Infrared characterization of group VIB metal carbonyls adsorbed on .gamma.-alumina

Abstract

xylene CpV(CO), + bpy -V(bpy), + unidentified products (3 1 presence of bpy leads to the formation of unidentifiable products.The structure of 2 consists of discrete cis-(~&H~)V(CO)~.bpy molecules possessing an imposed crystallographic Cm symmetry ( Figure 2). The vanadium lies on the mirror plane bisecting the C 3 4 3 ' and C16-Cl6' bonds. The coordination geometry around the metal center is square pyramidal with the two nitrogen atoms from bpy and two carbon atoms from the carbonyls on the basal plane and the centroid of $-bonded Cp ring on the apex. The vanadium lies at 0.898 (1) A from the basal plane, which is perfectly planar for symmetry requirements. Bond distances and angles in the vanadium coordination sphere are in agreement with the correspondin ones observed in complex 1, the V-N distance ring and bpy are as expected. Complex 2 does not display any special spectroscopic features. Two intense absorptions are present in the IR spectrum (v(CO),,,,,, 1843 cm-'; u(CO),,, 1780 cm-'), as expected for a cis-dicarbonyl transition-metal derivative. The Cp resonances are present as singlets in the 'H N M R (4.80 ppm) and 13C N M R (96.55 ppm) spectra, and the resonances of the coordinated bpy are as expected for an ABCD spin system. No resonances attributable to carbonyl being 2.138 (4) x . All bond distances and angles within the Cp (13) Herzog, S. Z. Anorg. Allg. Chem. 1958, 294, 155.groups have been observed in the 13C N M R spectrum.Attempts to utilize 1 for oxidative-addition reactions with a diverse range of substrates such as COz, C02-like molecules, azobenzene, diazoalkanes, and organic azides have led to the formation of CPV(CO)~ as the main product. We believe that the low affinity for CO of the mono(cyclopentadieny1vanadium-(111)) derivatives formed during the oxidative-addition reactions is responsible for such a failure. In other words, for each molecule of 1 that undergoes oxidative addition, three molecules of CO are released. Fast reaction of 1 with CO leads to the unreactive CpV(CO), in 75% yield. Efforts to isolate other species from the reaction mixtures have been unsuccessful so far.

Improving Purity and Size Control of Iron‐ and Molybdenum‐Supported Nanoparticles Prepared by OMCVD from their Carbonyl Precursors

“…[1] As far as OM precursors are concerned, zero-valent metal carbonyl complexes are appealing candidates since i) they are commercially available at low prices, ii) they often present high vapor pressure, and iii) they allow a simple decomposition pathway that leads to a metal(0) deposit. In particular, the deposition of molybdenum [3][4][5][6] and iron [7][8][9] on high surface area substrates has been studied because of its importance in numerous catalytic reactions. [10][11][12] Metal chlorides or ferrocene have been used, but their decomposition requires high temperatures and may induce contamination.…”

“…[10][11][12] Metal chlorides or ferrocene have been used, but their decomposition requires high temperatures and may induce contamination. [1] For [Fe(CO) 5 ] and [Mo(CO) 6 ] that decompose at lower temperatures, the main concern is also the purity of the deposit, which usually contains significant amounts of residual carbon (carbides, oxycarbides) arising from the activation of the carbonyl ligand on the metal centre. [13][14][15] Interestingly, these OM complexes are known to be active homogeneous catalysts for the water gas shift reaction (WGSR) Equation 1, [16,17] and we suggest that this reactivity could be exploited to perform deposition in the presence of water vapor, in order to decrease carbon contamination in the deposit via the metal-catalyzed formation of CO 2 and H 2 (Eq.…”

“…In a first set of experiments, depositions were performed on porous g-alumina powders in a fluidized bed reactor at 220 -C and under reduced pressure, starting from [Fe(CO) 5 ] or [Mo(CO) 6 ] in the presence, or absence, of water vapor. The deposits (10% wt/wt on g-alumina) were first characterized by X-ray photoelectron spectroscopy (XPS) in order to evaluate their purity regarding carbon contamination.…”

“…[19] Although it has been shown that these metal carbonyl complexes are active for WGSR at relatively low temperatures (110-180 -C), [20] the presence of small amounts of carbon in the final deposit may suggest that operating at temperatures higher than 220 -C is preferable; however, in that case, precursor gas phase decomposition may occur (vide supra 2 , which have already been reported. [22] When water vapor is introduced during the experiments, the deposit obtained from [Fe(CO) 5 ] at 220 -C consists of metallic iron (70% wt/ wt) and Fe 2 O 3 (30% wt/wt) as determined by XPS and Mö ssbauer spectroscopy (supporting information). Iron carbide was noticeably absent from the deposit (see Fig.…”

“…[23] As far as CO 2 production is concerned, the catalytic studies on WGSR have shown that, when starting from [Mo(CO) 6 ] and [Fe(CO) 5 ], it is necessary to operate in a basic medium. [24,25] Indeed, the presence of OH S ion allows the formation of a metal hydroxycarbonyl species, which is the key intermediate of the catalytic cycle from which CO 2 and a hydride species are produced.…”