Paul D. Prince

Hypervalent hydridosilicates: synthesis, structure and hydride bridging.

A range of hydridosilicate anions has been prepared and characterised by spectroscopic, structural and computational methods. The general approach involved reaction of KH with a neutral silane precursor in the presence of [18]crown-6. In this manner, [K([18]crown-6)]+ salts of [Ph3SiH2](-) (1), [Ph3SiF2](-) (9), and [(p-FC6H4)3SiHF](-)/[(p-FC6H4)3SiH2](-) (12) were stabilised and characterized by NMR spectroscopy and X-ray diffraction. In each case, the anion adopts a trigonal bipyramidal (TBP) geometry with three equatorial phenyl groups eclipsing the axial Si-H/Si-F bonds. The Si-H[dot dot dot]K distances, along with DFT calculations on 1, indicate an electrostatic interaction that does not dictate the geometry adopted by the anion. A [H2SiOiPr3](-) salt (7) has also been crystallised in the same way; X-ray diffraction shows in this case a distorted TBP array with axial hydride ligands, and both Si-H[...]K and Si-O[...]K interactions. 1H NMR exchange experiments show 1 to undergo facile hydride exchange with Ph3SiH. Compound 1 acts as a good hydride transfer reagent to a variety of substrates, but its high reactivity often results in redistribution and other side reactions.

Supramolecular interactions in metal tosylate complexes

Ammonium tosylate, hydrated metal tosylates ([Ca(H2O)4(p-SO3C6H4CH3)2] and [M(H2O)]6(p-SO3C6H4CH3)2 (M=Mg, Mn, Fe, Co, Ni and Zn) and [M(H2O)2(15-crown-5)](p-SO3C6H4CH3)2 (M=Mn, Co and Zn) have been crystallised from aqueous media and their structures determined by X-ray crystallography. The ammonium complex is an anhydrous species with a complex hydrogen bonding array. The structure of the calcium complex shows the tosylate is bound directly to the calcium centre through the SO3 moiety, while the remaining isomorphous complexes all have a hexahydrated metal centre involved in a complex hydrogen bonded network through M–OH2⋯O–S interactions. The crown ether containing compounds [M(H2O)2(15-crown-5)(p-SO3C6H4CH3)2] (M=Mn, Co and Zn) have crown-encapsulated M(H2O)22+ ions with tosylate ions involved in hydrogen bonding bridging the cations in a one-dimensional polymer.

Anisotropic thermal expansion in 18-crown-6·2 H2O·2 HNO3

Reaction of aqueous HNO3 with 18-crown-6 results in the isolation of the neutral inclusion compound 18-crown-6·2 H2O·2 HNO3. Variable temperature single crystal X-ray and neutron diffraction data reveal that the triclinic (P) unit cell undergoes a highly anisotropic change in shape with temperature, with the crystallographic β angle changing smoothly from 66.56° to 69.03° between room temperature and 20 K. This arises from a change in shape of the crown ether in response to increases in hydrogen bond distances in the HNO3⋯H2O⋯crown ether chain.

C-Donor lariat ether ‘scorpionates’

Structural studies on a range of Ag+ and Pb2+ complexes of N-allyl and N-butenyl lariat ethers are reported. In the case of smaller ligands with allyl side arms (L = N-allylaza-15-crown-5 and N-azaallyl-18-crown-6), coordination polymers of type [Ag(L)]+∞ exhibiting Ag+⋯π interactions are observed. Increasing the length of the side arm to N-butenylaza-18-crown-6 gives a monomeric ‘scorpionate’ species in which the Ag+ ion is simultaneously bound to the macrocyclic portion and side arm of a single ligand. NMR titration results indicate that the Ag+⋯π interactions persist in solution. In the case of Pb2+ complexes no side arm involvement is observed in any case. The novel protonated complex (H3O)(N-allylaza-18-crown-6)[Cu2I3] is also reported.

Single crystal neutron and X-ray diffraction studies of (H7O3)[AuCl4]·15-crown-5

The single crystal neutron diffraction structure at 80 K of (H7O3)[AuCl4]·15-crown-5 is presented. The H7O3+ ion is unsymmetrical with the positive charge lying predominantly at one end of the chain. The oxonium ion is stabilised by hydrogen bonding to the crown ethers to form an infinite hydrogen-bonded polymer, and also by a bifurcated interaction with the [AuCl4]− anion. The OH bond distances and H atom thermal ellipsoids indicate a profound influence of the hydrogen bonding network on the oxonium ion structure. Improved X-ray data are also reported.

Weak Interactions in Silver Complexes of 15-Crown-5

Abstract The X-ray crystal structures of two closely related Ag(I) complexes of 15-crown-5 and benzo-15-crown-5 are reported. In the case of [Ag(15-crown-5)2][SbF6] 1, pointing one of its oxygen atoms away from the Ag+ cation enables one of the crown ligands to take part in an intermolecular C‒H…O hydrogen bond. The analogous benzo-15-crown-5 species, [Ag(benzo-15-crown-5)2][SbF6] 2, is too rigid to attain the necessary conformation. Crystal data for 1: P21/c, a = 8.4481(3), b = 25.5813(9), c = 13.2773(4) A, β = 101.354(2)°. Z = 4, unique data: 5187 R 1 [F 2 > 2σ(F 2)] 0.0259. Compound 2: P1, a = 8.6511 (15) A, b =10.2322(18) A, c = 19.291(3) A, α = 103.704 (2)°, β = 101.274(2)°, γ = 95.952(2)°, Z = 2, unique data: 5803 R 1 [F 2>2σ(F 2)] 0.0931.

Weak interactions induce asymmetry in the crystal structures of triaryl derivatives of group 14 elements

A search of the CSD shows that 42% of compounds of type Ph3EX (E = group 14 element, X = halogen) possess more than one molecule in the asymmetric unit (Z′ > 1). This phenomenon is rationalised in terms of CH⋯X hydrogen bonding and confirmed by the preparation of Ph3GeI. A remarkable Z′ = 4 structure of Ph3GeCl is shown to arise from site-selective inclusion of Ph3GeH impurity.

Dimerization of tris(o-ureidobenzyl)amines: a novel class of aggregates

Dimeric aggregates are formed by the assembly of two tripodal moieties which are held together, both in solution and in the solid state, by a belt of 6 hydrogen-bonded urea functions.

SYNTHESIS OF O-PROTECTED MANDELAMTOE AND ITS ELABORATION TO 5-HYDROXY-l,5-DIPHENYLHYDANTOIN

inum-containing catalyst A for the hydration of nitriles to amides, and its application to the synthesis of atenolol.4 Since it was found that A does not catalyze the direct hydration of mandelonitrile 1 to mandelamide 4, we decided to investigate whether an 0-protected cyanohydrin could be converted to the amide (Scheme). Mandelonitrile 1 was converted to the mixed acetal 2s which was hydrated to 3 in 88% yield using A as catalyst; removal of the protecting group with dilute acid gave mandelamide 4. Since some difficulties were encountered when we tried to catalyze the reaction between 3 and phenyl isocyanate, the thermal reaction of 3 with phenyl isocyanate was performed in refluxing toluene and gave the substituted urea 5a, which was not isolated, and which on deprotection gave N-mandelyl-N-phenylurea 5b. The thermal reaction of amides with phenyl isocyanate was originally reported (without solvent) by Kiihn6 in 1884, and subsequently in toluene7 or xylene8 as solvent. may be achieved using borate ion catalysis? involving the formation of a

Structure and bonding of KSiH3 and its 18-crown-6 derivatives: unusual ambidentate behavior of the SiH3(-) anion.

Density functional theory (DFT) calculations of [K(18-crown-6)SiH(3)] (1) and KSiH(3) (2) have shown that both the classical tet and non-classical inv coordination modes of the [SiH(3)](-) anion to the K(+) ion are energetically accessible. Single-crystal X-ray structures of the tet and inv derivatives [K(18-crown-6)SiH(3)·THF] (1a) and [K(18-crown-6)SiH(3)·HSiPh(3)] (1b) confirm this conclusion, showing that small changes in the coordination sphere of the metal are sufficient to alter the orientation of the anion. A topological analysis of the calculated electron densities for 1 and 2 reveals that the K···Si interaction in the tet conformer of 2 possesses a significant amount of covalent character. In contrast, the inv form of 2 displays primarily electrostatic character for the K···Si and K···H interactions. Incorporation of the 18-crown-6 ligand in 1 reduces the polarizing power of the K(+) cation, hardening the cation-anion interaction in both conformers. The experimental structures of 1a and 1b bear out these conclusions, with the strongly bound tetrahydrofuran (THF) ligand softening the K(+) ion in 1a and favoring the tet conformer, while the weakly interacting HSiPh(3) ligand in 1b has minimal effect on the K(+) center, resulting in an inv orientation.