Magnetically recoverable Fe 3 O 4 @ Au-coated nanoscale catalysts for A 3-coupling reaction

Chloroauric acid (HAuCl4), sodium borohydride (NaBH4), Iron(II) sulfate heptahydrate (FeSO4.7H2O), piperidine, chloroform, methanol, acetonitrile, phenylacetylene and polyethyleneimine (PEI, branched, Mw ≈ 25,000 g mol-1) were obtained from Sigma-Aldrich, Australia. 2-pyridinecarboxaldehyde, 3-pyridinecarboxaldehyde, 4-pyridinecarboxaldehyde, p-chlorobenzaldehyde, 2-thiophenecarboxaldehyde and 2-furaldehyde were obtained from Sigma-Aldrich, Australia. Potassium nitrate (KNO3), sodium citrate (C6H5Na3O7.H2O) and benzaldehyde were obtained from Ajax Finechem, Australia. Sodium hydroxide (NaOH), ptolualdehyde and 3-nitrobenzaldehyde were obtained Fluka, Australia. Hydroxylamine hydrochloride (NH2OH.HCl) was obtained from VWR, Australia. 4-methoxybenzaldehyde was obtained from Acros Organics, Australia. 4-fluorobenzaldehyde and 1-naphthaldehyde were obtained from Alfa Aesar, Australia. Formaldehyde, 37% w/w was obtained from Chem Supply, Australia. All chemicals were used as received with no further purification.

presence of a variable concentration of PEI (0 to 4 g/L) for two hours.Fe(OH) 2 was oxidised to Fe 3 O 4 nanoparticles with PEI coating on the surface.These Fe 3 O 4 -PEI nanoparticles formed were separated magnetically and the particles were rinsed using Milli-Q water five times and finally kept as a suspension in 80 mL of Milli-Q water.

Au-seed preparation:
Citrate-stabilised Au seed particles were prepared as reported by Brown et al. 2   Briefly, the aqueous HAuCl 4 solution (90 mL, 1%) was mixed with sodium citrate (2 mL, 38.8 mM) under vigorous stirring at room temperature.NaBH 4 (1 mL, 0.075 %) was then added and stirred for another 5 minutes.
2 mL of Fe 3 O 4 -PEI suspension was stirred with 90 mL of Au seed colloidal for two hours.
The Fe 3 O 4 -PEI-Au seed formed were separated magnetically and rinsed using Milli-Q water five times.In the presence of PEI (5 g/L) solution, these particles were heated at 60 °C for one hour so as to functionalize their surfaces with PEI.The particles were then rinsed five times with Milli-Q water and dispersed in 20 mL Milli-Q water.
The Au-coated Fe 3 O 4 nanoparticles formed were magnetically separated and rinsed using Milli-Q water five times and dispersed in 20 mL Milli-Q water.

Transmission Electron Microscopy (TEM):
Morphologies of nanoparticles were analysed using transmission electron microscopy (TEM).
Nanoparticles were dropped and dried on carbon-coated copper grids and imaged using a JEOL 2100 TEM operating at an accelerating voltage of 120 kV.The size of the nanoparticles was determined using ImageJ software (NIH, USA).A minimum of 200 particles was measured, and the data introduced as the average ± standard error mean.The High-angle annular dark-field (HAADF) STEM images, Energy-dispersive X-ray spectroscopy (EDX) -point mode (elemental analysis) and mapping mode (elemental maps) were obtained on the FEI Titan G2 80-200 TEM/STEM operating at an accelerating voltage of 200 kV.

A 3 -coupling reaction:
In a test tube, Fe 3 O 4 @Au (10 mol %), benzaldehyde (1 mmol), piperidine (1 mmol), and phenylacetylene (1 mmol) were added in 3 mL of toluene and stirred under a nitrogen atmosphere for 48 hours at 100 °C with reflex.The reaction mixture was cooled to room temperature and catalyst was recovered magnetically.The catalyst then was washed with toluene and acetone for three times and air dried for recycling study.Induced couple plasma (ICP) analysis of the recycling reaction mixture after recovered the catalyst for Au and Fe concentrations as followed Au (0.06, 0.12, 0.13, 0.30 and 0.41 mg/L) and Fe (0.18, 1.3, 1.8, 0.94 and 3 mg/L) from the first to fifth recycle respectively.
The crude product was analysed using 1 H NMR. All the products are known compounds.

The computational studies
The geometries of 13 starting compounds were optimised at B3LYP/6-311G(d,p) level of theory.The Cartesian coordinates (.xyz) from the optimised geometries were extracted to generate an input (.cif) for CrystalExplorer 3.2.Promolecular density surface was generated for each molecule.The lowest unoccupied molecular orbital (LUMO) and electrostatic potential (ESP) properties of each molecule were mapped on the corresponding promolecular density surface.Both LUMO and ESP were calculated at B3LYP/6-311G (d,p) level.

H-NMR Analysis
The propargylamine products were analysed by 1D 1 H-NMR.All NMR experiments were performed at 298 K on Varian 400 NMR spectrometer.1, Product of entry 1).