Search

A series of iridium complexes with bis(diisopropylphenyl)iminoacenaphtene (dpp-bian) ligands, [Ir(cod)(dpp-bian)Cl] (1), [Ir(cod)(NO)(dpp-bian)](BF4)2 (2) and [Ir(cod)(dpp-bian)](BF4) (3), were prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis and cyclic voltammetry (CV). The structures of 1–3 feature a square planar backbone consisting of two C = C π-bonds of 1,5-cyclooctadiene (cod) and two nitrogen atoms of dpp-bian supplemented with a chloride ion (for 1) or a NO group (for 2) to complete a square-pyramidal geometry. In the nitrosyl complex 2, the Ir-N-O group has a bent geometry (the angle is 125°). The CV data for 1 and 3 show two reversible waves between 0 and -1.6 V (vs. Ag/AgCl). Reversible oxidation was also found at E1/2 = 0.60 V for 1. Magnetochemical measurements for 2 in a range from 1.77 to 300 K revealed an increase in the magnetic moment with increasing temperature up to 1.2 μB (at 300 K). Nitrosyl complex 2 is unstable in solution and loses its NO group to yield [Ir(cod)(dpp-bian)](BF4) (3). A paramagnetic complex, [Ir(cod)(dpp-bian)](BF4)2 (4), was also detected in the solution of 2 as a result of its decomposition. The EPR spectrum of 4 in CH2Cl2 is described by the spin Hamiltonian Ĥ = gβHŜ with S = 1/2 and gxx = gyy = 2.393 and gzz = 1.88, which are characteristic of the low-spin 5d7-Ir(II) state. DFT calculations were carried out in order to rationalize the experimental results. [ABSTRACT FROM AUTHOR]

The complex [V2S4(nBu2dtc)4] (1) (dtc = dithiocarbamate) was prepared by a self‐assembly reaction from [VO(nBu2dtc)3] and H2S. 1H, 13C, and 51V NMR spectra indicate the presence in solution of two isomers (centrosymmetric and non‐centrosymmetric) with different relative orientations of the dithiocarbamate chelate rings. Thermogravimetric studies of 1 show that the thermolysis products are VS2 (in He) or VS (in H2). The cyclic voltammogram (CV) in dichloromethane reveals a chemically reversible one‐electron oxidation at +0.61 V followed by an irreversible oxidation at +1.51 V (vs. Ag/AgCl). The redox processes can be attributed to V‐centered oxidation. This interpretation is supported by DFT calculations, indicating the predominantly V–V bonding character of the HOMO in both cases. The removal of one electron from the HOMO causes weakening of the V–V bond in 1+. The mixed‐valence V(IV/V) product of the one‐electron oxidation, [V2S4(nBu2dtc)4](BF4) {[1](BF4)}, was isolated from the reaction with NOBF4 and characterized by elemental analysis, IR spectroscopy, mass spectrometry (ESI‐MS), CV, EPR spectroscopy, and magnetochemistry. The EPR spectrum of [1](BF4) in dichloromethane exhibits a single 15‐line signal arising from the hyperfine interaction between the unpaired electron and two equivalent 51V nuclei with I = 7/2, indicating complete delocalization of the unpaired electron over both metal centers. The magnetic behavior of [1](BF4) confirms the presence of one unpaired electron and the mixed‐valence V(IV/V) oxidation state without any significant magnetic exchange interactions between the paramagnetic complexes. [ABSTRACT FROM AUTHOR]

A new monoiminoacenaphthenone 3,5-(CF3)2C6H3-mian (complex 2) was synthesized and further exploited, along with the already known monoiminoacenaphthenone dpp-mian, to obtain oxidovanadium(IV) complexes [VOCl2(dpp-mian)(CH3CN)] (3) and [VOCl(3,5-(CF3)2C6H3-bian)(H2O)][VOCl3(3,5-(CF3)2C6H3-bian)]·2.85DME (4) from [VOCl2(CH3CN)2(H2O)] (1) or [VCl3(THF)3]. The structure of all compounds was determined using X-ray structural analysis. The vanadium atom in these structures has an octahedral coordination environment. Complex 4 has an unexpected structure. Firstly, it contains 3,5-(CF3)2C6H3-bian instead of 3,5-(CF3)2C6H3-mian. Secondly, it has a binuclear structure, in contrast to 3, in which two oxovanadium parts are linked to each other through V=O···V interaction. This interaction is non-covalent in origin, according to DFT calculations. In structures 2 and 3, non-covalent π-π staking interactions between acenaphthene moieties of the neighboring molecules (distances are 3.36–3.40 Å) with an estimated energy of 3 kcal/mol were also found. The redox properties of the obtained compounds were studied using cyclic voltammetry in solution. In all cases, the reduction processes initiated by the redox-active nature of the mian or bian ligand were identified. The paramagnetic nature of complexes 3 and 4 has been proven by EPR spectroscopy. Complexes 3 and 4 exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The yields of products of cyclohexane oxidation were 43% (complex 3) and 27% (complex 4). Based on the data regarding the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play the most crucial role in the reaction. The initial products in the reactions with alkanes are alkyl hydroperoxides, which are easily reduced to their corresponding alcohols by the action of triphenylphosphine (PPh3). According to the DFT calculations, the difference in the catalytic activity of 3 and 4 is most likely associated with a different mechanism for the generation of ●OH radicals. For complex 4 with electron-withdrawing CF3 substituents at the diimine ligand, an alternative mechanism, different from Fenton's and involving a redox-active ligand, is assumed. [ABSTRACT FROM AUTHOR]

Graphical abstract The first {Nb 2 S 4 } dithiophosphinate complex, [ NbIVNbIV S 4 (S 2 PiBu 2) 4 ] (1), has been synthesized. Remarkably, cyclic voltammetry of 1 displays two chemically reversible niobium-centered one-electron oxidation processes. The one-electron oxidation product [ NbVNbIV S 4 (S 2 PiBu 2) 4 ]+ (1 +) was prepared in situ and characterized by EPR. Abstract A new diisobutyldithiophosphinate complex, [Nb 2 S 4 (S 2 PiBu 2) 4 ] (1), was obtained by a ligand substitution reaction using (Bu 4 N) 4 [Nb 2 S 4 (NCS) 8 ] and NaS 2 PiBu 2 ·3H 2 O. Its crystal structure has been determined. The Nb Nb distance is 2.9034(7) Å. The cyclic voltammogram (CV) of 1 in dichloromethane exhibits two successive chemically reversible one-electron oxidation waves at +0.55 and +1.10 V (versus Ag/AgCl) attributed to the NbIV/NbV couple. This is the first {Nb 2 S 4 } cluster that shows two reversible oxidations. The paramagnetic mixed-valence Nb(IV/V) product of the one-electron oxidation, [Nb 2 S 4 (S 2 PiBu 2) 4 ]+ (1 +), was generated in situ. The EPR spectrum of 1 + in acetonitrile reveals a 19-line signal arising from the hyperfine interaction between the unpaired electron and two equivalent 93Nb nuclei with I = 9/2, indicating complete delocalization of the unpaired electron over both metal centers. DFT calculations have been performed for the complexes [Nb 2 S 4 (S 2 PMe 2) 4 ], [Nb 2 S 4 (S 2 P(OMe) 2) 4 ], [Nb 2 S 4 (S 2 CNMe 2) 4 ] and [Nb 2 S 4 (S 2 COMe) 4 ] and their single and double oxidized species in order to explain the peculiarities of their redox behavior. The results show that the HOMOs responsible for oxidation have a predominantly metallic character in all cases, but they are significantly more high-lying for the dithiophosphinate and dithiocarbamate complexes, which explains their ability to be oxidized. [ABSTRACT FROM AUTHOR]