Sander Gaemers

Density‐Functional Computation of 99Ru NMR Parameters

Gradient-corrected and hybrid variants of density-functional theory are used to compute the geometries and 99Ru chemical shifts of RuO4, [RuCp2], [K4Ru(CN)6], [Ru3(CO)12], [Ru(CO)3X3]- (X=Cl, I), [Ru(CO)2Cl4]2-, [Ru(bipy)3]2+, and [Ru(CO)2(iPr-DAB)(X)(Y)] [XY= Cl2, I2, MeCl, MeI, or (SnMe3)2]. For this set of compounds, substituent effects on delta(99Ru) are somewhat underestimated with the BPW91 pure density functional but are described well by the B3LYP hybrid functional, which can also be used to reproduce empirical trends in electric field gradients (EFGs) at the Ru nucleus qualitatively. In the [Ru(CO)2(iPr-DAB)XY] series, trends in the computed EFGs parallel those in the observed 99Ru NMR linewidths, in accordance with the quadrupolar relaxation mechanism expected for this nucleus. For this series of compounds, the use of X-ray-derived geometries affords a worse correlation between calculated EFGs and experimental linewidths than does the use of optimized geometries.

MULTINUCLEAR MAGNETIC RESONANCE STUDIES UNDER PRESSURE OF GASES AND IN SUPERCRITICAL MEDIA EMPLOYING A NOVEL TITANIUM-SAPPHIRE HIGH-PRESSURE CELL WITH PRESSURE SENSOR

A novel titanium–sapphire high‐pressure NMR cell equipped with a pressure sensor is presented. It enables the accurate and continuous in situ determination of the pressure in samples under pressure of gases and in supercritical CO2 . The homogeneity over the cell in commercial probes is excellent. The usefulness of this NMR cell is demonstrated in several 17O and 14N experiments in supercritical CO2. Furthermore, 1H NMR with concomitant monitoring of the hydrogen gas consumption during a hydrogenation reaction in solution is treated. Important characteristics are the accuracy combined with simplicity and flexibility of operation.

14N NMR spectroscopy of tertiary amines in supercritical fluids

The linewidths of 14N NMR resonances of tertiary amines and nitrogen‐containing heterocycles were studied in liquefied gases and supercritical fluids. Owing to a lower rotational correlation time of the solutes in the low‐viscosity fluids, the 14N NMR linewidths were smaller than those in benzene solutions, but to a lesser extent than theoretically achievable based on the relative solvent viscosities. The discrepancy is attributed to the free rotor correlation time, which contributes considerably to the rotational correlation time at high temperatures and low viscosities. The use of liquid CO2 gives better results than supercritical CO2. Copyright

Transition Metal (53Cr, 59Co, 91Zr, and 95Mo) and 14N NMR Spectroscopy of Coordination Compounds Containing Nitrogen Donor Ligands in Low-Viscosity Fluids

Appreciable decreases of the line widths of NMR resonances of the quadrupolar nuclei 14N, 53Cr, 59Co, 91Zr, and 95Mo have been obtained in supercritical solvents and in low-viscosity liquefied gases. Several α-diimines R1N=C(R2)−C(R2)=NR1 and their coordination compounds have been studied. Regarding the solubility of two α-diimines and some Cr, Zr, and Mo complexes it appears that the addition of small amounts of a modifier (acetone, CH2Cl2, THF) results in enhanced solubility of compounds without detrimental effects on the line widths. The use of HP NMR tubes (with and without pressure sensor) is very appropriate for measurements of NMR spectra under high pressure in supercritical fluids and liquefied gases of low viscosity. In several cases it appeared that the use of liquefied gases is more straightforward than the use of supercritical fluids, and gives similar or better results in terms of reduction of line widths.

Binding Properties of Two Novel Phosphane-Modified Tetrapodants and Their Bimetallic Transition Metal Complexes

Two novel phosphane ligands 3 and 4 based on the rigid diphenylglycoluril molecule have been synthesized and characterised. Binding studies with 3 and 4, using 1,3-dihydroxybenzene derivatives reveal that ligands 3 and 4 behave similarly to clip molecule 5, which has the same binding site as ligands 3 and 4. The size of the flexible spacers in the ligands has been varied and the effect of this variation on the association constant of resorcinol derivatives has been determined. These cavity-containing ligands are able to coordinate two transition metal centres, leading to bimetallic macrocycles. The metallamacrocycles formed from 4 containing platinum or rhodium bind the guest, olivetol (5-pentylbenzene-1,3-diol), almost four times as strongly as the free tetrapodant 4. Complexes of 4 having palladium centres display similar or reduced binding affinities for resorcinol derivatives, when compared to free 4. Metal complexes of ligand 3 do not form host-guest complexes, probably because of a too small a ring-size of the metallamacrocycle.

The Methylation of Alkenes to Triptyls with Dimethyl Carbonate

A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls.Graphical Abstract.

Selective C-H Bond Activation with Na2PtCl4 in inverted micelles.

The selective C−H activation of n-heptane and methylcyclohexane with Na2PtCl4 under mild conditions in water in inverted micelles is described.