Regina Louise MacKay

Recovering phosphorus from soil: a root solution?

Marc I. Stutter,*,† Charles A. Shand,† Timothy S. George,† Martin S. A. Blackwell,‡ Roland Bol,‡ Regina L. MacKay, Alan E. Richardson, Leo M. Condron, Benjamin L. Turner, and Philip M. Haygarth †The James Hutton Institute, Aberdeen, AB15 8QH, U.K. and Dundee, DD2 5DA, U.K. ‡Rothamstead Research North Wyke, Devon, EX20 2SB, U.K. College of Life Sciences, University of Dundee, Dundee, DD1 5EH, U.K. CSIRO Plant Industry, Black Mountain, Canberra, ACT 2601, Australia Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln 7647, Canterbury, New Zealand Smithsonian Tropical Research Institute, Republic of Panama Lancaster Environment Centre, Lancaster University, LA1 4YQ, U.K.

Observation of slowed rotation about the η6-arene–chromium bond in the tripodal chromium complexes of the trimers of bicyclo[2.2.1]hept-2-yne: intramolecular rotational barriers in organometallic complexes and their correlation with internal non-bonding interactions and structural changes

The all-syn1 and syn-anti-syn2 trimers of bicyclo[2.2.1]hept-2-yne have been considered as realistic role models for some of the intramolecular rotational behaviour of hexaethylbenzene in its metal complexes. Both 1 and 2 complex to chromium as arenes rather than as cyclohexatrienes. The variable-temperature 75.5 MHz 13C-{1H} NMR spectra of a series of complexes [Cr(η6-arene)(CO)2L](L = CO, CS, or PPh3) have been observed and restricted rotation about the chromium–arene bond detected at very low temperatures only for the tricarbonyl complex of 2 and the dicarbonyl(triphenylphosphine) complex of 1. A detailed structural analysis covering twenty-one metal complexes of 1, 2, hexaethylbenzene, 1,3,5-triethyl-2,4,6-tris(trimethylsilylmethyl)benzene, hexamethylbenzene, hexa-n-propylbenzene, and pentaethylacetophenone is reported and conclusions presented concerning the effects of intramolecular strain on ground-state structures and on internal mobility.

Observation of slowed rotation about the (η6-arene)-chromium bond in the chromium tricarbonyl complex of thesyn-anti-syn trimer of bicyclo[2.2.1]hept-2-yne

SummaryThe crystal and molecular structures are reported for the chromium tricarbonyl complexes of the sterically-demanding and rigidsyn-anti-syn andall-syn trimers of bicyclo[2.2.1]hept-2-yne, (3-Cr) and (4-Cr). At very low temperatures, a decoalescence phenomenon occurs in the 75.49 MHz13C-{1H}-NMR spectrum of (3-Cr) and is unambiguously assigned to slowed rotation about the (η6-arene)-chromium bond.ZusammenfassungDie Kristallstrukturen der Chromtricarbonyl-Komplexe der sterisch anspruchsvollen und starren Trimeren des Bicyclo[2.2.1]hept-2-in[syn-anti-syn (3-Cr),all-syn (4-Cr)] wurden bestimmt. Bei sehr tiefen Temperaturen tritt im 75.49 MHz13C-{1H}-NMR-Spektrum von (3-Cr) ein Dekoaleszenzphänomen auf, das eindeutig durch eine verlangsamte Rotation um die (η6-Arene)-Chrom-Bindung hervorgerufen wird.

Unequivocal evidence for restricted rotation about a metal-arene bond caused by the steric effects of proximal ethyl groups; Crystal structure of dicarbonyltriphenylphosphine-(η6-1,3,5-triethyl- 2,4,6-tris(trimethylsilylmethyl)benzene)molybdenum(0)

The crystal structure of dicarbonyltriphenylphosphine(η6-1,3,5-triethyl-2,4,6- tris(trimethylsilylmethyl)benzene)molybdenum(0), (4) shows that the complexed arene adopts a conformation in which the three trimethylsilylmethyl groups and one ethyl group are on the side of the benzene ring plane distal to the molybdenum while the other two ethyl groups are on the proximal side. Decoalescence phenomena are observed in the 75.47 MHz 13C-1H NMR spectrum of 4 and, most notably, at 145 K two carbonyl resonances are resolved. The decoalescence phenomena are assigned to: (i) slowed ethyl group rotation; (ii) slowed rotation of the triphenylphosphine ligand about the Mo

Restricted rotation about a metal–arene bond caused by the steric effects of proximal ethyl groups; stereodynamics of some complexes of 1,3,5-triethyl-2,4,6-tris(trimethylsilylmethyl)benzene

z.sbnd;P bond; (iii) slowed rotation about the arene-metal tripodal moiety bond.

Association constants for the electron-donor–acceptor complexes of indole and 1-methylindole with 1-(2,4,6-trinitrophenyl)propan-2-one from nuclear magnetic resonance shift measurements. An anomalous scatchard plot

1,3,5-Triethyl-2,4,6-trineopentylbenzene 5 and 1,3,5-triethyl-2,4,6-tris(trimethylsilylmethyl)benzene 6 are considered as realistic role models for the intramolecular rotational behaviour of hexaethylbenzene in its metal complexes. Empirical force-field calculations are reported for the ten diastereomeric conformers of 5 and 6 which fall into four sets depending on the number of syn interactions. Variable-temperature 75.5 MHz 13C-{1H} NMR spectra have been recorded for dicarbonylthiocarbonyl-, dicarbonyl(η2-cis-cycloctene- and dicarbonyl(triphenylphosphine)-[η6-1,3,5-triethyl-2,4,6-tris(trimethylsilymethyl)benzene]molybdenum(0). Decoalescence phenomena are observed for the three complexes and line-shape-fitting studies gave the barriers for rotation about molybdenum–arene bond.

The elimination of internal and external references in nuclear magnetic resonance determinations of fast equilibria with particular reference to electron-donor–acceptor (EDA) complex formation

Changes (Δ) in the chemical shifts of the protons in the n.m.r. spectrum of the electron acceptor 1-(2,4,6-trinitrophenyl)propan-2-one (A) as a function of added electron donor (D) have been measured for D = indole and D = 1-methylindole, in carbon tetrachloride solution. Although the Scatchard plot (Δ/[D]0vs.Δ) for the methyl probe in the system involving indole is of an unusual shape, it yields values for parameters on the basis of a double equilibrium involving the formation of DA and D2A which are consistent with values for the other 1H probes and also for values of the corresponding 1-methylindole system. The effect of the probable n-merisation of D molecules on the values of the constants for the association of D with A has been estimated.

Land use and soil factors affecting accumulation of phosphorus species in temperate soils

N.m.r. determinations of the association of electron donors (D) and electron acceptors (A), in solutions where [D]≫[A], generally involve the use of a reference, either internal or external. Where two or more n.m.r. probes are available in the A molecule, the difference(s) of the shifts of these probes can be used to calculate the association constants K1 and K2 for the formation of DA and D2A, respectively. These differences are independent of any reference. The method therefore provides a check on the reliability of references in determinations in which they are used. Specifically, we have applied this method to experimental data which had been obtained orginally to provide shifts relative to an internal reference. The general agreement between the two sets of values of K1 and of K2, also of the corresponding shift differences text-decoration:overlineΔΔ0(1) and text-decoration:overlineΔΔ0(2) provides a new and independent justification for using an internal reference in the original experiments.