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Aromaticity/antiaromaticity transition metals

Examples of Aromatic/Antiaromatic Transition Metal Systems. 294... [Pg.275]

In Sect. 3 of current work we presented a few examples of aromatic/antiaromatic transition metal systems. We have shown that triatomic gold clusters Au and Au J are s-AO based a-aromatic and o-antiaromatic, respectively. Na2Zns cluster was shown to have one 5c-2e n-bond composed out of 4p-AOs of three Zn atoms and 3s-AOs of two Na atoms thus, it is a it-aromatic system with no contribution from a-bonding in the Z113 kernel. The Hg4 cluster is a doubly p-AO based both o - and 71-aromatic system. The MosOg" species renders its d-radial-AO based a-aromaticity. The ScJ cluster is an example of a system with d-AO based double (a-and 71-) aromaticity with one completely bonding 3c-2e d-radial based a-bond and one completely bonding 3c-2e d-radial n-bond. [Pg.303]

The discovery of an aromatic character of compounds containing the AI4 [28] and antiaromatic character of Al " anion [29] has stimulated the studies of the aromaticity of many similar and other types of metal clusters [30]. Several reviews are already available on the subject (Ref. [31] presents the all-metal aromaticity and antiaromaticity, whereas Ref. [32,33] discuss the aromaticity in transition metals). To the best of our knowledge, this chapter is the first report discussing the aromaticity of metal clusters in connection with the PSM. [Pg.278]

Consequently, transition metal clusters offer the chance of having mnltiple-type multiple-fold aromaticity. Indeed, transition metal clusters could be o-, jt-, and/or 8-aromatic, nonaromatic, or antiaromatic and any combination of them. [Pg.331]

Despite its unsaturated nature, benzene with its sweet aroma, isolated by Michael Faraday in 1825 [1], demonstrates low chemical reactivity. This feature gave rise to the entire class of unsaturated organic substances called aromatic compounds. Thus, the aromaticity and low reactivity were connected from the very beginning. The aromaticity and reactivity in organic chemistry is thoroughly reviewed in the book by Matito et al. [2]. The concepts of aromaticity and antiaromaticity have been recendy extended into main group and transition metal clusters [3-10], The current chapter will discuss relationship among aromaticity, stability, and reactivity in clusters. [Pg.439]

Several phosphete-containing transition metal complexes have been structurally determined. In their crystallographic structures, phosphete rings indicated their delocalized structures. Therefore, the aromaticity and antiaromaticity of these classes of compounds attract special attention, and encourages comparison to the highly antiaromatic cyclobutadienes. [Pg.485]

Thermodynamic aspects of 1,3-diborolanes, 2,3-dihydro-l//-l,3-diboroles, 1,3-azaborolidines, 2,3-dihydro-l,3-thia-boroles 2,3-dihydro-l//-l,3-stannaboroles, or 2,3-dihydro-l//-l,3-silaboroles are only sparsely mentioned. It has been found that the 127t-electron antiaromatic heterocycle 23 is stabilized by electron delocalization via the boron atom (cf. compound 9) <2002ZN1125>. Noteworthy is the comparison between the 8jt-electron antiaromatic 2,3-dihydro-l,3-benzothiaborole 24 or 4jt-electron antiaromatic 2,3-dihydro-l,3-thiaborole 26 and the corresponding lOtt-electron 25 or 67t-electron 27 aromatic lithium compounds, the latter forming stable Jt-coordinated transition metal complexes. [Pg.1231]

In this chapter, we focus on aromaticity and antiaromaticity in inorganic compounds only. It means that the chemical species, which will be discussed, do not contain carbon atoms in their cyclic structures. There are a few review articles [17-25], which discuss different aspects of aromaticity and antiaromaticity in inorganic chemistry. Before we go further, we would like to outline the structure of this chapter. First, we describe criteria that are commonly used for probing aromaticity. Second, we consider inorganic aromatic molecules, which we loosely call conventional aromatic molecules. These molecules are simply isoelectronic species to one of the organic aromatic molecule. Third, we focus on what we loosely call unconventional aromatic molecules composed of main group atoms and transition-metal atoms. Finally, we conclude the chapter with a summary and short outlook. [Pg.422]

As multinuclear transition-metal clusters were found to be more catalyticaUy active that mononuclear complexes, we believe that catalysis also could be a new area of advancement of aromaticity and antiaromaticity concepts for explaining catalytic activity. Complex active sites of enzymes could be another area where aromaticity and antiaromaticity may be useful. [Pg.440]

Aromatic/Antiaromatic Three-Membered Rings of Transition Metal Atoms... [Pg.234]

The most comprehensive theoretical insight into the problem of aromaticity of cyclic transition metal systems was discussed in detail in a very recent review article published in Phys Chem Chem Phys by Boldyrev and coworkers [17], In this article the multifold nature of aromaticity, antiaromaticity, and even conflicting aromaticity (a-, Tt- and 8-aromaticity) has been analyzed in terms of the chemical bonding and electron counting rules. Therefore, we will discuss and comment herein on the latest developments in the field of stable aromatic three-membered rings of transition metal atoms. [Pg.234]

To the best of our knowledge, the aromaticity/antiaromaticity of the aforementioned bare three-member rings of transition metal atoms has not been studied so far. However, the aromaticity/antiaromaticity of ligand-stabilized three-membered... [Pg.237]

The above chemical bonding analysis on model triatomic and tetratomic systems can be used for assessing aromaticity/antiaromaticity in real molecules and clusters. However, hybridization may complicate this analysis. We will now present a few examples where aromaticity/antiaromaticity in transition metal systems allows us to rationalize chemical bonding. [Pg.294]

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. [Pg.294]

Due to the more complicated nodal structure of d-AOs that can form 8-bond in addition to a- and tc-bonds, transition-metal systems can provide a more diverse array of aromaticity-antiaromaticity combinations. However, so far only few transition metal systems with d-AO based aromaticity have been reported. [Pg.298]

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. [Pg.301]


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See also in sourсe #XX -- [ Pg.234 , Pg.296 ]




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