Abstract
The reactivity of the terminal zirconium(iv) oxo complex, O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Zr(MesNPiPr2)3CoCNtBu (2), is explored, revealing unique redox activity imparted by the pendent redox active cobalt(i) center. Oxo complex 2 can be chemically reduced using Na/Hg or Ph3C• to afford the ZrIV/Co0 complexes [(μ-Na)OZr(MesNPiPr2)3CoCNtBu]2 (3) and Ph3COZr(MesNPiPr2)3CoCNtBu (4), respectively. Based on the cyclic voltammogram of 2, Ph3˙ should not be sufficiently reducing to achieve the chemical reduction of 2, but sufficient driving force for the reaction is provided by the nucleophilicity of the terminal oxo fragment and its affinity to bind Ph3C+. Accordingly, 2 reacts readily with [Ph3C][BPh4] and Ph3CCl to afford [Ph3COZr(MesNPiPr2)3CoCNtBu][BPh4] ([5][BPh4]) and Ph3COZr(MesNPiPr2)3CoCl (6), respectively. The chemical oxidation of 2 is also investigated, revealing that oxidation of 2 is accompanied by immediate hydrogen atom abstraction to afford the hydroxide complex [HOZr(MesNPiPr2)3CoCNtBu]+ ([9]+). Thus it is posited that the transient [OZr(MesNPiPr2)3CoCNtBu]+ [2]+ cation generated upon oxidation combines the basicity of a nucleophilic early metal oxo fragment with the oxidizing power of the appended cobalt center to facilitate H-atom abstraction.
Highlights
Metal oxo compounds are proposed to play key roles in many essential chemical transformations such as oxidation reactions,1–8 oxygen transfer reactions,9,10 C–H activations,11 and oxygen evolution reactions (OER).12 In order to understand these important oxygenation/oxidation reactions, great efforts have been made to isolate and study the electronic structure and reactivity of metal oxo compounds.Despite the high oxophilicity13 and low d electron counts that should favor metal-oxo multiple bond formation, examples of terminal oxo complexes of group 4 metals (Ti, Zr, Hf) are relatively scarce, especially for Zr and Hf
The reactivity of the terminal zirconium(IV) oxo complex, O^Zr(MesNPiPr2)3CoCNtBu (2), is explored, revealing unique redox activity imparted by the pendent redox active cobalt(I) center
Based on the cyclic voltammogram of 2, Ph3c should not be sufficiently reducing to achieve the chemical reduction of 2, but sufficient driving force for the reaction is provided by the nucleophilicity of the terminal oxo fragment and its affinity to bind Ph3C+
Summary
Metal oxo compounds are proposed to play key roles in many essential chemical transformations such as oxidation reactions,1–8 oxygen transfer reactions,9,10 C–H activations,11 and oxygen evolution reactions (OER).12 In order to understand these important oxygenation/oxidation reactions, great efforts have been made to isolate and study the electronic structure and reactivity of metal oxo compounds.Despite the high oxophilicity13 and low d electron counts that should favor metal-oxo multiple bond formation, examples of terminal oxo complexes of group 4 metals (Ti, Zr, Hf) are relatively scarce, especially for Zr and Hf. It is posited that the transient [OZr(MesNPiPr2)3CoCNtBu]+ [2]+ cation generated upon oxidation combines the basicity of a nucleophilic early metal oxo fragment with the oxidizing power of the appended cobalt center to facilitate H-atom abstraction.
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