A radical change: Cyclic alkyl(amino) carbenes formed zwitterionic adducts with SiCl4, which were further converted into carbon‐centered stable radicals by changing the donor‐acceptor C→Si coordinate bond into a CSi covalent bond through a KC8 reduction. As the carbon radical site was directly bonded to a SiCl3 unit, a radical center that is right next to an acceptor has been generated.

Symmetrical N‐heterocyclic 1,1′,3,3′‐tetrahydro‐2,2′‐bi‐1,3,2‐diazaphospholes and 2,2′‐bi‐1,3,2‐diazaphospholidines are prepared by time‐saving, sequential “one‐pot” syntheses starting from 1,4‐diazabutadienes or N‐alkyl or N‐aryl‐substituted ethane‐1,2‐diamines. This method offers high selectivity and minimizes the loss of products owing to unwanted hydrolysis, and thus grants high product yields. In some cases, secondary phosphanes were formed together with or instead of diphosphanes. This reaction is explained by a follow‐up process involving homolytic fission of diphosphanes to give phosphanyl radicals, which then react with ammonium salts to give a mixture of secondary phosphanes and chlorophosphanes. Even if its synthetic scope is as yet limited, this approach seems promising in offering superior selectivity and higher yields than common synthetic protocols that rely on the use of complex hydrides as reducing agents. In addition to the reductive conversion of diphosphanes into secondary phosphanes, a reverse reaction under exposure of the reactants to light is also reported.

Compound (Me2 -cAAC:)2 Co(0) (2; Me2 -cAAC:=cyclic (alkyl) amino carbene; :C(CH2 )(CMe2 )2 N-2,6-iPr2 C6 H3 ) was synthesized by the reduction of the precursor (Me2 -cAAC:)2 Co(I) Cl (1) with KC8 in THF. The cyclic voltammogram of 1 exhibited one-electron reduction, which suggests that synthesis of a bent 2-metallaallene (2) from 1 should be possible. Compound 2 contains one cobalt atom in the formal oxidation state zero, which is stabilized by two Me2 -cAAC: ligands. Bond lengths from X-ray diffraction are 1.871(2) and 1.877(2) Å with a C-Co-C bond angle of 170.12(8)°. The EPR spectrum of 2 exhibited a broad resonance attributed to the unique quasi-linear structure, which favors near degeneracy and gives rise to very rapid relaxation conditions. The cAACCo bond in 2 can be considered as a typical Dewar-Chatt-Duncanson type of bonding, which in turn retains 2.5 electron pairs on the Co atom as nonbonding electrons.

The diamagnetic complexes [Ru(tpm)(bqdi)(Cl)]ClO(4) ([1]ClO(4)) (tpm = tris(1-pyrazolyl)methane, bqdi = o-benzoquinonediimine) and [Ru(tpm)(bqdi)(H(2)O)](ClO(4))(2) ([2](ClO(4))(2)) have been synthesized. The valence state-sensitive bond distances of coordinated bqdi [C-N: 1.311(5)/1.322(5) Å in [1]ClO(4); 1.316(7)/1.314(7) Å in molecule A and 1.315(6)/1.299(7) Å in molecule B of [2](ClO(4))(2)] imply its fully oxidised quinonediimine (bqdi(0)) character. DFT calculations of 1(+) confirm the {Ru(II)-bqdi(0)} versus the antiferromagnetically coupled {Ru(III)-bqdi˙(-)} alternative. The (1)H NMR spectra of [1]ClO(4) in different solvents show variations in chemical shift positions of the NH (bqdi) and CH (tpm) proton resonances due to their different degrees of acidity in different solvents. In CH(3)CN/0.1 mol dm(-3) Et(4)NClO(4), [1]ClO(4) undergoes one reversible Ru(II)⇌ Ru(III) oxidation and two reductions, the reversible first electron uptake being bqdi based (bqdi(0)/bqdi˙(-)). The electrogenerated paramagnetic species {Ru(III)-bqdi(0)}(1(2+)) and {Ru(II)-Q˙(-)}(1) exhibit Ru(III)-type (1(2+): = 2.211/Δg = 0.580) and radical-type (1: g = 1.988) EPR signals, respectively, as is confirmed by calculated spin densities (Ru: 0.767 in 1(2+), bqdi: 0.857 in 1). The aqua complex [2](ClO(4))(2) exhibits two one-electron oxidations at pH = 7, suggesting the formation of {Ru(IV)[double bond, length as m-dash]O} species. The electronic spectral features of 1(n) (n = charge associated with the different redox states of the chloro complex: 2+, 1+, 0) in CH(3)CN and of 2(2+) in H(2)O have been interpreted based on the TD-DFT calculations. The application potential of the aqua complex 2(2+) as a pre-catalyst towards the epoxidation of olefins has been explored in the presence of the sacrificial oxidant PhI(OAc)(2) in CH(2)Cl(2) at 298 K, showing the desired selectivity with a wide variety of alkenes. DFT calculations based on styrene as the model substrate predict that the epoxidation reaction proceeds through a concerted transition state pathway.

The homolytic P-P bond fission in a series of sterically congested tetraaminodiphosphanes (R2N)2P-P(NR2)2 ({4}2-{9}2, two of which were newly synthesized and fully characterized) into diaminophosphanyl radicals (R2N)2P˙ (4-9) was monitored by VT EPR spectroscopy. Determination of the radical concentration from the EPR spectra permitted to calculate free dissociation energies ΔGDiss(295) as well as dissociation enthalpies ΔHDiss and entropies ΔSDiss, respectively. Large positive values of ΔGDiss(295) indicate that the degree of dissociation is in most cases low, and the concentration of persistent radicals--even if they are spectroscopically observable at ambient temperature--remains small. Appreciable dissociation was established only for the sterically highly congested acyclic derivative {9}2. Analysis of the trends in experimental data in connection with DFT studies indicate that radical formation is favoured by large entropy contributions and the energetic effect of structural relaxation (geometrical distortions and conformational changes in acyclic derivatives) in the radicals, and disfavoured by attractive dispersion forces. Comparison of the energetics of formation for CC-saturated N-heterocyclic diphosphanes and the 7π-radical 3c indicates that the effect of energetic stabilization by π-electron delocalization in the latter is visible, but stands back behind those of steric and entropic contributions. Evaluation of spectroscopic and computational data indicates that diaminophosphanyl radicals exhibit, in contrast to aminophosphenium cations, no strong energetic preference for a planar arrangement of the (R2N)2P unit.