Retaining Catalyst Performance at High Temperature
COMMUNICATIONS
Table 2. Comparison of tetraphosphine and bisphosphine ligands.[a]
Entry
Substrate
T [8C]
Ligand
n:i[b]
Linear [%][c]
Isomerization [%][d]
TON[e]
TOF[f] [hÀ1]
1
2
3
4
5
6
7
8
1-octene
1-octene
1-octene
1-octene
1-octene
1-octene
1-hexene
1-hexene
1-hexene
1-hexene
1-hexene
1-hexene
140
140
120
120
100
100
140
140
120
120
100
100
1
45.2
2.4
97.8
70.6
98.0
96.7
98.1
97.8
97.8
83.1
98.0
97.3
98.0
97.7
6.5
24
1.8103
1.5103
1.8103
1.8103
1.8103
1.6103
1.8103
1.6103
1.8103
1.8103
1.8103
1.7103
9.3103
6.2103
7.3103
5.7103
2.5103
3.4103
9.5103
8.7103
6.6103
6.0103
3.3103
2.6103
Bisbi
1
Bisbi
1
Bisbi
49.8
29.5
50.5
45.2
43.8
4.9
48.5
35.8
48.6
43.2
5.8
8.7
5.6
6.7
7.7
20
7.1
9.1
6.6
9.4
1
Bisbi
1
Bisbi
9
10
11
12
1
Bisbi
[a]
S/C=2000, [Rh]=1.0 mM, ligand/Rh ratio=4:1, CO/H2 =10/10 atm, reaction time=1 h, toluene as solvent, decane as in-
ternal standard.
Linear/branched ratio, determined based on GC.
Percentage of linear aldehyde in all aldehydes.
Isomerization to internal olefins.
[b]
[c]
[d]
[e]
[f]
Turnover number, determined based on GC.
Turnover frequency, determined based on GC, reaction time=10 min.
stirred for 10 min until all residues had dissolved. The or-
ganic phase was separated. The aqueous phase was extract-
ed with CH2Cl2 (225 mL). The combined organic phase
was washed with saturated aqueous NaCl solution (50 mL)
and dried over Na2SO4. The solvent was removed under re-
duced pressure to obtain an off-white solid. To the crude
solid was added EtOAc (10 mL). The resulting suspension
was stirred for 30 min and filtered. The residue was washed
with cold EtOAc (25 mL) to give the pure borane-protect-
ed title compound as a colorless solid; yield: 2.5 g (73.8%).
1H NMR (300 MHz, CDCl2): d=7.58–7.52 (m, 16H), 7.45-
.39 (m, 8H),7.36–7.31 (m, 16H), 7.03–6.97 (m, 2H), 6.87–
6.84 (m, 4H), 3.16 (d, J=13.4 Hz, 8H), 1.53–0.75 (bs, 12H);
13C NMR (75 MHz, CD2Cl2): d=133.1, 132.5 (d, J=9.1 Hz),
Synthesis of 4
To a solution of 3 (2.2 g, 4.2 mmol) in DMF (80 mL) was
added LiCl (2.82 g, 67.2 mmol). The reaction mixture was
stirred at room temperature for 6 h. The reaction mixture
was cooled to 08C and 5% aqueous HCl solution (30 mL)
was added carefully. After stirring for 5 min, the mixture
was extracted with ether (440 mL) and washed with satu-
rated aqueous NaCl solution (80 mL). The organic layer was
separated, dried over Na2SO4 and concentrated to dryness.
Pure product was obtained by recrystallization from CH2Cl2/
hexanes as a white solid; yield: 1.35 g (93%). 1H NMR
(300 MHz, CD2Cl2): d=7.74–7.62 (m, 4H), 7.59–7.56 (m,
2H), 4.28 (s, 8H); 13C NMR (75 MHz, CD2Cl2): d=137.0,
135.8, 131.2, 130.2, 45.0; HR-MS (EI+): m/z=345.9850,
calcd. for C16H14Cl4 [M+]: 345.9853.
131.5, 131.3, 130.6, 130.4, 129.2 (d, J=9.9 Hz), 127.5, 30.2 (d,
31
J=30 Hz);
P NMR (146 Hz, CD2Cl2): d=15.2; HR-MS
(ES+): m/z=1025.4431, calcd. for C64H66NaP4B4 [M+Na+]:
1025.4385.
Synthesis of 5
To
a
cooled (À788C) solution of diphenylphosphine
(2.32 mL, 13.2 mmol) in THF (10 mL) was added n-BuLi
(5.28 mL, 2.5M solution in hexane, 13.2 mmol) dropwise.
After stirring for 10 min, the reaction mixture was allowed
to warm to room temperature and stirred for 30 min. The
reaction mixture was cooled to À788C and 4 (1.05 g,
3 mmol) in THF (10 mL) was added dropwise. After addi-
tion, the reaction mixture was allowed to warm to room
temperature slowly and stirred overnight. The reaction mix-
ture was cooled to 08C and a cold 1.0M THF solution of
BH3 (132 mL, 132 mmol) was added dropwise. The mixture
was allowed to warm to room temperature and stirred for
4 h. The reaction mixture was cooled to 08C and water was
added carefully to quench the excess BH3. The volatile ma-
terial was removed under vacuum. To the residue were
added CH2Cl2 (50 mL) and water (50 mL). The mixture was
Synthesis of Ligand 1
To a solution of DABCO (448 mg, 4 mmol) in toluene
(10 mL) was added 5 (501 mg, 0.5 mmol) in portions. The re-
sulting suspension was stirred for 30 min at room tempera-
ture and slowly heated to 608C. The stirring was continued
for 6 h at 608C. The reaction mixture was cooled to room
temperature and additional toluene (10 mL) was added. The
diluted solution was charged on a short silica gel column
through cannula and eluted with toluene (40 mL). The sol-
vent was removed under vacuum to give the desired ligand
1
as a white solid; yield: 376 mg (79.4%). H NMR (300 MHz,
CDCl2): d=7.32–7.22 (m, 40H), 6.91–6.86 (m, 2H), 6.76–
6.74 (m, 4H), 3.24 (s, 8H); 13C NMR (75 MHz, CD2Cl2): d=
139.6, 139.3, 137.1, 137.0, 133.5, 133.3, 128.9, 128.7, 127.4,
Adv. Synth. Catal. 2007, 349, 1582 – 1586
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1585