Three Reactions, One Catalyst: A Multi‐Purpose Platinum(IV) Complex and its Silica‐Supported Homologue for Environmentally Friendly Processes

Abstract

Although platinum nanoparticles and complexes ‐especially of Pt(0) and Pt(II)‐ are well known catalysts, siloxane‐based platinum complexes are rarely reported. Herein, a Platinum(IV) complex of 4‐aminopyridinium‐modified disiloxane was prepared and characterized by medium and far infrared spectroscopy, NMR and EDX. The formation of the complex was monitored by UV–Vis spectroscopy, which showed the high affinity and selectivity of this ligand for Pt, with a stability constant of 7.53·103 M−1. The catalytic activity of the siloxane‐based complex was tested in three types of reactions: reduction of p‐nitrophenol, oxidation of glucose and starch, and hydrosilylation. The hydrophobic behavior of the permethylated disiloxane moiety ensures good hydrolytic stability, while the N‐donor ligand stabilizes the in‐situ formed Pt nanoparticles. The generation of Pt nanoparticles during p‐nitrophenol reduction was confirmed by TEM and SEM. Contrary to most reports, the aerobic oxidation of mono‐ and polysaccharides occurred without oxidation agents or mediators added, in mild conditions, at room temperature and pH ~9. The same metal complex was found active in hydrosilylation of vinyl‐siloxanes with temperature‐modulated rate, thus being useful in silicone cross‐linking systems without the need of inhibitors. The method was adapted to one‐pot synthesis of silica‐supported Pt(IV) complex, which acted as efficient and reusable heterogeneous hydrosilylation catalyst, limiting the contamination of the product with Pt. This approach is promising for superior valorization of scarcely available and expensive platinum metal. By the same method, multifunctional soluble complexes and mesoporous silica may be obtained, with tunable catalytic performance.

Synthesis, characterization, and some metal complexes of bis(isocyanide)disiloxane, showing catalytic activity

“…The reduction of p ‐nitrophenol with NaBH 4 was tested in the presence of iCN‐Pt (as DMSO solution). The reaction was relatively slow (Figure S9a) compared with a previously reported Pt(IV) complex, [ 46 ] obeying first‐order kinetic model, with k a = 2.7 × 10 −3 min −1 ( R 2 = 0.9811). A 10‐min induction period was observed, when we suppose that the Pt complex is reduced to Pt(0) by NaBH 4 , as demonstrated previously [ 46 ] and suggested by a transmission electron microscopy (TEM) image of Pt nanoparticles (NPs) separated after the reaction (Figure S9b).…”

Space and Time Crystal Engineering in Developing Futuristic Chemical Technology

“…A movement started more than a decade ago in engineering a catalyst with a multipurpose role [33]. A common trend is going on by accommodating different catalytically active nanoparticles in the same composite [34] or the same catalyst material under different reaction conditions to develop a multipurpose catalyst [35][36][37].…”

One‐pot reduction‐hydrophobization of heterogenized platinum with 1,1,3,3‐tetramethyldisiloxane

“…When the Si H functionalized silicone oil, PDMHS, was used with TMDS as a reducing agent and in the presence of MTMS as a cross-linking agent (M2 reaction model), in the IR spectrum (Figure S19) of the reaction mixture, the disappearance of the absorption band corresponding to the Si H bond from 2158 cm À1 was also noticed. In the 1 H NMR spectrum (Figure S20), the characteristic peaks were found at δ = 0.07 (s, CH 3 Si) and 4.22 (residual Si H), while the 13 C NMR spectrum (Figure S21) showed δ = 1.05 (CH 3 Si). 29 Si NMR spectrum clearly indicated the presence of both difunctional and trifunctional silicon: δ = 7.65 (CH 3 Si CH 3 ), À22.01 (Si O Si), À53.48, À67.8 (Si-trifunctional) (Figure S22) [44] .…”

“…After devolatilization under vacuum at 50 C, 12 h, M1-M3 reaction mixtures were analyzed by FTIR and NMR ( 1 H, 13 C, and 29 Si) spectroscopy.…”

“…[ 11 ] Besides hydrophobicity, these supports should not contain active groups that could catalyze undesirable side reactions, like isomerization. [ 5 ] Platinum is commonly deposited as a complex [ 12 ] or fine dispersion on silica, [ 12,13 ] alumina, [ 14 ] ceramic, [ 14 ] glass, [ 12 ] metallic, [ 15 ] or carbon [ 16,17 ] substrates, but the active carbon (simple [ 7 ] or fluorinated [ 5 ] ) is also preferred. In specific hydrosilylation reactions, the styrene‐divinylbenzene (SDVB) copolymers have been used as alternatives, [ 7,18 ] due to their hydrophobicity, [ 5 ] pore diameters larger than those of active carbon‐supported catalysts, [ 7 ] high specific surface area, and easy accessibility.…”