Full Paper
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tion (35 mg, 90%). H NMR (300 MHz, (CD ) CO): d=9.11 (dd, J=5,
791 (w), 763 (w), 740 (w), 721 (w), 558 (s); UV/Vis (MeCN): lmax
3
2
2
7
1
8
, 1H, ArꢀH), 8.42 (dd, J=8, 1, 1H, ArꢀH), 8.29 (d, J=8, 1H, ArꢀH),
.91 (d, J=8, 1H, ArꢀH), 7.88 (d, J=8, 1H, ArꢀH), 7.73 (dd, J=8, 5,
H, ArꢀH), 7.68 (d, J=8, 1H, ArꢀH), 7.12 (s, 2H, ArꢀH), 6.63 (td, J=
, 1, 1H, ArꢀH), 6.57 (td, J=8, 1, 1H, ArꢀH), 6.49 (d, J=8, 1H, Arꢀ
(e )=207 (70.7), 282 (34.4), 305 (sh, 17), 338 nm (sh, 5ꢂ
max
3
ꢀ1
ꢀ1
+
10 mol cm ); HRMS (ESI): m/z calcd for C H ClF N O PIr :
4
0
42
6
4
3
2
+
ꢀ
999.2211 [M +[PF ] ]; found: 999.2189; elemental analysis calcd
6
(%) for C H ClF N O P Ir.H O: C 41.33, H 3.82, N 4.82; found: C
40
42
12
4
3
2
2
H), 6.47 (d, J=8, 1H, ArꢀH). 5.50 (s, 1H, 2-BIH), 4.63 (d, J=16, 1H,
41.51, H 3.52, N 4.79.
CH ), 4.57 (d, J=16, 1H, CH ), 3.80 (s, 6H, OMe), 3.61 (s, 3H, OMe),
2
2
2
.59 ppm (s, 3H, NMe); UV/Vis (MeCN): l (emax)=223 (86.7), 266
max
Chemical reduction
3
ꢀ1
ꢀ1
(
37.2), 316 nm (br, sh, 9ꢂ10 mol cm ); HRMS (ESI): m/z calcd for
+
+
BI
C H N O : 493.2240 [M+H ]; found: 493.2243.
Separate chemical reductions of [Cp*Rh(L )Cl][PF ] were per-
6 2
3
0
29
4
3
formed using excess formate ion, sodium cyanoborohydride, and
sodium borohydride in [D ]MeOH and in [D ]MeCN. The reactions
BI+
BI
[
Cp*Rh(L )Cl][PF ] : A solution of [L ][PF ] (50 mg, 0.0786) in
6 2 6
4
5
MeCN (1 mL) was added to a solution of [Cp*RhCl2]2 (27 mg,
.0437 mmol) in MeCN (2 mL) at which point the colour changed
from red to orange-yellow. The reaction mixture was stirred for
0 min. The crude product was precipitated with K[PF ] (sat., aq.),
collected by filtration and recrystallised from acetone/methanol to
give [Cp*Rh(L )Cl][PF6]2 as an orange-yellow powder (74 mg,
1
were monitored by NMR spectroscopy. In all cases, the H NMR
spectra of the reaction solution revealed complicated mixtures to
have formed, and clear information about formation of rhodium
hydride intermediates or species with benzimidazoline groups was
not obtained. Individual compounds could not be isolated from
the reaction mixtures by crystallisation or, for several reactions on
a larger scale, through use of conventional chromatographic tech-
niques.
0
3
6
BI+
1
8
9%). H NMR (400 MHz, (CD ) CO): d=9.62 (dd, J=5, 1, 1H, Arꢀ
3
2
H), 9.05 (dd, J=8, 1, 1H, ArꢀH), 8.86 (d, J=8, ArꢀH), 8.32–8.40 (m,
2
7
H, 2ꢂArꢀH), 8.31 (d, J=8, 1H, ArꢀH), 8.07 (d, J=8, 1H, ArꢀH),
.76 (td, J=8, 1, 1H, ArꢀH), 7.66 (s, br, 1H, ArꢀH), 7.64 (s, br, 1H,
Transfer hydrogenation catalysis
ArꢀH), 7.57 (d, J=8, 1H, ArꢀH), 7.47 (td, J=8, 1, 1H, ArꢀH), 6.92
(
(
d, J=17, 1H, CH ), 6.43 (d, J=17, 1H, CH ), 4.24 (s, 3H, NMe), 3.96
2 2
A 1:1 sodium formate/formic acid solution was made as follows;
sodium formate (17.95 g, dried at 1108C for 1 h before use,
s, br, 3H, OMe), 3.93 (s, br, 3H, OMe), 3.90 (s, 3H, OMe), 1.70 (Cp*ꢀ
1
9
1
Me); F{ H} NMR (376.3 MHz, (CD ) CO): d=72.63 ppm (J=700,
3
2
0
.264 mol) and formic acid (13.81 g, 88% in water, 0.264 mol) were
ꢀ
13
1
[
PF ] ); C{ H} NMR (100.7 MHz, (CD ) CO): d=158.33, 155.76,
6 3 2
placed in a 1.00 L volumetric flask and made up to volume with
MeOH. The solution was shaken until the sodium formate was
completely dissolved.
1
1
1
55.66, 154.38, 153.19, 147.13, 146.68, 143.20, 141.92, 140.74,
33.49, 132.23, 131.70, 131.21, 129.04, 128.65, 128.49, 128.46,
28.37, 124.83, 116.14, 114.73, 114.60, 108.92 (25ꢂCaryl), 99.09 (d,
Imine (0.240 mmol), metal catalyst (0.0024 mmol), and silver triflate
(0.0026 mmol) were combined in a Schlenk flask and dissolved in
MeOH (9.00 mL). The solution was deaerated with a steady stream
of dinitrogen for approximately 10 minutes, at which point a por-
tion of the methanolic solution of 1:1 formic acid/sodium formate
J
=4, Cp*) 61.01 (CH ), 57.04 (OMe), 53.87 (OMe), 33.86 (NMe),
2
CꢀRh
ꢀ1
9
1
1
1
(
3
.56 (Cp*ꢀMe); FT-IR: cm 2946 (w), 2841 (w), 1629 (w), 1587 (m),
514 (m), 1495 (m), 1483 (s), 1472 (s), 1430 (m), 1418 (m) 1396 (m),
378 (w), 1359 (w), 1331 (m), 1249 (m), 1233 (w), 1160 (w), 1129 (s),
019 (m), 994 (m), 908 (w), 841 (vs), 790 (m), 760 (m), 741 (w), 724
(1.00 mL, 0.530 mmol total) was injected. The solution was purged
w), 558 ppm (s); UV/Vis (MeCN): l (emax)=206 (71.0), 279 (37.9),
max
03 nm (sh, 15ꢂ10 mol cm ); HRMS (ESI): m/z calcd for
3
ꢀ1
ꢀ1
with high-purity nitrogen for 5 min., at which point the flask was
sealed under nitrogen. Aliquots were taken at various intervals, the
+
2+
ꢀ
C H ClF N O PRh : 909.1637 [M +[PF ] ]; found: 909.1622; ele-
4
0
42
6
4
3
6
MeOH removed, the residue taken up in CDCl and analysed by
3
mental analysis calcd (%) for C H ClF N O P Rh.H O: C 44.77, H
.13, N 5.22; found: C 44.89, H 3.74, N 5.14.
40
42
12
4
3
2
2
1
H NMR spectroscopy. The NMR spectra revealed the reaction mix-
4
tures contained no side-products and so yields could be calculated
from the integrals of the NMR signals using the formula:
(% amine)/(% amine + % imine)ꢂ100. Representative NMR spectra
are presented in the Supporting Information, Figure 7S.
BI+
BI
[
(
Cp*Ir(L )Cl][PF ] : A solution of [L ][PF ] (50 mg, 0.0786) in MeCN
6 2 6
1 mL) was added to a solution of [Cp*IrCl ] (35 mg, 0.0439 mmol)
in MeCN (2 mL) at which point the colour changed from red to
orange-yellow. The reaction mixture was stirred for 30 min. The
2
2
crude product was precipitated using K[PF ] (sat., aq.), collected by
filtration and recrystallised from acetone/methanol to give
6
X-ray crystallography
BI+
BI
BI
[
Cp*Ir(L )Cl][PF6]2 as pale yellow microcrystals (84 mg, 93%).
The X-ray diffraction measurements for [L ][PF ] and [Cp*Ir(L )Cl]
6
1
H NMR (400 MHz, (CD ) CO): d=9.59 (dd, J=5, 1, 1H, ArꢀH), 9.05
[PF ] were carried out on a Bruker Kappa II CCD diffractometer at
3
2
6 2
(
dd, J=8, 1, 1H, ArꢀH), 8.87 (d, J=8, ArꢀH), 8.42 (d, J=8, 1H, Arꢀ
150 K by using graphite-monochromated MoKa radiation (l=
H), 8.38 (dd, J=8, 5, 1H, ArꢀH), 8.35 (d, J=8, 1H, ArꢀH), 8.22 (d,
J=8, 1H, ArꢀH), 8.21 (d, J=8, 1H, ArꢀH), 7.78 (td, J=8, 1, 1H, Arꢀ
H), 7.71 (s, br, 1H, ArꢀH), 7.60 (s, br, 1H, ArꢀH), 7.56 (d, J=8, 1H,
0.710723 ꢁ). Symmetry-related absorption corrections using the
[33]
program SADABS were applied and the data were corrected for
[34]
Lorentz and polarisation effects using Bruker APEX2 software.
The structures were solved by direct methods and the full-matrix
least-squares refinement was carried out using SHELXL. Non-hy-
drogen atoms were refined anisotropically.
ArꢀH), 7.50 (t, J=8, 1, 1H, ArꢀH), 6.89 (d, J=17, 1H, CH ), 6.34 (d,
2
[35]
J=17, 1H, CH ), 4.25 (s, 3H, NMe), 3.95 (s, br, 3H, OMe), 3.90 (s, br,
2
19
1
3
(
H, OMe), 3.89 (s, 3H, OMe), 1.67 (Cp*ꢀMe); F{ H} NMR
ꢀ
6
13
1
376.3 MHz, (CD ) CO): d=72.63 ppm (J=700, [PF ] ); C{ H} NMR
3
2
(
1
1
100.7 MHz, (CD ) CO): d=158.38, 156.30, 156.18, 154.12, 153.85,
3 2
49.10, 148.37, 143.78, 142.68, 141.26, 134.10, 132.96, 132.22,
31.86, 129.77, 129.50, 129.34, 129.07, 128.98, 125.28, 116.61,
Computational methods
Standard density functional theory calculations were carried out
[36]
1
5
15.25, 115.11, 109.46, 109.31 (25ꢂCaryl), 91.79 (Cp*), 61.55 (CH2),
7.55 (OMe), 55.21 (OMe), 34.39 (NMe), 9.86 ppm (Cp*ꢀMe); FT-IR:
cm 2947 (w), 2846 (w), 1621 (w), 1586 (m), 1514 (m), 1496 (m),
with Gaussian 09. Geometries were optimised with the M06L
[37]
[38]
procedure in conjunction with the def2-SVP basis set Follow-
ing each geometry optimisation, harmonic frequency analysis was
carried out to confirm the nature of the stationary point as a mini-
mum or a transition state. The reaction profile was examined using
ꢀ1
1
1
481 (s), 1472 (s), 1431 (w), 1418 (m), 1359 (w), 1332 (m), 1251 (m),
232 (w), 1162 (w), 1128 (s), 1029 (w), 995 (w), 909 (w), 841 (vs),
&
&
Chem. Eur. J. 2014, 20, 1 – 15
12
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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