Mixed clusters metal-carbon

Figure 9.61 ToF mass spectrum of metal-carbon cluster ions (TiC2+ and ZrnCm+ cluster ions) using a titanium-zirconium (50 50) mixed alloy rod produced in a laser vaporization source (Nd YAG, = 532 nmj and ionization by a XeCI excimer laser (308 ). ( . M. Davis, S. J. Peppernick and A. W Castleman, J. Chem. Phys., 124, 164304(2006). Reproduced by permission of American Institute of Physics.)...

Figure 1.4. Mixed metal-carbon cluster compounds (metal-hydrocarbon n complexes) ( denotes hypercarbons).

MIXED METAL-CARBON CLUSTERS AND METAL CARBIDES... 

K-bonding electrons to form the metal-carbon bonds their structures may be regarded as mixed metal-carbon clusters, the shapes of which clearly reflect the numbers of electrons available as do the mixed boron-carbon cluster shapes of carboranes. All are members of the same family of hypercarbon systems. 

If the compounds shown in Figures 4.1 and 4.2 are regarded as mixed metal-carbon clusters, the pyramidal shapes of their MC skeletons will be seen to be those appropriate for nido systems in which (n -1-1) skeletal atoms are formally held together by (n -1- 3) skeletal bond pairs. This number includes the n pairs of electrons in the ring carbon-carbon o bonds as well as the three pairs of electrons in their K-systems. For example, in the cyclobutadiene complex (r " -C4H4)Fe(CO)3, 5 each CH unit can contribute three electrons, and the Fe(CO)3 unit can contribute two electrons for skeletal bonding, making... 

COMPLEXES OF UNSATURATED ORGANIC LIGANDS WITH TWO OR MORE METAL ATOMS MIXED METAL-CARBON CLUSTERS... 

Figure 4.10. Skeletal structures of mixed metal-carbon clusters containing two or more metal atoms.

To underline the structural and bonding relationship between these mixed metal-carbon cluster species and carboranes, we list the formulae of representative examples in Table 4.1, classified according to the numbers of skeletal bonding electrons they contain and thus according to their structural type (closo, nido, or arachno ). 

This last compound, treated as a mixed metal-carbon cluster Ic4(( ()) iT R (R = the one-electron carboxylate ligand COOMe) contains six skeletal bond pairs to hold together its five skeietai atoms (one carbon atom and four metal atoms). It is therefore a closo cluster, with the expected trigonal bipyramidal shape defined by its skeietai carbon and metai atoms. 

This chapter has shown how hypercarbon atoms and metal atoms can form mixed metal-carbon cluster systems. Our concern has been mainly with... 

The possibility of coordination of a two-electron ligand, in addition to arene, to the ruthenium or osmium atom provides a route to mixed metal or cluster compounds. Cocondensation of arene with ruthenium or osmium vapors has recently allowed access to new types of arene metal complexes and clusters. In addition, arene ruthenium and osmium appear to be useful and specific catalyst precursors, apart from classic hydrogenation, for carbon-hydrogen bond activation and activation of alkynes such compounds may become valuable reagents for organic syntheses. 

Table I. Fragmentation of Mixed-Metal Tetranuclear Clusters with Carbon Monoxide at 1 Atmosphere Pressure (17)...

A number of elegant syntheses of mixed-metal clusters have been accomplished through the condensation of unsaturated metal complexes with metal donors. For example, condensation of the unsaturated cluster H20s3(CO)io with the alkylidyne see Alkylidyne) complex CpW(CO)2(CR) produces H20s3W(/u.3-CR)(C0)i2. Metal-metal, metal-carbon, or carbon-carbon multiple bonds may serve as the sites for metal fragment condensation. Other examples are shown in equations (80 and (9). 

Sheng, H., Xu, R, Yao, Y, Zhang, Y, and Shen, Q. (2007) Novel mixed-metal alkoxide clusters of lanthanide and sodium synthesis and extremely active catalysts for the polymerization of e-caprolactone and trimethylene carbonate. Inorganic Chemistry, 46, 7722-7724. 

Except for the trimethylenemethane complex, complexes of the types shown in Figure 4.8 can be treated as arachno mixed metal-carbon MC clusters, formally containing (n -1- 4) skeletal bond pairs to hold their (n + 1) skeletal atoms together. ... 

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