Titanium complexes bidentate

Polysulfides of several metals can be prepared by reaction of the metals with excess sulfur in liquid NH3 (group IA metals) or by heating sulfur with the molten metal sulfide. The polysulfide ion binds to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms (as a so-called bidentate ligand). One example is an unusual titanium complex containing the S52-ion that is produced by the following reaction (the use of h to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16) ... 

For several of these bidentate phosphine assemblies crystal structures were obtained. Figure 10.13 (Table 10.8) shows the crystal structure of octahedrally coordinated titanium complex 39. 

Polyethylene-Wock-poly(clhylcnc-co-norbornene) (PE-fo-P(E-co-NBl ) block copolymer was successfully synthesized by a titanium complex with two non-symmetric bidentate /J-cnaminokclonalo ligands [136,137]. Bis(pyrrolide-imine)titanium complex also has the ability to produce the PE-fo-P(E-co-NBE) block copolymer. PE-fo-PS was synthesized via sequential monomer addition during homogeneous polymerization with bis(phenoxy-imine)metal catalysts [138]. 

Other titanium complexes supported by acetylacetonate 17-19, " showing similar structural analogies with 12-16, were reported to have comparable moderate catalytic activities, stereoselectivity and polydispersity for the bulk ROP of rac-LA (Scheme 6.2). In totality, the activity of these complexes seems to be limited, probably by a substantial 7t-donation interaction from the anionic 0,0-bidentate-type ligands to the Ti " Lewis acid that consequently decreases the rate of polymerisation in addition to the sterically crowded complexes limiting the incoming monomer approach. 

FIGURE 14.12 Structures of titanium complexes 66,67 with bidentate N, A Cbis(trimethylsilyl) benzamidate ligands. 

He, L.P., Liu, J.Y., Li, Y.G. et al. (2009) High-temperature Uving copolymerization of ethylene with norbomene by titanium complexes bearing bidentate [0,P] Ugands. Macmmolecules, 42,8566-8570. 

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... 

Peroxidic Compounds. When hydrogen peroxide is added to a solution of titanium(IV) compounds, an intense, stable, yellow solution is obtained, which forms the basis of a sensitive method for determining small amounts of titanium. The color probably results from the peroxo complex [Ti(02)(0H)(H20)J, and crystalline salts such as K2[Ti(02)(S0 2] H20 can be isolated from alkaline solutions. The peroxo ligand is bidentate the two oxygen atoms ate equidistant from the titanium (98). 

Titanium and zirconium chemistry has some unique features the chair conformation of the M2N4 metallocycle in the exobidentate complexes and endo-bidentate coordination. 

Both types of complex are extremely air-sensitive and are paramagnetic, with one unpaired electron per titanium atom. Their formulation as monomeric, symmetrical, bidentate, chelate complexes, (IV) and (V), has been established from spectral, magnetic, and molecular-weight data. 

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