## 3 Results
### Catalytic Experiments  
The most important advantage for the use of Pt(PLLA-Bipy)Cl\({}_{2}\) is the lack of solubility in the reaction medium at room temperature, while it was completely soluble under catalytic conditions (see Figure 5). This behavior, known as the \"ponytail\" effect, allows catalysis to be carried out in the homogeneous phase while the catalyst may be easily separated at the end of the process as a heterogeneous system. In contrast, the Pt(Bipy)Cl\({}_{2}\) complex did not show this property. Figure 4: UV–Vis spectra of (**a**) Pt(Bipy)Cl\({}_{2}\), (**b**) PLLA-Bipy and (**c**) Pt(PLLA-Bipy)Cl\({}_{2}\) collected in CH\({}_{2}\)Cl\({}_{2}\) solution (M = 0.005 mol/L). Figure 3: Magnification of the NMR spectra in the aromatic region of (**a**) PLLA-Bipy, (**b**) Pt(PLLA-Bipy)Cl\({}_{2}\) and (**c**) [Pt(PLLA-Bipy)Cl\({}_{2}\)]\({}_{2}\) recovered after ID4. Catalytic performances of Pt(PLLA-Bipy)Cl\({}_{2}\) and Pt(Bipy)Cl\({}_{2}\) were tested under different conditions of time and pressure as shown in Table 1.  
First, Pt(Bipy)Cl\({}_{2}\) was tested as a reference catalyst to evaluate its behavior in the hydrogenation of 2-cyclohex-1-one as a model substrate. The results of ID 1 showed the total inactivity of this catalyst as shown by the absence of hydrogenation products after catalysis. In contrast, the reaction performed in the presence of Pt(PLLA-Bipy)Cl\({}_{2}\) as the catalyst achieved a conversion of 73% and a total selectivity for the reduction of the carbon-carbon double bond in the same conditions. After increasing the reaction time from 3 to 6 h, the catalytic performances of Pt(PLLA-Bipy)Cl\({}_{2}\) reached a conversion of 99% with a total selectivity toward the reduction of carbon-carbon unsaturation (ID3). The catalyst was still active and selective after three catalytic cycles, although the conversion dropped to 39%. This was probably due to the formation of higher hindered [Pt(PLLA-Bipy)Cl\({}_{2}\)]\({}_{2}\) (Figure 6) instead of a merely Pt leaching, according to a theoretical study reported by [PERSON] et al. [30]. This hypothesis was supported by the NMR spectra of the recovered catalysts (Figure 3c), where the resonances of the Bipy ligands slightly shifted and the spectrum did not show any signal of free Bipy. A further increment of hydrogen pressure from 1.1 to 2.2 MPa gave a conversion of 95% with total selectivity. Under these conditions, the catalyst deactivation after three catalytic runs was the same as ID4. This result supports the deactivation mechanism above-mentioned and exclude the formation of nanoparticles that are more active than molecular complexes [31]. Figure 5: The catalytic reaction mixture of (**a**) Pt(PLLA-Bipy)Cl\({}_{2}\) under reaction conditions, (**b**) Pt(PLLA-Bipy)Cl\({}_{2}\) before and after catalysis at room temperature, (**c**) Pt(Bipy)Cl\({}_{2}\) at room and reaction temperature. Figure 6: Structure of the hypothesized dimeric specie [Pt(PLLA-Bipy)Cl\({}_{2}\)]\({}_{2}\). The solubility of the catalytic system Pt(PLLA-Bipy)Cl\({}_{2}\) is very different from the behavior of other heterogeneous systems previously described [32; 33] as it acts as a non-supported catalyst during the reaction, leaving the C=O functionality untouched. Different results were obtained in the hydrogenation of (E)-but-2-enal using the complex Pt(PLLA-Bipy)Cl\({}_{2}\) in the same conditions of the previously reported experiments. In these tests, a conversion of 96-97% was reached using a reaction time of 6 h and a hydrogen pressure of 2.2 MPa (ID7 and ID8). During the hydrogenation of an \(\alpha\),\(\beta\)-unsaturated aldehyde, a remarkable selectivity was achieved toward the complete hydrogenation of the C=C double bond, but also of the -CHO group with the formation of 1-butanol (selectivity 88-89%) and butanal (selectivity 3-4%). The different products formed during the two hydroganations may be attributed to the high reactivity of the aldehyde group (-CHO) of (E)-but-2-enal if compared with the carbonyl group (=CO) of 2-cyclohex-1-one.