Zirconium imidate

Diazametallacycles of the type Cp2Zr[Bu NC( = NR )NR ] have been prepared according to Scheme 92 from terminal zirconium imides and carbodiimides. A second series of analogous compounds was synthesized starting... 

Watson was the first to show that methane could be attacked by a Group IB metal reagent, in a reaction termed cr-bond metathesis . This reaction probably proceeds via electrophilic attack on the C— bond by the reagent (equation 8). Marks describ a nondegenerate example (equation 9) and Wolczan-ski has shown that a zirconium imidate (Zr=NR) can also activate methane, the basic amine group receiving the proton released from methane Equation 10). 

Additional haUdes can be removed from the above insoluble ammonolysis product by reaction with potassium imide to form zirconium imide [87227-54-1]... 

Amides, Imides, Alkamides. When zirconium tetrachloride reacts with hquid ammonia, only one chloride is displaced to form a white precipitate, insoluble in hquid ammonia (227) ... 

Thus, jyn-adducts arise predominantly, as expected, according to the Zimmerman-Traxier model. Provided that either boron or zirconium is the enolate-metal atom, high syn selectivity is achieved. The total amount of anti-adducts is lower than 2% in the case of amides 1 and 2, and it approaches zero when the other reagents arc used94 . The induced stereoselectivities are impressive for the amides and remarkable in the case of the imides. 

Alkoxides and imido are used as anionic ligands in zirconium and titanium catalysts for the polymerisation of alkenes, sometimes as the only anions, but often in combination with cyclopentadienyl ligands. Imides linked to cyclopentadienyl groups form part of the single-site catalyst developed by Dow (Chapter 10) (Figure 1.9, 1). In very different titanium catalysts, namely those used for epoxidation of alkenes, also alkoxide ligands are used (Chapter 14). 

It must also be pointed out that other basic materials have been synthesized which present no surface oxygens and hydroxyls, but other types of active sites whose exact nature remains controversial. These type of solids are, for example, impregnated imides and nitrides on zeolites and alumina, amorphous oxynitrides obtained by treatment with ammonia or aluminium orthophosphate, zirconium phosphate, aluminium vanadate or galloaluminophosphate, and KF supported on alumina/1,3,41 One of the main advantages of these solids with respect to basic oxides is their resistance to carbon dioxide or water. 

Chiral Lewis acids are known. Indeed, an air stable and storable chiral Lewis acid catalyst has been prepared, a chiral zirconium catalyst combined with molecular sieves powder. Association of a bulky silicon group with the bis(trifluoromethanesulfonyl)imide anion leads to enhancement of the electro-phihc character of R3SiNTf2. The presence of a chiral substituent derived from ( )-myrtenal on the silicon atom led to a chiral silicon Lewis acid. ... 

While metallocenes are ubiquitous in organometallic and polymer chemistry, few such complexes have been reported to catalyze the Diels-Alder process in high enantioselectivity [127,128,129]. Thebis(tetrahydroindenyl)zirconium tri-flate 60 and the corresponding titanocene are electrophilic to the extent that they catalyze the low-temperature cycloadditions of acrylate and crotonate imides with cyclopentadiene with good diastereoselectivity and excellent enantioselec-tion (Scheme 48). The reactivity of 60 is noteworthy since the corresponding reaction using the crotonyl imide with highly reactive catalysts 31a or 44 requires temperatures of -15 and 25 °C, respectively. 

Chiral amides (222) and (223) and imides (224) and (225) have also been studied as reagents for asymmetric aldol reactions. These reagents show excellent diastereofacial preferences as their boron and zirconium enolates, but generally show poor selectivity as their lithium enolates. The reader is referred to other chapters in this volume for a discussion of these and related reagents. 

Additives used in final products Fillers carbon fiber, glass fiber, graphite, nano-zirconium oxide, PTFE, titanium dioxide Other melt stabilizers (e.g., zinc oxide or zinc sulfide, phcsphites, phosphcnites) Antistatics fatty quaternary ammcnium ccmpounds, quaternary or tertiary ammonium ions and bis(perfluoroalkanesulfonyl)imide ... 

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