Methyl Iodide Oxidative Addition to Rhodium(I) Complexes: a DFT and NMR Study of [Rh(FcCOCHCOCF3)(CO)(PPh3)] and the Rhodium(III) Reaction Products

A theoretical (DFT) study of the equilibrium geometry of the possible reaction products of the oxidative addition reaction [Rh(FcCOCHCOCF3)(CO)(PPh3)] + CH3I (Fc = ferrocenyl), consistent with experimental observations, revealed that the first alkyl product results from trans addition to RhI. Isomerization via an acyl intermediate leads to a second octahedral alkyl product with the PPh3 group and the iodide above and below the square plane. Theoretical computations also revealed that the thermodynamic acyl product adopts a square-pyramidal geometry with the COCH3 group in the apical position.Keywords: DFT, computational, rhodium, β-diketone, NMRPDF and Supplementry file attache

A DFT and NBO Analysis of the Bonding in Titanocenyl Complexes containing a Five-membered L,L’ - cyclic Ligand: L,L’ = O,O’; S,S’ or Se,Se’

An NBO analysis of the electron distribution in the DFT-optimized geometries of different Cp2TiIV(L,L’-BID) complexes with L,L’-BID=dioxolene, dithiolene or diselenolene, showed that a large degree of folding along the L…L axis is needed for sufficient Ti←L π-donation. The out of plane folding for maximum Ti←L π donation increases with larger Ti–L bond lengths: Cp2TiIV(O,O’-BID) (~35°) < Cp2TiIV(S,S’-BID) (47° average) < Cp2>TiIV(Se,Se’-BID) (50° average).Keywords: Gaussian, NBO, TitanoceneAttached PDF and Supplementary Fil

Structure of Coordination Complexes: The Synergy between NMR Spectroscopy and Computational Chemistry

Illustrative examples of how NMR spectroscopy and computational chemistry data can be used in synergy to gain information on structure, coordination mode, bonding, symmetry and isomeric distribution of transition metal complexes, is presented. Isomer distribution and the most stable structures in a series of Ti(β-diketonato)2Cl2 and Ti(β-diketonato)2(biphen) complexes as determined by density functional theory (DFT) methods and the application of the Boltzmann equation, are in agreement with crystal structures and variable temperature NMR results. Secondly, the DFT determined coordination mode of the 4-amino-3,5-bis(pyridine-2-yl)-1,2,4-triazole, (bpt-NH2) which has the appropriate chemical geometry to behave as anionic or neutral bidentate chelating group to form a 5- or 6-membered complex, is shown to be in agreement with 1H NMR shifts for [Rh(bpy)2(bpt-NH)]2+, [Rh(phen)2(bpt-NH)]2+, [Rh(bpt-NH)(cod)] and [Ir(bpt-NH)(cod)] (cod = 1,5-cyclooctadiene, phen = 1,10-phenanthroline, bpy = 2,2’-bipyridine). The oxidative addition of CH3I to [Rh(β-diketonato)(CO)(PPh3)] complexes consist of three reaction steps and involves isomers of two different RhIII-alkyl and two different RhIII-acyl species. For this reaction experimental 1H NMR techniques complement the stereochemistry of reaction intermediates and products as calculated by density functional theory. NMR properties, in agreement with computational results, proved to be useful to access the nature of the κ3 to κ2 distortion in coinage metal-ethylene complexes supported by tris(pyrazolyl)borates. The last example showed that NMR, X-ray crystal and computational results showed C2 symmetry for a series of metal(II) complexes coordinated to a 16-membered pentaaza macrocycle.Keywords: DFT, computational, organometallic, NMR spectroscop

Thienyl-containing &#946-Diketones: Synthesis, Characterization, Crystal Structure and Keto-enol Kinetics

1-phenyl-3-(2-thenoyl)-1,3-propanedione, Hbth, pKa’ = 9.006(8) and 1,3-di(2-thenoyl)- 1,3-propanedione, Hdtm, pKa’ = 8.893(3) were prepared by the Claisen condensation of ethyl 2-thiophenecarboxylate with an appropriate ketone under the influence of lithium diisopropylamide (LDA). The group electronegativity of the thienyl group is 2.10 (Gordy scale) as calculated froma linear group electronegativity vs. methyl ester IR carbonyl stretching wavenumber relationship. A crystal structure determination of Hbth (orthorhombic, Pbca, Z=8, R=0.0290) shows asymmetrical enolization on the side of the phenyl group. The preferred enol isomer of β-diketones containing more than one aromatic moiety that crystallizes in the solid state is determined by the resonance driving force stabilization of the thienyl or any other aromatic group, rather than the stabilization by resonance due to the phenyl group. The slow conversion of the enol isomers to the keto-enol equilibrium position was followed in CDCl3 solution by NMR spectroscopy.Keywords: β-Diketone, thienyl, crystal structure, keto-enol tautomerism, resonanc

Carbonyl Substitution in β-Diketonatodicarbonyl-rhodium(I) by Cyclo-octadiene: Relationships with Experimental, Electronic and Calculated Parameters

The substitution rate constant of the reaction between [Rh(β-diketonato)(CO)2] and cyclo-octadiene is related to various empirical parameters and density functional theory calculated energies and charges, β-diketonato = R’COCHCOR. Results indicate that especially the Hammett meta substituent constants (σ), the Lever electronic parameters (EL) and the density functional theory calculated energies and charges predict the substitution rate constant to a high degree of accuracy, for example: ln k2=8.48 (σR+σR’) – 2.24 (R2=0.99)=31.8 ΣEL – 63.0 (R2=0.99)=– 9.16 EHOMO – 52.1 (R2=0.97)=101 ΣQMulliken(Rh(CO)2) – 49.9 (R2 = 0.99).KEYWORDS BETA-diketone, rhodium, substitution; dicarbonyl, cyclo-octadiene, DFT

The Uptake and Distribution of 15N enriched Nitrate by three Rootstock Cultivars grafted to Chenin blanc

The uptake and distribution of nitrogen by the rootstocks 99R, 101-14 Mgt and 140 Ruggeri grafted to Chenin blanc in sand culture, were determined using 15N enriched potassium nitrate. The K15N03 was applied at the end of rapid shoot growth and the vines were sampled at veraison. Although vines grafted on 99R showed less aerial- and root growth than those ~n 101-14 Mgt and 140 Ruggeri, nitrogen was absorbed equally well by all three rootstocks.The distribution of newly absorbed nitrogen could be accurately determined by means of 15N, and at veraison more than half of newly absorbed N was found in the leaves and shoots, and about 15% in the bunches. It was clear that nitrogen which accumulated in the bunches during the period of investigation, was derived primarily from previously assimilated N in the roots and mature wood

Liming and Choice of Rootstocks as Cultural Techniques for Vines in Acid Soils

The effect of soil acidity on the performance of Chenin blanc vines grafted on 15 rootstock cultivars was determined in a pot experiment by liming a typically acid soil at pH (KCI) 4,1 (Control), to a pH of 5,0 (Treatment 1) and pH 6,0 (Treatment 2). On average the shoot masses of vines from Treatment 1 and Treatment 2 were respectively 27% and 870/o higher than those of the control. Root masses were increased by 11 O/o and 320/o respectively, indicating that the locally accepted norm of liming acid soils to a pH of 5,0 or to a point where exchangeable aluminium is decreased to less than 0,2 meq/100 g of soil, may be insufficient for most rootstocks. The beneficial effect of lime on the performance of vines could have been partly due to an improvement in the structure of the soil as indicated by lower mechanical resistances of the limed soils. The detrimental effect of soil acidity on the performance of vines could be reduced by the correct choice of rootstocks. The cultivars 140 Ruggeri, USVIT 8-7, 110 Richter, 99 Richter and USVIT 2-1 were best suited for use on acid soils while 101-14 Mgt, 44-53 Malegue, S04 , Rupestris du Lot and USVIT 3-6 proved less suitable for the acid soil used in this investigation

Seasonal Uptake of Nutrients by Chenin Blanc in Sand Culture: II. Phosphorus, Potassium, Calcium and Magnesium

The seasonal uptake of phosphorus, potassium, calcium and magnesium as well as their distribution in the vine were determined for Chenin blanc/99R vines grown in sand culture under South African climatic conditions. Phosphorus absorption showed two distinct peaks-the first ranging from after bud burst until veraison, and the second, less prominent, from about five weeks after harvest into the leaf fall period.Potassium was absorbed from about three weeks after bud burst until four to five weeks after harvest. No potassium was absorbed during leaf fall. Active absorption of calcium started after bud burst and continued until veraison. A second, less pronounced absorption period occurred during the six weeks before leaf fall. Similarly, absorption of magnesium started after bud burst and continued until veraison, after which the absorption rate decreased and ceased with the onset of leaf fall. A significant amount of the phosphorus and potassium absorbed during the post harvest period was retained in the permanent parts of the vine. However, most of the post harvest calcium and magnesium gains were lost through leaf fall. Most of the calcium retained by the permanent parts of the vine, was stored in the bark. There was an apparent translocation of potassium from the leaves to the permanent structure of the vine during leaf fall. This was not noticeable for any of the other three nutrients

Nutrient Consumption by Chenin Blanc grown in Sand Culture and Seasonal Changes in the Chemical Composition of Leaf Blades and Petioles

The seasonal utilization of N, P, K, Ca and Mg by the various aerial and underground organs of bearing Chenin blanc/99R grown in sand culture under South African climatic conditions was tabulated. During the production of one ton of grapes, the bunches accumulated 1,39; 0,25; 1,98; 0,17 and 0,09 kg N, P, K, Ca and Mg respectively, the permanent parts of the vine accumulated a further 0,73; 0,10; 0,19; 0,14 and 0,08 kg, and the vegetative growth (leaves plus prunings) accumulated 1,77; 0,37; 0,88; 1,70 and 0,43 kg. Appreciable seasonal changes were found in the chemical composition of both leaf blades and petioles. The petioles showed a reasonably stable composition during the month following bloom verifying the results of other workers, and samples for analyses should, therefore, be collected at this stage. However, the nutrient concentrations in the leaf blades remained unstable. The nutrient export figures obtained in this experiment may be used in conjunction with occasional petiole analyses as a basis for fertilizer recommendations. However, in the case of petiole analyses reliable norms are still lacking

Seasonal Uptake of Nutrients by Chenin blanc in Sand Culture: I. Nitrogen

The seasonal uptake and the distribution of nitrogen were determined for Chenin blanc/99R, grown in sand culture under South African conditions. Whole vines were sampled 14 times in the course of one year. Two distinct absorption peaks were found-the first starting after bud burst and lasting up to veraison, while the second extended from harvest into the leaf fall period. The amount of nitrogen absorbed during the second (post harvest) period amounted to 34% of the total for the season, and most of this was stored in the roots.The amount of nitrogen removed by the crop (1,39kg/ton of grapes) compared well with relevant literature, but the amount of nitrogen in leaves and canes associated with this, differed from results obtained in other countries