## Materials and Methods
### Reactivity with Acids
Furthermore, the presence of \({}^{195}\)Pt satellites for the H\({}_{4}\), H\({}_{5}\) and H\({}_{6^{\prime}}\) protons demonstrates that the ligand is still coordinated to platinum center, as well as the DMSO and methyl groups (DMSO: singlet with satellites at \(\delta\) = 3.29 ppm, \({}^{3}\)]\({}_{\text{Pt-H}}\) = 20.3 Hz; methyl: singlet with satellites at \(\delta\) = 0.76 ppm, \({}^{2}\)]\({}_{\text{Pt-H}}\) = 80.8 Hz). It is worth noting that the corresponding [Pt(bpy\({}^{6\text{Et}}\)-H)(Me)(DMSO)]/[Pt(bpy\({}^{6\text{Et}\ast}\))(Me)(DMSO)]\({}^{+}\) complexes, **1b**/**3b**, constitute an uncommon Bronsted\(-\)Lowry acid\(-\)base conjugated couple. Protonation reactions of this type are of potential interest. Recently, protonation and deprotonation of the Ir(III) rollover complex [Ir(PPh\({}_{3}\))\({}_{2}\)(bpy-H)(CI)(H)] lead to reversible switching of the emission (from bluish-green to yellowish-orange and vice versa), demonstrating that it is an \"aggregation induced phosphorescence\" (AIP) active rollover complex, able to act as a multi-stimuli responsive luminescence material [36]. This easy protonation is likely due to the good basicity of the uncoordinated nitrogen atom and to a not excessive electron density on the Pt atom. The Pt-C(sp\({}^{2}\)) and Pt-C(sp\({}^{3}\)) bonds appear to be fairly stable under these conditions. In contrast, no signs of protonation were detected in the reaction of complex **1a**. The reaction was also followed by means of \({}^{1}\)H NMR spectroscopy, observing rapid liberation of methane (a singlet at 0.18 ppm) and no signs of N-H protons. The Pt-CH\({}_{3}\) signal disappears with the appearance of methane. The spectra showed the presence of several species in solution which we were not able to identify. Even isolation in the solid state of the reaction products did not allow us to characterize the formed species. It seems, overall, that in the case of complex **1a**, electrophilic attack occurs on the Pt center or on the Pt-CH\({}_{3}\) bond. The resulting liberation of methane leads to unstable species and, finally, to decomposition. The different behavior of the two bipyridine ligands is likely due to the scarce basicity of the uncoordinated nitrogen in bpy\({}^{6\text{OMe}}\) combined to a higher electron density on the Pt center. In addition, the planar configuration induced by metalation reduces the availability of the nitrogen lone pair due to the proximity of the C(3')-H hydrogen. The reaction of complexes **1a**-**b** with HCl is different from that with [H\({}_{3}\)O-18-crown-6][BF\({}_{4}\)]. It is worth noting that in this case **1a** and **1b** react in the same way, leading to methane elimination and formation of the corresponding chloride derivatives [Pt(bpy\({}^{6\text{R}}\)-H)Cl(DMSO)] (R = OMe, **4a**; R = Et, **4b**), which can be isolated with good yields and characterized. The reaction process can be simplified following a \"one pot\" procedure, reacting [Pt(DMSO)\({}_{2}\)Me\({}_{2}\)] with bpy\({}^{6\text{R}}\) at 50 \({}^{\circ}\)C and adding HCl after the rollover reaction has taken place. The \({}^{1}\)H NMR spectrum allows an easy characterization of the products. In particular, the signal of the coordinated DMSO, coupled to \({}^{195}\)Pt, indicates a _trans_ N-Pt-DMSO disposition, as suggested by the high value of \({}^{3}\)J(Pt-H), 23.6 and 23.3 Hz for **4a** and **4b**, respectively, to be compared to 18.2 and 18.1 Hz in **1a** and **1b**. In this case, the reaction likely involves a Cl-assisted mechanism, which may proceed through an oxidative addition/reductive elimination pathway. In an oxidative-addition ionic mechanism, halide ion attack and protonation occur separately. In the two possible pathways either protonation of the metal or coordination of chloride may be the first step [80]. Complexes **4a-b** were tested with [H\({}_{3}\)O-18-crown-6][BF\({}_{4}\)] in the same conditions as **1a-b** (1 h, r.t. in acetone solution). The outcome of the reaction of the chloride species is, also in this case, different for the two complexes.