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Table 4. Dehydrogenative coupling of amines and alcohols catalyzed by 7.[a]
purification. NMR spectra were recorded on
a
Bruker
AVANCHE 400 spectrometer (1H NMR, 400.13 MHz; 13C NMR,
100.62 MHz; 31P NMR, 161.98 MHz). Chemical shifts are reported in
1
δ referenced to H (residual) and 13C signals of deuterated solvents
as internal standards or to the 31P signal of 85 % H3PO4 as an exter-
nal standard. Elemental analysis was performed by ICR Analytical
Laboratory, Kyoto University.
Entry
Amine
Alcohol
Conv.
Yield [%][c]
[%][b,c]
8
9
Preparation of Complexes 5–7: Complex 1 (102 mg, 0.12 mmol)
was dissolved in toluene (8 mL) and heated at 70 °C overnight. The
dark brown solution was concentrated to dryness to form a dark
brown solid of 2, which was dissolved in THF (8 mL) at room tem-
1
2
3
4
5
6
7
8
PhCH2NH2
PhCH2CH2NH2
CH3(CH2)7NH2
cyclo-C6H11NH2
PhNH2
PhCH2NH2
PhCH2NH2
PhCH2NH2
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
99
91
77
99
93
6
7
7
93
83
70
93
65
10
4
perature. A solution of tBuNC in THF (0.6 M, 0.2 mL) and a solution
6
of tBuOK (13 mg, 0.12 mmol) in THF (2 mL) were added in sequence.
The solution color changed to greenish black. The solution was
stirred for 10 min, and volatile substances were evaporated under
vacuum. The crude product was dissolved in Et2O and filtered
through a Celite pad to remove the precipitate of KCl. The filtrate
was concentrated, layered with hexane, and allowed to stand at
–35 °C overnight to give dark green crystals of 5, which were col-
lected by filtration, washed with hexane three times, and then dried
under vacuum (81 mg, 0.088 mmol, 76 %). Complexes 6 and 7 were
similarly synthesized in 89 and 64 % yields using PMe3 (1 equiv.,
PhCH2OH
25
23
67
10
CH3(CH2)7OH
cyclo-C6H11OH
PhCH(OH)CH3
97
88
88[d]
36
[a] Reactions were carried out using amine (1 mmol), alcohol (1.5 mmol), and
catalyst 7 (1 mol-%) in toluene (0.3 mL) at reflux. Reaction time: 24 h (entries
1, 2, 4); 120 h (entries 3, 5–8). [b] Conversion of amine. [c] Confirmed by 1H
NMR spectroscopy using mesitylene as an internal standard. [d] Some addi-
tional products including PhCOPh were formed.
1.0
M toluene solution) and PPh3 instead of tBuNC, respectively.
Conclusion
[Ir(tBuNC)(PPEP*)] (5): 1H NMR (C6D6, 25 °C): δ = 7.67–7.58 (m, 4
We have reported the catalytic application of IrI complexes
bearing a dearomatized PNP-pincer-type phosphaalkene ligand
(PPEP*) to the N-alkylation of amines with alcohols. Complexes
of formula [Ir(L)(PPEP*)] [L = Cl– (3), CO (4), tBuNC (5), PMe3 (6),
PPh3 (7)] could be prepared in one pot from [IrCl(BPEP)] (1)
coordinated with bis(phosphaethenyl)pyridine (BPEP). Although
catalytic N-alkylation often needs the addition of a strong base
to the system,[9] complexes 3–7 successfully catalyzed the reac-
tion under base-free conditions to afford N-alkylated amines
and imines in high yields. The product selectivity could be con-
trolled by the choice of auxiliary ligands (L) as well as the reac-
tion conditions. Complexes 4 and 5 bearing π-accepting ligands
(CO, tBuNC) formed N-alkylated amines as the major products,
and the selectivity for the formation of PhCH2NHCH2Ph (8a)
from PhCH2CH2 and PhCH2OH reached 92 % in a closed reac-
tion system. In contrast, complex 7 bearing PPh3 as L produced
imines as the major products, and the product yield of
PhCH2N=CHPh (9a) reached 93 % under a nitrogen-gas flow.
We also demonstrated that the remarkable change in product
selectivity depending on L may be rationalized by taking the
reactivity difference of presumed intermediate C towards amine
elimination (step d in Scheme 2) into consideration; namely,
this step was dramatically accelerated by CO (Scheme 4).
H, PyCH=P + Ar), 7.29 (s, 1 H, Ar), 6.46 (dd, JH,H = 8.7 Hz, JP, H
6.2 Hz, 1 H, Py), 6.02 (m, 1 H, Py), 5.48 (dd, JH,H = 6.8 Hz, JP, H
=
=
6.8 Hz, 1 H, Py), 4.16 (vt, Japp = 4.7 Hz, 1 H, Py=CHP), 2.72 (br. d,
JP, H = 14.4 Hz, 1 H, PCH2), 2.08 (s, 9 H, CH3), 1.99 (s, 9 H, CH3), 1.93
(dd, JH,H = 14.4 Hz, JP, H = 7.3 Hz, 1 H, PCH2), 1.87 (s, 9 H, CH3), 1.44
(s, 3 H, CH3), 1.37 (s, 3 H, CH3), 1.28 (s, 9 H, CH3), 1.27 (s, 9 H, CH3),
0.76 (s, 9 H, CH3) ppm. 13C{1H} NMR (C6D6, 25 °C): δ = 173.5 (d, JP, C
=
19 Hz), 162.6 (s), 160.2 (dd, JP, C = 17 and 3 Hz), 159.9 (d, JP, C = 56 Hz,
PyCH=P), 157.7 (s), 157.0 (s), 154.8 (d, JP, C = 9 Hz), 153.1 (d, JP, C
=
2 Hz), 152.5 (s), 149.0 (t, JP, C = 8 Hz, CN), 133.0 (dd, JP, C = 7 and
4 Hz), 131.8 (dd, JP, C = 45 and 4 Hz), 131.0 (d, JP, C = 12 Hz), 123.6
(d, JP, C = 8 Hz), 122.7 (d, JP, C = 7 Hz), 122.5 (d, JP, C = 7 Hz), 118.8 (d,
JP, C = 9 Hz), 118.2 (dd, JP, C = 20 and 15 Hz), 104.9 (d, JP, C = 38 Hz),
79.8 (d, JP, C = 61 Hz, Py=CHP), 55.3 (s), 43.9 (s), 42.9 (d, JP, C = 41 Hz),
39.6 (s), 39.4 (s), 38.6 (s), 35.6 (s), 35.4 (s), 35.3 (s), 34.8 (s), 34.1 (s),
33.5 (s), 32.3 (d, JP, C = 8 Hz), 31.8 (s), 31.7 (s), 31.1 (s) ppm. 31P{1H}
NMR (C6D6, 25 °C): δ = 238.2 (d, JP, P = 360 Hz), 18.9 (d, JP, P = 360 Hz)
ppm. IR (ATR): ν = 2063 cm–1 (νNC). C48H71IrN2P2 (930.27): calcd. C
˜
61.97, H 7.69, N 3.01; found C 61.92, H 7.77, N 2.89.
[Ir(PMe3)(PPEP*)] (6): 1H NMR (C6D6, 25 °C): δ = 8.23 (dd, JP, H
=
16.2 Hz, JP, H = 4.2 Hz, 1 H, PyCH=P), 7.68 (s, 1 H, Ar), 7.63 (s, 2 H,
Ar), 7.29 (s, 1 H, Ar), 6.61 (dd, JH,H = 6.8 Hz, JP, H = 6.8 Hz, 1 H, Py),
6.14 (m, 1 H, Py), 5.82 (dd, JH,H = 6.6 Hz, JP, H = 6.6 Hz, 1 H, Py), 4.16
(vt, Japp = 4.6 Hz, 1 H, Py=CHP), 2.57 (br. d, JP, H = 14.1 Hz, 1 H, PCH2),
2.02 (s, 9 H, CH3), 1.92 (s, 9 H, CH3), 1.78 (s, 10 H, PCH2 + CH3), 1.43
(s, 3 H, CH3), 1.34 (s, 3 H, CH3), 1.29 (s, 9 H, CH3), 1.27 (s, 9 H, CH3),
1.06 (d, JP, H = 8.4 Hz, 9 H, PMe3) ppm. 13C{1H} NMR (C6D6, 25 °C):
δ = 173.1 (d, JP, C = 19 Hz), 162.8 (t, JP, C = 4 Hz), 159.6 (dd, JP, C = 15
and 4 Hz), 157.8 (dd, JP, C = 57 and 3 Hz, PyCH=P), 156.1 (s), 156.0
(s), 154.2 (d, JP, C = 9 Hz), 153.1 (d, JP, C = 2 Hz), 152.6 (d, JP, C = 2 Hz),
133.8 (dd, JP, C = 42 and 4 Hz), 133.3 (dd, JP, C = 7 and 4 Hz), 131.8
(d, JP, C = 15 Hz), 124.3 (d, JP, C = 8 Hz), 124.2 (d, JP, C = 7 Hz), 123.5
(d, JP, C = 7 Hz), 119.2 (d, JP, C = 9 Hz), 116.7 (dd, JP, C = 20 and 15 Hz),
103.4 (d, JP, C = 37 Hz), 78.7 (dd, JP, C = 62 and 3 Hz, Py=CHP), 44.2
Experimental Section
General Considerations: All manipulations were carried under a
nitrogen atmosphere using standard Schlenk techniques and a
glove box. Nitrogen gas was dried by passing it through a P2O5
column (Merck, SICAPENT). Toluene (Kanto, dehydrated), hexane,
and Et2O (Wako, dehydrated) were used as received. THF was dried
with sodium/benzophenone, distilled, and stored over activated
MS4A molecular sieves. [IrCl(BPEP)] (1),[12] [IrCl(PPEP)] (2),[7] [K(18- (t, JP, C = 3 Hz), 42.0 (d, JP, C = 39 Hz), 40.2 (s), 39.7 (s), 38.6 (s), 35.6
crown-6)][IrCl(PPEP*)] (3a),[7] [Ir(CO)(PPEP*)] (4),[7] and [Ir(NHPh)-
(PPEP)] (10)[7] were prepared as previously reported. Other chemi-
cals were purchased from commercial sources and used without
(s), 35.5 (s), 35.4 (s), 34.7 (s), 34.5 (s), 34.4 (d, JP, C = 1 Hz), 32.6 (d,
J
P, C = 9 Hz), 31.9 (s), 31.7 (s), 20.6 (d, JP, C = 35 Hz, PMe3) ppm. 31P{1H}
NMR (C6D6, 25 °C): δ = 233.9 (dd, JP, P = 357 and 18 Hz), 18.2 (dd,
Eur. J. Inorg. Chem. 2016, 754–760
758
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