Cyclopentadienyl zirconium complexes

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. ... 

Fig. 6.20. Syndiotactic polymerization of propene with isopropyl(l-fluorenyl-cyclopentadienyl) zirconium complexes. See also Fig. 6.19. The cyclopentadienyl ligand above the plane is drawn in full. The fluorenyl ligand below the plane is drawn with dotted lines.

Dimethylpyrazine (48) and the cationic bis(cyclopentadienyl) zirconium complex (49) gave an isolable intermediate formulated as the complex (50) and thence 2,5-dimethyl-3-(pent-l-enyl) pyrazine (51) [one pot procedure complex (49), CH2C12, 23°C, 15 min then HC=CPr J, 23°C, 2.5 h 88%] 868 several analogues, like 2,5-dimethyl-3,6-bis[l-methyl-2-(trimethylsilyl)-vinyl] pyrazine (51a) (61%), were made similarly.868... 

Epoxidation of allylic alcohols using metallocene catalysts was reported as shown in Equation 78 [83]. Cyclopentadienyl zirconium complexes such as CpZrCl3 and Cp2ZrCl2 could act as a catalyst for epoxidation of allyl alcohol (178) with TBHP to afford epoxide (179) in a good yield. In both cases, the anti isomer was the major product, and Cp2ZrCl2 showed better stereoselectivity. To obtain the product in high yield, hexane was the best choice as a solvent although the catalysts were less soluble. 

Scheme 15 Reactivity of mixed indenyl-cyclopentadienyl zirconium complexes toward...

Bemskoetter WH, Lobkovsky E, Chirik PJ. Kinetics and mechanism of N2 hydrogenation in bis(cyclopentadienyl) zirconium complexes and dinitrogen functionalization by 1,2-addition of a saturated C-H bond. J Am Chem Soc. 2005 127 14051-14061. 

The cyclopentadienyl triflate complexes of zirconium and titanium 51 and 52 (Figure 3.7) are also active catalysts [51]. Their activity has been tested in a wide variety of dienes and dienophiles. It is noteworthy that even at low catalyst loadings, rate accelerations between 10 and > 10 times have been observed. No special precautions were taken to dry the solvents or the substrates, in contrast with the traditional Lewis acids which require either predried solvents or high catalyst loadings. 

Preparation of Functionally Substituted rj-Cyclopentadienyl Dicarbonyl Complexes of Titanium and Zirconium... 

The metallocene complexes are only used in catalytic amounts and may be recovered from the reaction mixture. Bis() 5-cyclopentadienyl)zirconium(TV) chloride (Cp2ZrCI2) and fluoride (Cp2ZrF2) in the presence of magnesium/mercury(II) chloride are equally effective. 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

Bis(cyclopentadienyl)zirconium(III) complexes alkynyl-bridged complexes, 4, 749 dinitrogen complexes, 4, 747 electrochemical reduction, 4, 745 phosphido-bridged complexes, 4, 750 Bis(cyclopentadienyl)zirconium(IV) complexes electrochemical reduction, 4, 745 with M-C r/)-bonds, 4, 895 with M-C r/i2-bonds, 4, 887 with M-C r/i3-bonds, 4, 884 with M-H bonds, 4, 878 with M-N bonds, 4, 910 with M-0 bonds, 4, 917 with M-P bonds, 4, 927 with M-S bonds, 4, 930 with M-Si bonds, 4, 925 non-functionalized metallocene halides, 4, 870 ring-functionalized metallocene halides, 4, 874 Bis(cyclopentadienyl)zirconium(III) halides, in organic synthesis, 4, 754... 

Cyclopentadienyl aryl complexes, with niobium, 5, 66 Cyclopentadienyl bis(phosphine)amide zirconium compounds, dicarbonyl complexes, 4, 702. -Cyclopentadienyl-carbanionic complexes, with Zr(IV),... 

Mono(cyclooctatetraenyl) lanthanide(III) compounds, synthesis and characteristics, 4, 124 Mono(cyclooctatetraenyl) zirconium(III) compounds, preparation and reactions, 4, 743 Mono(cyclopentadienyl) amido complexes alkane elimination, 4, 446 amine elimination, 4, 442 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

Mononitrosyl complexes, with chromium, 5, 301 Mononuclear bis(cyclopentadienyl) zirconium(III) complexes, characteristics, 4, 746... 

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. 

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