Synthesis, Solid‐State NMR Characterization, and Application for Hydrogenation Reactions of a Novel Wilkinson’s‐Type Immobilized Catalyst

Abstract

Silica nanoparticles (SiNPs) were chosen as a solid support material for the immobilization of a new Wilkinson's-type catalyst. In a first step, polymer molecules (poly(triphenylphosphine)ethylene (PTPPE); 4-diphenylphosphine styrene as monomer) were grafted onto the silica nanoparticles by surface-initiated photoinferter-mediated polymerization (SI-PIMP). The catalyst was then created by binding rhodium (Rh) to the polymer side chains, with RhCl3⋅x H2O as a precursor. The triphenylphosphine units and rhodium as Rh(I) provide an environment to form Wilkinson's catalyst-like structures. Employing multinuclear ((31)P, (29)Si, and (13)C) solid-state NMR spectroscopy (SSNMR), the structure of the catalyst bound to the polymer and the intermediates of the grafting reaction have been characterized. Finally, first applications of this catalyst in hydrogenation reactions employing para-enriched hydrogen gas (PHIP experiments) and an assessment of its leaching properties are presented.

Single‐Atom Gold Catalysis in the Context of Developments in Parahydrogen‐Induced Polarization

“…These values for the highly isolated monoatomic catalyst (or small gold cluster that may be formed during the reaction as it was shown earlier14) are higher than those observed for metal nanoparticles supported on various oxides (0.3–1.2 %) in the same reaction 17. Moreover, the enhancement factor of 21 for the signal of CH 3 group of butane is five times larger than that obtained for the single‐site rhodium immobilized catalyst 18. The result obtained here is unique because even in the case of dissociative chemisorption of hydrogen molecules it can be expected that the hydrogen atoms cannot move freely on the catalyst and thus should not lose the nuclear spin correlation if the highly isolated monoatomic catalyst is used.…”

Heterogeneous Microtesla SABRE Enhancement of 15N NMR Signals

“…where the catalyst is in a different phase from the substrate) to combat these issues and better enable implementation of parahydrogen-based approaches for medical/imaging applications. Recent work towards that end includes the immobilization of homogeneous complexes to solid supports for SABRE [22,23] and for PHIP [17,24,25] or supported/bulk metal/metal oxide catalysts use for PHIP. [17,26–29] …”

Development of new methods in modern selective organic synthesis: preparation of functionalized molecules with atomic precision

“…The immobilized Wilkinson's complex was later studied in another work. 665 The results of control experiments confirmed the formation of PHIP effects in the heterogeneous reaction but the effect was weak (the 1 H NMR signal increased 3.5 ± 4.4-fold). The PHIP observed for propyne hydrogenation in deuteriobenzene on Wilkinson's complex immobilized on modified silica gel allowed researchers to establish the syn-addition of hydrogen to the triple bond to give propylene, which is also typical of homogeneous hydrogenation of alkynes on this complex.…”