Benzene complexes with metals

Known as crown ethers because of their crown-like shape, these ethers contain cavities that are ideal for forming complexes with metal ions. It is this property that allows ordinary salts to dissolve in organic solvents. For example, potassium permanganate is usually insoluble in benzene, but readily dissolves in benzene if [18]-crown-6 ether is added. This solution is useful because it allows oxidation with potassium permanganate to be carried out in organic solvents. The potassium ion (shown in green) is just the right size to fit into the cavity in the crown ether. 

The HO-energy of a ir-system can be changed, e.g. by occupied orbitals of hetero-atoms which are relative donors or acceptors for the HO s. This can also be true of interactions of the LUMO s of the tr-system with vacant AO s of heteroatoms. The consequences e.g. for the preference of certain conformers relative to the type and position of perturbations in tricarbonyl-chromium benzene complexes (organo-metallic example) are described in Figure 2 of Scheme 2.1-4 together with the consequences for the reactivities in benzene derivatives (example of organic chemistry) due to rektive donor- or acceptor-perturbations (see also Scheme 2.1-2 Fig. 2). 

Although the chromium compound is the best known of the benzene complexes, other metals form similar complexes with benzene and its derivatives. 

In contrast to the plethora of mononuclear complexes of six-electron donor ligands, there are few containing metal-metal bonds. Especially scarce are arene complexes with metal-metal bonds. One example is provided by reaction of V(CO)6 with benzene or other aromatic molecules ... 

A-Benzoyl-A-phenylhydroxylamine [304-88-1] M 213.2, m 121-122". RecrystaUise it from hot water, benzene Et20/hexane or acetic acid. It complexes with metals. [Beilstein 15 III 8,15 IV 7.]... 

Iwamoto, T. Kiyoki. M. Malsuura, N. Thermally stable cyclohcxadicnyl radicals produced in the benzene clathrates with metal complex host latices. Chem. Lett. 1975,... 

Ferrocene was the first organometallic guest incorporated and numerous spectroscopic and electrochemical studies have been performed on ferrocene, substituted ferrocene, and related metallocene (e.g. cobaltocene) inclusion complexes (444-469]. Half-sandwich cyclopentadienyl- and benzene-metal carbonyl complexes have also been studied quite extensively [470-479] as have // -allyl metal (palladium) complexes [480], diene metal (rhodium) complexes [481-484], acetylene cobalt carbonyl cluster complexes [485], and complexes with metal carbonyls, e.g. Fe(CO)5, Mn2(CO)io, and CoNO(CO)3 [485a]. 

A large number of bi-functional reagents which form strong coordination complexes with metal ions have been investigated. These complexes are more soluble in non-polar organic solvents such as benzene or carbon tetrachloride than in the aqueous phase, and are therefore extractable. Of these compounds the fluorlnated... 

Figure 10.2 The catechol side chain of DOPA is capable of forming reversible interactions and irreversible covalent bonds. The benzene ring of the catechol is capable of n-n interactions (A). Catechol -OH groups can function both as a hydrogen bond donor and acceptor (B). Catechol forms strong coordination complexes with metal ions (C). When catechol is oxidized to form highly reactive quinone (D), it can undergo dimer formation (E) and subsequently polymerize into oligomers. Quinone can form intermolecular crosslinking with nucleophile such as -NH2 through Schiff base substitution (F) and Michael-type addition (G).

DBC complexes with metal salts in the water-benzene system are the products of the interfacial reaction [119]. The measured work of adsorption (15.9 kJ/mol) can be taken as a sum of the free energy of complex formation and work of adsorption of DBC at the water-benzene interface. The dissolution of complexes in bulk phases was neglected. The interfacial constants of complex formation (Table 3) calculated from the work of adsorption are close to the constants determined in the mixed solvent - water-tetrahydrofuran [114]. The only exceptions are the complexes of DBC with Ba " and La salts. Apparently this is due to stronger Coulomb repulsion of ions in DBC-salt complexes at the interface as compared to the bulk phases. (At the interface, the anions... 

Platinum-group metals (qv) form complexes with chelating polymers with various 8-mercaptoquinoline [491-33-8] derivatives (83) (see Chelating agents). Hydroxy-substituted quinolines have been incorporated in phenol—formaldehyde resins (84). Stannic chloride catalyzes the condensation of bis(chloromethyl)benzene with quinoline (85). 

The work of Hyatt on cyclotriveratrylene—derived octopus molecules contrasts with this. Of course, these species have the advantage of ligand directionality absent in the benzene-derived octopus molecules. Except for the shortest-armed of the species (i.e., n = 1), all of the complexing agents (i.e., n = 2—4) were capable of complexing alkali metal cations. Synthesis of these species was accomplished as indicated below in Eq. (7.7). These variations of the original octopus molecules were also shown to catalyze the reaction between benzyl chloride and potassium acetate in acetonitrile solution and to effect the Wittig reaction between benzaldehyde and benzyltriphenylphos-phonium chloride. 

Bis ( -arene) metal complexes have been made for many transition metals by the AI/AICI3 reduction method and cationic species [M( j -Ar)2]"" " are also well established for n = 1, 2, and 3. Numerous arenas besides benzene have been used, the next most common being l,3,5-Mc3C6H3 (mesitylene) and CeMce. Reaction of arenas with metal carbonyls in high-boiling solvents or under the influence of ultraviolet light results in the displacement of 3CO and the formation of arena-metal carbonyls ... 

Whereas acyclic sulfoxides form complexes with various metal salts, thiirane oxides react with copper(II) chloride or bromide163 in benzene at room temperature to give the thiolsulfonate 146a. In alcoholic solution below 0 °C the major products are sulfinates (149). Similar results are obtained in the reaction of thiirane oxides with ethanesulfinyl chloride163 as summarized in equation 60. 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

Among the compounds that form complexes with silver and other metals are benzene (represented as in 9) and cyclooctatetraene. When the metal involved has a coordination number >1, more than one donor molecule participates. In many cases, this extra electron density comes from CO groups, which in these eomplexes are called carbonyl groups. Thus, benzene-chromium tricarbonyl (10) is a stable compound. Three arrows are shown, since all three aromatic bonding orbitals contribute some electron density to the metal. Metallocenes (p. 53) may be considered a special case of this type of complex, although the bonding in metallocenes is much stronger. 

Borazine is isoelectronic and isostructural with benzene and may act as a six-electron donor in complex chemistry. In contrast to arene ligands of arene-transi-tion-metal complexes, coordinated borazines lose their planarity and are slightly puckered . Nevertheless, the B atoms show interactions with metal atoms. 

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