M.S. Yoon et al. / Journal of Organometallic Chemistry 691 (2006) 5927–5934
5929
in glacial acetic acid (1.7 mL) was heated at 120–125 ꢁC for
8 h under argon. Then, most of the acetic acid was removed
under reduced pressure, and the residue was taken up with
water (40 mL) and extracted with ethyl acetate (2 · 40 mL).
The organic phase was washed with a 5% NaOH solution
and then with H2O. After being dried over anhydrous
Na2SO4, the solvent was evaporated and the residue was
purified by chromatography on silica gel (ethyl acetate/n-
hexane = 1/9) to give pure 9 as a white solid. Yield:
25.7, 21.6. HRMS (FAB) calcd. for C30H31N2Pt
(M ꢁ OTf)+: 614.2135, found 614.2139.
[(5R,7R)-1,3-Bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-
methanoquinolin-2-yl)phenyl]palladium chloride (5b). A mix-
ture of the NCN ligand 9 (0.10 g, 0.24 mmol), K2PdCl4
(0.08 g, 0.24 mmol), and glacial acetic acid (5 mL) was
refluxed for 3 days. The mixture was allowed to cool to
room temperature. The bright grey solid was filtered off
and washed sequentially with H2O, MeOH, and Et2O to
give the pure 5b as a bright yellow solid in 57% yield
25
0.15 g (42%). MP: 145–146 ꢁC. ½aꢂD ꢁ115.8 (c 1.0, CHCl3).
25
1H NMR (CDCl3, 300 MHz): d 0.70 (s, 6H,CH3), 1.33 (d,
J = 9.5 Hz, 2H, CHHendo), 1.43 (s, 6H, CH3), 2.41 (m, 2H,
CH), 2.71 (m, 2H, CHHexo), 2.80 (t, J = 5.5 Hz, 2H, CH),
3.21 (d, J = 2.7 Hz, 4H, CH2), 7.28 (d, J = 7.8 Hz, 2H, Py–
H), 7.51 (m, 3H, Py–H), 7.98 (d, J = 7.8 Hz, Py–H), 8.51 (s,
1H, Ar–H). 13C NMR (CDCl3, 75 MHz): d 156.3, 154.4,
140.0, 139.9, 133.1, 128.6, 126.3, 124.8, 117.0, 45.8, 39.8,
39.1, 36.3, 31.6, 25.6, 20.9. HRMS (FAB) Calcd. for
C30H33N2 (M + H)+: 421.2644, found 421.2639.
(0.075 g). MP 312–313 ꢁC. ½aꢂD ꢁ197.0 (c 1.0, CHCl3). H
NMR (CDCl3, 300 MHz): d 0.72 (s, 6H,CH3), 1.29 (d,
J = 9.6 Hz, 2H, CHHendo), 1.39 (s, 6H, CH3), 2.43 (m,
2H, CH), 2.62 (m, 2H, CHHexo), 2.77 (t, J = 5.7 Hz, 2H,
CH), 4.11 and 3.99 (ABX, JAB = 19.2 Hz, Dm = 0.12 Hz,
4H, CH2), 7.10 (m, 1H, Ar–H), 7.22 (d, 2H, Ar–H), 7.34
(s, 4H, Py–H). 13C NMR (CDCl3, 75 MHz): d 167.1,
162.5, 161.9, 144.2, 143.3, 135.6, 124.8, 122.5, 115.5, 47.3,
40.2, 39.0, 38.8, 31.2, 25.8, 21.7. HRMS (FAB) calcd. for
C30H31N2Pd (M ꢁ Cl)+ 525.1522, found 525.1534.
1
[(5R,7R)-1,3-Bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-
methanoquinolin-2-yl)phenyl]platinum chloride (5a) and its
triflate analogue 6a. A solution of the NCN ligand 9
(0.37 g, 0.87 mmol) and K2PtCl4 (0.36 g, 0.87 mmol) in
acetic acid (12 ml) was refluxed for 3 days. The progress
of the reaction was monitored by thin layer chromatogra-
phy after taking small aliquots and treating them with
water. The mixture was allowed to cool to room tempera-
ture (The appearance of a red color indicated the presence
of unreacted K2PtCl4). The bright yellow solid was filtered
and washed sequentially with water, MeOH, and Et2O to
give pure 5a. Yield: 0.47 g (83%). MP > 328 ꢁC (dec.).
3. Results and discussion
3.1. Synthesis and structure analysis
The enantiomerically pure ligand was prepared accord-
ing to Scheme 1. 1,3-Bis(pyridinoacetyl)benzene diiodide
was obtained in 93% yield from 1,3-diacetylbenzene by
reacting with iodine in pyridine [22]. (1R)-(+)-b-pinocarv-
one was prepared in 70–80% yield from commercially
available (1S)-(ꢁ)-b-pinene (97% ee) following the litera-
ture procedure [23]. The promising NCN pincer ligand
was readily accessible in 42% yield by reaction of 1,3-
bis(pyridinoacetyl)benzene diiodide (8) with (1R)-(+)-pino-
carvone following the Kro¨hnke condensation [24]. The
ligand was purified by chromatography on silica gel (ethyl
25
½aꢂD ꢁ260.8 (c 1.0, CHCl3). 1H NMR (CDCl3,
300 MHz): d 0.72 (s, 6H,CH3), 1.29 (d, J = 9.6 Hz, 2H,
CHHendo), 1.38 (s, 6H, CH3), 2.44 (m, 2H, CH), 2.63 (m,
2H, CHHexo), 2.78 (t, J = 5.8 Hz, 2H, CH), 4.30 and 4.12
(ABX, JAB = 19.3 Hz, Dm = 0.18 Hz, 4H, CH2), 7.14 (m,
1H, Ar–H), 7.25 (d, 2H, Ar–H), 7.37 (s, 4H, Py–H). 13C
NMR (CDCl3, 75 MHz): d 164.9, 163.6, 154.5, 143.4,
142.1, 135.8, 123.4, 122.6, 115.7, 47.4, 40.3, 38.9, 38.8,
30.9, 25.8, 21.7. HRMS (FAB) calcd. for C30H31N2Pt
(M ꢁ Cl)+: 614.2135, found 614.2139.
25
acetate/n-hexane=1/9) as a white solid (½aꢂD ꢁ 115.8 (c 1.0,
CHCl3)).
With the chiral bis(pyridine) based NCN pincer ligand 9
in hand, we decided to synthesize the cyclometallated
A solution of the chloroplatinum pincer complex 5a
(0.44 g, 0.67 mmol) and silver triflate (0.17 g, 0.67 mmol)
in dichloromethane (20 mL) was stirred at 25 ꢁC for 2 h,
by which time all the starting complex was consumed.
The mixture was filtered through Celite to remove silver
chloride and washed with dichloromethane. The solvent
was evaporated to give air-stable 6a as a pale yellow crys-
I
I
I2, Pyridine
100 oC, 3h
N
N
O
O
O
O
8
AcONH4,
AcOH
reflux, 5 - 6 h
SeO2, CCl4
reflux, 10 h
25
talline solid. Yield: 0.52 g (98%). MP: 192–193 ꢁC. ½aꢂD
O
1
ꢁ244.2 (c 1.0, CHCl3). H NMR (CDCl3, 300 MHz): d
(1S)-(–)-β-pinene
0.73 (s, 6H, CH3), 1.30 (d, J = 9.8 Hz, 2H, CHHendo),
1.40 (s, 6H, CH3), 1.69 (bs, 2H, H2O), 2.44 (m, 2H, CH),
2.67 (m, 2H, CHHexo), 2.81 (t, J = 5.6 Hz, 2H, CH), 3.72
and 3.57 (ABX, JAB = 18.9 Hz, Dm = 0.16 Hz, 4H, CH2),
7.17 (m, 3H, Ar–H), 7.39 (m, 4H, Py–H). 13C NMR
(CDCl3, 75 MHz): d 163.5, 162.8, 144.0, 142.0, 136.5,
124.7, 122.7, 118.0, 116.2, 47.3, 40.1, 39.0, 36.5, 30.9,
N
N
(R,R)-(–)-9
Scheme 1. Synthesis of the chiral NCN pincer ligand (R,R)-(ꢁ)-9.