The syntheses and properties of novel, extremely strong uncharged polyaminophosphazene bases up to a high level of steric hindrance are described. Most of the systems were readily prepared in up to molar quantities and conveniently recovered from their salts. They are of appreciable to high chemical and thermal stability. Crystal structures of their salts were determined in order to parametrize a force field, which is utilized in molecular modeling studies. The latter offer a rationalization of the high conformational mobility of these systems. These bases cover a range of ca. 15 pK units in basicity and extend the range of uncharged auxiliary bases by ca. 19 pK units up to DMsopKsH+ values of 34-35. They are proposed as a novel class of auxiliary bases for deprotonation of very low acidic compounds where chemists have been so far left to classical metalorganic bases. Depending on the basicity range and the degree of steric protection of the basic center, these systems are particularly applicable to E2 elimination or to in situ generation of highly reactive "naked" anions.Uncharged nitrogen bases have a long tradition as widely used and often irreplaceable standard reagents in organic synthesis; many attempts to improve basicity and to reduce nucleophilicity have been reported"] since the classical work of Hunig et a1.L21. Until recently, amidines and guanidines as described by Eiter et al.f31, Eschenmoser et al.f4I, and Barton et al. ['] were generally considered the strongest synthetically useful auxiliary bases. In the early sixties there was a single report by Flynn et a1.L8] concerning applications of a somewhat stronger isobiguanide base. This base was even commercially available, but surprisingly has not been accepted by synthetic chemists.In connection with our own activities in this field we exploited among other s t r u~t u r e s [~~'~] the structural type of peralkylated triaminoiminophosphoranes. The simplest representative 1 was already known" l] and in our hands turned out to be of unprecedented base strength among kinetically active uncharged bases. The derivatives of this leading structure we synthesized s~bsequently['~,'~] proved to be chemically very stable, highly versatile and easy to recover auxiliary bases with a very broad range of steric shielding of the basic enter[',^*'^]. The Concept of Phosphazene BasesAt the outset there was the question, whether it would be possible to further enhance basicity by the same formal "homologization" which converts weakly basic tertiary amines to strongly basic triaminoiminophosphoranes.

Das thermische Verhalten der Verbindungen CsGeX3 (X  Cl, Br, I), durch Umsetzungen von Ge(OH)2 mit CsX in wäßrigen HX‐Lösungen erhalten, wurde unter Verwendung von Röntgenbeugung, Ramanspektroskopie und DTA/DSC untersucht. Die Verbindungen sind dimorph. Bei den Tieftemperaturmodifikationen L‐CsGeX3 werden rhomboedrische Verzerrungsvarianten der Perowskitstruktur (Raumgruppe R3m), bei den Hochtemperaturformen H‐CsGeX3 die kubische Perowskitstruktur gefunden. Die reversiblen Phasentransformationen werden als Ordnungs‐Unordnungs‐Übergänge infolge von Platzwechselvorgängen der Ge‐Atome bei den H‐Formen gedeutet. Die Umwandlungstemperaturen steigen in der Reihe CsGeCl3 (155°C), CsGeBr3 (238°C), CsGeI3 (277°C) an.

No abstract

No abstract

No abstract