Titanium and Zirconium Complexes

On heating (II) at 130°C under N2, a product of stoichiometry CgHg-(TiCl2Al2CIg)3N was obtained (429). Hydrolysis of this product, which is presumably a nitride, gave a stoichiometric amount of ammonia. 

The reaction of 2-butyne, TiCI, and EtaAljCIs followed by hydrolysis yielded a product of stoichiometry Ci2Hi8Ti(OH)Cl2. The same product was obtained when the 2-butyne was replaced by hexamethylbenzene. The compound was formulated as a rr-complex of hexamethylbenzene which is supported by the observation of only one methyl resonance in the NMR 433). 

---

These lithium derivatives were found to be excellent reagents for the introduction of the new amidinate scorpionate ligands into Group 4 metal complexes, and a series of neutral titanium and zirconium complexes were prepared according to Scheme 189 and fully characterized. 

The use of titanium and zirconium complexes as electron shuttles to transfer electrons from excess aluminum present in the reaction solution to the fluorinated substrate has been described,210 e.g. formation of perfluoronaphthalene from perfluorodecahydronaphthalene. 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

C-N chelation has also been observed for the titanium and zirconium complexes (68), (69), and (70). These compounds belong to the class of the sterically hindered phosphoraniminato complexes, and exhibit modest catalytic activity in ethene polymerization. The complex formation is reflected by the elongation of the NP bond length, 163.1(3) pm in (70) versus 156.2(1) pm in the free ligand... 

Dimerization of ethylene in the presence of homogeneous titanium and zirconium complexes proceeds with mass selectivity up to 98-99 % with respect to 1-butene, but one always observes at least 0.5 - 1% mass of polymer formation which creates problems when scaling up. 

The results of dimerization of ethylene in the presence of the obtained nickel, titanium and zirconium complexes with different macroligands and OAC are given in Table 1. The temperature in all the experiments was 313 K pressure 0,2 MPa OAC/Ni molar ratio of 10 and OAC/Ti or Zr of 4. 

However, the trend in the phosphorus resonances of the isostructural titanium and zirconium complexes strikes us as odd. We know that the chemical shift moves upfield, not downfleld, as one moves down the triad. In our two examples, the trend is reversed. The only logical explanation would seem that the larger zirconium atom favours the cr-complex over the 7 -complex, and thus the downfleld shift seen in the transition from titanium to zirconium reflects the extent of the 7 -complex present in the true structure of this complex. 

Carbosilane dendrimers containing titanium and zirconium complexes on their periphery have been prepared and used in olefin polymerization reactions.Generally, the best synthetic route to these materials involves the synthesis of generations of suitably functionalized dendrimers to which the metal is added in the final step giving products such as 276. Routes involving the incorporation of pre-metallated building blocks gave only low yields of the desired dendrimers. 

A suitable entry into titanium and zirconium complex chemistry is the use of group IV amides and alkoxides. For example, when Ti(OEt)4 reacted with 2 equiv. of (roc)-2 in heptane, the titanium bis(disiloxide) 3 could be isolated in 91 % yield as a yellow microcrystalline material. Tbe results of the X-ray analysis (Fig. 1) of 3 confirm the expected extensive shielding of the titanium atom by the two sterically demanding disiloxide ligands. The geometry around the titanium atom is described best as distorted tetrahedral, with an 02-Til-02 chelate angle of 99° and an 02-T11-01 angle of 115.5°. 

F. Chen, M. Kapon, J. D. Woollins, M. S. Eisen, OrganometaUics 2009, 28, 2391-2400. Bis(imidodithiodiphosphinato) titanium and zirconium complexes Synthesis, characterization, and their catalytic activity in the polymerization of a-olefins. 

The first hydroaminations by this mechanism were reported by Bergman with zircono-cene complexes and by Livinghouse with monocyclopentadienyl titanium and zirconium complexes. Bergman reported the intermolecular addition of a hindered aniline to an alkyne. The hindrance of the aniline was important to prevent formation of stable dimeric complexes containing bridging imido groups. Livinghouse reported intramolecular reactions that occurred at lower temperatures over shorter times. The intramolecularity of this process allows the [2+2] cycloaddition of the imido complex with the alkyne to be faster than the dimerization. 

In the case of titanium and zirconium, complexes possessing + 3 and + 2 oxidation states of the central ion are known, for example, TiR2 (R = PhCH2, Ph), TiR3 [R = (Me3Si)2CH, CCl=NMe], [ZrPh2(ether)2], etc. Alkyl compounds of... 

---