Andreas Ohff

Intramolekulare Cyclisierung von terminal disubstituierten α, ω-Diinen an Titanocen “Cp2Ti” mit einer nachfolgenden, ungewöhnlichen Cp-ringöffnung und neuen intramolekularen CC-Knüpfung

Abstract The reaction of Cp 2 Ti(Me 3 SiC 2 SiMe 3 ) ( 1 ) with terminal disubstituted α,ω-diynes RC≡C(CH 2 ) n C≡CR affords, after substitution of Me 3 SiC 2 SiMe 3 , bicyclic titanacyclopentadienes via intramolecular cyclization. The stability of the obtained products 2, 3 and 5 is determined by the spacer length ( n = 2, 4, 5, 6). The four-membered ring derivatives ( n = 2) 2a and 2b were obtained in good yield. In the case of n = 4 the bicyclic six-membered ring 3 was formed at first, which rearranges to a stable tricyclic η 4 : η 3 -dihydroindenyl-Ti complex 4 by Cp cleavage and intramolecular CC coupling. Complex 4 was characterized by X-ray structure analysis and NMR spectroscopy. An increase of spacer length ( n > 4) provides indefinable secondary and decomposition products.

Regioselektive reaktionen der fremdligandfreien titanocen-alkin-komplexe Cp2Ti(RC2SiMe3) (R = Me3Si,Ph, tBu, nBu)☆

Abstract Depending on different substituents in the reaction of Cp 2 TiCl 2 with magnesium and the alkynylsilanes RC≡CSiMe 3 (R = SiMe 3 , Ph, t Bu, n Bu, n Pr, Me) in tetrahydrofuran, titanacyclopropenes (R = SiMe 3 , Ph, t Bu 1 , n Bu 2 ), symmetrical substituted titanacyclopentadienes (R = Me 5 ) or in a competition reaction both types of complexes (R = n Pr 3 and 4 ) were obtained. The compound Cp 2 Ti( t BuC 2 SiMe 3 ) 1 is the first example of a titanocene complex with an alkyl substituted alkyne without further ligands and was characterized by X-ray crystal structure analysis. The structural and spectroscopical data of 1 were compared with those of other well known complexes of that type, e.g. Cp 2 Ti(Me 3 SiC 2 SiMe 3 ) and Cp 2 Ti(PhC 2 SiMe 3 ) to investigate the influence of different substituents ( t Bu, SiMe 3 , Ph) upon alkyne complexation. The chemo- and regio-selectivities of the obtained alkyne complexes was studied in reactions with alkynes, alcohols, carbon dioxide and acetone. The reaction course depends mostly on steric restrictions, being in the first step kinetically favored at the Si-substituted C-atom of the alkyne and giving β-SiMe 3 -substituted products, which rearrange in some cases into the thermodynamically more stable α-SiMe 3 -substituted products.

Si–H Activation in Titanocene and Zirconocene Complexes of Alkynylsilanes RC≡CSiMe2H (R=tBu, Ph, SiMe3, SiMe2H): A Model To Understand Catalytic Reactions of Hydrosilanes

An agostic interaction between the Si–H bond and the metal center (depicted on the right) is the characteristic feature of the title complexes, which could be prepared by acetylene exchange reactions. IR, NMR, and X-ray structural investigations reveal that the effect of the Si-H-metal interaction is considerably stronger at low temperatures and in the solid state. This mode of bond activation is important in active catalysts for hydrosilylation and dehydrogenative polysilane reactions.

DARSTELLUNG UND REGIOSELEKTIVE REAKTIONEN DES PHOSPHINFREIEN ZIRCONOCEN-ALKIN-KOMPLEXES CP2ZR(THF)(TBUC2SIME3)

Abstract The reaction of Cp 2 ZrCl 2 with magnesium and t BuC 2 SiMe 3 in tetrahydrofuran yields the first zirconocene complex with an alkyl substituted alkyne without additional phosphine ligands Cp 2 Zr(THF)( t BuC 2 SiMe 3 ) 1 . That complex is stable at room temperature and was characterized by its IR and NMR spectra. The spectroscopical data of 1 were compared with those of the well known complex of that type Cp 2 Zr(THF)(Me 3 SiC 2 SiMe 3 ) 2 to study the influence of different sterical and electronical influences of the substituents ( t Bu and SiMe 3 ) upon alkyne complexation. The chemo- and regio-selectivity of complex 1 was studied in a hydrogen transfer reaction and in reactions with carbon dioxide and acetone. The results show mostly a kinetically favored reaction at the Si-substituted C-atom of the complexed alkyne, giving the β-SiMe 3 -product, which rearranges into the thermodynamically more stable α-SiMe 3 -substituted products. In contrast to titanocene in the case of zirconocene complexes coupling reactions of RC≡CSiMe 3 (R = SiMe 3 , t Bu) could be realized.

Zu Reaktionen disubstituierter Butadiine mit Titanocen-Komplexen

The mode of the reaction of titanocene “Cp2Ti” with disubstituted butadiynes RCCCCR′ depends strongly on the nature of the substituents R and R′. For R  R′  SiMe3 the starting butadiyne is split by titanocene to yield the dinuclear complex [Cp2Ti(CCSiMe3)]2 (1). For other symmetrically substituted (R  R′  Ph or tBu) or unsymmetrically substituted butadiynes (R  SiMe3, R′  Ph or R  SiMe3, R′  tBu) the reaction proceeds to dinuclear complexes with a central 1,4-disubstituted μ-η(1–3),η(2–4)-trans, ittrans-butadiene unit (“zig-zag-butadiyne”) between the two titanium centres (R  R′ =tBu (2); R  SiMe3, R′  tBu (3a); R  SiMe3, R′  Ph (3b)). Complexes 2 and 3a were characterized by X-ray structure analyses.

Zirkonadihydrofuran-komplexe: Darstellung, struktur und reaktivitäts-betrachtungen

The zirconocene alkyne complexes Cp2Zr(THF)(Me3SiCCSiMe3) (1) and Cp2Zr(py)(Me3SiC CSiMe3) (2) react with acetone to yield the new zirconadihydrofurane complex Cp2ZrOC(Me2) C(SiMe3)C(SiMe3) (3). Reaction of 3 with tolan gives, under substitution of the alkyne moiety, a further dihydrofurane compound Cp2ZrOC(Me2)C(Ph)C(Ph) (4). Complexes 3 and 4 are characterized by NMR and X-ray structure analyses. They are compared with the known titanocene complex Cp2 TiOC(Me2)C(Ph)C(Ph) (5) to study the influence of the metals M = Ti, Zr and the substituents R = Ph, SiMe3 in selected metalladihydrofuranes Cp2MOC(Me2)C(R) C(R). Although the structures of complexes 3 and 4 are similar, the complexes display different reactivities. Thus 3 is capable of reacting with tolan, CO2 and water at room temperature, while 4 is inactive towards these compounds under the same conditions.

Reaktion eines titanocen—Alkin-Komplexes mit trialkylammoniumtetraphenylborat—eine neue darstellungsweise und erste kristallstrukturanalyse von neutralligandhaltigen kationischen titanocen(III-komplexen [{Cp2Ti(L)2+}{BPh4−}]1

Abstract The catioanic d1-titanocene complexes [{Cp2Ti(L)2+}{BPh4−}] with L = THF (1) and pyridine (2) were very simply prepared by the reaction of [Cp2Ti(Me3SiCCSiMe3)] with trimethylammoniumtetraphenylborate via a le−-oxidation of the 14e−-Cp2Ti-unit to the paramagnetic titanium(III) complex under evolution of molecular hydrogen and the alkyne. Complex 2 is the first example of such a cationic-only neutral-ligand containing complexes without anionic ligands that has been characterized by an X-ray structure analysis.

Influence of solvents on the insertion of methacrolein into zirconacyclopropenes

The reaction of Cp2Zr(L)(η2-Me3SiC2) (L = THF, py) with equimolar amounts of H2C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product Cp2ZrOCH(CME=CH2)C(SiMe3)=C(SiMe3)1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [ Cp2ZrOCH=CMeCH2]22 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively. Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination.