Bioinspired Redox Active Pseudotetrahedral Ni(II) Thiolate and Phenolate Complexes: Synthesis, Characterization, Alkylation Kinetics and Molecular Oxygen Activation

A series of new environmentally and catalytically significant bioinorganic redox active pseudotetrahedral Ni(II) thiolate and Ni(II) phenolate (S=1, d⁸) complexes were synthesized and fully characterized as small molecular models in order to study the coordination mode of the Ni-S bond that is biologically significant in anaerobic and archaebacterial enzymes. During this characterization a unique Ni-S ligation mode was discovered and modulated by steric titration and details were further investigated. Nickel thiolate bond reactivity towards electrophilic alkylation with methyl iodide (MeI) is briefly discussed. A series of new Ni(II) phenolate complexes were synthesized and characterized as well as their O₂ activation activity were investigated as a model for nickel substituted Copper Amine Oxidase (CAO). During this O₂ reduction investigation, depending on the ligand bulk on the parent Tp^Ph,Me/Tp^Me,Me ligand (where, Tp^Ph,Me= hydrotris{3-phenyl-5-methyl pyrazol-1-yl}borate; Tp^Me,Me= hydrotris{3,5-dimethyl pyrazol-1-yl}borate) either a C-H or a C=C bond activation was observed. In addition, surprisingly where C-H activation was not possible, a CO₂ capture activity was observed by a reactive intermediate nickel species.