The designs of the catalytically active ruthenium complexes (Figure ) drew inspiration from our prior work on alcohol and ammonia oxidation with immobilised catalysts. [Ru(tpada)(bpy-NMe2)(Cl)](PF6) (1, where tpada is 4'-(adamantan-1-yl)-2,2':6',2''terpyridine and bpy-NMe2 is 4,4'-bis(dimethylamino)-2,2'bipyridyl) has previously demonstrated activity in ammonia oxidation when tethered to a β-cyclodextrin-modified electrode. In contrast, [Ru(tpada)(pic)(Cl)] (2, where pic is picolinate) and [Ru(terpy)(ada-pic)(Cl)] (3, where terpy is 2,2':6',2''-terpyridine and ada-pic is 4-(1-adamantyl) picolinate) are adapted versions of an immobilised C-H activation catalyst. A common characteristic among these complexes is the presence of an adamantyl group, crucial for the stable binding to macrocyclic host molecules such as pillar [6]arene (PA [6], 4). PA [6] was derived from 1,4-bis(ethoxy)pillar [6]arene (PA [6]Et), synthesised with slight modifications to a literature procedure (see SI), followed by deprotection of the ether groups with boron tribromide. Immobilisation of 4 was achieved by simply immersing mesoporous indium tin oxide (mITO) electrodes in a 0.1 mM methanolic solution of the macrocycle for 90 min. Multilayer formation, observed during the soaking treatment, was eliminated by cyclic voltammetry (CV) in 0.2 M NaClO4 prior to functionalisation with ruthenium catalysts (Figure ). The disappearance of the oxidative wave, attributed to the oxidation of the phenolic unit to hydroquinone, and the determined surface loading of 4 (1.81 ± 0.17 nmol cm -2 geometric area), quantified through desorption studies in 1 M methanolic KOH (Figure , Table ), signifies the removal of all non-covalently bound PA [6]. Theoretical calculations indicate that PA [6] initially pre-organises with the phenol units oriented perpendicularly to the ITO surface through hydrogen bonding with an adsorption energy of -1.18 eV (Figure ). This positions the cavity pointing away from the surface, allowing guest binding to occur. Following the initial hydrogen bonding, it is expected that dehydration occurs on the surface, leading to the formation of covalent bonds (Figure ), similar to processes observed in the adsorption of carboxylic and phosphonic acids on TiO2. Following the dehydration, the interaction energy is -6.92 eV. The anchoring of the three guest molecules (1-3) was accomplished by immersing PA [6]-functionalised mITO electrodes in methanolic solutions of the complexes (0.1 mM) for 16 h. The geometric surface loading, determined by integration of the Ru II /Ru III oxidative wave observed during CV measurements, was 2.05 ± 0.10 nmol cm -2 for the three guest molecules (Table ), which is within the error range for a 1:1 host-guest complex with PA [6]. We note that physisorbed Ru complexes do not stably bind to bare mITO, as evidenced by the negligible Ru II /Ru III oxidative wave during CV measurements on the second scan (Figure ). of [Ru(tpada)(bpy-NMe2)(Cl)](PF6)