Organometallics
Article
RajanBabu have demonstrated that stoichiometric amounts of
in place with eicosane, which was placed inside a plastic straw.
Magnetization data at 100 K from 0 to 7 T were used as a
ferromagnetic-free purity test. Direct current (dc) variable temper-
ature magnetic susceptibility measurements were collected in the
temperature range 3−295 K under an applied field of 0.1 T. The
magnetism data were corrected for the small diamagnetic contribution
of the gel capsule containing the sample and the straw and the
diamagnetic contribution of the compounds. Magnetic susceptibility
Cp TiCl can open epoxides to carbon-centered radicals that
2
35,36
can cyclize onto CC double bonds;
the Gansauer group
̈
37,38
has made the one-electron reduction of epoxides catalytic
38
and used a variety of H· donors, such as 1,4-cyclohexadiene,
3
6
35
39
40
Bu SnH, thiols, silanes, or precious-metal hydrides, to
3
reduce the resulting carbon-centered radicals. Our group has
shown that CpCr(CO) H, with a Cr−H bond dissociation
33
3
data were modeled in PHI.
−
1
energy of 62 kcal mol , can transfer H· to different organic
X-ray diffraction data were collected on a Bruker Apex II
structures were solved using direct methods and standard difference
map techniques and were refined by full-matrix least-squares
4
1−45
substrates
H pressure.
and be regenerated from CpCr(CO) · under
3
4
6
2
We have successfully combined Ti and Cr in the dual
cooperative catalyst mentioned at the end of the Introduction,
which hydrogenates epoxides to anti-Markovnikov alcohols.
The heterobimetallic Ti/Cr complexes we have just made can
achieve catalytic activity comparable to the original system. In
2
47−49
procedures on F with SHELXTL (version 2014/7).
Crystallo-
graphic data for the structures have been deposited with the
Materials. Tetrahydrofuran and benzene were distilled from
sodium/benzophenone ketyl under Ar. Pentane was stirred over
sulfuric acid for several days to remove any olefins and then was
distilled from sodium under Ar. Toluene was purified by the method
50
of Grubbs. Deuterated solvents (Cambridge Isotopes) were purified
by vacuum transfer from the appropriate drying agent (potassium
metal for benzene-d and toluene-d and P O for acetonitrile-d3).
Na[CpCr(CO) ], and HCpCr(CO) separately, and gives a
3
3
6
8
4
10
yield of anti-Markovnikov alcohol comparable to that achieved
with our previous catalysts.
Synthetic Procedures. Bis(trimethylsilyl)acetylene (BTMSA)
was purchased from Sigma-Aldrich Co. and used as received.
Cp TiCl and Cp* TiCl were obtained as a gift from Boulder
2
2
2
2
Scientific Co. and used as received. Cp Ti(BTMSA), Cp* Ti-
SUMMARY AND CONLUSIONS
We have found that the reactions of CpCr(CO) H with
2
2
■
24,25
19
51−54
(BTMSA),
Cp*(C Me CH )TiCH , and CpCr(CO) H
5 4 2 3 3
3
were prepared by literature methods. The hydrogenation reaction of
the epoxide substrate was set up according to the literature
Rosenthal complexes, Cp Ti(BTMSA) and Cp* Ti(BTMSA),
2
2
afforded heterobimetallic compounds 1 and 2. Our reactions
23
procedure.
appear to proceed through the addition of CpCr(CO) H
3
[Cp Ti···(OC)Cr(CO) Cp] (1). Cp Ti(BTMSA) (174.2 mg, 0.50
2
2
2
2
2
IV
“
Cp Ti” and “Cp* Ti”, giving rise to Ti -H intermediates that
mmol) and CpCr(CO) H (109.1 mg, 0.50 mmol) were loaded in a
2
2
3
lose H to form the Ti−Cr complexes 1 and 2 featuring
paramagnetic Ti centers. In the solid state, 1 and 2 both
20 mL vial and then dissolved in 2 mL of benzene in a glovebox.
2
III
Immediate color change to green and evolution of H were observed.
2
Green crystals developed within minutes. The solution was left
undisturbed overnight and then decanted. The crystals were washed
with 5 mL of pentane and dried under vacuum. Yield: 160 mg (84%).
adopt a dimeric geometry, which involved a 12-membered
“
Ti Cr ” ring held together with Ti−O−C−Cr bridging
2
2
carbonyls. The terminal carbonyls in 1 and 2 are trans. DFT
−
1
IV
ATR-FTIR: 1914, 1827, 1606 cm . Anal. Calcd for C36
H30Cr O Ti
2 6 2
calculations confirm that the loss of H from the Ti -H
2
(%): C, 57.02; H, 3.99. Found: C, 41.68; H, 3.96. The low C value
III
intermediateforming the Ti -Cr dimeris exergonic by
might be due to the air/moisture sensitivity of 1 and carbide
about 14.2 kcal mol− in the gas phase. Upon dissolution in
polar coordinating solvents such as acetonitrile, the dimers fall
apart into separated ion pairs. Finally, we have successfully
used compound 1 to catalyze the hydrogenation of an epoxide
to the anti-Markovnikov alcohol.
1
21
formation, as pointed out in the literature on a similar compound.
[
Cp* Ti···(OC)Cr(CO) Cp] (2). Cp* Ti(BTMSA) (244.9 mg,
2 2 2 2 2
0
.50 mmol) and CpCr(CO) H (109.1 mg, 0.50 mmol) were loaded
3
in a 20 mL vial and then dissolved in 2 mL of benzene in a glovebox.
The resulting dark red solution was stirred overnight before layering 3
mL of pentane at room temperature. Dark red crystals were formed,
1
EXPERIMENTAL SECTION
General Methods. Unless otherwise noted, all manipulations
were carried out in an Ar-filled inert atmosphere box (O < 1 ppm) or
under Ar by standard Schlenk techniques. Glassware was flame- or
isolated, and dried under vacuum. Yield: 210 mg (82%). H NMR
■
(
1
500 MHz, C D , 298 K) δ 11.43 (br, C Me , 60H), 5.37 (br, Cp,
0H). ATR-FTIR: 1914, 1827, 1607 cm . Anal. Calcd for
6 6 5 5
−
1
2
C H Cr O Ti (%): C, 64.74; H, 6.79. Found: C, 61.00; H, 6.78.
56 70
2
6
2
The low C value might be due to the air/moisture sensitivity of 2 and
oven-dried immediately prior to use. NMR spectra were recorded on
1
13
carbide formation, as pointed out in the literature on a similar
collected on a Bruker Alpha II FT-IR instrument. Solution samples for
electronic spectroscopy were prepared under argon. Absorption
spectra were recorded on a Cary 60 UV−vis. Absorption maxima were
obtained by spectral deconvolution using Igor64. Elemental analyses
were carried out at Midwest Microlab. EPR spectra were recorded on
a Bruker EMX spectrometer at ambient temperature in deoxygenated
acetonitrile and deuterated benzene solution in a 3 mm (inner
diameter) quartz tube. EPR simulations were performed with Bruker’s
EasySpin software. Magnetic susceptibility measurements were
performed using a Cryogenics S700X SQUID magnetometer. The
loose polycrystalline sample was placed into a gel capsule and secured
21
compound.
Cp* Ti(CH )···(OC)Cr(CO) Cp (3). CpCr(CO) H (109.1 mg,
2
3
2
2
3
0.50 mmol) in 2 mL of toluene was added dropwise to a toluene (2
mL) solution of Cp*(C Me CH )TiCH (166.2 mg, 0.50 mol) in a
5
4
2
3
20 mL vial in a glovebox. The solution was layered with 4 mL of
pentane and stored at −40 °C. Crystals of compound 3 grew, then
1
were isolated, and dried under vacuum. Yield: 210 mg (76%). H
NMR (500 MHz, C
30H), 0.57 (s, Ti-Me, 3H). C NMR (126 MHz, C
247.2, 242.5, 124.1, 85.1, 57.2, 11.5. ATR-FTIR: 1915, 1828, 1608
D
8
, 298 K) δ 4.76 (s, Cp, 5H), 1.37 (s, C
Me
D , 298 K) δ
8
,
7
5
5
1
3
7
−
1
cm . Anal. Calcd for C H CrO Ti (%): C, 65.17; H, 7.17. Found:
2
9
38
3
C, 65.37; H, 7.24.
E
Organometallics XXXX, XXX, XXX−XXX