One-pot amination of aldehydes and ketones over heterogeneous catalysts for production of secondary amines

Figures & data

Figure 1. Reductive amination of cyclohexanone with benzylamine. Adapted fromRef. ^[10] Open access.

Figure 2. Reductive one-pot amination of nitrobenzene with benzaldehyde adapted from.^[28–30] Copyright permission from John Wiley & Sons and from Royal Society of Chemistry.

Figure 3. A simplified scheme for reductive amination of an aldehyde/ketone with a primary amine and one-pot reductive amination of nitroarene to the corresponding secondary amine using an aldehyde/ketone. Aldehyde can be prepared from an alcohol.

Table 1. Amination of aldehyde and ketones with amines using molecular hydrogen.^a Notation: AM amine, IM imine, AL alcohol, KET ketone, ALD aldehyde.

Entry	Reaction	Catalyst	Conditions	Yield of products (%)	Ref
1		Pd/NiO	25°C, 1 bar H2, cALD = 0.28 M, nAM: nALD = 5:6, ethanol, 12 h	YAM = 98	^[Citation15]
2		polystyrene embedded N-heterocyclic carbene-linked Pd	80°C, 35 bar H2, cALD = 0.28 M, nAM: nALD = 1:1, water, 8 h	YAM = 91	^[Citation17]
3		Fe@Pd/C	80°C, 30 bar H2, cALD = 0.16 M, nAM: nALD = 1:1, water, 8 h	YAM = 94	^[Citation11]
4		No catalyst, Cu-Al layered double hydroxide	25°C, cALD = 0.025 M, nAM:nALD = 1:1, methanol, 3 h 120°C, 20 bar H2	YAM = 94	^[Citation71]
5		Pd-Cu supported on β-cyclodextrin	100°C, 15 bar H2, cALD = 0.23 M, nAM:nALD = 1:0.5, MW irradiation, ethanol	YAM = 73	^[Citation66]
6		Pd/NiO	25°C, 1 bar H2, c0,ALD = 0.46 M, nAM:nALD = 1:1, ethanol, 12 h	YAM = 86	^[Citation15]
7		polystyrene embedded N-heterocyclic carbene-linked Pd	80°C, 35 bar H2, cKET = 0.28 M, nAM: nALD = 1:1, water, 8 h	YAM = 73	^[Citation17]
8		Fe@Pd/C	80°C, 30 bar H2, cALD = 0.16 M, nAM: nALD L = 1:1, water, 8 h	YAM = 89	^[Citation11]
9		polystyrene embedded N-heterocyclic carbene-linked Pd	80°C, 35 bar H2, cKET = 0.28 M, nAM: nALD= 1:1, water, 8 h	YAM = 93	^[Citation17]
10		Pd/NiO	25°C, 1 bar H2, cALD = 0.46 M, nAM: nALD = 1:1, ethanol, 12 h	YAM = 90	^[Citation15]
11		Pd/NiO	25°C, 1 bar H2, cALD = 0.46 M, nAM: nALD = 1:1, ethanol, 12 h	YAM = 97	^[Citation15]
12		polystyrene embedded N-heterocyclic carbene-linked Pd	80°C, 35 bar H2, cALD = 0.28 M, nAM: nALD = 5:6, water, 8 h	YAM = 87	^[Citation17]
13		Pd/C, 2.7 nm	100°C, 3 bar H2, cAL = 0.83 M, nAM: nALD = 1:1, TFT, 1 h	YAM = 100	^[Citation67]
14		Au/SiO2-SO3H Ir/SiO2-SO3H Pt/SiO2-SO3H Pt/SiO2 colloid Pt/SiO2 impregnated	90°C, 50 bar H2, cALD = 0.1 M, cAM = 0.1 M, nAM: nALD = 5:6, ethyl acetate, 8 h	YAM = 3 YAM = 24 YAM = 23 YAM = 8 YAM = 8	^[Citation26]
15		Pt/SiO2-SO3H	90°C, 50 bar H2, cALD = 0.1 M, cAM = 0.1 M, nAM: nALD = 5:6, methanol, 8 h	YAM = 5	^[Citation26]
16		Pt/SiO2-SO3H	90°C, 50 bar H2, cALD = 0.1 M, cAM = 0.1 M, nAM: nALD = 5:6, water, 8 h	YAM = 11	^[Citation26]
17		Pt/SiO2-SO3H	90°C, 50 bar H2, cALD = 0.1 M, cAM = 0.1 M, nAM: nALD = 5:6, THF, 8 h	YAM = 15	^[Citation26]
18		UiO-67- paraphenylenediamine-Pd	50^°C, 5 bar H2, cAL = 0.04 M, nAM: nALD = 1:1, ethanol, 2 h	YAM = 97	^[Citation68]
19		Pd/C	100°C, 3 bar H2, cALD = 0.83 M, nAM: nALD = 1:1, TFT, 1 h	YAM = 100	^[Citation67]
20		UiO-67-para-phenylenediamine-Pd	25°C, 1 bar H2, cALD = 0.28 M, nAM:nALD = 5:6, ethanol, 2 h	YAM = 96	^[Citation68]
21		Au/Al2O3	120°C, 10 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 43	^[Citation24]
22		Au/C	120°C, 10 bar H2, cALD = 0.025 M, cAM = 0.025 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 4	^[Citation24]
23		Pt/Al2O3	25°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 74	^[Citation24]
24		Pt/Al2O3	10°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 85	^[Citation24]
25		Pd/C	10°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 86	^[Citation24]
26		Pt/Al2O3	25°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 99	^[Citation24]
27		Pt/C	25°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 99	^[Citation24]
28		Pt/Al2O3	25°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, ethanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 81	^[Citation24]
29		Pt/Al2O3	25°C, 5 bar H2, cAL = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, isopropanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 20	^[Citation24]
30		Pt/Al2O3	35°C, 5 bar H2, cALD = 0.05 M, cAM = 0.05 M, nAM: nALD = 1:1, methanol, 0.5 h, liquid flow rate = 0.5 mL min^−1, H2 flow rate = 30 mL min^−1	YAM = 98	^[Citation24]
31		Ru/C	25°C, 10 bar H2,4 bar NH3, cKET = 0.33 M, nKET = 1 mmol, methanol, 2 h, Ru:KET = 1:100	YAM = 88	^[Citation25]
32		Pt/C	25°C, 10 bar H2,4 bar NH3, cKET = 0.33 M, nKET = 1 mmol, methanol, 2 h, Ru:KET = 1:100	YAM = 10	^[Citation25]
33		Rh/C	25°C, 10 bar H2,4 bar NH3, cKET = 0.33 M, nKET = 1 mmol, methanol, 2 h, Ru:KET = 1:100	YAM = 89	^[Citation25]
34		Pd/C	25°C, 10 bar H2,4 bar NH3, cKET = 0.33 M, nKET = 1 mmol, methanol, 2 h, Ru:KET = 1:100	YAM = 72	^[Citation25]
35		polystyrene supported Pd-N-heterocyclic carbene	80°C, 35 bar H2, cKET = 0.28 M, nAM:nKET = 5:6, water, 8 h	YAM = 91	^[Citation17]
36		Fe@Pd/C	80°C, 30 bar H2, cKET = 0.16 M, nAM:nKET = 1:1, water, 8 h	YAM = 94	^[Citation11]
37		polystyrene supported Pd – N-heterocyclic carbene	80°C, 35 bar H2, cKET = 0.28 M, nAM:nKET = 5:6, water, 8 h	YAM = 94	^[Citation17]
38		Au/TiO2	100°C, 30 bar H2, cyclohexane, nAM: nKET = 1:1, toluene, 4 h	YAM = 72 YIM = 17	^[Citation10]
39		Cu/SiO2	100°C, 1 bar H2, cKET = not given, nAM: nKET = 3:1, toluene, 24 h	YAM = 12	^[Citation69]
40		Pd, polyethyleneimine, 2 nm	50°C, 3 bar H2, water, MgCl2, cKET = 0.18 M, nAM: nKET = 1:1, water, 21 h	YAM = 52	^[Citation21]
41		Cu/SiO2	100°C, 1 bar H2, cKET = not given, nAM: nKET = 3:1, toluene, 24 h	YAM = 86	^[Citation69]
42		Pd/MIL-101	90°C, 10 bar H2, cKET = 0.05 M, nAM: nKET = 2:1, hexane, 16 h	YAM = 90 YAM2 = 10^b	^[Citation61]
43		Pd, polyethyleneimine, 2 nm	50°C, 3 bar H2, water, MgCl2, cKET = 0.18 M, nAM: nKET = 1:1, water, 21 h	YAM = 12	^[Citation21]
44		Au/TiO2	100°C, 10 bar H2, cKET = 0.13 M, nAM: nKET = 1:1, cyclohexane, 5 h	YAM = 11 YIM = 4 YAL = 3	^[Citation10]
45		Pd/C	25°C, 3 bar H2, ethanol (20 mL/g of AM), 12–48 h	YAM = 52- YAM = 96	^[Citation27]

^aCatalyst properties are described in Table S1.

^b1-(4-fluorophenyl)ethan-1-amine.

Table 2. Reductive amination of α-methyltryptamine derivative to N-alkyl-α-methyltryptamine derivative after 18 h. Adapted from Ref. ^[27] Copyright permission from Elsevier Ltd.

Entry	Carbonyl compound	N-alkyl-α-methyltryptamine derivative	Yield (%)
1			YAM = 78
2			YAM = 56
3			YAM = 52
4			YAM = 32
5		No desired product	YAM = 0
6		No desired product	YAM = 0

Figure 4. Reductive amination of α-methyltryptamine derivative into N,N-dialkyl-α-methyltryptamine derivative adapted from.^[27] Copyright permission from Elsevier Ltd.

Table 3. Solvent effect in reductive amination of furfural with aniline over Pt/SiO₂–SO₃ catalyst. Reaction conditions: furfural, 6 mmol; aniline, 5 mmol; catalyst, 0.15 mol%; ethyl acetate, 40 mL; H₂ pressure, 5 MPa; room temperature; 8 h, adapted from Ref .^[26] Copyright from Elsevier Ltd.

Entry	Solvent	Conversion^a (%)	Imine yield (%)	Amine yield (%)
1	Methanol	46	41.4	5.1
2	Water	24	13.2	11.3
3	THF	69	66.1	14.9
4	Ethyl acetate	72	51.2	21.3

^aConversion of aniline determined by GC.

Table 4. Reductive amination of AMF with primary amines R-NH₂ over Pt/Al₂O₃ catalyst adapted from Ref. ^[24].

Entry	R in R-NH2 and in the product	Duration of condensation step (h)	T (◦C)	Yield^b (%)
							others
1	Ph	2	25	<0.5	99	n.d.	n.d.
2	p-CH3C6H4	2	25	<0.5	99	n.d.	n.d.
3	m-CH3C6H4	2	25	<0.5	99	n.d.	n.d.
4	o-CH3C6H4	16	25	2	96	2	n.d.
5	o-CH3C6H4	16	35	1	97	2	n.d.
6	p-CH3OC6H4	2	25	<1	99	n.d.	n.d.
7	p-FC6H4	3	35	<1	98	1	n.d.
8	p-ClC6H4	3	35	<0.5	97	2	n.d.
9	p-BrC6H4	3	25	5	88	5	n.d.
10	p-BrC6H4	3	35	4	87	6	2
11	p-IC6H4	3	25	2	74	<1	23
12	p-IC6H4	16	15	2	87	<1	9
13		3	35	18	41	15	1
14	m-ClC6H4	3	35	15	80	5	n.d.
15	m-ClC6H4	3	55	6	83	11	n.d.
16	o-ClC6H4	2	35	9	49	16	1
17	cyclohexyl	2	35	17	49	n.d.	34
18	cyclohexyl	2	55	2	56	n.d.	42
19	n-dodecyl	2	35	18	66	n.d.	16
20	n-hexyl	2	35	25	67	n.d.	8
21	n-hexyl	2	55	3	82	n.d.	15

^aConditions: AMF, (0.05 M), primary amine (0.05 M), Pt/Al₂O₃ catalyst, 185 mg, methanol, 5 bar H₂, liquid flow rate 0.5 ml/min, H₂ flow rate 30 ml/min, reaction time 30–33 min.

^bThe product yields were determined by ¹H NMR

Figure 5. Product distributions of reductive amination of cyclohexanone over Group VIII metal-based catalysts in methanol and water. Reaction conditions: Cyclohexanone 1 mmol, catalyst 0.02 g, solvent 3 mL, under 9 bar hydrogen, T = 25°C, agitator speed = 1000 rpm, time = 2 h adapted from Ref. ^[25] Notation: 1 methanol, 2 water as a solvent. Copyright from Elsevier Ltd.

Figure 6. Concentration profiles in HMF amination with aniline over Pd supported on poly-para-phenylenediamine modified metal organic framework catalyst UiO-67 in ethanol at 50°C under 5 bar hydrogen adapted from.^[68] Notation: (■) HMF conversion, (▲) imine and (●) amine yield. Copyright permission from Royal Society of Chemistry.

Figure 7. Scheme of reductive amination of AMF with different aromatic and aliphatic amines adapted from.^[24] Copyright permission from Elsevier Ltd.

Figure 8. Reaction mechanism for formation of an imine from a carbonyl compound and an amine.^[82]

Table 5. Secondary amines from aldehyde/ketones and amines using other hydrogen sources than molecular hydrogen. Notation: FA formic acid, SILP supported ionic liquid phase. Notation: Y yield, AM amine, S selectivity

Entry	Reaction	Catalyst	Conditions	Yield of product (%)	Ref
1		Pd-Cu β–cyclodextrin	180°C, FA-microwave assisted, 15 bar N2, ethanol	YAM = 54	^[Citation66]
2		Au/TiO2	60°C, FA, tert-butanol, 3 h	YAM = 98	^[Citation13]
3		Au/TiO2	60°C, FA, tert-butanol, 22 h	YAM = 91	^[Citation13]
4		Pd-Cu supported on β–cyclo-dextrin	100°C, FA-microwave, 15 bar N2, ethanol	YAM = 37	^[Citation66]
5		SILP(ionic liquid is 1-carboxymethyl-3-methyl-imidazolium bis(trifluoromethy lsulfonyl)imide)	40°C, FA+trimethylamine, 5 h	YAM = 30	^[Citation14]
6		Co2Rh2/C	100°C, 5 bar CO, water, THF, 6 h	YAM = 98	^[Citation54]
7		Rh/C	160°C, 50 bar CO, THF, 20 h	YAM = 82	^[Citation75]
8		Au/TiO2	60°C, 20 bar CO, Methanol-water, 2.5 h	YAM>99	^[Citation84]
9		Solid acid	25°C, NaBH4, 8 min	YAM = 94	^[Citation12]
10		sulfonic acid supported hydroxyapatite encapsulated γ-Fe2O3	25°C, NaBH4, ethanol, 40 min	YAM = 94	^[Citation19]
11		SiO2-H2SO4	25°C, NaBH4, THF, 0.07 h	YAM = 95	^[Citation16]
12		SiO2-H2SO4	25°C, NaBH4, THF, 0.07 h	YAM = 96	^[Citation16]
13		sulfonic acid supported hydroxyapatite encapsulated γ-Fe2O3	25°C, NaBH4, ethanol, 40 min	YAM = 87	^[Citation19]
14		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar, benzaldehyde (1.1 mmol), aniline (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 75	^[Citation2]
15		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar aldehyde, (1.1 mmol), aniline (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 82	^[Citation2]
16		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar, aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 74	^[Citation2]
17		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar, aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h	YAM = 60	^[Citation2]
18		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar,aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h	YAM = 44	^[Citation2]
19		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar,aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 60	^[Citation2]
20		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar,aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 63	^[Citation2]
21		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar,aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h	YAM = 37	^[Citation2]
22		Fe powder + Pd/C in CO2/H2O system	80°C, PCO2 = 80 bar, aldehyde (1.1 mmol), amine (1 mmol), catalyst 5 mol%, H2O (3 mL), Fe (3 mmol), 15 h.	YAM = 11	^[Citation2]
23		t-ZrO2 an example of tertiary amine synthesis	160°C, 0.3 MPa of N2, 0.2 g of reactant, 0.05 g of catalyst, in 15 mL of anhydrous DMF, reaction time 6 h,	YAM = 72.6 S > 99%	^[Citation85]

Figure 9. Conversion of HMF (■) and concentration profiles of alkyliminefuran (▲), alkylaminofuran (●) and 2,5-bis-(hydroxymethyl)furan (o) in amination of HMF with aniline over Au/TiO₂ at 60°C under 20 bar in 1:1 methanol water mixture as a solvent adapted from Ref. ^[84]. Copyright permission from Royal Society of Chemistry.

Figure 10. Pd/C-catalyzed reductive amination of aldehydes with Fe in CO₂/H₂O system adapted from Ref. ^[2] Copyright of Elsevier Ltd.

Figure 11. Isotope labeling experiments adapted from Ref. ^[2] Copyright permission from Elsevier Ltd.

Table 6. Comparison of different methods of N-benzylcyclohexylamine preparation. Notation: Y yield, AM amine, IM imine.

Reaction	Catalyst	Conditions	Yield of product (%)	Ref.
	Au/TiO2	100°C, 30 bar H2, cyclohexane, 4 h	YAM = 72 YIM = 17	^[Citation10]
	PS-Pd-NHC (N-heterocyclic carbine)	80°C, 35 bar H2, water, 8 h	YAM = 91	^[Citation17]
	Ionic liquid, (carboxymethyl)-1-methyl-1 H-imidazol-3-ium-bis(trifluoro-methyl)sulfonyl)amine supported on silica	FA+triethylamine, 40°C, acetonitrile, 5 h	YAM = 30	^[Citation14]
	Au/TiO2	70°C, FA, tert-butanol, 5 h	YAM = 97	^[Citation13]
	CH0.6O0.35S0.14 solid acid catalyst	NaBH4, 25°C, tert- butanol, 10 min	YAM = 90	^[Citation12]
	Sulfonic acid supported hydroxyapatite encapsulated γ-Fe2O3 nanocrystallites	25°C, NaBH4, ethanol, 2 min	YAM = 90	^[Citation19]

Table 7. The highest yields of secondary amines resulted from amination of aldehydes and ketones with nitrocompounds over heterogeneous catalysts using molecular hydrogen. Notation: n_N:n_Ald and n_N:n_Ald denote the molar ratio of nitro compound to aldehyde and ketone, respectively, c_Ald and c_ket denote initial concentrations of aldehyde and ketone, respectively.

Entry	reaction	Catalyst	Conditions	Conversion (%)	Yield (%)	Ref.
1		UiO-66-IrL	100°C, 6 bar H2, nN:nAld = 1:1.5, cAld = 0.8 M, 2-propanol, 24 h	99	YAM = 99	^[Citation1]
2		Pt-MIL-101-SI	110°C, 5 bar H2, nN:nAld = 1:1, cAld = 1.42 M, toluene, 48 h	>99	YAM = 91 YIM = 4 YAL = 5	^[Citation30]
3		Pd/polymer	25°C, 1 bar H2, nN:nAld = 1:1, cAld = 0.83 M, methanol, 5.5 h	Not given	YAM = 95	^[Citation46]
4		Gum acacia-Pd	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.12 M, methanol, 6 h	Not given	YAM = 88	^[Citation47]
5		Pd^0Fe3O4-SiO2	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol-water, 2.5 h	Not given	YAM = 93	^[Citation52]
6		Pd2Ag1@MIL-101	25°C, 2 bar H2, nN:nAld = 1:1, cAld = 0.23 M, ethanol, 30 h	99	YAM = 71 YAL = 15 Yaniline = 15	^[Citation65]
7		Pd/Fe3O4	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol, 6 h	Not given	YAM = 94	^[Citation51]
8		Pd nanoparticles on Sour Cherry tree gum	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol, 6 h	Not given	YAM = 92	^[Citation59]
9		Pd@Fe3O4-NH2-starch	25°C, 1 bar H2, nN:nAld = 1:1, cBA = 0.12 M, ethanol, 2 h	Not given	YAM = 88	^[Citation60]
10		Pd/Fe3O4-C	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.16 M, water, 8 h	99	YAM = 92	^[Citation90]
11		Pd/hollow magnetic mesoporous silica, Fe3O4-NH2	25°C, 1 bar H2, nN:nAld = 1:1.2, cAld = 0.23 M, ethanol, 8 h	100	YAM = 94.2	^[Citation23]
12		Co3O4 nitrogen doped carbon graphitic carbon (NGrC)	110°C, 50 bar H2, nN:nAld = 1:2, cAld = 0.34 M, THF-water, 24 h	Not given	YAM = 95	^[Citation29]
13		Co supported on mesoporous nitrogen doped carbon (mCN-900, 900 denotes pyrolyzed temperature)	130°C, 10 bar H2, nN:nAld = 1:1.5, cAld = 0.05 M, ethanol, no time given	Not given	YAM = 93.6 YIM = 6.4	^[Citation62]
14		Fe2O3 supported on nitrogen doped graphitic carbon	160°C, 70 bar H2, nN:nAld = 1:2, cAld = 0.34 M, THF-water, 24 h	Not given	YAM = 85	^[Citation28]
15		Pd^0Fe3O4-SiO2	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol-water, 2 h	Not given	YAM = 91	^[Citation52]
16		Pt nanowire (NW)	100°C, 1 bar H2, nN:nAld = 1.1:1, cAld = 0.45 M, toluene, 24 h	Not given	YAM = 92.6	^[Citation70]
17		Pd nanoparticles on Sour Cherry tree gum	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol, 6 h	Not given	YAM = 90		^[Citation59]
18		Pd^0Fe3O4-SiO2	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol-water, 3 h	Not given	YAM = 91		^[Citation52]
19		Pt NW	100°C, 1 bar H2, nN:nAld = 1.1:1, cAld = 0.45 M, toluene, 24 h	Not given	YAM = 94.7		^[Citation70]
20		Co/mCN-900	150°C, 10 bar H2, nN:nAld = 1:1.5, cAld = 0.05 M, ethanol, no time given	Not given	YAM = 99.9		^[Citation62]
21		Pt nanowire (NW)	100°C, 1 bar H2, nN:nAld = 1.1:1, cAld = 0.44 M, toluene, 24 h	Not given	YAM = 71.2		^[Citation70]
22		Pd nanoparticles stabilized on Sour Cherry tree gum	25°C, 1 bar H2, nN:nAld = 1.2:1, cAld = 0.2 M, ethanol, 6 h	Not given	YAM = 93		^[Citation59]
23		Pd@MIL-101	110°C, 5 bar H2, nN:nket = 1:1, cket = 1.438 M, toluene, 40 h	92	YAM = 90.5		^[Citation30]
24		Pd@Fe3O4-NH2/starch	25°C, 1 bar H2, nN:nket = 1:1, cket = 0.12 M, ethanol:water, 2 h	Not given	YAM = 83		^[Citation60]
25		Pd2Ag1@MIL-101	110°C, 2 bar H2, nN:nket = 1:1, cket = 0.23 M, ethanol, 30 h	65	YAM = 46		^[Citation65]
26		Pd@MIL-101	110°C, 5 bar H2, nN:nket = 1:1, cket = 1.438 M, toluene, 70 h	>99	YAM = 82		^[Citation30]
27		Pd/Fe3O4	25°C, 1 bar H2, nN:nket = 1:1, cket = 0.19 M, ethanol, 20 h	0	YAM = 0		^[Citation51]
28		Co3O4 supported on nitrogen doped graphitic carbon (NGr@C)	160°C, 50 bar H2, nN:nket not given, cket = not given, THF, paratoluene sulfonic acid (p-TsOH), mol. sieves, 24 h	Not given	YAM = 76		^[Citation29]
29		Au/Fe2O3	120°C, 20 bar H2, nN:nAld = 1:1.5, cAld = 0.2 M, toluene, 6 h	Not given	YAM = 80		^[Citation91]
30		Au/Fe2O3	120°C, 20 bar H2, nN:nAld = 1:1.5, cAld = 0.2 M, toluene, 6 h	Not given	YAM = 96		^[Citation91]

Figure 12. Reductive amination of 4-methylfurfural with nitrocyclohexane over Au/TiO₂ adapted from Ref. ^[94] Copyright permission from Elsevier Ltd.

Figure 13. Effect of temperature in reductive amination of benzaldehyde with nitrobenzene over Co supported on mesoporous nitrogen doped carbon (square) adapted from Ref. ^[62] and over Fe₂O₃ supported on nitrogen doped graphitic carbon (circle) adapted from Ref. ^[28] Notation: open symbol imine, solid symbol amine. Copyright permissions from John Wiley & Sons and from Elsevier Ltd.

Figure 14. Mechanism for one-pot reductive amination of nitroarenes with aldehydes.^[82].

Figure 15. Effect of temperature in reductive amination of benzaldehyde with nitrobenzene over Co supported on nitrogen doped carbon (CN-600, pyrolyzed at 600°C) (ball) adapted from Ref. ^[53] and over Co supported on nitrogen doped carbon (CN-800, pyrolyzed at 800°C) (rectangular) adapted from Ref. ^[56] in the presence of formic acid. Notation: open symbol: imine, solid symbol: amine. Copyright permissions from Elsevier Ltd and from American Chemical Society.

Figure 16. The reaction mechanism for one-pot reductive amination of nitrobenzene with benzaldehyde using the CO/H₂O assisted system.^[95] Copyright Elsevier Ltd.

Table 8. Hydrogen sources other than molecular hydrogen used in amination of benzaldehyde with nitrobenzene over heterogeneous catalysts. Notation: N nitro compound, BA benzaldehyde.

Entry	Reaction	Catalyst	Dmetal (nm)	Hydrogen source	Conditions	Yield of product (%)	Ref.
1		Au-SiO2-NH2	4.5	Formic acid	80°C, THF, quinuclidine, 6 h	YAM = 90	^[Citation49]
2		Ni/H-mZSM-5	3–5	NaBH4	25°C, cBA = 0.04 M, N:BA = 1:1, DMF, 80 min	YAM = 95	^[Citation50]
3		Co- supported on nitrogen modified carbon (CN)	25.9	Formic acid	110°C, 10 bar N2, cBA = 0.1 M, N:BA = 1:2, THF, 10 h	YAM = 100	^[Citation56]
4		Co- supported on nitrogen modified carbon (CN)			170°C, water, 30 bar CO, cBA = 0.83 M, water, N:BA = 1:2	YAM = 90	^[Citation90]
5		Co2Rh2/C	n.d.	CO and water	120°C, THF, 24 h	YAM = 92	^[Citation54]
6				CO and water	170°C, 40 bar CO, cBA = 0.19 M, water, N:BA = 1:2, 10 h	YAM = 99.4	^[95]
7		Co-supported on nitrogen modified carbon (CN)	8.2	Formic acid, THF	190°C, 10 bar N2, cBA = 0.1 M, THF, N:BA = 1:2, 15 h	YAM = 96 YIM = 4	^[Citation53]

Table 9. One-pot reductive amination of aldehydes with nitroarenes over Ni/H-mZSM-5 with NaBH₄ as a reducing agent ^a.[50].

Entry	Carbonyl compoud	Nitro compound	Product	Yield^b (%)	Time (min)	TOF^c (h^−Citation1)
1				YAM = 98 YAM = 95^d	35 80	29.0 12.3
2				YAM = 96	30	33.1
3				YAM = 95	40	24.6
4				YAM = 96	45	22.1
5				YAM = 97	35	28.7
6				YAM = 97	30	33.4
7				YAM = 93	40	24.1
8				YAM = 95	40	24.6
9				YAM = 84	65	13.4

^aReaction conditions: aldehyde compound (2 mmol), nitro aromatic compound (2 mmol), Ni/H-mZSM-5 (0.05 g), NaBH₄ (6 mmol), and H₂O (5 mL), room temperature.

^bIsolated yield after work-up.

^cTurn-over number (mol product/mol Ni) and turn-over frequency (mol product/(mol Ni·h)).

^dReaction conditions: aldehyde compound (2 mmol), nitro aromatic compound (2 mmol), Ni/H-mZSM-5 (0.05 g), NaBH₄ (6 mmol), and DMF (5 mL), at room temperature.

^eScale-up conditions: benzaldehyde (30 mmol), nitrobenzene (30 mmol), catalyst (0.75 g), NaBH₄ (90 mmol), and H₂O (150 mL), room temperature.

Figure 17. Concentration profiles for the reactant and products in benzaldehyde amination with nitrobenzene over Co supported on nitrogen doped carbon in the presence of formic acid at 150°C in THF as a solvent, adapted from.^[56] Notation: Molar percentage of nitrobenzene (■), N-benzylideneaniline (●), aniline (▲) and N-benzylaniline (o). Copyright permission from Elsevier Ltd.

Figure 18. Effect of CO pressure in reductive amination of benzaldehyde with a) nitrobenzene over Co supported on nitrogen modified carbon catalyst in water at 170°C after 10 h adapted from^[95] notation: solid symbol – amine, open symbol – imine and b) 4-methoxynitrobenzene over Co₂Rh₂/C at 120°C after 12 h in THF and a small amount of water adapted from,^[54] notation: solid symbol – amine, open symbol – tertiary amine, a and b denote the yield of secondary amine and tertiary amine, respectively after 24 h. Copyright permissions from Elsevier Ltd and from American Chemical Society.

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