Cyclopentadienyl and substituted

Cyclopentadienyl and Substituted Cyclopentadienyl Complexes. Thorium complexes containing cyclopentadienyl rings (Cp),... 

Cyclopentadienyl (and substituted variants thereof) has been the most versatile ligand used in organolanthanide chemistry. Unlike the situation with the d-block metals, where a maximum of two pentahapto- () -)cyclopentadienyls can coordinate, up to three -cyclopentadienyls can be found for the lanthanides, in keeping with the higher coordination numbers found for the f-block elements. In terms of the space occupied, a -cyclopentadienyl takes up three sites in the coordination sphere. Three types of compound can be obtained, depending upon the stoichiometry of the reaction mixture ... 

The organometalllc chemistry of the rare earths is predominantly, though not exclusively, that of cyclopentadienyl and substituted cyclopentadienyl compounds (Fig. 11). These complexes were the first organometal-lic rare earths to be synthesized and comprise three series RE(C5H5)3, RE(CsH5)2X, and RE(CsH5)X2. They are prepared by the reaction of the lanthanide chloride with the stoichiometric amount of NaCsHs ... 

Metallocene Catalysts. Polymerization of cycloolefins with Kaminsky catalysts (combinations of metallocenes and methylaluminoxane) produces polymers with a completely different stmcture. The reactions proceeds via the double-bond opening in cycloolefins and the formation of C—C bonds between adjacent rings (31,32). If the metallocene complexes contain bridged and substituted cyclopentadienyl rings, such as ethylene(hisindenyl)zirconium dichloride, the polymers are stereoregular and have the i j -diisotactic stmcture. 

Table 1. Energy barriers to ring rotation in unsubstituted and substituted cyclopentadienyl transition metal complexes.

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Linear correlations between l(L) and Hammett substituent constants for substituted jr-cyclopentadienyl and 7r-arene ligands [69], for other substituted Kgands,... 

Ring Substitution Reactions of Metal-Cyclopentadienyls and Metal-Arenes... 

Hydrocarbon anions, such as cyclopentadienyl and analogs (fluorenyl, indenyl, pentadienyl), substitute for fluoride, leading, for example, to phenylcyclopentadiene as a Cr(CO)3 complex on the arene (equation 15).67... 

The reaction of the transition-metal fragments with main group 15 elements directly has proven a very fruitful field for exploration. The methodology has been successful for a wide range of metal complexes. These fall generally into three basic types (1) reactions with cyclopentadienyl metal carbonyls, (2) reactions with homoleptic metal carbonyls and substituted derivatives, and (3) reactions with metal cations in the presence of a multi-dentate chelating ligand. 

From 1995 to 2000, catalyst profiles of several ruthenium catalysts bearing pyridine-diimide 1 [13], diiminocarbene 2 [14], diamine-arene 3 [15],phos-phino-arene 4 [16], and substituted cyclopentadienyl 5 and 6 [17, 18] were shown to have good activity for the cydopropanation (Fig. 1). At the relatively high reaction temperature of 60-100 °C,they also gave moderate-to-high yields over 90%. It is interesting in that the dipyridine-diimide complex 1 and the p-cymene-carbene complex 2 show high trans selectivity, 86 14 and 82 18, respectively. 

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