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 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 DeltarG°(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.

Salts of electrophilic cations and Lewis acid-base adducts with weakly coordinating anions

Ines Raabe

During the last decades, weakly coordinating anions (WCAs) have become a field of great interest both in basic and applied chemistry, as – if compared to "normal" classical anions like Cl- or SO42- – they have a lot of unique and unusual properties, such as high solubility in low dielectric media (like CH2Cl2 or toluene), "pseudo gas phase conditions" in condensed phases and the stabilization of strong electrophilic cations as well as of weakly bound and low charged complexes. Within the present thesis, several contributions to the chemistry of WCAs were made: Based on quantum chemical calculations, the stability of the most widely used WCAs have been investigated, using parameters such as the fluoride ion affinity (FIA), partial charges or frontier orbital energies. One class of the WCAs, the poly- and perfluorinated alkoxyaluminates of the type [Al(ORF)4]- and [(RFO)3Al-F-Al(ORF)3]-, has been used to investigate weakly bound Ag(P4S3) Lewis acid-base adducts and electrophilic cations: When the silver salts of fluorinated alkoxyaluminates are reacted with P4S3, different structure types are found for the adducts, depending on the anion used. The dynamics of these complexes has been explored by different spectroscopic methods (IR, Raman, MAS-NMR, NMR in solution) and X-ray diffraction. The first structurally characterized trihalocarbenium ions CI3+ as salts of different aluminates have been prepared and fully characterized using various spectroscopic techniques, e.g. NMR and vibrational spectroscopy, as well as single-crystal diffraction. The Lewis acidities of the halocarbenium ions have been investigated both on experimental and theoretical grounds and they have been compared to those of the isoelectronic haloboranes. The NO2+ salt of the [Al(OC(CF3)3)4]- anion has been synthesized by a metathesis reaction. It has been reacted with P4 in order to obtain naked phosphorus cations Px+. Another project was the synthesis and characterization of the tetraalkylammonium salts of the [Al(ORF)4]- anions, a promising class of substances for the use in electrochemical applications in non-polar solvents. All subjects treated experimentally within this thesis have been accompanied by quantum chemical calculations.

EPFL2007

Extending the Coordination Chemistry of Molecular P4S3: The Polymeric Ag(P4S3)+ and Ag(P4S3)2+ Cations

Upon reacting P4S3 with AgAl(hfip)4 and AgAl(pftb)4 [hfip = OC(H)(CF3)2; pftb = OC(CF3)3], the compds. Ag(P4S3)Al(hfip)4 (1) and Ag(P4S3)2+[Al(pftb)4]- (2) formed in CS2 or CS2/CH2Cl2 soln., resp. Compds. 1 and 2 were characterized by single-crystal x-ray structure detns., Raman and soln. NMR spectroscopy, and elemental analyses. One-dimensional chains of [Ag(P4S3)x]... (x = 1 (1); x = 2 (2)) formed in the solid state with P4S3 ligands that bridge through a 1,3-P,S, a 2,4-P,S, or a 3,4-P,P h1 coordination to the silver ions. Compd. 2 with the least basic anion contains the 1st homoleptic metal(P4S3) complex. Compds. 1 and 2 also include the long sought sulfur coordination of P4S3. Raman spectra of 1 and 2 were assigned from DFT calcns. of related species. The influence of the silver coordination on the geometry of the P4S3 cage is discussed, addnl. aided by DFT calcns. Consequences for the frequently obsd. degrdn. of the cage are suggested. An exptl. silver ion affinity scale based on the solid-state structures of several weak Lewis acid base adducts (L)AgAl(hfip)4 is given. The affinity of the ligand L to the silver ion increases according to P4 < CH2Cl2 < P4S3 < S8 < 1,2-C2H4Cl2 < toluene. [on SciFinder (R)]

2002

Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis, Structure, and Activity in Stoichiometric and Catalytic C—C Bond Forming Reactions of Alkyl Halides

Xile Hu, Rosario Scopelliti, Oleg Vechorkin

NiII complexes of the new pincer amidobis(amine) ligand are described. The Ni chloride complex catalyzes Kumada-Corriu-Tamao coupling of unactivated alkyl halides with alkyl Grignard reagents, as well as double C-C coupling of CH2Cl2 with alkyl Grignard reagents (see schemes). The synthesis, properties, and reactivity of nickel(II) complexes of a newly developed pincer amidobis(amine) ligand (MeNN2) are described. Neutral or cationic complexes [(MeNN2)NiX] (X=OTf (6), OC(O)CH3 (7), CH3CN (8), OMe (9)) were prepared by salt metathesis or chloride abstraction from the previously reported [(MeNN2)NiCl] (1). The Lewis acidity of the {(MeNN2)Ni} fragment was measured by the 1H NMR chemical shift of the coordinated CH3CN molecule in 8. Electrochemical measurements on 1 and 8 indicate that the electron-donating properties of NN2 are similar to those of the analogous amidobis(phosphine) (pnp) ligands. The solid-state structures of 6-8 were determined and compared to those of 1 and [(MeNN2)NiEt] (3). In all complexes, the MeNN2 ligand coordinates to the NiII ion in a mer fashion, and the square-planar coordination sphere of the metal is completed by an additional donor. The coordination chemistry of MeNN2 thus resembles that of other three-dentate pincer ligands, for example, pnp and arylbis(amine) (ncn). Reactions of 2 with alkyl monohalides, dichlorides, and trichlorides were investigated. Selective CC bond formation was observed in many cases. Based on these reactions, efficient Kumada-Corriu-Tamao coupling of unactivated alkyl halides and alkyl Grignard reagents with 1 as the precatalyst was developed. Good yields were obtained for the coupling of primary and secondary iodides and bromides. Double C-C coupling of CH2Cl2 with alkyl Grignard reagents by 1 was also realized. The scope and limitations of these transformations were studied. Evidence was found for a radical pathway in Ni-catalyzed C-C cross-coupling reactions, which involves NiII alkyl intermediates.