Zirconocene methyl chloride

Reaction of N-(2-bromoallyl)-N-prop-2-ynylamines 72 with tert-butyllithium, followed by reaction with zirconocene methyl chloride and subsequent cyclization gives 1,1-lithio-zirconioalkenes 73 via 74 and intermediate 75 (Scheme 7.23) [144,145], Treatment of the lithiozirconium complex 73 with deuterated sulfuric acid leads to the trideuterated pyrrolidine 76. 

The azazirconacyclopentane derivatives 231, obtained from the reactions of amines with zirconocene methyl chloride followed by addition of the corresponding terminal alkenes, have led to the formation of azetidine derivatives 232 on treatment with iodine (Scheme 48) <1997JOC5953>. 

Zirconocene methyl amide complexes 1 are readily prepared by addition of lithiated secondary or N-silyl amines to zirconocene methyl chloride [17] or zirconocene methyl triflate [18] (Eq. 1). Loss of methane from 1 yields zirconaaziridines which, in the presence of THF or PMe3, can be isolated as the adducts 2 in high yield and purity. This synthetic method is ideal when the isolation and characterization of the resulting zirconaaziridine is desired, as the C-H activation and concomitant methane evolution occur with the formation of little side product. 

Barluenga et al. have demonstrated that the reaction of organolithium compounds 45 with zirconocene methyl chloride in THF, followed by addition of different vinyl bromides and further heating to +65 °C, led to dienes 46 and 47 in different ratios (Scheme 19) [50]. The latter was demonstrated to be dependent on the structure of the starting organolithium compound and of the vinyl bromide used. Thus, with the use of nonsubstituted vinyl bromide 48, a mixture of regioisomeric dienes 49 and 50 was obtained, the branched one being the major isomer (Scheme 20). A reverse ratio was obtained for the trans-/3-bro-... 

Zirconium-aryne complexes have found applications in organic synthesis. For example, treating diallylamine 22 with BuLi and zirconocene(methyl) chloride forms an aryne-zirconium complex that undergoes intramolecular olefin insertion to yield metallacycle 23, and trapping this metallacycle with iodine gives 24, further manipulation of which allows rapid construction of 25, an analogue of the pharmacophore of the antitumour agent CC-1065 [21] (Scheme 4). 

Lithiation of commercially available bromoarenes (281) followed by treatment with zirconocene (methyl) chloride affords zirconocene complexes of substituted benzynes (283), which react with symmetric alkynes and l-(trimethylsilyl)propyne to give single regioisomeric zirconacycles, (284) and (285), respectively (Scheme 66). Both (284) and (285) react with disulfur dichloride to produce benzothiophenes (286) and (287), respectively, in 60-80% isolated yields in a one-pot procedure <89JOC2793>. Protodesilylation of (287) can be accomplished in >90% yield to give the corresponding 2-unsubstituted benzothiophenes by treatment with tetrabutylammonium fluoride in tetrahydrofuran. Application of the procedure to the preparation of 2,3-dihydrobenzo[6]thiophenes was also reported <9iOM537>. 

An alternative route to the methyl vinyl zirconocenes 11 is based on the reaction between a vinyllithium 15 and zirconocene methyl chloride. This approach has been used to form several ri -alkyne complexes. ... 

Several examples of p-chloride elimination are shown in Equations 10.24-10.29. Reaction of vinyl chloride with cationic zirconocene-alkyl complexes (Equations 10.24a and 10.24b) forms propylene and the corresponding zirconocene-chloride complex as the initial products. Tlie final products result from polymerization of the propylene by the starting zirconocene-alkyl species, and generation of a dinuclear cationic chloride species from the resulting cationic chloride complex and a zirconocene dichloride by a less-defined pathway. The propylene is formed by the process shown in Equation 10.24b. Insertion of vinyl chloride into the zirconocene methyl, followed by p-chloride elimination from the p-chloroalkyl intermediate generates propylene and a cationic chloride complex. 

Hydrozirconation of allenic systems preferentially leads to allylic zirconocenes, which are highly reactive and thus very useful organometallic reagents. Allenic sulfides react in the expected fashion to give the (E)-y-thiophenylallylzirconocene chloride 20 (Scheme 4.18) [47]. These intermediates, upon introduction of an aldehyde or methyl ketone, give predominantly the anti isomer (ratios from 82 18 to > 97 3). Exclusive 1,2-addition was observed by Suzuki et al. in the case of an a,f5-unsaturated aldehyde. As long as the steric demands of the two substituents attached to the ketone carbonyl are significantly different, synthetically useful levels of selectivity can be achieved. 

The stereospecific construction of the trisubstituted double bond of the side chain at C-1 of carbazomadurins A (253) and B (254) was achieved using Negishi s zirconium-catalyzed carboalumination of alkynes 758 and 763, respectively. Reaction of 5-methyl-l-hexyne (758) with trimethylalane in the presence of zirconocene dichloride, followed by the addition of iodine, afforded the vinyl iodide 759 with the desired E-configuration of the double bond. Halogen-metal exchange with ferf-butyllithium, and reaction of the intermediate vinyllithium compound with tributyltin chloride, provided the vinylstannane 751a (603) (Scheme 5.79). 

The application of achiral cationic zirconocene compounds for methyl methacrylate polymerisation, e.g. a mixture of [Cp 2ZrMe(THF)]+[BPh4] and Cp 2ZrMe2 in methylene chloride solution, leads to the formation of syndio-tactic poly(methyl methacrylate). The species responsible for propagation are believed to be the bimetallic ones, involving cationic zirconium enolate and neutral zirconocene, which facilitates the process. Propagation is postulated to occur via the Michael reaction between the coordinating monomer and the cationic enolate [537] ... 

Thus, we have shown that, in addition to the known methyl and chloride ancillary ligands in zirconocenes, amido ligands can also be activated by strong Lewis acids such as MAO, producing cationic complexes active in the polymerization of tt-olefins. 

Unlike the insertion of 2-monosubstituted alkenyl carbenoids (69, 70, and 73), the reaction of 2,2-disubstituted alkenyl carbenoids with alkenyl zirconocene chlorides afforded the expected products as a mixture of stereoisomers. Thus, when 77, derived from the deprotonation of the stereodefined E-l-chloro-2-methyl-l-octene 76, was reacted with -l-hexenylzirconocene chloride 78 at low temperature, a partial inversion of configuration at the alkenyl carbenoid center occurred before or during the rearrangement to afford the expected metalated diene 79 with an E Z isomeric ratio of 58 42 after hydrolysis (see 80, Scheme 27) [53]. The poor stereocontrol was attributed to the metal-assisted ionization [58-60], which promotes the interconversion of the E- to the Z-alkenyl carbenoids 77. The latter occurs at a rate comparable with that of the insertion into organozirconocene chloride, and hence this is responsible for the loss of stereochemistry. 

Suzuki and Suga reported the use of clays as solid acids to support and activate metallocene catalysts for olefin polymerization. They were able to use much less alkylaluminmn cocatalyst relative to solution polymerization conditions. The clays were slurried with AlMeg in toluene, then treated with a solution containing zirconocene dichloride, II, and AIMeg. The metallocenium cation was presumed formed via abstraction of chloride and/or methyl ligands by acidic sites on the surface of the clay, and the low basicity of the clay smface was proposed to stabilize the coordinatively unsaturated cation. Propylene was copolymerized with 250 psi ethylene at 70°C. For acid-treated KIO montmorillonite, an activity of 3300 X 10 kg polymer/(g Zr h) was obtained. Catalysts based on vermiculite, kaolin, and synthetic hectorite all showed lower but still appreciable activities. In this brief report, the Al/Zr ratio was not specified, and the clay dispersion was not reported. 

Like 3 hydrogen eliminations, 3-alkyl eliminations require an open coordination site. This site is generated in the scandocene system by dissociation of PMej and in the zirconocene and hafnocene complexes by dissociation of the borate from the zwitterionic species. - The open coordination site is generated in the platinum system by abstraction of chloride and is generated in the ruthenium complex by dissociation of the monodentate phosphme. - The mild conditions for 3-methyl elimination from the ruthenium metalla-cycle is surprising, considering that it would seem to require the propellane-type transition state shown in Equation 10.21. 

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