Cationic zirconium complexes

A variety of cation-induced cyclization approaches to systems of this type have been introduced. Reaction of hydroxyethylthiocyanates (236) with a tertiary alcohol, R OH, in sulfuric acid gives the 2-iminooxathiolanes (237) (Equation (35)) <92Z0R418> and treatment of glycidyl esters such as (238) with cationic zirconium complexes such as (239) and AgC104 gives the dioxolane (240) (Equation... 

By treatment of 159 and 164 with methyllithium, Erker obtained 167 and 168 in 57% and 80% yield, respectively the latter was also characterized by X-ray-crystallography (Scheme 27). Treatment of 167 and 168 with 1 equiv of tris(pentafluorophenyl)-borane caused a methyl transfer with formation of cationic zirconium complexes 169 (91%) and 170 (95%) 169 was also structurally characterized. Addition of a second equivalent of the borane gave dicationic 171 in 93% yield. Treatment of 171 with dichloromethane resulted in an immediate reaction to give 172, which also was structurally characterized. The similar complex 173 was obtained by treatment of 164 with tris(pentafluorophenyl)borane (88%). Addition of acetonitrile to 171 gave 174 (89%), and with 2,6-dimethylphenylisonitrile, 175 was formed in 81% yield. Complexes 169, 170, and 172 show an interesting dynamic NMR behavior corresponding to... 

Cationic zirconium complexes (88) having diketonato ligands were examined for selective epoxide ring opening (Equation 40) [45]. The catalysts showed higher activity than simple metal halides such as TiCU and ZrCU, and various epoxides (87) were converted into (89) and/or (90) effectively. When R and R" in (87) were alkyl groups, the product selectivity of the catalyst (88) were moderate to low. But with styrene oxide (R =Ph, R" =H), alkoxy alcohol (89) was obtained with high selectivity. 

The (pentamethylcyclopentadienyl)zirconium amidinate unit also served as a platform for the synthesis and characterization of remarkable cationic and zwitterionic allyl zirconium complexes derived from trimethylenemethane (TMM). A direct synthetic route to the neutral precursors was found in the... 

Then, contrary to what was reported previously, the olefin dissociates from the zirconium metal complex. This conclusion was further supported by other experimental observations. However, it cannot be completely excluded that competition between dissociative and direct rearrangement pathways could occur with the different isomerization processes studied up to now. Note that with cationic zirconocene complexes [Cp2Zr-alkyl], DFT studies suggest that Zr-alkyl isomerizations occur by the classical reaction route, i.e. 3-H transfer, olefin rotation, and reinsertion into the Zr-H bond the olefin ligand appears to remain coordinated to the Zr metal center [89]. 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

Jordan RF, Bajgur CS, Dasher WE, Rheingold AL (1987) Hydrogenation of cationic dicyclopentadienylzirconium(IV) alkyl complexes. Characterization of cationic zirconium(IV) hydrides. Organometallics 6 1041-1051... 

Cation exchange, solvent extraction and Raman spectroscopic studies of highly acidic zirconium sulfate solutions suggest that these solutions contain a mixture of solution species having from one to four sulfate ligands per Zr atom.153,351 The sulfato-zirconium complexes appear to be somewhat more stable than the analogous hafnium complexes.351... 

Cationic [ZrBz3]+ species are capable of polymerising oc-olefins such as propylene, 1-butene and 1-pentene at elevated temperature. It is worth emphasising that the non-metallocene [Zr(CH2Ph)3] + [PhCH2B(C6F5)3] catalyst, which is a cationic arene zirconium complex [189], is capable, at least partially, of isospecific a-olefin polymerisation at relatively high temperature [162,189,190],... 

Dimethylpyrazine (48) and the cationic bis(cyclopentadienyl) zirconium complex (49) gave an isolable intermediate formulated as the complex (50) and thence 2,5-dimethyl-3-(pent-l-enyl) pyrazine (51) [one pot procedure complex (49), CH2C12, 23°C, 15 min then HC=CPr J, 23°C, 2.5 h 88%] 868 several analogues, like 2,5-dimethyl-3,6-bis[l-methyl-2-(trimethylsilyl)-vinyl] pyrazine (51a) (61%), were made similarly.868... 

Specific examples of alkene insertions are the reactions of cationic hydrides [Cp2ZrH(L)]+ to give metal alkyls which may either be stabilized by agostic interactions, as in (21-XLII), or free of such interactions (21-XLIII), depending on L.180 The insertion of isobutene into M—C bonds of electron-deficient zirconium complexes was found to be reversible.109... 

Cationic P compounds exhibit several modes of reactivity, including coordination to Lewis acids oxidation by acids, water, and alkyl chlorides and substitution of the stabilizing phosphine ligands by stronger donors (Scheme 17). Some of these P and As cations have also been shown to be useful sources of P and As ions that provide zirconium complexes (12) containing unique square-planar Pn environments (equation 22). ... 

Type Cationic zirconium synthetic wax complex Appearance White milky emulsion pH 3.8... 

Phosphonium-bridged cationic //// //-metallocenes 1161 have been synthesized by salt metathesis, as illustrated in Scheme 274.903 Methylation of the zirconium complex yields the methyl derivative 1162, which reacts rapidly with CO at room temperature to give the acyl derivative 1163. The molecular structures of the dichloride complexes have been determined by X-ray diffraction. 

Bochmann, M. Lancaster, S.J. Base-free cationic zirconium benzyl complexes as highly active polymerization catalysts. Organometallics 1992,12, 633. 

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