Article
were synthesized, and [Li(bimcaHomo)] and [K(bimcaHomo)] were
generated in situ according to the literature. Liquid chemicals from
commercial suppliers were degassed through freeze−pump−thaw
5b
5b
1
13
cycles prior to use. H and C NMR spectra were recorded using a
Bruker AVANCE II+ 400 spectrometer. Chemical shifts δ (ppm) are
given relative to the solvent’s residual proton and carbon signals,
respectively: THF-d , 3.58 ppm ( H NMR) and 67.57 ppm ( C
NMR); C D , 7.16 ppm ( H NMR) and 128.39 ppm ( C NMR). H
1
13
8
1
13
1
6
6
NMR data for diamagnetic compounds are reported as follows:
chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, br = broad, m = multiplet), coupling constants (Hz),
integration, assignment. The assignment of peaks is based on 2D
NMR correlation and NOE spectra.
X-ray Data Collection and Structure Analysis. Suitable crystals
Homo
collection (except for [Co(bimca
Supporting Information) was carried out on a Bruker APEX Duo
CCD with an Incoatec IμS Microsource with a Quazar MX mirror
using Mo Kα radiation (λ = 0.71073 Å) and a graphite
monochromator. Corrections for absorption effects were applied
Figure 6. Solid-state molecular structure of 8. Atoms are shown with
anisotropic atomic displacement parameters at the 50% probability
level. The cocrystallized benzene molecule and the hydrogen atoms
24a
(
except for the hydrido ligands) are omitted for clarity. The crystal
using SADABS. All structures were solved by direct methods using
24
structures of 7 and 8 are isomorphous. Selected bond lengths (Å) and
angles (deg): Rh1−N9 = 2.062(2), Rh1−C2′ = 2.037(2), Rh1−C7′ =
SHELXT and refined using SHELXL. In the case of structure 1 and
25
Homo
[Co(bimca
)2]Br the SQUEEZE routine was applied for
2
2
.029(2), Rh2−N59 = 2.035(2), Rh2−C52′ = 2.036(2), Rh2−C57′ =
.029(2), Rh1−Rh2 = 2.9335(3); N9−Rh1−Rh2 = 107.53(5), N59−
disordered solvent.
Synthesis of [Co(bimca
Homo
)Br] (1). CoCl (9.5 mg, 73 μmol, 1
2
Rh2−Rh1 = 108.97(5). The metal−hydrogen bond lengths and
angles were fixed at Rh1−H1a = 1.54, Rh1−H2a = 1.58, Rh2−H1b =
equiv) was added to a previously prepared solution of [Li-
Homo
(bimca
)] (73.4 μmol) at room temperature. The solution was
1
.54, Rh2−H2b = 1.58 on the basis of DFT calculations. Hydrogen
shaken for 2 min. After 12 h, the brown crystals that appeared were
filtered, washed with THF (0.5 mL × 3), and dried in vacuo. Single
crystals suitable for X-ray diffraction were obtained (39.1 mg).
Although C, H, N analysis reveals residual impurities, most probably
LiBr and THF, the material can be used directly in the next step. Anal.
Calcd for C H BrCoN ·0.25LiBr·1.25C H O: C, 60.88; H, 6.55; N,
bridges: 2.54 Å (Rh1−H2b) and 2.79 Å (Rh2−H2a).
possibly due to a paramagnetic influence. More detailed
analyses are beyond the scope of this investigation.
3
4
40
5
4
8
9
.10. Found: C, 61.02; H, 6.30; N, 8.95.
Homo
)] (2) from [Co(bimcaHomo)Br] (1).
CONCLUSIONS
Synthesis of [Co(bimca
■
Homo
To a suspension of [Co(bimca
)Br] (1) (39.1 mg from the
On the basis of the pentadentate pincer bis-NHC ligand
material obtained above) in THF (2.0 mL) was added KC (8.0 mg,
Homo
8
bimca
, the corresponding cobalt complex 2 was success-
59 μmol). The suspension was stirred at room temperature for 12 h in
fully synthesized by a deprotonation−transmetalation−reduc-
an argon-filled glovebox. After completion of the reaction, the mixture
was filtered with a syringe filter and purified by column
tion sequence starting from CoCl which involves [Co-
2
Homo
Homo
(
bimca
)Br] (1), in which the bimca
ligand shows a
chromatography using THF as eluent in the glovebox. [Co-
Homo
tetradentate coordination mode. The iridium catalyst 4 was
(bimca
)] (2) containing 0.75 mol of THF (13.0 mg, 21 μmol,
synthesized straightforwardly by transmetalation of [Li-
28% yield over two steps) was obtained as a red solid after removal of
the solvent. Single crystals suitable for X-ray diffraction were grown
from a concentrated solution of 2 in toluene and pentane at −30 °C.
Homo
(
bimca
)] with [Ir(μ-Cl)(COD)] . In contrast to the
2
highly reactive rhodium analogue 3, complexes 2 and 4 were
much less active in the nucleophilic epoxide isomerization.
This can be ascribed to the lower oxidation potential of 2 in
comparison to 3 and in the case of 4 to a higher oxidation
potential, which is also displayed in the increasing metal-
lacyclopropane character of the coordinated N-homoallyl
moieties. When the reaction was carried out in the presence
1
4
H NMR (400 MHz, THF-d ): δ 8.00 (d, J = 1.3 Hz, 2H, H-4/5),
8
HH
3
4
7
7
2
2
.79 (d, J = 1.0 Hz, 2H, H-5′), 7.37 (d, J = 1.3 Hz, 2H, H-2/
HH
HH
3
2/3
), 6.91 (d, J = 1.0 Hz, 2H, H-4′), 4.38 (br ps t, JHH = 12.6 Hz,
HH
2
H, H-12 ), 4.11−4.02 (m, 2H, H-14), 3.72 (br d, J = 12.3 Hz,
ax
HH
3
H, H-12 ), 3.21 (d, J = 8.0 Hz, 2H, H-15 ), 2.86−2.80 (m, 2H,
eq
HH
cis
3
H-13 ), 2.54 (br d, J = 11.3 Hz, 2H, H-15 ), 1.59−1.50 (m,
eq
HH
trans
1
3
2H, H-13 ), 1.50 (s, 18H, H-11). C NMR (101 MHz, THF-d ): δ
ax
8
of 1 bar of H , an increased activity was observed: however,
191.1 (C2′), 138.6 (C3/6), 136.5 (C1a/8a), 128.5 (C4a/5a), 125.4
2
this was at the cost of side reactions. The successful
hydrogenation of the N-homoallyl to N-n-butyl substituents
and the formation of hydrido pincer complexes under these
conditions was confirmed by the X-ray structure analyses of 7
(C1/8), 122.4 (C4′), 115.9 (C5′), 115.0 (C4/5), 107.6 (C2/7), 66.1
(
C15), 57.5 (C14), 50.8 (C12), 35.6 (C13 and C10), 33.0 (C11).
Anal. Calcd for C H N Co·0.75C H O: C, 70.35; H, 7.34; N, 11.09.
Found: C, 70.49; H, 7.47; N, 11.08.
34 40
5
4
8
Homo
Synthesis of [Co(bimca
)] (2) from [Co(PPh ) Cl]. To a
3 3
Homo
(
Ir) and 8 (Rh). Further investigations of these interesting
freshly generated solution of [Li(bimca
)] (29.3 μmol) in THF
complexes will be the subject of future work in our group.
(
0.6 mL) was added [Co(PPh ) Cl] (25.6 mg, 29.3 μmol). The
3 3
mixture was shaken until the cobalt precursor was fully dissolved.
After completion of the reaction, the mixture was purified by column
EXPERIMENTAL SECTION
■
General Information. Unless otherwise noted, all reactions were
carried out under an argon atmosphere in dried and degassed solvents
using Schlenk techniques. All glassware was stored in a preheated
oven prior to use. Toluene, pentane, benzene, and tetrahydrofuran
were purchased from Sigma-Aldrich and dried using an MBraun SPS-
chromatography using THF as eluent in an argon-filled glovebox.
Homo
[Co(bimca
)] (2) was obtained as a red solid after removal of the
solvent; however, it contained residual PPh . The NMR data
3
correspond to the results obtained by starting with 1.
In Situ Generation of LiX Containing [Ir(bimcaHomo)] (4LiX).
8
00 solvent purification system. The lithium and potassium bases
[Ir(μ-Cl)(COD)] (9.7 mg, 15 μmol) was added to a previously
2
Homo
used were obtained from commercial suppliers, dried under vacuum,
and used without further purification. KC8 and Rh(bimca
prepared solution of [Li(bimca
)] (29 μmol) in THF (0.6 mL) at
23
Homo 5b
)
room temperature. The solution was stirred for 30 min. In situ
F
Organometallics XXXX, XXX, XXX−XXX