Silsesquioxane Lego Chemistry : Catalytic Receptor Ensembles for Alkene Epoxidation
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Silsesquioxane lego chemistry : catalytic receptor ensembles for alkene epoxidation Citation for published version (APA): Gerritsen, G. (2011). Silsesquioxane lego chemistry : catalytic receptor ensembles for alkene epoxidation. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR719867 DOI: 10.6100/IR719867 Document status and date: Published: 01/01/2011 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 01. Oct. 2021 Silsesquioxane Lego Chemistry: Catalytic receptor ensembles for alkene epoxidation PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de rector magnificus, prof.dr.ir. C.J. van Duijn, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op dinsdag 13 december 2011 om 14.00 uur door Gijsbert Gerritsen geboren te Nijkerk Dit proefschrift is goedgekeurd door de promotoren: prof.dr. D. Vogt en prof.dr. R.A. van Santen Copromotor: dr. H.C.L. Abbenhuis Gerritsen, G. Silsesquioxane Lego Chemistry: Catalytic receptor ensembles for alkene epoxidation Technische Universiteit Eindhoven A catalogue record is available from the Eindhoven University of Technology Library ISBN: 978-90-386-3029-8 Subject headings: silsesquioxane modification, titanium, epoxidation, catalyst stability. Copyright © 2011 by G. Gerritsen Het in dit proefschrift beschreven onderzoek is uitgevoerd onder auspiciën van de National Research School Combination Catalysis (NRSC‐C) met ondersteuning van de Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO, programma Combinatoriële Chemie) en ondersteuning van Hybrid Catalysis B.V. Coverontwerp: F. Goris en G. Gerritsen Gedrukt bij de Universiteitsdrukkerij, Technische Universiteit Eindhoven Contents Chapter 1. General introduction and the scope of this thesis 1 Chapter 2. Practical routes to functionalized silsesquioxane compounds 15 Chapter 3. Functionalized silsesquioxane triols for catalysis research 39 Chapter 4. Synthesis and characterization of Titanium silsesquioxanes with 61 organofunctionalized ancillaries Chapter 5. Titanium silsesquioxanes screened in catalytic epoxidation 91 Summary 107 Samenvatting 111 Dankwoord 115 List of publications 117 Curriculum vitae 119 Chapter 1 General introduction and the scope of this thesis _____________________________________________________________________ Abstract: The history and the latest developments in silsesquioxane chemistry are reviewed. Especially the state of the art of the application of metal-containing silsesquioxane derivatives in catalysis is provided. The scope of this thesis is revealed and relates to bio-inspired, silsesquioxane-based catalytic ensembles, enabling more sustainable epoxidation chemistry. ___________________________________________________________ 1.1 Introduction As reported by Sprung and Günther in 1955, silsesquioxanes appeared as white precipitates in silane polymerizations.1 The name silsesquioxane, (in which ‘sil’ stands for silicon, ‘sesqui’, comes from Latin semisque, “and a half”, and ‘oxane’ refers to any saturated oxygen compound) refers to any compound in which the ratio of Si to O is 1.5, meaning that silicon is trivalent towards oxygen, leaving its fourth valency to another substituent, typically H or an organic group. This results in a general formula of (RSiO1.5)n (for integer oxygen numbers, n must be an even number). This also includes polymeric and resinous materials. The most interesting class are molecular silsesquioxanes, also referred to as POSSTM (Polyhedral Oligomeric SilSesquioxanes, a trademark of Hybrid Plastics Inc.). The POSS compounds can be divided into completely condensed structures, (Fig. 1.1), corresponding with (RSiO1.5)n (n = 4, 6, 8, 10, 12), and incompletely condensed silsesquioxanes, containing silanol groups and being of a more complex genral 2 formula (Fig. 1.2). -1- Chapter 1 O Si O O Si O O O Si Si Si Si Si Si O O O Si O O O O O Si Si Si Si Si Si O Si O O O O O Si Si O O O O O O O O O O Si O O O O Si Si O Si O O O O Si O Si O O Si O O O O Si O Si O Si O O Si O Si Si O O O Si Si O Si Si O Si Si O Si O Si O Si O R4 R6 R8 R10 R12 T4 T6 T8 T10 T12 Fig. 1.1 Completely condensed silsesquioxane structures An easier notation for silsesquioxanes is Tn, for completely condensed structures and Tn(OH)m for OH-containing structures. The T stands for a corner silicon atom, bonded to three oxygen atoms. Though n and m are dependent, for a quick recognition, they are treated as independent. So T4 stands for R4Si4O6. 3 Tetrameric silsesquioxanes are only known with R = i-C3H7 and t-C4H9 , whereas 4 hexamers are known for R = c-C5H9 and c-C6H11 , though the scope has been 5 expanded more recently with i-C4H9, n-octyl, Ph, (CH2)2CMe2CH2CO2Me . Octameric silsesquioxanes are encountered more generally with a variety of alkyl, substituted alkyl, cycloalkyl and aromatic organic groups. The isobutyl group, has a strong tendency to form octamer T8. Larger aggregates T10 and T12 are generally known for R = H, Me, Vinyl and Phenyl. Incompletely condensed silsesquioxanes have two origins: Like completely condensed silsesquioxanes, a) direct synthesis through hydrolytic condensation of silane starting materials, such as trialkoxysilanes (RSiOR’)3 or trichlorsilanes (RSiCl3) under appropriate conditions or b) silyl ether opening of completely condensed silsesquioxanes. OH O Si O Si OH O Si O Si OH Si O OH OH HO HO O O O O Si Si OH Si Si O OH Si Si OH Si Si OH O Si Si O O O O O OH O OH O O O O O Si OH O O O Si O Si Si O Si Si O Si R O O O Si Si O O O O R6 Si O Si Si O Si Si O Si R7 R8 R8 Silanetriol T6(OH)4 T7(OH)3 T8(endo-OH)2 T8(exo-OH)2 Fig.1.2 Incompletely condensed silsesquioxane structures -2- Chapter 1 1.2 Metal-containing silsesquioxanes Feher et al. initiated the research towards the use of silsesquioxane molecules as ligands for main group and transition metals at the end of the 1980s,6 considering silsesquioxanes as models for industrially used silica supports. The resemblance of silsesquioxanes to silica supports is not only apparent from the molecular structure, but the electronic properties of silsesquioxane silanol groups mimic the behavior of silica as well. Important characteristics which can be replicated in silsesquioxane chemistry include electron withdrawing bonding sites,7 interactions with adjacent oxygen donors8 which contribute to the stability of clusters grafted onto surfaces,[8] and a defined orientation of surface hydroxyl groups which can dictate the selectivity by which reagents react with the surface. For example, the considerably enhanced alkene metathesis activity of surface carbene complexes over those of their homogeneous analogues, has been similarly exhibited in silsesquioxane chemistry.9 In Figure 1.3, a few important structural similarities between silsesquioxanes and schematized silica surfaces are depicted. First of all, the defined orientation of the silanol groups, which is also present in silsesquioxanes, may ensure a strong multi-dentate bonding to metals. Furthermore, silsesquioxanes have enough residual siloxane bridges to resemble the silica surface and these residual siloxane bridges can interact with the metal. defined orientation of surface hydroxyl groups OH interactions with adjacent oxygen atoms HO Si O O Si O Si Si O M O O Si O Si O O O HO Si O Si Si O Si O O Si O Si O O Si as electron withdrawing as a CF3 group Fig. 1.3 Schematic overview of a silica-based catalyst support, indicating important surface properties Since the discovery of silsesquioxanes, a rich coordination chemistry has been developed with metals and metalloids throughout the periodic table; at present, these involve: Li, Na, K, Be, Mg, Sc, Y, La, U, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Ru, -3- Chapter 1 Os, Co, Rh, Pt, Cu, Au, Zn, Al, Ga, Tl, Ge, Sn, Pb, As, Sb, Bi. Metal-containing silsesquioxanes have been subject to several reviews.10 1.3 Catalysis with metal-containing silsesquioxanes Metal-containing silsesquioxane derivatives provide new catalysts with both homogeneous and heterogeneous applicability. The steric and electronic properties of silsesquioxane silanolate ligands render metal centers more Lewis acidic than conventional alkoxide or siloxide ligands do.