When Do Strongly Coupled Diradicals Show Strongly Coupled Reactivity? Thermodynamics and Kinetics of Hydrogen Atom Transfer Reactions of Palladium and Platinum Bis(iminosemiquinone) Complexes.

The 2,2'-biphenylene-bridged bis(iminosemiquinone) complexes ( BuClip)M [ BuClipH = 4,4'-di- tert-butyl- N, N'-bis(3,5-di- tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl; M = Pd, Pt] can be reduced to the bis(aminophenoxide) complexes ( BuClipH)M by reaction with hydrazobenzene (M = Pd) or by catalytic hydrogenation (M = Pt). The palladium complex with one aminophenoxide ligand and one iminosemiquinone ligand, ( BuClipH)Pd, is generated by comproportionation of ( BuClip)Pd with ( BuClipH)Pd in a process that is both slow (0.06 M s in toluene at 23 °C) and only modestly favorable ( K = 1.

Group 10 Bis(iminosemiquinone) Complexes: Measurement of Singlet-Triplet Gaps and Analysis of the Effects of Metal and Geometry on Electronic Structure.

Bis(iminosemiquinone) complexes of divalent group 10 metals have been described as having open-shell singlet ground states characteristic of very strong coupling between the two ligand radicals. By using the nonlinear temperature dependence of the chemical shifts of the H NMR spectra, the singlet-triplet gaps in seven of these compounds have been measured, with the nickel compounds having gaps of about 2400 cm and the palladium compounds about 1800 cm. Bis(iminosemiquinone)platinum complexes have singlet-triplet gaps too large to measure by this technique (over 2800 cm, estimated to be about 3000 cm), though bis(3,5-di- tert-butylbenzosemiquinonato)platinum(II) has a measurable singlet-triplet gap of 1850 cm.

A chelating bis(aminophenol) ligand bridged by a 1,1'-ferrocene-bis(para-phenylene) linker.

1,1'-Bis(4-(2-hydroxy-3,5-di-tert-butylphenyl)aminophenyl)ferrocene (pFlipH) is prepared in three steps from commercially available 1,1'-ferrocenediboronic acid or its pinacol ester. The suitability of the ligand to bind as a tetradentate ligand in a cis, planar fashion has been confirmed by formation of a square planar palladium bis-iminosemiquinone (pFlip)Pd. The linker unit appears to be structurally similar to 1,1'-ferrocenediyl, but the electronic interaction of the ferrocene with the aminophenols is minimal.