Polynuclear cluster precursor

Supported nanoparticles are related to the idea of starting with polynuclear cluster precursors. While there is no clear line that divides polynuclear clusters from nanoparticles, clusters are generally small, low nuclearity (MnL n = 3-20), structurally well-characterized species approximately 1-2 nm in size. Nanoparticles are larger (>2 nm) and frequently defined by a size distribution rather than a discrete number of atoms and ligands [41]. In the area of catalysis, gold nanopar-... 

In this context, much effort has also been invested in controlling the nuclearity of the catalyst ensemble through the selection of its precursor. One area in which considerable progress has been made involves the adsorption of polynuclear clusters onto supports [33]. Examples involving the immobilization of small, preformed polynuclear clusters on supports are the reactions of carbonyl clusters of the late metals [16, 34], the binding of polyoxometalates (POMs) and their neutral alkoxy analogues [35] and heteropolyacids such as the Keggin cluster [36, 37]. 

Gates and Lamb (64) found that, by heating either Os3(CO)i2 or Os3(CO)i2 bound to MgO under a CO -I- H2 atmosphere at 200-280°C, thermally stable clusters, [H30s4(C0)j2] and Osio(CO)24(C) , were formed in high yield and extracted as the PPN salt. The remaining solid had an IR spectrum characteristic of the red complex [OsioC(CO)24] , which was also extracted as the PPN salt. Similarly, several oxide-promoted syntheses (64-67) have been reported for specific polynuclear cluster complexes using the smaller carbonyl precursors grafted on metal oxide supports ... 

The intermediacy of polynuclear cluster species in catalytic cycles has been unequivocally proved in few occasions only. These occasions are those that use catalyst precursors derived from the face-bridged compound [Ru3(, -H)(/i3-ampy)(CO)9] (38) (Table 1, entries 24, 25, 27, 29-31) and from the heteronuclear cluster [Ru6Pt3( 3-H)(/z-H)3(CO)2i] (58),cases in which the study of the catalytic activity has been accompanied by the identification of intermediate cluster... 

Sometimes, also polynuclear clusters such as Rh4(CO)j2 or Rh6(CO)26 were submitted to the formation of rhodium catalysts [18]. Metallic rhodium embedded in inorganic materials (carbon, AI2O3) was tested for mini-plant manufacturing. In this context, the frequently phosphorus ligands [PPhj, P(OPh)3] were added with the intention to detach rhodium from the heterogeneous layer (activated rhodium catalyst = ARC) [19, 20] More recently, ligand (Xantphos, PPhj, BIPHEPHOS)-modified or unmodified rhodium(O) nanoparticles were used as catalyst precursors for solventless hydroformylation [21]. It is assumed that under the reaction conditions these metal nanoparticles decompose and merge into soluble mononuclear Rh species, which in turn catalyze the hydroformylation. 

The cluster formation reactions considered in this review occur in technetium-concentrated solutions of hydrohalogenic acids. From comparison of the data reported in [9,11,44,49,50,53,68,72,73,75,76,118] it follows that the ions [Tc2X6]2b (X = Cl,Br) are immediate precursors to polynuclear technetium... 

Ligand displacement from labile precursors has led to the homoleptic clusters Ni4(CNR)7, Ni4(CNR)6 and Ni8(CNBu )12 (27,22), Pt3(CNR)6 (23), and Pt7(CNXylyl),2 (20), which represent rare examples of polynuclear homoleptic metal(O)-isocyanide clusters. 

The reaction of the cluster [Ni (CO)i2]-2 with trialkyltin halides form [Ni(SnRCl2)4 (CO)]-2 (R = Me, Bu), which are precursors of polynuclear [Nin(SnR)2(CO)i8]-2, based upon a Ni-centered NiioSn2 icosahedral cage231. 

The vast majority of the currently known heteronuclear cluster compounds containing M(PR3) (M = Cu, Ag, or Au, R = alkyl or aryl) units were synthesized by treating an anionic mono-, di-, or polynuclear precursor with the complexes [MX(PR3)j (X = Cl, Br, or I). The first example of... 

Biomimetic Synthesis of Nanoparticles Carbonyl Complexes of the Transition Metals Metallic Materials Deposition Metal-organic Precursors Polynuclear Organometallic Cluster Complexes Porous Inorganic Materials Self-assembled Inorganic Architectures Semiconductor Nanocrystal Quantum Dots Sol-Gel Encapsulation of Metal and Semiconductor Nanocrystals. 

Chemists have prepared metal complexes containing metal atoms/ions as a means to understand better the structure, chemical bonding, and properties of metals and metal ions. One of the first efforts to affix these metal complexes to a surface as a means to create a supported catalyst was reported by Ballard followed by reports collected by Yermakov, et al. and Basset et al. We distinguish here between metal complexes that contain zero-valent metals and those that show metal cations and we limit this review to complexes containing metal ions as others have published extensive reviews of zero-valent, metal clusters and their chemistryIn our previous three reviews on the chemistry of supported, polynuclear metal complexes, we described efforts to synthesize and characterize oxide-supported, metal complexes as adsorbents, catalysts and precursors to supported metal oxides. In one application of this technology, efforts were... 

This section surveys the use of various di-, tri-, and polynuclear ruthenium complexes as precursors for the homogeneous hydroformylation of alkenes. Several arbitrary assumptions have been made so as to include dinuclear starting complexes which are strictly not cluster compounds. Moreover, no distinction is made between neutral and anionic precursors. Also, in several cases, particularly in the patents, information is lacking concerning the intermediate species involved in the catalytic cycles. Interestingly, half of the described systems come from patents, and there are few fundamental studies which clearly establish the implication of cluster species during the catalysis. 

These results raise doubts about the possible intermediacy of polynuclear catalytic species when edge-bridged trinuclear carbonyl cluster complexes are used as catalyst precursors. 

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