Titanium complexes monodentate

The chemistry of complexes having achiral ligands is based solely on the geometrical arrangement on titanium. Optically active alcohols are the most favored monodentate ligands. Cyclopentadienyl is also well suited for chiral modification of titanium complexes. 

With the monodentate fluoride ion, it is difficult to have two H2O ligands in trails allowing condensation of opposed coplanar edges. This mode of condensation is possible only with a bidentate ligand ([HSO4]) which leaves only one water molecule in the coordination sphere. As a result, only anatase can form. In both cases, this mechanism may only take place if the complexes are sufficiently stable. Equilibria between various species are probably involved. Under these conditions, it is difficult to know what is the precursor of the solid. Since the oxide always contains some amount of sulfate difficult to remove, it is reasonable to speculate that the complexes are rather stable and that the formation of the solid takes place by incorporation of the sulfated titanium complexes by olation. This is also probably the case with the fluoride. Therefore, the complexing ions of titanium... 

As previously discussed for organotitanium reagents, the nature of the added Lewis acid influences the geometiy of the reactive conformer. For example, TiCl4 prefers hexacoordinated complexes, and it induces cycloadditions of benzyl ester of IV-acryloylproline 31 through an s-cis chelate whose Si face is not shielded by a chlorine bound to titanium. The opposite facial selectivity is observed under EtAlCl2 catalysis, probably because the s-trans monodentate complex is the reac-... 

The mechanistic rationale for the dramatic Lewis acid effect on the course of the Engler indole/benzofuran synthesis involving styrenes is illustrated in Scheme 3. Whereas titanium forms a bidentate complex 11 with the C-1 carbonyl and C-alkoxy oxygens, which leads to the dihydroindole (equation 1), boron trifluoride engages in monodentate complexation 12 with the sulfonyl nitrogen, leading to dihydrobenzofuran formation (equation 2) [3, 4]. Likewise, the reaction between 11 and an enol ether derived from 4-piperidone is depicted in equation 3 [5]. 

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