## 4 Conclusions  
The behavior of cyclometalated rollover complexes reflects a delicate balance of different contribution from the metal, the ancillary ligands, and the rollover cyclometalated bipyridine. In particular, the nature of the substituent in 6-substituted-2,2\({}^{\prime}\)-bipyridines affects not only their behavior towards C(3)-H bond activation, but also the reactivity of the resulting rollover complexes. All these considerations are also valid for classic cyclometalated complexes; in addition, \"rollover\" deprotonated ligands have the peculiarity of being no more a spectator in the reactivity of the complex but may act as a \"ligand with multiple personalities\" due to the presence of the uncoordinated nitrogen. As a consequence of the behavior of Pt(II) cyclometalated rollover complexes with 6-ethyl-2,2\({}^{\prime}\)-bipyridine (bpy\({}^{6\text{Et}}\)) and 6-methoxy-2,2\({}^{\prime}\)-bipyridine (bpy\({}^{6\text{OMe}}\)), two ligands with similar steric hindrance but different electronic properties, is very different. In particular, the new complexes react in very different ways towards protonation: in addition to differences given by substituents and ancillary ligands, the reaction is complicated by the presence of several nucleophilic centers in the complexes. Experiments showed that all the bpy\({}^{6\text{Et}}\) rollover complexes can be easily protonated by [H\({}_{3}\)O-18-crown-6][BF\({}_{4}\)], whereas no evidence of nitrogen-protonation was found for bpy\({}^{6\text{OMe}}\) complexes, with the possible exception of complex **6a**. Indeed, reaction of complex [Pt(bpy\({}^{6\text{OMe}}\)-H)(Me)(PPh\({}_{3}\))] with [H\({}_{3}\)O-18-crown-6][BF\({}_{4}\)] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy\({}^{\text{OMe}}\))(Me)(PPh\({}_{3}\))]\({}^{+}\). Surprisingly, only the isomer with the _cis_-PPh\({}_{3}\)-OMe geometry is formed, in spite of an expected instability due to steric hindrance of the PPh\({}_{3}\) ligand (cone angle 145\({}^{\circ}\)). Surprisingly, the OMe substituent is situated in the neighborhood of the phenyl rings of the bulky PPh\({}_{3}\) rather than close to the much smaller methyl ligand. This result reminds us that too often the cone angle is considered as a real \"solid cone\", which is not always true. This result is interesting and may elicit a reflection on the use and interpretation of the cone angle concept. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/10/19/6665/1](http://www.mdpi.com/2076-3417/10/19/6665/1)]([http://www.mdpi.com/2076-3417/10/19/6665/1](http://www.mdpi.com/2076-3417/10/19/6665/1)), DFT-based coordinates for the equilibrium geometry for compounds **8a**, **8a**-**iso**; **1a**, **1b**, **1e**; **3a**, **3b**, **3e**; **4a**, **4b**, **4e**; **5a**, **5b**; **5e**; **6a**, **6b**, **6e**; **7a**, **7b**, **7e**; **9a**, **9b**, **9e**; **10a**, **10b**, **10c**. Scheme for the protonation reactions. Table S1: Coordinates for the equilibrium geometry for  
geometry of **6e:** Figure S26: Optimized geometry of **9e:** Figure S27: Optimized geometry of **7e:** Figure S28: Optimized geometry of **10e:**  
Conceptualization, A.Z. ; Formal analysis, A.Z., L.M., M.I.P., S.P., M.S. and S.S.; Funding acquisition, A.Z., M.I.P. and S.S.; Investigation, A.Z., L.M., M.I.P., S.P. and M.S. ; Methodology, A.Z., L.M. and M.I.P. ; Resources, A.Z., M.I.P. and S.S.; Software, L.M. ; Supervision, A.Z. ; Writing--original draft, A.Z., L.M., M.I.P., S.P. and M.S. ; Writing--review & editing, A.Z., L.M., M.I.P., S.P. and S.S. All authors have read and agreed to the published version of the manuscript. This research was funded by Universita degli Studi di Sassari (\"Fondo di Ateneo per la ricerca 2019\") and Regione Autonoma della Sardegna (grant CRP-78365\" Complessi di Au e Pt derivanti da donatori calogeni e pnicogeni: applicazione quali antimicrobici\", L.R. 7 agosto 2007 n. 7, annualita 2013).