Cations oxygen bonding

The cationic tantalum dihydride Cp2(CO)Ta(H)2]+ reacts at room temperature with acetone to generate the alcohol complex [Cp2(C0)Ta(H01Pr)]+, which was isolated and characterized [45]. The mechanism appears to involve protonation of the ketone by the dihydride, followed by hydride transfer from the neutral hydride. The OH of the coordinated alcohol in the cationic tantalum alcohol complex can be deprotonated to produce the tantalum alkoxide complex [Cp2(C0)Ta(01Pr)]. Attempts to make the reaction catalytic by carrying out the reaction under H2 at 60 °C were unsuccessful. The strong bond between oxygen and an early transition metal such as Ta appears to preclude catalytic reactivity in this example. 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

Figure 1.10 shows the relationship between bond strength and degree of covalence in cation-oxygen bonds for cations with 18, 36, and 54 electrons (note that in table 1.9 the parameters of equation 1.48 are identical for the three isoelectronic series). By combining equation 1.48 with a modified form of Donnay s (1969) equation ... 

Table 1.10 General parameters for relationship between bond strength and bond length in cation-oxygen bonds (adapted from Brown and Shannon, 1973).

Ziolkowski, J. and Dzienbaj, L. (1985). Empirical relationships between individual cation oxygen bond length and bond-energy in crystals and molecules. J. Solid State Chem. 57, 291-9. 

It is useful as a point of departure, to briefly describe the basic crystal lattice common to phyllosilicates. The elementary character is the SiO tetrahedral linkage of an essentially two-dimensional, hexagonally symmetric, network. One side of this "sheet network is coordinated with other cation-oxygen complexes joined by an important component of covalent bonding while the other is coordinated by essentially ionic bonding or van der Waals type bonds. The key to phyllosilicate structures is the oxygen network which determines the shape and extent of the structure. 

Fritz and Lunsford (10), as well as Lombardo et al. (11), have suggested that the effective extraframework Al is present in the f cages as cations that are bridge-bonded through oxygen atoms. In order to test this hypothesis, one would like to ion-exchange Al3+... 

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