Reactivity of divalent germanium alkoxide complexes is in sharp contrast to the heavier tin and lead analogues.

The chemistry of ß-diketiminate germanium alkoxide complexes has been examined and shown to be in sharp contrast to its heavier congeners. For instance, (BDI)GeOR (BDI = [{N(2,6-(i)Pr(2)C(6)H(3))C(Me)}(2)CH], R = (i)Pr, (s)Bu, (t)Bu) does not react with carbon dioxide to form a metal carbonate complex. Addition of aliphatic electrophiles, such as methyl iodide or methyl triflate, results in the net oxidative addition to the germanium, giving cationic tetravalent germanium complexes, [(BDI)Ge(Me)OR][X] (X = I, OTf). An examination of the contrasting reactivities of the alkoxide ligand and the germanium loan pair with Lewis acids yielded the unusual germanium(II)-copper(I) adduct, {µ(2)-Cu(2)I(2)}[(BDI)GeO(t)Bu](2). This complex not only displays a rare example of a divalent Ge-Cu bond, but is the first example in which a planar Cu(2)I(2) diamond core possesses a three-coordinate copper bound to another metal center.

Activation of carbon dioxide by divalent tin alkoxides complexes.

A series of terminal tin(II) alkoxides have been synthesized utilizing the bulky ß-diketiminate ligand [{N(2,6-(i)Pr(2)C(6)H(3))-C(Me)}(2)CH] (BDI). The nucleophilicities of these alkoxides have been examined, and unexpected trends were observed. For instance, (BDI)SnOR only reacts with highly activated aliphatic electrophiles such as methyl triflate, but reacts reversibly with carbon dioxide. Both the rate of reaction and the degree of reversibility is dependent upon minor changes in the alkoxide ligand, with the bulkier tert-butoxide ligand displaying slower reactivity than the corresponding isopropyl ligand, although the latter system is a more exergonic reaction. Density Function Theory (DFT) calculations show that the differences in the reversibility of carbon dioxide insertion can be attributed to the ground-state energy differences of tin alkoxides while the rate of reaction is attributed to relative bond strengths of the Sn-O bonds. The mechanism of carbon dioxide insertion is discussed.

Superbasicity of a bis-guanidino compound with a flexible linker: a theoretical and experimental study.

The bis-guanidino compound H(2)C{hpp}(2) (I; hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) has been converted to the monocation [I-H](+) and isolated as the chloride and tetraphenylborate salts. Solution-state spectroscopic data do not differentiate the protonated guanidinium from the neutral guanidino group but suggest intramolecular "-N-H...N=" hydrogen bonding to form an eight-membered C(3)N(4)H heterocycle. Solid-state CPMAS (15)N NMR spectroscopy confirms protonation at one of the imine nitrogens, although line broadening is consistent with solid-state proton transfer between guanidine functionalities. X-ray diffraction data have been recorded over the temperature range 50-273 K. Examination of the carbon-nitrogen bond lengths suggests a degree of "partial protonation" of the neutral guanidino group at higher temperatures, with greater localization of the proton at one nitrogen position as the temperature is lowered. Difference electron density maps generated from high-resolution X-ray diffraction studies at 110 K give the first direct experimental evidence for proton transfer in a poly(guanidino) system. Computational analysis of I and its conjugate acid [I-H](+) indicate strong cationic resonance stabilization of the guanidinium group, with the nonprotonated group also stabilized, albeit to a lesser extent. The maximum barrier to proton transfer calculated using the Boese-Martin for kinetics method was 2.8 kcal mol(-1), with hydrogen-bond compression evident in the transition state; addition of zero-point vibrational energy values leads to the conclusion that the proton transfer is barrierless, implying that the proton shuttles freely between the two nitrogen atoms. Calculations determining the gas-phase proton affinity and the pK(a) in acetonitrile both indicate that compound I should behave as a superbase. This has been confirmed by spectrophotometric titrations in MeCN using polyphosphazene references, which give an average pK(a) of 28.98 +/- 0.05. Triadic analysis indicates that the dominant term causing the high basicity is the relaxation energy.

beta-Diiminato complexes of arsenic including the formally AsI compound [As3L3] [L = [N(C6H3Pri2-2,6)C(H)]2CPh].

The reaction of the potassium beta-diiminate KL (L = [[N(Ar)C(H)](2)CPh](-); Ar = C(6)H(3)Pr(i)(2)-2,6) with AsI(3) gave [AsI(2)L] (1), which upon reduction with KC(8) produced [(kappa(1)-L)(2)As-As[double bond, length as m-dash]As(kappa(2)-L)] (2), having a unique bent chain of the three arsenic atoms in the formal oxidation states +2, 0 and +1.

Reductive disproportionation of carbon dioxide to carbonate and squarate products using a mixed-sandwich U(III) complex.

The mixed-sandwich U(III) complexes [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-CpR)(THF)] (R=Me5, Me4H) react with CO2 to give free CO and the U(IV) carbonate products [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-CpR)]2(micro-eta1:eta2-CO3)]; the latter has been structurally characterised for R=Me4H; a 25% molar excess of the U(III) reductant gives a mixture of the carbonate and squarate [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-C5Me4H)]2(micro-eta2:eta2-C4O4) products-the first synthesis of an oxocarbon from a CO2 carbon source.

Catalytic 2,3,4-hexatriene formation by terminal alkyne coupling at calcium.

Heteroleptic calcium amides effect the catalytic dimerisation of the terminal alkyne CH(3)OCH(2)C[triple bond, length as m-dash]CH to the hexatriene (CH(3)OCH(2))CH[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CH(CH(2)OCH(3)) under mild conditions; the reaction is proposed to occur via a dimeric calcium acetylide intermediate and to be promoted by polarisation of the electron density within the alkynide C[triple bond, length as m-dash]C bonds.

Varied reactions of [M(L)]3 with HgCl2, FeBr2, CeCl3, AgOTf; ligand transfer, nucleophilic attack with recombination and/or fragmentation [M = Li or Na; L = N(SiMe3){C(H)N}3SiMe3].

The crystalline compounds [Hg{N(R)C(H)NR}(2)] (1), [Fe(L)(2)](2) (2), [Ce(L)(2)Cl](2) (3), [(AlMe(2))(3){(N(R)C(H)NC(H)N)(2)C(H)NC(H)NR}] (4), and [Ag(8)Na{(N(R)C(H)N)(2)(C(H)N)(4)R}(3)] (5) were obtained from [Li(L)](3) (A) (for 1) or [Na(L)](3) (B) and HgCl(2), FeBr(2), CeCl(3), Al(Cl)Me(2), and AgOTf, respectively [L = N(R){C(H)N}(3)R; R = SiMe(3)]. Compounds 1, 2, 3, and 5 were prepared in tetrahydrofuran (THF) at 20 degrees C; for 4, it was C(6)H(14) at -78 degrees C. NMR data for 1 showed only a single SiMe(3) environment for 1, implicating a fast exchange process. Single crystal X-ray data showed dinuclear structures for 2 and 3. Each ligand [L](-) in crystalline 2 was bound to each of the two Fe atoms in a kappa(1)- or kappa(2)-fashion, respectively, with one NSiMe(3) group of the former unattached; this was consistent with VT (1)H NMR spectral data indicative of fast exchange (at 313 K) between axial kappa(1)- and equatorial kappa(2)-N,N'-coordination to Fe. The magnetic moment for 2 in C(6)H(6) was appropriate for high-spin octahedral Fe(II). The ligands [L](-) in crystalline 3 are arranged in a helical fashion. The NMR spectra of 4 in C(6)D(5)CD(3) showed that there is an equilibrium between two asymmetric structures; minor co-products were 4', assigned as a symmetrical isomer of 4, and N(R)C(H)NR(2). The anion of 5 is proposed to be identical to that of 4'. Routes to the ligands of 1, 4, 4', and 5 are suggested; the key feature is that the ligand [L](-), unless tethered in an appropriate metal-containing matrix (as in A, B, 2, or 3), is labile because of SiMe(3) mobility, fragmentation, and/or recombination.

Carbon dioxide activation by "non-nucleophilic" lead alkoxides.

A series of terminal lead alkoxides have been synthesized utilizing the bulky beta-diketiminate ligand [{N(2,6-(i)Pr(2)C(6)H(3))C(Me)}(2)CH](-) (BDI). The nucleophilicities of these alkoxides have been examined, and unexpected trends were observed. For instance, (BDI)PbOR reacts with methyl iodide only under forcing conditions yet reacts readily, but reversibly, with carbon dioxide. The degree of reversibility is strongly dependent upon minor changes in the R group. For instance, when R = isopropyl, the reversibility is only observed when the resulting alkyl carbonate is treated with other heterocumulenes; however, when R = tert-butyl, the reversibility is apparent upon any application of reduced pressure to the corresponding alkyl carbonate. The differences in the reversibility of carbon dioxide insertion are attributed to the ground-state energy differences of lead alkoxides. The mechanism of carbon dioxide insertion is discussed.

Galactose-conjugates of the oseltamivir pharmacophore--new tools for the characterization of influenza virus neuraminidases.

We describe the synthesis of mimetics of the alpha2-3 and alpha2-6 sialogalactoside substrates of influenza neuraminidase which include the oseltamivir pharmacophore, and report the sub-nanomolar affinities for these novel neuraminidase inhibitors. The challenge of synthesizing a Phospha-Oseltamivir/Tamiphosphor monoester involving the secondary 3-hydroxy group of galactose required to mimic the alpha2-3 sialogalactoside has been overcome by palladium-promoted coupling of the oseltamivir-derived vinyl iodide with a protected galactose-3-phosphonate. The difference in binding of these two inhibitors to a given influenza neuraminidase should be a function of its alpha2-3/alpha2-6-selectivity, an important, but not yet fully understood factor in the adaptation of highly pathogenic avian influenza viruses to human hosts.

Mechanistic studies on the reductive cyclooligomerisation of CO by U(III) mixed sandwich complexes; the molecular structure of [(U(eta-C8H6{Si(i)Pr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2).

The stoichiometric reaction of 1 equiv of CO with [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)] affords the linear diuranium ynediolate complex [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2) which does not react with further CO to give the deltate derivative [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta2-C3O3). Spectroscopic and computational studies suggest a plausible mechanism for the formation of the deltate complex, in which a "zig-zag" diuranium ynediolate species is the key intermediate.

Activation and reduction of diethyl ether by low valent uranium: formation of the trimetallic, mixed valence uranium oxo species [U(CpRR')(mu-I)2]3(mu3-O) (CpRR' = C5Me5, C5Me4H, C5H4SiMe3).

The reaction of UI3 and KCpRR' (CpRR' = pentamethylcyclopentadienyl, trimethylsilylcyclopentadienyl or tetramethylcyclopentadienyl) in diethyl ether results in the two-electron reduction of the solvent to form trimetallic, mixed valence uranium oxo species.

Triazenide complexes of the heavier alkaline earths: synthesis, characterization, and suitability for hydroamination catalysis.

A series of triazenide complexes of the heavier alkaline earths, Ca, Sr and Ba, have been synthesized by either protonolysis or salt metathesis routes. Although complexes of the form [{Ar 2N 3}M{N(SiMe 3) 2}(THF) n ] (M = Ca, n = 2; M = Sr, n = 3; Ar = 2,6-diisopropylphenyl) and [{Ar 2N 3}Ca(I)(THF) 2] 2 could be isolated and characterized by X-ray crystallography, solution studies revealed the propensity of these species to undergo Schlenk-like redistribution with the formation of [{Ar 2N 3} 2M(THF) n ] (M = Ca, n = 1; M = Sr, n = 2). The latter compounds have been synthesized independently. In the case of the large barium dication, attempts to synthesize the heaviest analogue of the series, [{Ar 2N 3} 2Ba(THF) n ], failed and led instead to the isolation of the potassium barate complex [K{Ar 2N 3}Ba{N(SiMe 3) 2} 2(THF) 4]. Single crystal X-ray diffraction studies demonstrated that, although in all the aforementioned cases the triazenide ligand binds to the electrophilic group 2 metal centers via symmetrical kappa (2)- N, N-chelates, in the latter compound an unprecedented bridging mode is observed in which the triazenide ligand coordinates through both terminal and internal nitrogen centers. A series of density-functional theory computational experiments have been undertaken to assist in our understanding of this phenomenon. In further experiments, the calcium and strontium amide derivatives [{Ar 2N 3}M{N(SiMe 3) 2}(THF) n ] (M = Ca, n = 2; M = Sr, n = 3) proved to be catalytically active for the intramolecular hydroamination of 1-amino-2,2-diphenylpent-4-ene to form 2-methyl-4,4-diphenylpyrrolidine, with the calcium species demonstrating a higher turnover number than the strontium analogue ( 2a, TOF = 500 h (-1); 2b, TOF = 75 h (-1)). In these instances, because of ambiguities in the structural charcterization of the precatalyst in solution, such quantification holds little value and detailed catalytic studies have not been conducted.

A Lewis-basic, dionio-substituted phosphane.

Bis{guanidine} H(2)C{hpp}(2)[hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine] reacts with PPhCl(2) to generate the dionio-substituted phosphane, [H(2)C{hpp}(2)PPh](2+)[Cl](-)(2) which, despite the formally dicationic phosphorus centre, forms an unprecedented coordination compound with platinum.

Poly{guanidinium} salts: application in the preparation of a coordinatively saturated aluminium cation.

Protonation of the linked bis(guanidine), H(2)C{hpp}(2), affords isolated guanidinium salts that have been used to prepare a coordinatively saturated aluminium cation.

beta-Diiminato ligand (L) transformations in reactions of KL with PI3 and I2 [L = {N(C6H3Pr(i)2-2,6)C(H)}2CPh].

The reaction of the potassium beta-diiminate KL (L = [{N(Ar)C(H)}(2)CPh](-); Ar = C(6)H(3)Pr(i)(2)-2,6) with PI(3) unexpectedly produced a phosphenium salt of the intermolecularly C,C-coupled ligand [P(I){N(Ar)CH}(2)C(C(6)H(4)-4)C(Ph)(CH[double bond, length as m-dash]NAr)(2)](+)[I(3)](-), while an intramolecularly N,N-coupled salt [N[upper bond 1 start](Ar)C(H)C(Ph)C(H)N[upper bond 1 end](Ar)](+)[I(5)](-) was isolated from KL + I(2).

Mn2 bis(pentalene): a mixed-spin bimetallic with two extremes of bonding within the same molecule.

Structural, magnetic and theoretical studies show that the bimetallic pentalene complex, Mn(2)(C(8)H(4)(1,4-Si(i)Pr(3)))(2), contains both high and low spin Mn(ii) in two very different sites.

Synthesis and reactivity of alkyl-palladium N-heterocyclic carbene complexes.

The transamination of alkyl-palladium halide N-heterocyclic carbene complexes has enabled the isolation of products that reveal interesting insights into the factors which might be barriers to the development of a palladium-catalysed alkyl-amination reaction.

Quantitative structure-antifungal activity relationships of some benzohydrazides against Botrytis cinerea.

Fourteen benzohydrazides have been synthesized and evaluated for their in vitro antifungal activity against the phytopathogenic fungus Botrytis cinerea. The best antifungal activity was observed for the N',N'-dibenzylbenzohydrazides 3b-d and for the N-aminoisoindoline-derived benzohydrazide 5. A quantitative structure-activity relationship (QSAR) study has been developed using a topological substructural molecular design (TOPS-MODE) approach to interpret the antifungal activity of these synthetic compounds. The model described 98.3% of the experimental variance, with a standard deviation of 4.02. The influence of an ortho substituent on the conformation of the benzohydrazides was investigated by X-ray crystallography and supported by QSAR study. Several aspects of the structure-activity relationships are discussed in terms of the contribution of different bonds to the antifungal activity, thereby making the relationships between structure and biological activity more transparent.

Aggregation behaviour of thallium(I) beta-diketiminates.

Modulation of the steric requirements of a number of N-aryl beta-diketiminate ligands results in the isolation of a variety of Tl(I) compounds with different stabilities and nuclearities.

Facile formation of a homoleptic Ce(IV) amide via aerobic oxidation.

Oxidation of [Ce(NCy2)3(thf)] or [Ce(NCy2)4Li(thf)] with dry air produced the first homoleptic Ce(IV) amide [Ce(NCy2)4].