Synthesis surface-mediated

Supported metal carbonyl clusters are alternatively formed from mononuclear metal complexes by surface-mediated synthesis [5,13] examples are [HIr4(CO)ii] formed from Ir(CO)2(acac) on MgO and Rh CCOlie formed from Rh(CO)2(acac) on y-Al203 [5,12,13]. These syntheses are carried out in the presence of gas-phase CO and in the absence of solvents. Synthesis of metal carbonyl clusters on oxide supports apparently often involves hydroxyl groups or water on the support surface analogous chemistry occurs in solution [ 14]. A synthesis from a mononuclear metal complex precursor is usually characterized by a yield less than that attained as a result of simple adsorption of a preformed metal cluster, and consequently the latter precursors are preferred when the goal is a high yield of the cluster on the support an exception is made when the clusters do not fit into the pores of the support (e.g., a zeolite), and a smaller precursor is needed. 

The field of surface-mediated synthesis of metal carbonyl clusters has developed briskly in recent years [4-6], although many organometallic chemists still seem to be unfamiliar with the methods or consider themselves ill-equipped to carry them out. In a typical synthesis, a metal salt or an organometallic precursor is brought from solution or the gas phase onto a high-area porous metal oxide, and then gas-phase reactants are brought in contact with the sample to cause conversion of the surface species into the desired products. In these syntheses, characteristics such as the acid-base properties of the support influence fhe chemisfry, much as a solvenf or coreactant influences fhe chemisfry in a convenfional synfhesis. An advanfage of... 

An early example of surface-mediated synthesis led to the conversion of Os3(CO)i2 into [Os5C(CO)i4] [13]. Quantitative characterization of the formation of this cluster on MgO by C NMR spectroscopy [15] showed that the synthesis gave [OssCCCOIh] " in a yield of about 65% other products included triosmium and tetraosmiimi carbonyl clusters. A schematic representation of the surface chemistry is shown in Fig. 1. 

Fig.1 Surface-mediated synthesis of osmium carbonyl clusters on the surface of MgO...

Surface-mediated synthesis of bimetalhc carbonyl clusters is a rarity Xu et al. [43] prepared [PtRh5(CO)i5] on MgO from Na2PtCl6 and RhCl3 XH2O in CO at room temperature the yield was 84%. 

Finally, the surface-mediated synthesis of ruthenium carbonyl complexes has also been used to prepare supported ruthenium particles. Using silica as a reaction medium and conventional salts, apart from Ru3(CO)i2, mononuclear Ru(CO)j, and high nuclearity carbonyl-derived species can be obtained by CO reductive carbonylation [127, 128]. This opens new routes to preparing tailored supported ruthenium particles. 

In addition, surface-mediated synthesis results a powerful tool in the preparation of surface carbonyl species (homo- or heteronuclear) that are further precursors of supported, tailored metallic catalysts. 

Figure 15.1 Ordered nanoscale structures of mesoporous materials such as FSM-16 and HMM-1 (Et-HMM-1) as the silica and organosilica templates for surface-mediated synthesis of metal/alloy nanowires and nanoparticles.

Surface-Mediated Synthesis of Metal/Alloy Nanowires Using Mesoporous Templates... 

Surface-Mediated Synthesis of Metai/AHoy Nanowires Using Mesoporous Templates 603... 

Other Surface-Mediated Synthesis of Metal Nanowires on Porous Membrane and Graphite Steps... 

H3Re3(CO)i2] is deprotonated on MgOyoo to give [H2Re3(CO)i2] [67]. In addition, when a slurry of [Re2(CO)io], hexane and hydroxylated MgO is stirred at temperatures higher than -50°C, [Re2(CO)9] " is formed (Scheme 16.1) [68]. In this surface-mediated synthesis, it is necessary to use an hydroxylated MgO surface because. 

Ni and Co or of oxophilic metals, for example. Re, is still poorly studied the surface-mediated synthesis of bimetallic carbonyl clusters is limited to a few examples the surface-mediated synthesis of metal compounds without carbonyl ligands has just begun with the silica-mediated synthesis of [RhH2(PMe3)4] by treatment of bis (allyl) rhodium with PMe3 followed by H2 [121] the silica-mediated synthesis of tantalum clusters has been investigated recently but the products were not extracted from the surface-for example, treatment of silica physisorbed Ta(CH2Ph)5 in H2 at 523 K for 20 h led to tri-tantalum clusters, as shown by EXAFS spectroscopy [122]. 

Gates, B. C., Surface-mediated synthesis of metal clusters. J. Mol. Catal. 86,95 (1994). 

Supported metal clusters are often prepared by (a) bonding of precursor metal carbonyl clusters followed by removal of carbonyl ligands attempting to maintain the metal clusters frame intact, (b) surface-mediated synthesis in which the supported... 

Hexairidium clusters supported on 7-AI2O3 were also examined for catalytic activity for toluene hydrogenation. [Ir6(CO)i5]2- was formed by surface-mediated synthesis on 7-AI2O3 powder by treatment of adsorbed Ir(CO)2(acac) in CO at 373 K and 1 atm. Treatment in He at 573 K caused decarbonylation without fragmentation of the cluster frame, giving as indicated by EXAFS analysis. The supported Ir clusters were catalytically active for... 

With this attractive surface-mediated synthesis, high total yields (76%) of [H40s4(C0)i2] can be obtained. ... 

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