The activity of Pt/SiO₂ catalysts obtained by the sol-gel method in the hydrosilylation of 1-alkynes

Abstract

Heterogeneous platinum catalysts (Pt/SiO 2 ) obtained by the sol-gel process at pH 3 and 9 have been used in the hydrosilylation reaction of 1-alkynes using various silanes. Once the catalysts were activated they were used in the hydrosilylation of 1-alkynes after a short induction period. The product distribution was quite similar in either case but important differences in catalytic activity and turnover reactions were observed. The catalyst obtained in the basic medium after each reaction lost its catalytic activity, so further activation was needed. To understand this behavior, the catalysts were characterized by 29 Si CPMAS NMR, FT IR, and BET surface area measurements. The 29 Si CPMAS NMR studies showed the presence of terminal and bridged hydroxyl groups in the Pt/SiO 2 catalyst at pH = 9. Similar results were observed by FT IR analysis because of the catalysts' synthetic conditions. Résumé : On a utilisé des catalyseurs homogènes de platine (Pt/SiO 2 ) obtenus par le procédé sol-gel à des pH de 3 et de 9 pour effectuer l'hydrosilylation d'alc-1-ynes à l'aide de divers silanes. Une fois les catalyseurs activés, ils étaient utilisés pour effectuer l'hydrosilylation des alc-1-ynes après une courte période d'induction. La distribution des produits est très semblable dans les deux cas, mais on a observé des différences importantes dans l'activité catalytique et dans les réactions de changement. Le catalyseur obtenu en milieu basique perd son activité après chaque réaction et on doit donc procéder à chaque fois à une nouvelle activation. Dans le but de comprendre ce comportement, on a procédé à une caractérisation des catalyseurs par RMN « CPMAS » du 29 Si, par spectroscopie IR à transformée de Fourrier et par des mesures « BET » de l'aire de la surface. Les études de RMN CPMAS du 29 Si ont montré que la présence de groupes hydroxyles pontés et terminaux est minimale dans le catalyseur de Pt/SiO 2 obtenu à un pH de 9. Des résultats semblables ont été obtenus par l'analyse du spectre IR à transformée de Fourier en raison des conditions de synthèse du catalyseur.

Asymmetric Catalysis at Chiral Metal Surfaces

“…In addition to Pt group metals and Ni, even bimetallic compositions with significant synergic effect between the components have been recommended as effective catalysts. [410][411][412][413][414][415][416] …”

Hydrosilylation of alkynes catalysed by platinum on titania

“…Heterogeneous catalysts offer several advantages over the homogeneous counterparts, such as easy recovery, easy recycling, and enhanced stability [13,14]. To the best of our knowledge, only three reports describe the heterogeneous platinum-catalysed hydrosilylation of alkynes, involving platinum on carbon [15], platinum on silica [16], and unsupported platinum oxide [17]. Although high yields and good selectivities were generally achieved, an inert atmosphere was mandatory and the catalysts could not be reused.…”

Regiochemical Aspects of the Platinum Oxide Catalyzed Hydrosilylation of Alkynes

“…With terminal alkynes (R 2 6 Recently, the use of N-heterocyclic carbene platinum(0) complexes has produced good b-selectivity allowing the synthesis of E-vinyldisiloxanes. 7 Excellent yields and b-selectivity can also be achieved by using ligand-free platinum catalysts (Pt/C, Pt/ silica gel) 8,9 providing a significant cost advantages over homogeneous and elaborate platinum complexes. If solutions to the problems associated with the hydrosilylation of terminal alkynes mediated by platinum catalysts are satisfactory in favor of the b-isomers, the reaction with unsymmetrical internal alkynes, particularly those with one or two aromatic rings, has received scant attention, 8 probably because of the difficulty in controlling the regioselectivity of the H-Si bond addition.…”