Ruthenium-catalyzed hydroboration and dehydrogenative borylation of linear and cyclic alkenes with pinacolborane

Article abstract of DOI:10.1021/om0610851

The bis(dihydrogen)ruthenium complex RuH₂(H₂) ₂(PCy₃)₂ (1) catalyzes efficiently the borylation of linear and cyclic alkenes with pinacolborane. Similar results are obtained by using RuH[(μ-H)₂Bpin](σ-HBpin)(PCy ₃)₂ (2) as catalytic precursor. Selective hydroboration into the corresponding linear pinacol boronate is achieved in the case of 1 -hexene, 1 -octene, styrene, and allylbenzene. In the case of styrene, phenethyl pinacolboronate is isolated in 87% yield. Faster conversions of HBpin are obtained by increasing the alkeneiborane ratio, with less than 10% of alkene hydrogenation. Isomerization into trans-β-methylstyrene is observed in the case of allylbenzene. Dehydrogenative borylation is competitive with ethylene and cyclic alkenes with large rings. Hydroboration of cyclohexene is highly favored, whereas for cyclodecene, vinylboronate is produced with only traces of allylboronate. Cyclooctene provides the two unsaturated boron-attached products, vinyl- and allylboronate in a 1:3 ratio, whereas only allylboronate is obtained from cycloheptene. The coupling of cyclodecenyl pinacolboronate with the aryl bromide (CF₃)₂C₆H₃Br, using standard catalytic Suzuki-Miyaura conditions, gives the corresponding product (CF ₃)₂C₆H₃(C₁₀H ₁₇) in 85% yield. Mechanistic investigations allow the characterization of the hydrido-(boryl)(ethylene) complex RuH(Bpin)(C ₂H₄)(PCy₃)₂ (3) as a key intermediate in the catalytic cycle.

Full text of DOI:10.1021/om0610851

Organometallics 2007, 26, 1191-1195
1191
Ruthenium-Catalyzed Hydroboration and Dehydrogenative
Borylation of Linear and Cyclic Alkenes with Pinacolborane
Ana Caballero and Sylviane Sabo-Etienne*
Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 04,
France
ReceiVed NoVember 30, 2006
The bis(dihydrogen)ruthenium complex RuH2(H2)2(PCy3)2 (1) catalyzes efficiently the borylation of
linear and cyclic alkenes with pinacolborane. Similar results are obtained by using RuH[(µ-H)2Bpin](σ-
HBpin)(PCy3)2 (2) as catalytic precursor. Selective hydroboration into the corresponding linear pinacol
boronate is achieved in the case of 1-hexene, 1-octene, styrene, and allylbenzene. In the case of styrene,
phenethyl pinacolboronate is isolated in 87% yield. Faster conversions of HBpin are obtained by increasing
the alkene:borane ratio, with less than 10% of alkene hydrogenation. Isomerization into trans-â-
methylstyrene is observed in the case of allylbenzene. Dehydrogenative borylation is competitive with
ethylene and cyclic alkenes with large rings. Hydroboration of cyclohexene is highly favored, whereas
for cyclodecene, vinylboronate is produced with only traces of allylboronate. Cyclooctene provides the
two unsaturated boron-attached products, vinyl- and allylboronate in a 1:3 ratio, whereas only allylboronate
is obtained from cycloheptene. The coupling of cyclodecenyl pinacolboronate with the aryl bromide
(CF3)2C6H3Br, using standard catalytic Suzuki-Miyaura conditions, gives the corresponding product
(CF3)2C6H3(C10H17) in 85% yield. Mechanistic investigations allow the characterization of the hydrido-
(boryl)(ethylene) complex RuH(Bpin)(C2H4)(PCy3)2 (3) as a key intermediate in the catalytic cycle.
In view of the previous results we have obtained in hydrosi-
lylation and dehydrogenative silylation of alkenes with the bis-
(dihydrogen) ruthenium complex RuH2(H2)2(PCy3)2 (1) as an
effective catalyst,8 we have undertaken a similar study on
pinacolborane activation, a reagent that has received little
attention by comparison to catecholborane. The presence in 1
of two labile σ-dihydrogen ligands is a key feature allowing an
easy access to formally a 14-electron intermediate. In the case
of borane activation, we have shown that substitution of the
two σ-ligands by pinacolborane leads to the formation of RuH-
[(µ-H)2Bpin](σ-HBpin)(PCy3)2 (2), a complex in which the two
borane ligands are bonded to the metal in different modes,
σ-coordination and dihydroborate ligation.9 We now report that
1 and 2 serve as active catalyst precursors not only for
hydroboration of various alkenes with pinacolborane but more
interestingly for dehydrogenative borylation of ethylene and
cyclic alkenes. Moreover, mechanistic investigations allow the
characterization of a hydrido(boryl)(ethylene) complex, RuH-
(Bpin)(C2H4)(PCy3)2 (3), a key intermediate for catalyzed alkene
hydroboration.
Introduction
The synthetic utility of the hydroboration of carbon-carbon
multiple bonds is well established.1 Importantly, metal-catalyzed
hydroborations are largely dominated by rhodium systems and
catecholborane.2 Alkene boronic esters have been of particular
interest due to their potential to act as useful intermediates in
organic synthesis, in particular for Suzuki-Miyaura cross-
coupling.3 They are usually prepared by hydroboration of
alkynes.1,2 The search for other synthetic routes toward alkene
boronic esters using alkenes, which are easily prepared and
commercially available with a wide variety of functionalities,
is attractive.4 Dehydrogenative borylation of alkenes, the
competing reaction of catalyzed alkene hydroboration, represents
an interesting alternative.5,6 Recently, it was shown that rhodium-
catalyzed dehydrogenative borylation of alkenes could be
favored, leading to 1,1-disubstituted vinylboronates, without
sacrificial hydrogenation of the alkene substrate.7
* Corresponding author. Tel: + 33 5 61 33 31 77. Fax: +33 5 61 55
30 03. E-mail: sabo@lcc-toulouse.fr.
(1) (a) Hall, D. G., Ed. Boronic Acids. Preparation and Applications in
Organic Synthesis and Medicine; Wiley-VCH: Weinheim, 2005. (b)
Crudden, C. M.; Edwards, D. Eur. J. Org. Chem. 2003, 4695. (c)
Ramanchandran, P. V.; Brown, H. C. Recents Advances in Borane
Chemistry. Organoboranes for Synthesis; ACS Symp. Ser. 783; American
Chemical Society: Washington, DC, 2001. (d) Beletskaya, I.; Pelter, A.
Tetrahedron 1997, 53, 4957. (e) Burgess, K.; Ohlmeyer, M. J. Chem. ReV.
1991, 91, 1179.
Results and Discussion
The catalytic experiments were performed at room temper-
ature using a catalyst/pinacolborane ratio of 1:100 and an alkene
ratio varying from 100 to 1000. The results are summarized in
(2) Carroll, A.-M.; O’Sullivan, T. P.; Guiry, P. J. AdV. Synth. Catal. 2005,
347, 609.
(7) Coapes, R. B.; Souza, F. E. S.; Thomas, R. L.; Hall, J. J.; Marder, T.
B. Chem. Commun. 2003, 614, and references therein.
(3) (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (b) Miyaura,
N. Top. Cur. Chem. 2002, 219, 11. (c) Vaultier, M.; Alcaraz, G. Sci. Synth.
2005, 6, 721.
(4) Morrill, C.; Grubbs, R. H. J. Org. Chem. 2003, 68, 6031.
(5) Burgess, K.; van der Donk, W. A.; Westcott, S. A.; Marder, T. B.;
Baker, R. T.; Calabrese, J. C. J. Am. Chem. Soc. 1992, 114, 9350.
(6) Murata, M.; Kawakita, K.; Asana, T.; Watanabe, S.; Masuda, Y. Bull.
Chem. Soc. Jpn. 2002, 75, 825.
(8) (a) Christ, M. L.; Sabo-Etienne, S.; Chaudret, B. Organometallics
1995, 14, 1082. (b) Delpech, F.; Mansas, J.; Leuser, H.; Sabo-Etienne, S.;
Chaudret, B. Organometallics, 2000, 19, 5750. (c) Lachaize, S.; Sabo-
Etienne, S.; Donnadieu, B.; Chaudret, B. Chem. Commun. 2003, 214.
(9) (a) Montiel-Palma, V.; Lumbierres, M.; Donnadieu, B.; Sabo-Etienne,
S.; Chaudret, B. J. Am. Chem. Soc. 2002, 124, 5624. (b) Lachaize, S.;
Essalah, K.; Montiel-Palma, V.; Vendier, L.; Chaudret, B.; Barthelat, J.-
C.; Sabo-Etienne, S. Organometallics 2005, 24, 2935.
10.1021/om0610851 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/01/2007

1192 Organometallics, Vol. 26, No. 5, 2007
Table 1. Hydroboration of Alkenes with Pinacolboranea
Caballero and Sabo-Etienne
time
RBpin selectivity
saturated:unsaturated
entry
substrate
1-hexene
1-octene
styrene
styrene
styrene
allylbenzene
ethylene
ethylene
HBpin:substrate
(min)c
1
2
3
4
100:100
100:100
100:100
100:200
100:500
100:200
100:3 bar
100:3 bar
100:200
100:100
10
10
180
150
75
15
60
60
15
>99:0
>99:0
>99:0
>99:0
>99:0
>99:0
>99:0
82:18
98:2
5
6
7b
8
9
10
tert-butylethylene
cyclohexene
70
96:4
a Typical reaction conditions: a mixture of pinacolborane (100 equiv) and alkene (100 to 1000 equiv) was added to a solution of 1 or 2 (1 equiv) in 2
b
mL of THF and stirred at room temperature. The reaction was monitored by either GC-MS or a combination of GC-MS and NMR spectroscopy. THF was
c
replaced by toluene. Time to achieve total conversion of HBpin. For entries 7 and 8, the reaction was only checked after 1 h.
Table 2. Dehydrogenative Borylation of Ethylene and Cyclic Alkenes with Pinacolboranea
time
RBpin selectivity
saturated:unsaturated
entry
substrate
ethylene
cycloheptene
cycloheptene
HBpin:substrate
(min)b
1
2
3
4
5
6
7
8
9
100:20 bar
100:100
100:200
100:1000
100:100
100:200
100:1000
100:200
100:1000
15
570
360
420
240
120
120
330
60
44:56
80:20
70:30
47:53
57:43
30:70
22:78
29:71
20:80
cycloheptene
cis-cyclooctene
cis-cyclooctene
cis-cyclooctene
trans-cyclodecene
trans-cyclodecene
a Typical reaction conditions: a mixture of pinacolborane (100 equiv) and alkene (100 to 1000 equiv) was added to a solution of 1 or 2 (1 equiv) in 2
b
mL of THF and stirred at room temperature. The reaction was monitored by either GC-MS or a combination of GC-MS and NMR spectroscopy. Time to
achieve total conversion of HBpin.
Scheme 1
As shown by GC-MS and NMR, hydroboration of styrene leads
exclusively to the formation of the linear product, and phenethyl
pinacolboronate was isolated in 87% yield. Excess styrene
significantly improves the activity (compare entries 3-5).
Remarkably, hydrogenation of styrene into ethylbenzene remains
a minor reaction (less than 10%).7 Recent studies show that
iridium catalyst precursors are also highly selective for the
formation of the linear product (up to 99% with a 5% mixture
of [IrCl(COD)]2 and dppp), whereas the analogous rhodium
system gave almost a 1:1 branched-to-linear ratio. Better results
were obtained by using RhCl(CO)(PPh3)2 as catalyst precursor
(76% of phenethyl pinacolboronate was obtained when using
RhCl(CO)(PPh3)2/HBpin/styrene in a 1:40:33 ratio).12,13 Using
[RhCl(cod)]2 as a catalyst precursor caused dehydrogenative
coupling, but in that case styrene acted as a hydrogen acceptor
with production of ethylbenzene in 46% yield.14,6 The reaction
of allybenzene with HBpin (Table 1, entry 6) led in our system
to comparable results with styrene. In particular, when using
200 equiv of allylbenzene, conversion of HBpin was total within
15 min, with quantitative formation of the corresponding linear
boronate. As shown by NMR and GC-MS measurements, excess
olefin was isomerized into trans-â-methylstyrene and we
detected only traces of the hydrogenated product, i.e., propyl-
benzene.
Tables 1 and 2. The conditions were not optimized but serve
as a guideline to investigate the catalytic activity of 1 or 2 on
a variety of alkenes. A few linear and cyclic alkenes were
selected. Access to boron-substituted cyclic olefins is highly
desirable,10 as they can serve as useful synthetic intermediates
in particular for C-C bond formation through Suzuki coupling
reactions. Moreover, the synthesis of cyclic 1-alkenylboron
compounds cannot be easily performed by hydroboration of
alkynes because of limited availability of the starting cy-
cloalkynes.11
Total conversion of HBpin is observed within 15 min to a
few hours depending on the alkene, and either one, two, or the
three reactions depicted in Scheme 1 can be observed, i.e.,
dehydrogenative borylation (eq 1), hydroboration (eq 2), or
hydrogenation (eq 3). We will also see that in some cases
isomerization of the starting alkene can be observed, particularly
when the alkene:HBpin ratio is higher than 1.
As expected, in the case of ethylene, an increase of pressure
favored the dehydrogenative borylation process, and under 20
bar of ethylene (see Table 1, entries 7, 8, and Table 2, entry 1)
up to 56% of vinylpinacolboronate was obtained. It should be
noted in that case that the nature of the solvent had a slight
effect on the selectivity, with dehydrogenative borylation favored
In the case of linear alkenes such as 1-hexene and 1-octene,
selective hydroboration to the corresponding saturated alkyl
pinacolboronate is achieved within 10 min (95% isolated yield).
(12) Yamamoto, Y.; Fujikawa, R.; Umemoto, T.; Miyaura, N. Tetrahe-
dron 2004, 60, 10695.
(13) Crudden, C. M.; Hleba, Y. B.; Chen, A. C. J. Am. Chem. Soc. 2004,
126, 9200.
(14) Murata, M.; Watanabe, S.; Masuda, Y. Tetrahedron Lett. 1999, 40,
2585.
(10) Renaud, J.; Ouellet, S. G. J. Am. Chem. Soc. 1998, 120, 7995.
(11) Takagi, J.; Takahashi, K.; Ishiyama, T.; Miyaura, N. J. Am. Chem.
Soc. 2002, 124, 8001.

Ru-Catalyzed Hydroboration and DehydrogenatiVe Borylation
Organometallics, Vol. 26, No. 5, 2007 1193
Scheme 2. Borylation of Cyclic Alkenes
investigated. The progress of the reactions was monitored by
1H and 31P NMR spectroscopies. In a first step, 10 equiv of
HBpin was added to a C7D8 solution of 1, leading as expected
to 2 as the only organometallic species. Then 20 equiv of either
cyclohexene or cyclooctene was added to the mixture. After 4
h of stirring, 2 remained the only organometallic species that
could be detected by NMR and the catalysis proceeds.
In contrast, in the case of ethylene, a new organometallic
complex was detected and formulated as RuH(Bpin)(C2H4)-
(PCy3)2 (3) on the basis of NMR data (see Scheme 4). 3 is
characterized in 1H NMR by a triplet at - 5.77 ppm (JPH ) 35
Hz) for the hydride resonance and one singlet at 2.85 ppm for
the ethylene resonance in free rotation. The two signals integrate
in a 1:4 ratio. The ethylene resonance is observed in the 13C-
{1H} NMR spectrum at 42.0 ppm, and the assignment is
confirmed by a HMQC experiment. The 11B{1H} NMR
spectrum shows one singlet at 34.6 ppm, in the same range
observed for related σ-pinacolborane ruthenium complexes. It
is thus difficult to discriminate a boryl from a σ-borane
formulation. A similar problem is found when comparing the
29Si NMR chemical shift of silyl and σ-silane complexes.18
However, the hydride signal is very sharp, in agreement with a
hydrido(boryl) formulation with no sign of B-H interaction.
Any attempt to isolate 3 was unsuccessful and led to decom-
position and formation of the known ethylene complex RuH-
(C2H4){P(η3-C6H8)Cy2}(PCy3) (4),8a together with the boronate
products.
Scheme 3. Proposed Pathway for the Formation of
Vinylboronates and Allylboronates
by using a polar solvent such as THF. Introduction of a bulky
substituent on ethylene leads to selective hydroboration, as
observed in the case of tertiobutylethylene (Table 1, entry 9).
The results on cyclic alkenes are listed in Table 2. The
selectivity and activity depend on the size of the alkene cycle.
Competitive dehydrogenative borylation can be achieved, lead-
ing to the formation of the corresponding vinylboronate or
allylboronate (see Scheme 2). Using an excess of olefin versus
HBpin led to partial hydrogenation (20 to 45% depending on
the conditions) into the corresponding cyclic alkane. Hydrobo-
ration of cyclohexene (see Table 1, entry 10), is highly favored,
whereas in the case of cyclodecene, vinylboronate was produced
with only traces of allylboronate (see Table 2, entries 8, 9).
Cyclooctene provided the two unsaturated boron-attached
products, vinyl- and allylboronate in a 1:3 ratio, whereas only
allylboronate was obtained from cycloheptene. It is noteworthy
that allylboronate compounds are also versatile intermediates.
Their stability allows them to be successfully applied in efficient
catalytic enantioselective allylboration methods and in tandem
reaction processes.15,16
Scheme 4. Formation of the Hydrido(boryl)(ethylene)
Complex RuH(Bpin)(C2H4)(PCy3)2 (3)
It seems likely that, for the cyclic alkenes, selectivity depends
on one of the key steps in the catalytic process, which is the
formation of a boryl alkene species. Boryl migratory insertion
would then result in a â-borylalkyl intermediate, which can
undergo â-hydride elimination to produce either vinylboronate
or allylboronate as depicted in Scheme 3, this step being
controlled by conformational factors, or alternatively can
undergo reductive elimination leading to the hydroboration
product.
The usefulness of our method to produce boron-substituted
cyclic olefins was demonstrated by the coupling of cyclodecenyl
pinacolboronate with the aryl bromide (CF3)2C6H3Br, using
standard catalytic Suzuki-Miyaura conditions (see eq 4 and
Experimental Section).17 The resulting coupling product
(CF3)2C6H3(C10H17) was isolated in 85% yield and characterized
by NMR and GC-MS.
It is worth comparing these results with those we obtained
when studying a similar process by replacing the borane reagent
by a silane. Thus, bubbling ethylene to a solution of 1 with 2
equiv of HSiMe2Cl led to total conversion of the starting silane
and formation of the corresponding chlorodimethylvinylsilane
as a result of dehydrogenative silylation. The new ethylene
complex RuH(SiMe2Cl)(C2H4)(PCy3)2 (5), an analogous species
of 3, was detected.8c In the two systems, an unsaturated 16-
electron species containing the three key ligands involved in
the catalytic process, i.e., a hydride, an ethylene, and a boryl
(or a silyl), is thus characterized. It is remarkable that 3 and 5
remain unsaturated even in the presence of an excess of ethylene
or borane (or silane), respectively. This can be attributed to the
strong trans influence of the boryl (or silyl) ligand. Such a strong
trans influence of boryl ligands has been recently outlined by
Lin and Marder.19 It is noteworthy that five-coordinated boryl
Ru species of general formula RuCl(BR2)(CO)(PPh3)2 have been
previously reported.20 In our system, it is only when the two
substrates, ethylene and pinacolborane, are both present in the
To gain some insight into the mechanism of our systems,
the following stoichiometric and catalytic reactions were
(15) Ito, H.; Kawakami, C.; Sawamura, M. J. Am. Chem. Soc. 2005,
127, 16034.
(16) (a) Selander, N.; Sebelius, S.; Estay, C.; Szabo, K. J. Eur. J. Org.
Chem. 2006, 4085. (b) Sebelius, S.; Wallner, O. A.; Szabo, K. J. Org. Lett.
2003, 5, 3065.
(17) Miyaura, N.; Ishiyama, T.; Sasaki, H.; Ishikawa, M.; Satoh, M.;
Suzuki, A. J. Am. Chem. Soc. 1989, 111, 314.
(18) (a) Lachaize, S.; Sabo-Etienne, S. Eur. J. Inorg. Chem. 2006, 2115.
(b) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
(19) Zhu, J.; Lin, Z.; Marder, T. B. Inorg. Chem. 2005, 44, 9384.
(20) Irvine, G. J.; Roper, W. R.; Wright, L. J. Organometallics 1997,
16, 2291.

1194 Organometallics, Vol. 26, No. 5, 2007
Caballero and Sabo-Etienne
δ 13.0, 24.8, 30.0, 83.1, 125.5, 128.0, 128.2, 144.4. EI-MS: m/z
232 (M+), 217, 203, 189, 175, 159, 133, 119, 105, 91, 77, 59, 41.
2-(3-Phenylpropyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane.12 1H NMR (CDCl3, 250.13 MHz): δ 0.86 (t, 2H, J ) 8 Hz),
1.27 (s, 12H), 1.76 (m, 2H), 2.64 (t, 2H, J ) 8 Hz), 7.10-7.40 (m,
5 Ar-H). 13C{1H}NMR (CDCl3, 62.89 MHz): δ 10.1, 24.8, 26.1,
38.6, 82.9, 125.5, 128.1, 128.5, 142.7. EI-MS: m/z 246 (M+), 231,
189, 173, 127, 118, 105, 85, 77, 65, 55, 41.
reaction mixture that the reaction proceeds and the catalytic
products are obtained. 3 can be considered as the catalyst resting
state.
In summary, the nature of the olefin controls the selectivity
toward hydroboration or dehydrogenative borylation. In the case
of cyclic alkenes, conformational properties have a dramatic
influence on both the rate and the selectivity of the reactions.
Hydroboration of a C6 ring was selectively achieved, whereas
allylboronate (for C7), a mixture of allylboronate and vinylbo-
ronate (for C8), and only vinylboronate (for C10) were isolated,
respectively. Remarkably, using 2 as catalyst precursor instead
of 1 for hydroboration or dehydrogenative borylation led to the
same results (same activity and selectivity). We were able to
characterize the hydrido(boryl)ethylene complex 3, a complex
incorporating the three key ligands necessary for the catalysis
to proceed. It is remarkable that 3 is analogous to the silyl
complex we previously identified. This encourages us to work
on mapping out the similarity between silane and borane
activation.
2-(2-tert-Butylethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane.22 1H NMR (CDCl3, 250.13 MHz): δ 0.72 (t, 2H, J ) 8 Hz),
0.86 (s, 9H), 1.26 (s, 12H), 1.32 (t, 2H, J ) 8 Hz). 13C{1H} NMR
(CDCl3, 62.89 MHz): δ 7.0, 24.8, 28.8, 30.8, 37.7, 82.8. EI-MS:
m/z 212 (M+), 197, 169, 157, 129, 113, 101, 83, 69, 57, 43.
2-(Cyclohexyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.12 1
H
NMR (CDCl3, 250.13 MHz): δ 0.93-1.00 (m, 1H), 1.23 (s, 12H),
1.26-1.40 (m, 4H), 1.54-1.70 (m, 6H). 13C{1H} NMR (CDCl3,
62.89 MHz): δ 24.7, 26.7, 27.1, 27.9, 82.7. EI-MS: m/z 210 (M+),
195, 167, 153, 139, 129, 124, 109, 85, 69, 55, 41.
1
2-(Cycloheptyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. H
NMR (CDCl3, 250.13 MHz): δ 0.80-1.05 (m, 1H), 1.19 (s, 12H),
1.40-2.20 (m, 12H). 13C{1H} NMR (CDCl3, 62.89 MHz): δ 24.5,
28.3, 28.9, 29.5, 82.7. EI-MS: m/z 224 (M+), 209, 182, 167, 138,
123, 101, 96, 83, 55, 39.
Experimental Section
2-(2-Cycloheptenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane. 1H NMR (CDCl3, 250.13 MHz): δ 1.21 (s, 12H), 1.40-2.20
(m, 9H), 5.71 (m, 2H). 13C{1H} NMR (CDCl3, 62.89 MHz): δ
24.7, 27.2, 28.8, 29.7, 33.1, 82.9, 132.2, 133.2. EI-MS: m/z 222
(M+), 207, 181, 165, 138, 121, 101, 85, 67, 41.
2-(Cyclooctyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. 1H NMR
(CDCl3, 250.13 MHz): δ 0.80-1.05 (m, 1H), 1.21 (s, 12H), 1.40-
2.40 (m, 14H). 13C{1H} NMR (CDCl3, 62.89 MHz) δ 24.5, 82.7.
EI-MS: m/z 238 (M+), 223, 209, 194, 180, 152, 124, 109, 84, 55,
41.
2-(2-Cyclooctenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. 1H
NMR (CDCl3, 250.13 MHz): δ 1.23 (s, 12H), 1.40-2.40 (m, 11H),
5.62 (m, 2H). 13C{1H} NMR (CDCl3, 62.89 MHz): δ 24.6, 83.0,
130.2, 130.4. EI-MS: m/z 236 (M+), 221, 208, 194, 179, 165, 151,
135, 108, 84, 67, 41.
General Methods. All preparations were carried out under an
oxygen-free argon atmosphere using conventional Schlenk tech-
niques. Solvents were dried and distilled prior to use. Alkenes and
pinacolborane were purchased from a commercial supplier and
employed without any further purification. The ruthenium com-
plexes 1 and 2 were prepared following literature procedures.8,9
GC data were collected with a HP 4890A instrument. GC-mass
spectra were measured at 70 eV on a HP 5973 attached to a HP
6890, and NMR experiments were acquired on Bruker ARX250,
AV400, and AV500 spectrometers.
General Catalytic Reaction of Alkenes and Pinacolborane.
A mixture of pinacolborane (1.5 mmol) and alkene (1.5 to 15 mmol)
was added to a solution of 1 or 2 (0.015 mmol) in 2 mL of THF
and stirred at room temperature. The reaction was monitored by
GC and stopped after total consumption of HBpin.
2-(1-Cyclooctenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane.11 1H NMR (CDCl3, 250.13 MHz): δ 1.26 (s, 12H), 1.35-
1.50 (m, 8H), 2.20-2.40 (m, 4H), 6.56 (t, 1H, J ) 8.0 Hz). 13C{1H}
NMR (CDCl3, 62.89 MHz): δ 24.7, 25.9, 26.2, 26.4, 27.1, 28.8,
29.6, 82.9, 145.9. EI-MS: m/z 236 (M+), 221, 208, 194, 179, 165,
151, 135, 108, 84, 67, 41.
2-(Cyclodecyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. 1H NMR
(CDCl3, 250.13 MHz): δ 0.80-1.05 (m, 1H), 1.25 (s, 12H), 1.40-
3.00 (m, 18H). 13C{1H} NMR (CDCl3, 62.89 MHz): δ 24.5, 82.7.
EI-MS: m/z 266 (M+), 251, 223, 209, 195, 180, 166, 152, 129,
101, 84, 69, 55, 41.
2-(1-Cyclodecenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.
1H NMR (CDCl3, 250.13 MHz): δ 1.27 (s, 12H), 1.40-3.00 (m,
16H), 6.37 (t, 1H, J ) 8.3 Hz). 13C{1H} NMR (CDCl3, 62.89
MHz): δ 24.7, 82.8, 145.9. EI-MS: m/z 264 (M+), 249, 221, 207,
179, 164, 136, 121, 101, 84, 69, 55, 41.
General Procedure for Intermolecular Cross-Coupling. The
literature procedure was followed.17 A solution of PdCl2(dppf)
(0.01mmol), 3,5-bis(trifluoromethyl)bromobenzene (0.3 mmol),
cyclodecenyl pinacolboronate (0.3 mmol), and aqueous NaOH (2
mL of 0.5 M solution) in THF was refluxed overnight. After the
reaction was completed, the product was extracted with ether,
washed with brine, and dried over MgSO4.
The solvent was removed under vacuum, and the products were
purified by Kugelro¨hr distillation. The boronate products were
characterized by GC-MS and NMR. Their NMR spectra agreed
with those reported in the referenced papers.
The following blank experiments were performed: a mixture of
pinacolborane (1.5 mmol), alkene (tert-butylethylene, 1-hexene,
1-octene, cyclohexene, styrene, or cyclooctene) (1.5 mmol-3 mmol),
and cyclooctane or cyclohexane (0.32 mmol) as internal standard
was dissolved in 2 mL of THF and stirred at room temperature for
30 min to 1 h. The reaction was monitored by GC. In each case,
no reaction was observed.
2-(Hexyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.21 1H NMR
(CDCl3, 250.13 MHz): δ 0.79 (t, 2H, J ) 7.6 Hz), 0.89 (t, 3H, J
) 6.6 Hz), 1.26 (s, 12H), 1.29 (m, 4H), 1.41 (m, 4H). 13C{1H}
NMR (CDCl3, 62.89 MHz): δ 10.1, 14.1, 22.6, 23.9, 24.8, 31.6,
32.1, 82.8. EI-MS: m/z 212 (M+), 197, 183, 169, 155, 128, 113,
98, 84, 69, 55, 41.
2-(Octyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.12 1H NMR
(CDCl3, 250.13 MHz): δ 0.76 (t, 2H, J ) 7.5 Hz), 0.87 (t, 3H, J
) 6.8 Hz), 1.24 (s, 12H), 1.21-1.29 (m, 10H), 1.38-1.41 (m, 2H).
13C{1H}NMR (CDCl3, 62.89 MHz): δ 10.1, 14.1, 22.6, 23.9, 24.8,
29.2, 29.3, 31.8, 32.4, 82.8. EI-MS: m/z 240 (M+), 225, 197, 183,
169, 154, 129, 111, 85, 69, 55, 43.
1-[3,5-Bis(trifluoromethyl)phenyl]cyclodecene. 1H NMR (CDCl3,
400.13 MHz): δ 1.24-1.72 (m, 12H), 2.48 (q, 2H, J ) 7.0 Hz),
2.79 (t, 2H, J ) 6.5 Hz), 5.81 (t, 1H, J ) 8.3 Hz), 7.76 (s, 1 Ar-
H), 7.80 (s, 2 Ar-H). 13C{1H} NMR (CDCl3, 100.61 MHz): δ
2-(2-Phenylethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.12
1H NMR (CDCl3, 250.13 MHz): δ 1.19 (t, 2H, J ) 8.1 Hz), 1.26
(s, 12H), 2.80 (t, 2H, J ) 8.2 Hz), 7.18 (m, 1 Ar-H), 7.27 (m, 2
Ar-H), 7.30 (m, 2 Ar-H). 13C{1H} NMR (CDCl3, 62.89 MHz):
(22) Guennouni, N.; Lhermitte, F.; Cochard, S.; Carboni, B. Tetrahedron
1995, 51, 6999.
(21) Brown, H. C.; Imai, T. J. Am. Chem. Soc. 1983, 105, 6285.

Ru-Catalyzed Hydroboration and DehydrogenatiVe Borylation
Organometallics, Vol. 26, No. 5, 2007 1195
20.4, 21.3, 24.7, 25.7, 26.2, 26.5, 26.9, 27.4, 120.3, 126.4, 133.1,
137.6, 145.0. 19F{1H} NMR (CDCl3, 188.30 MHz): δ 13.2. EI-
MS: m/z 350 (M+), 331, 308, 293, 278, 254, 227, 212, 197, 177,
151, 128, 113, 96, 67, 41.
ppm (C2H4 protons) and the signal at 42.0 ppm (C2H4 carbons)
and a correlation between the signal at 1.12 ppm (Bpin protons)
and the signal at 24.7 ppm (Bpin methyl carbons).
RuH(Bpin)(C2H4)(PCy3)2 (3). The reaction of 2 with ethylene
was followed by NMR. Ethylene was bubbled for 1 min through a
suspension of 2 (20 mg, 0.02 mmol) in 0.7 mL of C7D8 in a NMR
tube. 1H NMR (C6D6, 293 K, 500.33 MHz): δ -5.77 (t, 1H, 2JPH
) 34.1 Hz, RuH), 1.12 (s, 12H, Bpin), 1.28-2.25 (m, 66H, PCy3),
2.85 (pseudo t, 4H, ethylene). 11B{1H} NMR (C6D6, 293 K, 160.52
MHz): δ 34.6. 31P{1H} NMR (C6D6, 293 K, 101.25 MHz): δ 59.7
(s). 13C{1H} NMR (C6D6, 293 K, 125.80 MHz): δ 24.7 (br, CH3),
Acknowledgment. We thank the CNRS and the European
Network IDECAT for support. A.C. thanks the Spanish “Min-
isterio de Educacio´n y Ciencia” for a postdoctoral fellowship.
Supporting Information Available: NMR spectra of the new
compounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
42.0 (br, C ethylene), 82.5 (br, C). The HMQC H-13C (C6D6,
293 K) experiment shows a correlation between the signal at 2.85
OM0610851