Group 13 Superacid Adducts of [PCl2N]3.

Irrespective of the order of the addition of reagents, the reactions of [PCl2N]3 with MX3 (MX3 = AlCl3, AlBr3, GaCl3) in the presence of water or gaseous HX give the air- and light-sensitive superacid adducts [PCl2N]3·HMX4. The reactions are quantitative when HX is used. These reactions illustrate a Lewis acid/Brønsted acid dichotomy in which Lewis acid chemistry can become Brønsted acid chemistry in the presence of adventitious water or HX. The crystal structures of all three [PCl2N]3·HMX4 adducts show that protonation weakens the two P-N bonds that flank the protonated nitrogen atom. Variable-temperature NMR studies indicate that exchange in solution occurs in [PCl2N]3·HMX4, even at lower temperatures than those for [PCl2N]3·MX3. The fragility of [PCl2N]3·HMX4 at or near room temperature and in the presence of light suggests that such adducts are not involved directly as intermediates in the high-temperature ring-opening polymerization (ROP) of [PCl2N]3 to give [PCl2N]n. Attempts to catalyze or initiate the ROP of [PCl2N]3 with the addition of [PCl2N]3·HMX4 at room temperature or at 70 °C were not successful.

Structure and conformation of the medium-sized chlorophosphazene rings.

Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization-mass spectroscopy (ESI-MS), their (31)P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3-5, 6, 8). The crystal structures of [P(OPh)2N]7 and [P(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.

Interfacing multistage mass spectrometry with liquid chromatography or ion mobility separation for synthetic polymer analysis.

Synthetic polymers are naturally mixtures of homologs, even in pure form. More complexity is introduced by the presence of different comonomers, end groups and/or macromolecular architectures. The analysis of such systems is substantially facilitated by interfacing mass spectrometry (MS), which disperses based on mass, with an additional level of separation involving either interactive liquid chromatography (LC) or ion mobility (IM) spectrometry, both of which are readily coupled online with electrospray ionization and MS detection. IM-MS separates in the gas phase, post-ionization and, therefore, is ideally suitable for labile and reactive polymers. Its usefulness is illustrated with the characterization of non-covalent siloxane-saccharide complexes, metallosupramolecular assemblies and an air- and moisture-sensitive inorganic polymer, poly(dichlorophosphazene). Conversely, LC-MS which separates in solution phase, before ionization, is most effective for the analysis of polymeric mixtures whose components differ in polarity. Interactive LC conditions can be optimized to disperse by the content of hydrophobic units, as is demonstrated for amphiphilic polyether copolymers and sugar-based nonionic surfactant blends. Both LC-MS and IM-MS can be extended into a third dimension by tandem mass spectrometry (MS(2)) studies on select oligomers, in order to obtain insight into individual end groups and isomeric architectures, comonomer sequences and degree of substitution, for example, by hydrophobic functionalities.

Crown ether complexes of HPCl6.

The reactions of HCl, PCl5, and a crown ether (12-crown-4 or 18-crown-6) in CHCl3 under anaerobic conditions give complexes of the superacid HPCl6: [H(12-crown-4)][PCl6 ] and [H(18-crown-6)2][PCl6]. The crystal structures indicate that the proton lies roughly in the center of the 12-crown-4 molecule in [H(12-crown-4)][PCl6 ] whereas it lies between two oxygen atoms of two different 18-crown-6 molecules in [H(18-crown-6)2][PCl6].

Electron transfer dissociation versus collisionally activated dissociation of cationized biodegradable polyesters.

Biodegradable polyesters were ionized by electrospray ionization and characterized by tandem mass spectrometry using collisionally activated dissociation (CAD) and electron transfer dissociation (ETD) as activation methods. The compounds studied include one homopolymer, polylactide and two copolymers, poly(ethylene adipate) and poly(butylene adipate). CAD of [M+2Na](2+) ions from these polyesters proceeds via charge-remote 1,5-H rearrangements over the ester groups, leading to cleavages at the (CO)O-alkyl bonds. ETD of the same precursor ions creates a radical anion at the site of electron attachment, which fragments by radical-induced cleavage of the (CO)O-alkyl bonds and by intramolecular nucleophilic substitution at the (CO)-O bonds. In contrast to CAD, ETD produces fragments in one charge state only and does not cause consecutive fragmentations, which simplifies spectral interpretation and permits conclusive identification of the correct end groups. The radical-site reactions occurring during ETD are very similar with those reported for ETD of protonated peptides. Unlike multiply protonated species, multiply sodiated precursors form ion pairs (salt bridges) after electron transfer, thereby promoting dissociations via nucleophilic displacement in addition to the radical-site dissociations typical in ETD.