# Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application
## 3 Polymer-Inorganic Coordinated Hybrids: Complexation-Induced Properties
### Pyridine-Based Polymers
#### 3.1.3 Catalytic Activity of Coordination Complexes of PVPs with Metal Ions  
The complexes between P4 VP and many kinds of transition metals have high catalytic activity for many reactions. The selective and efficient electrochemical reduction of CO\({}_{2}\) to single products is crucial for solar fuel development. The catalytic activity of systems of cobalt phthalocyanine (CoPc) encapsulated within a P4 VP membrane was investigated by [PERSON] and coworkers [108; 109]. This system is designed to improve both the activity and selectivity of CoPc for CO\({}_{2}\) reduction while suppressing the competitive hydrogen evolution reaction (HER). The goal is to selectively convert CO\({}_{2}\) into useful products like carbon monoxide (CO) with high efficiency, which is crucial for renewable energy applications such as solar fuel development. The encapsulation of CoPc within P4 VP significantly increases the catalytic activity for CO\({}_{2}\) reduction compared to the parent CoPc complex. When CoPc is used alone, it shows modest activity and is not very selective, often generating a significant amount of H\({}_{2}\) alongside CO. However, the CoPc-P4 VP system demonstrates improved selectivity for CO\({}_{2}\) reduction due to the unique coordination environment created by the P4 VP polymer. The proposed mechanism for the enhanced catalytic activity of the CoPc-P4 VP system involves multiple steps (Figure 5a). The authors describe three primary factors contributing to the system's improved selectivity and activity for CO\({}_{2}\) reduction over the hydrogen evolution reaction (HER). First, the axial coordination of the pyridyl groups from the P4 VP to the Co(II) center of cobalt phthalocyanine (CoPc) increases the nucleophilicity of the metal center, facilitating stronger CO\({}_{2}\) binding. This modification alters the rate-determining step of the reaction, shifting it from CO\({}_{2}\) binding toa subsequent protonation event. Additionally, the polymer environment creates hydrogen bonding interactions in the secondary coordination sphere, which help stabilize the CO2 intermediates. The proton delivery to the active site is controlled by pyridine residues in the P4 VP, which act as proton relays. This proton relay system selectively facilitates CO2 reduction by providing a slower, more controlled proton transport, which reduces proton availability for completing the HER. The encapsulated CoPc-P4 VP complex, therefore, shows significantly higher selectivity for the CO2 to CO conversion, with much less H2 production compared to non-encapsulated CoPc. Ruthenium complexes are among the most interesting coordination complexes, and they have attracted great attention over the past decades due to their appealing biological, catalytic, electronic, and optical properties. Ruthenium(II)-P4 VP complex has been applied as a highly efficient water oxidation catalyst [110], taking advantage of the polymer's flexible and charged environment. This system demonstrates impressive catalytic performance, with high turnover numbers (TONs) ranging from 1200 to 1700, making it more efficient than small-molecule analogs like [Ru(bda)(pic)2]. The coordination between P4 VP and Ru in this system allows for a unique single-site water nucleophilic attack (WNA) mechanism, which differs from the commonly observed interaction between two metal oxide  
Figure 5: (**a**) An illustration of cobalt phthalocyanine (CoPc) encapsulated within a hydrophobic poly-4-vinylpyridine (P4 VP) membrane highlighting the postulated primary-, secondary-, and outer-coordination sphere effects [109]. (**b**) Schematic synthesis of a P4 VP–Ru polymer–metal complex by a combination of RAFT polymerization and a pyridine/DMSO exchange reaction [110]. (**c**) Proposed structure of Ru-PVP/CNT [111]. (**d**) Proposed Cu(II) structures in the fresh catalysts [112]. (**e**) Left: structure of the redox polymer osmium bipyridine PVP. Right: schematic cross section of the glucose-sensitive FMOSFET [113].