Search PubMed⌕ Search

Biomedical subjects

Alan H Cowley

Publications and source records attributed to Alan H Cowley.

24 records · Page 2Linked to original sources
PubMed2003

Synthesis of 1,2,4-triazol-5-ylidenes and their interaction with acetonitrile and chalcogens.

Two new, more convenient methods for the synthesis of 1,2,4-triazol-5-ylidenes are described. Four new 1,2,4-triazol-5-ylidenes have been prepared using these methods: 1-(1-adamantyl)-3,4-diphenyl-1,2,4-triazol-5-ylidene (2a), 1-(1-adamantyl)-3-phenyl-4-(p-bromophenyl)-1,2,4-triazol-5-ylidene (2b), 1-(1-adamantyl)-3-phenyl-4-(alpha-naphthyl)-1,2,4-triazol-5-ylidene (2c), and 1-(1-adamantyl)-3,4-di(p-bromophenyl)-1,2,4-triazol-5-ylidene (2d). The X-ray crystal structures of 2d and the precursor salt 1-(1-adamantyl)-3,4-di(p-bromophenyl)-1,2,4-triazolium bromide (1e) are described. Compound 2a reacts with CH(3)CN via C-H insertion to form 1-(1-adamantyl)-3,4-diphenyl-5-cyanomethyl-5H-1,2,4-triazoline (3), and 2a and 2d react with elemental sulfur and elemental selenium, respectively, to form the corresponding thione (4) and selenone (5).

Journal Article↗
PubMed2002

Anisotropic NMR interaction tensors in the decamethylaluminocenium cation.

Solid-state NMR experiments, analytical and numerical simulations of solid NMR powder patterns, ab initio self-consistent field and hybrid density functional theory calculations, and single-crystal X-ray diffraction are used to characterize the molecular structure and anisotropic NMR interaction tensors in the bis(pentamethylcyclopentadienyl)aluminum cation, [Cp(2)Al](+). This highly symmetric main group metallocene has a structure analogous to that of ferrocene and the cobaltocenium cation. The single-crystal X-ray diffraction structure is reported for [Cp(2)Al][AlCl(4)]. Solid-state (27)Al[(1)H] magic-angle spinning and static NMR experiments are used to study the aluminum chemical shielding and electric field gradient tensors, revealing axial symmetry in both cases with a large chemical shielding span of Omega = 83(3) ppm and a small nuclear quadrupole coupling constant, C(Q)((27)Al) = 0.86(10) MHz. Carbon-13 CPMAS NMR experiments in combination with ab initio calculations and simulations of the effects of chemical exchange on (13)C static powder patterns reveal dynamic rotation of rings and suggest a low internal rotational barrier for this process. Theoretical computations of interaction tensors using the Gaussian 98 and Amsterdam Density Functional software packages are in good agreement with experiment and lend insight into the molecular origin of these NMR interactions. Orientations of the NMR tensors determined from theory, the large chemical shielding span, and the very small value of C(Q)((27)Al) can all be rationalized in terms of the high molecular symmetry.

Aluminum↗