A Boron-Fluorinated Tris(pyrazolyl)borate Ligand ((F) Tp*) and Its Mono- and Dinuclear Copper Complexes [Cu((F) Tp*)2 ] and [Cu2 ((F) Tp*)2 ]: Synthesis, Structures, and DFT Calculations.

Reaction of [Si(3,5-Me2 pz)4 ] (1) with [Cu(MeCN)4 ][BF4 ] (2) gave the mono- and dinuclear copper complexes [Cu2 ((F) Tp*)2 ] (3) and [Cu((F) Tp*)2 ] (4). Both complexes contain the so-far unprecedented boron-fluorinated (F) Tp* ligand ([FB(3,5-Me2 pz)3 ](-) with pz=pyrazolyl) originating from 1, acting as a pyrazolyl transfer reagent, and the [BF4 ](-) counter anion of 2, serving as the source of the {BF} entity. The solid-state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu((F) Tp*)(MeCN)], is observed in acetonitrile. The short Cu⋅⋅⋅Cu distance of 269.16 pm in the solid-state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu-Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi-reversible at higher scan rates) oxidation process centred at E(pa) =-0.23 V (E(0) 1/2 =-0.27 V) (vs. Fc/Fc(+) ). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF4 ] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu((F) Tp*)2 ] (4). As expected for a Jahn-Teller-active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.

Crystalline Cyclic (Alkyl)(amino)carbene-tetrafluoropyridyl Radical.

A stable cyclic (alkyl)(amino)carbene (CAAC) 1 inserts into the para-CF bond of pentafluoropyridine, and after fluoride abstraction, the iminium-pyridyl adduct [3](+) was isolated. A cyclic voltammetry study shows a reversible three-state redox system involving [3](+) , [3](⋅) , and [3](-) . The CAAC-pyridyl radical [3](⋅) , obtained by reduction of [3](+) with magnesium, has been spectroscopically and crystallographically characterized. In contrast to the lack of π communication between the CAAC and the pyridine units in cation [3](+) , the unpaired electron of [3](⋅) is delocalized over an extended π system involving both heterocycles.

High-coordinate gold(I) complexes with dithiocarboxylate ligands.

Ferrocene dithiocarboxylate has been introduced into the chemistry of gold(I) and copper(I). First, a modified synthesis of piperidinium ferrocene dithiocarboxylate (1) is reported. Reaction of this reagent with [Au(tht)Cl] in the presence of different phosphines resulted in monomeric, dimeric, and polymeric structures. Although gold(I) is usually two coordinate, mainly three- and four-fold coordinated compounds were obtained by using ferrocene dithiocarboxylate as ligands. The isolated compounds are [(FcCSS)Au(PPh3)2] (2) (FcCSS = ferrocene dithiocarboxylate), [(FcCSS)Au2(dppm)2] (3) (dppm = bis(diphenylphosphino)methane), and [(FcCSS)Au(dppf)]n (4) (dppf = bis(diphenylphosphino)ferrocene) [{(FcCSS)Au}2(dppp)] (5) (dppp = bis(diphenylphosphino)propane). The FcCSS ligand shows a remarkable flexible coordination mode. It coordinates either in a monodentate, a chelating, or in a metal bridging mode. In the four gold(I) complexes 2-5 four different coordination modes of the FcCSS ligand are seen. Attempts to extend this rich coordination chemistry to other coinage metals were only partly successful. [(FcCSS)Cu(PPh3)2] (6) was obtained from the reaction of piperidinium ferrocene dithiocarboxylate with [(Ph3P)3CuCl]. (57)Fe-Mössbauer spectroscopy was performed for compounds 2-4. The spectra show isomer shifts and quadrupole splittings that are typical for diamagnetic ferrocenes.

Homoleptic tetrakis(silyl) complexes of Pd(0) and Pt(0) featuring metal-centred heterocubane structures: evidence for the existence of the corresponding mononuclear Pd(I) and Pt(I) complexes.

We report on the first homoleptic tetrakis(silyl) complexes of zerovalent Group 10 metals. The compounds [MLi4{Si(3,5-Me2pz)3}4] (M=Pd and Pt; 3,5-Me2 pz=3,5-dimethylpyrazolyl) exhibit very appealing metal-centred heterocubane structures with the central d(10) metal atoms surrounded by four silicon and four lithium atoms. Both compounds were characterised in detail, including X-ray crystal-structure analysis and 2D NMR spectroscopic methods such as (7)Li,(29 Si and (7)Li,(195)Pt HMQC. Cyclic voltammetry studies, in combination with density functional theory (DFT) calculations, revealed that the corresponding mononuclear cationic d(9)-M(I) and dicationic d(8)-M(II) complexes are accessible by stepwise one-electron oxidation of the title compounds. Electron paramagnetic resonance (EPR) investigations provided evidence for the existence of the corresponding paramagnetic palladium(I) and platinum(I) complexes.

Development of a metal-ion-mediated base pair for electron transfer in DNA.

A new C-nucleoside structurally based on the hydroxyquinoline ligand was synthesized that is able to form stable pairs in DNA in both the absence and the presence of metal ions. The interactions between the metal centers in adjacent Cu(II)-mediated base pairs in DNA were probed by electron paramagnetic resonance (EPR) spectroscopy. The metal-metal distance falls into the range of previously reported values. Fluorescence studies with a donor-DNA-acceptor system indicate that photoinduced charge-transfer processes across these metal-ion-mediated base pairs in DNA occur more efficiently than over natural base pairs.

Intramolecular phosphorus-phosphorus bond formation within a Co2P4 core.

The reduction of [(Cp‴Co)2(µ,η(2:2)-P2)2] (Cp‴ = 1,2,4-tBu3C5H2) with the samarocenes, [(C5Me4R)2Sm(THF)n] (R = Me or n-propyl), gives [(Cp‴Co)2P4Sm(C5Me4R)2]. This is the first example of an intramolecular P-P coupling in a polyphosphide complex upon reduction of the transition metal. The formation of the P-P bond is not a result of the direct reduction of the phosphorus atoms but is induced by a rearrangement of the positive charges between the metal atoms.

Diaryldichalcogenide radical cations.

One-electron oxidation of two series of diaryldichalcogenides (C6F5E)2 (13a-c) and (2,6-Mes2C6H3E)2 (16a-c) was studied (E = S, Se, Te). The reaction of 13a and 13b with AsF5 and SbF5 gave rise to the formation of thermally unstable radical cations [(C6F5S)2]˙+ (14a) and [(C6F5Se)2]˙+ (14b) that were isolated as [Sb2F11]- and [As2F11]- salts, respectively. The reaction of 13c with AsF5 afforded only the product of a Te-C bond cleavage, namely the previously known dication [Te4]2+ that was isolated as [AsF6]- salt. The reaction of (2,6-Mes2C6H3E)2 (16a-c) with [NO][SbF6] provided the corresponding radical cations [(2,6-Mes2C6H3E)2]˙+ (17a-c; E = S, Se, Te) in the form of thermally stable [SbF6]- salts in nearly quantitative yields. The electronic and structural properties of these radical cations were probed by X-ray diffraction analysis, EPR spectroscopy, and density functional theory calculations and other methods.

Alkynyl-functionalised and linked bicyclo[1.1.1]pentanes of group 14.

We report the synthesis and properties of alkynyl-functionalised and -bridged bicyclo[1.1.1]pentane derivatives consisting of the heavier group 14 elements silicon and tin.