Tunable Aminooxy-Functionalized Monolayer-Protected Gold Clusters for Non-Polar or Aqueous Oximation Reactions

Aminooxy (-ONH2) groups are well known for their chemoselective reactions with carbonyl compounds, specifically aldehydes and ketones. The versatility of aminooxy chemistry has proven to be an attractive feature that continues to stimulate new applications. This work describes application of aminooxy 'click chemistry' on the surface of gold nanoparticles. We present here a trifunctional amine-containing aminooxy alkane thiol ligand for use in the functionalization of gold monolayer protected clusters (Au MPCs). Diethanolamine is readily transformed into an organic-soluble aminooxy thiol (AOT) ligand using a short synthetic path. The synthesized AOT ligand was coated on ≤ 2 nm diameter hexanethiolate (C₆S)-capped Au MPCs using a ligand exchange protocol to afford organic-soluble AOT/C₆S (1:1 ratio) Au mixed monolayer protected clusters (MMPCs). This work describes the synthesis of Au(C₆S)(AOT) MMPCs and representative oximation reactions with various types of aldehyde-containing molecules, highlighting the ease and versatility of the chemistry and how amine protonation can be used to switch solubility characteristics.