Search

Cationic tetrahedra: condensed phase access to the tetrahedral cations [EP3]+ (E = S, Se, Te) isoelectronic to P4 or AsP3 was found by the reactions of ECl3[WCA] with P4 ([WCA]– = [Al(ORF)4]– and [F(Al(ORF)3)2]–; –RF = –C(CF3)3)., Condensed phase access to the unprecedented tetrahedral cations [EP3]+ (E = S, Se, Te) was achieved through the reaction of ECl3[WCA] with white phosphorus ([WCA]– = [Al(ORF)4]– and [F(Al(ORF)3)2]–; –RF = –C(CF3)3). Previously, [EP3]+ was only known from gas phase MS investigations. By contrast, the reaction of ECl3[A] with the known P33– synthon Na[Nb(ODipp)3(P3)] (enabling AsP3 synthesis), led to formation of P4. The cations [EP3]+ were characterized by multinuclear NMR spectroscopy in combination with high-level quantum chemical calculations. Their bonding situation is described with several approaches including Atoms in Molecules and Natural Bond Orbital analysis. The first series of well-soluble salts ECl3[WCA] was synthesized and fully characterized as starting materials for the studies on this elusive class of [EP3]+ cations. Yet, with high [ECl3]+ fluoride ion affinity values between 775 (S), 803 (Se) and 844 (Te) kJ mol–1, well exceeding typical phosphenium ions, these well-soluble ECl3[WCA] salts could be relevant in view of the renewed interest in strong (also cationic) Lewis acids.

The formation of simple non-classical silylium ions from [Me3Si]+ sources and alkenes or alkynes was investigated, but mainly oligomerization was observed. Yet, the reaction with MeC 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CMe led to a room temperature stable cyclobutenyl cation. DFT calculations suggest that a non-classical silylium ion intermediate was formed on the way to this product., Instead of yielding the desired non-classical silylium ions, the reactions of different alkenes/alkynes with several [Me3Si]+ sources mostly led to oligomerization, or – in the presence of Me3SiH – hydrosilylation of the alkenes/alkynes. Yet, from the reaction of 2-butyne with ion-like Me3Si–F–Al(ORF)3 (RF = C(CF3)3) the salt of the silylated tetramethyl cyclobutenyl cation [Me4C4–SiMe3]+[al–f–al]–1 ([al–f–al]– = [(RFO)3Al–F–Al(ORF)3]–) was obtained in good yield (NMR, scXRD, Raman, and IR). All the experimental and calculated evidence suggest a mechanism in which 1 was formed via a non-classical silylium ion as an intermediate. The removal of the [Me3Si]+ moiety from the cation in 1 was investigated as a means to provide free tetramethyl cyclobutadiene (CBD). However, the addition of [NMe4]F, in order to release Me3SiF and form CBD, led to the unexpected deprotonation of the cation. The addition of 4-dimethylaminopyridine to remove the [Me3Si]+ cation as a Lewis acid/base adduct, led to an adduct with the four-membered ring in the direct neighborhood of the Me3Si group. By the addition of Et2O to a solution of 1, the [F–Al(ORF)3]– anion (and Et2O–Al(ORF)3) was generated from the [al–f–al]– counterion. Subsequently, the [F–Al(ORF)3]– anion abstracted the [Me3Si]+ moiety from [Me4C4–SiMe3]+, probably releasing CBD. However, due to the immediate reaction of CBD with [Me4C4–SiMe3]+ and subsequent oligomerization, it was not possible to use CBD in follow-up chemistry.

The complexes Ag(L)n[WCA] (L=P4S3, P4Se3, As4S3, and As4S4; [WCA]=[Al(ORF)4]− and [F{Al(ORF)3}2]−; RF=C(CF3)3; WCA=weakly coordinating anion) were tested for their performance as ligand-transfer reagents to transfer the poorly soluble nortricyclane cages P4S3, P4Se3, and As4S3 as well as realgar As4S4 to different transition-metal fragments. As4S4 and As4S3 with the poorest solubility did not yield complexes. However, the more soluble silver-coordinated P4S3 and P4Se3 cages were transferred to the electron-poor Fp+ moiety ([CpFe(CO)2]+). Thus, reaction of the silver salt in the presence of the ligand with Fp−Br yielded [Fp−P4S3][Al(ORF)4] (1 a), [Fp−P4S3][F(Al(ORF)3)2] (1 b), and [Fp−P4Se3][Al(ORF)4] (2). Reactions with P4S3 also yielded [FpPPh3−P4S3][Al(ORF)4] (3), a complex with the more electron-rich monophosphine-substituted Fp+ analogue [FpPPh3]+ ([CpFe(PPh3)(CO)]+). All complex salts were characterized by single-crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh3 moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to σ and π donation from the slightly P−P and P−E antibonding P4E3-cage HOMO (e symmetry) to the metal acceptor fragment.