1974
M. Janssen et al. / Tetrahedron Letters 51 (2010) 1971–1975
In conclusion, we have reported on the synthesis of a new class
3.3. TP3
1-Naphthol was used as the phenol. Yield: [2.1 mmol, 2.2 g,
of tetraphenol-based diphosphite ligands. The ligands were tested
in the rhodium-catalyzed hydroformylation of 1-octene and trans-
2-octene. In the hydroformylation of 1-octene, Rh/TP3 showed
good regioselectivity toward the desired nonanal (l/b = 19.6 in
the beginning of the reaction). In order to explain the differences
in catalytic performance among the ligands, the electronic proper-
ties of the ligands were compared via the Tolman electronic
parameter m. As this parameter shows no significant differences
for the ligands, the different performance in catalysis is attributed
to steric and conformational changes.
70%]. 1H NMR (400 MHz, CDCl3): d 8.18 (d, J = 8 Hz, 2H), 7.82 (d,
J = 8 Hz, 2H), 7.68–7.60 (m, 2H), 7.46–7.42 (m, 3H), 7.42–7.47 (m,
8H), 7.28 (s, 4H), 7.09–7.05 (m, 3H), 6.95–6.85 (m, 6H), 5.60 (s,
2H), 1.13 (s, 36H). 13C NMR (125 MHz, CD2Cl2): 147.71, 147.63,
146.44, 146.32, 134.87, 134.59, 128.72, 127.64, 127.52, 127.44,
127.35, 126.62, 126.51, 126.25, 126.08, 125.84, 125.73, 125.58,
125.26, 124.24, 123.82, 123.12, 122.54, 122.28, 115.10, 114.87,
95.04, 34.32, 31.43. 31P NMR (162 MHz, CDCl3): d 131.38. Elemen-
tal Anal. Calcd for C68H68O6P2: C, 78.29; H, 6.57. Found: C, 77.93; H,
6.23.
2. Synthesis of 4,40,4,4000-tetra-tert -butyl-2,20,2,2000-
(phenylenemethanediyl)tetraphenol (TP0)
3.4. TP4
A mixture of p-tert-butylphenol (72 g, 0.48 mol) and isophthalic
dicarboxaldehyde (8.1 g, 0.06 mol) was heated with stirring until a
homogeneous melt had formed (100–110 °C). Concentrated HCl
(8 ml) was added and the reaction continued for a further 6 h.
The excess phenol was then removed by steam distillation and
the residue was recrystallized from acetone. Yield: [0.0429 mol,
29.94 g, 71.5%]. 1H NMR (400 MHz, CDCl3): d 7.28–7.24 (m, 1H),
7.11–7.05 (m, 7H), 6.93 (d, J = 2.4 Hz, 4H), 6.71 (d, J = 8.4 Hz, 4H),
5.83 (s, 2H), 5.24 (br s, 4H, –OH), 1.13 (s, 36H). 13C NMR
2,4-Di-tert-butylphenol was used as the phenol. Yield:
[2.4 mmol, 2.8 g, 81%]. 1H NMR (400 MHz, CDCl3): d 7.30 (d,
J = 2.5 Hz, 2H), 7.28–7.20 (m, 8H), 7.08–7.01 (m, 6H), 6.78–6.74
(m, 2H), 6.61 (dt, J = 4.9 Hz, 0.8 Hz, 4H), 5.83 (s, 2H), 1.42 (s,
18H), 1.29 (s, 54H). 13C NMR (125 MHz, CD2Cl2): 151.58, 149.08,
147.85, 147.49, 146.54, 146.08, 145.75, 138.95, 133.85, 128.79,
126.45, 125.34, 124.92, 124.53, 124.03, 123.50, 123.02, 119.89,
119.07, 118.84, 118.70, 110.41, 45.76, 34.90, 34.82, 34.33, 34.22,
31.18, 29.95. 31P NMR (81 MHz, CD2Cl2): d 122.12. Elemental Anal.
Calcd for C76H96O2P2ꢂCH2Cl2: C, 73.84; H, 7.89. Found: C, 74.32; H,
8.19.
(100 MHz, CDCl3):
d 150.93, 143.65, 141.99, 128.11, 127.28,
124.64, 115.74, 77.66, 77.02, 76.39, 45.14, 34.04, 31.40. Elemental
Anal. Calcd for C48H58O4ꢂ2(CH3)CO: C, 79.57; H, 8.66. Found: C,
79.74; H, 8.43.
3.5. TP5
3. General synthesis of tetraphenol ligands
2-Methyl-6-tert-butylphenol was used as the phenol. Yield:
[2.3 mmol, 2.5 g, 78%]. 1H NMR (400 MHz, CDCl3): d 7.30 (d,
J = 2.5 Hz, 2H), 7.26–7.20 (m, 6H), 7.13–7.03 (m, 8H), 7.01–6.90
(m, 4H), 6.77–6.65 (m, 2H), 6.22 (s, 2H), 2.52 (s, 6H), 1.49 (s,
54H). 13C NMR (125 MHz, CD2Cl2): 149.44, 149.35, 147.82,
147.53, 146.92, 146.88, 145.97, 145.80, 139.54, 139.30, 139.21,
138.97, 128.70, 127.58, 124.68, 124.57, 124.40, 123.94, 123.16,
120.48, 115.12, 114.88, 35.08, 32.53, 31.27, 30.00, 25.78. 31P
NMR (81 MHz, CD2Cl2): d 172.59. Elemental Anal. Calcd for
C70H84O6P2ꢂCH2Cl2: C, 72.99; H, 7.42. Found: C, 72.32; H, 7.57.
The tetraphenol backbone (TP0) (2.1 g, 3 mmol) and Et3N
(5.4 ml, 36 mmol) were added dropwise to a solution of PCl3
(0.6 mg, 6.5 mmol) in 35 ml of THF at ꢀ10 °C and the mixture
was stirred for 30 min. The appropriate phenol (6.05 mmol) dis-
solved in 10 ml of THF was added dropwise at ꢀ10 °C. The mixture
was stirred for 1 h at room temperature. Salts were filtered off over
a short pad of basic alumina (4 cm) and all the volatiles were evap-
orated. The residue was recrystallized from acetone/isopropanol to
yield the desired product as a white powder.
4. Synthesis of (L)Ni(CO)2
3.1. TP1
10 mg (0.036 mmol) Ni(cod)2,17 and 1 equiv of TP ligand
(0.036 mmol) were dissolved in 2 mL of toluene. CO was bubbled
through the slightly yellow solution for 30 s, during which the
solution turned colorless. All the volatiles were removed in vacuo
and the remaining solid was used in the ATR-IR measurement.
4-tert-Butylphenol was used as the phenol. Yield: [0.96 mmol,
1.01 g, 32%]. 1H NMR (400 MHz, CDCl3): d 7.38–7.35 (m, 2H),
7.33–7.30 (m, 2H), 7.24 (d, J = 2.9 Hz, 4H), 7.20–7.06 (m, 8H),
6.99 (dd, J = 8.5, 0.9, 4H), 6.85–6.77 (m, 4H), 5.77 (s, 2H), 1.08 (s,
54H). 13C NMR (125 MHz, CD2Cl2): 150.08, 149.96, 147.34,
146.99, 143.45, 134.50, 128.58, 128.14, 127.94, 126.48, 126.37,
126.24, 126.14, 125.47, 125.31, 123.40, 120.31, 120.22, 120.16,
53.24, 34.32, 34.25, 31.83, 31.14. 31P NMR (CD2Cl2): d 122.08. Ele-
mental Anal. Calcd for C68H80O6P2: C, 77.39; H, 7.64. Found: C,
77.33; H, 7.45.
5. General procedure for the hydroformylation experiments
Reactions were carried out in an AMTEC SPR16 parallel setup.
Rh(acac)(CO)2 (3.7 mg, 14.4
lmol) and 4 equiv of the ligand
(57.6 mol) were dissolved in 5 mL of toluene and transferred into
l
3.2. TP2
an argon-filled reaction vessel. The reaction vessel was heated and
pressured to the desired temperature and pressure. After 2 h of
preformation, the substrate mixture consisting of 18 mmol of 1-oc-
tene and 6 mmol of decane (internal standard) was added. The
reaction vessel was pressured and heated to the desired reaction
pressure and temperature.
2-tert-Butyl-4-methoxyphenol was used as the phenol. Yield:
[0.84 mmol, 937 mg, 28%]. 1H NMR (400 MHz, CDCl3): d 7.47–
7.43 (m, 2H), 7.33 (s, 4H), 7.11–6.96 (m, 12H), 6.48–6.43 (m, 4H),
5.72 (s, 2H), 3.29 (s, 6H), 1.36 (s, 18H), 1.09 (s, 36H). 13C NMR
(125 MHz, CD2Cl2): 155.57, 147.77, 146.54, 146.43, 144.89,
144.60, 141.82, 141.78, 133.76, 128.87, 128.74, 128.06, 127.80,
127.02, 126.48, 125.29, 125.14, 122.93, 120.41, 120.11, 114.32,
109.99, 55.57, 45.57, 34.67, 34.16, 31.11, 29.15. 31P NMR
(81 MHz, CDCl3): d 122.61.
Acknowledgments
This work has been financially supported by Evonik Oxeno and
in part by the National Research School Combination on Catalysis