Phosphinophosphiniden-Phosphorane tBu2P?P = P(R)tBu2 aus Li(THF)2[η2-(tBu2P)2P] und Alkylhalogeniden

The Phosphinophosphinidene-phosphoranes ^tBu₂P? P = P(R)^tBu₂ from Li(THF)₂[η²-(^tBu₂P)₂P] and Alkyl Halides We report the formation of ^tBu₂P? P = P(R)^tBu₂ a and (^tBu₂)₂PR b (with R = Me, Et, ⁿPr, ⁱPr, ⁿBu, PhCH₂, H₂C = CH? CH₂ and CF₃) reactions of Li(THF)₂[η²-(^tBu₂P)₂P] 2 with MeCl, MeI, EtCl, EtBr, ⁿPrCl, ⁿPrBr, ⁱPrCl, ⁿBuBr, PhCH₂Cl, H₂C = CH? CH₂Cl or CF₃Br. In THF solutions the ylidic compounds a predominate, whereas in pentane the corresponding triphosphanes b are preferrably formed. With ClCH₂? CH = CH₂ only b is produced; CF₃Br however yields both ^tBu₂P? P = P(Br)^tBu₂ and ^tBu₂P? P = P(CF₃)^tBu₂, but no b . The ratio of a:b is influenced by the reaction temperature, too. The compounds ^tBu₂P? P = P(Et)^tBu₂ 4a and (^tBu₂P)₂PEt 4 b , e. g., are produced in a ratio of 4:3 at ?70°C in THF, and 1:1 at 20°C; whereas 1:1 is obtained at ?70°C in pentane, and 1:2 at 20°C. Neither ^tBuCl nor H₂C = CHCl react with 2 . The compounds a decompose thermally or under UV irradiation forming ^tBu₂PR and the cyclophosphanes (^tBu₂P)_nP_n.     

Reaktionen des [(me3Si)2P]2PLi mit Chlorphosphanen

Reactions of [(me₃Si)₂P]₂PLi with Chlorophosphanes [(me₃Si)₂P]₂PLi 1 with (C₆H₅)₂PCl yields only a small amount of the expected [(me₃Si)₂P]₂P–P(C₆H₅)₂ 2 ; the main products are (me₃Si)₂P–P(C₆H₅)₂ 3 and (C₆H₅)₂P–P(C₆H₅)₂ 4 besides some (me₃Si)₃P 5 and (C₆H₅)₂P–Sime₃ 6. 3 and 4 result from the metallation of (C₆H₅)₂PCl by 1 t-buPCl₂ and 1 form the P₃-ring (me₃Si)(me₃C)P₃[P(Sime₃)₂] 9 as main product besides some [(me₃Si)₂P]₂P–Sime₃ 7 and 5. 9 is afforded by elimination of me₃SiCl, from the initially formed unstable [(me₃Si)₂P]₂P–P(Cl)Cme₃ 10 . Similarly 1 and PCl₃ yield mainly the P₃-ring (me₃Si)(Cl)P₃ · [P(Sime₃)₂] 11 due to elimination of me₃SiCl from [(me₃Si)₂P]₂P–PCl₂.     

Reaktionen von Silylphosphanen mit Schwefel

Reactions of Silylphosphines with Sulphur We report about reactions of Me₂P? SiMe₃ 2 , MeP(SiMe₃)₂ 3 , (Me₃Si)₃P 4 , P₂(SiMe₃)₄ 5 , and (Me₃Si)₃P₇ 1 with elemental sulphur. Without using a solvent 2 reacts very vigorously. The reactions with 3 and 4 show less reactivity which is even more reduced with 5 and 1 . With equivalent amounts of sulphur the reactions with 2 , 3 , 4 lead to compounds with highest content of sulphur. These compounds are Me₃SiS? P(S)Me₂ 9 from 2 , (Me₃SiS)₂P(S)Me 13 from 3 and (Me₃SiS)₃P(S) 16 from 4 . Besides, the by-products (Me₃Si)₂S 8 , P₂Me₄ 7 , and Me₂P(S)? P(S)Me₂ 11 can be obtained. The reactions of silylphosphines in a pentane solution run much slower so that the formation of intermediates can be observed. Reaction with 2 yields Me₃SiS? PMe₂ 6 and Me₂P(S)PMe₂ 10 , which lead to the final products in a further reaction with sulphur. From 3 (Me₃SiS)(Me₃Si)PMe 14 and (Me₃SiS)₂PMe 12 can be obtained which react with sulphur to (Me₃SiS)₂P(S)Me 13. 4 leads to the intermediates (Me₃SiS)(Me₃Si)₂P 18 , (Me₃SiS)₂(Me₃Si)P 17 , (Me₃SiS)₃P 15 yielding (Me₃SiS)₃P(S) 16 with excess sulphur. Depending on the molar ratio (P₂SiMe₃)₄ 5 reacts to (Me₃Si)₂P? P(SSiMe₃)(Sime₃), (Me₃SiS)(Me₃Si)P? P(SSiMe₃). (Diastereoisomer ratio 10:1), (Me₃SiS)₂P? P(SiMe₃)₂ and (Me₃SiS)₂P? P(SSiMe₃)(Sime₃). With the molar ratio 1:4 the reaction yields (Me₃SiS)₂P? P(SSiMe₃)₂ (main product), (Me₃SiS)₃P(S) and (Me₃SiS)₃P. All silylated silylphosphines tend to decompose under formation of (Me₃Si)₂S. (Me₃Si)₃P₇ reacts with sulphur at 20°C (15 h) under decomposition of the P₇-cage and formation of (Me₃SiS)₃P(S). The products of the reaction of 5 with sulphur in hexane solution (molar ratio more than 1:3) undergo readily further reactions at 60°C under cleavage of P? P bonds and splitting off (Me₃Si)₂S, leading to (Me₃SiS)₃P(S) and cage molecules like P₄S₃, P₄S₇, and P₄S₁₀ and P? S-polymers. (Me₃SiS)₃P(S) isi thermally unstable and decomposes to P₄S₁₀ and (Me₃Si)₂S. Sulphur-containing silylphosphines like (Me₃SiS)P(S)Me₂ react with HBr at ?78°C under formation of Me₃SiBr (quantitative cleavage of the Si? S bond) and Me₂P(S)SH, which reacts with HBr to produce H₂S and Me₂P(S)Br.     

Darstellung SiH-haltiger Silylphosphine und Untersuchung ihrer PMR-Spektren

The preparation of SiH-containing silylphosphines from SiH-containing chlorosilanes is successful by using an excess of chlorosilans. Chemical shift data and coupling constants of the compounds H_xSi[P(C₂H₅)₂]_4?x and (CH₃)_xSi[P(C₂H₅)₂]_4?x are communicated and compared with those of H_xSiX_4?x and (CH₃)_xSiX_4?x (X = halogen or H).     

Controlled anodic generation of the catalyst in kinetic continuous flow analysis

Controlled anodic dissolution of copper in a separate generator cell yields well-defined concentrations of catalyst, depending on the voltage applied. This adjustable generation of copper catalyst makes it possible to determine iron over a wide range of concentration (10–1500 μg Fe³⁺ ml^-1) via the iron(III)—thiosulphate reaction. By the copper(II)-catalyzed hydrogen peroxide—hydroquinone reaction, EDTA can be determined as an inhibitor (0.5–5 μg ml^-1) and cadmium(II) as a reactivator (1–10 μg ml^-1). As zinc(II) forms complexes with 2,2'-bipyridine, which activates copper in this reaction, it can be determined (5–50 μg Zn²⁺ ml^-1) by measuring the decrease in activation. The electrogeneration of silver ion as a catalyst is also described. The sulphanilic acid—peroxodisulphate reaction is catalyzed by silver(I), which is again activated by 2,2'-bipyridine. Zinc(II) can be determined (0.29–2.9 mg Zn²⁺ ml^-1) by the same principle as in the copper(II)-catalyzed reaction.     

Bildung siliciumorganischer Verbindungen. LVI. Reaktionen Si- und C-chlorierter 1,3,5-Trisilapentane mit CH3MgCl

Formation of Organosilicon Compounds. LVI. Reactions of Si- and C-Chlorinated 1,3,5-Trisilapentanes with CH₃MgCl (Cl₃Si? CCl₂)₂SiCl₂ (1) reacts with an excess of meMgCl (me = CH₃) forming me₃Si? C?C? Sime₃ (2), Sime₄, H₂C?C(Sime₃)[CH(Sime₃)₂] (3) as main products and (me₃Si)₂C? CH(Sime₃) and as by-products. The cleavage reaction of (1) to (2) and (3) does not occur when the meMgCl-concentration is lowered. The reaction is started by the formation of a GRIGNARD reagent at a CCl-group in compound (1). Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ forms with ; me₃Si? CCl₂? SiCl₂? CHCl? SiCl₃ forms (me₃Si)₂C?CH(Sime₃). A reaction sequence is given.     

Bildung und Reaktionen P-funktioneller Phosphane

Formation and Reaction of P-functional Phosphanes The reaction of (me₃Si)₂PLi · 2 THF a (me = CH₃) with PCl₃ b at ?78°C via the intermediate (me₃Si)₂P? PCl₂ 1 yields [(me₃Si)₂P]₂PCl 2 and [(me₃Si)₂P]₂P? P(Sime₃)₂ 3 . By addition of me₃CLi c to the reaction mixture of a and b (molar ratio a:b:c (molar ratio a:b:c = 1:1:1) at ?60°C, 2 is formed as a main product, which reacts on to yield [(me₃Si)₂P]₂PH 4 (white crystals, mp = 73°C). By reactions of a:b:c in a molar ratio of 1:1:2 the cyclotetraphosphane (me₃C)₃ (me₃Si)P₄ 7 is accessible, and the additional formation of (me₃Si)₂PLi · 2 THF, (me₃Si)₃P and Li₃P₇ · 3 THF 13 was detected. Warming (me₃Si)₂P? PCl(Cme₃) 5 to 20°C produces cis- and trans-cyclotetraphosphanes (me₃Si)₂(me₃C)₂P₄. By running the reaction of a and b at ?78°C and adding me₃CLi only after 24 h, additionally to (me₃Si)₂P? PH Cme₃) and (me₃Si)₃P also (me₃Si)₂P? P(Cme₃)? P(Cme₃)? P (Sime₃)₂ is obtained, which is formed by metallation of (me₃Si)₂P? PCl(Cme₃) with me₃CLi and by further reaction of the intermediate (me₃Si)₂P? PLi(Cme₃) with (me₃Si)₂P? PCl(Cme₃). The reaction of (me₃Si₃)P with PCl₃ at ?78°C only yields (me₃Si)₂P? PCl₂ 1 and me₃SiCl. On addition of me₃CLi (?78°C, molar ratio = 1:1:1) preferrably 2 and (me₃Si)₂P? PCl(Cme₃) are formed, whereas after warming the mixture to 20°C, 4 and (me₃Si)₂P? PH(Cme₃) are found to be the main products. These reactions are induced by the cleavage of 1 by means of me₃CLi, and by the formation of (me₃Si)₂PLi and me₃C? PCl₂.     

Investigation of the electrocatalytic oxidation of formate and ethanol at platinum black under microbial fuel cell conditions

In this communication, we discuss the electro-oxidation of the fermentation products formate and ethanol at platinum black modified electrodes under microbial fuel cell conditions, i.e., at neutral pH, room temperature, and in microbial culture solutions. The electrocatalytic oxidation was studied using cyclic voltammetry, chronoamperometry, and potentiostatic coulometry. Current densities up to 6 mA cm⁻² at 0.2 V oxidation potential and 97% coulombic efficiency were observed for the electro-oxidation of 100 mM solutions of formate in pH 7 buffer solution. Electrode deactivation could be successfully prevented using an oxidative potential reactivation procedure. Polymer coating, however, fully stopped the formate oxidation. As expected, the electro-oxidation of ethanol was less efficient—with a limiting current density being 600 μA cm⁻².Dedicated to Professor Dr. Alan M. Bond on the occasion of this 60th birthday.     

Structural characterization of a pentacene monolayer on an amorphous SiO2 substrate with grazing incidence x-ray diffraction

Grazing incidence X-ray diffraction reveals that a pentacene monolayer, grown on an amorphous SiO2 substrate that is commonly used as a dielectric layer in organic thin film transistors (OTFTs), is crystalline. A preliminary energy-minimized model of the monolayer, based on the GIXD data, reveals that the pentacene molecules adopt a herringbone arrangement with their long axes tilted slightly from the substrate normal. Although this arrangement resembles the general packing features of the (001) layer in single crystals of bulk pentacene, the monolayer lattice parameters and crystal structure differ from those of the bulk. Because carrier transport in pentacene OTFTs is presumed to occur in the semiconductor layers near the dielectric interface, the discovery of a crystalline monolayer structure on amorphous SiO2 has important implications for transport in OTFTs.     

Engineering entangled photon pairs with metal–organic frameworks

The discovery and design of new materials with competitive optical frequency conversion efficiencies can accelerate the development of scalable photonic quantum technologies. Metal–organic framework (MOF) crystals without inversion symmetry have shown potential for these applications, given their nonlinear optical properties and the combinatorial number of possibilities for MOF self-assembly. In order to accelerate the discovery of MOF materials for quantum optical technologies, scalable computational assessment tools are needed. We develop a multi-scale methodology to study the wavefunction of entangled photon pairs generated by selected non-centrosymmetric MOF crystals via spontaneous parametric down-conversion (SPDC). Starting from an optimized crystal structure, we predict the shape of the G⁽²⁾ intensity correlation function for coincidence detection of the entangled pairs, produced under conditions of collinear type-I phase matching. The effective nonlinearities and photon pair correlation times obtained are comparable to those available with inorganic crystal standards. Our work thus provides fundamental insights into the structure–property relationships for entangled photon generation with metal–organic frameworks, paving the way for the automated discovery of molecular materials for optical quantum technology.

The discovery and design of new materials with competitive optical frequency conversion efficiencies can accelerate the development of scalable photonic quantum technologies.