Abstract
In this study, the ligand L1 was synthesized via the Schiff-base condensation reaction and
treated with [Pd(CH3CN)2Cl2], [Ru(p-cymene)Cl2]2, [Cp*IrCl2]2 and [Pt(CH3CN)2Cl2] under
the applicable reaction conditions resulting in the formation of four novel complexes (C1-C4).
The ligands and complexes were characterised by 1H and 13C{1H} Nuclear Magnetic
Resonance Spectroscopy (NMR), Infrared Spectroscopy (FTIR), High-Resolution Mass
Spectrometry (HR-MS), and CHN analysis. The study of these methods revealed that the
relevant metal centres were successfully coordinated with the intended ligand.
A mesoporous silica support, SBA-15, bearing silanol (Si-OH) groups, was also synthesised,
and complexes C1, C2, and C3 were immobilised to produce homogeneous and heterogeneous
catalysts. The silica support and the catalysts were characterised using Brunauer-Emmett-
Teller (BET), Scanning Electron Microscope (SEM), Transmission Electron Microscopy
(TEM), powdered X-ray diffraction spectroscopy (P-XRD), Inductively Coupled Plasma -
Optical Emission Spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS) and
Thermogravimetric analysis (TGA). The characterisation results indicated that the catalyst
supports' structural integrity was preserved throughout the immobilisation procedure. The
complexes were linked to silica supports, according to results from ICP-OES analyses.
The complexes, as well as immobilized catalysts, were used as pre-catalysts in the
hydrodeoxygenation of the aldol product, A1, (3Z, 5E)-6-(furan-2-yl)-3-(furan-2-
ylmethylene)-4-oxohex-5-enoic acid. The reaction conditions were optimised at 120 °C, 40 bar
hydrogen gas for 24 h, with catalyst loading of 0.007 mmol with methanol acting as the solvent
and glacial acetic acid as a co-catalyst due to its Lewis acid properties. The catalysts (C1, C2,
and C4) displayed excellent selectivity for saturation of the double bonds and removal of the
newly formed aldol condensation double bond (>98%), yielding a mixture of hydrocarbon
products.
The catalytic products were characterised using gas chromatography-mass spectrometry (GCMS)
and authenticated with synthesised standards. Using complexes C1–C4 and the
corresponding immobilised catalysts supported on SBA-15, hydrodeoxygenation of A1 to
different hydrocarbons was accomplished. The Pd(II) and Ru(II) pre-catalysts performed better
than the other complexes under established conditions, which were 120 °C, 40 bar, 24 h, in
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MeOH and with glacial acetic acid as a co-catalyst. The use of glacial acetic acid in the catalytic
system resulted in higher conversion and improved product selectivity. The immobilised
complexes were then used under these established conditions; IrL1/SBA-15 was outperformed
by the PdL1/SBA-15 and RuL1/SBA-15 catalysts. Overall, complex C1 was the bestperforming
and easy-to-synthesize complex.