Titanium complexes properties

The above example outlines a general problem in immobilized molecular catalysts - multiple types of sites are often produced. To this end, we are developing techniques to prepare well-defined immobilized organometallic catalysts on silica supports with isolated catalytic sites (7). Our new strategy is demonstrated by creation of isolated titanium complexes on a mesoporous silica support. These new materials are characterized in detail and their catalytic properties in test reactions (polymerization of ethylene) indicate improved catalytic performance over supported catalysts prepared via conventional means (8). The generality of this catalyst design approach is discussed and additional immobilized metal complex catalysts are considered. 

The OEt-substituted Zr(IV)-boratabenzene complex has been employed in an interesting dual-catalyst approach to the synthesis of branched polyethylene.47 Capitalizing on the ability of this boratabenzene complex to generate 1-alkenes (Scheme 25) and the ability of the titanium complex illustrated in Scheme 27 to copolymerize ethylene and 1-alkenes, with a two-catalyst system one can produce branched polyethlene using ethylene as the only monomer (Scheme 27). The structure and properties of the branched polyethylene can be altered by adjusting the reaction conditions. 

The outstanding properties of binaphthol (BINOL) as a ligand in chiral Lewis acidic metal complexes were also demonstrated highly successfully by Mikami [108, 109] using a binol-titanium complex 2-69a. Even in the cycloaddition of methyl glyoxylate 2-66 to 1 -methoxy-1,3-butadiene 2-65 which usually shows only a low selectivity, a reasonable cis/trans-selectivity and an excellent enantioselectivity could be obtained in the presence of catalytic amounts of this complex. 

Due to their metal complexation properties, Buono et al. have envisioned the use of titanium alkoxide-chiral o-hydroxyarylphosphine oxides complexes in a catalytic enantioselective trimethylsilylcyanation reaction of various aromatic aldehydes [56] (Table 6). 

The alkyl transfer properties of dialkyl zinc reagents have been studied in the reaction of Zn[CH(SiMe3>2]2 with TiCU- The monoalkyl trichloro titanium complex TiCl3[CH(SiMe3)2] was obtained in 83% yield.10... 

It has been established that the replacement of Cp with an indenyl or fluorenyl ligand has important effects on the catalytic properties of these type of complexes. Monoindenyl and monofluorenyl titanium complexes can generally be prepared by employing dehalosilylation (or analogous dehalostannylation) (Scheme 172), and several such complexes have been described. 

Group 4 transition aza-metal-diene complexes have received considerable attention because of their unique M-N and M-C bonding properties and their high reactivity toward a broad range of electrophiles and unsaturated hydrocarbons. Reduction of CpTiCl3 with magnesium in THF in the presence of the appropriate 1-aza-l,3-diene affords the 1-aza-l,3-diene titanium complexes CpTiCl[N(R)CH=C(Me)CH(Ph)] (Scheme 217). Spectroscopic data indicate that the aza-diene ligands adopt a cis-supine conformation in the case of the Buc derivative a solution equilibrium with the /)nw-disposition is observed. The chemical shifts of the terminal carbon atoms of the aza-diene... 

The synthesis of the Ind-amido titanium complexes [(C9H5R)SiMe2NBut]TiX2 (Scheme 304) with alkoxo and amido substituents at 2- and 3-indenyl position has been reported and the molecular structures of the derivatives for R = NMe2 and N(CH2)4 have been determined by X-ray diffraction. The methyl derivatives are activated with B(C6F5)3 and studied as catalytic systems for the ethylene/l-octene co-polymerization. A dramatic effect of the indenyl substituent nature on catalyst efficiency and polymer properties is observed.740... 

Ind-amido titanium complexes with o -alkenyl functions in position 2 of the indenyl ring have been synthesized and characterized. After activation with MAO, these complexes were used as homogeneous and heterogeneous catalysts for the homopolymerization of ethylene and propylene and the co-polymerization of ethylene and 1,7-octadiene.406 A series of alkyl-, u -alkenyl-, and u -phenylalkyl-substituted Cp- and Ind-amido dichloro titanium complexes have been synthesized and characterized. The cj-phenylalkyl-substituted complexes react with LiBu to give metallacycles via a CH activation reaction on the ortho-position of the phenyl group (Scheme 305).741 742 After activation with MAO, these complexes catalyze ethylene polymerizations. The substituents on the aromatic system influence the polymerization activity of the catalysts and the properties of the polyethylene. The u -alkenyl-substituted catalysts show self-immobilization in ethylene polymerization. 

Examples of chiral Cp titanium complexes containing dialkoxo ligands, including fluoro derivatives, are shown in Scheme 363. The fluroro ligands might add catalytic properties to the compounds.887... 

The chemistry of early transition metal complexes containing a chalcogenido-metal bond is an area of continuing interest because of their unusual electronic structures and properties, and the relevance of such compounds as models for several important industrial catalytic processes. A variety of titanium complexes containing Ti-S bonds are known and this chemistry has been reviewed.1003,1004... 

One of the most remarkable aspect on the bis-Cp titanium derivative chemistry has been the production of new and unprecedented variety of polyolefins. The use of this type of complexes as Ziegler-Natta pre-catalyts for the olefin polymerization has opened new possibilities to produce polyolefins with different properties, and significant effort has been devoted to the design of new bis-Cp catalyst structures. This section summarizes simple aspects related to the polymerization of ct-olefins catalyzed by bis-Cp titanium complexes containing a cr-Ti-C bond. A more comprehensive review of the catalytic applications of titanium complexes in the a-olefin polymerization processes is covered in Chapter 4.09. 

Bis-Cp acetylide titanium complexes have drawn considerable attention in regard to their third-order non-linear optical properties.2002... 

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