Chlorodiethylaluminum supported on silica: A dinuclear aluminum surface species with bridging μ2-Cl-ligand as a highly efficient co-catalyst for the Ni-catalyzed dimerization of ethene

doi:10.1016/j.jcat.2014.02.006

Journal of Catalysis

Volume 313, May 2014, Pages 46-54

https://doi.org/10.1016/j.jcat.2014.02.006 Get rights and content

Highlights

•
Highly efficient supported co-catalysts for the Ni-catalyzed ethene dimerization.
•
Silica-supported Et₂AlCl co-catalysts prepared via Surface Organometallic Chemistry.
•
Silica-supported dinuclear alkylaluminum species with μ²-Cl bridge.
•
Characterization by high-fields 27Al SS-NMR and NMR signatures calculations using DFT.

Abstract

Silica-supported chloro alkyl aluminum co-catalysts (DEAC@support) were prepared via Surface Organometallic Chemistry by contacting diethylaluminum chloride (DEAC) and high specific surface silica materials, i.e. SBA-15, MCM-41, and Aerosil SiO₂. Such systems efficiently activate NiCl₂(PBu₃)₂ for catalytic ethene dimerization, with turnover frequency (TOF) reaching up to 498,000 mol_C2H4/(mol_Ni h) for DEAC@MCM-41. A detailed analysis of the DEAC@SBA-15 co-catalyst structure by solid-state aluminum-27 NMR at high-field (17.6 T and 20.0 T) and ultrafast spinning rates allows to detect six sites, characterized by a distribution of quadrupolar interaction principal values C_Q and isotropic chemical shifts δ_iso. Identification of the corresponding Al-grafted structures was possible by comparison of the experimental NMR signatures with these calculated by DFT on a wide range of models for the aluminum species (mono- versus di-nuclear, mono- versus bis-grafted with bridging Cl or ethyl). Most of the sites were identified as dinuclear species with retention of the structure of DEAC, namely with the presence of μ²-Cl-ligands between two aluminum, and this probably explains the high catalytic performance of this silica-supported co-catalysts.

Graphical abstract

Introduction

Many catalytic systems require co-catalysts or activators to form the highly reactive intermediates necessary for efficient catalytic cycles [1], [2]. In olefin oligomerization/polymerization, alkylaluminums have long been recognized as superior co-catalysts [1], [3], [4], [5], [6], [7], [8], [9]. For example, methylaluminoxane (MAO) is among the best co-catalysts for metal-catalyzed olefin polymerization, despite its unknown structure [10], [11], [12], [13], [14], [15], [16]. In most cases, MAO is used in very large excess (100–2000 equiv. compared to the metal catalysts) [17], [18], [19], [20], [21], [22], which remains a severe problem for industrial processes.

There have been tremendous efforts aimed toward developing alternatives to MAO, in particular heterogeneous variants that could simplify chemical processes [23]. One approach is to support molecular aluminum compounds on large surface area supports [24], [25], [26]. Despite the promise of this method, most materials reported to date result in poor catalytic activity. For example, grafting trialkylaluminum reagents on dehydroxylated silica results in well-defined alkylaluminum environments [27], [28], [29], but generally do not activate transition metal pre-catalysts [30]. One of the reasons for the poor co-catalytic activity is that the silica support is heavily modified by reaction with the trialkylaluminum by alkyl transfer of Al single bond R groups to nearby siloxane bridges $(SiOSi)$ to form surface alkylsilane moieties, which are unreactive toward metal pre-catalysts. The surface Al species are “incorporated” into the silica matrix as Al(OSi)_n species [28], [29], [31]. In contrast, very promising alternative co-catalysts have been found for the ethene oligomerization or polymerization based on chloroalkylaluminum derivatives (2–15 equiv per metal pre-catalysts ratio) [32], [33]. Combining the alkylating properties with the high Lewis acidity from the Cl single bond Al in the chloroalkylaluminum is essential to react with the metal pre-catalyst [34], [35], [36] and to generate the active sites [37], [38].

Here, we describe the preparation of supported diethylaluminum chloride (DEAC) on partially dehydroxylated silica using Surface Organometallic Chemistry [39], [40], [41], their use as co-catalyst in the NiCl₂(PBu₃)₂-catalyzed dimerization of ethene [42], and the detailed characterization of surface species by aluminum-27 solid-state NMR spectroscopy at high-fields and ultrafast spinning rates combined with first principle calculations [29], [31]. We found that the dominating species on the silica surface are bis-grafted dinuclear aluminum surface species with bridging Cl-ligands, which likely account for the very high activities in these materials because the core DEAC structure is conserved on the surface.

Section snippets

Materials

The grafting reaction was carried out under inert atmosphere using dry and freshly distilled solvents. Tetraethoxysilane (TEOS), pluronic P123, pentane, 1 M hexane solution of Et₃Al (TEA) and Et₂AlCl, (DEAC) were purchased from Sigma–Aldrich. Mesoporous SBA-15 and MCM-41 were synthesized following the procedure previously reported in the literature.[43], [44] Aerosil SiO₂ was Aerosil Degussa 200 selling Silicon Dioxide. Elemental analyses were performed at Mikroanalytisches Labor Pascher. Gas

Results and discussion

The solid co-catalysts were prepared by grafting diethylaluminum chloride (DEAC) in pentane/hexanes mixtures on high specific surface area silica, SBA-15 [57], partially dehydroxylated at 500 °C (SBA₅₀₀). SBA₅₀₀ has a silanol coverage of 1.3–1.4 OH nm⁻² (1.5–1.6 mmol g⁻¹; surface area 690 m² g⁻¹). Contacting SBA₅₀₀ with a solution of DEAC results in the evolution of ca. 1 equiv of ethane per surface silanol. Aluminum and carbon elemental analysis were 5.59 and 6.53 wt%, respectively; values which

Acknowledgments

This publication is based on work supported by Award No.UK-C0017, made by King Abdullah University of Science and Technology (KAUST), and by the TGE RMN THC Fr3050. The authors thank the PSMN at ENS of Lyon for the attribution of CPU time.

References (61)

C. Janiak
Coord. Chem. Rev.
(2006)
K.P. Bryliakov et al.
Coord. Chem. Rev.
(2012)
E. Zurek et al.
Prog. Polym. Sci.
(2004)
C. Bianchini et al.
Coord. Chem. Rev.
(2010)
M. Bochmann
J. Organomet. Chem.
(2004)
M. Tada et al.
Coord. Chem. Rev.
(2007)
J.-P. Amoureux et al.
J. Magn. Reson., Ser. A
(1996)
D. Massiot et al.
Res. Ser. A
(1996)
R. Ahlrichs et al.
Chem. Phys. Lett.
(1989)
J. Zhang et al.
J. Mol. Catal. A: Chem.
(2005)

E.Y.-X. Chen et al.

Chem. Rev.

(2000)

M. Bochmann

Organometallics

(2010)

K. Ziegler et al.

Angew. Chem.

(1955)

L.L. Böhm

Angew. Chem. Int. Ed.

(2003)

W. Kaminsky

J. Polym. Sci. Polym. Chem.

(2004)

D.B. Malpass

Commercially available metal alkyls and their use in polyolefin catalysts

R. Gao et al.

Catal. Sci. Technol.

(2013)

H. Sinn et al.

Angew. Chem.

(1980)

W. Kaminsky

J. Chem. Soc., Dalton Trans.

(1998)

L. Negureanu et al.

J. Am. Chem. Soc.

(2006)

W.J.v. Rensburg et al.

Organometallics

(2007)

Z. Boudene et al.

Organometallics

(2012)

W. Kaminsky

Macromolecules

(2012)

G.J.P. Britovsek et al.

Angew. Chem. Int. Ed.

(1999)

S.D. Ittel et al.

Chem. Rev.

(2000)

H. Makio et al.

Chem. Rev.

(2011)

K. Nomura et al.

Dalton Trans.

(2011)

V.C. Gibson et al.

Chem. Rev.

(2003)

G.G. Hlatky

Chem. Rev.

(2000)

L.K. Van Looveren et al.

Angew. Chem. Int. Ed.

(1998)

Cited by (40)

Hosting AlCl<inf>3</inf> on ternary metal oxide composites for catalytic oligomerization of 1-decene: Revealing the role of supports via performance evaluation and DFT calculation
2022, Microporous and Mesoporous Materials
Citation Excerpt :
Generally, the products synthesized by direct employment of pure active species need further treatments including catalyst separation, neutralization, water washing and thorough removal of ionic species, which usually lead to both environmental issues and economic concerns. To address the aforementioned problems, many efforts have been made in recent years to host active species on functionalized supports with the aim to realize the sustainable industrial applications of Lewis acid catalysts [10–12]. For instance, tremendous porous materials such as silica gel [13], activated carbon [14], montmorillonite [15], molecular sieve [16], graphite [17], polystyrene [18], activated alumina [19] have been developed and used as supports of AlCl3, one of the most extensively used Lewis acid catalysts in various chemical conversions.
Enhancing catalytic activity and stability of supported Lewis acid catalysts remain a particular challenge owing to the limited understanding and unsatisfactory tuning of the interplay between the active components and the supports. Herein, upon immobilizing AlCl₃ on a series of ternary metal oxides including La₂O₃–Al₂O₃–SiO₂, NiO–Al₂O₃–SiO₂ and Ga₂O₃–Al₂O₃–SiO₂, we clearly revealed the influence of the compositions and structures of the supports on the catalyst performances through experiments together with density functional theory (DFT) calculations. The catalytic performances of the supported samples were evaluated by oligomerization of 1-decene using both batch reactor and fixed-bed apparatus. The results suggest that the AlCl₃ supported by NiO–Al₂O₃–SiO₂ composites exhibits the highest catalytic activity and stability because of its positive pore structure and thereof the high loading of active species. Importantly, DFT calculations indicate that the variations of the host-guest interaction energy between the ternary oxide composites and AlCl₃ are in good agreement with the experimental results. This study highlights the compositions and structures of the supports are crucial to the catalytic performances of Lewis acid catalysts, and provides fundamental guidance for design of high-performance supported catalysts.
Organometallic Chemistry on Oxide Surfaces
2022, Comprehensive Organometallic Chemistry IV: Volume 1-15
This article describes how functionalities present on three representative oxide surfaces affect structures of organometallic sites supported on these oxides. This is an important strategy to access more active and selective heterogeneous catalysts. We treat the functionalities on oxide surfaces as ligands, and relate the behavior of surface functionalities to concepts familiar to the organometallic chemist who is accustomed to working in solution. We discuss the surface chemistry (i.e. ligand properties) of SiO₂, Al₂O₃, and sulfated metal oxides (SMOs), and show how the surface chemistry of these oxides affects interactions with organometallics, is discussed.
Formation of Strong Boron Lewis Acid Sites on Silica
2024, Inorganic Chemistry
MAO- and Borate-Free Activating Supports for Group 4 Metallocene and Post-Metallocene Catalysts of α-Olefin Polymerization and Oligomerization
2023, Polymers
Effects of surface acidity on the structure of organometallics supported on oxide surfaces
2023, Chemical Communications
Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica
2022, Angewandte Chemie - International Edition

View all citing articles on Scopus

View full text

Chlorodiethylaluminum supported on silica: A dinuclear aluminum surface species with bridging μ2-Cl-ligand as a highly efficient co-catalyst for the Ni-catalyzed dimerization of ethene

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Results and discussion

Acknowledgments

Coord. Chem. Rev.

Coord. Chem. Rev.

Prog. Polym. Sci.

Coord. Chem. Rev.

J. Organomet. Chem.

Coord. Chem. Rev.

J. Magn. Reson., Ser. A

Res. Ser. A

Chem. Phys. Lett.

J. Mol. Catal. A: Chem.

Chem. Rev.

Organometallics

Angew. Chem.

Angew. Chem. Int. Ed.

J. Polym. Sci. Polym. Chem.

Commercially available metal alkyls and their use in polyolefin catalysts

Catal. Sci. Technol.

Angew. Chem.

J. Chem. Soc., Dalton Trans.

J. Am. Chem. Soc.

Organometallics

Organometallics

Macromolecules

Angew. Chem. Int. Ed.

Chem. Rev.

Chem. Rev.

Dalton Trans.

Chem. Rev.

Chem. Rev.

Angew. Chem. Int. Ed.

Chlorodiethylaluminum supported on silica: A dinuclear aluminum surface species with bridging μ²-Cl-ligand as a highly efficient co-catalyst for the Ni-catalyzed dimerization of ethene