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 Cp2 Fe+ to give [Cr4 (HL)4 (μ4 -O)]2+ , still containing divalent Cr. Reduction (KC8 ) of [CrL]2 by two electrons gives [K2 (THF)3 Cr3 L3 (μ3 -O)], and by four electrons gives [K4 (THF)10 Cr2 L2 (μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K4 (THF)10 Cr2 L2 (μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L3- and CrII , 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 [Cr2 L2 (semiquinone)2 ], while pre-reduced [CrL]2 2- reacts with quinone to give [K3 (THF)3 Cr2 L2 (catecholate)2 (μ-OH)], a product of capture of two undercoordinated LCr(catecholate)1- by hydroxide.
Keywords: aggregates; chromium; oxo; pincer ligands; reduction.
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