Silver Complexes of Cyclic Hexachlorotriphosphazene

The first solid‐state structures of complexed P3N3X6 (X=halogen) are reported for X=Cl. The compounds were obtained from P3N3Cl6 and Ag[Al(OR)4] salts in CH2Cl2/CS2 solution. The very weakly coordinating anion with R=C(CF3)3 led to the salt Ag(P3N3Cl6)2+[Al(OR)4]− (1), but the more strongly coordina...

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Bibliographic Details
Published in:Chemistry : a European journal 2006-02, Vol.12 (7), p.1997-2008
Main Authors: Gonsior, Marcin, Antonijevic, Sasa, Krossing, Ingo
Format: Article
Language:English
Subjects:
ab initio calculations
cations
NMR spectroscopy
phosphazenes
silver
weakly coordinating anions
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Summary:The first solid‐state structures of complexed P3N3X6 (X=halogen) are reported for X=Cl. The compounds were obtained from P3N3Cl6 and Ag[Al(OR)4] salts in CH2Cl2/CS2 solution. The very weakly coordinating anion with R=C(CF3)3 led to the salt Ag(P3N3Cl6)2+[Al(OR)4]− (1), but the more strongly coordinating anion with R′=C(CH3)(CF3)2 gave the molecular adduct (P3N3Cl6)AgAl(OR′)4 (3). Crystals of [Ag(CH2Cl2)(P3N3Cl6)2]+[Al(OR)4]− (2), in which Ag+ is coordinated by two phosphazene and one CH2Cl2 ligands, were isolated from CH2Cl2 solution. The three compounds were characterized by their X‐ray structures, and 1 and 3 also by NMR and vibrational spectroscopy. Solution and solid‐state 31P NMR investigations in combination with quantum chemically calculated chemical shifts show that the 31P NMR shifts of free and silver‐coordinated P3N3Cl6 differ by less than 3 ppm and indicate a very weakly bound P3N3Cl6 ligand in 1. The experimental silver ion affinity (SIA) of the phosphazene ligand was derived from the solid‐state structure of 3. The SIA shows that (PNCl2)3 is only a slightly stronger Lewis base than P4 and CH2Cl2, while other ligands such as S8, P4S3, toluene, and 1,2‐Cl2C2H4 are far stronger ligands towards the silver cation. The energetics of the complexes were assessed with inclusion of entropic, thermal, and solvation contributions (MP2/TZVPP, COSMO). The formation of the cations in 1, 2, and 3 was calculated to be exergonic by ΔrG°(CH2Cl2)=−97, −107, and −27 kJ mol−1, respectively. All prepared complexes are thermally stable; formation of P3N3Cl5+ and AgCl was not observed, even at 60 °C in an ultrasonic bath. Therefore, the formation of P3N3Cl5+ was investigated by quantum chemical calculations. Other possible reaction pathways that could lead to the successful preparation of P3N3X5+ salts were defined. Complexation or ionization? The Ag+ ion of Ag[Al(ORF)4] reacts with cyclic P3N3Cl6 by complexation to give the first structurally characterized complexes of P3N3X6 (X=halogen). Although P3N3Cl5+ formation is thermodynamically possible, the Ag+/P3N3Cl6 mixture resists ionization even at 60 °C in an ultrasonic bath (see scheme; R=C(CF3)3, R′=C(CH3)(CF3)2). The picture shows the structure of the cation in Ag(η1‐P3N3Cl6)2+[Al(OR)4]−.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.200500236