Zirconium complex zirconocenes

The use of a zirconium complex (dibutylzirconocene, — 78 °C to rt, 2 h) to induce intramolecular co-cyclization of A-methyl-5-azanona-l,8-diene to an intermediate zirconacycle was a key step in a new azepane synthetic route hydrolysis (MeOH, aq. NaHC03) of this intermediate then realized the trans- 1,4,5-trimethylazepane in 75% yield the active reagent for the initial cyclization was zirconocene (1-butene). The overall transformation represents a type d ring construction process <2006SL3439>. This synthetically versatile process is also applicable to aza eneyne and aza diyne precursors as well as benz-fused analogues. 

Synthesis, reactions, and physical properties of stable mononuclear platinum and zirconium complexes of cyclohexyne reported prior to the late 1980s have been comprehensively covered in earlier reviews.2-8 More recently, reaction of the zirconocene complex of cyclohexyne with trimethyla-luminum and trimethylgallium has been reported to give 247 and 248, respectively [Eq. (36)].57-58 These products are novel because four atoms (carbons Cl and C3, the transition metal, and the main group metal) are covalently bonded to an sp2 hybridized carbon (C2) in a planar tetracoordi-nate fashion. Synthesis of this type of complex, which Erker describes as anti-van t Hoff/LeBel, does not require the strained cycloalkyne ring zirconocene complexes of acyclic alkynes react similarly.57-58... 

Stable zirconium, platinum, molybdenum, and tungsten complexes of cyclooctyne, a zirconium complex of cydoocta-5-enyne, and a bimetallic molybdenum complex of cyclocta-3,7-dienyne have been discussed in earlier reviews.28 More recently, two stable zirconocene complexes of cycloocta-trienyne (275 and 276) have been prepared101 by /3-hydride elimination from 274 in the presence of PMe2R [Eq. (45)]. 

They are based on various metals. Such as zirconium, complexed with cyclopentadienide anions. This type of compound is called a zirconocene and is used with organoalu-minum to make highly regular polymers. The catalyst has the ability to flip back and forth from making atactic to isotactic polypropylene in the same polymerization. The alternating tacticity of the polymer breaks up the crystallinity of the chains and yields an elastomer. Metallocene catalysts are currently very expensive and cannot yet polymerize dienes such as butadiene, so they have only enjoyed limited commercial success in elastomers. However, this is one of the most intense fields of polymer research and many new product breakthroughs are expected in the near future. 

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. 

The results of 1H- and 13C-NMR analysis of the complexes 11-13 are given in Table 8. For comparison, the NMR resonances of the corresponding fragments of the zirconocene dichloride and free diamine used in the synthesis of amido zirconium complexes are also shown. 

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. 

Zirconocene dichloride reacts with dibromomethane in the presence of Zn to yield a methylene-zirconium complex 4.105, which is used for the methylenation of carbon compounds to produce the terminal alkenes h... 

A variety of ani a-bridged complexes such as (143) resembling those of ans a-zirconocenes have also been reported. Moreover, reduction of the zirconium complexes with n-BuLi in the presence of PMes provides an entry point to Zr(II) complexes (144) their reactivity toward aUcynes has been studied in detail. ... 

Zrrconocene, ZrCp2, generated in situ from zirconocene derivatives, mediates diverse ring-closures. Thus treatment of 2,4,4-trimethyl-l,6-heptadiene with butyllithium and Bu2ZrCp2 yields the zirconium complex 218, which gives 1,1,3,3,5-pentamethylcyclopentane on aqueous work-up (equation 111). The reaction of 1,7-octadiene with butyknagnesium chloride and a catalytic amount of zirconocene dichloride, followed by water, gives frons-l,2-dimethylcyclohexane (219) in excellent yield (equation 113) similarly, the diene ether 220 affords the cyclopentane derivative 221 (equation 113). ... 

Heterobimetallic /x-oxo complexes 854 are formed via halide displacement reactions between trioxo anions such as [Cp M(0)3] (M = Mo, W) and Cp2ZrCl2655 (Scheme 214). The corresponding heterotrinuclear complexes 855 are obtained by addition of 2 equiv. of trioxoanion complexes to zirconocene dichloride. Other heterobimetallic complexes such as //-773-C02-bridged ruthenium-zirconium and rhenium-zirconium complexes have also been prepared.656... 

Chiral zirconocene complexes have also been studied as catalysts for the hydrogenation of nonfunctionalized olefins115. Using homogeneous Ziegler Natta-type catalyst systems derived from [ethylenebis(4,5.6,7-tetrahydro-l-indenyl)]zirconium complexes and methyl aluminoxane [A1(CH3)0] , 2-phenyl-l-butene was hydrogenated in 36% optical yield (20 bar H2, benzene, 25 °C). Under the same conditions, the reaction of styrene with D2 gave optically active 1,2-dideuteroethylbenzene with 65% ee. 

Similar behavior is observed for calix[4]arene (5ee Calixarenes) complexes of the type (89). " Moreover, the oxygen donor atoms are particularly appropriate for the oxophilic early transition metals. A rich chemistry has been developed with complexes containing zirconium- carbon bonds. In this area, aryne zirconocene compounds can be thermally generated and isolated without trimethylphosphane additional coordination. Zirconium-butadiene chemistry has been explored as well and constitutes a source of zirconium complexes. 

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). 

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