The Influence of Nucleophilic and Redox Pincer Character as well as Alkali Metals on the Capture of Oxygen Substrates: The Case of Chromium(II)

Dimeric CrL]₂, where L is the conjugate base of bis-pyrazolyl pyridine, is evaluated for its ability to undergo inner sphere and outer sphere redox chemistry. It reacts with Cp₂Fe⁺ to give Cr₄(HL)₄(μ₄-O)]²⁺, still containing divalent Cr. Reduction (KC₈) of CrL]₂ by two electrons gives K₂(THF)₃Cr₃L₃(μ₃-O)], and by four electrons gives K₄(THF)₁₀Cr₂L₂(μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. K₄(THF)₁₀Cr₂L₂(μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L³⁻ and Cr^II, illustrating that this pincer is proton-responsive, redox active, and a versatile donor to associated K⁺ ions here. The K⁺ electrophiles interact with electron-rich oxo, but do not significantly (>5 kcal mol⁻¹) alter spin state energies. Inner sphere oxidation of CrL]₂ with a quinone gives Cr₂L₂(semiquinone)₂], while pre-reduced CrL]₂²⁻ reacts with quinone to give K₃(THF)₃Cr₂L₂(catecholate)₂(μ-OH)], a product of capture of two undercoordinated LCr(catecholate)¹⁻ by hydroxide.