Higher nuclearity carbonyl clusters

Osmium forms numerous condensed carbonyl clusters because of its ability to readily form Os(CO)4 and Os(CO)3 units which can exhibit different geometries and bonding modes. However, higher-nuclearity osmium clusters with EMc2 (E = Ge, Sn) units usually have an open, planar arrangements of metal atoms. This is because EMe2 is isolobal with Os(CO)4, which adopts an octahedral coordination. ... 

Hydroformylation of 2,4,4-trimethyl-l-pentene, catalyzed by the high-nuclearity carbonyl cluster [Rhi2(CO)3o] at higher temperatures and pressures, also proceeded via cluster fragmentation driven by CO pressure, as shown by IR spectroscopy. 

The main synthetic route to high nuclearity metal carbonyl clusters involves a condensation process (/) a reaction induced by coordinatively unsaturated species or (2) a reaction between coordinatively saturated species in different oxidation states. As an example of (/), Os2(CO)22 can be condensed to form a series of higher coordinated species (89). 

Addition of either nucleophilic or electrophilic metallic species can result in the capping of triangular- or square-metal faces in carbonyl clusters. These redox reactions provide high yield syntheses of higher nuclearity clusters and somewhat resemble surface reconstruction on metals. With a few examples,... 

Platinum carbonylate anion clusters like [Pt3(CO)6] can be obtained by alkaline reduction of [PtCh] in a CO atmosphere. From [Pt3(CO)s] other higher nuclear-ity anions can be obtained. In this context, several examples have been reported in which this type of anionic cluster is used in the preparation of catalysts by impregnation or exchange methods. Salts of [Pt3 (CO)6 ] (n = 3, 5) have been used to prepare, by impregnation, dispersed platinum on ZnO and MgO [49] and, by ion exchange methods, to prepare Pt3 /C electrodes for the electrocatalytic oxidation of methanol [50]. A salt of [Pti2(CO)24] has recently been used to prepare... 

Metal carbonyl anions react with main group halides and oxides to yield a number of main-group transition-metal carbonyl complexes in good yields. These complexes serve as starting materials for a number of higher nuclearity cluster complexes. 

Although anionic species with nickel in the oxidation state -I have been postulated, such as [Ni2(CO)6]2, these have not been confirmed. Nickel does, however, form a number of anionic carbonyl clusters with higher nuclearity, e.g., [Ni5(CO)l2]2-, in which the metal carries a partial negative charge. 

Low-valent palladium and platinum form numerous clusters, usually based on the M3 triangle, as in the carbonyl phosphine complexes 18-H-I. Higher nuclearity clusters can be built up from edge-sharing triangles, e.g., the butterfly structure 18-H-II. 

From the other directions, there have been a number of studies of the cluster species that are formed when mononuclear iridium precursors are deposited onto inorganic supports and then subjected to carbon monoxide pressures. Gates and coworkers have shown that Ir(CO)2(acac) will form higher nuclearity iridium carbonyl clusters, the exact nature of which depends on the substrate and the carbonylation conditions. For zeolite NaY, they have observed that Ir(CO)2(acac) will yield both It4(CO)i2 (45) and fr6(CO)i6... 

Carbonylation of different palladium complexes, often in the presence of phosphines, led to the synthesis of a variety of clusters including halocarbonyl clusters of unknown nucle-arity [PdX(CO)] (X = Cl, Br), and phosphine-carbonyl clusters from tetrameric [Pd4(CO)s(PR3)4] to high nuclear-ity compounds such as [Pd38(/r -CO)4(/u. -CO)24(PEt3)i2]. From these preformed clusters, nanosized cluster compounds of higher nuclearity such as [Pd69(CO)36(PEt3)ig] can be prepared. ... 

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