Characterization of a silica-supported trinuclear osmium carbonyl cluster by magic-angle-spinning carbon-13 NMR spectroscopy

Abstract

In recent years, there has been great interest in the use of transition-metal carbonyl clusters to prepare highly dispersed metal particles on oxide supports.1"4 In addition to providing a route to novel catalysts, these supported clusters may also afford relatively well-defined surface structures. Definitive assignments have proven elusive, however, even within the application of such techniques as extended X-ray absorption fine structure (EXAFS) spectroscopy5,6 and magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy.7 In this communication we show for the first time that it is possible to obtain highly resolved (line widths <2 ppm) 13C NMR spectra of a supported transition-metal carbonyl cluster through the use of high-field operation as well as magic-angle spinning.Impregnation of silica or alumina with a solution of Os3(CO)12, followed by thermal activation at 100-150 °C, apparently produces a single, strongly bound cluster believed to have one of the structures 1-3.8 It has not been possible to distinguish unambiguously between these possibilities using IR data in the carbonyl stretch region8"11 or EXAFS data.5'6'10•11 Although structure 1 has been most widely accepted, on the basis of gas evolution measurements,8 both 25 and 312 have also been suggested to be the correct structure. We show below that the three possibilities can be distinguished readily by 13C NMR analysis, which provides incisive spectroscopic evidence in support of structure 1.

Novel High-Yield Method for the Synthesis of [Os3(CO)10(μ-H)(μ-OSiR2R‘)] Species and X-ray Characterization of [Os3(CO)10(μ-H)(μ-OSiPh2OSiPh2OH)] and [Os3(CO)10(μ-H)(μ-OSiPh2OH)], First Molecular Models of Osmium Surface Species Anchored to Vicinal and Geminal Surface Silanols

“…Although we cannot give at the moment a satisfactory explanation, these results are in agreement with the observation that silica-anchored [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)] can be prepared only with loadings less than 4 wt % Os/SiO 2 , , which corresponds to a grafting on less than 5% of the total surface silanol groups when working with Degussa Aerosil 200 (number of surface silanols equals ca. 4.9 OH/nm 2 , corresponding to 1.5 mmol OH/g SiO 2 ) .…”

“…Since the pioneering work of Ugo and Basset on the covalent binding of the “Os 3 (CO) 10 (μ-H)” fragment to the silica surface via surface silanol groups, − a lot of spectroscopic work has been devoted to confirm the nature of the species formed by interaction of [Os 3 (CO) 12 ] with silica at ca. 150 °C because, based only on infrared evidence, the triosmium core could bind a single surface oxygen, to form [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)], or two surface oxygens to form [Os 3 (CO) 10 (μ-OSi⋮) 2 ]. − Evidence for the binding via a single surface silanol group has been reached by infrared, − Raman, EXAFS 1b,6,7 and 13 C NMR spectroscopies. Computer modeling , and the reaction of [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)] with HF(aq) and HCl(aq) to give [Os 3 (CO) 10 (μ-H)(μ-OH)] and [Os 3 (CO) 10 (μ-H)(μ-Cl)], respectively, confirmed the binding of the osmium carbonyl cluster to the silica surface via only one silanol group and its hydridic nature.…”

Unusual platinum hydrides with nitrogen ligands

“…Although minor signals are sometimes observed, the presence, in the *H NMR spectra, of one signal only for the CH3 and CH protons indicates that one conformer is largely predominant in solution. As previously reported for complex I,4 a small coupling to platinum is observed (80 MHz) for the CH3 protons (fn-n = 4 Hz), suggesting some kind of interaction of this group with the metal7 and supporting a structure similar to that found for complex II.8 (6) The solvato derivatives [Pt(N-N-C)(S)][BF4], where S is acetone or water, were obtained by reaction of I with AgBF4 (molar ratio 1:1) in dry or moist acetone, respectively. Complex IV can be obtained under strictly controlled conditions, in acetone solution at room temperature in the presence of a large excess of potassium formate.…”

Synthesis and Characterization of Osmium-Containing Silsesquioxanes: High-Yield Routes to {Os3(CO)10(μ-H)[(μ-O)Si7O10(c-C6H11)7]} and the New Clusters {Os3(CO)10(μ-H)[(μ-O)Si7O9(OH)2(c-C6H11)7]}, {[Os3(CO)10(μ-H)]2(μ-O)2Si7O9(OH)(c-C6H11Lucenti1, Feher2 2006Organometallics14180View full textAdd to dashboardCite

“…One of the early success stories in surface organometallic chemistry was the reaction of silica with [Os 3 (CO) 12 ], which produces a structurally well-defined silica-supported cluster attached to the surface via a single siloxy group. − A variety of techniques were used to characterize this cluster, and its structure was assigned unambiguously as [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)] on the basis of IR, ,, Raman, , and solid-state NMR spectroscopies, EXAFS, , and computer modeling ,, or on the basis of its similarity to structurally analogous homogeneous compounds (e.g., [Os 3 (CO) 10 (μ-H)(μ-OSiR 3 )] (R = Et, Ph). ,,,,, This work convincingly established that (1) silica could indeed be viewed as a ligand, (2) the reaction of silica with an organometallic compound could be highly selective, and (3) the characterization of silica-supported complexes could be achieved with a degree of accuracy and confidence that is approaching the corresponding solution organometallic complexes.…”