J.M. Gichumbi et al. / Journal of Molecular Catalysis A: Chemical 416 (2016) 29–38
31
(
80 mg, 0.42 mmol) in 10 ml ethanol. The mixture was stirred in
p-cymene); 5.63 (d, JHH = 6.12 Hz, 1H, Ar, p-cymene); 5.56 (d,
JHH = 6.12 Hz, 1H, Ar, p-cymene); 2.61 (m, 1H, CH(CH ) ), 2.35 (d,
an ice bath maintained at zero degrees for two hours resulting in
orange or yellow solids, isolated by gravity filtration, washed with
diethyl ether and dried in vacuo.
3
2
JHH = 6.56 Hz, 6H, CH-Me (cymene)); 2.14 (s, 3H, p-Me (cymene));
2
13
0.97 (s,6H, 2CH ).
C NMR (400 MHz, DMSO-d ). ı 166.74
3
6
2
a
(CH N), 155.90 (C -Py), 154.57 (Py); 149.70 (Py); 139.88 (Py);
2
◦
decomp.) 1H NMR
Orange powder, yield 83%, m.p. 190.0 C
400 MHz, DMSO-d ): ı 9.56 (d, JHH = 5.4 Hz, 1H, Py); 8.88 (s, 1H,
CH N); 8.30 (m, 2H, Py); 7.89 (m, 1H, Py); 7.38 (s, 2H, Ar); 7.22(s,
(
138.42 (Py); 137.58 (Ar); 130.24 (Ar); 129.76 (Ar); 128.71(Ar);
122.91(Ar);120.09 (Ar); 105.13 (Ar, p-cymene); 103.04 (Ar, p-
cymene); 86.47(Ar, p-cymene); 85.80 (Ar, p-cymene); 85.30 (Ar,
(
6
1
1
H, Ar), 6.02 (d, JHH = 6.24 Hz,1H, p-cymene); 5.74(d, JHH = 6.20 Hz,
H, p-cymene); 5.65 (d, JHH = 6.12 Hz, 1H, Ar, p-cymene); 5.56
p-cymene); 85.19 (Ar, p-cymene); 30.46 (CH -, p-cymene); 21.74
3
(CH , p-cymene); 21.44 (CH , p-cymene); 19.52 (CH , p-cymene);
3
3
3
−
19.19 (CH ), 18.21(CH ). IR (KBr, cm ): 1610 ( CH N), 830 (P-F).
3 3
1
(
d, JHH = 6.12 Hz, 1H, Ar, p-cymene), 2.50 (m, 1H, CH(CH ) );
3
2
2
1
1
.40 (s, 3H, p-Me (cymene)); 2.13 (m, 6H, CH-Me (cymene));
Anal. Calcd for [C24H28ClN Ru] PF C, 46.05; H, 4.51; N, 4.48. Found:
2
2 6
1
3
+
.01(m,6H,2CH ). C NMR (400 MHz, DMSO-d ). ı 167.3 (C -Py),
45.10; H, 4.59; N, 4.64 .MS (ESI, M/Z): 481.0976 for [C24H28ClN Ru]
3
6
2
2
55.9 (CH N), 155.5(Py); 151.9 (Py); 139.9 (Py); 138.8 (Py); 129.44
(
(
(
Ar); 131.1(Ar); 129.8 (Ar); 128.8 (Ar);119.9 (Ar);105.5 (Ar); 86.3
Ar, p-cymene); 85.8 (Ar, p-cymene)); 85.6 (Ar, p-cymene)) 85.3
Ar, p-cymene)) 30.4 (CH - p-cymene); 21.7 (CH , p-cymene);
2.3. X-ray crystallography
Crystals of compounds 1a, 1d and 2c suitable for X-ray diffrac-
tion studies were grown by slow diffusion of hexane layered over
solutions of the compounds in dry acetone. Crystals were selected
and glued onto the tip of glass fibres. The crystals were then
mounted in a stream of cold nitrogen at 100(1) K and centred in
the X-ray beam by using a video camera. The crystal evaluation and
data collection were performed on a Bruker Smart APEX II diffrac-
tometer to crystal distance of 4.00 cm. The initial cell matrix was
obtained from three series of scans at different starting angles. Each
3
3
2
1.3 (CH , p-cymene); 20.89 (CH , p-cymene); 18.1(CH ). IR (KBr,
3 3 3
−
1
cm ): 1608 ( CH N), 828 (P-F). Anal. Calcd for [C24H28ClN Ru]
PF6 C, 46.05; H, 4.51; N, 4.48. Found: C, 45.98; H, 3.80; N, 4.51 MS
2
+
(
ESI, M/Z): 481.0981 for [C24H28ClN Ru]
2
2
b
The procedure described above for 2a was used except ligand b
was used (74 mg, 0.35 mmol).
Orange powder, yield 82%, m.p. 193.5 C
400 MHz, DMSO-d ): ı 9.62 (d, JHH = 5.36 H Hz, 1H, Py); 8.83 (s, 1H,
◦
decomp.) 1H NMR
(
◦ ◦
(
series consisted of 12 frames collected at intervals of 0.5 in a 6
6
CH N); 8.24 (m, 1H, Py); 7.93 (m, 1H, Py); 7.52 (s, 1H, Ar); 7.34
s, 2H, Ar), 5.98 (s, 1H, p-cymene); 5.72 (d, JHH = 6.16 H Hz, 2H, p-
cymene); 5.28 (s, 1H, Ar, p-cymene); 2.61 (m, 1H, CH(CH ) ); 2.41
range with the exposure time of about 10 s per frame. The reflec-
tions were successfully indexed by an automated indexing routine
built into the APEX II programme suite [30]. The final cell constants
were calculated from a set of 6460 strong reflections from the actual
data collection. Data collection method involved scans of width
(
3
2
(
s, 3H, p-Me(cymene)); 2.26 (s, 3H, CH-Me (cymene)); 2.08 (s, 3H,
13
CH-Me (cymene)); 1.02 (m, 6H, 2CH ). C NMR (400 MHz, DMSO-
3
◦
+
d ). ı 171.1930 (C -Py), 156.5 (CH N), 154.8(Py); 140.48 (Py);
0.5 . Data reduction was carried out using the programme SAINT
6
2
1
39.12 (Py); 130.57 (Py); 130.30 (Ar); 129.63 (Ar); 126.4 (Ar); 120.8
[30]. The structure was solved by direct methods using SHELXS [31]
and refined by SHELXL [30]. Non-H atoms were positioned geomet-
rically and allowed to ride on their respective parent atoms. All
H atoms were refined isotropically. The absorption correction was
based on fitting a function to the empirical transmission surface as
sampled by multiple equivalent measurements [30]. Crystal data
and structure refinement information for compounds 1a, 1d and
2c are summarized in Table 1.
(
Ar); 101.8(Ar); 86.3 (Ar, p-cymene); 87.4 (Ar, p-cymene)); 30.8
(
CH - p-cymene); 22.6 (CH , p-cymene); 21.6 (CH , p-cymene);
3
3
3
−
0.8 (CH , p-cymene); 18.5(CH ). IR (KBr, cm ): 1618 ( CH N),
3 3
1
2
8
4
29 (P-F). Anal. Calcd for [C24H28ClN Ru] PF6 C, 46.05; H, 4.51; N,
.48. Found: C, 45.40; H, 4.68; N, 4.23. MS (ESI, M/Z): 481.0997 for
2
+
[
C24H28ClN Ru]
2
2
c
The procedure described above for 2a was used except ligand c
was used (74 mg, 0.35 mmol).
2.4. General procedure for transfer hydrogenation of ketones
Orange powder, yield 85%, m.p. 207.0 C (decomp.) 1H NMR
◦
(
400 MHz, DMSO-d ): ı 9.62 (d, JHH = 5.28 Hz, 1H, Py); 8.87 (s, 1H,
In a typical experiment the ketone (8.5 mmol), ruthenium(II)
complex (0.00425 mmol) and NaOH (3.4 mmol) in 10 ml 2-propanol
were introduced into a Schlenk tube fitted with a reflux condenser
6
CH N); 8.34(m, 2H, Py); 7.93 (t, 1H, Py); 7.39 (d, JHH = 7.76 Hz,
1
2
H, Ar); 7.26 (d, JHH = 7.64 Hz, 1H, Ar), 5.95(d, JHH = 5.96 Hz,
H, p-cymene); 5.73(d, JHH = 6.00 Hz, 2H, p-cymene); 5.34(d,
◦
and heated to 82 C in an inert atmosphere. The reaction was then
JHH = 4.92 Hz, 1H, Ar, p-cymene); 2.51 (m, 1H, CH(CH ) ); 2.36
monitored at various time intervals by the use of GC. This was
achieved by taking an aliquot which was first passed through a
pad of silica and then injected (0.1 l) into the GC. The correspond-
ing alcohol was the only product detected in all cases. The identity
of the alcohol was confirmed by comparison with commercially
available (Aldrich Chemical Co.) pure samples.
3
2
(
d, JHH = 10.84 Hz, 6H, CH-Me2 (cymene)); 2.09 (s, 3H, p-Me
(
cymene)); 1.05(d, JHH = 6.72HZ, 3H,CH ); 0.96 (d, JHH = 6.80 Hz,
3
1
3
3
1
1
H,CH ).
C NMR (400 MHz, DMSO-d ). ı 170.43 (C -Py),
3
6 2
54.35 (CH N), 151.18(Py); 140.01(Py); 136.05(Py); 131.43(Py);
30.01(Ar); 129.17(Ar); 123.24(Ar); 105.73(Ar);100.66 (Ar); 87.27
(
Ar, p-cymene); 86.91 (Ar, p-cymene)); 86.36 (Ar, p-cymene); 30.38
(
CH - p-cymene); 22.02 (CH , p-cymene); 20.93 (CH , p-cymene);
3. Results and discussions
3
3
3
−
0.49 (CH , p-cymene); 17.89 (CH ); 17.13 (CH ). IR (KBr, cm ):
3 3 3
1
2
1
4
4
611 ( CH N), 829 (P-F). Anal. Calcd for [C24H28ClN Ru] PF6 C,
3.1. Synthesis and characterization of cationic iminopyridyl
Ru(II)-arene complexes
2
6.05; H, 4.51; N, 4.48. Found: 45.62; H, 4.02; N, 4.58. MS (ESI, M/Z):
+
81.0993 for [C24H28ClN Ru]
2
2
d
The mononuclear iminopyridyl complexes 1a–1d and 2a–2d
were synthesized by stirring the ruthenium dimers [( -
6
The procedure described above for 2a was used except ligand d
was used (74 mg, 0.35 mmol).
arene)Ru(-Cl)Cl]2 (where arene = C H6 or p-cymene) with the
corresponding N,N -chelating ligand a–d respectively, in methanol
6
Yellow powder, yield 82%, m.p. 198.0 C (decomp.) 1H NMR
◦
ꢀ
(
400 MHz, DMSO-d ): ı 9.56 (d, JHH = 5.44 Hz,1H, Py); 8.87 (s, 1H,
or DCM at room temperature (Scheme 1).
6
CH N); 8.29 (m, 2H, Py); 7.87(m, 1H, Py); 7.55 (m, 2H, Ar); 7.38(m,
H, Ar), 6.06(d, JHH = 6.24 Hz,1H, p-cymene); 5.74(d, JHH = 6.2 Hz,1H,
The coordination of the ligand to form the complexes was
confirmed by comparing the IR spectra, by looking at the
1