Iminophosphanes: Unconventional Compounds of Main Group Elements

The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as “exotic” in main group chemistry. While the rich chemistry of P? C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry.     

Synthesis and characterisation of phosphane-substituted Co3C clusters having a pendant allyl side-chain

Substituted μ₃-carbido-capped tricobalt carbonyl clusters have been synthesised by reaction of [Co₃(μ₃-C(O)OCH₂CHCH₂)(CO)₉] with a range of monodentate and chelating phosphane ligands. The products have been characterised by microanalysis, IR and NMR spectroscopy, mass spectrometry and, in the case of [Co₃(μ₃-CR)(CO)₇(dppe)], [Co₃(μ₃-CR)(CO)₇(dppm)], [Co₃(μ₃-CR)(CO)₇(PPh₃)₂], [Co₃(μ₃-CR)(CO)₇(PMe₃)₂] and [Co₃(μ₃-CR)(CO)₆(PEt₃)₃] (R=C(O)OCH₂CHCH₂), single crystal X-ray diffraction.     

A three-component reaction between alkenes, secondary phosphanes, and elemental selenium: a novel, efficient, atom-economic synthesis of diselenophosphinic esters

A novel, convenient, atom-economic approach toward the synthesis of diselenophosphinic esters has been developed via the three-component reaction between aryl- or hetarylalkenes secondary phosphanes, and elemental selenium. The reaction proceeds without a catalyst (85 °C, 3 h, 1,4-dioxane) to afford the target compounds in good to high yields.     

Über die Oxo‐cyclotetraphosphane (PBut)4O1–4

Contributions to the Chemistry of Phosphorus. 243 On the Oxocyclotetraphosphanes (PBu^t)₄O_1–4 Under suitable conditions, the reaction of tetra‐tert‐butylcyclotetraphosphane, (PBu^t)₄, with dry atmospheric oxygen gives rise to the corresponding monoxide (PBu^t)₄O ( 1 ) which has been isolated by column chromatography. The reaction with hydrogen peroxide furnishes a mixture of oxocyclotetraphosphanes (PBu^t)₄O_1–4 consisting of two constitutionally isomeric dioxides (PBu^t)₄O₂ ( 2 a , 2 b ), the trioxide (PBu^t)₄O₃ ( 3 ), and the tetraoxide (PBu^t)₄O₄ ( 4 ), in addition to 1 . According to the ³¹P NMR parameters the oxygen atoms are exclusively exocyclically bonded to the phosphorus four‐membered ring. Which of the P atoms are present as λ⁵‐phosphorus follows from the different low‐field shifts of the individual P nuclei compared with the starting compound. Accordingly, 1 is 1,2,3,4‐Tetra‐tert‐butyl‐1‐oxocyclotetraphosphane, 2 a and 2 b are 1,2,3,4‐Tetra‐tert‐butyl‐1,2‐dioxo‐ and ‐1,3‐dioxocyclotetraphosphane, respectively, 3 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3‐trioxocyclotetraphosphane, and 4 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3,4‐tetraoxocyclotetraphosphane. When the oxidation reaction proceeds a fission of the P₄ ring takes place.     

P(SiiPr3)3: the First Trisilylphosphane Derivative with an almost Planar Three‐Coordinated Phosphorus Atom

The title compound ( 1 ) was obtained by salt‐metathesis reaction of iPr₃SiPLi₂ with two molar equiv. of iPr₃SiOTf (OTf = OSO₂CF₃) in 34% yield. Surprisingly, ( 1 ) consists of an 4 : 1 mixture of the two diastereomers ( 1 a ) and ( 1 b ), which do not interconvert to each other even at their decomposition temperature (> 70 °C). They represent different iPr‐rotational isomers which are separated by an unusual high rotational barrier (> 25 kcal mol^–1), resulting from hindered rotations around the Si–C and C–C bonds. The unexpectedly small magnitude of the ¹J(Si, P) coupling constant of ( 1 a ) (9.4 Hz) and ( 1 b ) (9.0 Hz) reflects unusual electronic properties of the Si₃P skeleton. Hitherto only ( 1 a ) could be isolated in the form of single‐crystals and its structure was determined by X‐ray diffraction analysis. The P‐atom in ( 1 a ) is almost planar coordinated (sum of bond angles = 359.789(3)°), but the Si–P‐distance (2.264(7) Å) resembles those values of related silylphosphanes with pyramidally coordinated P atoms. Although MNDO calculations revealed two other iPr‐rotational isomers with similar energy, they prove that the Si₃P skeleton prefers the trigonal‐planar arrangement due to steric congestion.     

Kristallstrukturelle,Festkörper‐31P‐CP/MAS‐NMR,TOSS, 31P‐COSY‐NMR und mechanistische Beiträge zur Koordinationschemie des Octacarbonyldicobalts mit den Liganden Bis(diphenylphosphanyl)amin,Bis(diphenylphosphanyl)methan und 1,1,1‐Tris(diphenylphosphanyl)ethan

Chemistry of Polyfunctional Molecules. 133. X‐Ray Crystal Structural, Solid‐state ³¹P CP/MAS NMR, TOSS, ³¹P COSY NMR, and Mechanistic Contributions to the Co‐ordination Chemistry of Octacarbonyldicobalt with the Ligands Bis(diphenylphosphanyl)amine, Bis(diphenylphosphanyl)methane, and 1,1,1‐Tris(diphenylphosphanyl)ethane Co₂(CO)₈ reacts with bis(diphenylphosphanyl)amine, HN(PPh₂)₂ (Hdppa, 1 ), in two steps to afford the known compound [Co(CO)(Hdppa‐κ²P)₂][Co(CO)₄] · 2 THF ( 6 a · 2 THF). The intermediate [Co(CO)₂(Hdppa‐κ²P) · (Hdppa‐κP)][Co(CO)₄] · dioxane · n‐pentane ( 5 · dioxane · n‐pentane) was isolated for the first time and was characterized by X‐ray analysis. The cation 5 ⁺ exhibits a slightly distorted trigonal‐bipyramidal geometry. Detailed ³¹P‐NMR investigations (solid‐state CP/MAS NMR, TOSS, ³¹P‐COSY, ³¹P‐EXSY) showed that the additional tautomer [Co(CO)₂(Hdppa‐κ²P)(Ph₂P–N=P(H)Ph₂‐κP)]⁺ ( 5 ′⁺) is present in solution. The tautomer equilibrium is slow in the NMR time scale. In contrast to the solid state only tetragonal pyramidal species of 5 are found in solution. At –90 °C there is slow exchange between the three diastereomeric species 5 a ⁺– 5 c ⁺. Compound 5 forms [Co(CO) · (Hdppa‐κ²P)₂]BPh₄ · THF ( 6 b · THF) in THF with NaBPh₄ under CO‐Elimination. A X‐ray diffraction investigation shows that the cation 6 ⁺ consists of a slightly distorted trigonal‐bipyramidal co‐ordination polyeder. However, a distorted tetragonal‐pyramidal structure has been found for the cation 7 ⁺ of the related compound [Co(CO)(dppm)₂][Co(CO)₄] · 2 THF ( 7 · 2 THF; dppm = bis(diphenylphosphanyl)methane, Ph₂PCH₂PPh₂). A comparison with the known [8] trigonal‐bipyramidal stereoisomer, ascertained for 7 ⁺ of the solvent‐free 7 , is described. In solutions of 6 a · 2 THF and 7 · 2 THF ¹³C{¹H}‐ and ³¹P{¹H}‐NMR spectra indicate an exchange of all CO and organophosphane molecules between cobalt(I) cation and cobalt(–I) anion. A concerted mechanism for the exchange process is discussed. CO elimination leads to discontinuance of the cyclic mechanism by forming binuclear substitution products such as the isolated Co₂(CO)₂ · (μ‐CO)₂(μ‐dppm)₂ · 0.83 THF ( 8 · 0.83 THF), which was characterized by spectroscopy and X‐ray analysis. For the dissolved [Co(CO)₂CH₃C(CH₂PPh₂)₃][Co(CO)₄] · 0.83 n‐pentane ( 9 a · 0.83 n‐pentane) no CO and triphos exchange processes between the cation and the anion are observed. Metathesis of 9 a · 0.83 n‐pentane with NaBPh₄ yields [Co(CO)₂CH₃C(CH₂PPh₂)₃]BPh₄ ( 9 b ) which has been characterized by single‐crystal X‐ray analysis. The cation shows a small distorted tetragonal‐pyramidal structure.     

Reactions of Polyfluoroarenes with MenE‐MMe3 Reagents (MenE = Me2As,Me2P,Me2N,and MeS; M = Si,Sn): Synthesis of Polyfluoroaryl MenE Compounds

Trimethylsilyldimethylarsane Me₃SiAsMe₂ was used as a reagent for the substitution of fluorine in polyfluoroarenes C₆F₅X (X = F, H, Cl) and C₅NF₅ by the Me₂As group. The reactions occur between 50 — 180 °C, either in benzene or without solvent, to give as a rule 4‐X‐1‐(dimethylarsano)tetrafluorobenzenes XC₆F₄AsMe₂, ( 1—3 ) and 4‐dimethylarsano‐tetrafluoropyridine C₅NF₄AsMe₂ ( 4 ), respectively, in yields between 43 and 94 %. In the case of C₆F₆, also double substitution is observed affording 1, 4‐bis(dimethylarsano)tetrafluorobenzene 5 in addition to the monosubstituted derivative. The time and temperature dependencies of the reactions increase in the sequence: C₆F₆< C₆F₅H < C₆F₅Cl < C₅NF₅. The arsanes 1 and 4 were transformed to the potentially valuable bidentate ligands 1‐(dimethylarsano)‐4‐(dimethylphosphano)tetrafluorobenzene 6 and 4‐(dimethylarsano)‐2‐(dimethylphosphano)trifluoropyridine 8 by reaction with trimethylsilyl‐dimethylphosphane Me₃SiPMe₂. 6 reacts with oxygen to yield the corresponding phosphane oxide 7 . Trimethylsilyl‐dimethylamine Me₃SiNMe₂ also was successfully tested as a reagent for the dimethylamination of polyfluoroarenes C₆F₅X [X = F, H, Cl, CF₃, P(S)Me₂], 1‐P(S)Me₂‐4‐H‐C₆F₄ and 4‐X‐C₅NF₄ [X = F, PMe₂, P(S)Me₂]. Sulfuration of the new Me₂P derivatives 8 and 20 leads to the corresponding thiophosphanes 9 and 21 (Schemes 2 and 3). Furthermore, the recently reported very efficient one‐pot synthesis of Me₂P substituted polyfluoroarenes (e.g. XC₆F₄PMe₂ with X = F, Me₂PC₆F₄) was extended to the preparation of Me₂As and MeS derivatives of pentafluoropyridine using a mixture of Me₃SnH, As₂Me₄ (or S₂Me₂) and C₅NF₅ as precursors for the one‐pot reaction. The expected products 4‐(dimethylarsano)tetrafluoropyridine 4 and 4‐(methylthio)tetrafluoropyridine 22 , respectively, were obtained in 84 and 82 % isolated yields. The novel compounds were characterized by spectroscopic (NMR, MS) and analytical data. Compounds 5 , 7 , 9 and 21 could be isolated in form of single crystals and their structures have been studied by X‐ray diffraction.     

Ungewöhnliche Reaktivität der Silicium-Phosphor-Doppelbindung in einem Silyliden(fluorsilyl)phosphan: intramolekulare C,H-Inserierung und seine Umwandlung in ein neues Silyliden(silyl)phosphan

Unusual Reactivity of the Silicon-Phosphorus Double Bond in a Silylidene(fluorosilyl)phosphane: Intramolecular C, H Insertion and its Conversion in a New Silylidene(silyl)phosphane Thermolysis of the (fluoro-tert.butyl-2,4,6-triisopropylphenylsilyl)-tert.butyl-2,4,6-triisopropylphenylsilylidenephosphane (“Phosphasilene”) ( 1 ) in toluene at 130 °C leads, under C,H-activation of a methyl group of a ortho-isopropyl group, to the constitutional isomeric silyl(fluorosilyl)phosphane ( 2 ), whose structure has been crystallographically established. It crystallizes racemically and possesses a benzosilacyclopent-2-ene moiety as major structural motif. Lithiation of 2 leads to the corresponding lithium phosphanide ( 3 ), which eliminates LiF at 80 °C in toluene and, concomitantly, furnishes the colorless new silylidene(silyl)phosphane ( 4 ) in the form of its two diasteromers (Z : E ca. 1 : 2). The ³¹P NMR chemical shifts of δ = –29.95 and –31.75 are practically identical with the value of 1 , and the ²⁹Si NMR spectrum shows resonance signals at characteristically low field (δ = 222.5 (¹J(Si, P) = 160 Hz), 221.8 (¹J(Si, P) = 161 Hz)). An single-crystal X-ray diffraction analysis of an enantiomeric form of the E-isomer reveals a Si=P distance of 2.063(2) Å, whereas the Si–P single bond distance of 2.246(2) Å is ca. 8% longer. The low coordinated silicon center is trigonal planar surrounded and the Si–P–Si angle is 108.09(8)°.     

Evolving Opportunities in Structure Solution from Powder Diffraction Data—Crystal Structure Determination of a Molecular System with Twelve Variable Torsion Angles

The genetic algorithm approach , in which a population of trial structures is allowed to evolve subject to well-defined procedures for mating, mutation, and natural selection, was employed to solve the complex molecular crystal structure of Ph₂P(O)(CH₂)₇P(O)Ph₂ directly from powder diffraction data. The structure solution reveals an interesting (perhaps unexpected) molecular conformation (see picture), which emphasizes the importance of allowing complete conformational flexibility of the molecule in the structure solution calculation.     

Zur analytischen und präparativen Trennung von funktionellen Carbosilanen und Phosphanen mit Hilfe der SFC (Supercritical-Fluid-Chromatography)

Analytical and Preparative Separation of Functional Carbosilanes and Phosphanes by Means of SFC (Supercritical Fluid Chromatography) Analytical and preparative separations of functional silanes, carbosilanes and phosphanes by means of SFC (supercritical fluid chromatography) using CO₂ or CF₃Cl as mobile phases are reported. The detecting system (an IR high pressure cell) of the apparatus which was developed by us is depicted. The separation of mixtures containing silanes with strongly polarizing groups proceeds successfully with Nucleosil-C₁₈ and CO₂ according to the molecular weights. Large differences in the polarity of the compounds give rise to a separation according to molecular weights, smaller ones to the types of compounds. The advantages of a separation by SFC are demonstrated using a mixture of 1,3,5-trisilacyclohexanes with SiH, CCl₂ and SiF groups. The preparative separation is demonstrated using a mixture of 4 different groups of a toral 22 carbosilanes. Eight fractions were obtained each of which containing the compounds with the same number of Si atoms. The final separation was achieved by means of a pressure program (Nucleosil-C₁₈, CO₂). The preparative isolation of a cyclic phosphinoborane from a mixture of three components of the same type as well as the isolation of (Me₃Si)₃P from a mixture of P-rich silylphosphanes is reported.