Contrasting the reactivity of ethylene and propylene with P/Al and P/B frustrated Lewis pairs

Article abstract of DOI:10.1021/om400222w

Frustrated Lewis pairs (FLPs) derived from R₃P (R = otol, Mes) and B(C₆F₅)₃ or AlX₃ (X = halide, C₆F₅) add to ethylene. Similarly, the P/B FLP adds across propylene, whereas the P/Al systems react with propylene to effect propylene dimerization via a C-H bond activation and C-C bond formation, affording an Al-bound 2-methylpentene complex.

Full text of DOI:10.1021/om400222w

Article
pubs.acs.org/Organometallics
Contrasting the Reactivity of Ethylene and Propylene with P/Al and
P/B Frustrated Lewis Pairs
Gabriel Menard,† Lina Tran,† Jenny S. J. McCahill,‡ Alan J. Lough,† and Douglas W. Stephan*,†
́
†Department of Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3H6
‡Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4
S
* Supporting Information
ABSTRACT: Frustrated Lewis pairs (FLPs) derived from
R3P (R = otol, Mes) and B(C6F5)3 or AlX3 (X = halide, C6F5)
add to ethylene. Similarly, the P/B FLP adds across propylene,
whereas the P/Al systems react with propylene to effect
propylene dimerization via a C−H bond activation and C−C
bond formation, affording an Al-bound 2-methylpentene
complex.
Scheme 1. Reactions of Olefins with FLPs
INTRODUCTION
■
The observation that frustrated Lewis pairs (FLPs), which are
combinations of sterically congested Lewis acids and bases, can
effect H2 activation is certainly remarkable.1 This finding has
resulted in the advent of metal-free stoichiometric and catalytic
hydrogenations for a growing range of substrates2 and
extensions to asymmetric reductions.3 FLPs have also been
exploited for other applications in materials science4 and in
strategies to capture and activate a variety of other small
molecules.2i While efforts in this area continue, the application
of the reactivity of FLPs to activate other small molecules has
also garnered much attention.5
The first paper in which FLP activation of a small molecule
other than H2 was reported described the addition of P/B FLPs
to terminal olefins, including ethylene and hexene.6 Sub-
sequently, Erker and co-workers described the addition of
intramolecular FLPs to other olefins in a similar fashion
(Scheme 1).7 In a more recent study, we showed that van der
Waals interactions between the olefin and a Lewis acidic
borane8 activates the olefin for nucleophilic attack by a variety
of nucleophiles, providing an avenue to form new C−P, C−N,
C−C, and C−H bonds.9
The impact of variations in the Lewis acid in such reactions
with olefins has received limited attention. While combinations
of phosphine with the alane Al(C6F5)3 react with ethylene to
give addition products analogous to those in the borane case,
reaction of the FLP tBu3P/Al(C6F5)3 with isobutylene has been
shown to proceed via an alternate route involving C−H bond
activation, generating a reactive bridging allyl bis-Al anion salt
(Scheme 1).10
“conventional FLP fashion”, the P/Al FLPs effect C−H bond
activation and dimerization of propylene.
RESULTS AND DISCUSSION
■
The combination of a phosphine (R3P, R = Mes, otol) and
Al(C6F5)3·tol in a 1/1 ratio in bromobenzene was exposed to
an atmosphere of ethylene. In the case of Mes3P/Al(C6F5)3 a
new species appears, as evidenced by a 31P{1H} NMR
resonance at 19 ppm. In addition, two new 1H NMR
resonances in the aliphatic region were also observed that
were consistent with a PCH2CH2Al linkage. The 19F{1H} and
In this present study we further explore the differing
reactivities of P/B and P/Al FLPs in reactions with ethylene
and propylene. In the case of the Al Lewis acids, we exploit
simple Al halides and demonstrate that two formula units of
these Lewis acids are required to stabilize addition to ethylene.
In contrast, while P/B FLPs are shown to add to propylene in a
Special Issue: Applications of Electrophilic Main Group Organo-
metallic Molecules
Received: March 16, 2013
© XXXX American Chemical Society
A
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Article
27Al NMR spectra were consistent with the presence of a four-
coordinate aluminate anion. Collectively, these data indicate the
formulation of the product as Mes3P(CH2CH2)Al(C6F5)3.
While this species was stable under an ethylene atmosphere, it
could not be isolated in its absence. Rapid loss of ethylene and
regeneration of the initial components, PMes3 and Al(C6F5)3,
indicates that the binding of ethylene is reversible.
In contrast, the corresponding reaction of the less sterically
hindered phosphine (otol)3P with Al(C6F5)3 and ethylene led
to the isolation of the single product 1 in 77% yield. The
31P{1H} NMR resonance at 29 ppm and two distinct 1H
resonances at 3.34 and 0.60 ppm suggest the analogous
formulation (otol)3P(CH2CH2)Al(C6F5)3 (1), a fact that was
confirmed by single-crystal X-ray diffraction (Figure 1). This
species is directly analogous to the previously reported species
Figure 2. POV-Ray depiction of the molecular structure of 3: C, black;
P, orange; Al, teal; Br, scarlet. Analogous structures are obtained for 2
and 4 (see the Supporting Information). H atoms are omitted for
clarity.
10
tBu3P(CH2CH2)Al(C6F5)3 and tBu3P(CH2CH2)B(C6F5)3,6
and the metric parameters are very similar.
1.874(3), 1.862(3), and 1.89(1) Å, respectively. These are
significantly longer than those seen in 1 (1.830(7) Å) and
tBu3P(CH2CH2)Al(C6F5)3 (1.833(2) Å).10 In contrast, the
corresponding C−Al bond lengths in 2−4 (1.950(3), 1.946(3),
and 1.95(1) Å, respectively) are also similar to those found in
other aluminates derived from Al(C6F5)3.5s,11 The presence of
the halide bridge between the Al centers presumably enhances
the Lewis acidity of the C-bound AlX3 center and thus stabilizes
the zwitterionic form. A related situation was observed in the
capture of CO2 with the bis-borane 1,2-C6H4(BCl2)25b where a
B−Cl−B interaction enhanced the thermal stability of the
bound CO2.
The analogous reactions of propylene were also explored.
For a point of comparison, tBu3P/B(C6F5)3 was first reacted
with propylene. In this case crystals of 5 were isolated in 63%
yield. The 11B{1H} and 31P{1H} NMR spectra gave rise to
signals at −11.6 and 56.9 ppm, respectively. These data as well
Figure 1. POV-Ray depiction of the molecular structure of 1: C, black;
P, orange; Al, teal; F, pink. H atoms are omitted for clarity.
The FLPs derived from Mes3P/AlX3 (X = Cl, Br, I) were also
reacted with ethylene (Scheme 2). In these cases, the reactions
1
as the H, 13C{1H}, and 19F NMR spectra were completely
consistent with the formation of tBu3P(CH(CH3)CH2)B-
(C6F5)3 (5), by direct analogy to the previously reported
ethylene analog. Crystallographic data further confirmed this
observation (Figure 3).
Scheme 2. Reactions of Ethylene with Mes3P/AlX3 FLPs
It should be noted that alternation of the tBu3P/B(C6F5)3
ratio to 1/2 had no impact on the formation of 5. In sharp
were complete in 2 h and each led to a single product, as
evidenced by the formation of new signals in the 31P{1H} and
1H NMR spectra. While the NMR data suggest the formation
of the species Mes3P(CH2CH2)AlX3, attempts to obtain pure
products were unsuccessful, as redissolved powders revealed a
1H NMR signal consistent with the liberation of ethylene.
However, using a 1/2 PMes3/AlX3 ratio under ethylene
afforded the isolation of stable products with the formulation
Mes3P(CH2CH2)(AlX3)2 (X = Cl (2), Br (3), I (4)). Single
crystals suitable for X-ray diffraction were obtained for each of
these compounds (Figure 2; see the Supporting Information).
The structures of 2−4 reveal that a second equivalent of AlX3
is halide-bridged to the carbon-bound Al and display similar
features, with P−C bond lengths to the ethylene fragment of
Figure 3. POV-Ray depiction of the molecular structure of 5. C, black;
P, orange; B, yellow-green; F, pink. H atoms are omitted for clarity.
B
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contrast, reactions of propylene with 1/2 Mes3P/AlX3 solutions
did not lead to addition products. In all cases, the 31P{1H}
NMR spectra exhibited a doublet at −26 ppm (1JP−H = 482 Hz)
consistent with the formation of the [Mes3PH]+ cation.11 The
formation of this product was accelerated using AlI3. After 24 h
under propylene, the 27Al NMR spectrum indicated the
presence of two separate signals at 130 (broad) and −25
ppm (sharp). This latter signal results from the known [AlI4]−
anion,5f and addition of hexanes prompted the precipitation of
the salt [Mes3PH][AlI4] (6). The second product was isolated
proposed allyl intermediate was derived from the analogous
reaction of Mes3P/Al(C6F5)3 with propylene. In this case, 19F
NMR spectroscopy revealed the initial formation of a single F-
containing product concomitant with resonances attributable to
the [Mes3PH]+ cation in the 31P NMR spectrum. A triplet of
triplets and a broad singlet were observed in the 1H NMR in a
1/4 ratio, together with the resonances arising from the
phosphonium cation (Figure S1, Supporting Information).
These data are consistent with the generation of the symmetric
σ - a l l y l b i s ( a l u m i n a t e ) s p e c i e s [ M e s 3 P H ] -
[(C6F5)3AlCH2CHCH2Al(C6F5)3]. This species is directly
analogous to the previously reported salt generated from the
analogous deprotonation of isobutylene (Scheme 1).10 The
steric bulk of Al(C6F5)3 is thought to kinetically slow
subsequent reaction with propylene, allowing the observation
of this species. Nonetheless, attempts to isolate the present allyl
product in an analytically pure form were unsuccessful, due to
the presence of some dimerization product (Figure S1).
In summary, the addition of Al/PMes3 FLPs with ethylene
has been shown to be reversible, although in the case of Al
halides 2 equiv of AlX3 serves to stabilize the addition products.
The corresponding reactivity of these FLPs with propylene
further illustrates the divergent reactivity, as the B/P FLP forms
a stable addition product whereas the Al/P FLP effects C−H
bond activation, resulting in the dimerization of propylene to
afford the intramolecular alane−olefin complex 7. We are
continuing to study the reactions of various FLPs with olefins
and alkynes in an effort to uncover unique reactivity that can be
exploited for catalysis and synthetic applications.
1
as an oil from the filtrate. The H NMR spectrum displayed
nine separate resonances. Detailed analysis of the 1D and 2D
NMR spectra established this product as CH2CHCH2C-
(Me)HCH2AlI2 (7) (Figure 4), in which the pendant olefin is
1
Figure 4. H NMR (600 MHz) spectrum of 7 in C6D5Br.
strongly coordinated to Al. This binding together with
formation of the chiral center at the carbon β to Al makes all
the protons in the fragment inequivalent (except the methyl
group), resulting in a rather complex coupling pattern of the 1H
NMR spectrum (Figure 4). As an example, the β olefinic CH is
seen to couple to the terminal olefinic protons as well as the
adjacent inequivalent methylene protons, affording a well-
resolved 16-line signal (Figure 4, insert). The strong binding of
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed
under an atmosphere of dry, oxygen-free N2 by means of standard
Schlenk or glovebox techniques (Innovative Technology glovebox
equipped with a −38 °C freezer). Hexanes and pentane (Aldrich) were
dried using an Innovative Technologies solvent system. Fluorobenzene
and bromobenzene were purchased from Aldrich and dried on P2O5
for several days and vacuum-distilled onto 4 Å molecular sieves prior
to use. Trimethylaluminum (TMA), (o-tol)3P, and Mes3P were
purchased from Strem and used without further purification. AlX3 were
purchased from Strem and sublimed three times prior to use under
vacuum using a −78 °C cold finger and a 100 °C (X = Cl), 80 °C (X =
Br), or 150 °C (X = I) bath. Me2SiHCl was purchased from Aldrich
and used without further purification. B(C6F5)3 was purchased from
Boulder Scientific, sublimed under vacuum, and then treated with
excess Me2SiHCl for 4 h and resublimed after removal of volatiles.
Al(C6F5)3·tol was prepared from B(C6F5)3 and TMA in toluene by a
known procedure.13 Ethylene (grade 3.0) and propylene (grade 2.5)
were purchased from Linde and passed through a Restek oxygen
scrubber and a Restek moisture trap prior to use. NMR spectra were
obtained on a Bruker Avance 400 MHz, a Varian 400 MHz, or an
Agilent 600 MHz NMR spectrometer, and spectra were referenced to
the residual solvent of C6D5Br or to an external reference (27Al,
Al(NO3)3; 31P, 85% H3PO4; 19F, CFCl3). Chemical shifts listed are in
ppm, and absolute values of the coupling constants are in Hz. NMR
assignments are supported by additional 2D experiments. Elemental
analyses (C, H) were performed in house.
the olefinic unit to Al also results in a significant shift of the 13
C
NMR resonances of the olefinic carbons to 123.0 and 163.5
ppm for the terminal and substituted carbons, respectively,
indicative of a markedly polarized bond. The corresponding
27Al NMR spectrum showed a broad signal at 130.0 ppm. The
strong binding of the olefin to Al in 7 stands in contrast to
previously described B species containing pendant olefin
units,11 where the olefin−boron interaction is weak and is
described as a “van der Waals” interaction. Presumably the
increased Lewis acidity at Al, as well as its more diffuse vacant p
orbital, prompts more efficient overlap with the olefinic π
orbital.
The formation of 6 and 7 is thought to proceed via initial
deprotonation of propylene, generating an allyl intermediate.
Subsequent insertion of a second equivalent of propylene
liberates 6 and generates 7 (Scheme 3). Support for the
Scheme 3. Proposed Reaction Pathway to 6 and 7
Synthesis of (otol)3P(CH2CH2)Al(C6F5)3 (1) or Mes3P(CH2CH2)-
(AlX3)2 (X = Cl (2), Br (3), I (4)). These compounds were all
synthesized in a similar fashion; therefore, only one synthesis is
described. A 50 mL Schlenk bomb equipped with a Teflon cap was
charged with Mes3P (150 mg, 0.39 mmol) and AlBr3 (206 mg, 0.77
mmol) in 10 mL of fluorobenzene. The bomb was transferred to the
Schlenk line equipped with an ethylene outlet. The bomb was
degassed at room temperature, filled with ethylene, and sealed. The
solution was stirred rapidly overnight (ca. 12 h). The ethylene
C
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atmosphere was removed. Precipitation using hexanes (ca. 5−10 mL)
afforded a white solid, which was filtered and dried on a frit. In all cases
vapor diffusion of pentane into a bromobenzene solution or slow
cooling yielded single crystals suitable for X-ray crystallography.
para-C6F5), −165.5 (mt, 6F, m-C6F5). 31P{1H} NMR (THF-d8, 121
MHz, 300 K): δ 56.9. Anal. Calcd for C33H33BF15P: C, 52.40; H, 4.40.
Found: C, 52.14; H, 4.36.
Reaction of PMes3/AlI3 with Propylene To Generate 6 and 7.
A 50 mL Schlenk bomb equipped with a Teflon cap was charged with
Mes3P (286 mg, 0.74 mmol) and AlI3 (600 mg, 1.47 mmol) in 10 mL
of fluorobenzene. The bomb was transferred to a Schlenk line
equipped with a propylene outlet. The bomb was degassed at room
temperature, filled with propylene, and sealed. The mixture was stirred
rapidly for 36 h. The propylene atmosphere and solvent were removed
in vacuo. Hexanes (ca. 20 mL) was added to the remaining oily
residue, and the mixture was stirred vigorously for 1 h, upon which
time a white precipitate formed. The solid was filtered on a glass frit
and washed with copious amounts of hexanes. The isolated yield of 6
was 480 mg (0.52 mmol, 71%). The solvent was thoroughly removed
from the filtrate to obtain an oil. Pentane (10 mL) was added to this,
and a residual precipitate was filtered on Celite. The solvent from this
filtrate was thoroughly removed to give 120 mg of 7 as a viscous oil
(0.33 mmol, 45%).
1
1: isolated yield 77%. H NMR (400 MHz, C6D5Br): δ 7.37−6.91
2
3
(m, 12H), 3.34 (dt, JH−P = 8 Hz, JH−H = 8 Hz, 2H, P−CH2), 1.85
(bs, 9H, o-CH3), 0.63−0.55 (m, 2H, CH2Al). 31P{1H} NMR (161
MHz, C6D5Br): δ 29. 27Al NMR (104 MHz, C6D5Br): δ 142 (bs, ν1/2
= ca. 2300 Hz). 19F{1H} NMR (376 MHz, C6D5Br): δ −121.4 (dd,
4
3
3JF−F = 30 Hz, JF−F = 12 Hz, 6F, o-C6F5), −155.9 (t, JF−F = 20 Hz,
3F, p-C6F5), −162.2 (m, 6F, m-C6F5). 13C{1H} NMR (100 MHz,
C6D5Br): δ 150.0 (dm, JC−F = 236 Hz), 142.9 (d, JC−P = 7.5 Hz),
1
1
1
140.4 (dm, JC−F = 248 Hz), 136.6 (dm, JC−F = 249 Hz), 134.6 (d,
JC−P = 2 Hz), 134.4 (d, JC−P = 10 Hz), 133.5 (d, JC−P = 10 Hz), 127.2
(d, JC−P = 12 Hz), 118.9 (m, i-C6F5), 117.2 (d, JC−P = 79 Hz, i-C6H4),
23.4 (d, 1JC−P = 34 Hz, PCH2), 22.2 (d, 3JC−P = 4 Hz, o-CH3), 6.0 (bs,
CH2Al). Anal. Calcd for C41H25AlF15P + 0.5C6H5F: C, 58.16; H, 3.05.
Found: C, 58.65; H, 2.93.
1
2: isolated yield 76%. H NMR (400 MHz, C6D5Br): δ 6.68 (bs,
6. 1H NMR (400 MHz, C6D5Br): δ 8.19 (d, 1JH−P = 482 Hz, 1H, P-
H), 6.78 (bs, 3H), 6.73 (bs, 3H), 2.16 (bs, 9H, o-CH3Mes), 2.11 (s, 9H,
p-CH3Mes), 1.80 (bs, 9H, o-CH3Mes). 31P{1H} NMR (161 MHz,
C6D5Br): δ −26.0. 27Al NMR (104 MHz, C6D5Br): δ −25. 13C{1H}
6H), 3.28 (dt, 2JH−P = 9 Hz, 3JH−H = 9 Hz, 2H, P−CH2), 2.08 (bs, 9H,
o-CH3Mes), 2.05 (s, 9H, p-CH3Mes), 1.73 (bs, 9H, o-CH3Mes), 0.68 (bs,
2H, CH2-Al). 31P{1H} NMR (161 MHz, C6D5Br): δ 20.0. 27Al NMR
(104 MHz, C6D5Br): δ 106.0 (bs, ν1/2 = 1200 Hz). 13C{1H} NMR
4
4
NMR (100 MHz, C6D5Br): δ 146.7 (d, JC−P = 3 Hz, p-C6H2), 143.7
(100 MHz, C6D5Br): δ 144.3 (d, JC−P = 3 Hz, p-C6H2), 143.6 (d,
2JC−P = 10 Hz, o-C6H2), 132.8 (d, JC−P = 12 Hz, m-C6H2), 120.2 (d,
3
(bs, o-C6H2), 142.9 (bs, o-C6H2), 133.1 (bs, m-C6H2), 131.9 (bs, m-
C6H2), 111.4 (d, 1JC−P = 83 Hz, i-C6H2), 22.3 (bs, o-CH3Mes), 22.1 (bs,
o-CH3Mes), 21.6 (s, p-CH3Mes). Anal. Calcd for C27H34AlI4P: C, 35.09;
H, 3.71. Found: C, 35.01; H, 3.75.
1JC−P = 73 Hz, i-C6H2), 34.8 (d, JC−P = 39 Hz, PCH2), 24.9 (bs, o-
1
CH3Mes), 24.1 (bs, o-CH3Mes), 21.1 (s, p-CH3Mes), 10.0 (bs, CH2Al).
Anal. Calcd for C29H37Al2Cl6P: C, 50.98; H, 5.46. Found: C, 50.76; H,
5.48.
7. 1H NMR (600 MHz, C6D5Br): δ 6.73 (dddd, 3JH −H = 18, 3JH −H
c
b
c
d
= 11, 3J
= 9, 3J
= 4.9, 1H, Hc), 5.62 (dd, 3J
= 9, 2J
=
3: isolated yield 79%.1H NMR (400 MHz, C6D5Br): δ 6.69 (bs,
6H), 3.31 (dt, 2JH−P = 9 Hz, 3JH−H = 9 Hz, 2H, P−CH2), 2.11 (bs, 9H,
o-CH3Mes), 2.05 (s, 9H, p-CH3Mes), 1.74 (bs, 9H, o-CH3Mes), 0.89 (bs,
2H, CH2-Al). 31P{1H} NMR (161 MHz, C6D5Br): δ 21.0. 27Al NMR
(104 MHz, C6D5Br): δ blank (signal lost in the probe signal). 13C{1H}
Hc−Ha
Hc−He
Ha−Hc
Ha−Hb
3
2
4
2, 1H, Ha), 5.48 (ddd, JH −H = 18, JH −H = 3, JH −H = 2, 1H, Hb),
b
c
b
a
b
e
1.93 (ddddd, 2JH −H = 12, 3JH −H = 5.1, 3JH −H = 3, 4JH −H = 2, 4JH −H
e
d
e
c
e
f
e
b
e
h
= 2, 1H, He), 1.83−1.71 (m, 1H, Hf), 1.37 (ddd, 2JH −H = 11, 3JH −H
=
d
e
d
c
3
3
4
11, JH −H = 11, 1H, Hd), 0.87 (d, JH−H = 6.5, CH3, 3H), 0.57 (ddd,
NMR (100 MHz, C6D5Br): δ 144.3 (d, JC−P = 3 Hz, p-C6H2), 143.6
d
f
f
2
3
3
4
2
2JH −H = 14, JH −H = 4, JH −H = 2, 1H, Hh), 0.03 (dd, JH −H = 14,
(d, JC−P = 10 Hz, o-C6H2), 132.8 (d, JC−P = 11 Hz, m-C6H2), 120.1
(d, 1JC−P = 74 Hz, i-C6H2), 34.9 (d, 1JC−P = 39 Hz, PCH2), 25.0 (bs, o-
CH3Mes), 23.9 (bs, o-CH3Mes), 21.0 (s, p-CH3Mes), 13.0 (bs, CH2Al).
Anal. Calcd for C29H37Al2Br6P: C, 36.67; H, 3.93. Found: C, 37.24; H,
4.01.
h
g
h
f
h
e
g
h
3
J
= 12, 1H, Hg). 27Al NMR (104 MHz, C6D5Br): δ 130.0 (bs, ν1/2
Hg−Hf
= 2000 Hz). 13C{1H} NMR (150 MHz, C6D5Br): δ 163.5 (s, C2),
123.0 (s, C1), 45.4 (s, C3), 33.4 (s, C4), 25.7 (s, CH3), 23.8 (bs, C5). A
satisfactory elemental analysis for this compound could not be
obtained, despite repeated attempts.
1
4: isolated yield 71%. H NMR (400 MHz, C6D5Br): δ 6.76 (bs,
2
3
3H), 6.63 (bs, 3H), 3.34 (dt, JH−P = 10 Hz, JH−H = 8 Hz, 2H, P−
CH2), 2.18 (bs, 9H, o-CH3Mes), 2.05 (s, 9H, p-CH3Mes), 1.74 (bs, 9H,
X-ray Data Collection, Reduction, Solution, and Refinement.
Single crystals were coated in Paratone-N oil in the glovebox, mounted
on a MiTegen Micromount, and placed under an N2 stream. The data
were collected on a Bruker Apex II diffractometer. The data were
collected at 150( 2) or 293( 2) K for all crystals. Data reduction was
performed using the SAINT software package and an absorption
correction applied using SADABS. The structures were solved by
direct methods using XS and refined by full-matrix least squares on F2
using XL as implemented in the SHELXTL suite of programs.14 All
non-hydrogen atoms were refined anisotropically. Carbon-bound
hydrogen atoms were placed in calculated positions using an
appropriate riding model and coupled isotropic temperature factors
(see the Supporting Information).
o-CH3Mes), 1.19 (dt, JH−P = 10 Hz, JH−H = 10 Hz, 2H, CH2-Al).
31P{1H} NMR (161 MHz, C6D5Br): δ 18.8. 27Al NMR (104 MHz,
C6D5Br): δ −15.0 (bs, ν1/2 = 1500 Hz). 13C{1H} NMR (100 MHz,
C6D5Br): δ 144.4 (d, 4JC−P = 3 Hz, p-C6H2), 143.6 (d, 2JC−P = 9 Hz, o-
3
3
3
1
C6H2), 132.9 (d, JC−P = 12 Hz, m-C6H2), 120.2 (d, JC−P = 73 Hz, i-
C6H2), 35.6 (d, JC−P = 39 Hz, PCH2), 25.6 (bs, o-CH3Mes), 24.0 (bs,
1
o-CH3Mes), 21.1 (s, p-CH3Mes), 14.3 (bs, CH2−Al). Anal. Calcd for
C29H37Al2I6P: C, 28.27; H, 3.03. Found: C, 28.41; H, 3.27.
Synthesis of tBu3P(CH(CH3)CH2)B(C6F5)3 (5). To a solution of
B(C6F5)3 (0.473 g, 0.92 mmol) in C6H5Br (50 mL) under propylene
purge was added a solution of tBu3P (0.258 g, 1.28 mmol) in C6H5Br
(2 mL). The solution was purged with propylene for 4 h, and the
reaction mixture was stirred under 1 atm of propylene at room
temperature for 12 h. The solvent was removed in vacuo, the residue
was dissolved in CH2Cl2, and hexanes was added to precipitate a white
solid. The solid was filtered and washed with hexane several times and
dried in vacuo. Yield: 0.436 g (63%). Crystals suitable for X-ray
diffraction were grown from a layered CH2Cl2/pentane solution at 25
°C. 1H NMR (THF-d8, 300 MHz, 300 K): δ 2.72 (br, 1H, PCH), 2.30
(br, 2H, BCH2), 1.59 (d, 27H, 3JH−P = 13 Hz, tBu), 1.57 (m, 3H, Me).
11B{1H} NMR (THF-d8, 96 MHz, 300 K): δ −11.6. 13C{1H} NMR
(THF-d8, 75 MHz, 300 K): partial δ 149.2 (dm, 1JC−F = 237 Hz, ortho-
ASSOCIATED CONTENT
■
S
* Supporting Information
A CIF file giving crystallographic data. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
1
1
C6F5), 139.1 (dm, JC−F = 230 Hz, para-C6F5), 137.57 (dm, JC−F
=
*E-mail for D.W.S.: dstephan@chem.utoronto.ca.
1
t
1
245 Hz, meta-C6F5), 41.6 (d, JC−P = 25 Hz, Bu), 33.7 (d, JC−P = 22
t
Hz, PCH), 31.2 (s, Bu), 18.9 (s, Me). 19F NMR (THF-d8, 282 MHz,
Notes
3
300 K): δ −129.1 (br, s, 6F, o-C6F5), −162.4 (t, 3F, JF−F = 20 Hz,
The authors declare no competing financial interest.
D
dx.doi.org/10.1021/om400222w | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(7) (a) Voss, T.; Sortais, J.-B.; Frohlich, R.; Kehr, G.; Erker, G.
Organometallics 2011, 30, 584. (b) Sortais, J. B.; Voss, T.; Kehr, G.;
̈
ACKNOWLEDGMENTS
■
D.W.S. is grateful for the financial support of the NSERC of
Canada and the award of a Canada Research Chair. G.M.
gratefully acknowledges the financial support of the NSERC
and Walter C. Sumner Fellowships.
Frohlich, R.; Erker, G. Chem. Commun. 2009, 7417.
̈
(8) Zhao, X. X.; Stephan, D. W. J. Am. Chem. Soc. 2011, 133, 12448.
(9) Zhao, X. X.; Stephan, D. W. Chem. Sci. 2012, 3, 2123.
(10) Men
4409.
́
ard, G.; Stephan, D. W. Angew. Chem., Int. Ed. 2012, 51,
(11) Men
8272.
́
ard, G.; Stephan, D. W. Angew. Chem., Int. Ed. 2012, 51,
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dx.doi.org/10.1021/om400222w | Organometallics XXXX, XXX, XXX−XXX