Elusive Antimony‐Centered Radical Cations: Isolation,Characterization, Crystal Structures,and Reactivity Studies

One‐electron oxidation of the stibines Aryl₃Sb ( 1 , Aryl=2,6‐ⁱ Pr₂‐4‐OMe‐C₆H₂; 2 , Aryl=2,4,6‐ⁱ Pr₃‐C₆H₂) with AgSbF₆ and NaBAryl^F₄ (Aryl^F=3,5‐(CF₃)₂C₆H₃) afforded the first structurally characterized examples of antimony‐centered radical cations 1 ^.+[BAryl^F₄]⁻ and 2 ^.+[BAryl^F₄]⁻. Their molecular and electronic structures were investigated by single‐crystal X‐ray diffraction, electron paramagnetic resonance spectroscopy (EPR) and UV/Vis absorption spectroscopy, in conjunction with theoretical calculations. Moreover, their reactivity was investigated. The reaction of 2 ^.+[BAryl^F₄]⁻ and p ‐benzoquinone afforded a dinuclear antimony dication salt 3 ²⁺[BAryl^F₄]₂⁻, which was characterized by NMR spectroscopy and X‐ray diffraction analysis. The formation of the dication 3 ²⁺ further confirms that the isolated stibine radical cations are antimony‐centered.     

Dioxygen Activation by Redox-Active Bis(aldimine) Ligand Bridged Diruthenium Complex Possessing Singlet Ground State

The unexplored ‘actor’ behavior of redox-active bis(aldimine) congener, p-phenylene-bis(picoline)aldimine (L1), towards dioxygen activation and subsequent functionalization of its backbone was demonstrated on coordination with {Ru(acac)₂} (acac= acetylacetonate). Reaction under aerobic condition led to the one-pot generation of dinuclear complexes with unperturbed L1, imino-carboxamido (L2⁻), and bis(carboxamido) (L3²⁻)-bridged isovalent {Ru^II(μ-L1)Ru^II}, 1/ {Ru^III(μ-L3²⁻)Ru^III}, 3 and mixed-valent {Ru^II(μ-L2⁻)Ru^III}, 2 . Authentication of the complexes along with the redox non-innocence behavior of their bridge have been validated through structure, spectroelectrochemistry and DFT calculations. Kinetic and isotope labelling experiments together with DFT analyzed transition states justified the consideration of redox shuttling at metal/L1 interface for ³O₂ activation despite of the closed shell configuration of 1 (S=0) to give carboxamido derived 2 / 3 .     

Preparation and Conformation of Organo‐Bridged Bis[tris(arylchalcogenolato)tin] Compounds – An Experimental and Quantum Chemical Study

Seven organo‐bridged bis[tris(arylchalcogenolato)tin] compounds with the general formulae (R′E)₃Sn–R–Sn(ER′)₃ (R = –(CH₂)₄–, 1,4‐bis(methyl)benzene, 4,4′‐bis(methyl)biphenyl; R′ = Ph, 1‐Np, 2‐Np; E = S, Se) were synthesized and characterized by means of X‐ray diffractometry as well as NMR spectroscopy. Three different conformations of the arylchalcogenolato groups ER′ with respect to the bridging group R were rationalized and explained by means of quantum chemical investigations.     

Ba2In2Q5 (Q = S,Se): Synthesis,Crystal Structures,Electronic Structures,and Optical Properties

Two ternary metal chalcogenides, Ba₂In₂Q₅ (Q = S, Se) were successfully synthesized by solid‐state reactions. They are isostructural and crystallize in the orthorhombic space group Pbca (no. 61). Both of them have a similar three‐dimensional (3D) framework structure, which is composed of [InQ₄] (Q = S, Se) tetrahedra that are alternatingly connected on layer in the ab plane, with Ba²⁺ cations arranged between In–S or In–Se layers for electric charge balance. The measured Raman and IR spectra show that title compounds have broad transparency range up to 20 μm. From the UV/Vis/NIR diffuse reflectance spectra, it can be seen that the bandgaps of Ba₂In₂S₅ and Ba₂In₂S₅ are 2.47 eV and 2.12 eV, which are larger than these of the calculation values (Ba₂In₂S₅, 2.362 eV and Ba₂In₂Se₅, 1.908 eV), respectively. The calculated partial densities of states indicate that the bandgaps are determined by the interaction of S‐3p and In‐5s (Ba₂In₂S₅) or Se‐4p and In‐5s (Ba₂In₂Se₅), respectively. The calculated birefringences (Δn) are about 0.03 (Ba₂In₂S₅) and 0.05 (Ba₂In₂Se₅) as the wavelength above 1 μm, respectively.     

Energetic Salts Based on Monoanions of N,N‐Bis(1H‐tetrazol‐5‐yl)amine and 5,5′‐Bis(tetrazole)

High‐density energetic salts that contain nitrogen‐rich cations and the 5‐(tetrazol‐5‐ylamino)tetrazolate (HBTA^?) or the 5‐(tetrazol‐5‐yl)tetrazolate (HBT^?) anion were readily synthesized by the metathesis reactions of sulfate salts with barium compounds, such as bis[5‐(tetrazol‐5‐ylamino)tetrazolate] (Ba(HBTA)₂), barium iminobis(5‐tetrazolate) (BaBTA), or barium 5,5′‐bis(tetrazolate) (BaBT) in aqueous solution. All salts were fully characterized by IR spectroscopy, multinuclear (¹H, ¹³C, ¹⁵N) NMR spectroscopy, elemental analyses, density, differential scanning calorimetry (DSC), and impact sensitivity. Ba(HBTA)₂ ? 4 H₂O crystallizes in the triclinic space group P$\bar 1$ , as determined by single‐crystal X‐ray diffraction, with a density of 2.177 g cm^?3. The densities of the other organic energetic salts range between 1.55 and 1.75 g cm^?3 as measured by a gas pycnometer. The detonation pressure (P) values calculated for these salts range from 19.4 to 33.6 GPa, and the detonation velocities (ν_D) range from 7677 to 9487 m s^?1, which make them competitive energetic materials. Solid‐state ¹³C NMR spectroscopy was used as an effective technique to determine the structure of the products that were obtained from the metathesis reactions of biguanidinium sulfate with barium iminobis(5‐tetrazolate) (BaBTA). Thus, the structure was determined as an HBTA salt by the comparison of its solid‐state ¹³C NMR spectroscopy with those of ammonium 5‐(tetrazol‐5‐ylamino)tetrazolate (AHBTA) and diammonium iminobis(5‐tetrazolate) (A₂BTA).     

N‐Trimethylsilyl‐aminophosphines: Solution‐state Structures,Studied by Multinuclear Magnetic Resonance and DFT Methods

A novel fairly stable N‐trimethylsilylamino(dichloro)phosphine was prepared, in which the nitrogen atom bears a 9‐borabicyclo[3.3.1]nonyl group. The gas phase structures of various amino‐ and silylaminophosphines including a phosphenium cation and an amino(imono)phosphine were optimized at the B3LYP/6‐311+G(d,p) level of theory, and NMR parameters were calculated. Both magnitude and sign of the two‐bond coupling constants ²J(³¹P,N,¹³C) and ²J(³¹P,N,²⁹Si), known to be sensitive towards the respective conformation, are well reproduced by the calculations. This also holds for ¹J(³¹P,¹⁵N), although calculated values ¹K(³¹P,¹⁵N) (all < 0) are slightly more negative [¹J(³¹P,¹⁵N) more positive] than experimental values.     

Crystal Structures and Characterizations of Bis(pyrrolidinedithiocarbamato) Cu(II) and Zn(II) Complexes

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Crystal Structures and Characterizations of Bis(pyrrolidinedithiocarbamato)Cu（Ⅱ） and Zn(Ⅱ） Complexes

The structures of [Cu (S₂CN (CH₂)₄)₂] (1) and [Zn₂(S₂CN‐(CH₂)₄)₄] (2) have been determined by X‐ray crystallography analysis. They are all isomorphous and triclinic, space group of P1^?, with Z = 1. The lattice parameters of compound 1 is: a = 0.63483(2) nm, b = 0.74972(3) nm, c=0.78390(1) mn, α = 75.912(2)°, β = 78.634(2)° and γ = 86.845(2)°; compound 2: a = 0.78707(6) nm, b=0.79823(6) nm, c = 1.23246(9) nm, α = 74.813(2)°, β = 73.048(2)° and γ = 88.036(2)°. The copper atom is located on a crystallographic inversion center and zinc atom lies across centers of symmetry. The Cu(II) ion has a square‐planar geometry while Zn(II) has a distorted tetrahedral geometry. The thermal gravity (TG) data indicate that no structural transitions in the two compounds were abserved and the decomposition products can adsorb gas. Also they all have a high thermal stability.     

Bis phenylene flattened 13-membered tetraamide macrocyclic ligand (TAML) for square planar cobalt(III)*

Abstract

The preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (¹H NMR) compound, which becomes an S = 0 diamagnetic octahedral species in excess d₅-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E_½ value (0.66 V vs SCE) among all investigated Co^III TAML complexes. The oxidation results in a neutral blue species which is consistent with a Co^III/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other Co^III TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the Co^III/radical-cation ligand formulation rather than with a Co^IV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [V^VO(OCHMe₂)₃] were not successful. TAML-free decavanadate was isolated instead.     

Influence of ionization on the conformational preferences of peptide models. Ramachandran surfaces of N‐formyl‐glycine amide and N‐formyl‐alanine amide radical cations

Ramachandran maps of neutral and ionized HCO–Gly–NH₂ and HCO–Ala–NH₂ peptide models have been built at the B3LYP/6‐31++G(d,p) level of calculation. Direct optimizations using B3LYP and the recently developed MPWB1K functional have also been carried out, as well as single‐point calculations at the CCSD(T) level of theory with the 6‐311++G(2df,2p) basis set. Results indicate that for both peptide models ionization can cause drastic changes in the shape of the PES in such a way that highly disallowed regions in neutral PES become low‐energy regions in the radical cation surface. The structures localized in such regions, and are highly stabilized due to the formation of 2‐centre‐3‐electron interactions between the two carbonyl oxygens. Inclusion of solvent effects by the conductor‐like polarizable continuum model (CPCM) shows that the solute‐solvent interaction energy plays an important role in determining the stability order. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Preparation,Spectroscopic Properties,and Crystal Structures of Fe2(CO)6(μ‐CO)(μ‐CF2)2, Fe2(CO)6(μ‐CO)2(μ‐CF2), and Fe2(CO)6(μ‐CF2)(PPh3)2 – Theoretical Studies of Methylenic vs. Carbonyl Bridges in Diiron Complexes

The reaction of Na₂[Fe(CO)₄] with Br₂CF₂ in n‐pentane generates a mixture of the compounds (CO)₃Fe(μ‐CO)_3–n(μ‐CF₂)_nFe(CO)₃ ( 2 , n = 2; 3 , n = 1) in low yields with 3 as the main product. 3 is obtained free from 2 by reacting Br₂CF₂ with Na₂[Fe₂(CO)₈]. The non‐isolable monomeric complex (CO)₄Fe=CF₂ ( 1 ) can probably considered as the precursor for 2 . 3 reacts with PPh₃ with replacement of two CO ligands to form Fe₂(CO)₆(μ‐CF₂)(PPh₃)₂ ( 4 ). The complexes 2 – 4 were characterized by single crystal X‐ray diffraction. While the structure of 2 is strictly similar to that of Fe₂(CO)₉, the structure of 3 can better be described as a resulting from superposition of the two enantiomers 3 a and 3 b with two semibridging CO groups. Quantum chemical DFT calculations for the series (CO)₃Fe(μCO)_3–n(μ‐CF₂)_nFe(CO)₃ (n = 0, 1, 2, 3) as well as for the corresponding (μ‐CH₂) derivatives indicate that the progressively larger σ donor and π acceptor properties for the bridging ligands, in the order CO < CF₂ < CH₂, favor a stronger Fe–Fe bond.     

Ansa‐Bridged Bis(benzene) Titanium Complexes

Taking advantage of an improved synthesis of [Ti(η⁶‐C₆H₆)₂], we report here the first examples of ansa‐bridged bis(benzene) titanium complexes. Deprotonation of [Ti(η⁶‐C₆H₆)₂] with nBuLi in the presence of N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (pmdta) leads to the corresponding 1,1′‐dilithio salt [Ti(η⁶‐C₆H₅Li)₂] ? pmdta that enables the preparation of the first one‐ and two‐atom‐bridged complexes by simple salt metathesis. The ansa complexes were fully characterized (NMR spectroscopy, UV/Vis spectroscopy, elemental analysis, and X‐ray crystallography) and further studied electrochemically and computationally. Moreover, [Ti(η⁶‐C₆H₆)₂] is found to react with the Lewis base 1,3‐dimethylimidazole‐2‐ylidene (IMe) to give the bent sandwich complex [Ti(η⁶‐C₆H₆)₂(IMe)].     

Synthesis,spectroscopic properties,density functional theory calculations and nonlinear optical properties of novel complexes of 5‐hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions

5‐Hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin (L) has been synthesized and its novel complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions have also been prepared and identified using various analytical tools. The complexes are octahedral binding via one/two oxygen, nitrogen atoms for 1:1 and 1:2 complexes and two/three coordinated water molecules. All the prepared solid complexes behave as neutral in dimethylformamide. The optimized structures of the studied complexes were theoretically investigated at the B3LYP/6‐311G** level. Molecular stability and bond strengths were investigated by applying natural bond orbital analysis. The geometries of the studied complexes are non‐planar as indicated from the values of dihedral angles. The global properties of hardness, global softness and electronegativity were computed. The calculated small energy gap between highest occupied and lowest unoccupied molecular orbital energies shows that charge transfer occurs within the complexes. The obtained total static dipole moment, mean polarizability, anisotropy of polarizability and mean first‐order hyperpolarizability (<β>) were compared with those of urea as a reference material. The results for <β> showed that the complexes are excellent candidates as nonlinear optical materials. The three‐dimensional plots of the molecular electrostatic potential for some selected complexes were investigated.     

Energetic Ethylene‐ and Propylene‐Bridged Bis(nitroiminotetrazolate) Salts

High energy density materials with ethylene‐ and propylene bis(5‐nitroiminotetrazolate) as the anions are reported; all salts were fully characterized by IR, and ¹H, ¹³C, and ¹⁵N NMR spectroscopy as well as elemental analyses. In addition, the heats of formation (ΔH_f) and the detonation pressures (P) and velocities (D) were calculated.

     

Synthesis,Structures and DFT Studies of Imido‐bridged and (Bis)ligand‐coordinated Titanium Complexes

Syntheses and structures of five imido‐bridged dinuclear titanium complexes and two (bis)ligand‐coordinated mononuclear titanium complexes are reported. Addition of 1 or 2 equiv. of Schiff base ligand (((1H‐pyrrol‐2‐yl)methylene)amino)‐2,3‐dihydro‐1H‐inden‐2‐ol (H₂L) to Ti(NMe₂)₄ resulted in transamination with 4 equiv. of dimethylamides generating a (bis)ligand‐coordinated complex Ti(L)₂ ( 1 ). Treatment of Ti(NMe₂)₄ with 1 equiv. of ^tBuNH₂ followed by addition of 1 equiv. of H₂L afforded an imido‐bridged complex [Ti(L)(N^tBu)]₂ ( 2 ). 1:1:1:1 reaction of Ti(NMe₂)₄/RNH₂/H₂L/py(or phen) produced imido‐bridgedcomplexes [Ti(L)(NPh)(py)]₂ ( 3 ), [Ti(L)(4‐F‐PhN)(py)]₂·Tol ( 4 ·Tol), [Ti(L)(4‐Cl‐PhN)(py)]₂·Tol·THF ( 5 ·Tol·THF), [Ti(L)(4‐Br‐PhN)(py)]₂·Tol ( 6 ·Tol) and a (bis)ligand‐coordinated complex Ti(L)₂·phen ( 7 ) (py = pyridine, phen = 1,10‐phenanthroline). Attempts to prepare the monomeric titianium imido complexes were unsuccessful. DFT studies show that the assumed compound which contains Ti = N species is less stable than imido‐bridged Ti‐N(R)‐Ti complexes, providing the better understanding of the experimental results.     

Synthesis,Optical Properties,and Electronic Structures of Fully Core‐Modified Porphyrin Dications and Isophlorins

The synthesis, structures, optical properties, and electronic structures of the tetraphenyltetrathiaporphyrin dication (S₄TPP²⁺, 6 ) and tetrakis(pentafluorophenyl)tetrathiaisophlorin (S₄F₂₀TPP, 7 ) are reported. S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were synthesized by acid‐catalyzed condensation of the corresponding hydroxylmethylthiophene, followed by oxidation. The electronic structures of S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were analyzed by using UV/Vis‐absorption spectroscopy and by magnetic circular dichroism (MCD) spectroscopy and the bands were assigned by using time‐dependent density functional theory (TD‐DFT) and ZINDO/s calculations. A red‐shift of the Q bands of S₄TPP²⁺ ( 6 ) is observed relative to the spectra of tetraphenylporphyrins because a destabilization of the HOMO leads to a narrower HOMO–LUMO band‐gap. Michl′s perimeter model was used to assign the absorption bands and MCD spectra of S₄F₂₀TPP ( 7 ). Current‐density maps and nucleus‐independent chemical‐shift (NICS) calculations of S₄TPP²⁺ ( 6 ) and of a model compound predict marked modification to the diamagnetic ring current, whilst nonaromatic character is predicted for S₄F₂₀TPP ( 7 ).     

Molecular and Crystal Structures of Pentafluorophenyl‐platinum(II) Complexes with Bis(diphenylphosphino)methane,Bis(diphenylarsino)methane and 1,2‐Bis(diphenylarsino)ethane

The X‐ray crystal structures of [PtCl₂(dppm)], [Pt(C₆F₅)₂L] (L = dppm (bis(diphenylphosphino)methane), dpam (bis(diphenylarsino)methane), dpae (bis(diphenylarsino)ethane)) and [PtCl(C₆F₅)(dpae)] show the complexes to be monomeric with chelating dipnictido ligands, and not alternatives with bridging ligands. In [Pt(C₆F₅)₂(dpam)₂], there are two unidentate diarsine ligands in a cis‐arrangement.     

Investigating the Mechanism of Palladium‐Catalyzed Radical Oxidative C(sp3)−H Carbonylation: A DFT Study

Palladium (Pd)‐catalyzed radical oxidative C?H carbonylation of alkanes is a useful method for functionalizing hydrocarbons, but there is still a lack of understanding of the mechanism, which restricts the application of this reaction. In this work, density functional theory (DFT) calculations were carried out to study the mechanism for a Pd‐catalyzed radical esterification reaction. Two plausible reaction pathways have been proposed and validated by DFT calculations. The computational results reveal that the generated alkyl radical prefers to add to the carbon monoxide (CO) molecule to form a carbonyl radical before bonding with the Pd species. Radical addition onto Pd followed by CO migratory insertion was unfavorable owing to the high energy barrier of the migratory insertion step. The regioselectivity of the C(sp³)?H carbonylation was also investigated by DFT. The results show that the regioselectivity is controlled by both the bond dissociation energy of the reacting C?H bond and the stability of the corresponding generated carbon radical. Competitive side reactions also affected the yield and regioselectivity owing to the rapid consumption of the stable radical intermediate.