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The preparation and structural characterization of a series of group 4 complexes supported by 2,2'-phenylphosphinobis(4,6-di-tert-butylphenolate) ([OPO]2-) are described. The reaction of either H2[OPO] with Ti(OR)4 (R = Et, iPr) or Li2[OPO] with TiCl4(THF)2 produced yellowish-orange crystals of Ti[OPO]2, regardless of the stoichiometry of the starting materials employed. Comproportionation of the bis-ligand complex Ti[OPO]2 with 1 equiv of TiCl4(THF)2 led to the formation of [OPO]TiCl2(THF) as brownish-red crystals. Surprisingly, treatment of H2[OPO] with [(Me3Si)2N]2MCl2 (M = Zr, Hf), irrespective of the molar ratio, generated colorless crystals of the corresponding bis-ligand complex [OPO]2M(OH2) as an aqua adduct. The solution and solid-state structures of these group 4 complexes were all characterized by multinuclear NMR spectroscopy and X-ray crystallography, respectively.

Limited availability of fossil energy and serious environmental pollution have caused the emergence of bio‐oil, which can serve as an alternative and promising green energy source. However, bio‐oil generated from the rapid pyrolysis of biomass cannot be utilized immediately owing to its corrosivity, instability, and low heating value. Herein, the electrocatalytic hydrogenation (ECH) process towards bio‐oil upgrading is reviewed. Specifically, the ECH integrates the advantages of mild operating conditions, no petrochemically derived hydrogen and good controllability. The influence of different factors on the conversion of bio‐oil components and product selectivity in the ECH process are presented comprehensively. In addition, various reaction mechanisms are discussed in the designed ECH systems. Finally, some challenges need to be further overcome for real bio‐oil reduction in the ECH process: exploration of efficient multifunctional electrocatalysts for specific bio‐oil components and determination of the dominant steps in the complicated reaction path network.

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