Untersuchungen zur Reaktivität in den Systemen A/Cu/M/O (A = Na–Cs und M = Co,Ni, Cu,Ag); Synthese und Kristallstrukturen von K3Cu5O4 und Cs3Cu5O4

Reactivity in the Systems A/Cu/M/O (A = Na–Cs and M = Co, Ni, Cu, Ag); Synthesis and Crystal Structures of K₃Cu₅O₄ und Cs₃Cu₅O₄ The systems A/Cu/M/O with A = Na–Cs and M = Co, Ni, Cu, Ag have been investigated with preparative, thermoanalytical and in situ X‐ray techniques to study the reactivity. For the redox reaction Co/CuO in the presence of Na₂O the intermediate, NaCuO, has been characterized. K₃Cu₅O₄ was obtained by annealing intimate mixtures of K₂O and CuO (molar ratio 1 : 1) in Ag containers at 500 °C. Cs₃Cu₅O₄ could be synthezised by reaction of KCuO₂ with Cs₂O (molar ratio 1 : 1) in Cu containers at 500 °C. Both compounds crystallize in the space group P2₁/c with Z = 4 isotypic to Rb₃Cu₅O₄ [IPDS data, Mo–Kα; K₃Cu₅O₄: a = 946.0(1), b = 735.61(6), c = 1401.3(2) pm, β = 107.21(1)°; 2249 F²(hkl), R₁ = 7.09%, wR₂ = 11.42%; Cs₃Cu₅O₄: a = 1027.7(1), b = 761.42(7), c = 1473.4(2) pm, β = 106.46(1)°, 1712 F²(hkl), R₁ = 6.04%, wR₂ = 14.22%]. Force constants obtained from FIR experiments for the deformation mode δ(O–Cu–O), the Madelung Part of the Lattice Energie, MAPLE, Effective Coordination Numbers, ECoN, calculated via Mean Effective Ionenradii, MEFIR, are given.     

Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit

The sterically hindered Schiff bases (L³–L⁵), prepared from 3,5‐dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)₄ for asymmetric oxidation of aryl methyl sulfides with H₂O₂ as terminal oxidant. Among the ligands L³–L⁵, L⁴ with a tert‐butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)₄ in a molar ratio of 100:1:1.2:120 for sulfide:Ti(OiPr)₄:ligand:H₂O₂ in CH₂Cl₂ at 0 °C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4‐bromophenyl sulfide and methyl 4‐methoxyphenyl sulfide with H₂O₂ catalyzed by the Ti(OiPr)₄–L⁴ system gave 79–84% yields and 54–59% ee of the corresponding sulfoxides in CH₂Cl₂ at 20 °C. The chiral induction capability of the cumenyl‐modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert‐butyl groups at the 3,5‐positions of the salicylidenyl unit. Copyright © 2011 John Wiley & Sons, Ltd.     

Thiomethylation of amino alcohols using formaldehyde and hydrogen sulfide

Three-component condensations of formaldehyde with hydrogen sulfide and hydroxylamine or amino alcohols at a ratio of 3:2:1 give 47–73% of N-hydroxy(or hydroxyalkyl)-1,3,5-dithiazinanes. The reactions of CH₂O with H₂S and hydroxylamine or α-amino alcohols at a ratio of 4:3:1 involve both amino and hydroxy groups, leading to the corresponding dithiazinanes. 4-Aminobutan-1-ol reacts with CH₂O and H₂S under analogous conditions only at the amino group to form 4-(1,3,5-dithiazinan-5-yl)butan-1-ol.     

A Direct Amination of Isoprene by Aniline – Catalyzed by Palladium Complexes

The reaction of isoprene with aniline, catalyzed by Pd (acac)₂–(RO)₃P‐CF₃COOH, (1:4:4) (R = Me, Et, acac = (CH₃CO)₂CH‐) in MeCN solution, results in high (up to 89 mol.%) selectivity of N–(3‐methyl‐2‐buten‐1‐yl) aniline. The presence of telomeric products in the reaction mixture is observed at a P/Pd ratio of 1:2 and 1:1. The use of (1,1,1‐trifluoro, 4‐perfluorocyclo hexyl ‐2,4‐butanedionato) palladium as the catalyst gives rise to 92 mol% mol.selectivity of telomers by the favored tail‐to‐head and head to head coupling.     

Selective photometric determination of low conentrations of selenium(IV) and selenium(VI) in bottled drinking water

A procedure is developed for the selective photometric determination of selenium(IV) in bottled drinking water by the oxidation of Methylene Blue in 1 M HCl to colorless decomposition products and of selenium(VI) by its interaction with the specified reagent at pH 5–6 with the formation of a colored ion pair. The limits of detection are 1 and 0.8 µg/L, respectively. At the concentration of selenium(IV) 2 µg/L, the admissible weight ratios are: SeO₄^2-, Br₃^- (1: 20); Br^– (1: 60); I^–, IO₃^- and IO₄^- (1: 100). At equal concentration of selenium(VI), the following species: SeO₄^2-(1: 20); Br₃^-, Br^–, I^–, IO₃^-, and IO₄^- (1: 100) do not interfere with the determination. Other anions and cations present in highly mineralized waters do not interfere with the determination. The relative error of determination is 8–10% in the concentration range 2–10 µg/L of selenium(IV) and selenium(VI) and does not exceed 5% in their concentration range of 10–100 µg/L.     

Effect of acid treatment of Corich core–Ptrich shell/C electrocatalyst on oxygen reduction reaction

Co_{rich core}–Pt_{rich shell}/C prepared by thermal decomposition and chemical reduction methods were treated by 20% H₂SO₄ aqueous solution and used as the electrocatalysts for the oxygen reduction reaction (ORR). The particle size range of Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1) on carbon powder support decreased from 3–8 to 1–6 nm when the time for the electrocatalysts immersed and treated with 20% H₂SO₄ aqueous solution increased from 0 to 4 h. Using Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1)/C treated with 20% H₂SO₄ from 0 to 4 h as the working electrode, the open circuit potential of ORR in 0.5 M HClO₄ aqueous solution increased from 0.9995 to 1.0155 V, and the current density, mass activity, and specific activity at the overpotential of 0.1 V increased from 0.619 mA cm^?2, 6.184 A g^?1, and 18.614 μA cm^?2 to 0.912 mA cm^?2, 15.544 A g^?1, and 23.413 μA cm^?2, respectively.     

Selective photometric redox determination of periodate and iodate ions in bottled drinking water

method has been developed for the selective photometric redox determination of periodate and iodate ions in bottled drinking water based on redox reactions of analytes with Methylene Blue with different duration of processes, products of which form the analytical signal. The limits of detection for periodate and iodate ions are 0.5 and 0.2 µg/L, respectively. The allowable weight ratios for concomitant ions for (at the analyte concentration 2 µg/L) are as follows: I^–, Br^–, IO₃^–, BrO₃^–, ClO^–, CIO^–, CIO₂^–, CIO₃^– and CIO₄^–(1: 100); and for IO₃^– (1 µg/L) are: BrO₃^–₂^–, NO (1: 60), CIO^–, CIO₂^–, (1: 100), and I^–, Br^–, IO₄^–, CIO₃^–, and CIO₄^– (1: 200). The HCIO₃^–, Cl^–, and SO₄^2- anions and Ca²⁺, Mg²⁺, Na⁺, K²⁺, and NH₄⁺ cations are macrocomponents of drinking water and at total concentrations up to 10 g/L do not affect the results of analysis. In the concentration range 1–10 µg/L of IO₄^– andIO₃^–, the total error of determination is 5–7%.     

Solid–liquid Equilibria in the Quaternary System Na+, Mg2+//Cl–, SO2–4–H2O at 25 and 30°C

The isoplethic sections in the diagram of the quaternary system Na⁺ , Mg²⁺ //Cl^– , SO^2– ₄ –H₂ O were established at 25 and 30oC by analytical and conductometric measurements. Three compounds can be observed in the isoplethic sections: NaCl, Na₂ SO₄ and MgNa₂ (SO₄ )₂ 4 H₂ O. Seven fields are determined, relating to the precipitation of one, two or three salts. The solubility range of MgNa₂ (SO₄ )₂ 4 H₂ O is wide, while the liquidus curve of Na₂ SO₄ is very short. The compositions, expressed in Jänecke coordinates, at the eutonic and peritonic points, respectively, were: 42.70% Cl^– and 745% H₂ O; 79.47% Cl^– and 787% H₂ O; 71.6% Cl^– and 744% H₂ O at 25°C; and 48.80% Cl^– and 715% H₂ O; 80.20% Cl^– and 778% H₂ O; 70.14% Cl^– and 707% H₂ O at 30°C.     

Synthesis of poly(4‐vinylpyridine) by reverse atom transfer radical polymerization

Controlled radical polymerization of 4‐vinylpyridine (4VP) was achieved in a 50 vol % 1‐methyl‐2‐pyrrolidone/water solvent mixture using a 2,2′‐azobis(2,4‐dimethylpentanitrile) initiator and a CuCl₂/2,2′‐bipyridine catalyst–ligand complex, for an initial monomer concentration of [M]₀ = 2.32–3.24 M and a temperature range of 70–80 °C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First‐order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number–average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29–1.35 were indicative of controlled radical polymerization. The highest number–average degree of polymerization of 247 (number–average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 °C, [M]₀ = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70–80 °C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5748–5758, 2007     

Compositions of phases in the interaction of rare-earth metals with selenium

The interaction of rare-earth metals (Pr, Nd, Sm, Y, Er, and Yb) with selenium at Ln: Se = 1: 2, 2: 3, 3: 4, and 1: 1 under polythermal (293–1270 K) and isothermal (770 and 1170 K) heat treatment conditions was studied by differential thermal and X-ray powder diffraction analyses. While heating the reaction mixture, the exothermic events in the interaction between elements occur within the temperature ranges 620–750 K (Pr), 580–870 K (Sm), and 620–920 K (Er). X-ray powder diffraction analysis detected the formation of the following phases in the homogeneous state: at 770 K, LnSe₂ and Yb₂Se₃, and at 1170 K, Ln₃Se₄, Ln₂Se₃, and YbSe. Scanning electron microscopy showed that particles of the selenide phases are formed by 1 × 2–5-μm fragments, which constitute a spongy structure of agglomerates tens to hundreds of micrometers in size.     

Supercritical fluid extraction of the volatile oil from Santolina chamaecyparissus

Supercritical fluid extraction (SFE) of the volatile oil from Santolina chamaecyparissus L. flower heads was performed under different conditions of pressure, temperature, mean particle size and CO₂ flow rate. This oil was compared with the essential oil isolated by hydrodistillation (HD). The SFE volatile and essential oils were analysed by GC and GC‐MS. The range of the main volatile components obtained with HD and SFE were, respectively: 1,8‐cineole (25–30% and 7–48%), camphor (7–9% and 8–14%), borneol (7–8% and 2–11%), terpinen‐4‐ol (6–7% and 1–4%), terpinolene (1–4% and 1–7%) and isobornyl acetate (1–2% and 1–11%). The chemical composition of the extracts was greatly influenced by the conditions of pressure and temperature used. In fact, it was possible to enrich the sesquiterpene fraction by increasing the pressure from 8 to 9 MPa, while changing the temperature from 40 to 50°C at 90 bar enriched of the volatiles in n‐alkanes.     

Reactions of 1-aryl-2,2,2-trifluoroethanone oximes with tetrasulfur tetranitride: Novel synthesis of 5-aryl-5-trifluoromethyl-4H-1,3,2,4,6-dithiatriazines and 1-aryl-2,2,2-trifluoro-ethanonylidenaminosulfenamides

The reactions of 1-aryl-2,2,2-trifluoroethanone oximes with tetrasulfur tetranitride (S₄N₄) in toluene at reflux gave 5-aryl-5-trifluoromethyl-4H-1,3,2,4,6-dithiatriazines 2 , 1-aryl-2,2,2-trifluoroethanonyliden-aminosulfenamides 3 and sulfur in 0–37%, 7–53%, and 2–41% yields, respectively. Treatment of 2 with tributyltin hydride in the presence of azobisisobutyronitrile in benzene at 80° afforded 3 in excellent yields.     

Aromatic polyamides. III. Copoly(4,4′-oxanilideterephthalamide—4,4′-phenyleneterephthalamide): Synthesis,wet-spinning,fiber thermal characterization,and stability in sulfuric acid

Copoly(4,4′-oxanilideterephthalamide—4,4′-phenyleneterephthalamide) (A-202/PPD) was synthesized by reaction of 4,4′-diaminooxanilide, p-phenylenediamine, and terephthaloyl chloride in organic solvents. Copolymer inherent viscosities in H₂SO₄ as high as 10.3 were obtained. Isotropic copolymer solutions (4%—5% concentration) of A-202/40%–80% PPD were spun to fibers with tenacity/elongation/modulus at 1% extension in the 13–14 gpd/1.5%–2%/700–1000 gpd range. Oxamide and amide stabilities in 98–100% H₂SO₄ and 20% oleum were compared. Poly(4,4′-oxanilideterephthalamide) (A-202), A-202/PPD copolymers, and poly(4,4′-phenyleneterephthalamide) (PPT) were unstable in 20% oleum, but all proved relatively stable in 100% H₂SO₄. However, the oxamide linkage proved less stable than the amide linkage in 98% H₂SO₄. A-202 and A-202/PPD copolymers formed stable anisotropic spinning solutions in 1% oleum at 10–20% concentrations. Dynamic mechanical analyses (Vibron) showed no glass transition temperature (T_g) below 200°C. Dilatometric measurement of A-202/50% PPD revealed a T_g at 257°C. Differential thermal analyses of A-202/40–80% PPD exhibited endotherms at 470–480°C. Thermogravimetric analyses showed no significant weight loss below 400°C.     

Preparation of benzo[4,5]thiazolo[3,2-a]chromeno[4,3-d]pyrimidin-6-one derivatives using MgO-MgAl2O4 composite nano-powder

MgO-MgAl₂O₄ nanocomposite was prepared from the co-precipitation of Mg(NO₃)₂ and Al(NO₃)₃ salts, characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and fourier transform infrared spectroscopy (FTIR) techniques and evaluated in the synthesis of thirty five derivatives of benzo[4,5]thiazolo[3,2-a]chromeno[4,3-d]pyrimidin-6-ones (d₁-d₃₄) via the multi-component reaction of 4-hydroxycoumarins, aldehydes, and 2-aminobenzothiazole derivatives under solvent free condition. The catalytic activity of MgO-MgAl₂O₄ nanocomposite and the synthesis of the above mentioned compounds were investigated under thermal solvent free (times: 1.4–3 h; yields: 75–95%), ultrasonic irradiation (US) conditions (times: 1–2.5 h; yields: 69–97%) and using high-speed ball milling (HSBM) technique (times: 0.7–2.5 h; yields: 67–97%). In all cases, the products were obtained in excellent yields. Nuclear Magnetic Resonance (NMR) and MASS spectroscopy were used to characterize the structure of the desired product. The mechanism for the preparation of compounds d₁-d₃₄ was proposed and confirmed by ¹H NMR investigations.     

Reactions of S4N4 with tertiary phosphines—Synthesis of phosphiniminocyclothiazenes and their reactions

The reactions of S₄N₄ with phosphines of the type PhPR₂ ( 1–5 ) and PhR′PR [ 6–11 (R′ = dicyclohexylamino), R: 1,6 = pyrrolidino; 2,7 = piperidino; 3,8 = morpholino; 4,9 = N-methylpiperazino; 5,10 = hexamethylenimino; and 11 = anilino] afford the phosphiniminocyclotrithiazene derivatives, 12–22 at room temperature. Only in the case of the phosphine 10 was the disubstituted derivative 23 isolated (in 65% yield). The trithiazene derivatives of the chiral phosphines in refluxing CH₃CN produce the acyclic compounds →PN–S₃N, 24–27 in ca. 60% yield. Norbornadiene reacts at room temperature with the cyclotrithiazene derivatives to give the addition products 28–35 . →P=N–S₃N₃ derivatives are found to be stable in 2M NaOH. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8 : 225–232, 1997.     

Diacetonalkohol als Komplexligand. Die Kristallstrukturen von [MnBr2{O=C(Me)CH2–C(Me)2OH}2] und [M{O=C(Me)CH2–C(Me)2OH}2][MCl4] mit M = Fe,Co und Zn

Diacetone Alcohol as Complex Ligand. Crystal Structures of [MnBr₂{O=C(Me)CH₂–C(Me)₂OH}₂] and [M{O=C(Me)CH₂–C(Me)₂OH}₂][MCl₄] with M = Fe, Co, and Zn The metal halides MnBr₂ and MCl₂ (M = Fe, Co, Zn) react with diacetone alcohol (4-hydroxy-4-methyl-2-pentanon) forming the title compounds, which are characterized by IR spectroscopy and crystal structure analyses. [MnBr₂{O=C(Me)CH₂–C(Me₂)OH}₂] ( 1 ): Space group C2/c, Z = 4, lattice dimensions at 293 K: a = 1189.2(4), b = 1317.2(3), c = 1200.0(3) pm, β = 102.25(3)°, R₁ = 0.0256. In 1 the manganese atom is coordinated in a distorted octahedral fashion by the two cis bromine atoms and by the four oxygen atoms of the two diacetone alcohol chelating molecules. The distances Mn–[OH] (223.8 pm) and Mn–[O=C] (222.1 pm) are only slightly different. [M{O=C(Me)CH₂–C(Me)₂OH}₂][MCl₄] [M = Fe ( 2 ), Co ( 3 ), Zn ( 4 )]: 2 and 3 crystallize isotypically with each other in the space group Pc, Z = 4. Lattice dimensions for 2 at 293 K: a = 865.8(3), b = 926.3(2), c = 1401.5(1) pm, β = 104.19(2)°, R₁ = 0.0421. Lattice dimensions for 3 at 293 K: a = 872.3(1), b = 925.7(1), c = 1394.2(3) pm, β = 104.79(2)°, R₁ = 0.0481. As in 1 , the metal atoms of the [M{O=C(Me)CH₂–C(Me)₂OH}₂]²⁺ ions in 2 and 3 are chelated in a distorted octahedral fashion by two diacetone alcohol molecules and associated cis via two μ-Cl atoms of the [MCl₄]^2– anions to form strands. [Zn{O=C(Me)CH₂–C(Me)₂OH}₂][ZnCl₄] ( 4 ): Space group C2/c, Z = 4. Lattice dimensions at 213 K: a = 1582.27(13), b = 1356.15(13), c = 941.93(7) pm, β = 107.283(10)°, R₁ = 0.0328. The zinc atom of the dication in 4 is associated in a distorted octahedral fashion by the two diacetone alcohol chelating molecules in the equatorial positions and trans by two μ-Cl atoms of the [ZnCl₄]^2– ions to form strands.     

Zur oxidativen Addition von 1-Halogenalk-1-inen – Synthese und Struktur von Phenylalkinylpalladium-Komplexen

On the Oxidative Addition of 1-Halogenalk-1-ynes – Synthesis and Structure of Phenylalkynylpalladium Complexes [Pd(PPh₃)₄] ( 2 ) reacts with IC≡CPh and ClC≡CPh in the sense of an oxidative addition to give trans-[Pd(C≡CPh)X(PPh₃)₂] (X = I: 3 a , X = Cl: 3 b ). As side products trans-[PdX₂(PPh₃)₂] (X = I: 4 a , X = Cl: 4 b ; < 10%) and PhC≡C–C≡CPh ( 5 ; X = I: ca 30%, X = Cl: < 4%) are formed. 3 a and 3 b were characterized by NMR (¹H, ¹³C, ³¹P) and IR spectroscopies as well as by X-ray single-crystal structure analyses. In the crystals of 3 a and 3 b isolated molecules were found. The Pd–C≡C–Ph unit is linear in 3 a and approximately linear in 3 b [Pd–C≡C 174.2(6)°, C≡C–C 179,0(7)°].     

Synthesis and light emitting properties of polyacetylenes having pendent fluorene groups

Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA1 ), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) ( PFA2 ), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA3 ), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA4 ), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA5 ) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers ( M1–M5), using WCl₆, MoCl_5, and TaCl₅ as catalysts and n‐Bu₄Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m² at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m² at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006     

Phosphaniminato‐Acetato‐Komplexe von Cobalt und Cadmium mit M4N4‐Heterocuban‐Struktur

Phosphoraneiminato‐Acetato Complexes of Cobalt and Cadmium with M₄N₄ Heterocubane Structure The phosphoraneiminato‐acetato complexes [M(NPEt₃)(O₂C–CH₃)]₄ with M = Co and Cd are formed from the anhydrous metal(II) acetates with excess Me₃SiNPEt₃ at 180 °C. By crystallization from diethyl ether blue, moisture sensitive single crystals of [Co(NPEt₃) · (O₂C–CH₃)]₄ can be obtained, while colourless single crystals of [Cd(NPEt₃)(O₂C–CH₃)]₄ · 2 CH₂Cl₂ originate from dichloromethane solution. In vacuo the intercalary CH₂Cl₂ is released. The complexes are characterized by their IR spectra and by crystal structure analyses. In both complexes the metal atoms are associated via μ₃–N bridges of the (NPEt₃^–) groups to form heterocubanes. In the cobalt complex the acetato ligands are bonded in a semichelate fashion with a short Co–O and a long Co–O bond each (Co–O distances in average 199.5 and 257.4 pm). In the cadmium complex the acetato groups form almost symmetrical chelates (Cd–O distances in average 232.1 and 237.8 pm); this leads to a distorted trigonal‐bipyramidal arrangement at the cadmium atoms. [Co(NPEt₃)(O₂C–CH₃)]₄: Space group P 1, Z = 4, lattice dimensions at –60 °C: a = 1110.1(2), b = 2051.3(5), c = 2169.5(4) pm, α = 100.03(2)°, β = 103.404(15)°, γ = 97.63(2)°, R = 0.0480. [Cd(NPEt₃)(O₂C–CH₃)]₄ · 2 CH₂Cl₂: Space group C2/c, Z = 4, lattice dimensions at –80 °C: a = 1550.2(1), b = 2101.1(1), c = 1706.1(1) pm, β = 91.09(1)°, R = 0.0311.     

Conformational preferences of Si–Ph,H and Si–Ph,Me silacyclohexanes and 1,3-thiasilacyclohexanes. Additivity of conformational energies in 1,1-disubstituted heterocyclohexanes

The conformational equilibria of 1-phenyl-1-silacyclohexane 1, 3-phenyl-1,3-thiasilacyclohexane 2, 1-methyl-1-phenyl-1-silacyclohexane 3, and 3-methyl-3-phenyl-1,3-thiasilacyclohexane 4 have been studied for the first time by low temperature ¹³C NMR spectroscopy at 103 K. Predominance of the equatorial conformer of compound 1 (Ph_eq/Ph_ax=78%:22%) is much less than in its carbon analog, phenylcyclohexane (nearly 100% of Ph_eq). And in contrast to 1-methyl-1-phenylcyclohexane, the conformers with the equatorial Ph group are predominant for compounds 3 and 4: at 103 K, Ph_eq/Ph_ax ratios are 63%:37% (3) and 68%:32% (4). As the Si–C bonds are elongated with respect to C–C bonds, the barriers to ring inversion are only between 5.2–6.0 (ax→eq) and 5.4–6.0 (eq→ax) kcal mol^?1. Parallel calculations at the DFT and MP2 level of theory (as well as the G2 calculations for compound 1) show qualitative agreement with the experiment. The additivity/nonadditivity of conformational energies of substituents on cyclohexane and silacyclohexane derivatives is analyzed. The geminally disubstituted cyclohexanes containing a phenyl group show large deviations from additivity, whereas in 1-methyl-1-phenyl-1-silacyclohexane and 3-methyl-3-phenyl-1,3-thiasilacyclohexane the effects of the methyl and phenyl groups are almost additive. The reasons for the different conformational preferences in carbocyclic and heterocyclic compounds are analyzed using the homodesmotic reactions approach.