synthesized as authentic samples according to the literature. All
other chemicals were purchased from commercial sources and
used as received.
Typical Procedure for the Catalytic Hydrosilylation of
Olefins Using a Co Precatalyst. Co©Mesª (2.0 mg, 3.7 ¯mol)
or Co©Cyª (1.8 mg, 3.7 ¯mol) was placed in a Schlenk tube.
The air in the tube was replaced by N2. 1-Octene (571 ¯L, 3.74
mmol) and diphenylsilane (711 ¯L, 3.74 mmol) were added to
the tube. Sodium triethylborohydride (1.0 M in toluene, 37 ¯L,
37 ¯mol) was added to the tube for the activation of the
precatalyst. The homogenous wine-red solution was heated at
50 °C and stirred for 3 h. Then, the solution was exposed to air.
An excess amount of hexane was added to the solvent and the
catalyst was removed through short column (silica gel). After
concentration, the product was subjected to GC analysis to
determine the yield.
N-(1-[2,2¤-Bipyridine-6-yl]ethylidene)-cyclohexylamine
(Lc). A mixture of cyclohexylamine (1.8 mL, 15 mmol), La
(2.0 g, 10 mmol), and p-toluene sulfonic acid monohydrate (53
mg, 0.30 mmol) in toluene (22 mL) was heated to reflux temper-
ature for 15 h using a Dean-Stark apparatus. After the mixture
was cooled to room temperature, K2CO3 (41 mg, 0.60 mmol)
was added to the mixture and stirred for 1 h. After filtration,
volatile materials were removed from the filtrate under reduced
pressure, and the residue was washed with hexane (4 mL © 3)
and dried to obtain c as a yellow powder (0.76 g, 27%).
1H NMR (400 MHz, CDCl3, δ, ppm): 1.25-1.62 (m, 5H), 1.68-
1.78 (m, 3H), 1.82-1.88 (m, 2H), 2.48 (s, 3H, CCH3), 3.58-
3.62 (m, 1H, NCH), 7.30 (ddd, 1H, J = 8.0, 4.8, 1.2 Hz), 7.82
(dd, 1H, J = 8.0, 8.0 Hz), 7.83 (ddd, 1H, J = 8.0, 8.0, 1.2
Hz), 8.11 (dd, 1H, J = 8.0, 0.8 Hz), 8.39 (dd, 1H, J = 8.0,
0.8 Hz), 8.52 (d, 1H, J = 8.0 Hz), 8.68 (d, 1H, J = 4.8 Hz).
13C{1H} NMR (100.4 MHz, CDCl3, δ, ppm): 13.75, 24.99,
25.98, 33.62, 60.43, 121.11, 121.19, 121.21, 123.75, 136.96,
137.36, 149.24, 154.50, 156.48, 157.81, 164.07. Elemental
analysis. Calcd. for C18H21N3: C, 77.38; H, 7.58; N, 15.04;
Found: C, 77.08; H, 7.54; N, 14.83. HRMS (DART):
[M + H]+ Calcd. for C18H22N3: 280.18137; Found: 280.18191.
N-(1-[2,2¤-Bipyridine-6-yl]ethylidene)-cyclohexylamine
Cobalt(II) Bromide (Co©Cyª). CoBr2 (0.297 g, 1.36 mmol)
and Lc (0.379 g, 1.36 mmol) were placed in a Schlenk tube.
The air in the tube was replaced by N2. THF (12 mL) was added
to the tube and the mixture was stirred for 15 h. The preci-
pitate formed during the reaction was collected by filtration
and washed with THF (4 mL © 2) and hexane (4 mL © 2) and
dried to obtain Co©Cyª as a yellowish powder (0.51 g, 76%).
Elemental analysis. Calcd. for C40H52Br4Co2N6O2 [2M +
THF + H2O]: C, 44.22; H, 4.82; N, 7.74; Found: C, 44.34;
H, 4.25; N, 7.77. HRMS (FAB): calcd for C21H18BrF3N3Co
[M ¹ Br]+, 417.0251; found, 417.0266.
Scheme 6.
3. Conclusion
Many cobalt catalysts for hydrosilylation of olefins have
been reported, but most of them produce a mixture of anti-
Markovnikov and Markovnikov products. Only a limited num-
ber of Co catalysts show regioselective hydrosilylation, but an
effective way to control the selectivity has not been reported.
We found that a Co-iminobipyridine complex with a Mes
substituent on the imino nitrogen (Co©Mesª) shows a catal-
ytic activity for hydrosilylation of olefins to give a mixture of
anti-Markovnikov and Markovnikov products whereas a Co-
iminobipyridine complex with a Cy substituent (Co©Cyª)
produces the anti-Markovnikov product selectively. The X-ray
structures of Co©Mesª and Co©Cyª suggest that the Cy sub-
stituent narrows active space around the Co more than the Mes
substituent but these two substituents did not give a large
difference in the Co-Br bond lengths. Therefore, we proposed
that the steric demand rather than the electronic effect of the Cy
substituent plays a dominant role to show the regioselective
hydrosilylation.
4. Experimental Section
General Information. All reactions were carried out under
N2 using Schlenk techniques. All solvents were dried and
stored under N2. H and 13C{1H} NMR spectra were recorded
1
on a JEOL JNM-AL 400 spectrometer. The residual peaks of
the solvent were used as an internal standard. NMR measure-
ment of the cobalt complexes were difficult because they were
practically insoluble in common solvents. GC analyses were
carried out using a Shimadzu GC-2014 equipped with an Rtx-
5MS (RESTEC, 30 m, 0.25 mmID, 0.25 ¯m) capillary column.
Product yields were determined based on the calibration curve
of each authentic sample. FAB-MS measurement was conduct-
ed using JEOL JMS-700(2).
X-ray Diffraction Data Collection and Determination of
the Structure. The single crystals of Co-iminobipyridine
complexes were obtained from slow diffusion of ether into an
acetone solution of Co complexes. Data for Co©Mesª were
collected at 150(2) K with a Rigaku AFC11 with Saturn 724+
CCD diffractometer using monochromated MoKα radiation
(- = 0.710747 ¡). Data for Co©Cyª were collected at 220(2) K
with a Rigaku/MSC Mercury CCD diffractometer using graph-
ite monochromated MoKα radiation (- = 0.71070 ¡). Those
Materials.
La and Lb in Scheme 1 were synthesized
according to literature methods.5 Hydrosilylation products, 1,9l
2,6 3,9o 4,6 6,15 7,20 8a,8 8b,8 9,6 10,21 11,16e 1322 and 1423 were
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