Complex zirconium

The crystal structure of ( j -C5H4-tBu)2Zr[( 7 C5H4)2Fe] is shown in Fig. 7-5 [21]. The zirconium atom has a pseudotetrahedral geometry. The cyclopentadienyl rings of the ferrocene unit are eclipsed and deviate somewhat from the parallel disposition (dihedral angle 6°). 

As illustrated in Fig. 7-6, in tetrahydrofuran (THF) solution the complex undergoes a one-electron oxidation to the corresponding stable monocation ( ° (A i/Ai) = 4-0.52 V), which, in the presence of traces of water, evolves to a more easily oxidizable hydroxo species ( ° (A 2/A2) = 4-0.25 V) [22]. 

The crystal structure of (j -C5H4-rBu)2Zr[(fy -C5H4Se)2Fe] has been reported 

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Alkenyl zirconium complexes derived from alkynes form C—C bonds when added to aHyUc palladium complexes. The stereochemistry differs from that found in reactions of corresponding carbanions with aHyl—Pd in a way that suggests the Cp2ZrRCl alkylates first at Pd, rather than by direct attack on the aUyl group (259). 

Thermolysis of the t]-coordinated zirconium complex of thiophene Cp2Zr(SiMc3) (C4H3S) is a thienyl ring cleavage reaction (920M1646). 

Thus, a novel chiral zirconium complex for asymmetric aza Diels-Alder reactions has been developed by efficient catalyst optimization using both solid-phase and liquid-phase approaches. High yields, high selectivity, and low loading of the catalyst have been achieved, and the effectiveness of chiral catalyst optimization using a combination of solid-phase and liquid-phase methods has been demonstrated. 

Zirconium complexes, 3, 363-440 acetylacetone, 2,372,377 ligand exchange reactions, 2, 381 rearrangement, 2, 383 alkyl... 

In certain cases, free guanidines can also serve as precursors to Group 4 metal guanidinate complexes. The bis(guanidinato) bis(benzyl)zirconium complex [Pr NHC(NPr )2]2Zr(CH2Ph)2 was obtained by addition of 2 equivalents of... 

Protonolysis of the f/ -styrene zirconium complex Cp Zr(t/ -PhCHCH2) [MeC(NPr )2] with 2 equivalents of Bu NH2 provided a high yield of a novel bis(amido) complex according to Scheme 93. ... 

As shown in Scheme 94, the fj -styrene zirconium complex Cp Zr (f/ -PhCHCH2)[MeC(NPr )2] also served as starting material in the synthesis of alkyl-substituted 1,3-diene complexes of (pentamethylcyclopentadienyl)zirco-nium amidinates. NMR spectroscopy as well as single-crystal X-ray analyses of these complexes revealed that they are best described by the Zr(lV) a, n-metallacyclopent-3-ene limiting resonance form rather than as Zr(ll) f/ -diene complexes. ... 

The (pentamethylcyclopentadienyl)zirconium amidinate unit also served as a platform for the synthesis and characterization of remarkable cationic and zwitterionic allyl zirconium complexes derived from trimethylenemethane (TMM). A direct synthetic route to the neutral precursors was found in the... 

These lithium derivatives were found to be excellent reagents for the introduction of the new amidinate scorpionate ligands into Group 4 metal complexes, and a series of neutral titanium and zirconium complexes were prepared according to Scheme 189 and fully characterized. 

The crystal structure of a mono(cyclopentadienyl)zirconium complex containing a novel Me2Si-linked bis(amidinate) ligand was reported (Scheme 203). In this compound the central Zr atom is octahedrally coordinated with the bis(amidi-nate) acting as a tridentate ligand. ... 

In this method, one alkyne is treated with Schwartz s reagent (see 15-17) to produce a vinylic zirconium intermediate. Addition of MeLi or MeMgBr, followed by the second alkyne, gives another intermediate, which, when treated with aqueous acid, gives the diene in moderate-to-good yields. The stereoisomer shown is the one formed in usually close to 100% purity. If the second intermediate is treated with I2 instead of aqueous acid, the 1,4-diiodo-1,3-diene is obtained instead, in comparable yield and isomeric purity. This reaction can also be done intramolecularly Diynes 56 can be cyclized to ( , E) exocychc dienes 57 by treatment with a zirconium complex. 

Similar reactions, in which two alkyl groups are added to a triple bond, have been carried out with trialkylalanes R3AI, with zirconium complexes as catalysts. ... 

Ally] ethers and iodobenzene have also been added using a zirconium complex. Similarly, allyl ethers and allyl chlorides have been added. ... 

The complexes are formed with 68% (R = t-Bu) and 73% [R = Me2Si(t-Bu)N] yield in warm (85°C) toluene in the course of 90 min. Surprisingly, the B—N distance is extended only a little ( 0.03 A), compared with the free iminoborane. In contrast to this side-on coordinated iminoborane, the zirconium complex (rj -Cp)2ZrCl(H)... 

Titanium-acetylene complexes 29 generated in situ from acetylenes, Ti(0-i-Pr)4 and /-PrMgX react with imines to form azatitanacyclopentenes 30 which then react with carbon monoxide under atmospheric pressure to provide pyrroles 31 <96TL7787>. This reaction, which utilizes commercially available reagents is an improvement over a related procedure via the corresponding zirconium complexes under 1500 psi CO <89JA776>. 

Stable zirconate complexes of type 31 have also been described by the [3 + 2] cycloaddition of a-phosphino zirconaindene with alkyne derivatives, and the method has been extended to the synthesis of zirconium complexes from various heterocumulenes X=C=Y (X,Y=0,S,CyN) (Scheme 15) [69,70]. 

The first organometallic zirconium complexes to be prepared all contained Zr( 1V) and were reported almost contemporaneously. The reaction of Zr(TPP)-(OAc)2 with RLi or RMgBr produced the dialkyl complexes Zr(TPP)R2 (R = Me, Et, n-Bu or Ph), characterized by. spectroscopy. The development of the chlorozirconium complexes opened up the chemistry further, with... 

Perhaps chemists will be able to mimic nature without duplicating the iron-sulfur-molybdenum structure. For example, a zirconium complex with tetramethyl cyclopentadiene can bind dinitrogen in a manner that breaks the NON bond, as shown below. Treatment with hydrogen gas results in formation of small amounts of ammonia. Although the yields are too low to make this a viable commercial process, researchers hope to make the process more efficient through chemical modifications and changes in conditions. 

The case of butane is noteworthy since the selectivity at low conversions indicates that there is no selectivity in the overall hydrogenolysis step between n- and sec-butyl zirconium surface intermediates, while earUer studies had shown that the -alkyl zirconium complexes were more stable than sec-alkyl derivatives (Table 3 and Scheme 23) [94]. 

Dianionic bis(amide) ligands bearing additional donor atoms have been described by several researchers. High activities for ethylene polymerization are observed for pyridyldiamido zirconium complexes such as (42) (1,500gmmol-1 bar-1 h-1),145 although the corresponding titanium complex is much less active.146... 

In general, Group 4 benzamidinates show poor activities as olefin polymerization catalysts.158-162 However, bis(benzamidinate) complex (52) affords isotactic PP (>95% mmmm) at >7 atm propylene pressure 163 at ambient pressure atactic PP is produced.164 An unsymmetrical tris (benzamidinate) zirconium complex has also been shown to afford highly isotactic PP.165... 

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