Dienyl zirconium

Reduction of a toluene solution of bis(r>-pentamethylcyclopenta-dienyl)zirconium dichloride with sodium amalgam under dinitrogen yields the permanganate-red colored dinitrogen complex 22 (35)... 

The addition of Cp2Zr(H)Cl, known as the Schwartz reagent [30], to different alkenes and alkynes is known to be a facile process [31]. Therefore, the hydrozirconation of a variety of readily available enynes 12 is among the first methods developed for the stereoselective preparation of dienyl zirconium reagents 13. This process is both completely chemo- and regioselective with a syn addition of the zirconium hydride across the alkyne [32] (Scheme 5). From the same intermediate, the Zr atom can be isomerized in its internal position such as in 15 via a zirconacyclopropene intermediate 14. Moreover, the addition of trimethylstannyl chloride to 14 led to the stannylated dienyl zirconocene 16 [33] (Scheme 5). 

A different approach for the in situ preparation of 2-zirconated 1,3-dienes 68 was reported by Szymoniak and Bertus et al.,by treatment of 2-silyloxy-l,3-di-enes 81 with dialkylzirconocene 21 (Scheme 28) [61]. The zirconocene induced the C-0 bond cleavage of 81 and led to the dienyl zirconium compound 68,... 

As usual, to further increase the scope of the reaction, transmetalation of dienyl zirconium complexes, such as 124-127Zr, into the corresponding dienyl organocopper derivatives was performed. Surprisingly, when 126Zr was trans-metalated to copper derivatives by addition of a catalytic amount of CuCl/2LiCl in the presence of allyl chloride for 1 h at +50 °C, a partial isomerization of the dienyl system was found (Scheme 49). 

HOMOALLYLIC ALCOHOLS AUyltin dilluoro iodide. Dichlorobis( cyclo-penta-dienyl)titanium. Ethylaluminum dichloride. Stannous fluoride. Trimethyl-aluminum-Dichlorobisfcyclopenta dienyl)zirconium. 

Lithium aluminum hydride-Dichlorobis-(cyclopenta-dienyl)zirconium, 237-... 

Analogous dienyl zirconium compounds can be prepared by addition of unconjugated dienes that contain enol ethers to 105 (Scheme 19).56-58 These reactions are believed to proceed by initial coordination of the terminal olefin followed by isomerization via zirconocene allyl hydride intermediates to eventually yield zirconacyclopentanes that... 

Zirconium enolates are formed by reaction of the corresponding lithium enolates with bis(cyclopenta-dienyl)zirconium dichloride.Complete retention of enolate geometry accompanies the metal exchange. Both ( )- and (Z) zirconium enolates have been shown to undergo selective kinetic aldol condensation to give mainly syn/erythro products (Scheme 44).<56- > Again, the enolate derived from norbomanone provides an exception to the rale (Scheme 45). ... 

It was assumed that the hthium etiolate adopts a fraws-configuration that was believed to be maintained after transmetallation with dichloro(dicyclopenta-dienyl)zirconium that was performed below —60°C. When, however, the zirconium enolate was kept at —30 "C, the subsequent aldol addition led to nearly equal amounts of syn- andawti-diastereomers - a result that indicates a traws-cis isomerization of the zirconium enolates at elevated temperatures. Compared to the aldol addition with the acetate (fJ)-173, the topicity in the approach of the enolate is reversed Ik for the acetate, ul for the propionate. This seems to... 

Along similar lines, Schwartz and Gell later reported that tertiary phosphines would also induce reductive elimination in bis(i7-cyclopenta-dienyl) (cyclohexylmethyl) (hydrido)zirconium resulting in high yields of zirconocene bis(phosphine) complexes (53-55). Carbon monoxide was found to readily react with a benzene solution of Cp2Zr(PMePh2)2... 

Figure 3.8 Zirconium and hafnium dicyclopentadienyl-1,3-dienyl complexes. See text for explanation of the structures.

Another class V catalyst, derived from 2,2-dimethylpropylidene(cyclopenta-dienyl) (9-fluorenyl)zirconium dichloride [t-BuCH(Cp)(Flu)ZrCl2] (Table 3.1), appeared to be an excellent catalyst for syndiospecific propylene polymerisation [107,137]. 

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. 

On the contrary, once unsymmetrical zirconacydopentadiene 20 (Scheme 13) is obtained regiospecifically, the formation of stereodefined metalated dienyl zirconocenes 26 requires a regiospecific reaction of only one carbon-zirconium... 

In this tandem allylic C-H bond activation, followed by an elimination reaction, substituted l-zircono-lZ,3 -dienes (zirconium moiety at the terminal position of the dienyl system) were easily prepared as unique isomers. With the idea of extending this methodology to the stereoselective synthesis of 3-zircono-1,3-diene (zirconium moiety at the internal position of the dienyl system), 119 was prepared and the reactivity was investigated with (1-butene)ZrCp2 21 (119 was obtained by carbocupration of the a-allyl alkoxy-allene, Scheme 35) [79]. When 119 was submitted to the tandem reaction, the diene 120 was isolated after hydrolysis as a unique ( ,Z) isomer in 75% isolated yield (Scheme 44). 

In this multi-authored monograph, several experts and leaders in the field bring the reader up to date in these various areas of research (synthesis and reactivity of zirconaaziridine derivatives, zirconocene-silene complexes, ste-reodefined dienyl zirconocenes complexes, octahedral allylic and heteroallylic zirconium complexes as catalysts for the polymerization of olefins and finally the use of zirconocene complexes for the preparation of cyclopropane derivatives). It is their expertise that will familiarize the reader with the essence of the topic. 

Dienyl Titanium and Zirconium Reagents 133.6 Propargylic Titanium Reagents... 

Alkenyl and dienyl groups can be present in Ti and Zr complexes as well. Vinyltitanium compounds cannot be exploited for nucleophilic additions, however, due to their propensity to undergo oxidative coupling reactions,likewise transition metal derivatives. Vinylzirconium compounds (20) can be prepared from alkynes (hydrozirconation equation 12) by action of zirconium derivatives like (19). ... 

Various bridged boratabenzene zirconium complexes have been synthesized by salt metathesis, including ethylene-bridged bis(A,A-diisopropylaminoboratabenzene)zirconium complexes 1235, dimethylsilylene-bridged bis(A,A-diisopropylaminoboratabenzene)zirconium dichloride 1236, and dimethylmethylene-bridged (cyclopenta-dienyl)(A,A-diisopropylaminoboratabenzene)zirconium complexes 1237.944 As the crystal structures of the dimethyl... 

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