The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and several group 4 benzamidinate complexes are presented. The use of the cis-octahedral C(2)-symmetry compounds was studied to shed light on the conceptual applicability of these complexes as potential catalysts for the stereoregular polymerization of propylene. We demonstrate that the stereoregular polymerization of propylene catalyzed by early-transition metal octahedral benzamidinate complexes, activated with either MAO or B(C(6)F(5))(3) as cocatalysts, can be modulated by pressure (from atactic to isotactic through elastomers). The different effects in the polymerization process such as the nature of solvent or cocatalyst, temperature, pressure, molar ratio catalyst:cocatalyst, and the relationship between the symmetry of the complex and the polymer microstructure have been investigated. When the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (9) was activated with MAO, it was found to be a good catalyst for the polymerization of propylene, at atmospheric pressure, producing an oily polymer resembling an atactic polypropylene. Being activated with B(C(6)F(5))(3), complex 9 produces a highly isotactic (mmmm = 98%) product. Likewise, when the polymerization of propylene was performed with complex 9 and MAO at high pressure (liquid propylene), a highly stereoregular polymer was also obtained. Larger activities and stereoregularities were achieved by performing the reaction in CH(2)Cl(2) as compared to toluene. Contrary to complex 9, at atmospheric pressure the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)TiMe(2) (10) is not active either in CH(2)Cl(2) or in toluene. At high pressure, complex 10 produces elastomeric polypropylene. Activities of the isolobal complexes [C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (11) and [C(6)H(4)C(NTMS)(2)](2)TiMe(2) (12) were found to be larger than those of complexes 9 and 10, respectively. Contrary to the structures of the elastomeric polypropylenes described in the literature, the obtained elastomers are characterized by frequent alternation of the isotactic domains with stereodefects. The stereoregular errors are formed by the intramolecular epimerization of the growing chain at the last inserted unit. The epimerization reaction was corroborated through the isomerization of alkenes.

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Artificial calcite lining represents a novel technique for the rehabilitation of water mains. Calcite linings, similar to the commonly used cement-mortar linings, are of porous nature. The corrosion protection mechanisms of calcite linings were investigated by polarization techniques, complemented by scanning electron microscopy observations and energy dispersive spectrometry analyses. The effect of time on lining durability was examined by exposure of coated mild steel (1020) coupons in a controlled flowing water system. Iron ion distributions in calcite sections, before and after exposure to water flow, indicate that the calcite corrosion protection mechanism is based mainly on accumulation of corrosion products inside the lining. At the calcite−metal interface, a protective film is formed. At the calcite−water interface, the calcite structure, being alkaline with respect to the water, promotes precipitation of the iron ions and blockage of the pores near that interface. The formation of this protective oxide film was evident from the polarization data which showed that both the anodic Tafel constant and the polarization resistance increase with time. This paper also examines the applicability of potentiodynamic and linear polarization techniques for the characterization of the corrosion protection of a porous lining, such as calcite. It is shown that these convenient electrochemical techniques provide reliable and meaningful corrosion protection information.