DOI: 10.1039/C7CC01910F
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Meso-TBP-1@Ir exhibited homogeneous distribution of C, N, Ir
elements (Figure S12, ESI). No aggregated Ir particles was
observed by (HR)TEM image of Meso-TBP-1@Ir, probably due
to the strong coordination ability of TB functionality towards Ir
complex (Figure S13, ESI). XPS measurement was performed to
investigate the coordination site and oxidation state of Ir species
(Figure S14, ESI). BE of Ir4f7/2 in Meso-TBP-1@Ir was located at
62.3 eV, together with BE of 65.3 eV for Ir4f5/2, which was similar
with Ir(II) in the half-sandwich Ir-bipyridine derivatives reported in
the literature (Ir4f7/2: 62.1 eV).22 Correspondingly, the BE of
Cl2p3/2 was observed at 197.8 eV. Subsequently, the resultant
Meso-TBP-1@Ir was applied in the methylation of amines using
MeOH without any other additives. The methylation reaction of
morpholine (1a) with methanol was selected to investigate the
influence of various reaction parameters (For reaction
parameters screening, see Table S1, ESI). Almost no N-
methylmorpholine (2a) was formed in the absence of any catalyst
(entry 1, Table S1, ESI), while 89% yield of 2a was obtained at
110 oC within 24 h catalyzed by Meso-TBP-1@Ir without any
other additives, which was even higher than that obtained over
a
Scheme 1. Methylation of amines with methanol.
Reaction conditions:
morpholine 1 mmol, [Ir] 3 mol%, MeOH 4 mL, 110 oC, 24 h. Yield of 2a was
determined by GC using dodecane as the internal standard.
In summary, mesoporous TB-functionalized POPs have
been synthesized using sulfonic acid group functionalized IL both
as catalyst and reaction medium together with H2O. This
aqueous acidic IL solution was also feasible in the preparation of
mesoporous benzimidazole-functionalized POPs. The integration
of TB ligands gave the polymer strong coordination ability with
Ir(II) complex. The resultant Meso-TBP-1@Ir exhibited
extraordinary catalytic performance in the N-methylation of
amines using methanol together with high stability and easy
recyclability. We thank the National Natural Science Foundation
of China (Nos. 21673256, 21402208, 21403252, 21503239).
the corresponding homogeneous [IrCp*Cl2]2
(2a yield: 81%)
under the same other conditions (Scheme 1).The yield of 2a was
83% and 89% respectively taking Meso-TBP-2@Ir and Meso-
TBP-3@Ir as catalyst under the same reaction conditions.
Notably, 2a yield was decreased to 63% using microporous TB-
MOP (pore width: 1.69 nm) with the same skeleton as support
using the same catalyst loading of Ir, indicating the
advantageous mesoporosity of Meso-TBP-1-1.5 for mass
transfer. Methylation products of other aliphatic secondary
Notes and references
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,
amines (2b-2e) were also obtained in moderate to high yields
(60~94%) (Scheme S1, ESI). N, N-Dimethylbenzylamines with
electro-donating (2f) or electro-withdrawing (2g) group on the
benzene ring with yield of 78% and 95% were achieved,
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2h-2k. While n-butylamine gave lower yield of the corresponding
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dimethylation product (21, 62%). Notably, 48% yield of N-
ethylmorpholine (2m) and 94% yield of N-isobutylmorpholine (2n
were obtained taking ethanol and isobutanol as the
corresponding alkylation reagents. Based on the previous
)
a possible reaction
mechanism was also proposed (Scheme S2, ESI). In the
repeating reactions, the catalytic activity of Meso-TBP-1@Ir was
well retained after recycling the catalyst for five times (Figure
S15, ESI). The XPS analysis on the recycled catalyst showed
that the Ir species were still in the Ir(II) form (Figure S16, ESI).
For leaching test, the heterogeneous catalyst was separated
through centrifugation after the reaction being performed for 6 h
(
2a yield: 69%), and the liquid supernatant was detected by ICP-
OES. It was demonstrated that Ir species were undetectable
4082-4088.
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22 K. Park, G. H. Gunasekar , N. Prakash, K.-D. Jung and S. Yoon,
(<10 ppb) in the liquid phase and the yield of 2a kept constant
o
after the reaction was further conducted for 24 h at 110 C. All
these indicated the excellent stability and activity of Meso-TBP-
1@Ir as a heterogeneous catalyst for the methylation of amines
with MeOH.
ChemSusChem, 2015, 8, 3410-3413.
4 | J. Name., 2012, 00, 1-3
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