Aromaticity, all transition metal

Keywords Adaptive natural density partitioning All transition metal aromaticity Chemical bonding Cluster Multifold aromaticity... 

Summary Though multiple bonding in transition metal compounds had been discussed in the literature for more than four decades, the discovery of aromaticity in all transition metal systems (cyclic systems composed out of transition metal atoms) was made only few years ago. In the compounds composed out of main group elements one may expect sigma-(CT-) and pi-(n-) aromaticity only. In all transition metal systems one may expect two new types of aromaticity delta-(8-) and fi-((t)-) in addition to a- and n-aromaticity. 

Summary Complicated nature of aromaticity in all transition metal cyclic systems can be understood more easily on simplified model cyclic triatomic and tetratomic systems as examples of cyclic systems composed out of odd or even number of atoms, respectively. Counting rules for a-, n-, 8-, and singlet/triplet coupled triatomic and tetratomic systems depend on the nature of atomic orbitals involved in the formation of corresponding bonding/antibonding molecular orbitals. 

Summary There have been very few examples on the aromaticity/antiaromaticity in all-transition metal cycUc systems reported in the literature to this day. In the current section we give detailed discussion on antiaromaticity/antiaromaticity in Auj /AuJ, Na2Zns, Hg ", M03O , ScJ, Hfs, and Taj clusters. 

In order to build up dendrimers crqrable of exhibiting redox activity and light-induced functions, appropriate building blocks have to be used. In the last 20 years, extensive investigations carried out on the photochemical and electrochemical properties of transition metal compounds have shown that Ru(II) and Os(ll) complexes of aromatic M-heterocycles (Figure 1), e.g., Ru(bpy)j and Os(bpy)j (bpy = 2,2 -bipyridine), exhibit a unique combination of chemical stability, redox properties, excited state reactivity, luminescence, and excited state lifetime. Furthermore all these properties can be tuned within rather broad ranges by... 

Shul pin and coworkers have demonstrated, in several papers, that other peroxo vanadium complexes closely related to 36, containing in the coordination sphere amino acids, nitrogen-containing bases or weak carboxylic acids, are effective oxidants of saturated and aromatic hydrocarbons. An accurate account containing this work, together with results related to the use of other transition metals, has appeared415 and all the relevant literature can be found there. 

All these results were interpreted by a free-radical mechanism with the involvement of alkenes, and smaller (C3,C4) and larger (C7,C8) ring intermediates in aromatization. Skeletal isomerization was found to occur through vinyl shift and C3,C4 cyclic intermediates.202 Transition metals with the exception of Fe and Os, as well as Re, Co, and Cu, are active in aromatization of alkanes. Platinum,... 

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