ABSTRACT
Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi-grafted and mono-grafted single-site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono- versus bi-grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi-grafted species displayed higher activity than their mono-grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions.
ABSTRACT
Silica-supported titanium(IV) chloride is readily reduced by Mashima and co-workers' reagent (1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene) to afford materials active in ethylene polymerisation without need of aluminum alkyl cocatalyst.
Subject(s)
Chlorides/chemistry , Ethylenes/chemistry , Polyethylene/chemical synthesis , Silicon Dioxide/chemistry , Titanium/chemistry , Catalysis , Polyethylene/chemistryABSTRACT
Impregnation of [(AliBu(3))(Et(2)O)] on partially dehydroxylated SBA-15 affords a mesoporous material bearing the well-defined single site surface aluminium species [(≡SiO)(2)Al(iBu)(Et(2)O)].
ABSTRACT
An efficient and selective method for the monofunctionalization of p-tert-butylcalix[4]arene is described. A mono-de-O-functionalization of disubstituted p-tert-butylcalix[4]arenes using titanium tetrachloride was developed to synthesize a series of monosubstituted p-tert-butylcalix[4]arenes with the pendant functions being ethoxycarbonylmethyloxy, 3-ethoxycarbonylpropyloxy, cyanomethyloxy, 3-cyanopropyloxy, 4-bromobutyloxy, 3-hydroxypropyloxy, propyloxy, 2-methylpropyloxy, 3-butynyloxy, and 3-cyanopropyloxy groups. The reaction mechanism of the formation of 5,11,17,23-tetra-tert-butyl-26,27,28-trihydroxy-25-(3-ethoxycarbonylpropyloxy) calix[4]arene was studied by (1)H NMR and GC/mass spectroscopy monitoring. Reaction of TiCl4 with the disubstituted p-tert-butylcalix[4]arene produced the corresponding dioxocalix[4]arene titanium dichloride complex, which undergoes elimination of ethyl 4-chlorobutyrate, leading to a trioxocalix[4]arene titanium dichloride complex and to monosubstituted calix[4]arene after hydrolysis. These two complexes were also synthesized, isolated, and fully characterized.