title: A Multifunctional Pincer Ligand Supports Unsaturated Cobalt: Five Functionalities in One Pincer.
abstract: A pyridyl pincer ligand was developed to incorporate steric bulk, through a PtBu2arm, and proton responsivity, through a pyrazole pincer ligand arm, together with reactivity at benzylic hydrogen and redox activity within a 1,4 diazabutadiene moiety. Binding it to CoCl2yielded square-pyramidal [(PNNH)CoCl2], which was deprotonated by Li[N(SiMe3)2] to form [{Li(THF)2PNN}CoCl2]. Reduction of this LiCl adduct with KC8under CO atmosphere led to formation of CoImono- and dicarbonyl complexes, which can be protonated but also further deprotonated at the benzylic CH group to give a dearomatized pyridyl group. The ligand was characterized in its neutral, monoanionic, and dianionic forms, and the anions were shown to exist as intimate ion pairs with Li+bound to pyrazolate N and chloride bound to Lewis acidic cobalt. X-ray photoelectron spectroscopy was used to assay both Li content and cobalt oxidation states. The general character of binding of LiCl to a metal complex acidic at metal and nucleophilic at ligand (pyrazolate Nβ) is discussed, as are potential catalytic applications of the concept.
authors.affiliation: Department of Chemistry, Indiana University Bloomington, Bloomington, IN, 47405, USA.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Polezhaev
authors.affiliation: Department of Chemistry, Indiana University Bloomington, Bloomington, IN, 47405, USA.
authors.forename: Chun-Hsing
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Indiana University Bloomington, Bloomington, IN, 47405, USA.
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Losovyj
authors.affiliation: Department of Chemistry, Indiana University Bloomington, Bloomington, IN, 47405, USA.
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Caulton
keywords: N,P ligands; cobalt; frustrated Lewis pairs; ligand design; pincer ligands