Peter D. W. Boyd

Relativistic effects in gold chemistry. I. Diatomic gold compounds

Nonrelativistic and relativistic Hartree–Fock (HF) and configuration interaction (CI) calculations have been performed in order to analyze the relativistic and correlation effects in various diatomic gold compounds. It is found that relativistic effects reverse the trend in most molecular properties down the group (11). The consequences for gold chemistry are described. Relativistic bond stabilizations or destabilizations are dependent on the electronegativity of the ligand, showing the largest bond destabilization for AuF (86 kJ/mol at the CI level) and the largest stabilization for AuLi (−174 kJ/mol). Relativistic bond contractions lie between 1.09 (AuH+) and 0.16 A (AuF). Relativistic effects of various other properties are discussed. A number of as yet unmeasured spectroscopic properties, such as bondlengths (re), dissociation energies (De), force constants (ke), and dipole moments (μe), are predicted.

Regeneration of the Heart in Diabetes by Selective Copper Chelation

Heart disease is the major cause of death in diabetes, a disorder characterized by chronic hyperglycemia and cardiovascular complications. Although altered systemic regulation of transition metals in diabetes has been the subject of previous investigation, it is not known whether changed transition metal metabolism results in heart disease in common forms of diabetes and whether metal chelation can reverse the condition. We found that administration of the Cu-selective transition metal chelator trientine to rats with streptozotocin-induced diabetes caused increased urinary Cu excretion compared with matched controls. A Cu(II)-trientine complex was demonstrated in the urine of treated rats. In diabetic animals with established heart failure, we show here for the first time that 7 weeks of oral trientine therapy significantly alleviated heart failure without lowering blood glucose, substantially improved cardiomyocyte structure, and reversed elevations in left ventricular collagen and beta(1) integrin. Oral trientine treatment also caused elevated Cu excretion in humans with type 2 diabetes, in whom 6 months of treatment caused elevated left ventricular mass to decline significantly toward normal. These data implicate accumulation of elevated loosely bound Cu in the mechanism of cardiac damage in diabetes and support the use of selective Cu chelation in the treatment of this condition.

Extending supramolecular fullerene-porphyrin chemistry to pillared metal-organic frameworks

Porphyrins and fullerenes are spontaneously attracted to each other. This supramolecular recognition element can be exploited to produce ordered arrays of interleaved porphyrins and fullerenes. C60⋅H2TpyP⋅Pb(NO3)2⋅1.5TCE (H2TpyP = tetra-4-pyridylporphyrin; TCE = 1,1,2,2-tetrachloroethane) crystallizes in the tetragonal P4/n space group and the structure has been solved to high resolution. The Pb2+ ions connect the pyridylporphyrins in infinite sheets with an interlayer spacing of 12.1 Å. The fullerenes are intercalated between these layers, acting as pillars. The 6:6 ring juncture bonds of C60 are centered over the porphyrins, bringing the layers into strict tetragonal register. This arranagement identifies the fullerene–porphyrin interaction as a structure-defining element. The same motif is seen in a related ribbon structure having C70 intercalated into HgI2-linked H2TpyTP. The supramolecular design principles involved in assembling these chromophores may have applications in materials science.

A Fullerene Porphyrin Conjugate

Abstract Tetraphenylporphyrin and C 60 have been covalently linked in close proximity, via a pyrrolidine linkage. Through-space interaction of these two purple chromophores is demonstrated by electronic spectroscopy.

THE MERCURY-MERCURY BOND IN INORGANIC AND ORGANOMETALLIC COMPOUNDS - A THEORETICAL-STUDY

Abstract The effects of relativity and electron correlation in diatomic mercury HgX compounds and in linear HgX 2 and Hg 2 X 2 compounds (X=H, F, Cl, CH3 and CF 3 ) are investigated using relativistic pseudopotential and local density approximation calculations. The stability of the HgHg bond in Hg 2 X 2 is found to be influenced significantly by the electronegativity of the ligand X. Electronegative ligands such as fluorine (X=F) lead to strong mercury based radical character in the HgX monomer unit supporting an HgHg bond to form a stable Hg 2 X 2 . This effect diminishes for less electronegative ligands such as X=H or CH 3 where the unpaired electron is localized more towards the ligand X. As a consequence, HgHg bonding in Hg 2 (CH 3 ) 2 is very weak which may explain why organomercury compounds of the form Hg 2 R 2 (R=any organic group) have not yet been observed. Among these organomercury compounds Hg 2 (CF 3 ) 2 will be most stable. Relativistic and electron correlations effects are shown to have a significant influence on this trend. Hg 2 (CR 3 ) 2 is isolobal to Au 2 (PR 3 ) 2 and it is proposed that the Hg 2 (CR 3 ) 2 unit may be stabilized at other metal centres.

Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}2Pd2H]+: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Catalytic processes featuring N-heterocyclic carbene (NHC) ligands have been extensively studied following the isolation of free imidazol-2-ylidenes An important reaction class is the base-assisted palladium-mediated C–C/N coupling, such as the Sonogashira, Buchwald–Hartwig, and Mizoroki–Heck reactions

Synthesis and antimalarial and antituberculosis activities of a series of natural and unnatural 4-methoxy-6-styryl-pyran-2-ones, dihydro analogues and photo-dimers

Previous studies have identified the 3,6-dialkyl-4-hydroxy-pyran-2-one marine microbial metabolites pseudopyronines A and B to be modest growth inhibitors of Mycobacterium tuberculosis and a range of tropical diseases including Plasmodium falciparum and Leishmania donovani. In an effort to expand the structure-activity relationship of this compound class towards infectious diseases, a library of natural product and natural product-like 4-methoxy-6-styryl-pyran-2-ones and a subset of catalytically reduced examples were synthesized. In addition, the photochemical reactivity of several of the 4-methoxy-6-styryl-pyran-2-ones were investigated yielding head-to-head and head-to-tail cyclobutane dimers as well as examples of asymmetric aniba-dimer A-type dimers. All compounds were evaluated for cytotoxicity and activity against M. tuberculosis, P. falciparum, L. donovani, Trypanosoma brucei rhodesiense and Trypanosoma cruzi. Of the styryl-pyranones, natural product 3 and non-natural styrene and naphthalene substituted examples 13, 18, 21, 22 and 23 exhibited antimalarial activity (IC(50) <10 μM) with selectivity indices (SI) >10. Δ(7) Dihydro analogues were typically less active or lacked selectivity. Head-to-head and head-to-tail photodimers 5 and 34 exhibited moderate IC(50)s of 2.3 to 17 μM towards several of the parasitic organisms, while the aniba-dimer-type asymmetric dimers 31 and 33 were identified as being moderately active towards P. falciparum (IC(50) 1.5 and 1.7 μM) with good selectivity (SI ~80). The 4-tert-butyl aniba-dimer A analogue 33 also exhibited activity towards L. donovani (IC(50) 4.5 μM), suggesting further elaboration of this latter scaffold could lead to the identification of new leads for the dual treatment of malaria and leishmaniasis.

Extending the range of neutral N-donor ligands available for metal catalysts: N-[1-alkylpyridin-4(1H)-ylidene]amides in palladium-catalyzed cross-coupling reactions.

N-[1-Alkylpyridin-4(1H)-ylidene]amides (PYAs) are a new class of easily prepared, neutral N-donor ligands that share some features in common with N-heterocyclic carbenes. They are strongly electron-donating toward metal centers, and a palladium(II) complex of one of these ligands has been shown to successfully catalyze both the Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions.

Enhanced binding strengths of acyclic porphyrin hosts with endohedral metallofullerenes

The complementary use of spectroscopy and electrochemistry shed light onto the supramolecular interactions of calixarene scaffold bearing bisporphyrins 1 and 2 as hosts with a series of fullerenes –C60, Sc3N@C80, and Lu3N@C80 – as guest molecules. Importantly, the present work shows a noticeable variation in binding strength when C60 or endohedral fullerene guests are included into the bisporphyrins hosts. These sizeable differences could be clarified by computational models of the host–guest complexes, on the one hand, and a systematic investigation of the electron transfer chemistry, on the other hand. Detailed studies document an oxidative charge transfer (i.e., electron transfer from the bisporphyrin to the fullerene) for the C60 inclusion complexes, while a reductive charge transfer (i.e., electron transfer from the fullerene to porphyrin) is operative in the endohedral metallofullerene host–guest complexes.

Corrole as a Binucleating Ligand : Preparation, Molecular Structure and Density Functional Theory Study of Diboron Corroles

The reactions of BF3·OEt2 with four triaryl corroles (H3Cor) give the complexes [(B2OF2)(Cor)]- in which the corrole acts as a binucleating ligand. The new complexes were fully characterized, including an X-ray crystal structure of the triphenylcorrole complex. Density functional theory calculations support the observation that the boron atoms coordinate in two dipyrromethene sites in a cisoid geometry on one face of the macrocycle rather than in the alternative dipyrromethene/bipyrrole sites. The UV−visible spectra are insensitive to the corrole substituents, consistent with the lack of low-lying orbitals associated with the coordinated boron atoms.