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Catharine Esterhuysen

Publications and source records attributed to Catharine Esterhuysen.

11 recordsLinked to original sources
PubMed2006

Aurolysis of alpha-C-deprotonated group 6 aminocarbene and thiocarbene complexes with Ph3PAu+.

Deprotonated Fischer-type aminocarbene complexes, (CO)5M=C(NR2)CH3 (M = Cr or W; R = Me or propyl), react with Ph3PAu+ by metal group substitution - (CO)5M for Ph3PAu+--and attachment of the extricated M(CO)5 to the deprotonated methyl group. (The products may also be seen as aminovinylgold compounds coordinated to M(CO)5 moieties.) DFT calculations at the B3LYP level of theory using model compounds indicate a clear preference of the gold unit for central C to terminal coordination in the ligand [NMe2CCH2]-, whereas the Cr(CO)5 has a 7 kcal mol(-1) preference for C(vinyl) coordination compared to N-coordination. In related thiocarbenes, the sulfur donor atom should be the preferred point of attachment for the metal carbonyl unit. The latter prediction is borne out in practice, and in the three products isolated, including Ph3PAu{C(=CH2)SPh}Cr(CO)5 in a mixed crystal with [Ph3PAuSPh]Cr(CO)5, precisely this coordination mode is present. The latter component of the mixed crystal has also been prepared independently of the vinyl one.

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PubMed2005

Reactions of halogens with Pt(II) complexes of N-alkyl- and N,N-dialkyl-N'-benzoylthioureas: oxidative addition and formation of an I2 inclusion compound.

The treatment of cis-[Pt(II)(L(1a/b)-S,O)2] complexes of N,N-diethyl- (HL(1a)) and N,N-di(n-butyl)-N'-benzoylthiourea (HL(1b)) with I2 or Br2 in chloroform, leads to rapid oxidative addition to yield several geometric isomers of [Pt(IV)(L-S,O)(2)X(2)](X = I, Br); the reactions can be monitored by (195)Pt NMR and UV-visible spectrophotometry. The products cis-[Pt(IV)(L(1a)-S,O)2I2] and cis-[Pt(IV)(L(1a)-S,O)2Br2], which have been isolated and structurally characterized, are the first-reported crystal structures of complexes of Pt(iv) with this class of ligand. Molecules of 6 pack such that the I-Pt-I axes are essentially aligned, with unusually close nearest-neighbour iodide contacts (3.553(1)A). These short II intermolecular interactions lead to infinite chains of weakly connected molecules in crystals of the compound. No such interactions are evident in the corresponding crystals of . Reaction of the Pt(II) complex of N-propyl-N'-benzoylthiourea (H2L(2a))cis-/trans-[Pt(II)(H2L(2a)-S)2Br2] with Br2 also results in oxidative addition, to yield trans-Pt(IV)(H2L(2a)-S)2Br4. By contrast, treatment of cis-/trans-[Pt(II)(H2L(2a)-S)2I2] with I2 does not lead to an oxidative addition product, yielding instead an interesting iodine inclusion compound of Pt(II), trans-[Pt(II)(H2L(2a)-S)2I2.I2. In 8, short intermolecular II distances of 3.453(1)A between I2 and coordinated iodide ions in trans-[Pt(II)(H(2)L(2a)-S)(2)I(2)] molecules, result in infinite chains of weakly linked trans-[Pt(II)(H2L(2a)-S)2I2]...I2 groups in the lattice. However, the empirically estimated bond order of 0.75 for the included I2 molecules does not support the possible existence of discrete tetraiodide ions (I4(2-)) in the lattice of compound 8.

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PubMed2005

The nature of the chemical bond revisited: an energy-partitioning analysis of nonpolar bonds.

The nature of the chemical bond in nonpolar molecules has been investigated by energy-partitioning analysis (EPA) of the ADF program using DFT calculations. The EPA divides the bonding interactions into three major components, that is, the repulsive Pauli term, quasiclassical electrostatic interactions, and orbital interactions. The electrostatic and orbital terms are used to define the nature of the chemical bond. It is shown that nonpolar bonds between main-group elements of the first and higher octal rows of the periodic system, which are prototypical covalent bonds, have large attractive contributions from classical electrostatic interactions, which may even be stronger than the attractive orbital interactions. Fragments of molecules with totally symmetrical electron-density distributions, like the nitrogen atoms in N(2), may strongly attract each other through classical electrostatic forces, which constitute 30.0 % of the total attractive interactions. The electrostatic attraction can be enhanced by anisotropic charge distribution of the valence electrons of the atoms that have local areas of (negative) charge concentration. It is shown that the use of atomic partial charges in the analysis of the nature of the interatomic interactions may be misleading because they do not reveal the topography of the electronic charge distribution. Besides dinitrogen, four groups of molecules have been studied. The attractive binding interactions in H(n)E-EH(n) (E=Li to F; n=0-3) have between 20.7 (E=F) and 58.4 % (E=Be) electrostatic character. The substitution of hydrogen by fluorine does not lead to significant changes in the nature of the binding interactions in F(n)E-EF(n) (E=Be to O). The electrostatic contributions to the attractive interactions in F(n)E-EF(n) are between 29.8 (E=O) and 55.3 % (E=Be). The fluorine substituents have a significant effect on the Pauli repulsion in the nitrogen and oxygen compounds. This explains why F(2)N-NF(2) has a much weaker bond than H(2)N-NH(2), whereas the interaction energy in FO-OF is much stronger than in HO-OH. The orbital interactions make larger contributions to the double bonds in HB=BH, H(2)C=CH(2), and HN=NH (between 59.9 % in B(2)H(2) and 65.4 % in N(2)H(2)) than to the corresponding single bonds in H(n)E-EH(n). The orbital term Delta E(orb) (72.4 %) makes an even greater contribution to the HC triple bond CH triple bond. The contribution of Delta E(orb) to the H(n)E=EH(n) bond increases and the relative contribution of the pi bonding decreases as E becomes more electronegative. The pi-bonding interactions in HC triple bond CH amount to 44.4 % of the total orbital interactions. The interaction energy in H(3)E-EH(3) (E=C to Pb) decreases monotonically as the element E becomes heavier. The electrostatic contributions to the E-E bond increases from E=C (41.4 %) to E=Sn (55.1 %) but then decreases when E=Pb (51.7 %). A true understanding of the strength and trends of the chemical bonds can only be achieved when the Pauli repulsion is considered. In an absolute sense the repulsive Delta E(Pauli) term is in most cases the largest term in the EPA.

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PubMed2004

Resolution of (S,S)-4-(2,2,4-trimethylchroman-4-yl)phenyl camphanate and its 4-chromanyl epimer by crystallization.

Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) has been resolved by crystallization of the (S)-(-)-camphanic esters (S,S)- and (R,S)-4-(2,2,4-trimethylchroman-4-yl)phenyl 4,7,7-trimethyl-3-oxo-2-oxabicyclo[2.2.1]heptane-1-carboxylate, both C28H32O5, from 2-methoxyethanol, yielding the pure S,S diastereomer. The relative stereochemistry of both diastereomers has been determined by X-ray crystallography, from which the absolute stereochemistry could be deduced from the known configuration of the camphanate moiety. The crystallographic conformations have been analysed, including the 1:1 disorder of the R,S diastereomer.

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PubMed2004

Thione complexes of Rh(I): a first comparison with the bonding and catalytic activity of related carbene and imine compounds.

Heterocyclic mono(thione), trans-bis(thione), cis-bis(thione), trans-(carbene-thione), cis-(carbene-thione), trans-(phosphine-thione) and mono(imine) complexes of rhodium(I) have been prepared and fully characterised. Chloro(eta(4)-1,5-cyclooctadiene)(L)rhodium(I)(1a, L = 1,3-diisopropyl-4,5-dimethyl-2,3-dihydro-1H-imidazol-2-thione; 1b L = 1,3,4,5-tetramethyl-2,3-dihydro-1H-imidazol-2-thione) appear as isomers at room temperature due to slow coordination exchange on the S-donor atom. In the three structures determined, the substituent on the sulfur appears syn to Cl. Hindered rotation about the Rh-carbene bond is revealed in the NMR spectra of seven new complexes with isopropyl substituents on the heterocyclic carbene ligands. The trans influence of the thione ligands is smaller than that of carbenes but larger than that shown by imines and chloride. Thione complexes are better catalyst precursors than the carbene complexes for the hydroformylation of 1-hexene under the chosen reaction conditions: 80 degrees C, 8 MPa CO-H2(1:1), 16 h, 1:1000 catalyst to 1-hexene ratio.

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PubMed2004

The first bipodal thiocarbamic acid ester, O,O'-diethyl N,N'-(p-phenylenedicarbonyl)bis(thiocarbamate).

The title compound, C(14)H(16)N(2)O(4)S(2), is the first reported X-ray crystallographic structure determination of a bipodal O-alkyl N-benzoylthiocarbamate. This compound crystallizes in a cis-S,O orientation (Z,Z' configuration), with the two S/O moieties anti relative to one another, as indicated by the twofold rotation axis located at the center of the benzene ring.

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PubMed2004

Anionic Fischer-type carbene complexes as bidentate (N,O) ligands.

New polynuclear complexes, (L1)3M2 [M2 = Cr(III) (4a,4b), Fe(III) (5), Co(III) (8)], (L1)2M2(L2)2 [M2 = Co(II) (7), Ni(II) (9)], (L1)2M2(O)L2 [M2 = V(IV) (6)] and L1M2Cp2 [M2 = Ti(III) (10)] with L1 = (CO)5M1=C[C=NC(CH3)=CHS](O-)(M1 = Cr or W) and L2 = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M2) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region -0.51 to -1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal -- and other ligands attached thereto -- in the carbene complex ligand, playing an important role.

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PubMed2003

Comparison of side-on and end-on coordination of E2 ligands in complexes [W(CO)5E2] (E=N, P, As, Sb, Bi, Si-, Ge-, Sn-, Pb-).

Complexes of W(CO)(5) with neutral diatomic pnictogen ligands N(2), P(2), As(2), Sb(2), and Bi(2) and anionic Group 14 ligands Si(2) (2-), Ge(2) (2-), Sn(2) (2-), and Pb(2) (2-) coordinated in both side-on and end-on fashion have been optimized by using density functional theory at the BP86 level with valence sets of TZP quality. The calculated bond energies have been used to compare the preferential binding modes of each respective ligand. The results were interpreted by analyzing the nature of the interaction between the ligands and the metal fragment using an energy partitioning method. This yields quantitative information regarding the strength of covalent and electrostatic interactions between the metal and ligand, as well as the contributions by orbitals of different symmetry to the covalent bonding. Results show that all the ligands studied bind preferentially in a side-on coordination mode, with the exception of N(2), which prefers to coordinate in an end-on mode. The preference of the heavier homologues P(2)-Bi(2) for binding in a side-on mode over the end-on mode in the neutral complexes [(CO)(5)WE(2)] comes mainly from the much stronger electrostatic attraction in the former species. The energy difference between the side-on and end-on isomers of the negatively charged complexes with the ligands Si(2) (2-), Ge(2) (2-), Sn(2) (2-), and Pb(2) (2-) is much less and it cannot be ascribed to a particular bonding component.

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