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Pleas De ad l to o nn oT tr aa nd sj au cs t ti omn as rgins
Journal Name
ARTICLE
i
towards activation of other polar E-H bonds (E = main group of P Pr
element).
2
); 62.9 (d, J = 1.6 Hz, ArCH
2
DOI: 10.1039/D0DT02264K
115.2 (d, J = 1.9 Hz; CH); 125.2 (s, CH); 127.6 (s, CH); 128.7 (s,
CH); 129.3 (s, CH); 144.1 (d, J = 33.1 Hz, Cq); 146.6 (d, J = 2.1 Hz,
Cq); 154.6 (s, Cq); 166.4 (d, J = 10.0 Hz, Cq). C,H,N analysis (%):
Experimental Section
calcd for C19
H25BrNNiOP (452.99): C 50.38, H 5.56, N 3.09; found
C 50.79, H 5.77, N 3.20.
All manipulations were carried out using conventional inert
atmosphere glovebox and Schlenk techniques. All protonated
and deuterated solvents were dried by distillation from
appropriate drying agents. NMR spectra were obtained with
Generation of [(i-PrPOCN )Ni]
Ph
2
(C)
A: Reaction of (i-PrPOCNHPh)NiBr (A) with MeLi. A solution of
MeLi in Et O (1.6 mol/L, 75.0 µl, 0.132 mmol) was added to a
1
13
31
19
2
JEOL ECA-500 MHz ( H: 500 MHz; C: 125.8; P: 202.5; F:
i-Pr
HPh
70.6 MHz). 1H and C chemical shifts were referenced to
residual proton and naturally abundant C resonance of the
13
yellow solution of ( POCN )NiBr (A) (50 mg, 0.11 mmol) in
8.0 mL of toluene at -80 ℃ in a Schlenk tube equipped with a
Teflon valve. The reaction mixture was stirred for 30 min at -80
℃ and then slowly warmed up to room temperature and stirred
for additional 30 min. Then, the reaction mixture was heated at
4
1
3
3
1
deuterated solvent, respectively.
externally. 1 F-NMR spectra were
referenced to 85% H PO
externally referenced to C (δ –163.0 ppm) in C . Elemental
P-NMR spectra were
9
3
4
6
F
6
6 6
D
3
1
1
6
0 ℃ for 6 days and monitored by P{ H}-NMR. During the first
analysis was performed using Perkin Elmer 2400 Series II
CHNS/O Elemental Analyzer. X-ray crystallographic analysis was
performed using SMART APEX II area-detector diffractometer.
All reagents including aldehyde and ketone substrates and
additives for robustness tests for TH reactions were purchased
from Sigma-Aldrich and used without further purification unless
noted otherwise. 2-propanol was additionally dried over
activated 4Å molecular sieves. The preparation of N-phenyl
two days of heating the colour of the reaction mixture turned
from yellow to red-orange (notably, the same colour change
i-
was observed upon treatment of the closely related (
Pr
HBn
i-Pr
Bn
POCN )NiBr with MeLi to give [( POCN )Ni]
2 P 6 6
(δ in C D =
8
1
91.6 ppm), previously reported by Zargarian et al. After 72
3
1
1
hours at 60 ℃, P{ H}-NMR analysis revealed formation of
i-Pr
Ph
about 32% of [( POCN )Ni]
2
(C) (δ
P
in C
6
D
6
= 190.1 ppm; δ
P
in
i
H
PrOH = 192.2 ppm) along with unidentified decomposition
products (see Fig. S7 and Fig. S8 in the ESI†). Further heating of
the reaction mixture did not result in increased conversion of A
to C and showed formation of a complex mixture of unidentified
decomposition products. From the sample taken after 72 hours
at 60 ℃, all volatiles were pumped off, the residue was dried in
POCN aminophosphinite pincer ligand was performed
according to the literature procedures for analogous N-benzyl
8
H
derivative. For full characterization of N-phenyl POCN ligand
and intermediates in the synthesis of this ligand see the ESI.†
Preparation of (i-PrPOCNHPh)NiBr (A)
The aminophosphinite complex A was prepared according to vacuum and dissolved in 2-propanol (5.0 mL) to give red-orange
3
1
1
31
slightly modified procedure reported by Zargarian et al. for an solution. P{ H}-NMR analysis of this solution revealed the P-
analogous benzylamino derivative ( POCN )NiBr. A solution resonance of complex C being identical to the 31P-resonance of
ligand (640 mg; 2.03 mmol) the species observed during A-catalyzed transfer hydrogenation
and triethylamine (0.430 mL; 3.1 mmol) in 5.0 mL of toluene of benzophenone in 2-prpoanol (δ
i-Pr
HBn
8
i-Pr
HPh
of aminophosphinite POCN
i
P
in PrOH = 192.2 ppm) (see
was added at room temperature to the suspension of Fig. S9 and Fig. S10 in the ESI†), suggesting the latter species
NiBr (CH CN)
(580 mg; 1.93 mmol) in 10 mL of toluene. The being identical to complex C formed upon treatment of complex
2
3
2
colour of the reaction mixture changed to brown and the A with MeLi.
mixture was left at 60˚C with stirring overnight. After that the
B: Reaction of (i-PrPOCNHPh)NiBr (A) with KO Bu. A yellow
t
reaction mixture was filtered through glass frit, all volatiles
were pumped off and the residue was dried in vacuum and
washed with hexanes (2 x 5 mL) to give yellow powder. Yield:
solution of (i-PrPOCNHPh)NiBr (A) (10 mg, 0.022 mmol) in 0.6 mL
of 2-propanol was added at room temperature to solid KO Bu (5
mg, 0.044 mmol). Immediate colour change of the reaction
mixture to red-orange and formation of white precipitate was
observed. The mixture was transferred to an NMR tube
equipped with a Teflon valve and left at room temperature for
hours (the NMR tube was shaken from time to time). NMR
analysis after that showed almost exclusive formation of [(
2
POCN )Ni] (C) (see Fig. S11 and Fig. S12 in the ESI†).
Formation of the same complex was observed upon treatment
t
7
00 mg (80%). Single crystals of complex A suitable for X-ray
diffraction analysis were obtained by slow vaporization of Et
solution into hexanes at room temperature. H-NMR (500 MHz;
2
O
1
i
C
6
D
6
; δ, ppm): 1.06 (dd, J = 7.0 and 15.4 Hz, 3H, CH
3
, P Pr
2
); 1.11
4
i
(dd, J = 7.0 and 14.2 Hz, 3H, CH
3
, P Pr
2
); 1.20 (dd, J = 7.2 and 17.8
i-
i
i
Hz, 3H, CH
1
(
3
, P Pr
2
); 1.47 (dd, J = 7.2 and 17.8 Hz, 3H, CH
3
, P Pr
2
);
Pr
Ph
i
i
.89-2.00 (m, 1H, CH, P Pr
d, J = 16.0 Hz, 1H, ArCH ); 4.07 (dd, J = 7.2 and 16.0 Hz, 1H,
ArCH ); 4.77 (br d, J = 5.4 Hz, 1H, NH); 6.42 (d, J = 7.5 Hz, 1H, CH,
2 2
); 2.13-2.24 (m, 1H, CH, P Pr ); 3.68
2
t
of A with KO Bu in EtOH for 1 hour at room temperature (see
2
Fig. S13 in the ESI†). All attempts to isolate the product by
removal of the solvent and crystallization resulted in
decomposition to a mixture of unidentified compounds.
Ar); 6.65 (d, J = 7.9 Hz, 1H, CH, Ar); 6.86 (t, J = 7.4 Hz, 1H, CH,
Ar); 6.92 (t, J = 7.7 Hz, 1H, p-CH, NPh); 6.99 (t, J = 7.9 Hz, 2H, m-
CH, NPh); 7.17 (obscured by C
6
D
6
residual proton resonance,
3
1
1
2
H, o-CH, NPh). P{ H}-NMR (202.5 MHz; C D
6 6
; δ, ppm): 203.1 General procedure for A-catalyzed TH reactions
i
13
1
(s, P Pr
2
). C{ H}-NMR (125.8 MHz; C
6
D
6
; δ, ppm): 16.6 (d, J = 3.1
); 18.2 (d, J = 5.1 Hz, CH
); 28.6 (t, J = 24.3, 2 CH
For NMR scale reactions, a substrate of interest or a mixture of
substrates, as in robustness tests for transfer hydrogenation of
i
i
Hz, CH
3
2
of P Pr ); 17.5 (br s, CH
3
of P Pr
of P Pr
2
3
i
i
2
of P Pr ); 18.5 (d, J = 3.6 Hz, CH
3
2
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