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 Cp(2)Fe(+)to give [Cr-4(HL)(4)(mu(4)-O)](2+), still containing divalent Cr. Reduction (KC8) of [CrL](2)by two electrons gives [K-2(THF)(3)Cr3L3(mu(3)-O)], and by four electrons gives [K-4(THF)(10)Cr2L2(mu-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K-4(THF)(10)Cr2L2(mu-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L(3-)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](2)(2-)reacts with quinone to give [K-3(THF)(3)Cr2L2(catecholate)(2)(mu-OH)], a product of capture of two undercoordinated LCr(catecholate)(1-)by hydroxide.