Catalysts for the Transfer Dehydrogenation of Alkanes
FULL PAPER
1H NMR (400 MHz, C6D6): d=6.60 (s, 1H; Cpara-H), 5.79 (t, JPH =9 Hz,
2H; P-C=CH), 3.14 (m, 2H), 2.91 (m, 2H), 2.74–2.69 (m, 4H), 2.55 (m,
2H), 2.39 (m, 2H), 2.21 (m, 4H), 2.07 (m, 2H), 1.93–1.58 (overlapped
peak, 22H), 1.37–1.30 (m, 12H), 1.14 (s, 6H), 0.93 (s, 6H), À33.12 ppm
(t, JPH =14 Hz, 1H; IrH); 13C NMR (100 MHz, C6D6): d=150.44 (s, C),
145.37 (t, J=15 Hz, C), 144.81 (s, CH), 139.54 (t, J=7 Hz, C), 133.06 (t,
J=19 Hz, C), 124.28 (s, CH), 41.49 (s, CH2), 40.21 (t, J=5 Hz, C), 33.69
(t, J=12 Hz, CH), 32.80 (t, J=15 Hz, CH), 32.34 (s, CH2), 31.41 (s, CH3),
29.60 (s, CH3), 29.56 (s, CH2), 29.24 (s, CH2), 27.77 (s, CH2), 27.34 (t, J=
7 Hz, CH2), 27.17 (t, J=4 Hz, CH2), 27.00 (s, CH2), 26.94 (s, CH2), 26.85
(s, CH2), 26.49 (s, CH2), 26.38 ppm (s, CH2); 31P NMR (162 MHz, C6D6):
d=50.6 ppm; elemental analysis calcd (%) for C44H68ClIrP2 (886.63): C
59.60, H 7.73; found: C 59.82, H 7.60.
CH2), 40.26 (m, C), 32.76 (s, CH2), 30.67 (s, CH3), 29.93 ppm (s, CH3);
31P NMR (162 MHz, C6D6): d=37.58 ppm.
2
Data for 20’: 1H NMR (400 MHz, C6D6): d=À19.20 ppm (t, JPH
=
14.4 Hz, 1H; IrH); 31P NMR (162 MHz, C6D6): d=41.05 ppm; elemental
analysis calcd (%) for C46H47ClIrNP2 (903.49): C 61.15, H 5.24, N 1.55;
found: C 60.77, H 5.27, N 1.18.
Synthesis of the iridium tetrahydride complexes 26 (R=iPr) and 27 (R=
Cy): Compound 15 or 16 (67.5 mmol) and NaOtBu (13.0 mg, 135 mmol)
were added to a Schlenk flask in a glovebox and then the flask was
purged with H2 gas. Benzene (5 mL, nitrogen-free) was added to the
flask and the solution was stirred at room temperature for 30 min under
a flow of hydrogen gas. After removal of the solvent in vacuo, the residue
was taken up in a glovebox. The residue was dissolved in toluene and the
solution filtered through a membrane filter before being concentrated in
vacuo.
Synthesis of the (m2-Cl)2-bridged diiridium complexes 17 (R=Ph) and 18
(R=Xyl): Compound 12 or 13 (0.10 mmol) was treated with [IrACHTNUTRGNEUNG(cod)Cl]2
(0.10 mmol) in p-xylene (3.0 mL) at reflux for 15 h in an argon atmos-
phere. After removal of the solvent in vacuo at 1008C, the residue was
taken up in a glovebox. The residue was dissolved in toluene and purified
by filtration.
Compound [(7–6–7-iPrPCP)Ir(H4)] (26) was obtained as pale-yellow crys-
tals (71%) by recrystallization from toluene/n-hexane at À308C.
1H NMR (400 MHz, CD2Cl2): d=6.41 (s, 1H; Cpara-H), 5.54 (t, JPH =9 Hz,
2H; P-C=CH), 2.60 (t, JHH =5 Hz, 4H; CH2CH2), 1.82 (m, 4H; iPr), 1.74
(t, JHH =5 Hz, 4H; CH2CH2), 1.12 (s, 12H; Me), 1.08–0.95 (m, 24H; iPr),
À9.82 ppm (t, JPH =10 Hz, 4H; IrH); 31P NMR (162 MHz, CD2Cl2): d=
Compound [(7–6–7-PhPCP)Ir(H)
red solid by removal of the solvent. H NMR (400 MHz, C6D6): d=8.41–
8.31 (m, 4H), 8.25–8.16 (m, 4H), 7.43 (t, JPH =7 Hz, 2H), 7.26 (t, JPH
ACHTUGTNRENNUG(m2-Cl)2IrACHTUNTGREN(NUGN cod)] (17) was collected as a
1
=
1
63.2 ppm; H NMR (400 MHz, C6D6, under H2): d=6.70 (s, 1H; Cpara-H),
7 Hz, 2H), 7.10 (t, JPH =7 Hz, 4H), 6.97 (t, JPH =7 Hz, 2H), 6.60 (s, 1H),
5.91 (t, JPH =10 Hz, 2H), 3.73 (t, JHH =3 Hz, 2H), 3.69 (t, JHH =3 Hz,
2H), 2.83–2.69 (m, 4H), 1.78–1.54 (m, 4H), 1.01 (s, 6H), 0.75 (s, 6H),
À23.2 ppm (t, JPH =14 Hz, 1H; IrH); 13C NMR (100 MHz, C6D6): d=
147.83 (s, CH), 141.97 (t, J=17 Hz, C), 140.44 (t, J=8 Hz, C), 137.98 (t,
J=23 Hz, C), 135.17 (t, J=5 Hz, CH), 134.72 (s, C), 134.68 (t, J=7 Hz,
CH), 134.18 (t, J=27, C), 132.82 (t, J=23 Hz, C), 130.38 (s, CH), 129.78
(s, CH), 128.45 (t, J=6 Hz, CH), 127.89 (t, J=5 Hz, CH), 125.50 (s, CH),
62.02 (s, CH3), 61.18 (s, CH), 61.09 (s, CH), 41.28 (s, CH3), 40.57 (t, J=
6 Hz, C), 32.71 (s, CH3), 31.89 (s, CH3), 31.87 (s, CH3), 31.59 (s, CH2),
30.43 (s, CH3), 30.02 ppm (s, CH3); 31P NMR (162 MHz, C6D6): d=
41.3 ppm.
5.40 (t, JPH =9 Hz, 2H; P-C=CH), 2.76 (t, JHH =5 Hz, 4H; CH2CH2), 1.78
(t, JHH =5 Hz, 4H; CH2CH2), 1.67 (m, 4H; iPr), 1.13–1.07 (m, 24H; iPr),
1.03 (s, 12H; Me), À9.18 ppm (t,
J
PH =10 Hz, 4H; IrH); 13C NMR
(100 MHz, C6D6): d=155.65 (s, Cipso), 144.50 (t, J=15 Hz, C), 143.54 (s,
CH), 140.95 (t, J=15 Hz, C), 139.16 (t, J=7 Hz, C), 125.75 (s, CH), 40.97
(s, CH2), 40.03 (t, J=8 Hz, C), 32.62 (s, CH2), 30.75 (s, CH3, Me), 29.48
(s, CH3, Me), 19.4 (t, J=4 Hz, CH3, iPr), 18.4 ppm (s, CH3, iPr);
31P NMR (162 MHz, C6D6): d=64.4 ppm; elemental analysis calcd (%)
for C44H68ClIrP2 (693.94): C 55.39, H 7.99; found: C 55.75, H 8.27; T1
(400 MHz, min)=105 ms (IrH) at 213 K.
Compound [(7–6–7-CyPCP)Ir(H4)] (27) was obtained as a pale-brown
solid (81%) by removal of the solvent in vacuo. 1H NMR (400 MHz,
CD2Cl2): d=6.40 (s, 1H; Cpara-H), 5.52 (t, JPH =9 Hz, 2H; P-C=CH),
1.87–1.57 (m, 30H), 1.39–1.09 (m, 34H), À9.70 ppm (t, JPH =10 Hz, 4H;
IrH); 31P NMR (162 MHz, CD2Cl2): d=50.7 ppm; T1 (400 MHz, min)=
104 ms (IrH) at 223 K.
Compound [(7–6–7-XylPCP)Ir(H)
ACTHNUGTRENNUG(m2-Cl)2IrACHTUNTGREN(NUGN cod)] (18) was obtained as a
yellow solid by removal of the solvent. 1H NMR (400 MHz, C6D6): d=
7.99 (t, JPH =5 Hz, 4H), 7.86 (t, JPH =5 Hz, 4H), 6.95 (s, 2H), 6.73 (s,
2H), 6.53 (s, 1H), 6.19 (t, JPH =9 Hz, 2H), 3.74 (t, JHH =3 Hz, 2H), 3.67
(t, JHH =3 Hz, 2H), 2.78–2.72 (m, 4H), 2.33 (s, 12H), 2.16 (s, 12H), 1.08
(s, 6H), 0.92 (s, 6H), À23.5 ppm (t, JPH =14 Hz, 1H; IrH); 13C NMR
(100 MHz, C6D6): d=148.33 (s, CH), 142.78 (t, J=17 Hz, C), 140.28 (t,
J=8 Hz, C), 138.42 (t, J=22 Hz, C), 137.41 (t, J=5 Hz, C), 136.74 (t, J=
5 Hz, C), 134.72 (t, J=12 Hz, C), 133.28 (s, C), 133.06 (t, J=5 Hz, CH),
132.82 (s, C), 132.64 (t, J=7 Hz, CH), 132.14 (s, CH), 131.60 (s, CH),
125.34 (s, CH), 62.01 (s, CH3), 60.53 (s, CH), 60.43 (s, CH), 41.24 (s,
CH3), 40.65 (t, J=5 Hz, C), 32.73 (s, CH3), 31.87 (s, CH3), 31.56 (s, CH3),
31.53 (s, CH2), 30.30 (s, CH3), 30.10 (s, CH3), 21.68 (s, CH3), 21.37 ppm (s,
CH3); 31P NMR (162 MHz, C6D6): d=40.8 ppm.
Synthesis of the iridium tetrahydride complex 28 (R=Ph): NaOtBu
(6.2 mg, 0.065 mmol) was added to a [D6]benzene solution (0.7 mL, nitro-
gen-free) of 20 (and/or 20’) (14 mg, 0.016 mmol) in a glovebox filled with
argon. The solution was stirred at room temperature for 30 min and then
transferred into a NMR tube with a screw cap. After removal from the
glovebox, hydrogen gas was bubbled through the solution for 1 min and
then analyzed by NMR. Compound 28 could not be isolated. 1H NMR
(400 MHz, C6D6): d=À9.70 ppm (t, JPH =10 Hz, 4H; IrH); 31P NMR
(162 MHz, C6D6): d=50.7 ppm.
Synthesis of [(7–6–7-PhPCP)Ir(H)(Cl)
12 (96.9 mg, 0.153 mmol, containing a small amount of acetonitrile which
was the solvent of recrystallization) was treated with [Ir(cod)Cl]2
(50.1 mg, 74.5 mmol) in [D6]benzene (0.7 mL) at 1508C for 100 h in a
Youngꢁs NMR tube. After removal of the solvent in vacuo, the residue
was placed in a glovebox. The residue was washed with dry toluene and
dried in vacuo. A mixture (92.0 mg, 0.102 mmol, 75%) of 20 (trans,
major) and 20’ (cis) was obtained as a pale-yellow solid. Purification by
recrystallization from benzene/toluene gave only 20 as colorless crystals.
Notably, the hydrochloride complex with Ph2P groups could not be ob-
tained without acetonitrile in 12.
ACHTUNGTNER(NUNG MeCN)] (20 and 20’): Compound
Synthesis of the iridium carbonyl complexes 32 (R=iPr) and 33 (R=
Cy): Compound 15 or 16 (41.0 mmol) and NaOtBu (0.10 mmol) were dis-
solved in nitrogen-free benzene (2 mL) in a Schlenk flask under H2. The
solution was stirred at room temperature for 60 min (for 15)/10 min (for
16) under a flow of hydrogen gas. Then the hydrogen was exchanged
with CO and the flow maintained for 30 min (for 15)/10 min (for 16). The
excess CO gas was removed by using a flow of argon. The solvent was re-
moved under vacuum and the residue placed in a glovebox. The residue
was dissolved in toluene and purified by filtration (membrane filter).
Compound [(7–6–7-iPrPCP)Ir(CO)] (32) was obtained as a yellow solid
(81%) by removal of the solvent. M.p. 204–2068C; 1H NMR (400 MHz,
C6D6): d=6.73 (s, 1H; Cpara-H), 5.53 (t, JPH =9 Hz, 2H; P-C=CH), 2.75
(t, JHH =5 Hz, 4H; CH2CH2), 2.30 (sept., 4H; iPr), 1.79 (t, JHH =5 Hz,
4H; CH2CH2), 1.27–1.21 (overlapped peak, 24H; iPr), 1.00 ppm (s, 12H;
Me); 13C NMR (100 MHz, C6D6): d=197.83 (t, J=7 Hz, CO), 184.85 (t,
J=6 Hz, Cpara), 148.82 (t, J=10 Hz, Cipso), 143.11 (s, CH), 138.93 (t, J=
7 Hz, C), 138.32 (t, J=19 Hz, C), 127.76 (s, CH), 41.61 (s, C), 40.31 (t, J=
5 Hz, CH2), 32.95 (s, CH2), 30.65 (s, CH3, Me), 26.68 (t, J=14 Hz, CH,
iPr), 19.63 (t, J=2 Hz, CH3, iPr), 18.43 ppm (s, CH3, iPr); 31P NMR
(162 MHz, C6D6): d=76.3 ppm; IR (n-pentane): n˜CO =1934(3) cmÀ1; IR
AHCTUNGTRENNUNG
Data for 20: 1H NMR (400 MHz, C6D6): d=8.27 (m, 8H; PPhortho), 7.13–
7.00 (overlapped peak, 12H; PPh), 6.59 (s, 1H; Cpara-H), 5.86 (t, JPH
=
10 Hz, 2H; P-C=CH), 2.84 (m, 4H; CH2CH2), 1.77 (m, 4H; CH2CH2),
1.00 (s, 6H; Me), 0.78 (s, 6H; Me), 0.14 (s, 3H; CH3CN), À18.63 ppm (t,
2JPH =15.3 Hz, 1H; IrH); 13C NMR (100 MHz, C6D6): d=151.81 (C),
148.19 (s, CH), 146.44 (C), 142.80 (t, JPC =15 Hz, C), 140.13 (t, JPC =8 Hz,
C), 139.67 (t, JPC =22 Hz, C), 134.80 (t, JPC =6 Hz, CH), 134.59 (C),
134.20 (m, CH), 134.06 (C), 131.31 (C), 130.11 (s, CH), 129.45 (s, CH),
128.27 (m, CH), 128.09 (m, CH), 126.38 (C), 124.83 (m, CH), 41.43 (s,
Chem. Eur. J. 2013, 19, 10672 – 10689
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10687