Neue anorganische Ringsysteme. XXV. Das Disila-phospha(III)-diaza-cyclopentan-Ringsystem und seine Überführung in Phosphoniumderivate

Novel Inorganic Ring Systems. XXV. The Ring System of Disilaphospha(III) -diaza-cyclopentane and its Transformation to Phosphonium Derivatives According to equ. (1) derivatives A 1 – A 3 of the fivemembered Si₂PN₂ ring system are formed. They react' with methyl iodide (→ B 1 – B 3) and with carbon disulfide respectively (→ C 1 – C 3) giving compounds of phosphonium structure. The novel prepared substances are described in their properties and confirmed in their structure by elemental analysis, nuclear magnetic resonance and vibration spectroscopy.     

Novel Approach for Rapid and Efficient Synthesis of 2‐(3‐(4‐Aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one Derivatives and Screened Their Antimicrobial Activity

A series of compounds, viz. 2‐(3‐(4‐aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one 4 ( a – n ), have been synthesized by reaction of 3 ( a – n ) with thioglycolic acid in the presence of zinc chloride. Compounds 3 ( a – n ) have been synthesized by amination of formylated pyrazoles 2 ( A – B ), which were synthesized by formylation of 1 ( A – B ) by Vilsmeier–Haack reagent (POCl₃/DMF). Compounds 1 ( A – B ) were synthesized by condensation of hydrazide and substituted acetophenones under conventional method and microwave irradiation method. These compounds were identified on the basis of melting point range, Rf values, infrared, ¹H NMR, and mass spectral analysis. These compounds were evaluated for their in vitro antimicrobial activity, and their minimum inhibitory concentration was determined. Among them, compound 4b and compound 4l possess appreciable antimicrobial and antifungal activities. Antibacterial activity results showed that compounds containing electron‐withdrawing groups were more active than compounds containing electron‐releasing groups.     

Trichodermates A–F,New Cytotoxic Trichothecenes from the Plant Pathogenic Fungus Trichoderma sp.

Trichodermates A – F ( 1 – 6 , resp.), six new trichothecene polyunsaturated octadioic acid esters, and (?)‐harzianum B ( 7 ) were isolated from the fermentation extract of Trichoderma sp., a plant pathogenic fungus isolated from stem rot of an unidentified tree in Thailand. The structures of 1 – 7 were elucidated by NMR experiments. The absolute configuration at C(12) in 3 was assigned by in situ dimolybdenum circular dichroism method, whereas that in 7 was deduced after hydrolysis of 7 to 8 via modified Mosher's method. Compounds 1 and 2 showed modest cytotoxic activities against the K562 (human myelogenous leukemia) cell line with IC₅₀ values of 12.12 and 13.08 μM , respectively.     

Synthesis and Characterization of Ruthenium Complexes with Substituted Pyrazino[2,3‐f][1,10]‐phenanthroline (=Rppl; R=Me,COOH, COOMe)

A series of substituted pyrazino[2,3‐f][1,10]‐phenanthroline (Rppl) ligands (with R=Me, COOH, COOMe) were synthetized (see 1 – 4 in Scheme 1). The ligands can be visualized as formed by a bipyridine and a quinoxaline fragment (see A and B ). Homoleptic [Ru(R¹ppl)₃](PF₆)₂ and heteropleptic [Ru(R¹ppl){(R²)₂bpy}₂](PF₆)₂ (R¹=H, Me, COOMe and R²=H, Me) metal complexes 5 – 7 and 8 – 13 , respectively, based on these ligands were also synthesized and characterized by conventional techniques (Schemes 2 and 3, resp.). In the heteroleptic complexes, the R¹‐ppl ligand reduces at a less‐negative potential than the bpy ligand, reflecting the acceptor property conferred by the quinoxaline moiety. The potentiality of some of these complexes as solar‐cell dyes is discussed.     

Ein grünes,paramagnetisches Goldfluorid – Sn1−xAuxF4?

A Green Paramagnetic Gold Fluoride – Sn_1?xAu_xF₄? Green single crystals were obtained by heating (Au-tube, 450° – 500°C) a mixture of SnF₂ and AuF₃ (Sn : Au = 1 : 1) which correspond to the SnF₄-type [2, 3] (two single crystals, A: 762 I_o, R1 = 2.4%; B: 1591 I_o, R1 = 1.2% (SHELXL-93); I4/mmm (No. 139); B: a = 404.8(1) pm, c = 796.4(1) pm, c/a = 1.97, Z_F2 = 0.2354). Due to atom absorption and Mössbauer measurements the crystals contain Au. The compound is paramagnetic and follows the Curie-Weiß law (14.7–251.3 K, θ = ?12 K, μ/μ_B = 1.55). ESR-experiments confirm that Au is surrounded by 6 F^? according to Sn in SnF₄ (2 short (187.5 pm) and 4 longer (202.4 pm) distances). The observed Mössbauer spectra could not be interpreted yet, but they don't correspond to any known.     

The Haloboration of Tri‐tert‐butylazadiboriridine NB2R3: Ring Opening versus NB3 Cluster Formation

The azadiboriridine [–BR–NR–BR–] ( 1 ; R = tBu) is bromoborated at the B–B bond by alkyldibromoboranes R′BBr₂ to give the products Br–BR–NR=BR–BR′–Br ( 8 a – g : R′ = Me, Bu, iBu, Bzl, CH₂CHEt₂, CH₂Cy, CH₂(4‐C₆H₄tBu)). Two isomers of each of the products 8 a – g are formed and attributed to a cis/trans isomerism at the BN double bond; the isomerization is followed thermodynamically and kinetically by NMR methods with 8 a – d . The analogous chloroboration of 1 with BCl₃ yields Cl–BR–NR=BR–BCl₂ ( 8 h ), which at ambient temperature undergoes a degenerate exchange of the ligands Cl and BCl₂ along the B–N–B skeleton. At room temperature, the isomer Cl–BR–NR=BCl–BR–Cl ( 8 h ′) is slowly formed by an irreversible exchange of R and Cl along the B–B bond of 8 h . Different from BCl₃, the chloroborane BH₂Cl is simply added to the B–B bond of 1 under formation of the aza‐nido‐tetraborane NB₃R₃H₂Cl ( 2 b ). The chloroborane BHCl₂ gives a mixture of 8 h ′ and 2 b upon addition to 1 , apparently according to a preceding dismutation into BCl₃ and BH₂Cl. The configuration at the B3 atom of the nido‐clusters NB₃R₃H₂X (X = H, Cl) is discussed on the basis of the corresponding model molecules NB₃Me₃H₂X, whose structure and NMR signals are computed by the B3LYP method. The boranes 8 b – g can be debrominated with Li in the presence of tmen on applying ultrasound. The products are found to be the B‐borylated azadiboriridines [–BR–NR–B(BRR′)–] ( 9 b – g ). The 2‐borylazadiboriridines NB₃H₄ ( 9 h ) and NB₃Me₄ ( 9 i ) were found as local minima on the energy hyperface by the B3LYP method, but minima for structural isomers with lower energy were also found; the tetrahedral clusters NB₃R₄ give high‐energy minima with triplet ground states. Computations of the ¹¹B NMR shifts of 9 h and 9 i support the proposed structures of 9 b – g .     

π‐conjugated polymers having diaza[12]annulene rings and aminopenta‐2,4‐dienylidene groups generated by the ring opening of pyridinium rings

Reactions of N‐(2,4‐dinitrophenyl)pyridinium chloride with 2,5‐dimethyl‐1,4‐phenylenediamine in 1:2, 1:1.5, 1:1, and 2:1 molar ratios caused the ring opening of the pyridinium ring and thereby yielded polymers ( P1 – P4 ) consisting of 5‐(2,5‐dimethyl‐1,4‐phenylene)penta‐2,4‐dienylideneammonium chloride (unit A) and N‐2,5‐dimethyl‐1,4‐phenylene diaza[12]annulenium dichloride (unit B). The ¹H NMR spectra suggested that the composition ratios of unit A to unit B in P1 – P4 were 0.98:0.02, 0.94:0.06, 0.81:0.19, and 0.79:0.21, respectively. P1 – P4 showed an absorption maximum (λ_max) at a longer wavelength than the monomers because of the expansion of the π‐conjugation system. Films of P3 and P4 showed λ_max at a considerably longer wavelength than those in solution, and this was attributable to the ordered structures of the polymers in the solid state. Powder X‐ray diffraction analysis supported the ordered structures of P3 and P4 . Pellets molded from P3 and P4 exhibited a metallic luster, whereas those from P1 and P2 did not show such a luster. Cyclic voltammetry measurements indicated that P1 – P4 were electrochemically active in films. The thermal stability of the polymers depended on the composition ratios of unit A to unit B. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1507–1514, 2007     

Oligo(p‐phenyleneethynylene) (OPE) Molecular Wires: Synthesis and Length Dependence of Photoinduced Charge Transfer in OPEs with Triarylamine and Diaryloxadiazole End Groups

The systematic synthesis and photophysical, electrochemical and computational studies on an extended series of triphenylamine‐[C?C‐1,4‐C₆H₂(OR)₂]_n‐C?C‐diphenyl‐1,3,4‐oxadiazole dyad molecules (the OR groups are at 2,5‐positions of the para‐phenylene ring and R=C₆H₁₃; n=0–5, compounds 1 , 2 , 3 , 4 and 5 , respectively) are reported. Related molecules with identical end groups, triphenylamine‐C?C‐1,4‐C₆H₂(OR)₂‐C?C‐triphenylamine (R=C₆H₁₃; 6 ) and diphenyl‐1,3,4‐oxadiazole‐[C?C‐C₆H₂(OR)₂]₂‐C?C‐diphenyl‐1,3,4‐oxadiazole (R=C₆H₁₃; 7 ) were also studied. These D–B–A 1 – 5 , D–B–D 6 and A–B–A 7 (D=electron donor, B=bridge, A=electron acceptor) systems were synthesized using palladium‐catalysed cross‐coupling reactions of new p‐phenyleneethynylene building blocks. Steady‐state emission studies on the dyads 1 – 5 reveal a complicated behavior of the emission that is strongly medium dependent. In low polarity solvents the emission is characterized by a sharp high‐energy peak attributed to fluorescence from a locally excited (LE) state. In more polar environments the LE state is effectively quenched by transfer into an intramolecular charge‐transfer (ICT) state. The medium dependence is also observed in the quantum yields (QYs) which are high in cyclohexane and low in acetonitrile, thus also indicating charge‐transfer character. Low‐temperature emission spectra for 2 – 5 in dichloromethane and diethyl ether also reveal two distinct excited states, namely the LE state and the conventional ICT state, depending on solvent and temperature. Hybrid DFT calculations for 1 – 7 establish that the OPE bridge is involved in both frontier orbitals where the bridge character increases as the bridge length increases. Computed TD‐DFT data on 1 – 5 assign the emission maxima in cyclohexane as LE transitions. Each time‐resolved emission measurement on 2 – 7 in cyclohexane and diethyl ether reveals a wavelength dependent bi‐exponential decay of the emission with a fast component in the 5–61 ps range on blue detection and a slower approximately 1 ns phase, independent of detection wavelength. The fast component is attributed to LE fluorescence and this emission component is rate limited and quenched by transfer into an ICT state. The fast LE fluorescence component varies systematically with conjugation length for the series of D–B–A dyads 2 – 5 . An attenuation factor β of 0.15 Å^?1 was determined in accordance with an ICT superexchange mechanism.     

Hydrosilylation Induced by N→Si Intramolecular Coordination: Spontaneous Transformation of Organosilanes into 1‐Aza‐Silole‐Type Molecules in the Absence of a Catalyst

Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph₂L¹SiH ( 1 a ), PhL¹SiH₂ ( 2 a ), Ph₂L²SiH ( 3 a ), and PhL²SiH₂ ( 4 a ) containing a CH?N imine group (in which L¹ is the C,N‐chelating ligand {2‐[CH?N(C₆H₃‐2,6‐iPr₂)]C₆H₄}^? and L² is {2‐[CH?N(tBu)]C₆H₄}^?) yielded 1‐[2,6‐bis(diisopropyl)phenyl]‐2,2‐diphenyl‐1‐aza‐silole ( 1 ), 1‐[2,6‐bis(diisopropyl)phenyl]‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 2 ), 1‐tert‐butyl‐2,2‐diphenyl‐1‐aza‐silole ( 3 ), and 1‐tert‐butyl‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 4 ), respectively. Isolated organosilicon amides 1 – 4 are an outcome of the spontaneous hydrosilylation of the CH?N imine moiety induced by N→Si intramolecular coordination. Compounds 1–4 were characterized by NMR spectroscopy and X‐ray diffraction analysis. The geometries of organosilanes 1 a – 4 a and their corresponding hydrosilylated products 1 – 4 were optimized and fully characterized at the B3LYP/6‐31++G(d,p) level of theory. The molecular structure determination of 1 – 3 suggested the presence of a Si?N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor–acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si?N bond is highly polarized pointing to a predominantly zwitterionic Si⁺N^? bond in 1 – 4 . Since compounds 1 – 4 are hydrosilylated products of 1 a – 4 a , the free energies (ΔG₂₉₈), enthalpies (ΔH₂₉₈), and entropies (ΔH₂₉₈) were computed for the hydrosilylation reaction of 1 a – 4 a with both B3LYP and B3LYP‐D methods. On the basis of the very negative ΔG₂₉₈ values, the hydrosilylation reaction is highly exergonic and compounds 1 a – 4 a are spontaneously transformed into 1 – 4 in the absence of a catalyst.     

Exploring the Border between Concerted and Two‐Step Pathways of 1,3‐Dipolar Cycloadditions of Organic Azides to Cyclic Ketene N,X‐Acetals. – Synthesis and 15N‐NMR Spectra of Zwitterions and Spirocyclic Cycloadducts

Cyclic ketene N,X‐acetals 1 are electron‐rich dipolarophiles that undergo 1,3‐dipolar cycloaddition reactions with organic azides 2 ranging from alkyl to strongly electron‐deficient azides, e.g., picryl azide ( 2L ; R¹=2,4,6‐(NO₂)₃C₆H₂) and sulfonyl azides 2M – O (R¹=XSO₂; cf. Scheme 1). Reactions of the latter with the most‐nucleophilic ketene N,N‐acetals 1A provided the first examples for two‐step HOMO(dipolarophile)–LUMO(1,3‐dipole)‐controlled 1,3‐dipolar cycloadditions via intermediate zwitterions 3 . To set the stage for an exploration of the frontier between concerted and two‐step 1,3‐dipolar cycloadditions of this type, we first describe the scope and limitations of concerted cycloadditions of 2 to 1 and delineate a number of zwitterions 3 . Alkyl azides 2A – C add exclusively to ketene N,N‐acetals that are derived from 1H‐tetrazole (see 1A ) and 1H‐imidazole (see 1B , C ), while almost all aryl azides yield cycloadducts 4 with the ketene N,X‐acetals (X=NR, O, S) employed, except for the case of extreme steric hindrance of the 1,3‐dipole (see 2E ; R¹=2,4,6‐(^tBu)₃C₆H₂). The most electron‐deficient paradigm, 2L , affords zwitterions 16D , E in the reactions with 1A , while ketene N,O‐ and N,S‐acetals furnish products of unstable intermediate cycloadducts. By tuning the electronic and steric demands of aryl azides to those of ketene N,N‐acetals 1A , we discovered new borderlines between concerted and two‐step 1,3‐dipolar cycloadditions that involve similar pairs of dipoles and dipolarophiles: 4‐Nitrophenyl azide ( 2G ) and the 2,2‐dimethylpropylidene dipolarophile 1A (R, R=H, ^tBu) gave a cycloadduct 13 H , while 2‐nitrophenyl azide ( 2 H ) and the same dipolarophile afforded a zwitterion 16A . Isopropylidene dipolarophile 1A (R=Me) reacted with both 2G and 2 H to afford cycloadducts 13G , J ) but furnished a zwitterion 16B with 2,4‐dinitrophenyl azide ( 2I) . Likewise, 1A (R=Me) reacted with the isomeric encumbered nitrophenyl azides 2J and 2K to yield a cycloadduct 13L and a zwitterion 16C , respectively. These examples suggest that, in principle, a host of such borderlines exist which can be crossed by means of small structural variations of the reactants. Eventually, we use ¹⁵N‐NMR spectroscopy for the first time to characterize spirocyclic cycloadducts 10 – 14 and 17 (Table 6), and zwitterions 16 (Table 7).     

Two New Cytotoxic Spirostane‐Steroidal Saponins from the Roots of Bletilla striata

Two new spirostane‐steroidal saponins, bletilnoside A ( 1 ) and bletilnoside B ( 2 ), together with five known compounds, 3 – 7 , were isolated from the roots of Bletilla striata (Thunb .) Reichb . F. The structures of the new compounds were determined based on their 1D‐ and 2D‐NMR spectral data. The isolated compounds 1 – 7 were tested for cytotoxicity against four human tumor cells (A549, SK‐OV‐3, SK‐MEL‐2, and HCT15) in vitro using a sulforhodamin B bioassay, and compounds 1, 2 , and 5 showed significant cytotoxicities against all tested tumor cell lines with IC₅₀ values ranging from 3.98±0.16 to 12.10±0.40 μM .     

Über Oxotantalate der Lanthanide des Formeltyps MTaO4 (M = La – Nd,Sm – Lu)

About Lanthanide Oxotantalates with the Formula MTaO₄ (M = La – Nd, Sm – Lu) Besides being a by‐product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO₄ can be easily prepared by sintering lanthanide sesquioxide M₂O₃ and tantalum(V) oxide Ta₂O₅ with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M³⁺ cationic radius. For M = La – Pr the MTaO₄‐type tantalates crystallize in the space group P2₁/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A‐type) and as trigonal dodecahedron for the structure with the smaller ones (called as B‐type in the following). The coordination environment about the Ta⁵⁺ cations can be described as a slightly distorted octahedron (CN = 6) for the A‐type structure of MTaO₄ and a heavily distorted one (CN = 6) for the B‐type. The difference between the two types results from the interconnection of these [TaO₆]^7? octahedra. Whereas they are connected via four vertices to form corrugated layers according to parallel the bc‐plane in the A‐type, the octahedra of the B‐type MTaO₄ structure share edges to built up zig‐zag chains along the c axis.     

Zur Regioselektivität von Cycloadditionen photochemisch erzeugter Benzonitril-isopropylide. 51. Mitteilung über Photoreaktionen

On the regioselectivity of cycloaddition reactions of photochemically generated benzonitrile-isopropylides This paper deals with the physical and chemical differences of zwitterionic benzo-nitrile-isopropylides, which differ by a p-substituent in the phenyl ring (H, F, OCH₃; Scheme 2). These dipolar species (4–6) are produced by irradiation of the corresponding 2 H-azirines ( 1–3 ; Scheme 1) in a 2-methylpentane glass at ?185°. Their UV. spectra are reproduced in the Figure. The spectra of 4 and 5 are characterized by an ‘aromatic band’ at short wavelength, and a longer wavelength band at approximately 275 nm, which is considered to be characteristic of the nitrile-ylide system. The UV. spectrum of the methoxy derivative 6 , which shows a broad absorption at 260 nm, arises by an addition of the ‘nitrile-ylide band’ and the anisole band. The three dipolar species 4–6 do not show any significant differences in the regioselectivity of the cycloaddition with methyl α-methacrylate even though F and OCH₃ have quite different σ-constants (Scheme 1). The addition according to modus A is very much preferred (B/A = 0,076). – It seems, that the substituents F and OCH₃ do not affect the physical and chemical behaviour of the parent benzonitrile-isopropylide (4) . All three dipolar species 4–6 react regiospecifically according to modus A with methyl trifluoroacetate (Scheme 1). The regioselectivity is reduced in the cycloaddition of 4 with methyl propiolate and ethyl phenylpropiolate (B/A = 0,04 and 0,28, respectively). The reduced regioselectivity in the latter case may be attributed to a reduced polarity of the triple bond in the dipolarophile.     

Alternativ-Liganden. XXXII [1]. Neue Tetraphosphan-Nickelkomplexe mit Tripod-Liganden des Typs XM′ (OCH2PMe2)n(CH2CH2PR2)3 – n (M′ = Si,Ge; n = 0 – 3)

Alternative Ligands. XXXII [1]. Novel Tetraphosphane Nickel Complexes with Tripod-Ligands of the Type XM′(OCH₂PMe₂)_n(CH₂CH₂PR₂)_{3 – n} (M′ = Si, Ge; n = 0 – 3) Tripod Ligands of the type XM′(OCH₂PMe₂)_n(CH₂CH₂PMe_{23 – n} (M′ = Si, Ge; n = 0 – 3) ( 1 – 6 , Table 1) have been used together with PPh₃ or PMe₃ for the preparation of novel tetraphosphane complexes of Nickel. The representatives LNiPPh₃ ( 7 – 12 ) are obtained by reaction of Ni(COD)₂ (COD = 1,5-cyclooctadiene) with the corresponding ligands and PPh₃ in toluene in moderate yields. The synthesis of the derivatives LNiPMe₃ ( 13 – 18 ) is partly ( 16 – 18 ) accomplished in analogy to the Ph₃P-complexes; compounds 13 – 16 are obtained in higher yields by reaction of Ni(PMe₃)₄ with the respective ligand. As a rule, 13 – 18 cannot be separated from by-products. The trinuclear complex FSi(CH₂CH₂PMe₂)₃[Ni(PMe₂CH₂CH₂)₃SiF]₃ ( 19 ) is formed together with 18 in the reaction of Ni(COD)₂ with 6 and PMe₃. The new compounds have been characterized (if possible) by analytical (C, H), but in general by spectroscopic investigations (IR; ¹H-, ¹³C-, ¹⁹F-, ³¹P-NMR; MS). A weak, but significant Ni → Si interaction through the cage is indicated by the following results: (i) Large low-field shifts δδ_F of 35.2 ppm ( 12 ), 38.3 ppm ( 18 ) and 37.7 ppm ( 19 ); (ii) ⁶J(PF) coupling constants [or ³J(PNiSiF) through the cage] of 6.0 Hz ( 12 ) and 7.6 Hz ( 18 ) together with a low-field shift δδ_Si of 12.8 ppm ( 12 ); (iii) NiSi distances of 3.95 Å in 7 and 3.92 Å in 12 , accompanied by a compression of the cage along the Ni ··· Si axis. An additional release from the high charge density on Ni results from π-backbonding to the phosphane ligands.     

Neue wasserlösliche Osmiumkomplexe des 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)‐porphyrin‐Anions

Metal Complexes with Tetrapyrrole Ligands. LXXVI. New Water‐soluble Osmium Complexes of 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)porphyrin‐Anion The new symmetrical osmium(II) porphyrinates [Os(tpps₄)L₂]^4– ( 1 b – g ) are formed from [OsO₂(tpps₄)]^4– ( 1 a ) by reduction in presence of the ligands L. 1 e – g react with 1‐methylimidazole to yield the unsymmetrical complexes [Os(tpps₄)LL′]^4– ( 1 h – j ). Except for 1 g – h the osmium(II) porphyrinates are not inert in presence of air and are oxidized to the osmium(III) porphyrinates [Os(tpps₄)L₂]^3– ( 2 b – f ) and [Os(tpps₄)LL′]^3– ( 2 i – j ). These anions are deposited as sodium salts.     

Diborheterocyclen: Oxadiborolan – Oxadiborinan – Diazadiborinan

Diboron Heterocyclic Compounds: Oxadiborolane – Oxadiborinane – Diazadiborinane The diboryl compounds R(Cl)B(CH₂)_nB(Cl)R (R ? Cl or CH₃; n = 2, 3) and the silylated or stannylated starting materials [(CH₃)₃Y]₂X (Y ? Si or Sn; X ? S, NCH₃, O, NCH₃? NCH₃) were used for (5+1)- and (4+2)-cyclocondensation reactions. Dimethylether was an additional starting molecule. While no thiadiborinanes could be isolated, the nitrogen or oxygen containing heterocycles were formed in varying yields. Synthesis and properties of these compounds are described.     

N‐Heterocyclic Carbene Stabilized Boryl Radicals

The reaction of the 2‐(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4‐R‐C₆H₄)₂BX (R=H, X=Br; R=CH₃, X=Cl; R=CF₃, X=Cl) afforded the NHC‐stabilized borenium cations 10 a – c . Cyclic voltammetry revealed a linear correlation between the Hammett parameter σ _p of the para substituent and the half‐wave potential. Chemical reduction with decamethylcobaltocene, [(C₅Me₅)₂Co], furnished the corresponding radicals 11 a – c ; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a – c , with large hyperfine coupling constants to the boron isotopes ¹¹B and ¹⁰B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR₂) revealed for 11 a – c a spin density ratio (BR₂/NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X‐ray diffraction analysis.     

Kinetic Study and NBO Analysis of the Dehydrogenation Mechanism of Five‐membered Ring Heterocyclic 2,5‐Dihydro‐[furan,thiophene, selenophene

The theoretical study of the dehydrogenation of 2,5‐dihydro‐[furan ( 1 ), thiophene ( 2 ), and selenophene ( 3 )] was carried out using ab initio molecular orbital (MO) and density functional theory (DFT) methods at the B3LYP/6‐311G**//B3LYP/6‐311G** and MP2/6‐311G**//B3LYP/6‐311G** levels of theory. Among the used methods in this study, the obtained results show that B3LYP/6‐311G** method is in good agreement with the available experimental values. Based on the optimized ground state geometries using B3LYP/6‐311G** method, the natural bond orbital (NBO) analysis of donor‐acceptor (bond‐antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from non‐bonding lone‐pair orbitals [LP(e)_X3] to δ*_{C(1)  H(2)} antibonding orbital, decrease from compounds 1 to 3 . The LP(e)_X3→δ*_{C(1)  H(2)} resonance energies for compounds 1 – 3 are 23.37, 16.05 and 12.46 kJ/mol, respectively. Also, the LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the decrease of occupancies of LP(e)_X3 non‐bonding orbitals in ring of compounds 1 – 3 ( 3 > 2 > 1 ). The electronic delocalization from LP(e)_X3 non‐bonding orbitals to δ*_{C(1)  H(2)} antibonding orbital increases the ground state structure stability, Therefore, the decrease of LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the kinetic of the dehydrogenation reactions of compounds 1 – 3 (k ₁ >k ₂ >k ₃ ). Also, the donor‐acceptor interactions, as obtained from NBO analysis, revealed that the (_C(4)C(7)→δ*_{C(1)  H(2)} resonance energies decrease from compounds 1 to 3 . Further, the results showed that the energy gaps between (_C(4)C(7) bonding and δ*_{C(1)  H(2)} antibonding orbitals decrease from compounds 1 to 3 . The results suggest also that in compounds 1 – 3 , the hydrogen eliminations are controlled by LP(e)→δ* resonance energies. Analysis of bond order, natural bond orbital charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and synchronous six‐membered cyclic transition state type of mechanism.     

Phosphinsubstituierte Chelatliganden. XVIII. Penta- und Tetracarbonylmetall-Komplexe des Chroms,Molybdäns und Wolframs mit sekundären und tertiären Phosphinothioformamid-Liganden

Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)₆ (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)₅ · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)₅MPPh₂C(S)NHR¹] (R¹ ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)₅ · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R¹ ? Me₃Si, R² ? Ph) are obtained by direct photosubstitution of M(CO)₆ in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)₄M(PPh₂C(S)NHMe)₂] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH₂Br₂ to give the methylene bis(thioformirnidoesters) [Ph₂PC(NR¹)S]₂CH₂ (R¹ ? Ph (8), Me ( 9 )) in quantitative yields.     

Ga8Ir4B – ein Gallium-Iridiumborid mit isolierten,annähernd quadratisch planaren Ir4B-Gruppen in einer vom CaF2-Typ abgeleiteten Struktur

Ga₈Ir₄B – a Gallium Iridium Boride with isolated, nearly square planar Ir₄B Groups in a Structure derived from the CaF₂ Type The new compound Ga₈Ir₄B (tetragonal, I4₁/acd, a = 853.69(2) pm, c = 2 105.69(6) pm, Z = 8, 614 reflections, 31 parameters, R = 0.034) was prepared by reaction of the elements at 1 100°C. The structure is derived from the CaF₂ type. It contains isolated Ir₄B groups with boron in an unusual, nearly square planar coordination.