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.

Unequivocal answers to the questions in the title are not possible yet, but the strongest stable uncharged base, the PS compound 1, is 28‐29 pK units more basic than triethylamine. Compound 1 is easily prepared, readily soluble, and can be stored almost indefinitely at room temperature in the absence of moisture.

-Bindungslangen und den Koordinationszahlen der Na-Atome gibt. Generell nehmen die Bindungslangen schrittweise zu (2.364-2.396 (4), 2.424-2.489 (2), 2.373-2.613 A (3)), wenn die Koordinationszahl von vier (in 4) auf fiinf (in 2) oder sechs (in 3) steigt.Das IR-Spektrum von 2 (in Nujol) weist fur die Schwingung v,, (C=CSN) [5] Werte fur die entsprechende dreiatomige Einheit in 1: 178.

No abstract

The singlet–triplet splitting (2J=EST) is calculated in bis-[bromo-(N,N-diethylaminoethanolato)copper(II)], belonging to the group of alkoxo-bridged copper(II) dimers, by a recently proposed ab initio method. The singlet–triplet splitting energy is obtained by a perturbation expansion closely related to Anderson’s formalism. The role of all valence electrons is taken into account and it is shown to be very important in order to obtain a satisfying agreement with the experimental result. Two important facts, from a computational point of view, are tested: influence of the atomic basis set size, and influence of modifying of the ligands. Changes in the basis set of the bridging atoms can induce variations in the results from 10% to 20%. As a final result, the theoretical value of the real complex is calculated to 2J(calc)=−1095 cm−1 and agrees with the experimental one 2J(exp)=−817 cm−1.