André de Kock - MSc Supplementary data

A series of rhodium(III), iridium(III) and ruthenium(II)-based <i>N</i>-heterocyclic carbene (NHC) complexes were synthesised (<b>1</b>-<b>6</b>, <b>1S</b>, <b>3S</b> and <b>5S</b>). To achieve this the synthesis of a novel alkoxysilane tethered NHC ligand precursor (<b>L1</b>) and a secondary isopropyl functionalised NHC ligand precursor (<b>L2</b>) was completed. These precursors were synthesised by means of reacting 1‑methylimidazole with the appropriate alkyl halide. To obtain the NHC complexes, three metal precursors had to be synthesised first, which included [Cp*RhCl₂]₂, [Cp*IrCl₂]₂ and [(<i>p</i>‑cymene)RuCl₂]₂. An excess of silver(I) oxide was used in combination with the desired NHC ligand precursor (<b>L1 </b>or <b>L2</b>) (in the dark) <i>via</i> a method known as transmetalation. The subsequent addition of the appropriate metal precursor (Rh, Ir or Ru) is the last step in allowing the transmetalation reaction to proceed.This reaction afforded the silyl tethered complexes (<b>1</b>, <b>3</b> and <b>5</b>). Following their successful synthesis, these complexes were immobilised onto a coal fly ash (CFA)-based silica-support. The immobilisation process involved adding the appropriate metal complex to a stirring slurry of the silica nanoparticles in toluene. All the homogeneous complexes (<b>1</b>-<b>6</b>) were characterised by means of high‑resolution mass spectrometry (HR-MS), nuclear magnetic resonance (NMR) spectroscopy as well as single crystal X-ray diffractometry (SCXRD) where possible. The characterisation of the silica‑supported complexes (<b>1S</b>, <b>3S</b> and <b>5S</b>) was completed by means of thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), field emission scanning electron microscopy with energy dispersive spectroscopy (FESEM-EDS), Fourier-transform infrared (FTIR) spectroscopy and powder X‑ray diffraction (PXRD) analyses.These complexes were applied to the hydrosilylation of the internal alkyne diphenylacetylene and the transfer hydrogenation of ketones and aldehydes employing isopropyl alcohol (^<em>i</em>PrOH) as the hydrogen source. The ruthenium complexes (<b>5</b>, <b>5S</b> and <b>6</b>) delivered the best activity for the transfer hydrogenation reaction with TOF_ini values as high as 394.1 h^-1 and yields of &gt; 99%<b> </b>after 20 hours. The iridium complexes also performed better in the transfer hydrogenation reaction presenting with conversions of up to 52% and TOF_ini values as high as 48.0 h^-1. The hydrosilylation reaction was best catalysed by the rhodium complexes (<b>1</b>, <b>1S</b> and <b>2</b>) with conversions of up to 96% and TOF values of as large as 24.0 h^-1 within 1 h, which compared favourably to literature.The immobilised complexes (<b>1S</b>, <b>2S</b> and <b>3S</b>) were utilised in reusability studies. The Rh-NHC complex (<b>1S</b>) was utilised in the hydrosilylation reaction and could be recycled a total of 4 times with TOF values ranging between 5.94 h^-1 and 19.0 h^-1. Similarly, both the Ru and Ir‑NHC complexes (<b>5S</b> and <b>3S</b>) showed activity in four subsequent runs of the transfer hydrogenation reaction. Complex <b>3S</b> had TOF_ini values ranging from 13.5 h^-1 to 37.0 h^-1 with complex <b>5S</b> achieving TOF_ini values between 70.0 h^-1 and 118.5 h^-1.