In this review the processes occurring on the treatment of triphenylphosphane with tetrachloromethane are first reported; a key role is played here by (trichloromethyl)phosphonium chloride which reacts with a further amount of the phosphane to give the stable salt [chloro(triphenylphos-phoranediyl)methyl]triphenylphosphonium chloride by way of dichlorophosphorane and (dichloromethylene)phosphorane that is detectable only as an intermediate. The preparative application of the two-component system as a chlorinating, dehydrating, and P—N-linking reagent is ascribable to “phosphorylation” of the substrate in question through several reactive species. In these applications the reactions with the substrate compete with reactions of the two-component system with itself, so that the overall course of the reaction is in nearly all cases much more complex than was previously assumed. Nevertheless. very good results can be achieved by the use of this reagent, high yields and mild reaction conditions being characteristic.

Tertiary Phosphane/Tetrachloromethane, a Versatile Reagent for Chlorination, Dehydration, and P ? N Linkage

Many concepts used for a qualitative description of chemical bonding that originated in the early days of theoretical chemistry have been vindicated recently by quantum chemical calculations, at least as far as first row elements are concerned. However, many concepts that have been justified for first row elements (Li to Ne) cannot—contrary to widespread belief—be generalized to the higher main group elements. This applies particularly to the concept of hybridization, which should be viewed with considerable caution. The essential difference between the atoms of the first and higher rows is that the cores of the former contain only s-AOs, whereas the cores of the latter include at least s- and p-AOs. As a consequence, the s and p valence AOs of first row atoms are localized in roughly the same region of space, while the p valence AOs of higher row atoms are much more extended in space. This has the consequence that for the light main group elements both lone-pair repulsion and isovalent hybridization play a greater role than for the heavy main group elements. Furthermore, this implies that single bonds between first row elements are weak and multiple bonds are strong, whereas for the second or higher row elements single bonds are strong and multiple bonds weak. The “extended valence” (violation of the octet rule) observed in compounds of higher main group elements has very little to do with the availability of d-AOs but is due rather to the size of these atoms and thus to the reduced steric hindrance between ligands and, to a lesser extent, also to the lower electronegativity of the heavy atoms. A model based on the concept of electron-rich multicenter bonds is certainly closer to reality than one involving hybrids with the participation of d-AOs. The XO bonds in phosphane oxides, sulfoxides, oxo acids and related compounds are better formulated as semipolar rather than as true double bonds, even if they behave in some respects like double bonds.—The growing interest of theorists in compounds of higher main group elements parallels new and, in some instances, spectacular results of experimental research on the chemistry of these elements.

Chemical Bonding in Higher Main Group Elements

Recent advances in the staudinger reaction

In the first part, the theory of molecules in a magnetic field is reviewed with special attention to chemical shifts. The central role of the current density is pointed out. The gauge origin problem and its solution by means of the IGLO method is explained. Various methods for the calculation of chemical shifts are compared and the IGLO method is presented in detail both as far as computations and interpretation of the result are concerned.

The IGLO-Method: Ab-initio Calculation and Interpretation of NMR Chemical Shifts and Magnetic Susceptibilities

31P NMR chemical shifts of carbene-phosphinidene adducts as an indicator of the π-accepting properties of carbenes.

Diorganylchalkogendifluoride des Typs RR′EF2 (2a: E = S, R,R = Ph; 2b, c: E = Se. R,R′ = CH3 bzw. Ph; 2d—f: E = Te, R,R′ = CH3 bzw. Ph) werden durch Fluorierung der vorzugsweise phenylierten Chalkogenide 1a—f in Direktsynthese erhalten und die Vorteile des neuen Verfahrens gegenuber herkommlichen Methoden abgegrenzt. Aufgrund seines leichten Zuganges wird die Verwendung von Difluordiphenylsulfuran (2a) als SF4-analoges Fluorierungsmittel uberpruft. Durch partielle Fluorierung der kondensationsfahigen Monoorganylchalkogenide PhEX (3a: E = S. X = Si(CH3)3; 3b: E = Se, X = H) entstehen unter XF-Abspaltung die entsprechenden Dichalkogenide PhEEPh 4a bzw. b. Der kovalente Aufbau der Difluoride 2a—f wird durch die in allen Fallen beobachtete Triplettaufspaltung der 13C-[1H]-NMR-Signale bestatigt.



Diorgnylchalkogen(S,Se,Te) Difluorides by Direct Fluorination of Sulfides, Selenides, and Tellurides



Diorganylchalkogen difluorides of the type RR′EF2 (2a: E = S. R,R Ph:2b,c:E = Se. R.R′ = CH3 or Ph; 2d—f: E = Te, R,R′ = CH3 or Ph) are obtained by direct fluorination preferably of the phenylated chalkogenides 1a–f. The advantages of the new procedure compared to conventional methods are elucidated. Based on its easy accessability the use of difluorodiphenyl-sulfurane (2a) as SF4-analogous fluorination agent is tested. Partial fluorination of the condensable monoorganyl chalkogenides PhEX (3a: E = S, X = Si(CH3)3; 3b: E = Se, X = H) gives the corresponding dichalkogenides PhEEPh via XF-elimination. The covalent character of the difluorides 2a—f is confirmed by the triple splitting of the 3C-[1H] NMR signals observed in every case.

Diorganylchalkogen(S,Se,Te)-difluoride durch Direktfluorierung der Sulfide, Selenide und Telluride

Organylschwefeldiimide des Typs R N S N Si(CH3)3 (R = At, tBu, Ph) (2a, b, c) konnen durch Umsetzung der entsprechenden Sulfinylamine R NSO mit Lithium-bis(trimethylsilyl)amid in einem Eintopfverfahren gewonnen werden. Durch Ubertragung dieses Syntheseprinzips auf die kohlenstoffanalogen Isocyanate R NCO wird erstmals ein Monoorganylmonosilylcarbodiimid, R N C N Si(CH3)3 (5, R = tBu), zuganglich. Die thermische Symmetrisierung des Schwefel-diimids 2b zu (tBu N )2S (6) und [(CH3)3Si N ]2S (7) sowie die Ruckreaktion von 6 und 7 zum gemischt substituierten 2b wird 1H-NMR-spektroskopisch untersucht und die Gleichgewichts-konstante ermittelt. 2b wird beim Erwarmen mit Triphenylphosphin langsam zu den Iminophosphoranen Ph3P N tBu und Ph3P N Si(CH3)3 sowie Phosphinsulfid abgebaut. Mit PF5-Atherat reagiert 2b unter Halosilan-Kondensation zu dem Sulfazo-fluorphosphonium-Salz [F2P( N S N tBu)2]+ PF (8), mit Schwefeldichlorid entsprechend zum kettenformigen Trischwefeltetranitrid 9.



Preparation and Reactions of Monosilylated Organylsulfur Diimides



Organylsulfur diimides of the type R N S N Si(CH3)3 (R = Et, tBu, Ph) (2a, b, c) are obtained by the single stage reaction of sulfinylamines R NSO with lithium bis(trimethyl)silylamide. Application of this principle to the carbon analogue isocyanate made it possible to prepare a monoorganylmonosilylcarbodiimide R N C N (Si(CH3)3 (5, R = tBu) for the first time. The thermal symmetrization of the sulfur diimide 2b to (tBu N )2S (6) and [(CH3)3Si N ]2S (7) as well as the reverse reaction of 6 with 7 giving compound 2b with mixed substitution are studied by means of 1H n. m. r., and the equilibrium constant is determined. On heating with triphenylphosphine 2b is degraded slowly to the iminophosphoranes Ph3P N tBu and Ph3P N Si(CH3)3 and to phosphine sulfide. 2b undergoes a halosilane condensation with PF5-ether adduct to yield the sulfazofluorophosphonium salt [F2P( N S N tBu)2]+ PF, with sulfur dichloride 2b gives the corresponding straight-chain trisulfur tetranitride.

Darstellung und Reaktionsverhalten monosilylierter Organylschwefeldiimide

Das erste 1, 3, 4, 6-Tetraphospha-1, 5-hexadien, ein Molekül mit fluktuierenden Bindungen (identische Tetraphospha-Cope-Umlagerung) und Konfigurationsisomerie†

Die silylierten Triorganyliminophosphorane RR′2PNSi(CH3)31a–c (R, R′ = CH3, Ph) reagieren mit S4N4 unter Abspaltung von N,N′-Bis(trimethylsilyl)schwefel(IV)-diimid (3) und elementarem Schwefel zu den cyclischen S-(Phosphoranylidenamino)trithiatriazinen 2a–c, das Bis(iminophosphoran) (CH3)2P[NSi(CH3)3]-[CH2]3P(CH3)2[NSi(CH3)3] (5) entsprechend zu (CH3)2P(S3N4)–[(CH2]3P(CH3)2(S 3N4) (6). 2a–c sind durch Substitution des jeweiligen Phosphazo-Restes mit silyliertem Phosphinimin 1 ineinander uberfuhrbar. Die Reaktionsordnung und Gleichgewichtskonstante dieser Austauschreaktionen wird bestimmt. Die Spaltung des Cyclotri(thiazen)-Systems 2b durch N-(Trimethylsilyl)dimethylamin wird untersucht und mit dem entsprechenden S4N4-Abbau verglichen. Die GC-MS-Aufklarung der Nebenprodukte bringt neue Erkenntnisse uber den Reaktionsverlauf. Durch ESR-spektroskopische Untersuchung der thermischen Zersetzung von 2a–c und 6 sowie von (CH3)2NSNSNSi(CH3)3 konnen SN-Anionoradikale unterschiedlich hoher Konzentration nachgewiesen werden.



Synthesis, Substitution, and Degradation of Phosphazo-Cyclotri(thiazene) Compounds1



The silylated triorganyliminophosphoranes RR′2PNSi(CH3)31a–c (R,R′ = CH3, Ph) react with S4N4 with splitting off of N,N′-bis(trimethylsilyl)sulphur(IV) diimide and elementary sulphur to give the cyclic S-(phosphoranylidenamino)trithiatriazines 2a–c; the bis(iminophosphorane) (CH3)2P[NSi(CH3)3]– [CH2]3P(CH3)2 [NSi(CH3)3] (5) reacts analogously to yield (CH3)2P(S3N4)– [CH2]3P(CH3)2(S3N4) (6). 2a-c can be converted in to each other by replacing the respective phosphazo residue with a silylated phosphinimine1. The reaction order and equilibrium constant of this exchange reaction were determined. The cleavage of the cyclotri(thiazene) system 2b by the action of N-(trimethylsilyl)dimethylamine was studied and compared with the corresponding degradation of S4N4. The determination of the by-products of this reaction by means of GC and m. s. methods has furnished new information regarding the reaction course. E. s. r. spectroscopic studies of the thermal decomposition of 2a–c and 6 as well as of (CH3)2NSNSNSi(CH3)3 proved the presence of SN-anionic radicals in different concentrations.

Darstellung, Substitution und Abbau von Phosphazo-Cyclotri(thiazen)-Verbindungen

Difluoroarsoranes and Homologous Compounds R′R2EF2 (E = As, Sb, Bi) by Oxidative Direct Fluorination of Organoarsanes, Organostibanes, and Organobismuthanes†

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