ONO pincer type ligand complexes of Al(III) as efficient catalyst for chemical fixation of CO 2 to epoxides at atmospheric pressure Habib Ullah a,b , Bibimaryam Mousavi a,⇑ , Hussein A. Younus e , Zafar A.K. Khattak a,b , Suleman Suleman a,b , Muhammad T. Jan f , Baoyi Yu g , Somboon Chaemchuen a , Francis Verpoort a,b,c,d,⇑ a State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, PR China b School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, PR China c Center for Environmental and Energy Research (CEER), Ghent University Global Campus, 119 Songdomunhwa-Ro, Yeonsu-Gu, Incheon 21985, South Korea d National Research Tomsk Polytechnic University, Lenin Avenue 30, 634050 Tomsk, Russian Federation e Department of Chemistry, Faculty of Science, Fayoum University, Fayoum 63514, Egypt f Department of Chemistry, Islamia College University, Peshawar, KPK, Pakistan g Key Laboratory of Urban Agriculture (North China), Ministry of Agriculture, College of Biological Sciences Engineering, Beijing University of Agriculture, Beijing 102206, PR China article info Article history: Received 13 January 2019 Revised 12 July 2019 Accepted 15 July 2019 Keywords: CO 2 fixation Pincer ligand Aluminium complexes Cyclic carbonate Homogeneous catalysis abstract Carbon dioxide, the main cause of environmental pollution, its utilization to produce valuable products is of utmost interest. A series ONO pincer hydrazone based most active mono-nuclear Al(III) complexes were successfully synthesized and characterized with the help of NMR, IR, mass spectrometry and only complex 2a was confirmed by single-crystal analysis. The synthesized Al(III) complexes were then employed as capable catalysts for the solvent-free chemical fixation of CO 2 with epoxides at atmospheric pressure and could be reused five times without loss of any catalytic activity. In addition, the catalytic mechanism was investigated by analyzing intermediates via 1 H NMR, 13 C NMR, and mass MALDI-TOF. The excellent catalytic performance could be due to simultaneous attack and the opening of the epoxide by metal centers to form an alkoxide ion which activates the CO 2 the same time. Ó 2019 Elsevier Inc. All rights reserved. 1. Introduction Worldwide industrialization and rapid urbanization are posing serious threats to our environment due to the large-scale anthro- pogenic production of CO 2, which is greatly affecting the concept of green chemistry. Global warming and greenhouse effect are mainly originating from the CO 2 emission 1 . Nevertheless, the sci- entific community is taking a great and ever-increasing interest in the CO 2 transformation into valuable chemical products. Because of its abundance, ready availability, non-toxic and reusa- ble nature, CO 2 is a valuable one-carbon (C1) building block in organic transformations [1–3]. As a well-known fact, CO 2 has a high thermodynamic stability and kinetic inertness due to the car- bon is in its highest oxidation state hence making it a challenge to activate and valorise CO 2 to valuable products. Among the various approaches employed for CO 2 utilization, synthesis of cyclic car- bonates and polycarbonates from the chemical fixation of CO 2 to epoxides, are extensively studied and even well commercialized [2,4,5]. Environment-friendly and 100% atom efficient, the redox neutral fixation of CO 2 to epoxides to form cyclic carbonates with no appreciable toxicity [6–9] is specifically investigated in recent years because of its numerous uses as solvents, electrolytes, syn- thetic building blocks, fine chemicals, industrial lubricants and as monomers for polymers [10–14]. Over the past two decades, huge progress has been made in the chemical fixation of CO 2 to epoxides which can be clearly observed from the increase in the number of publications since 2000 [15]. Various metal complexes based on zinc [16–19], chromium [20–22], iron [23–26], cobalt [27–33], magnesium [17,34], vanadium [35–37], tin [38] etc. have been reported as catalyst for the CO 2 cycloaddition to epoxides. Among the metal complexes, aluminium has been extensively studied for the CO 2 /epoxides cycloaddition. This due to its environment- friendly nature, earth abundance, nontoxicity, and high Lewis acid- ity making aluminium the ideal choice for the ring-opening of epoxides [39]. Various research groups reported the CO 2 /epoxides cycloaddition with salen and related ligand-based monometallic [27,40–44] and bimetallic [39,45–50] aluminium complexes. Amongst the aluminium complexes, bimetallic aluminium(salen) complexes [51,52] reported by North and other groups [50] are https://doi.org/10.1016/j.jcat.2019.07.033 0021-9517/Ó 2019 Elsevier Inc. All rights reserved. ⇑ Corresponding authors at: State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, PR China. E-mail address: Francis.verpoort@ghent.ac.kr (F. Verpoort). Journal of Catalysis 377 (2019) 190–198 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat