Clusters, metal reactions

Parks E K, Welller B H, Bechthold P S, Hoffman W F, NIeman G C, Pobo L G and Riley S J 1988 Chemical probes of metal cluster structure reactions of Iron clusters with hydrogen, ammonia and water J. Chem. Rhys. 88 1622... 

Berg C, Beyer M, Achatz U, Joes S, Niedner-Schatteburg G and Bondybey V 1998 Effect of charge upon metal cluster chemistry reactions of Nb and Rh anions and cations with benzene J. Chem. Rhys. 108 5398... 

A particularly elegant route to metallacarbor-anes is the direct oxidative insertion of a metal centre into a c/oso-carborane cluster the reaction uses zero-valent derivatives of Ni, Pd and Pt in a concerted process which involves a nett transfer of electrons from the nucleophilic metal centre to the cage ... 

The solvothermal reaction between metal halides and polysulfide anions is also a useful method for the synthesis of metal-polysulfide clusters. Hydrothermal reaction of K2PtCl4 with K2S4 (5 eq) at 130 °C in a sealed tube... 

In conclusion, metal nanoclusters in DMF interact strongly with microwaves. In reactions catalysed by these clusters, the microwave heating may be tantamount to preferentially heating the catalytic site, which can lead to more effective catalysis. Such cluster-catalysed reactions can be in principle screened in parallel in multimode m/w ovens reducing both time and operational costs. However, the ovens must be adapted so that the parallel reactors are uniformly heated. 

In contrast with formation of three types of bpz-substituted RU3 cluster species, reactions of 2 with pyq induced isolation of monomer 45 and trimer 46 containing 6>rf/ 6>-metallated pyq depending on the reaction conditions [30]. Reduction of the 3+ trimeric complex 46 by addition of aqueous hydrazine gave neutral species 46a. Oxidation of 46a by addition of two equivalents of ferrocenium hexaflu-orophosphate afforded 2+ intercluster heterovalent complex46b containing two Ru30(0Ac)6(py)2II,III,m and one Ru30(OAc)5(py)2II,m,n moieties. 

VI. Transition Metal Triangles and Clusters VII. Reactions of Coordinated Ligands... 

The sections are divided by the coordination number of the reacting ion defined as the number of donor atoms that interact with the metal. The nomenclature used for the ligands is L for neutral molecules that act as ligands and X for anions that act as ligands. Most of the examples in this section will involve cations [ML ]+ or [MX ]+, but there will be a short section on bare metal anions, M . The anions of more complexity than M will be discussed in Section IV on clusters. Many reactions produce an initial product that continues to react resulting in further coordi-native changes and possibly redox changes. Tables I and II will indicate the initial reaction product and other major reaction products. 

Photoinduced deposition of various noble metals onto semiconductor particles has been extensively reported [310-315]. Several factors are controlling this reaction. To control the morphology of metal clusters with desired size and distribution pattern on a given surface area of titania, the most relevant factors are the surfactant, pH, local concentration of cations, and the source of cation [316], In the case of the Ag clusters, the reaction steps proposed include the creation of electron (e )-hole (p+) pairs, the reaction of holes with OH surface species, and the reaction of electrons with adsorbed Ag+ ions ... 

Mixed metal ruthenium/group 9 clusters also show rich chemistry. Synthetically, such clusters are generally synthesized by the addition of a metal chloride to an anionic boridocluster in a cluster expansion reaction. For example, [Ru3(CO)9BH4]- undergoes cluster expansion with [Ru(776-arene)Cl2]2 (arene = CgHsMe, MeCgH4-... 

The rich variety of active sites that can be present in zeolites (i) protonic acidic sites, which catalyze acid reactions (ii) Lewis-acid sites, which often act in association with basic sites (acid-base catalysis) (iii) basic sites (iv) redox sites, incorporated either in the zeolite framework (e.g., Ti of titanosHicates) or in the channels or cages (e.g., Pt clusters, metal complexes). Moreover, redox and acidic or basic sites can act in a concerted way for catalyzing bifunctional processes. 

The difference in reactivity of metal clusters and metal surfaces has also been well illustrated in these iridium-based systems [205]. A lack of reactivity of alkyli-dyne species on Ir4/y-Al203 with H2 is observed meanwhile, the chemisorption of H2 is not hindered. This behavior contrasts with that of metallic surfaces, which allow the reaction between alkylidyne species and H 2. It is inferred that over metallic clusters the reaction of H2 with alkyklidyne is not allowed because of the lack of available adjacent metal sites, which are necessary for the formation of the intermediates [205]. 

Examples of reductive cluster-opening and oxidative cluster-closing reactions are common in the chemistry of metal-hydrocarbon tt complexes. For example, bases convert nido- (hexa-hapto)arene-manganese tricarbonyl complexes into aracAno(pentahapto)-7T-cyclohexadienyl complexes 129,130, 217) ... 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Considerable advances in the field of transition metal cluster chemistry have been made during the last five years. They have confirmed that in many respects a cluster complex is comparable to a metallic surface. They have also shown that clusters allow reactions which are not observed with simple metal complexes. And they have finally demonstrated that structural and bonding properties of clusters require new concepts for their description. 

Synthesis of In the preceding description of metal clusters, synthetic reactions were given for... 

Accordingly, cluster formation reactions can be (a) (I) - (II) with L/M increase (usually by ligand addition) or (b) (III) -+ (II) with L/M decrease (by ligand removal or metal addition). The Zn2+/ SPh and Cu+/ SPh systems exemplify both directions of formation of molecular cages ... 

A second important factor in cluster formation reactions is the oxidation level, or possible change in oxidation level, of the metals or clusters. Under reducing conditions, direct interactions between metals can contribute to metal bonding, diminishing the requirement for bridging ligands. This type of cluster formation reactivity is seen in gold chemistry, in reactions such as (9),320 but it occurs also at the other end of the transition series in reactions such as (10).340... 

The key step in a cluster expansion reaction is the attachment of the incoming metal unit. Once this has taken place, a sequence of metal-metal bond formations accompanied by ligand eliminations can occur which is the reversal of the cluster unfolding reactions described in Section III,C. In uncontrolled cluster expansions, the first step is the combination of coor-dinatively unsaturated cluster and monometallic units, and the reaction is unlikely to stop at this stage. Under mild conditions the attachment may result from a nucleophile/electrophile combination, the products of which have been isolable in a few cases (see below). More insight into possible... 

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