Madeleine Schultz

Carbon Monoxide and Isocyanide Complexes of Trivalent Uranium Metallocenes

The [Cp′3U] metallocenes contain substituted cyclopentadienyl ligands and UIII with f3 electron configuration. They are good π donors and bind π-accepting ligands (L) such as carbon monoxide and isocyanides to form the corresponding adducts [Cp′3U(L)] (see scheme). The π-donating capability of the [Cp′3U] fragments appears to be readily modulated by the substituents on the cyclopentadienyl ligand.

Sterically crowded diphosphinomethane ligands: molecular structures, UV-photoelectron spectroscopy and a convenient general synthesis of tBu2PCH2PtBu2 and related species

A series of highly crowded symmetric and unsymmetric diphosphinomethanes R2PCH2PR′2, important ligands in transition metal chemistry and catalysis, namely tBu2PCH2PtBu2 (dtbpm, 1), Cy2PCH2PCy2 (dcpm, 2), tBu2PCH2PCy2 (ctbpm, 3), tBu2PCH2PiPr2 (iptbpm, 4) and tBu2PCH2PPh2 (ptbpm, 5), has been prepared in high yields, using a general and convenient route, which is described in detail for 1. Other than 4, which is a colourless liquid, these compounds are crystalline solids at room temperature. Their molecular structures have been determined by single crystal X-ray diffraction, along with that of the higher homologue of 1, tBu2CH2CH2tBu2 (dtbpe, 6). The solid-state structures of the dioxide of 1, tBu2P(O)CH2P(O)tBu2 (7), and of two phosphonium cations derived from 1, protonated [tBu2P(H)CH2PtBu2]+ (8+) and the chlorophosphonium ion [tBu2P(Cl)CH2PtBu2]+ (9+), are also described and show a distinct structural influence of the tetracoordinate P centres. The gas phase UV-photoelectron spectra of the diphosphines 1–6 have been measured. Their first two ionisation potentials are found to be nearly degenerate and all are in the low energy range from 7.5 to 7.8 eV. Comparison with related mono- and bidentate phosphines demonstrates that 1–6 are excellent σ-donors towards metals, in accord with their known coordination chemistry. Molecular geometries and electronic structures of the diphosphine systems have been studied by quantum chemical calculations and are compared to experiment. Unlike standard semiempirical methods (AM1, PM3, MNDO), which give rather poor minimum structures and seem inadequate for such sterically crowded systems, ab initio calculations (RHF/6-31G**) predict molecular geometries with reasonable accuracy and reflect the observed trends in experimental ionisation potentials.

Weak paramagnetism in compounds of the type Cp′2Yb(bipy)

Measuring the magnetic moments of solids that are air and moisture sensitive is difficult, particularly when the net magnetic moments are small, as is the case for the organometallic compounds described here. The use of quartz tubes to contain the compounds has been developed and applied to substituted ytterbocene bipyridine complexes, some of which were previously reported as diamagnetic. The SQUID measurements quantify the extent of paramagnetism and they correlate with the qualitative variable temperature 1H NMR spectra.

Coordination complexes of bivalent ansa-ytterbocenes: synthesis, structure and comparison with related unbridged ytterbocenes and ansa-ferrocenes

The dimethylsilyl bridged bis(cyclopentadienide) ligands, {[2,4-(Me3C)2C5H2]2SiMe2}2− and {[(Me3Si)2C5H2]2SiMe2}2−, have been prepared and used for the preparation of ansa-metallocene derivatives of iron and bivalent ytterbium metallocene adducts. The structures of two ansa-ferrocenes, as well as that of the free tetraene [2,4-(Me3C)2C5H3]2SiMe2, have been determined by X-ray crystallography; the lability of the Me3Si group leads to a different ring substitution pattern in the structure of ansa-{[3,4-(Me3Si)2C5H2]2SiMe2}Fe compared with that in ansa-{[2,4-(Me3C)2C5H2]2SiMe2}Fe. The structures of ansa-{[2,4-(Me3C)2C5H2]2SiMe2}Yb(OEt2) and an analogous ansa-ytterbocene isocyanide complex are also reported, and compared with those of non-bridged ytterbocene diethyl ether complexes. Short distances from the ytterbium atom to the diethyl ether β carbon atoms are observed in several structures, consistent with the tendency of ytterbium to maximise its coordination number. Spectroscopic properties for the ansa-ytterbocene etherates and the isocyanide complex are reported and compared with the corresponding adducts of non-bridged ytterbocenes. The reduced Cp(centroid)–metal–Cp(centroid) angle enforced by the ansa-bridge does not lead to significant changes in the optical spectra compared with unbridged metallocene diethyl ether and tetrahydrofuran adducts, but significant changes are observed in the isocyanide adducts; a model rationalising the red and blue shifts of λmax is proposed.

[P,P‐Di‐tert‐butyl‐N‐trimethylsilyl‐P‐(trimethylsilylamino)phosphine imidato‐κ2N,N′]bis(pyridine‐κN)lithium(I)

In the title compound, [Li(C14H36N2PSi2)(C5H5N)2], the bulky chelating monoanionic P,P-di-tert-butyl-N-trimethylsilyl-P-(trimethylsilylamino)phosphine imidate ligand and two pyridine ligands bind to Li in a pseudo-tetrahedral arrangement with twofold symmetry. The Li—Nphosphine distance is 2.048 (5) A, while the Li⋯P distance is 2.520 (6) A.

Supercritical Fluid Extraction of Metals Using Bis(2,4,4-trimethyl-pentyl)monothiophosphinic Acid as Chelating Agent for Subsequent ICP-MS Analyses of Mercury, Cadmium and Lead in Sediment

This study investigated and validated the optimum conditions for a supercritical fluid extraction (SFE) method using bis(2,4,4-trimethylpentyl)-monothiophosphinic acid as a chelating ligand, for subsequent ICP-MS analyses of mercury, cadmium and lead in sediment. Several combinations of pressure, temperature and modifier (P-T-M) conditions for SFE were tested and an appropriate collection solvent was also determined using a sediment certified reference material (CRM) as sample, to determine the optimum set of conditions. Validation results of the optimized method indicated high percent recoveries which are better compared to standard methods.

Synthesis of dianionic and trianionic chiral, chelating ligands based on amino acids

The synthesis of two new families of amino acid-containing chiral ligands, based on methyliminodiacetic acid and nitrilotriacetic acid cores, has been accomplished using a simple protection, solution phase amide coupling and deprotection strategy. The amino acids glycine, leucine, aspartic acid and phenylalanine were used to demonstrate the versatility of the synthetic route, and that no epimerisation occurs. Thus, the tridentate ligands bear C3 symmetry, while the bidentate ligands have C1 symmetry.

Characterisation of teacher professional knowledge and skill through content representations from tertiary chemistry educators

An established tool for collating secondary teachers’ pedagogical content knowledge (Loughrans CoRe) has been adapted for use by tertiary educators. Chemistry lecturers with a range of levels of experience were invited to participate in workshops through which the tool was piloted, refined and applied. We now present this refined tool for the tertiary teaching community to consider adopting. The teaching approaches of over 80 workshop participants were collected using the tool in a broad survey of tertiary chemistry teaching strategies. Participation in the workshops led to a significant gain in personal PCK for some individuals. Analysis of responses received in the workshops revealed that the consensus model of secondary teacher professional knowledge and skill is also applicable to the tertiary level, and that the CoRe is a useful way to gain insight into the knowledge bases and topic-specific professional knowledge of tertiary chemistry teachers. The data were aggregated and coded inductively to distil the types of strategies commonly found to be useful for teaching particular tertiary chemistry topics. This resulted in collation of over 300 teaching strategies for 19 different chemistry topics, representing significant topic-specific professional knowledge of tertiary practitioners. To share and sustain this collection of teaching strategies, a website was built that is searchable by either chemistry topic or by type of teaching strategy, making it immediately useful to practitioners. Usage analytics data for the website confirm that many users have accessed the resource, showing that this is a practical way to transfer information between chemistry educators.

Di-μ-iodido-bis­[(diethyl ether-κO)(η5-1,3-di-tert-butyl­cyclo­penta­dien­yl)ytterbium(II)]

The half-sandwich title compound, [Yb2(C13H21)2I2(C4H10O)2], crystallizes as a centrosymmetric dimer. The Yb atom is coordinated in a three-legged piano-stool geometry by a cyclopentadienyl ring, two I anions and the O atom of a diethyl ether molecule. The central Yb2I2 core is an approximate square.

Bis(η5-1,3-di-tert-butylcyclopentadienyl)chromium(II)

The title compound, [Cr(C13H21)2] or [h5-1,3-(Me3C)2C5H3]2Cr, a substituted chromocene, crystallizes with two independent half-molecules in the asymmetric unit, the molecules having twofold rotation symmetry. The compound is isostructural with the iron and cobalt analogues and is a bent metallocene.