Chemoselective Hydrogenation with Supported Organoplatinum(IV) Catalyst on Zn(II)-Modified Silica

Abstract

Well-defined organoplatinum(IV) sites were grafted on a Zn(II)-modified SiO support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV-vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H and TEM techniques revealed highly dispersed (methylcyclopentadienyl)methylplatinum(IV) sites on the surface ((MeCp)PtMe/Zn/SiO, 1). In addition, computational modeling suggests that the surface reaction of (MeCp)PtMe with Zn(II)-modified SiO support is thermodynamically favorable (Δ G = -12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH-TPD and DNP-enhanced O{H} SSNMR. In situ DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions.

Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites

“…[59][60][61][62][63][64]76 Recently, we have used 1 H{ 17 O} dipolar recoupling experiments to characterize the Brønsted acidity of surfaces. 36,65 These experiments, however, were found to have insufficient resolution to separate the O-H distances of the sites responsible for the Brønsted acidity of silica-aluminas from those of the non-acidic silanols and aluminols. One promising approach to improving the resolution is to spread the resonances along a third dimension during which the 1 H chemical shifts are allowed to evolve.…”

Stepwise construction of silica-supported tantalum/iridium heteropolymetallic catalysts using surface organometallic chemistry

“…This strategy has only been explored in very rare instances [13][14][15][16][17][18] and is different from sequential co-grafting or co-impregnation methods in which both metal sites are orthogonally attached to the support, independently of one another, and are typically converted to supported alloys or nanoparticles after thermal treatment. [19][20][21][22][23][24][25][26][27][28][ [29][30][31][32] The purpose of this article is to compare both routes (A and B) in the case of a tantalum-iridium system. We demonstrate that, although homogeneously distributed heterometallic species are formed using both approaches, the nature of the obtained surface species, and therefore the catalytic performances of these materials, are affected by the chosen synthetic methodology.…”

Indirectly Detected DNP‐Enhanced 17O NMR Spectroscopy: Observation of Non‐Protonated Near‐Surface Oxygen at Naturally Abundant Silica and Silica‐Alumina

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] As a matter of course, researchers have applied this emerging technique to the 17 O nuclide, and demonstrated that 17 O SS NMR spectra could be acquired at natural abundance from nanoparticles [4,9,[12][13][15][16][17] and even from surfaces. [9,[18][19][20][21] In the majority of studies, however, the hyperpolarization of 17 O nuclei has been achieved via protons using the route e À ! 1 H!…”