Reaction organometallic zirconium compound

Zirconium tetrachloride is instantly hydrolyzed in water to zirconium oxide dichloride octahydrate [13520-92-8]. Zirconium tetrachloride exchanges chlorine for 0x0 bonds in the reaction with hydroxylic ligands, forming alkoxides from alcohols (see Alkoxides, METAl). Zirconium tetrachloride combines with many Lewis bases such as dimethyl sulfoxide, phosphoms oxychloride and amines including ammonia, ethers, and ketones. The zirconium organometalLic compounds ate all derived from zirconium tetrachloride. 

Bis(i -cyclopentadienyl)titanium or titanocene, (Tj-C5H5)2Ti (1), and bis(i7-cyclopentadienyl)zirconium or zirconocene, (i7-C5H5)2Zr (2), although frequently referred to in the literature, have never actually been isolated as discrete chemical compounds. However, these molecules have been implicated as highly reactive intermediates in a wide variety of chemical reactions with olefins, hydrogen, carbon monoxide, and dinitrogen. In recent years some discrete, well-characterized bis(7j-cyclopenta-dienyl) and bis(Tj-pentamethylcyclopentadienyl) complexes of low-valent titanium and zirconium have been isolated and studied, and it has become possible to understand some of the reasons for the remarkable reactivity of titanocene- and zirconocene-related organometallics toward small unsaturated molecules. 

Apart from organometallic compounds there are a few other compounds of zerova-lent zirconium. The reduction of ZrCLt with lithium in the presence of bipyridine in THF gives violet Zr(bipy)4 where, doubtless, there is considerable delocalization of electrons over the ligands. The reaction of KCN or RbCN with ZrCl3 in liquid ammonia is reported to give M Zr(CN)5. 

Metathesis reactions and the use of dilithio compounds are the most frequently used methods for synthesis of these organometallic compounds. These reactions use almost exclusively zirconapentalenes, especially disubstituted with two cyclopentadiene rings on a zirconium atom. Ring expansions or contractions have not been reported. 

Alkynes are carbometallated with several organometallic compounds under mild conditions [3] but carbocupration has probably the greatest synthetic possibilities [4], associated with the zirconium-catalyzed methylalumination [5] reaction both proceed with very high stereoselectivity and afford the syn addition product as described in Scheme 7-2. 

Dialkyl and diaryl Ti and Zr derivatives (18) are somewhat less stable than their monosubstituted analogs. They are generally prepared by alkylation of the corresponding dichloro compounds (17 equation 1 1).i3,29,30 jjjg dichloro derivatives themselves can be prepared in turn by reaction of tetrachlorides with the required amount of organometallic species. For example, zirconocene dichloride is prepared by treating zirconium(IV) chloride with cyclopentadienylsodium. ... 

One promising approach to the adjustment of coordinative saturation is to alter the number of cyclopentadienyl rings. Since the great bulk of titanium, zirconium, and hafnium organometallic chemistry is that of ( 5115)2X1X2 systems, compounds such as the recently reported ( 5115)2-UCI2 (95) would seem to be ideal precursors. We (96) as well as others (97) have found this to be an incorrect formulation of the reaction product of U U and 2Tl 5H5. When the reaction is carried out in dimethoxy-ethane (DME) we find (96) by NMR that the product is actually a mixture of ( 5H5)3U land ( 5H5)U l3 DME (98). 

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