Metallocene derivatives

Reactions of the metallocene derivatives of molybdenum with pyrazole lead to the mononuclear complexes of the type 22. Structure 22 shows that it cannot be used as a ligand for the preparation of dinuclear complexes owing to geometric constraints [80JOM( 197)291 83JOM(253)53]. In acetone, an unusual complex 23 is formed [83JOM(253)53]. The bidentate ligand is the product of the reaction of pyrazole and acetone. 

METALLOCENE DERIVATIVES RADIATION CROSSLINKING TCNQ DERIVATIVES ENZYME IMMOBILIZATION... 

Kaminsky W, Engehausen R, Zoumis K (1992) Standardized polymerizations of ethylene and propene with bridged and unbridged metallocene derivates a comparison. Makromol Chem 193 1643-1651... 

Kagan et al. were the first to report the corresponding enantioselective catalytic hydrogenation using chiral metallocene derivatives [94, 95]. By using menthyl- and neomenthyl-substituted cyclopentadienyl titanium derivatives in the presence of activators (Scheme 6.5) [96], these authors observed low ee-values (7-14.9%) for the catalytic hydrogenation of 2-phenyl-l-butene into 2-phenylbutane. In contrast, no enantiomeric excess was obtained with the corresponding zirconocene derivatives. 

The complex, [Li(THF)3] [77S-C2B4H4(SiMe3)2](Cp IZrCy, was synthesized via reaction of (Cp )ZrCl3 with the dianion, [2,3-(SiMe3)2-2,3-C2B4H4]2. 24 This metallocene derivative can be described as an anionic, bent-sandwich... 

A recent new discovery is the fact that the hydrolysis of branched /3-alkyl-substituted aluminoxanes are, in some cases, as effective as co-catalysts in olefin polymerization as MAO.63,64 For example, when combined with the the metallocenes, Cp 2ZrCl2, the hydrolysis products (Al/HzO = 2) of R3A1 (R = Bu and Oct) produced akylated ion pairs with high polymerization activities.65 The same combinations with Cp2ZrCl2 did not produce active catalysts, a result interpreted as due to the inhibition of /3-hydride elimination in the substituted metallocene derivatives. 

In a systematical study, Golovin et al. investigated a series of metallocene derivatives in terms of their redox potentials, mass transport properties, and chemical and electrochemical stabilities in both electrochemical test cells and commercial-size AA rechargeable cells.Figure 43 shows the complete voltammetric scan of the ferrocene-containing elec-... 

Bercaw has investigated the application of the 6 2-symmetric, enantiomerically pure lanthanide metallocene derivative (i ,A)-BnBpYH 34 as a catalyst for the asymmetric cyclization/hydrosilylation of 1,5- and 1,6-dienes. Although 34 displayed high activity for the reaction of a number of dienes, asymmetric induction was low. In the best case, reaction of 3,3-dimethyl-1,5-hexadiene with phenylsilane catalyzed by 34 gave silylated cyclopentene 35 in 95% yield with 50% ee (Equation (25)). 

Metallocene derivatives may be named by either standard organic suffix (functional)7 or prefix nomenclature. Substituents are given the lowest numerical locants in the usual manner on the equivalent cyclopentadienyl rings of the ocene entity. The first ring is numbered 1 to 5 and the second ring is numbered V to 5. In metallocenes composed of multiple ocene groupings the cyclopentadienyl rings are further numbered 1" to 5", V" to 5", etc. The radical names -ocenyl, -ocenediyl, -ocenetriyl, etc. are used. For examples see Table 25. 

Many metallocene derivatives are known of other conjugated cyclic polyenes. Examples are bis(cyclooctatetraene)uranium (uranocene, 7) and bis-(pentalenylnickel), 8 (see Section 22-12B) ... 

The activation of y-CH bonds of the ligand N(SiMe3)2 has been observed in a number of early transition metal and actinide complexes.243 Attempts to prepare metallocene derivatives of this ligand for the Group IV metals lead to cyclometallation as shown (reactions 96 and 97).249,250... 

Titanocene dichloride was the first metallocene derivative to be converted53 into dithiolato complexes, for example compound (38). Some other examples of this structural type exist, and their structural features are described in Section 16.5.3.1. 

In general, the extensive series of metallocene derivatives that are known for the heavier elements of Group 14 have not been readily extrapolated to silicon chemistry. It is intriguing that in spite of a huge effort in this area over many years, decamethylsili-cocene remains the only derivative that has been comprehensively characterized, and the challenges with this chemistry are still numerous. 

The disadvantages of the PMS precursor are (1) MeSiFl3 is costly and pyrophoric, forming potentially explosive mixtures with ambient air, (2) the Ti/Zr dehydropolymerization catalysts are also pyrophoric, leading to pyrophoric PMS and (3) metallocene-derived PMS is also highly pyrophoric. For example, a 20 wt% increase was observed after exposure of PMS samples to dry air for 5 h at RT. In contrast, the mPMS derivative mentioned above exhibits only a 3 wt% increase in air over a 5 h period. 

Table III Summary of linear and nonlinear optical data on metallocene derivatives...

The same kinds of concepts may be applied to organometallic materials, where the presence of organometallic moieties such as metal carbonyls and metallocenes offers a great deal of scope for synthetic and electronic versatility. Metallocene derivatives such as 11.73 exhibit NLO properties as shown in Table 11.2. The (3 values are comparable to organic species of the same type, but do show additional behaviour due to mixing with metal states.73... 

Manganese complex, 46 Metallocene derivatives, Group 4, 18 Metallocene hydride, 14 Metallocenes, Group 4, mechanism proposed by Tilley, 14... 

Germyl metallocene derivatives of the early transition metals, Ti, Zr and Hf (M) have been synthesized by the combination of metallocene halides and germyl anions (equations 4 and 5)38-40. The cyclopentadienyl complexes Cp2M(GePh3)Cl39 are difficult to purify due to their instability in solution however, use of the pentamethylcyclopen-tadienyl group(Cp ) enhances both the solubility and stability of these complexes40,41. 

Unlike the compounds obtained with the heavier halogens, polyfluori-nated metallocene derivatives cannot be prepared from the permercurated metallocenes. Thermally stable pentafluorinated ruthenocenes have been made from the (oxocyclohexadienyl)(cyclopentadienyl)metal complexes by flash vacuum pyrolysis (Scheme 6).53 54 Decafluorometallocenes, [M(C5F5)2], are still unknown potential routes to these compounds starting from fluorinated cyclopentadiene (C5F5H)55 or from the decachlorometal-locenes48 have been unsuccessful. However, there seems to be no fundamental steric or electronic barrier to their eventual preparation. 

Metallocene derivatives containing azulenyl rings, (VI), were prepared by Iwama [5] and used to polymerized propylene. 

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