Group 3 and Lanthanides

Silica-grafted group 3 and lanthanide silylamides have been used as precursor to surface (3-diketonate complexes [(=SiO) Ln( Bu-COCHCO- C3F7)m(THF)i] 

A related silsesquioxane molecule is obtained by reaction of Cp Sc(acac)2 (acac = MeCOCHCOMe) with two equivalents of monosilanol la (R = CisHn), [(C6H )7Si70 Si-(p-0) Sc(acac)2]2 [52]. 

Titanium-silsesquioxanes tailored at modeling and understanding Ti-based heterogeneous catalysts form the largest family of M-POSS models. 

Titanium Alkoxides Silica-supported titanium(IV) alkoxides and Ti-silicalite are industrial epoxidation catalysts [53-56] and have been applied in deperoxidation reactions [57]. Computational and EXAFS data [53, 54] as well as spectroscopic investigations on the surface species [58] have indicated that the dominant active surface species is a four-coordinate trisUoxy complex [(=SiO)3TiOH] [59] whose coordination shell expands to six-coordinate during catalysis [60]. 

Condition A substrate is cyclohexene, solvent = CDCI3, T = 40°C CgHioiTBPH = 1 12 Ti C Hio = 5%w conversion measured after 1 h. 

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In a systematic study, it was demonstrated that, using a specially designed bulky benzamidinate ligand, it is possible to isolate mono(amidinato) dialkyl complexes over the full size range of the Group 3 and lanthanide metals, i.e., from scandium to lanthanum. The synthetic methods leading to the neutral and cationic bis(alkyls) are summarized in Scheme 56. Figure 18 displays the molecular structures of the cations obtained with Sc, Gd, and La. ... 

Table 12.7 Ethylene polymerization based on supported group 3 and lanthanide metallocene complexes-examples from relevant patents.

Single-site Group 3 and Lanthanide Series Metallocene Catalysts... 

Also, neutral group 3 and lanthanide series metallocenes form with olefins n complexes having formally a d° 16-electron configuration, which is favourable for the insertion reaction during olefin polymerisation (or oligomerisation) in the presence of these single-component catalysts [187]. 

The d group 3 and lanthanide complexes Cp MR are isoelectronic with the [Cp2MR]+ catalysts discussed in the previous section. These nonionic complexes are soluble in most hydrocarbons and as one-component systems make ideal models for many of the fundamental processes in polymerization catalysis. For example, an alkyl-alkene complex can be observed by NMR when Cp 2 YH is allowed to react with an o , )-diene (equation 13). ... 

Hogerheide, M.P., Boersma, J., and van Koten, G. (1996) Intramolecular coordination in Group 3 and lanthanide chemistry. An overview. Coordination Chemistry Reviews, 155, 87. 

Several key advances in the early 1980s generated renewed interest in the proposal that Cp2M(R) ions are active species in the soluble catalyst systems. Watson, Bercaw, Marks, and co-workers demonstrated that neutral group 3 and lanthanide metal systems of general type Cp 2M(R) and [Cp 2M(H)]2, which in monomeric form are isoelectronic (neglecting/ electrons) with Cp2M(R)" (M = Ti, Zr), are active ethylene polymerization catalysts [Eq. (I)] (22). In particular, Watson established that... 

The charge of the Cp2M(R)" species is probably not the critical feature for olefin polymerization activity. Rather, the high polymerization activities observed for neutral group 3 and lanthanide Cp 2M(R) complexes... 

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