Bonding states, copper oxides

The oxidation state situation in the oxidized copper oxides is O 11 and mixed Cun-CuIH by definition. There is no implication in this designation that the charge on copper has greatly increased beyond that of a pure Cu11 oxide. The electron was not removed from copper, but rather an antibonding electron was removed from the Cu-O bond. 

The bonding between Cu and O is ionic, with some covalent nature, in the copper oxide superconductors. The parent compounds are intrinsically insulating, and the superconducting state exists adjacent to the insulating phase (an-... 

Square-pyramidal coordination of copper and Cu-0 planes are common structural features in many of the high Tf, oxide superconductors that support this state. These poorly screened (highly ionic) compounds have occupied Cu-0 dpx bonding orbitals and empty Cu-0 dpo anti-bonding orbital partners. The combination of four and six coordination leads to similar layered structures and Cu-0 o and tr bonding. Our recent efforts preparing quaternary oxides with strongly basic counter cations, ssiall tetrahedrally coordinated cations and copper have led to a new series of layered copper oxides. 

The element gold belongs to the copper group 11 (formerly called subgroup IB) in the periodic table and has the electronic configuration IXe)4f 5d °6s. The 6s electron accounts for the +1 oxidation state, but the Sd electrons frequently participate in bonding. Most common oxidation states are +I and +II1. 

While such a process had initially been observed as an undesired side-reaction in transformations where copper salts were employed as re-oxidants [13], Chemler demonstrated that various aminohalogenation reactions proceed in THF or acetonitrile in the presence of potassium carbonate as base [14]. These reactions employ palladium trifluoroacetate or palladium dibromide as catalyst source and require a moderate excess of the copper oxidant (3-4 equiv) giving moderate to excellent yields. However, they usually suffer from rather low selectivity, either in the initial aminopalladation or via subsequent rearrangement pathways to provide mixtures of pyrrolidines and piperazines (Scheme 4.2, Eq. (4.3)). A stoichiometric control reaction in the presence of palladium bromide led only to the Wacker cydization together with an alkene isomerization product, suggesting that the presence of copper(II) salts is crucial for the overall process. The exact role of the copper(II) salts has not yet been darified and palladium intermediates of different oxidation states may be involved in the final stage of carbon-halogen bond formation. 

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