Interactions of organic nitroso compounds with metals.

Pnictine derivatives can behave as both 2e(-) donors (Lewis bases) and 2e(-) acceptors (Lewis acids). As prototypical ligands in the coordination chemistry of transition metals, amines and phosphines also form complexes with p-block Lewis acids, including a variety of pnictogen-centered acceptors. The inherent Lewis acidity of pnictogen centers can be enhanced by the introduction of a cationic charge, and this feature has been exploited in recent years in the development of compounds resulting from coordinate Pn-Pn and Pn-Pn' interactions. These compounds offer the unusual opportunity for homoatomic coordinate bonding and the development of complexes that possess a lone pair of electrons at the acceptor center. This Review presents new directions in the systematic extension of coordination chemistry from the transition series into the p-block.

Interpnictogen Cations: Exploring New Vistas in Coordination Chemistry

Self-assembly of cyclodextrins with meso-tetrakis(4-sulfonatophenyl)porphyrin in aqueous solution

The crystal structure of diquinuclidinium octabromide contains the hitherto unreported centrosymmetric planar, roughly Z-shaped Br82− anion. The Br3− anion in Me4PBr3 is only slightly distorted, whereas the Br3− distortion in quinuclidinium tribromide is considerable. Detailed examination of the geometry of asymmetric Br3− anions in crystals shows that the two Br–Br bond lengths are correlated and that the correlation is representable by a simple power function, leading to an estimate of the BrBr bond length in the symmetric Br3− anion of 2.541 {24} A. A relationship is also shown to exist between the N … Br and H(N) … Br distances in NH(N) … Br hydrogen bonds in organoammonium and related bromides. The high linear correlation of the XX bond lengths in the X82− (X = Br, I) anions provides a useful means of estimating Br–Br bond lengths from the corresponding II bond lengths and vice versa. Ab initio RHF/6–311 G* optimizations of the equilibrium geometries of several Brnm− anions reveal that linear Brn− are to be formulated as Br−(Br2)2k when n = 1, 5, 9 = 4k + 1, and as Br3−(Br2)2k when n = 3, 7 = 4k + 3. The V-shaped Br5− anion has an only slightly lower total electronic 6–311 G* energy than the linear Br5−. For Br7 the energy is lowest for the C3v (trihedral) configuration and increases in the order C3v < D3h (planar) D∞h (linear) for the other configurations examined.



Polyhalogenid-Anionen in Kristallen. 3. Das Br82−-Anion im Dichinuclidinium-Oktabromide – Die Kristallstrukturen von Me4PBr3 und Chinuclidiniumtribromid sowie ab initio-Berechnungen an Polybromidanionen



Die Kristallstruktur von Dichinuclidinium-Oktabromid enthalt das bisher unbekannte zentrosymmetrisch-planare, annahernd Z-formige Br82−-Anion. Im Me4PBr3 ist das Br3−-Anion nur wenig verzerrt, wogegen die Verzerrung von Br3− im Chinuclidiniumtribromid erheblich ist. Die genaue Prufung der Geometrie des asymmetrischen Br3−-Anions in Kristallen zeigt, Das die zwei BrBr-Bindungslangen einander entsprechen und die Ubereinstimmung durch eine einfache Kraftfunktion darstellbar ist, die zu einer geschatzten Bindungslange von BrBr im symmetrischen Br3−-Anion von 2,541{24} A fuhrt. Es wird auserdem gezeigt, das eine Beziehung besteht zwischen den N … Br- und H(N) … Br-Abstanden in den Wasserstoffbruckenbindungen NH(N) … Br der Organoammonium- und verwandter Bromide. Die gute lineare Ubereinstimmung der Bindungslangen XX in X82−-Anionen (X = Br, I) erlaubt die Abschatzung von BrBr-Bindungslangen aus entsprehenden II-Bindungslangen und umgekehrt. Ab initio RHF/6–311 G*-Optimierungen der Gleichgewichtsgeometrien von verschiedenen Brnm−-Anionen zeigen, das lineare Brn− als Br−(Br2)2k, fur n = 1, 5, 9 = 4k + 1 und als Br3− (Br2)2k, fur n = 3, 7 = 4k + 3, zu formulieren sind. Das V-formige Bn5− Anion hat nur eine wenig niedrigere Gesamtelektronenenergie 6–311 G* als das lineare Br5−. Beim Br7− ist die Energie am niedrigsten fur die C3v (trigonal pyramidale) Konfiguration und steigt in der Reihe C3v < D3v (trigonal planare) < D∞h (linear) fur die anderen untersuchten Konfigurationen an.

Polyhalide Anions in Crystals. 3. The Br82− anion in diquinuclidinium octabromide, the crystal structures of Me4PBr3 and quinuclidinium tribromide, and Ab initio calculations on polybromide anions

N-Nitrosamines are a class of compounds notorious both for the potent carcinogenicity of many of its members and for their widespread occurrence throughout the human environment, from air and water to our diets and drugs. Considerable effort has been dedicated to understanding N-nitrosamines as contaminants, and methods for their prevention, remediation, and detection are ongoing challenges. Understanding the chemistry of N-nitrosamines will be key to addressing these challenges. To facilitate such understanding, we focus in this Perspective on the structure, reactivity, and synthetic applications of N-nitrosamines with an emphasis on alkyl N-nitrosamines. The role of N-nitrosamines as water contaminants and the methods for their detection are also discussed.

An Organic Chemist's Guide to N-Nitrosamines: Their Structure, Reactivity, and Role as Contaminants.

Die Kristallstruktur der Titelverbindung wurde rontgenographisch bestimmt und bis zu einem R-Faktor von 0.049 (Rw = 0.041) verfeinert. Der PN-Bindungsabstand und die Geometrie am α-standigen Stickstoffatom werden mit struktur-ahnlichen Phosphorstickstoff-Verbindungen verglichen. Der fur eine PN-Einfachbindung relativ kurze Abstand ist eine Erklarung fur die bekannten Umwandlungen der Hydrazinophosphonium-Salze mit Nitrosierungsreagenzien.



Crystal Structure Determination of (N′N′-Dimethylhydrazino)triphenylphosphonium Bromide by X-Ray Technique



The structure of the title compound has been determined by X-ray cristal structure analysis and was refined to R = 0.049 (Rw = 0.041). The PN bond distance and the geometry of the nitrogen in α-position were compared with structurally analogous phosphor nitrogen compounds. The bond distance, which is relatively short for a PN single bond, gives an explanation for the known reactions of the hydrazinophosphonium salts with nitrosation reagents.

Röntgenographische Kristallstrukturbestimmung von (N′N′‐Dimethylhydrazino)triphenylphosphonium‐bromid

N-Alkoxydiazenium Salts with Substituted α-Positions



2,2,6,6-Tetramethyl-N-nitrosopiperidines can be easily alkylated in the usual manner with triethyloxonium tetrafluoroborate. The reaction of the corresponding N-alkoxydiazenium salts, bearing substituents in the α-position, with arene sulfinates seems to be a general route to N,N-disulfonylhydrazines. The condensation with N,N-disubstituted hydrazines providing an elegant route to asymmetric tetrazenes could be effected only in exceptional cases.

Ernst Stöldt

Papers

Röntgenographische Kristallstrukturbestimmung von (N′N′‐Dimethylhydrazino)triphenylphosphonium‐bromid

N‐Alkoxydiazenium‐Salze mit substituierten α‐Stellungen

Triazene Transfer with Activated 2‐Tetrazenes

Triazen-Gruppenübertragung mit aktivierten 2-Tetrazenen