Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1. Synthesis and Characterization

Abstract

Various silica-supported acetylacetonate and alkoxy zirconium(IV) complexes have been prepared and characterized by quantitative chemical measurements of the surface reaction products, quantitative surface microanalysis of the surface complexes, in situ infrared spectroscopy, CP-MAS 13 C NMR spectroscopy and EXAFS. The complex A C H T U N G T R E N N U N G ( SiO)ZrA C H T U N G T R E N N U N G (acac) 3 (acac = acetylacetonate ligand) (1) can be obtained by reaction of zirconium tetra- 4 ] with a silica surface previously dehydroxylated at 500 8C. The complexes 3 Zr À H with, respectively, acetylacetone and nbutanol at room temperature. The spectroscopic data, including EXAFS spectroscopy, confirm that in compound 1 the zirconium is linked to the surface by only one Si À O À Zr bond whereas in the case of compounds 2 and 3 the zirconium is linked to 3 surface oxygen atoms which are sigma bonded. EXAFS data indicate also that the acetylacetonate ligands behave as chelating ligands leading to a hepta-coordination around the zirconium atom in 1 and a penta-coordination in 2. In order to provide a molecular analogue of 1, the synthesis of the following polyoligosilsesquioxane derivative (c-C 5 H 9 ) 7 (1') was achieved. The compound 1' is obtained by reacting (c-C 5 H 9 ) 7 Si 8 O 11 A C H T U N G T R E N N U N G (CH 3 ) 2 (OH), 4, with an equimolecular amount of ZrA C H T U N G T R E N N U N G (acac) 4 . In the same manner, syntheses of complexes (c-C 5 H 9 ) 7 Si 7 O 12 ZrA C H T U N G T R E N N U N G (acac) (2') and of (c-C 5 H 9 ) 7 Si 7 O 12 ZrA C H T U N G T R E N N U N G (O-n-Bu) (3') were achieved by reaction of the unmodified trisilanol, (c-C 5 H 9 ) 7 Si 7 O 9 (OH) 3 , with respectively ZrA C H T U N G T R E N N U N G (acac) 4 and ZrA C H T U N G T R E N N U N G (O-n-Bu) 4 at 60 8C in tetrahydrofuran. Compounds 1', 2' and 3' can be considered as good models of 1, 2 and 3 since their spectroscopic properties are comparable with those of the surface complexes. The synthetic results obtained will permit us to study the catalytic properties of these surface complexes and of their molecular analogues with the ultimate goal of delineating clear structure-activity relationships.

Improved promoter effect in NiWS catalysts through a molecular approach and an optimized Ni edge decoration

“…This clearly highlights that previous enhancements provided by the CSC method are linked to the highly reactive W ethoxy precursor. In this peculiar case, IR and GC/MS analyses (Supporting Information) performed on Ni(W) materials and the liquid phase after deposition, respectively, suggest a release of acac ligands from the Ni coordination sphere, and their reaction with reactive groups of the ASA support (as proposed for similar complexes deposited onto Al 2 O 3[31] or SiO 2[32]) or surface W-ethoxy species. Overall, the formation of surface species containing both Ni and W would favour a more intimate contact between them during sulfide formation, which could explain the higher catalytic performances of CSC catalysts.…”

Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity, Recycling and Regeneration

“…Three silica-supported acetylacetonate and butoxy Zr(IV) complexes with different coordination spheres and links with the silica support have been prepared and fully characterized in Part 1 of this series of papers (for more details see ref. [13] ). ( SiO)ZrA C H T U N G T R E N N U N G (acac) 3 (acac = acetylacetonate ligand) (1) was obtained by direct reaction of ZrA C H T U N G T R E N N U N G (acac) 4 with silica (500) whereas ( SiO) 3 ZrA C H T U N G T R E N N U N G (acac) (2) and ( SiO) 3 ZrA C H T U N G T R E N N U N G (O-n-Bu) (n-Bu = butyl ligand) (3) were synthesized by reaction of ( SiO) 3 Zr À H with, respectively, acetylacetone and n-butanol at room temperature.…”

“…Polyoligosilsesquioxane analogues for each of the supported species have also been prepared from the trisilanol, (c-C 5 H 9 ) 7 Si 7 O 9 (OH) 3, to produce tripodal molecular models and from its derivative blocked on two silanol groups, (c-C 5 H 9 ) 7 Si 8 O 11 A C H T U N G T R E N N U N G (CH 3 ) 2 (OH), to provide monopodal models. [13] Catalytic Tests Protocol: The liquid phase transesterification of ethyl acrylate by n-butanol was chosen as a model reaction to evaluate the performance of the solid catalysts as well as that of their molecular analogues. The reaction was followed to equilibrium at a temperature of around 70 8C with an equimolar amount of ethyl acrylate and n-butanol.…”

“…This was accomplished via surface organometallic chemistry by extending established work from our laboratory on supported zirconium complexes. [12] We have described in part 1 of this series of publications [13] the synthesis and the characterization of three relatively well defined silica-supported acetylacetonate and butoxy zirconium(IV) complexes linked to the surface by one or three siloxane bonds, ( SiO) (2), and ( SiO) 3 ZrA C H T U N G T R E N N U N G (O-n-Bu) (3) as well as the synthesis of their soluble polyoligosilsesquioxy analogues (c- Figure 1). We wish now to examine the catalytic behaviour of these supported and molecular complexes in the transesterification of acrylates, the recycling of the surface species, easier to recover after the catalysis than their soluble analogues, and explore the question of catalyst ageing and regeneration.…”

“…Recall that, in Part 1 of this series of reports, [13] a series of silica-supported zirconium acetylacetonate and alkoxide complexes and their polyoligosilsesquioxane analogues were synthesized and fully characterized by a series of spectroscopic and chemical techniques. These complexes were submitted to the standard catalytic reaction protocol described above, together with the homogeneous benchmark catalysts, …”