No abstract

Lithium cyclopentadienide adds to a variety of isocyanates [R−NCO, R = tert-butyl (a), n-butyl (b), cyclohexyl (c), phenyl (d), 3-pyridyl (e), 2-tetrahydropyranyl (f), adamantyl (g)] to yield the monocarbamoyl-substituted cyclopentadienides C5H4CONHR- 3 admixed with varying amounts of the respective 1,2-dicarbamoyl-substituted C5H3(CONHR)2 - systems 4 and a corresponding quantity of the C5H5 - starting material. Subsequent treatment of these reaction mixtures with anhydrous FeCl2 gave the 1,1‘-dicarbamoylferrocenes 6 and the corresponding monocarbamoylferrocenes 5, which were easily separated by chromatography. The carbamoylferrocenes 5b, 5c, and 6d were characterized by X-ray crystal structure analyses. The (N-phenyl- and (N-adamantylcarbamoyl)cyclopentadienides were treated with CpTiCl3 to give the carboxamide-substituted titanocene dichloride complexes [Cp(C5H4CONHR)TiCl2] 8a (R = Ph) and 8b (R = adamantyl), respectively. Complex 8b was also characterized by X-ray diffraction. The valine ester-derived isocyanate reacts with lithium cyclopentadienide to give the N-valinyl-substituted carbamoylcyclopentadienide 3h. Subsequent treatment with FeCl2 or FeCl2/CpLi, respectively, produces the 1,1‘-difunctionalized ferrocene 6h or the monofunctionalized ferrocene 5h. Both complexes were characterized by X-ray crystal structure analyses.

The Lewis acid tris(pentafluorophenyl)borane adds to the (butadiene)group 4 metallocenes 1a−d (metallocene = Cp2Zr, Cp2Hf, (MeCp)2Zr, (Me3CCp)2Zr) to give the metallocene−(μ-C4H6)−borate−betaine complexes 2a−d. (Isoprene)zirconocene (1e) and (2-phenylbutadiene)zirconocene (1f) add the B(C6F5)3 reagent regioselectively at the carbon atom C-4 to give the complexes 2e and 2f, respectively. The complexes 2 all show a pronounced M···F−C interaction with one of the six ortho-B(C6F5)3 fluorine atoms. The resulting metallacyclic structures were characterized by X-ray diffraction of the complexes 2c and 2e (Zr···F ≈ 2.40 Å, angle Zr−F−C ≈ 140°). The bridging fluorine atom of the complexes in solution is characterized by an extreme upfield shift of its 19F NMR resonance (δ ≈ −210 to −220 ppm) relative to the signals of the remaining five o-F resonances of the B(C6F5)3 moiety (average δ ≈ −135 ppm). The 19F NMR spectra of the complexes 2 are dynamic even in the noncoordinating solvent toluene-d 8. All six o-fluorine signals equilibrate with coalescence temperatures around 240 K at 564 MHz to give a single resonance signal at high temperature. This fluorine equilibration process of the −B(C6F5)3 end of the metallocene−borate−betaine complexes 2 is very likely to proceed via a rate determining cleavage of the coordinative M···F−C interaction. From the activation barrier of this process, obtained from the dynamic fluorine NMR spectra, Zr···F bond dissociation energies of ca. 8.5 kcal/mol were estimated for the complexes 2. This magnitude of the M···F−C bond dissociation energy makes the internal fluorocarbon coordination a very suitable tool for protecting active electrophilic metal catalyst centers. The Zr···F−C bond of the complexes 2 is cleaved by the addition of the donor solvent THF with formation of acyclic 1,2-η2-allyl metallocene complexes.

An active catalyst for α‐olefin polymerization without addition of activator components has been discovered in the betain 2, which is formed in the title reaction shown below. Laser desorption mass spectrometry shows that B(C6F5)3‐containing polymers with a molecular weight distribution typical of Ziegler catalysts are formed.

Ein aktiver Katalysator für die α‐Olefin‐Polymerisation ohne Zusatz von Aktivatorkomponenten ist das Betain 2. das in der Titelreaktion entsteht. Die Bildung B(C6F5)3‐haltiger Polymere mit der typischen Molekulargewichtsverteilung für Ziegler‐Katalysatoren wird durch Laserdesorptions‐Massenspektrometrie nachgewiesen.