NNNO‐Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins

Main advances in the application of scorpionate-based catalytic systems for the preparation of sustainable polymers

Scorpionate ligands have emerged as pivotal components in the field of coordination chemistry and catalysis since the seminal work by Trofimenko in the late 1960s. These species have demonstrated an extraordinarily rich tridentate coordination chemistry, enhancing the stability of metal complexes. In addition, they offer the possibility of modifying the chemical and electronical features as κ3-ligands, providing a wide variety of potential substrates with multiple donor atoms. Furthermore, this type of ligand has shown wide versatility in its coordination mode and can adopt different binding arrangements, expanding its potential as a universal ligand. This review provides a comprehensive overview of the main advances in exploring scorpionate complexes based on the tris(1H-pyrazol-1-yl)borate and bis(1H-pyrazol-1-yl)methane moieties, which have been recently reported as efficient catalysts for the synthesis of sustainable polymers. Specifically, this work focuses on the preparation of biorenewable polylactides (PLAs), other polyesters and polycarbonates (PCs), derived from cyclohexene carbonate, polylactide-co-polycarbonate copolymers and alternative sustainable polymeric materials. Thus, we have faced this challenge by selecting and classifying the most well-performed scorpionate catalyst system, including divalent (magnesium, calcium, zinc and iron) and other metals (rare-earth metals and zirconium), for each of the catalytic processes mentioned above. This review represents the first contribution that summarises and illustrates the current state of the art related to the use of scorpionate-based systems as efficient catalysts for the preparation of sustainable polymer materials. This account finally aims to guide future research towards the development of more eco-friendly catalytic processes in promoting sustainable polymers to achieve relevant commodities.

Olefin Metathesis by First-Row Transition Metals

Catalytic olefin metathesis based on the second- and third-row transition metals has become one of the most powerful transformations in modern organic chemistry. The shift to first-row metals to produce fine and commodity chemicals would be an important achievement to complement existing methods with inexpensive and greener alternatives. In addition, those systems can offer unusual reactivity based on the unique electronic structure of the base metals. In this Minireview, we summarize the progress of the development of alkylidenes and metallacycles of first-row transition metals from scandium to nickel capable of performing cycloaddition and cycloreversion steps, crucial reactions in olefin metathesis. In addition, we will discuss systems capable of performing olefin metathesis; however, the nature of active species is not yet known.

Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

The production of 1-butene by ethylene dimerization is an important chemical industrial process currently implemented using homogeneous catalysts. Here, we describe a highly active heterogeneous catalyst (Ni-ZIF-8) for ethylene dimerization, which consists of isolating Ni-active sites selectively located on the crystal surface of a zeolitic imidazolate framework. Ni-ZIF-8 can be easily prepared by a simple one-pot synthesis method in which site-specific anchoring of Ni is achieved spontaneously because of the incompatibility between the d⁸ electronic configuration of Ni²⁺ and the three-dimensional framework of ZIF-8. The full exposure and square-planar coordination of the Ni sites accounts for the high catalytic activity of Ni-ZIF-8. It exhibits an average ethylene turnover frequency greater than 1 000 000 h^-1 (1-butene selectivity >85%) at 35 °C and 50 bar, far exceeding the activities of previously reported heterogeneous catalysts and many homogeneous catalysts under similar conditions. Moreover, compared to molecular Ni complexes used as homogeneous catalysts for ethylene dimerization, Ni-ZIF-8 has significantly higher stability and shows constant activity during 4 h of continuous reaction. Isotopic labeling experiments indicate that ethylene dimerization over Ni-ZIF-8 follows the Cossee-Arlman mechanism, and detailed characterizations combined with density functional theory calculations rationalize this observed high activity.