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] , 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 Cp Fe to give [Cr (HL) (μ -O)] , still containing divalent Cr. Reduction (KC ) of [CrL] by two electrons gives [K (THF) Cr L (μ -O)], and by four electrons gives [K (THF) Cr L (μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K (THF) Cr L (μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L and Cr , 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 ) alter spin state energies. Inner sphere oxidation of [CrL] with a quinone gives [Cr L (semiquinone) ], while pre-reduced [CrL] reacts with quinone to give [K (THF) Cr L (catecholate) (μ-OH)], a product of capture of two undercoordinated LCr(catecholate) by hydroxide.