrast to the structurally less responsive framework present
in ion-pair 4f.
Results and Discussion
Characterization of Stable Ion-Pairs 4a-f. Thermally
stable, and thus isolable, ion-pairs 4a-f are cleanly formed by
reaction of these diboranes with the corresponding trityl chloride,
(6) (a) Henderson, L. D.; Piers, W. E.; Irvine, G. J.; McDonald, R.
Organometallics 2002, 21, 340-345. (b) Williams, V. C.; Irvine, G. J.;
Piers, W. E.; Li, Z.; Collins, S.; Clegg, W.; Elsegood, M. R. J.; Marder, T.
B. Organometallics 2000, 19, 1619-1621. (c) Williams, V. C.; Piers, W.
E.; Clegg, W.; Elsegood, M. R. J.; Collins, S.; Marder, T. B. J. Am. Chem.
Soc. 1999, 121, 3244-3245.
(7) Lewis, S. P.; Taylor, N. J.; Piers, W. E.; Collins, S. J. Am. Chem.
Soc. 2003, 125, 14686-87.
(8) (a) Matyjaszewski, K.; Sigwalt, P. Macromolecules 1987, 20, 2679-
2689. (b) Laube, T.; Olah, G. A.; Bau, R. J. Am. Chem. Soc. 1997, 119,
3087-3092.
(9) Lewis, S. P. Ph.D. Thesis, The Univ. of Akron, Akron, OH, 2004,
299 pp. From: Diss. Abstr. Int. 2004, 65, 770; Chem. Abstr. 143:173195.
(10) Chai, J.; Lewis, S. P.; Collins, S. Manuscript in preparation.
(11) Chase, P. A.; Henderson, L. D.; Piers, W. E.; Parvez, M.; Clegg,
W.; Elsegood, M. R. J. Organometallics 2006, 25, 349-357.
(12) (a) Nuyken, O.; Vierle, M. Des. Monomers Polym. 2005, 8, 91-
105. (b) Kwon, Y.; Faust, R. AdV. Polym. Sci. 2004, 167, 107-135. (c)
Kennedy, J. P. Makromol. Chem., Macromol. Symp. 1990, 32, 119-29.
The metrical parameters associated with the bridging azide
ion in both structures are fairly similar. As expected N1-N2 is
significantly longer than N2-N3 in both structures, although
the difference is much more pronounced in ion-pair 4e [1.251-
(2) vs 1.120(2) Å] than in ion-pair 4f [1.199(2) vs 1.130(2) Å].
The central N atom in both structures is essentially sp-hybridized

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5669
Table 1. 19F Chemical Shifts and Assignments for Chelated Counteranions and Their Degradation Productsa
a Recorded in CD2Cl2 solution at 282 MHz and 25 °C unless otherwise noted. b19F NMR (CDCl3, 300 K, 282 MHz).
with bond angles of 179.3(2)° and 175.8(2)° in ion-pairs 4e and
4f, respectively.
amount of the hindered pyridine, DtBMP, present (entries 3-5).
On the other hand, the MW of the polymer formed was
uniformly lower and the initiator efficiencies (Ieff) higher,
consistent with more effective chain transfer and/or increased
initiation efficiency. As Ieff is greater than 100% (which is
expected if chain transfer is effective), the actual efficiency of
initiation cannot be directly discerned from these data.
Polymerizations initiated by CumN3 and diborane 1, in the
presence of excess or even reduced quantities of DtBMP, were
characterized by lower conversions in hydrocarbon media
compared to CumCl (Table 4, entries 6-8). Initiator efficiencies
were considerably reduced from those seen using CumCl,
suggesting reduced rates of chain transfer (which seems
unlikely) or less efficient initiation. Even in more polar media
such as CH2Cl2 or mixtures with hexane, conversions were low
The most significant difference between these two structures
lies in the more exposed nature of the azide ion in ion-pair 4f
versus 4e. Space-filling models show that both N2 and N3 are
clearly exposed in ion-pair 4f, while only the latter atom is
somewhat unprotected by the B(C6F5)2 rings in ion-pair 4e. In
particular, the twisting of these rings with respect to one another
in ion-pair 4e provides additional steric protection for the azide
ion that is not possible for diborole 2.
Isobutene Polymerization Using Cumyl Initiators and
Diborane 1 or 2. In comparison to results previously obtained
using CumCl and diborane 1 (e.g., Table 4, entries 1 and 2)7
isobutene polymerization using diborole 2 and this initiator
featured comparable conversions that are dependent on the

5670 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
Figure 1. Structures of the ion-pairs 4e (left) and 4f (right), with 30% probability displacement ellipsoids and selected atomic labels
depicted. The solvent molecules have been omitted.
Table 2. Selected Crystallographic and Refinement Data for Ion-Pairs 4e and 4f
4e
4f
chem form
[C19H15][C30B2F24N3]‚
CH2Cl2
[C19H15][C30B2F20N3]‚
CH2Cl2
fw
1208.2
1132.2
T
160 K
160 K
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/n
monoclinic
C2/c
9.5052(8)
24.039(2)
20.8556(17)
99.004(2)
4706.6(7)
4
37.975(4)
10.9235(11)
21.671(2)
91.987(2)
8984.5(15)
8
â (deg)
V (Å3)
Z
no. of data collected
no. of unique data, Rint
no. of refined params
R (F, F2 >2σ)
34 796
9233, 0.0312
768
0.0401
0.1126
37 471
10 539, 0.0380
694
0.0417
0.1097
R
w (F2, all data)
GOF (F2)
1.030
1.006
max., min. electron
0.65, -0.33
0.61, -0.55
density (e Å-3
)
(entries 9 and 10 vs 6), and surprisingly, addition of a solution
of µ-N3 ion pair 3e (Vide infra) prepared in CH2Cl2 at low
temperature to a mixture of DtBMP and isobutene in hexane
resulted in the lowest conversion (entries 11, 12).
(Vide supra), while the structure of ion-pair 3b was inferred by
the simple six-line pattern observed in the 19F NMR spectrum
of this mixture (Figure 2b, Table 1) along with the characteristic
resonances of the cumyl cation (Figure 2a).
Finally, even though CumOMe reacts with diborane 1 to form
the expected µ-OMe ion-pair 3c in polar media (Vide infra), no
polymer is formed from these two compounds in hexane and
only small quantities form in CH2Cl2 using preformed ion-pair
3c (entries 13-15). In view of the low conversions encountered
using diborane 1 and the variable-temperature NMR studies
involving either 1 or 2 and these cumyl initiators (to be described
next), isobutene polymerization using diborole 2 and either
CumOMe or CumN3 was not investigated.
As reported elsewhere, ion-pair 3a is unstable above -40
°C and decomposes cleanly to form indan 5, diborane 1, and
HCl (Scheme 2). In the case of ion-pair 3b, decomposition does
not rapidly occur until ∼0 °C (Figure 2). However, in addition
to indan 5 and diborole 2, the stable indanyl ion-pair 6 is
produced; this carbocation has been reported to form on
ionization of CumCl using SbF5 at sufficiently high tempera-
ture.13 Since benzene was also produced during the formation
of 6, the more Lewis acidic diborole 2 is capable of activating
HCl for ipso-substitution on indan 5 (or that the more thermally
stable ion-pair 3b is also effective for this process). The amount
of benzene formed (Figure 2) corresponds to only one-third of
the total amount of indanyl cation 6 generated. Electrophilic
Reaction of Cumyl Chloride (CumCl) with Diborane 1
or 2. We examined the reactions of these initiators, as well as
CumCl, with each diborane by variable-temperature 1H and 19
F
NMR spectroscopy in CD2Cl2 solution. In the case of CumCl
and either diborane, formation of µ-Cl ion-pairs 3a and 3b
occurs cleanly at low temperature. The structure of ion-pair 3a
was confirmed by comparison to that of stable trityl salt 4a
(13) Matyjaszewski, K.; Sigwalt, P. Macromolecules 1987, 20, 2679-
2689.

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5671
Table 3. Selected Bond Lengths and Angles for Ion-Pairs 4e
and 4f
compound 4e
compound 4f
Bond Lengths (Å)
B1-N1
B1-C1
B1-C7
B1-C13
B2-N1
B2-C6
B2-C19
B2-C25
N1-N2
N2-N3
1.630(3)
1.611(3)
B1-N1
B1-C1
B1-C7
B1-C18
B2-N1
B2-C6
B2-C19
B2-C30
N1-N2
N2-N3
1.643(3)
1.614(3)
1.630(3)
1.637(3)
1.680(3)
1.595(3)
1.629(3)
1.624(3)
1.130(2)
1.199(2)
1.643(3)
1.639(3)
1.627(3)
1.617(3)
1.654(3)
1.634(3)
1.251(2)
1.120(2)
Bond Angles (deg)
N1-B1-C1
N1-B1-C7
N1-B1-C13
C1-B1-C7
C1-B1-C13
C7-B1-C13
N1-B2-C6
N1-B2-C19
N1-B2-C25
C6-B2-C19
C6-B2-C25
C19-B2-C25
B1-N1-B2
B1-N1-N2
B2-N1-N2
N1-N2-N3
95.86(15)
113.27(16)
106.00(16)
107.48(16)
119.92(17)
113.17(17)
95.91(15)
113.28(16)
107.25(16)
108.53(16)
119.56(16)
111.48(16)
117.49(15)
120.81(16)
120.90(16)
179.3(2)
N1-B1-C1
N1-B1-C7
N1-B1-C18
C1-B1-C7
C1-B1-C18
C7-B1-C18
N1-B2-C6
N1-B2-C19
N1-B2-C30
C6-B2-C19
C6-B2-C30
C19-B2-C30
B1-N1-B2
B1-N1-N2
B2-N1-N2
N1-N2-N3
96.76(14)
114.28(16)
111.77(16)
116.97(17)
120.14(16)
97.90(15)
96.63(14)
106.41(14)
109.71(15)
124.36(17)
120.88(16)
97.96(15)
115.01(15)
123.31(16)
121.61(15)
175.82(19)
Table 4. Polymerization of Isobutene Using CumX Initiators
and Diborane 1 or 2a
[DtBMP]
(mM)
Mh w
yield
Ieff
(%)
Figure 2. (a) 1H NMR spectra of ion-pair 3b formed from diborole
2 and CumCl in CD2Cl2 at -20 °C (top spectrum). Signals due to
the cumyl cation of ion-pair 3b are labeled in the top spectrum,
while those due to indan 5 are labeled in the top inset and those of
indanyl cation 6 are labeled in the bottom spectrum, recorded at
25 °C. TFX ) tetrafluoro-p-xylene added as an internal standard.
(b) 19F NMR spectra of ion-pair 3b formed from diborole 2 and
CumCl in CD2Cl2 at -20 °C (top spectrum). Signals due to ion-
pair 3b are labeled (see Table 1 for labeling scheme), while those
due to diborole 2 are labeled analogously in the bottom spectrum
recorded at 25 °C. TFX ) tetrafluoro-p-xylene added as an internal
standard.
entry diborane CumX
(kg/mol)) PDI (%)
1
2
1
1
2
2
2
1
1
1
1
1
1
1
1
1
1
Cl
Cl
20.0
2.0
20.0
10.0
2.0
20.0
10.0
2.0
20.0
20.0
20.0
20.0
20.0
20.0
20.0
361
236
80
1.72
1.74
1.55
1.63
1.72
1.58
1.82
2.20
1.50
1.86
2.30
2.08
42
67
37
60
87
11
22
51
17
15
8
156
384
552
1091
739
82
152
129
70
3
Cl
4
Cl
69
5
Cl
156
158
206
667
275
339
261
185
6
N3
7
N3
8
N3
9b
10c
11d
12d
13
14f
15f
N3
N3
N3
N3
OMe
OMe
OMe
63
53
63
7
e
3
5
Scheme 2
75
139
1.52
3.82
52
110
a Stock solutions of DtBMP, diborane 1 or 2 (final concentration ) 2.0
mM), and CumX (final concentration ) 0.2 mM) in toluene were added in
that order to an isobutene solution (2.75 M in hexane) at -78 °C unless
b
otherwise noted. Reactions were quenched with MeOH after 1 h. Poly-
c
merization in 60:40 v/v hexane/CH2Cl2 solution. Polymerization in CH2Cl2
d
solution. A solution of diborane 1 and CumN3 in CH2Cl2 was prepared at
-78 °C and then added to DtBMP, and isobutene in hexane at that
e
f
temperature. No polymer formed. A solution of diborane 1 and CumOMe
in CH2Cl2 was prepared at -78 °C and then added to DtBMP, and isobutene
in CH2Cl2 at that temperature.
aromatic substitution on indan 5 by ion-pair 3b would also
provide ion-pair 6 and 2,2-diphenylpropane. An extra Me signal
is seen at 1.67 ppm (nearly co-incident with one of the Me
signals due to indan 5), which is in agreement with the chemical
shift reported for this material, and the total amount formed
corresponds to roughly the remaining two-thirds of ion-pair 6
produced.
are much more exposed (Vide supra), and so the chelated
counteranion can function more effectively in chain transfer
processes. Alternately, since indanyl cation 6 is produced only
using diborole 2, it is possible that the combination of HCl and
diborole 2 is much more competent for reinitiation of new chains
in apolar media compared with diborane 1.
Given the higher thermal stability of ion-pair 3b, it seems
likely that the reduced MW seen using diborole 2 and CumCl
in isobutene polymerization is partly a consequence of more
efficient ionization and thus initiation. On the other hand,
chelated ion-pairs derived from 2 feature bridging anions that
Reactions with Cumyl Methyl Ether (CumOMe). In the
case of CumOMe and excess diborane 1, ionization is observed
to form the expected µ-OMe ion-pair 3c. The structure of this
ion-pair is inferred from the spectroscopic data of the corre-
sponding stable trityl ion-pair 4c (Vide supra). As with µ-Cl

5672 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
Scheme 3
ion-pair 3a, µ-OMe ion-pair 3c is unstable in solution, and some
decomposition is evident even at -60 °C. The ion-pair
decomposes to form indan 5 and MeOH as an unobserved
byproduct. As reported elsewhere, diborane 1 is unstable in the
presence of substoichiometric amounts of MeOH, forming
borinic ester 7 and borane 8;14 essentially identical chemistry
is observed in the case of CumOMe (Scheme 3).
While this instability could explain the low conversions
observed in isobutene polymerizations, it should be borne in
mind that the polymerization experiments were conducted well
below the temperature at which this process is rapid (and at
lower concentrations of both initiator and diborane 1). On the
other hand, it is very likely that, after addition of one or
several isobutene units to ion-pair 3c, the resulting ion-pairs
are much less stable toward a similar degradation reaction, even
at low temperature, and borinic ester 7 and/or borane 8 are
insufficiently Lewis acidic to reinitiate polymerization of
isobutene.
-133 is due to two F nuclei which are probably accidentally
equivalent)]. This is because in the solid state15 and in solution
a strong, dative interaction between the BOMe group and the
adjacent borole moiety exists; when coupled with hindered
rotation of the biphenyl moiety and/or slow inversion at O, this
molecule is asymmetric.
We believe that MeOH adduct 9 forms via coordination of
CumOMe to the exo-side of diborole 2, which is sufficiently
Lewis acidic to form an unstable ion-pair; the ion-pair eliminates
R-Me-Sty to form adduct 9 (Scheme 3). R-Me-Sty is in turn
trapped by the cumyl cation (or in general protons) to form
indan 5 or higher oligomers of this type. The borinic ester 10
could form either directly from MeOH adduct 9 or indirectly
from ion-pair 3d, and in the latter case by protonation of the
counteranion by cumyl cation to form an (unobserved) endo-
MeOH adduct. It is evident from the VT NMR spectra depicted
in Figure 3b that the latter process is faster than the former
since exo-MeOH adduct 9 persists in solution at temperatures
as high as -20 °C, while ion-pair 3d is largely consumed at
this temperature. In view of this additional complexity, and the
fact that very little ion-pair 3d was produced at low temperature,
the use of diborole 2 as an initiator with CumOMe in isobutene
polymerization was not even studied, especially in view of the
low conversions already obtained with diborane 1 (Table 4).
Different chemistry was observed in the case of diborole 2
and CumOMe. The expected ion-pair 3d is formed, as verified
by comparison to stable ion-pair 4d (Vide supra); however, this
species is present only in small amounts (Figure 3a). The major
species present are diborole 2 along with a compound 9,
assigned as the exo-MeOH adduct of diborane 2 (Scheme 3).
This is based on the 12-line 19F NMR spectrum in solution at
low temperature (see Figure 3a and Table 1) similar to that
observed for the characterized mono-THF adduct,14 as well as
Reactions with Cumyl Azide (CumN3). The reactions of
diborane 1 and diborole 2 with CumN3 proved to be quite
interesting. As shown in Figure 4a reaction of diborane 1 with
CumN3 at -80 °C leads to a more complicated 1H NMR
spectrum but a simple five-line pattern in the corresponding
19F NMR spectrum. Ion-pair 3e, featuring the µ-N3 anion, is
definitely present (0.61 equiv), as verified by comparison to its
stable analogue 4e, but in addition to indan 5 (0.19 equiv)
another product 11a (0.20 equiv) is present with signals at δ
10.64 (br t, 1H) 7.6 (m, 3H), 7.2 (m, 2H), 2.85 (s, 3H), and
2.60 (s, 3H). This material corresponds to the iminium salt of
N-phenylacetone imine, as revealed by generation of an
analogous salt from an authentic sample of this imine and
Brookhart’s acid16 (see Supporting Information).
1
a doublet at δ 3.65 (JHH ) 3.9 Hz) in the H NMR spectrum
corresponding to 3H and a doublet of quartets at δ 6.53 (dq,
JHF ) 18.7 Hz, JHH ) 3.9 Hz) integrating to 1H (Figure 3b).
Also, significant quantities of indan 5 are present at low
temperature in addition to higher oligomers of R-methylstyrene
(R-Me-Sty). In particular, the presence of eight methyl signals
at high field, along with four AB spin systems, indicates the
formation of an indan bearing an additional cumyl group
resulting from trimerization of R-Me-Sty and subsequent
cyclization.
On warming above -60 °C, both ion-pair 3d and MeOH
adduct 9 decompose (at different temperature) to form indan 5
(from decomposition of 3d or acid-catalyzed dimerization of
R-Me-Sty) and the novel borinic ester 10, which forms from
both compounds 3d and 9; this ester results from proton-
mediated B-C cleavage of one of the borole rings in 2.
Borinic ester 10 has been independently prepared from
diborole 2 and stoichiometric amounts of MeOH and has been
fully characterized.14b,15 A characteristic feature of compound
10 is that 19 of the 20 F nuclei are chemical shift inequivalent
at room temperature [Figure 3a and Table 1 (the signal at δ
Iminium salt 11a is formed by protonation of this imine by,
for example, ion-pair 3e, where the imine is formed by
competing Schmidt rearrangement of CumN3, a process that is
known to be catalyzed by Lewis acids, including organobo-
ranes.17 We thus suspect that the low yields of polymer formed
using this initiator result from competitive ionization (which is
(15) Sciarone, T.; Henderson, L. D.; Lewis, S. P.; Collins, S.; Piers, W.
E. Manuscript in preparation.
(16) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920-3922.
(17) Desai, P.; Schildknegt, K.; Agrios, K. A.; Mossman, C.; Milligan,
G. L.; Aube, J. J. Am. Chem. Soc. 2000, 122, 7226-7232, and references
therein.
(14) (a) Lewis, S. P.; Henderson, L. D.; Chander, B. D.; Parvez, M.;
Piers, W. E.; Collins, S. J. Am. Chem. Soc. 2005, 127, 46-47. (b)
Henderson, L. D. Ph.D. Thesis, The University of Calgary, 2005.

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5673
1
Figure 4. (a) 19F NMR spectra of a mixture of diborole 2 and
CumOMe in CD2Cl2. Signals due to ion-pair 3d are indicated with
asterisks (top spectrum, -60 °C), while those due to diborole 2
are indicated with daggers (for chemical shifts and assignments
see Table 1). Signals due to MeOH adduct 9 are shaded in light
gray (see Table 1 for chemical shifts and tentative assignments),
while those due to borinic ester 10 formed at higher temperature
(bottom spectrum, 25 °C) are shaded in dark gray (see Table 1 for
chemical shifts and couplings). (b) Variable-temperature 1H NMR
spectra of a mixture of diborole 2 and CumOMe in CD2Cl2. Signals
due to MeOH adduct 9 are indicated in the inset spectra, and those
due to borinic ester 10 are indicated in the bottom spectrum.
Figure 3. (a) Variable-temperature H NMR spectra of ion-pair
3c formed from diborane 1 and CumOMe in CD2Cl2. Signals due
to the cumyl cation of ion-pair 3c are labeled in the top spectrum.
The signal due to the µ-OMe group of the anion is nearly coincident
with the -CMe2 moiety of the cation at low temperature but is
resolved at higher temperature (see middle spectrum). The Me group
of borinic ester 7 and the o-H of borane 8 are labeled in the bottom
spectrum. (b) Variable-temperature 19F NMR spectra of ion-pair
3c formed from diborane 1 and CumOMe in CD2Cl2. Signals due
to ion-pair 3c are labeled in the top spectrum (see Table 1 for
labeling scheme), while those due to diborane 1 are labeled
analogously. Signals due to borinic ester 7 [(C6F5)2BOMe] and
borane 8 [(C6F5)2B-(o-H)C6F4] are labeled in light gray (see Table
1 for labeling scheme) and dark gray (see Table 1 for labeling
scheme), respectively, in the bottom spectrum. TFX ) tetrafluoro-
p-xylene added as an internal standard.
iminium salt 11a also was generated. This result implies that
ionization of CumN3 by diborane 1 must be reVersible such
that any CumN3 generated undergoes competing, though ir-
reversible rearrangement to imine. This is the first clear
indication of reversible ionization with these diboranes and is
probably due to the linear and more exposed nature of the azide
ion in these compounds (Vide supra).
Hydrazoic acid is expected to be produced during decomposi-
tion of ion-pair 3e by analogy with the reactions of diborane 1
with CumCl; in this case, it is evident from Figure 4 that the
indanyl cation 6, partnered with the µ-N3 anion, and benzene
are also produced at elevated temperature and that this ion-pair
is stable at RT. The ultimate products resulting from this reaction
are a mixture of indan 5 (0.22 equiv), iminium salt 11a (0.43
equiv), and ion pair 6 (0.35 equiv).
stoichiometric in diborane and favored in a polar solvent) versus
rearrangement (which is catalytic in diborane and less affected
by solvent polarity). It is clear any of this unhindered imine
generated in situ would terminate both initiating and propagating
ion-pairs at rapid rates.5
Also, the iminium salt 11a that is formed represents a source
of common ions; as we have recently shown, even in polar
media with stable carbocations partnered with WCA, excess
common ions significantly suppress the rate at which these ion-
pairs undergo electrophilic addition reactions.18 Therefore, in
hydrocarbon (or even polar) media, the presence of variable
quantities of common ion will have a negative effect on the
rate of polymerization.
Similar chemistry was also observed in the case of CumN3
and diborole 2, although rearrangement to form iminium salt
11b was much more prominent compared to ionization to form
ion-pair 3f. The less hindered nature of this diborole will
facilitate binding of CumN3 to the exo-side, and the resulting
On warming a mixture of ion-pair 3e and iminium salt 11a
above -60 °C, indan 5 formed, but surprisingly additional
(18) Chai, J.; Lewis, S. P.; Kennedy, J. P.; Collins, S. Macromolecules,
published online Sep 20, 2007 http://dx.doi.org/10.1021/ma0711137.

5674 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
Figure 5. (a) Variable-temperature 19F NMR spectra of a mixture
of diborane 1 and CumN3 in CD2Cl2. Signals due to ion-pair 3e,
iminium salt 11a, and indanyl ion-pair 6 (which are coincident;
see Table 1 for shifts and assignments) are labeled in the top
spectrum, while those due to diborane 1 are indicated with asterisks
in the bottom spectrum. (b) Variable-temperature 1H NMR spectra
of a mixture of diborane 1 and CumN3 in CD2Cl2. Signals due to
ion-pair 3e, iminium salt 11a, and indanyl ion-pair 6 are labeled in
the top, middle, and bottom spectra, respectively.
Figure 6. (a) Variable-temperature 19F NMR spectra of a mixture
of diborole 2 and CumN3 in CD2Cl2. Signals due to ion-pair 3f
and iminium salt 11b (which are coincident; see Table 1 for
assignments) are labeled in the top and bottom spectra, while the
remaining signals in the latter spectrum are due to the degradation
product. (b) Variable-temperature 1H NMR spectra of a mixture of
diborole 2 and CumN3 in CD2Cl2. Signals due to ion-pair 3f and
iminium salt 11b are labeled in the top spectrum.
adduct could be more prone to rearrangement than ionization.
In contrast, unhindered donors such as CH3CN bind to the
interior of diborane 1, and this could facilitate direct ionization
in the case of CumN3. Also, ionization could be favored by
coordination of diborane to the terminal N of CumN3, whereas
rearrangement is facilitated by coordination to the internal N,
a process that would be favored for a less-hindered Lewis acid.
On warming above -60 °C, more indan 5 and iminium salt
11b were produced, but in addition degradation of diborole 2
was observed. In particular, a compound with a 16-line 19F NMR
spectrum is formed at the expense of diborole 2 on warming to
room temperature. An identical species was formed by treating
a mixture of diborole 2 with HN3 (generated in situ from [n-
Bu4N][N3] and CF3SO3H in CD2Cl2) but was accompanied by
extensive degradation. Evidently, this species forms from the
reaction of HN3 (liberated when forming indan 5) and diborole
2. Unfortunately, none of the routes investigated provided
material that could be readily purified, so the identity of this
degradation product is unknown. [It is interesting to note that
attempts to generate this degradation product by protonation of
the µ-N3 salt derived from diborole 2 and [nBu4N][N3] were
unsuccessful. This salt is inert toward anhydrous HCl in CD2-
Cl2 solution, while use of CF3SO3H resulted in degradation but
not to the same product.]
The above studies are instructive with respect to how
chelating diboranes react with cumyl initiators differing in the
nature of the ionizable group as well as the substituents on
boron. In essence, diborane 1 reacts to give the highest
proportion of chelated ion-pair 3, an effect that is largely
independent of anion, despite the higher kinetic and thermo-
dynamic Lewis acidity of diborole 2.11 Evidently, initial
coordination and ionization is highly sensitive to steric effects
in these diboranes, and the cleanliness, or even the course of
this reaction, is largely dependent on this issue.
The higher Lewis acidity of diborole 2, combined with the
tendency of donors to coordinate to the exo-side of this
compound, generally manifests itself in terms of ionization to
form unobserved (and unchelated) ion-pairs, which rapidly
degrade even at low temperature. Conversely, the chelated ion-
pairs that do form from 2 (generally in smaller quantities) appear

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5675
Scheme 4
to be more stable toward degradation than those formed from
1. In general, for sterically hindered CumX initiators, there is
no advantage to the use of diborole 2 and distinct disadvantages
considering the regioselectivity of initial initiator binding and
ionization.
Reactions of CumCl, CumOMe, and CumN3 with 2,4,4-
Trimethylpentene (TMP) in the Presence of Diborane 1 and
DtBMP. As a model for the polymerization experiments
summarized earlier, we decided to investigate the products
formed during oligomerization of TMP under conditions that
mirrored our experiments. 2,4,4-Trimethyl-1-pentene is known
to be an accurate model for reactions occurring in isobutene
polymerization,19 but the nature of the end groups is more
readily identified due to facile chain transfer reactions that limit
the degree of polymerization.19,20
The oligomerization of TMP (28 equiv) in the presence of
diborane 1 proceeds rapidly in CH2Cl2 or hydrocarbon solution
at low temperature to give a complex mixture of oligomeric
materials. GC-MS analysis of the crude product mixture
indicates formation of TMP-derived dimers (all five isomers19)
and much smaller amounts of higher oligomers. These higher
oligomers (trimers with m/z ) 336 can be detected by GC-
MS) are much less volatile than the dimer, and thus their relative
amounts are not accurately represented by GC analysis. The
1H NMR spectrum of the nonvolatile material, which corre-
sponds to ca. 50 wt % of the TMP added, shows multiple, broad,
and overlapping olefinic resonances largely consistent with
internal unsaturation with Xn ≈ 4.7 for oligomerizations
conducted at -78 °C. Complex mixtures of this type are not
uncommon when using very strong Lewis acids and uncontrolled
protic initiation, although we do note that the degree of
polymerization of the involatile material is quite high in
comparison to conventional Lewis acids.19,20
Scheme 5
When CumCl, CumN3, or CumOMe was used as initiator
under similar conditions (i.e., 1.0 equiv with respect to diborane
1), in the presence of the hindered pyridine DtBMP (0.24 equiv),
TMP oligomers were also formed and the dimer represents the
major volatile component in all cases. In general these product
mixtures were extremely complex (see Supporting Information
for representative GC-MS). Unlike the polymerization experi-
ments involving isobutene and these initiators, conversion of
TMP was quite high (>65% based on the amount of nonvolatile
material recovered) given the low ratio of monomer to initiator
in these experiments.
19F NMR spectra of the crude mixtures prior to chromatog-
raphy were consistent with the presence of chelated counter-
anions corresponding to 3a (X ) Cl), 3c (X ) OMe), and 3e
(X ) N3) being present (see Supporting Information). However,
it was unclear what the countercations were (presumably stable
oxonium acids [(MeOH)nH][1(µ-X)];14 these reactions were all
quenched with excess MeOH). In the case of CumCl there was
also evidence of anion degradation, since borinic ester 7 and
the MeOH adduct of borane 8 were detected following a MeOH
quench.
After separation of diborane 1 and its degradation products
by filtration through basic alumina, FT-IR spectroscopy of the
crude mixture formed from CumN3 failed to reveal the presence
of azide end groups. Substances bearing a cumyl group, which
were readily detected by TLC due to their quenching of
fluorescence under UV light, were partially separated from the
higher oligomers formed by preparative TLC and were identified
1
by a combination of H NMR spectroscopy and GC-MS.
As expected, indan 1419f is formed in variable amounts from
all three initiators and results from addition of cumyl cation to
TMP followed by cyclization (Scheme 5). In addition, we were
able to partially purify ring-alkylated indans 15 and 16, whose
identity was confirmed by GC-MS and 1H NMR spectroscopy.
These compounds form via electrophilic aromatic substitution
on indan 14 by either the 2,4,4-trimethylpentyl or the tert-butyl
cation. The latter cation can be formed by â-cleavage of the
former.3 [It is likely that this process, which results in
concomitant isobutene formation, is responsible for the higher
degree of oligomerization of TMP through copolymerization
with isobutene.] While only two isomers of tert-butylated indan
15 were detected, at least four isomers of indan 16 with m/z
values corresponding to 342 were present in some of these
mixtures. The two major isomers present had a simple AMX
(19) (a) Buchmann, W.; Desmazieres, B.; Morizur, J.-P.; Nguyen, H.
A.; Cheradame, H. Macromolecules 2000, 33, 660-677. (b) Buchmann,
W.; Desmazieres, B.; Morizur, J.-P.; Nguyen, H. A.; Cheradame, H.
Macromolecules 1998, 31, 220-228. (c) Coca, S.; Faust, R. Macromolecules
1997, 30, 649-651. (d) Schuetz, H.; Radeglia, R.; Heublein, G. Acta Polym.
1985, 36, 415-17. (e) Hasegawa, H.; Higashimura, T. J. Appl. Polym. Sci.
1982, 27, 171-81. (f) Nguyen A. H.; Kennedy, J. P. Polym. Bull. 1981, 6,
55-60.
(20) (a) Kaszas, G.; Puskas, J. E.; Kennedy, J. P.; Hager, W. G. J. Polym.
Sci., Part A: Polym. Chem. 1991, 29, 427-35. (b) Ivan, B.; Kennedy, J. P
J. Polym. Sci., Part A: Polym. Chem. 1990, 28, 89-104. (c) Cheradame,
H.; Habimana, J.; Rousset, E.; Chen, F. J. Macromolecules 1994, 27, 631.
(d) Rajabalitabar, B.; Nguyen, H. A.; Cheradame, H.; Chen, F. J. Eur. Polym.
J. 1995, 31, 73. (e) Rajabalitabar, B.; Nguyen, H. A.; Cheradame, H.; Chen,
F. J. Eur. Polym. J. 1995, 31, 297. (f) Rajabalitabar, B.; Nguyen, H. A.;
Cheradame, H. Makromol. Chem. Phys. 1995, 196, 3597. (g) Rajabalitabar,
B.; Nguyen, H. A.; Cheradame, H. Macromolecules 1996, 29, 514.

5676 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
Scheme 6
classical (and sterically unhindered) Lewis acids and these types
of initiators.19,20 However, the use of cumyl ethers as initiators
in living isobutene polymerization does not result in formation
of polymers with OR end groups (only 3° Cl are detected).21 In
these cases either the initiator or the end OR groups are
converted by excess Lewis acid into the corresponding chlorides,
a reaction that is not possible in the case of diborane 1. It is
also a little surprising that analogous rearrangements of CumN3
or related initiators were not seen in earlier work involving
classical Lewis acids and isobutene oligomerization;20c-f perhaps
this competing process accounts for the observation that, with
some Lewis acids, cumylation was efficient, but end-capping
by azide ion was not.
Finally, our results to date indicate a strong propensity for
these ion-pairs to undergo extensive chain transfer reactions in
isobutene polymerization or TMP oligomerization. In the
absence of DtBMP, it is clear from model studies involving
ion-pairs 3 that this transfer process involves these sterically
hindered, though weakly coordinating anions, acting as bases
toward the propagating chain end, rather than nucleophiles as
required for a controlled cationic polymerization.
spin system for the aromatic protons (i.e., dd, J ) 8, 2 Hz, 1H,
br d J ) 2 Hz, 1H; d, J ) 8 Hz, 1H), consistent with the
structure invoked for indan 16; the other two isomers detected
by GC-MS could result from addition of cumyl cation to the
exo (or possibly rearranged) dimer of TMP (both of these
compounds were among the major oligomers present19), fol-
lowed by cyclization (eq 2).
Conclusions
Although diborane 1 and diborole 2 are highly Lewis acidic
and irreversibly ionize cumyl-based initiators in polar media,
this reaction (both its rate and outcome) is highly dependent
on the initial binding of CumX to these hindered diboranes. In
general, diborane 1 is much more chemoselective in its reactions
with CumX initiators for ion-pair formation and so is better
suited to isobutene polymerization employing these compounds.
Unfortunately, the chelating anions that form are sterically
hindered, the resulting ion-pairs are contact ion-pairs in apolar
media, and thus polymerizations involving isobutene appear
dominated by counteranion-mediated chain transfer (or even
termination) reactions in a manner that appears strongly
correlated with the basicity of the bridging anion.
Controlled living polymerization of isobutene requires rapid
and reversible ionization of the 3° alkyl halide (or pseudohalide)
end group, coupled with efficient sequestration of acidic protons
by DtBMP or related additives.12 With CumN3 reversible
ionization is observed, but competing Schmidt rearrangement
leads to initiator (and probably chain-end) decomposition.
Therefore, future work will focus on the use of related initiators
that cannot undergo Lewis acid-mediated rearrangement.19 Also,
indirect evidence suggests that even strong Brønsted acids
formed during chain transfer can effectively reinitiate chain
growth in concert with these diboranes, even in the presence of
hindered bases such DtBMP. This result is quite unexpected
on the basis of work with classical Lewis acids and will be the
subject of future study.10
Other than these discrete compounds, it would appear that
the balance of the oligo-TMP present (the major nonvolatile
component) lacks cumyl end groups and thus is formed via chain
transfer. The relative amounts of the various products (i.e., 14-
16 vs oligo-TMP) were sensitive to the nature of CumX, with
CumCl giving the lowest amounts of the indanyl compounds
relative to TMP oligomers, and CumOMe the most. Evidently,
cumylation of TMP involving ion-pair 3 is occurring, but this
process is less efficient compared to chain transfer following,
for example, cyclization.
In an attempt to hinder chain transfer, the reaction of CumN3
and TMP in the presence of diborane 1 was also examined at
increased levels of DtBMP (1.0 equiv). The net result of this
approach was a drastic decrease in total conversion of TMP
(ca. 6-7%) with a change in product distribution. Here the
major products formed are a mixture of three alkenes, 17a-c,
arising from cumylation of TMP followed by elimination
(Scheme 6) and indan 5 (arising from analogous trapping of
R-Me-Sty by the cumyl cation).
It is surprising to find internal alkenes being formed in the
presence of DtBMP, which is usually highly selective for exo-
olefin formation. Although the exo-olefin 17a was the major
isomer formed, it is likely that the µ-N3 counteranion in ion-
pair 13 is sufficiently basic to reVersibly produce the various
products (Scheme 6), and it is the resulting adduct of hydrazoic
acid and diborane 1 that then reacts irreversibly with DtBMP.
[We cannot exclude the participation of adventitious water in
this deprotonation process followed by irreversible proton
transfer to DtBMP.]
Taken together, these experiments are consistent with (inef-
ficient) cationogenic initiation coupled with effective chain
transfer. We suspect the inefficiency of cationogenic initiation
is related to relatively slow ionization (due to steric hindrance
in these diboranes) coupled with the very high intrinsic reactivity
of the ion-pairs formed in situ.
Experimental Section
Unless otherwise noted, all reagents were obtained from com-
mercial sources and purified as required. All synthetic procedures
were carried out in glassware previously passivated with dichlo-
rodimethylsilane and were conducted under N2 using Schlenk
techniques or in an Innovative Technology glovebox. Hexanes,
diethyl ether, and toluene were purified by distillation from
potassium and benzophenone under N2 and stored over activated 4
Å molecular sieves. Dichloromethane was distilled from P2O5 and
stored over activated 4 Å molecular sieves. TMP was distilled and
Reversible termination to form telechelic materials [i.e.,
Cum-(CH2CMe2)n-CH2CMe2-X] has been documented for
(21) Mishra, M. K.; Kennedy, J. P. J. Macromol. Sci., Chem. 1987, A24,
933-48.

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5677
stored over activated 4 Å molecular sieves. DtBMP was sublimed
prior to use. Diboranes 16 and 2111 were synthesized using modified
versions of the original literature methods. Cumyl chloride was
prepared by bubbling HCl through predried R-methylstyrene and
distilled, degassed, and stored at -28 °C. Cumyl azide was prepared
using an existing literature method,20c while CumOMe was prepared
from cumyl alcohol and MeI as described below. We find the
Williamson ether synthesis22 to be more reliable for the synthesis
of CumOMe compared to the more commonly employed acid-
catalyzed reactions. In particular, the product is uncontaminated
with MeOH, CumOH, or other protic materials, which serve as
co-initiators of isobutene polymerization using diborane 1. N-Phen-
yl-2-iminopropane was prepared according to a literature method.23
[(Et2O)2H][B{3,5-(CF3)2C6H3}4] was prepared as described in the
literature16 and stored at -30 °C in the glovebox freezer prior to
use.
suspension of 2.0 g of KH (50.0 mmol) in 150 mL of THF at
-78 °C with stirring. The solution was warmed to RT and then
refluxed until evolution of H2 ceased. To the suspension of KH
and alkoxide was added 10 mL (excess) of dry MeI at -78 °C.
The mixture was allowed to warm to RT, then heated to reflux
and refluxed overnight. The suspension was cooled to RT and the
THF partially removed at 20 mmHg using a rotary evaporator. The
suspension was diluted with hexane and then filtered to remove
salts, washing with hexane. The hexane was evaporated at 20 mmHg
using a rotary evaporator. The crude product (>80% yield) was
purified by high-vacuum (10-3 mmHg) Kugelrohr distillation from
powdered CaH2.
Preparation of [Ph3C][1,2-C6F4(9-BC12F8)2-µ-Cl] (4b). 1,2-
C6F4(BC12F8)2 (200 mg, 0.26 mmol) and Ph3CCl (73 mg, 0.26
mmol) were stirred in CH2Cl2 (1 mL) for 18 h. An orange precipitate
was formed upon addition of hexanes (10 mL). The supernatant
was decanted, and the precipitate was washed with hexanes (20
mL) and dried in Vacuo to afford the product as an orange
powder. Yield: 204 mg (75%). 1H NMR (300 MHz, CD2Cl2, RT):
1
Routine H/19F NMR spectra were obtained on either Varian
1
Mercury or Gemini 300 MHz instruments. All H NMR spectra
were referenced with respect to residual deuterated solvent. 19F
NMR spectra were referenced with respect to tetrafluoro-p-xylene
(TFX: -146.21 CD2Cl2). Variable-temperature 1H/19F NMR spectra
were recorded on a Varian Inova 400 MHz instrument, the
thermocouple of which had been calibrated to within 5% of the
actual temperature using a methanol standard. The solvent used
for variable-temperature studies (CD2Cl2) was dried by vacuum
transfer from P2O5 and stored over activated 4 Å molecular sieves
prior to use.
3
3
δ 8.25 (t, J ) 7.5 Hz, 3H, p-C6H5), 7.86 (t, J ) 8.0 Hz, 6H,
m-C6H5), 7.63 (d, 3J ) 8.3 Hz, 6H, o-C6H5). 19F NMR (282 MHz,
CD2Cl2, RT): δ -131.9 (4F, C12F8), -136.0 (4F, C12F8), -137.0
(2F, C6F4), -156.5 (4F, C12F8), -157.7 (4F, C12F8), -161.3 (2F,
C6F4). 11B NMR (128 MHz, CD2Cl2, RT): δ 9.9. Anal. Calcd for
C49H15B2ClF20 (1040.70): C 56.55, H 1.45. Found: C 56.78, H
1.49.
Preparation of [Ph3C][1,2-C6F4(9-BC12F8)2-µ-OMe] (4d). 1,2-
C6F4(BC12F8)2 (0.030 g, 0.039 mmol) and Ph3COMe (0.011 g, 0.039
mmol) were weighed into a flask, and CH2Cl2 (2 mL) was added.
The reaction was stirred for 1 h, and the volatiles were removed in
Vacuo. The resulting product was pure by NMR spectroscopy. The
product was crystallized from CH2Cl2 layered with hexanes.
GC analyses were performed using a Hewlett-Packard 5890
instrument equipped with a flame ionization detector and a 30 m
× 0.25 mm HP-5 capillary column. A split injection (100:1 split
ratio) was performed with the injector at 275 °C and the detector
at 300 °C using the following temperature program: 50 °C (5 min)
to 250 °C (15 min) at 4 °C/min. Data were recorded using a HP
3395 Series II digital integrator; representative GC traces are
included as Supporting Information. GC-MS analyses were per-
formed using a Varian Series 3300 GC-ion-trap MS equipped with
a 30 m VXMS-5 column and an identical temperature program
using a 10:1 split ratio. A solvent delay of 6 min was employed
prior to data collection, and the entire mass range of 0-650 amu
was scanned; representative GC-MS data are also included as
Supporting Information.
1
Yield: 35 mg (85%). H NMR (300 MHz, CD2Cl2, RT): δ 8.26
3
3
(t, J ) 7.5 Hz, 3H, p-C6H5), 7.87 (t, J ) 7.5 Hz, 6H, m-C6H5),
7.66 (d, J ) 7.7 Hz, 6H, o-C6H5) 2.76 (s, 3H, OMe). 19F NMR
3
(282 MHz, CD2Cl2, RT): δ -131.9 (s, br, 4F, C12F8), -136.5 (s,
br, 4F, C12F8), -139.5 (AA′BB′ spin system, 2F, C6F4), -157.8
(d of t, J ) 18.1, 9.1 Hz, 4F, C12F8), -158.5 (m, 4F, C12F8), -162.5
(AA′BB′ spin system, 2F, C6F4). 11B{1H} NMR (128 MHz, CD2-
Cl2, RT): δ 7.6 (br s). Anal. Calcd for C50H18B2F20O (1036.28):
C 57.95, H 1.75. Found: C 57.74, H 2.15.
Preparative and analytical TLC was performed using Merck silica
gel 60 aluminum-backed plates, eluting with hexane. In the case
of preparative TLC no more than 20 mg of crude material was
separated on one entire plate.
Preparation of [Ph3C][1,2-C6F4(B(C6F5)2)2-µ-N3] (4e). Into a
flask containing triphenylmethylazide24 (0.14 g, 0.48 mmol) and
C6F4{B(C6F5)2}2 (0.40 g, 0.48 mmol) was condensed CH2Cl2 (25
mL). The solids rapidly dissolved upon warming to give a yellow-
orange solution, which was stirred for 1 h at ambient temperature.
The solvent was removed in Vacuo to afford the crude product as
a glass on the walls of the vessel. This was triturated with hexanes
(30 mL) for an extended period, affording an orange solid after
filtration and drying under reduced pressure. Sonication of the
product/hexanes mixture was often employed to aid in the isolation
Polyisobutene samples were analyzed by GPC at 35 °C, eluting
with THF at 1.0 mL/min using a Waters chromatograph equipped
with a set of linear Ultrastyragel columns, a Waters model 410
refractive index detector (DRI), a Viscotek model 110R differential
viscometer (DV), and a Wyatt Technology 18-angle DAWN EOS
multiangle light-scattering (MALLS) detector. Data were analyzed
with Viscotek’s TriSEC (random-coil approximation using data
from the DRI, DV, and 90° MALLS detectors) and also Wyatt
Technology’s ASTRA software using a literature value for dn/dc
supplied by Wyatt Technology. Although column calibration using
polystyrene standards was not employed, the values of the MW
averages of some narrow MWD polyisobutene standards (supplied
by American Polymer Standards Inc.) were checked against values
provided by this company and were found to be accurate to within
(10% for materials in excess of 10 kg/mol MW. The operator who
performed these analyses was initially unaware that some of the
samples analyzed were standards.
1
of the product in powder form. Yield: 0.49 g (91%). H NMR
3
(300 MHz, CD2Cl2, 300 K): δ 8.27 (t, J ) 8 Hz, 3H, p-C6H5),
7.88 (m, 6H, m-C6H5), 7.66 (d, 3J ) 8 Hz, 6H, o-C6H5). 19F NMR
(282 MHz, CD2Cl2, 300 K): δ -133.9 (m, 8F, o-C6F5), -137.8
(m, 2F, C6F4), -159.1 (t, 4F, p-C6F5), -162.8 (d, 2F, C6F4), -165.5
(m, 8F, m-C6F5). 11B NMR (64 MHz, CD2Cl2, 300 K): δ 0.5 (s).
Anal. Calcd for C49H15B2F24N3: C 52.4, H 1.4, N 3.7. Found: C
52.6, H 1.4, N, 3.6.
Preparation of [Ph3C][1,2-C6F4(9-BC12F8)2-µ-N3] (4f). 1,2-
C6F4(BC12F8)2 (0.030 g, 0.039 mmol) and Ph3CN3 (0.011 g, 0.039
mmol) were weighed into a vial, and CH2Cl2 (10 mL) was added.
The reaction was swirled until all solids were dissolved. Hexanes
(10 mL) was layered on top of the reaction mixture, and the vial
was capped and placed in the freezer (-40 °C). After 2 days large
Preparation of Cumyl Methyl Ether. A solution of 5.0 g (36.7
mmol) of cumyl alcohol in 20 mL of dry THF was added to a
(22) For a recent paper describing the use of a similar procedure to the
synthesis of hindered cumyl ethers see: Casarini, D.; Coluccini, C.; Lunazzi,
L.; Mazzanti, A. J. Org. Chem. 2006, 71, 4490-4496.
(24) Saunders, W. H., Jr.; Ware, J. C. J. Am. Chem. Soc. 1958, 80, 3328-
3332.
(23) Kyba, E. P. Org. Prep. Procedures 1970, 2, 149-156.

5678 Organometallics, Vol. 26, No. 23, 2007
Chai et al.
orange crystals had formed in the solution. The solution was
M in hexane); (2) 0.766 mL of a stock solution of diborane 1 (0.065
M in toluene); (3) 0.172 mL of a CumCl stock solution (0.029 M
in hexane). Polymerization was allowed to proceed for 1 h at
-78 °C under N2 before quenching with 1 mL of methanol. All
volatiles were removed and solids were washed with methanol prior
to being taken up in hexanes. The resultant polymer solution was
filtered, stripped of solvent, and dried in a vacuum oven at 30 in
Hg at 90 °C for 24 h to yield a clear solid or oil.
decanted and the crystals were dried in Vacuo. Yield: 0.030 g
1
(73%). H NMR (300 MHz, CD2Cl2, RT): 8.26 (t, J ) 7.5 Hz,
3H, p-C6H5), 7.87 (t, J ) 7.5 Hz, 6H, m-C6H5), 7.66 (d, J ) 7.7
Hz, 6H, o-C6H5). 13C{1H} NMR (75 MHz, CD2Cl2, RT): δ 209.4
(CPh3), 142.2 (CPh), 141.2 (CPh), 138.5 (CPh), 129.2 (CPh). Signals
for the C-F nuclei were not located. 19F NMR (282 MHz, CD2-
Cl2, RT): δ -132.2 (s, br, 4F), -135.9 (s, br, 4F), -138.4 (AA′BB′
spin system, 2F), -157.0 (d of t, 4F, J ) 18.1, 9.1 Hz), -157.9
(m, 4F), -161.6 (AA′BB′ spin system, 2F). 11B{1H} NMR (128
MHz, CD2Cl2, RT): δ 3.5 (br, s). A satisfactory analysis was not
obtained.
Reaction of N-Phenylacetone Imine with [(Et2O)2H][B{3,5-
(CF3)2C6H3}4]. To a solution of N-phenylacetone imine (2.7 mg,
0.02 mmol) in CD2Cl2 (0.5 mL) was added 16.6 mg of oxonium
1
acid at 25 °C. H and 19F NMR spectra were recorded, and the
former spectrum, overlaid with that due to a mixture of 11a and 5,
formed from diborane 1 and CumN3 is depicted in the Supporting
Information. Aside from the resonances due to diethyl ether and
those of the counteranion, the remaining Me and Ar-H resonances
overlapped perfectly with those due to 11a.
Preparation of 1,2-C6F4(B(OMe)C12HF8)(BC12F8) (10). Di-
borole 2 (250 mg, 0.33 mmol) was dissolved in toluene (5 mL).
Dry methanol (13 µL, 0.33 mmol) was injected via syringe. The
solution was stirred for 18 h at room temperature, during which
the bright yellow color of the starting material disappeared. Toluene
was removed under reduced pressure. Any residual toluene was
removed by the addition of hexanes and pumping off all volatile
materials. The product was obtained as a white powder, pure by
NMR spectroscopy. Yield: 185 mg (71%). Recrystallization from
General Procedure for Reactions of 1 or 2 with Cum-X in
CD2Cl2. To a screw-top, septum-sealed, 5 mm NMR tube were
added the desired amount of diborane 1 or 2 and TFX in CD2Cl2
at room temperature in a glovebox. The spectrum of the resulting
solution was then recorded to verify the concentration of diborane
with respect to TFX standard. The sample was ejected and cooled
in an acetone/dry ice bath under N2. Cum-X in CD2Cl2 was injected
slowly via syringe and the tube mixed with a vortex mixer. The
1
toluene (0.5 mL) affords crystalline material (63 mg, 24%). H
NMR (300 MHz, C6D6, 298 K): δ 6.52 (m, 1H, C6F4HC6F4B),
3.04 (s, 3H, B-OMe). (CD2Cl2, 298 K): δ 7.11 (m, 1H, ArF-H),
4.00 (s, 3H, B-OMe). 19F NMR (282 MHz, C6D6, 298 K): δ -127.3
(1F, C6F4), -130.4 (1F, C6F4HC6F4B), -131.4 (2F, BC12F8),
-133.1 (1F, C6F4), -135.7 (2F, C6F4HC6F4B + BC12F8), -136.0
(1F, C6F4HC6F4B), -136.1 (1F, BC12F8), -138.8 (1F, C6F4),
-142.2 (br, 1F, C6F4HC6F4B), -145.8 (1F, C6F4HC6F4B), -149.5
(1F, C6F4HC6F4B), -149.8 (1F, BC12F8), -150.3 (1F, BC12F8),
-150.8 (1F, C6F4HC6F4B), -151.6 (1F, C6F4HC6F4B), -153.8 (1F,
BC12F8), -154.1 (1F, C6F4), -154.5 (1F, BC12F8); (CD2Cl2, 298
K): δ -127.4 (1F), -130.1 (1F), -133.2 (2F), -133.9 (1F),
-135.5 (1F), -135.7 (1F), 136.1 (1F), -136.9 (1F), -141.3 (br,
1F), -141.6 (1F), -147.2 (1F), -151.2 (1F), -151.5 (1F), -151.9
(1F), -152.2 (1F), -152.7 (1F), -155.3 (2F), -155.6 (1F). 11B
NMR (128 MHz, C6D6, RT): 47.3 (br s, B-borole), 12.3 (br, s,
B-OMe). Anal. Calcd for C31H4B2F20O (793.96): C 46.90, H 0.51.
Found: C 46.72, H 0.67.
1
tube was immersed into a precooled (-80 °C) probe, and H and
19 F spectra were recorded at this temperature. The probe was
warmed in 20 °C increments, during which both 1H and 19F NMR
spectra were collected to monitor formation and subsequent
decomposition of the resulting ion-pairs.
Reaction of Diborane 1 with TMP. A flask was charged with
diborane (0.10 g, 0.12 mmol) in 3 mL of CH2Cl2 in a glovebox.
The flask was taken out of the glovebox and cooled to -78 °C,
and TMP (0.375 g, 3.35 mmol) was added slowly. The mixture
was stirred at -78 °C for 2 h and quenched with 1 mL of MeOH.
The resulting solution was filtered through a short Al2O3 column,
washing with benzene. The product mixture was analyzed by GC-
MS (see Supporting Information). The solution was then concen-
trated to dryness in Vacuo to provide a colorless oil. Yield: 0.198
g, 53%. This material was nonvolatile, though contaminated with
General Polymerization Procedure. Nitrogen gas was purified
by passing it first through a column packed with a 50:50 v/v mixture
of activated 3 Å molecular sieves and BASF R3-11 catalyst
followed by a second column packed with alternating layers of
activated 3 Å molecular sieves and Sicapent. Isobutylene was
purified by passing it through a column packed with a mixture
composed of 50:50 v/v activated 3 Å molecular sieves and BASF
R3-11 catalyst. The prepurified monomer was next condensed into
a graduated collection vessel held at -78 °C under a blanket of
nitrogen. The collected monomer was then degassed via three
sequential freeze-pump-thaw cycles prior to use. A representative
procedure for polymerization is given below with initiation using
diborane 1 and CumCl.
1
small quantities of dimer. A representative H NMR spectrum is
depicted in the Supporting Information indicating Xn ≈ 4.5.
General Procedure of Reaction of 1, TMP, and Cum-X in
the Presence of a Small Amount of DtBMP. To a flask were
added diborane (0.100 g, 0.12 mmol), DtBMP (6 mg, 0.029 mmol),
CH2Cl2 (3 mL), and TMP (0.375 g, 3.35 mmol) in a glovebox in
the sequence stated. The flask was taken out of the glovebox and
cooled to -78 °C, and Cum-X (1 mL, 0.12 M stock solution in
CH2Cl2, 0.12 mmol) was added slowly. The mixture was stirred at
-78 °C for 2 h and quenched with 1 mL of MeOH. The crude
mixtures were worked up as described above and analyzed by GC
and/or GC-MS. Then the reaction mixture was concentrated to
dryness in Vacuo and the residue extracted with hexane (3 × 10
mL). The hexane extracts were concentrated to dryness, and a
colorless oil was obtained, which was partially separated by
preparative TLC eluting with hexane.
A 250 mL round-bottom 24/40 single-neck flask was charged
with 11.6 g (17.5 mL) of hexanes, 0.82 g (1 mL) of trioctylalu-
minum, and a magnetic stir bar inside a glovebox. This was then
fitted with a 24/40 vacuum adapter equipped with a Teflon vacuum
stopcock and the apparatus connected to a vacuum line. The mixture
of solvent and drying agent was degassed using three freeze-
pump-thaw cycles and then charged with 5.5 mL monomer via
vacuum transfer.
Reaction of 1, TMP, and CumN3. Crude yield: 0.265 g, 71%.
Preparative TLC afforded two fractions, which appeared as dark
bands under UV light. Fraction 1: Rf ≈ 0.90, two major isomers
of 16 contaminated with TMP oligomers. Fraction 2: Rf, ≈ 0.82;
1,3,3-trimethyl-1-neopentylindan (14), contaminated with TMP
oligomers and trace amounts of 15. For GC-MS data of the mixture
and these compounds, see the Supporting Information.
Reaction of 1, TMP, and CumOMe. Crude yield: 0.251 g,
67%. Preparative TLC afforded two fractions, which appeared as
dark bands under UV light. Fraction 1: Rf ≈ 0.90, four isomers of
16 contaminated with TMP oligomers. Fraction 2: Rf ≈ 0.82,
This solution was then stirred at -78 °C for 30 min before
vacuum transferring both monomer and solvent to a second, two-
neck round-bottom flask attached to the vacuum line through
another 24/40 vacuum adapter and equipped with a septum inlet.
The contents of this flask were then warmed to -78 °C and stirred
for 15 min under N2 prior to injection of the following solutions
listed in order of addition: (1) 1 mL of DtBMP stock solution (0.5

Formation of Chelated Counteranions Using Lewis Acidic Diboranes
Organometallics, Vol. 26, No. 23, 2007 5679
mainly isomers of 15 (three compounds by GC-MS) contaminated
with TMP oligomers, and trace amounts of 14. For GC-MS data
of the mixture and these compounds, see the Supporting Informa-
tion.
Reaction of 1, TMP, and CumCl. Crude yield: 0.346 g, 88%.
This mixture was not separated by preparative TLC, but GC-MS
reveals the presence of compounds 14-16 with a product distribu-
tion resembling that formed from CumOMe.
proximately equidimensional block crystal of 4e. The structures
were solved by direct methods and refined on all unique F2 values,
with constrained riding H atoms. Each structure contains one CH2-
Cl2 molecule in the asymmetric unit. In 4f this is ordered, but in
4e it is extensively disordered; a reasonable approximation was
achieved with a model having three components, two of which share
C and one Cl atom.
Reaction of 1, TMP, and CumN3 in the Presence of Equimo-
lar DtBMP. To a flask was added diborane (0.1 g, 0.12 mmol),
DtBMP (25 mg, 0.12 mmol), CH2Cl2 (3 mL), and TMP (0.375 g,
3.35 mmol) in a glovebox in the stated sequence. The flask was
taken out of the glovebox and cooled to -78 °C, and CumN3 (1
mL, 0.12 M stock solution in CH2Cl2, 0.12 mmol) was added
slowly. The mixture was stirred at -78 °C for 2 h and quenched
with 1 mL of MeOH. Workup as described above provided a
colorless oil. Yield: 0.025 g, which consisted of a ca. 4.6:1 molar
ratio of 17:5 by 1H NMR spectroscopy The mixture was separated
by preparative TLC eluting with hexane. Fraction 1: Rf ≈ 0.90,
mixture of 17a-c. Fraction 2: Rf ≈ 0.75, 1,3,3-trimethyl-1-
phenylindan (5).
Acknowledgment. The authors thank the American Chemi-
cal Society, Petroleum Research Fund, the University of Akron,
and the Natural Sciences and Engineering Research Council of
Canada for financial support of this work, and the Engineering
and Physical Sciences Research Council (UK) for funding of
crystallographic equipment. The authors also thank Prof. Mark
Soucek of the Department of Polymer Engineering at the
University of Akron for access to a GC-MS instrument and Mr.
Jon Page of the Institute for Polymer Science at the University
of Akron for GPC analyses of polyisobutene samples.
Supporting Information Available: 1H NMR spectra of
iminium salt 11a. 19F NMR spectra of reaction mixtures resulting
from oligomerization of TMP using diborane 1 and CumCl, CumN3,
and CumOMe. GC-MS analyses of these product mixtures along
1
High-field H NMR spectra, including 2D COSY and NOESY
spectra, gHSQC, and HMBC 13C-1H spectra of compounds 17a-c
are included as Supporting Information. High-resolution mass
spectrum calcd for C17H26 230.2035, found (EI, 70 eV) 230.2029.
X-ray Crystallography. Data were collected at 160 K on a
Bruker SMART 1K CCD diffractometer with Mo KR radiation (λ
) 0.71073 Å). Absorption corrections for 4f, for which the crystal
was a thin plate, were made on the basis of repeated and symmetry-
equivalent reflections; no correction was applied for the ap-
1
with selected mass spectra of individual components. H NMR
spectra of partially purified indans 14-16. 2D COSY, NOESY 1H-
1H, and gHSQC, HMBC 1H-13C NMR spectra of alkenes 17a-c.
Crystallographic information files for 4e and 4f. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM700672Q