Stephan Gießmann

Disiloxanediolates and polyhedral metallasilsesquioxanes of the early transition metals and f-elements

Abstract Two modern areas of metallasiloxane chemistry are reviewed. The first part deals with the preparation and structural characterization of the first f-element compounds derived from tetraphenylsisiloxanediol. In the second part recent developments in the chemistry of polyhedral metallasilsesquioxanes are surveyed, with special emphasis being placed on early transition metal and f-element derivatives. Also highlighted are applications of these species in catalysis research.

Silsesquioxane Chemistry, 4.: Silsesquioxane Complexes of Titanium(III) and Titanium(IV)

Abstract Reaction of the incompletely condensed silsesquioxane derivative Cy7Si7O9(OH)3 (1) with Ti(OEt)4 affords the dimeric titanasilsesquioxane [(Cy7Si7O12)Ti(μ-OEt)(EtOH)]2 (13) in 81% yield. The known titanasilsesquioxane [Cy7Si7O11(OSiMe3)]2Ti (18) has been prepared through a modified procedure starting from titanium tetraalkoxides. Novel oxotitanium silsesquioxane derivatives are obtained from reactions of titanocene dihalides with Cy7Si7O9(OH)2(OSiMe3) (14). Cp2TiCl2 yields dinuclear (μ-O)[{Cy7Si7O11(OSiMe3)}TiCp]2 (19), while with Cp*2TiCl2 the trinuclear titanacycle Cp*2Ti3O3[Cy7Si7O11(OSiMe3)]2 (20) is obtained. In addition, a new synthetic route to model compounds for titanium catalysts immobilized on silica has been developed. Disilylated Cy7Si7O9(OH)(OSiMe3)2 (15) cleanly reacts with the ‘tucked-in’ fulvene complex Cp*Ti(C5Me4CH2) to give the titanium(III) silsesquioxane Cp*2Ti[Cy7Si7O10(OSiMe3)2] (21). In a similar manner treatment of Cp*Ti(C5Me4CH2) with Cy7Si7O9(OH)2(OSiMe3) (14) affords the mono(pentamethylcyclopentadienyl) complex Cp*Ti[Cy7Si7O11(OSiMe3)][Cy7Si7O10-(OH)(OSiMe3)] (22) which is an advanced model compound for a catalytically active titanium center on a silica surface. The molecular structures of these titanium silsesquioxane derivatives have been determined by X-ray diffraction analyses.

Silsesquioxane Chemistry, 5. Retention of the Cu4O4 core upon formation of the first copper(I) silsesquioxane from tetrameric copper(I)-t-butoxide

Abstract The first copper(I) silsesquioxane derivative, Cu4O4[Cy7Si7O9(OSiMe3)]2 (4) was prepared by reacting tetrameric copper(I)-t-butoxide, (CuOtBu)4 (3), with the monosilylated silsesquioxane precursor Cy7Si7O9(OH)2(OSiMe3) (2) in a 1:2 molar ratio. An X-ray diffraction study revealed the presence of a centrosymmetric dimer. A slightly puckered Cu4O4 ring forms the central part of a complex structure comprising nine eight-membered inorganic ring systems.

Silsesquioxane Chemistry II. Tin(IV) and Hafnium(IV) Compounds of Silsesquioxanes

Summary. Four complexes of silsesquioxanes with di- and triorganotin(IV) cations have been prepared; their composition was determined by standard analytical and spectroscopic methods. The results show that complexes containing an organotin(IV) moiety and the ligand in a 1:1 ratio are formed. FTIR spectra are consistent with the presence of Sn*O vibrations in the compounds. The structure of the complexes is discussed on the basis of Mößbauer and multinuclear (1H, 13C, 119Sn, and 29Si) NMR spectroscopic measurements. Comparison of the experimental quadrupole splitting (QS) with that calculated on the basis of the partial quadrupole splitting (PQS) concept revealed that the complexes formed with dialkyltin(IV) cations as well as the trialkyl derivatives have a regular tetrahedral structure. A new organohafnium silsesquioxane derivative ([Cy7Si7O12Hf(C5Me5)], Cy=cyclohexyl, 5), was prepared by treatment of [Cy7Si7O9(OH)3] with (C5Me5)HfMe3 under elimination of methane. The molecular structure of 5 was determined by X-ray crystallography.Zusammenfassung. Vier Komplexe von Silsesquioxanen mit Di- und Triorganozinn(IV)-Kationen wurden hergestellt; ihre Zusammensetzung wurde mit analytischen und spektroskopischen Standardmethoden bestimmt. Die Ergebnisse zeigen, daß in den gebildeten Komplexen Organozinneinheit und Ligand im Verhältnis von 1:1 vorhanden sind. FTIR-Spektren stehen im Einklang mit dem Auftreten von Sn*O-Schwingungen in den Verbindungen. Die Struktur der Komplexe wird auf der Grundlage von Mößbauer-Spektren und multinuklearen NMR-Experimenten (1H, 13C, 119Sn, 29Si) diskutiert. Ein Vergleich der experimentell beobachteten Quadrupolaufspaltung (QS) mit nach dem Konzept der partiellen Quadrupolaufspaltung (PQS) berechneten Werten ergab sowohl für die mit dem Dialkyzinn(IV)-Kation gebildeten Komplexe als auch für die Trialkylderivate eine regelmäßige tetraedrische Struktur. Ein neues Organohafniumsilsesquioxanderivat ([Cy7Si7O12Hf(C5Me5)], Cy=Cyclohexyl, 5) wurde durch Umsetzung von [Cy7Si7O9(OH)3] mit (C5Me5)HfMe3 unter Abspaltung von Methan hergestellt; seine Molekülstruktur wurde mittels Röntgenstrukturanalyse bestimmt.

A novel route to advanced model systems for silica-immobilized olefin polymerization catalysts

Constituting a novel synthetic route to model compounds for titanium catalysts immobilized on silica, the disilylated silsesquioxane derivative Cy7Si7O9(OH)(OSiMe3)2 2a, has been reacted with the ‘tucked-in’ fulvene complex Cp*Ti- (C5Me4CH2) to give the titanium(III) silsesquioxane Cp*2Ti[Cy7Si7O10(OSiMe3 )2] 3, while treatment of Cp*Ti- (C5Me4CH2) with Cy7Si7O9(OH)2(OSiMe3 ) 2b affords the mono(pentamethylcyclopentadienyl) complex Cp*Ti[Cy7- Si7O11(OSiMe3)][Cy7Si7 O10(OH)(OSiMe3)] 4 which is an advanced model compound for a catalytically active titanium center on a silica surface.