Wittmann, ChristopherPalamarciuc, OlegDascalu, MihaelaCazacu, MariaNesterov, Dmytro S.Pombeiro, ArmandoRapta, PeterArion, Vladimir B.2026-02-182026-02-182025-06-17Wittmann, C., Palamarciuc, O. Dascalu, M., Cazacu, M., Nesterov, D. S., Pombeiro, A. J. L., Rapta, P., & Arion, V. B. (2025). Copper(II) complex with a redox-noninnocent Schiff base bearing a tetraphenyldisiloxane unit: synthesis, structure and catalytic oxidation of cyclohexane. Dalton Transactions, 54, 10984-11005. https://10.1039/d5dt01028d1477-9226http://hdl.handle.net/10400.21/22665This work was funded by a grant from the Ministry of Research, Innovation and Digitalization, project no. PNRR-III-C9-2023-I8-99/31.07.2023 within the National Recovery and Resilience Plan (Romania), as well as by the Slovak Research and Development Agency under contract no. APVV-19-0024 and APVV-23-0195 (P. R.) and the grant agency VEGA (contract no. 1/0392/24). The authors acknowledge the Fundação para a Ciência e a Tecnologia (FCT), Portugal, through the projects UIDB/00100/2020 (https://doi.org/10.54499/UIDB/00100/2020), UIDP/00100/2020 (https://doi.org/10.54499/UIDP/00100/2020), LA/P/0056/2020 (https://doi.org/10.54499/LA/P/0056/2020) of Centro de Química Estrutural. We thank Mr Alexander Prado-Roller for X-ray diffraction measurements.Abstract An organic–inorganic diamine, 1,3-bis(aminopropyl)tetraphenyldisiloxane, was prepared and introduced as a flexible spacer into the structure of a salen-type Schiff base (H2L7) extending the available small library of similar compounds derived from 1,3-bis(aminopropyl)tetramethyldisiloxane and substituted 2-hydroxybenzaldehydes (H2L1–H2L6). Like the previously reported mononuclear copper(II) complexes [CuL1]–[CuL6], the new copper(II) complex [CuL7], obtained by reaction of Cu(OAc)2·H2O with H2L7 in a mixture of organic solvents, has a tetrahedrally distorted square-planar (N2O2) coordination geometry. X-ray crystallography has shown that compared to [CuL1]–[CuL6] the Si–O–Si angle in [CuL7] is even closer to linear due to stronger intramolecular interactions between Ph groups than between Me groups in the central–R2Si–O–SiR2– fragment (R = Ph and Me, respectively). [CuL7] can be electrochemically reversibly oxidised by two successive one-electron processes, generating stable phenoxyl mono- and diradicals. Both oxidations are ligand-centred, leading to the formation of coordinated phenoxyl radicals. The UV spectrum of [CuL7] consists of π → π* and LMCT σ → d transitions. The low-energy d–d absorption is well described by AILFT CAS(9,5)/NEVPT2 calculations. The one-electron oxidised compound [CuL7]+ should exist in the triplet ground state as 3[CuL7]+ with one unpaired electron located on the dx2−y2 orbital of copper(II) (d9, SCu = ½) and another electron on the molecular orbital (MO) comprising pz oxygen and carbon atoms of the phenoxyl radical (Srad = ½). The broad absorption in the vis-NIR region of the optical spectrum of the one-electron oxidised complex is due to intervalence charge transfer in the triplet species 3[CuL7]+, but not in the [CuL7]2+ one. The doubly oxidised [CuL7] species shows very close doublet and quartet states, where the doublet state has an unpaired electron located on the Cu(II) d-orbital, while the quartet state has one unpaired electron on the Cu(II) d-orbital and two unpaired electrons on π-bonding orbitals. In all state-averaged CASSCF cases, the occupation of the Cu(II) d-orbital is nearly 1.0, indicating its limited involvement in the excited states. Catalytic studies showed that [CuL7] acts as a catalyst for the oxidation of alkanes with peroxides under very unusual solvent-free conditions, converting cyclohexane into cyclohexanol and cyclohexanone (with hydrogen peroxide or tert-butyl hydroperoxide as the oxidant) or into cyclohexanol and ε-caprolactone (with m-chloroperoxybenzoic acid as the oxidant). Theoretical investigations of the catalytic reaction mechanisms disclosed the principal intermediates.engTetraphenyldisiloxane unitCatalytic oxidation of cyclohexaneUIDB/00100/2020UIDP/00100/2020research article10.1039/d5dt01028d1477-9234