Redox chemistry and H-atom abstraction reactivity of a terminal zirconium() oxo compound mediated by an appended cobalt() center

• Published in: Chemical science (Cambridge) Vol. 11; no. 39; pp. 1729 - 1736
• Main Authors: Zhang, Hongtu, Hatzis, Gillian P, Dickie, Diane A, Moore, Curtis E, Thomas, Christine M
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.10.2020; Royal Society of Chemistry (RSC); The Royal Society of Chemistry
• Subjects: Basicity; Chemical reduction; Chemistry; Cobalt compounds; Crystallography; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Oxidation
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d0sc04229c

The reactivity of the terminal zirconium( iv ) oxo complex, O&z.tbd;Zr(MesNP i Pr 2 ) 3 CoCN t Bu ( 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 Ph 3 C * to afford the Zr IV /Co 0 complexes [(μ-Na)OZr(MesNP i Pr 2 ) 3 CoCN t Bu] 2 ( 3 ) and Ph 3 COZr(MesNP i Pr 2 ) 3 CoCN t Bu ( 4 ), respectively. Based on the cyclic voltammogram of 2 , Ph 3 &z.rad; 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 Ph 3 C + . Accordingly, 2 reacts readily with [Ph 3 C][BPh 4 ] and Ph 3 CCl to afford [Ph 3 COZr(MesNP i Pr 2 ) 3 CoCN t Bu][BPh 4 ] ( [5][BPh 4 ] ) and Ph 3 COZr(MesNP i Pr 2 ) 3 CoCl ( 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(MesNP i Pr 2 ) 3 CoCN t Bu] + ( [9] + ). Thus it is posited that the transient [OZr(MesNP i Pr 2 ) 3 CoCN t Bu] + [ 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. Bimetallic cooperativity is demonstrated with a Co/Zr complex featuring both nucleophilic Zr( iv ) oxo and redox active Co sites.