Nearly Uniform MgO-Supported Pentaosmium Cluster Catalysts

Abstract

[Os5C(CO)14]2- was synthesized on the surface of MgO by reductive carbonylation of adsorbed Os3(CO)12 at 548 K and 1 bar. The supported species were characterized by infrared (IR), 13C NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR and EXAFS data are consistent with the presence of [Os5C(CO)14]2-, formed in a yield of about 65%, along with smaller osmium carbonyl clusters. As the supported clusters were decarbonylated in flowing He or H2, they were characterized by IR and EXAFS spectroscopies, which indicate that the decarbonylation was complete after each treatment at 573 K. The EXAFS data characterizing the sample treated in He determine an Os-Os first-shell coordination number of 3.4, matching that of [Os5C(CO)14]2- and indicating that the Os5C frame was retained after decarbonylation in He. Treatment of MgO-supported [Os5C(CO)14]2- in H2 at 573 K resulted in the formation of aggregated osmium clusters larger than Os5C. The catalytic activity of Os5C for toluene hydrogenation was found to be an order of magnitude less than that of the aggregated osmium clusters, which are metallic in character.

Supported Metal Cluster Catalysts

“…The image of Fig. The images are consistent with EXAFS, IR and 13 C NMR spectra, indicating that the predominant supported species were [Os 5 C(CO) 14 ] 2− [9]. The images are consistent with EXAFS, IR and 13 C NMR spectra, indicating that the predominant supported species were [Os 5 C(CO) 14 ] 2− [9].…”

“…For example, surface-mediated synthesis was used to convert Os 3 (CO) 12 into [Os 5 C(CO) 14 ] 2− on MgO [6,7,9], and comparable chemistry occurs in basic solutions. For example, surface-mediated synthesis was used to convert Os 3 (CO) 12 into [Os 5 C(CO) 14 ] 2− on MgO [6,7,9], and comparable chemistry occurs in basic solutions.…”

“…In principle, most of the known preparation methods [1,2,9], such as melt quenching, vapor and sputter deposition, and plating, can be used for the production of metallic glasses for catalytic studies.…”

The deposition of osmium carbonyl clusters onto inorganic oxide surfaces: A ToF-SIMS and IR spectroscopic study of the surface species

“…We have examined the cases where E = O ([Os 3 (CO) 10 (μ-H){μ-S(CH 2 ) 3 OH}], 6); S (8,9,10) or COO (11). In all cases, the negative mode ToF-SIMS spectra of the grafted osmium clusters showed major fragments attributable to [Os 3 (CO) n (μ-H)(μ-S)] − (n 9); that for 10 on ZnO is shown in Fig.…”

“…Such surface species are also important in surface-assisted syntheses. For example, [Os 5 C(CO) 14 ] 2− was synthesized on the surface of MgO by reductive carbonylation of adsorbed 1 at 548 K. The supported species was characterized by IR, 13 C NMR, and EXAFS spectroscopies [11]. Finally, the attachment of osmium clusters on functionalized silica which contain moieties such as [Ph 2 PCH 2 CH 2 Si(OEt) 3−x (OSi≡)] and [HS(CH 2 ) 3 Si(OMe) 3−x (OSi≡)], as well as the interaction between [Os 3 (CO) 10 (μ-H){μ-S(CH 2 ) 3 Si(OMe) 3 }] and silica have also been studied using IR spectroscopy [12].…”