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T. Chen et al. / Tetrahedron 63 (2007) 4874–4880
m/z (%): 426 (M+, 100), 344 (M+ꢁ82, 12), 255 (M+ꢁ171,
13), 241 (M+ꢁ185, 9); Anal. Calcd for C24H18N4O4 re-
quires: C, 67.70; H, 4.25; N, 13.14%. Found: C, 67.41; H,
4.01; N, 13.31%.
CDCl3, TMS): d 2.03 (s, 3H, Me), 4.35 (s, 6H, Me), 6.56
(d, J¼8.1 Hz, 2H, ArH), 6.70 (d, J¼7.2 Hz, 2H, ArH),
7.07 (t, J¼7.2 Hz, 2H, ArH), 7.15 (t, J¼7.2 Hz, ArH),
7.22–7.39 (m, 6H, ArH), 8.17 (d, J¼8.1 Hz, 2H, ArH);
MS (EI) m/z (%): 703 (M+ꢁ127, 9), 644 (M+ꢁ186, 25),
576 (M+ꢁ254, 11), 517 (M+ꢁ313, 100), 268 (M+ꢁ562, 17);
Anal. Calcd for C30H25I2N4O2Rh requires: C, 43.40; H,
3.04; N, 6.75%. Found: C, 43.72; H, 3.04; N, 6.27%.
3.1.2. Synthesis of compound 3. A mixture of 2 (852 mg,
2 mmol), 10% Pd–C (100 mg) in 100 mL of EtOAc was
stirred under H2 atmosphere (15 atm) at 60 ꢀC for 8 h. After
cooling to room temperature, Pd–C was removed by filtra-
tion. The solvent was evaporated under reduced pressure.
The residue was purified by silica gel flash column chroma-
tography (eluent: petroleum ether/ethyl acetate 4:1–1:1) to
give 3 as a white solid; yield: 688 mg (94%). Mp 235–
237 ꢀC; IR (CH2Cl2): n 3329, 3281, 2926, 2319, 1727,
3.1.6. Synthesis of bis-NHC–Ir(III) complex 7. A mixture
of
5
(134 mg, 0.20 mmol), [Ir(COD)Cl]2 (67 mg,
0.10 mmol), NaOAc (134 mg, 1.60 mmol), and KI (66 mg,
0.40 mmol) was stirred in CH3CN (12 mL) under reflux
for 24 h. After cooling, volatiles were removed under re-
duced pressure and the residue was purified by silica gel
flash column chromatography (eluent: petroleum ether/ethyl
acetate 1:1) to give a yellow solid, bis-NHC–Ir(III) complex
7. Yield: 117 mg (64%). A single crystal suitable for X-ray
crystal analysis was obtained by recrystallization from a
saturated solution of petroleum ether/ethyl acetate (1:1).
Mp>250 ꢀC (dec); IR (CH2Cl2): n 3058, 2950, 2374,
1616, 1507, 1262, 999, 748 cmꢁ1 1H NMR (300 MHz,
;
DMSO-d6): d 4.71 (br, 4H, NH2), 5.99 (br, 2H, NH), 6.50–
6.57 (m, 4H, ArH), 6.69–6.72 (m, 2H, ArH), 6.81–6.92
(m, 6H, ArH), 7.12–7.21 (m, 4H, ArH); MS (EI) m/z (%):
366 (M+, 100), 259 (M+ꢁ107, 46), 166 (M+ꢁ200, 15);
HRMS (EI) calcd for C24H22N4 (M+) requires 366.1844,
found: 366.1850.
1711, 1474, 1326, 1094, 954, 744 cmꢁ1
;
1H NMR
3.1.3. Synthesis of compound 4. Compound 3 (366 mg,
1.0 mmol), toluenesulfonic acid (20 mg), and triethyl ortho-
formate [HC(OC2H5)3] (10 mL) were heated at 100 ꢀC for
16 h. After the reaction mixture was cooled to room temper-
ature, 40 mL of petroleum ether was added to precipitate
white solid, filtered, and the precipitate was washed with
light petroleum ether to give 4 as a white solid; yield:
365 mg (95%). Mp 166–167 ꢀC; IR (CH2Cl2): n 3430,
3054, 2925, 2844, 1712, 1614, 1492, 1227, 1009, 787,
(300 MHz, CDCl3, TMS): d 2.05 (s, 3H, Me), 4.24 (s, 6H,
Me), 6.52 (d, J¼8.1 Hz, 2H, ArH), 6.67 (dd, J¼7.2,
1.5 Hz, 2H, ArH), 7.03–7.11 (m, 4H, ArH), 7.18 (t, J¼
7.2 Hz, 2H, ArH), 7.24–7.27 (m, 2H, ArH), 7.35 (dt, J¼
7.2, 1.5 Hz, 2H, ArH); MS (EI) m/z (%): 920 (M+, 11), 793
(M+ꢁ127, 38), 733 (M+ꢁ186, 9), 666 (M+ꢁ254, 30), 607
(M+ꢁ313, 100); Anal. Calcd for C30H25I2IrN4O2 requires:
C, 39.18; H, 2.74; N, 6.09%. Found: C, 39.37; H, 2.51; N
5.81%.
1
737 cmꢁ1; H NMR (300 MHz, CDCl3, TMS): d 6.51 (d,
2H, J¼8.1 Hz, ArH), 6.77 (t, 2H, J¼7.5 Hz, ArH), 7.01 (t,
2H, J¼7.5 Hz, ArH), 7.21 (s, 2H, NCHN), 7.26–7.28 (m,
2H, ArH), 7.47–7.53 (m, 4H, ArH), 7.55–7.60 (m, 2H, ArH),
7.71 (d, J¼7.5 Hz, 2H, ArH); 13C NMR (75 MHz, CDCl3):
d 109.2, 119.4, 122.3, 123.3, 125.9, 128.6, 129.6, 132.5,
132.8, 133.5, 133.6, 141.7, 142.4; MS (EI) m/z (%): 386 (M+,
100), 268 (M+ꢁ118, 51), 193 (M+ꢁ193, 5); Anal. Calcd for
C26H18N4 requires: C, 80.81; H, 4.69; N, 14.50%. Found: C,
80.48; H, 4.53; N, 14.40%.
3.1.7. Synthesis of NHC–Rh(I) complex 8. A mixture of 5
(134 mg, 0.20 mmol), [Rh(COD)Cl]2 (48 mg, 0.10 mmol),
KOtBu (50 mg, 0.45 mmol), and KI (66 mg, 0.40 mmol)
was stirred in THF (12 mL) under reflux for 24 h. After cool-
ing, volatiles were removed under reduced pressure and the
residue was purified by silica gel flash column chromato-
graphy (eluent: petroleum ether/ethyl acetate 5:1–3:1) to
give an orange solid, Rh(I) complex 8. Yield: 22 mg
(14%). A single crystal suitable for X-ray crystal analysis
was obtained by recrystallization from a saturated solution
of petroleum ether/ethyl acetate (4:1). Mp>250 ꢀC (dec);
IR (CH2Cl2): n 3061, 2956, 2925, 2317, 1722, 1494, 1384,
3.1.4. Synthesis of dibenzimidazolium salt 5. Compound 4
(386 mg, 1.0 mmol) and CH3I (0.48 mL, 8.0 mmol) in
CH3CN (10 mL) were stirred at 80 ꢀC for 5 h. After cooling
to room temperature, volatiles were removed under reduced
pressure and the obtained solid compound 5 was used for the
next reaction without further purification. MS (ESI) m/z:
543.1 (M+ꢁI), 208.1 (M+ꢁ2I)/2.
1
1338, 1081, 963, 746 cmꢁ1; H NMR (300 MHz, CDCl3,
TMS): d 0.83–0.98 (m, 2H, CH2), 1.07–1.15 (m, 1H, CH2),
1.38–1.53 (m, 3H, CH2), 1.69–1.71 (m, 1H, CH2), 1.78–1.91
(m, 1H, CH2), 2.16–2.23 (m, 1H, CH), 2.52–2.65 (m, 1H,
CH), 3.33 (s, 3H, Me), 4.20 (s, 3H, Me), 4.78–4.79 (m,
1H, CH), 4.88–4.92 (m, 1H, CH), 6.37–6.53 (m, 1H, ArH),
6.87–6.93 (m, 2H, ArH), 7.04–7.09 (m, 4H, ArH), 7.15–
7.23 (m, 5H, ArH), 7.46–7.51 (m, 2H, ArH), 8.06–8.21
(m, 1H, ArH), 8.74–8.76 (m, 1H, ArH); MS (ESI) m/z:
641.2 (M+ꢁI); HRMS (ESI) calcd for C36H34IrN4O
(M+ꢁI) requires 641.1788, found: 641.1753.
3.1.5. Synthesis of bis-NHC–Rh(III) complex 6. A mixture
of
5
(134 mg, 0.20 mmol), [Rh(COD)Cl]2 (48 mg,
0.10 mmol), NaOAc (134 mg, 1.60 mmol), and KI (66 mg,
0.40 mmol) was stirred in CH3CN (12 mL) under reflux
for 24 h. After cooling, volatiles were removed under re-
duced pressure and the residue was purified by silica gel
flash column chromatography (eluent: petroleum ether/ethyl
acetate 1:1) to give an orange solid, bis-NHC–Rh(III) com-
plex 6. Yield: 137 mg (83%). A single crystal suitable for X-
ray crystal analysis was obtained by recrystallization from
a saturated solution of petroleum ether/ethyl acetate (1:1).
Mp>250 ꢀC (dec); IR (CH2Cl2): n 3063, 2949, 2376, 1464,
3.1.8. Synthesis of NHC–Ir(I) complex 9. A mixture of 5
(134 mg, 0.20 mmol), [Ir(COD)Cl]2 (67 mg, 0.10 mmol),
KOtBu (50 mg, 0.45 mmol), and KI (66 mg, 0.40 mmol)
was stirred in THF (12 mL) under reflux for 24 h. After cool-
ing, volatiles were removed under reduced pressure and the
residue was purified by silica gel flash column chromato-
graphy (eluent: petroleum ether/ethyl acetate 4:1–3:1) to
1332, 1220, 1095, 949, 743 cmꢁ1 1H NMR (300 MHz,
;