Showing papers by "Peter S. White published in 2012"

The Ecology of Natural Disturbance and Patch Dynamics

Abstract: Introduction. Patch Dynamics in Nature. Adaptations of Plants and Animals in a Patch Dynamic Setting. Implications of Patch Dynamics for the Organization of Communities and the Functioning of Ecosystems. Synthesis.

Self-Assembled Multi-Component Catenanes: Structural Insights into an Adaptable Class of Molecular Receptors and [2]-Catenanes

Abstract: Under acidic conditions (50 equiv of TFA), combinations of hydrazide A-B monomers self-assemble into octameric [2]-catenanes with high selectivity for [132]2, where 1 is a d-Pro-X (X = Aib, Ac4c, Ac6c, l-4-Cl-PhGly)-derived monomer and 2 is an l-Pro′-l-arylGly (Pro′ = Pro, trans-F-Pro, trans-HO-Pro, aryl = naphthyl, phenyl)-derived monomer. Five different combinations of monomers were studied by X-ray crystallography. In each case, the unique aryl glycine unit is located in the core of the structure where the aryl ring templates a CH−π–CH sandwich. Analysis of metrical parameters indicates that this core region is highly conserved, while the more peripheral zones are flexible. 1H NMR spectroscopy indicate that the solid-state structures are largely retained in solution, though several non-C2-symmetric compounds have a net C2-symmetry that indicates accessible dynamic processes. Catenane dynamic processes were additionally probed through H/D exchange, with the core being inflexible relative to the peripher...

Reactivity studies on [Cp'FeI]2: monomeric amido, phenoxo, and alkyl complexes.

Abstract: A series of monomeric mono(cyclopentadienyl) iron amido, phenoxo, and alkyl complexes were synthesized, and their structure and reactivity are presented. The iron(II) centers in these 14VE one-legg...

[{Cp′Fe(μ-OH)}3]: the synthesis of a unique organometallic iron hydroxide

Abstract: The synthesis of a novel trimeric iron(II) hydroxo complex stabilized by the sterically demanding 1,2,4-tri-tert-butyl-cyclopentadienyl ligand is reported. The high-spin iron(II) centres exhibit weak antiferromagnetic exchange coupling.

Reactivity studies on [Cp′MnX(thf)]2: manganese amide and polyhydride synthesis

Abstract: The sterically encumbered 1,2,4-(Me3C)3C5H2 (Cp′) ligand allows the synthesis of stable high spin mono(cyclopentadienyl) manganese complexes [Cp′MnX(thf)]2 (X = Cl, Br, I; 1-X). Thermal stabilities of 1-X toward ligand redistribution to [Cp2′Mn] (2) and MnX2 depend on the bridging halide ligand. The kinetic stability of 1-I in solution even at elevated temperatures is noteworthy. Complexes 1 are useful starting materials for further functionalizations. Metathesis of 1-Cl with [LiN(SiMe3)2(OEt2)]2 yields the 13 valence-electron (VE) complex, [Cp′MnN(SiMe3)2] (3), while the manganese polyhydride cluster, [{Cp′Mn}4{MnH6}], was formed in the reaction of 1-I and KHBEt3. The 17 VE [MnH6]4− core of 4 is effectively shielded by four high spin [Cp′Mn]+ units. Magnetic susceptibility studies on 4 suggest weak electron exchange coupling between the spin carriers, but the spin state of the central [MnH6]4− fragment remained ambiguous. Therefore, the electronic structure of 4 was also analyzed by broken symmetry (BS) DFT calculations, which provided strong evidence for a low spin [MnH6]4− unit in agreement with previous spectrochemical studies performed on [FeH6]4−.

Synthesis and oxidation of d6 tungsten pincer complexes: a complete series of tungsten(II) hydridocarbonyl and halocarbonyl pincer complexes

Abstract: Reaction of the neutral PHNP ligand [HN(SiMe2CH2PPh2)2] with tungsten hexacarbonyl resulted in coordination of PHNP through both phosphorus donor atoms to form the tungsten complex [W(PHNP)(CO)4] (1). Reaction of PHNP with tris(acetonitrile)tricarbonyl tungsten gave both facial and meridional tridentate isomers [W(PHNP)(CO)3] (2-fac and 3-mer). These three d6 tungsten complexes could be interconverted under appropriate conditions. The thermodynamically favored isomer 3 was protonated to form seven-coordinate [W(PHNP)(CO)3H][BF4] (4). A related series of cationic tungsten(II) halide complexes was synthesized, [W(PHNP)(CO)3X]+ (6, X = I; 7, X = Br; 8, X = Cl; 9, X = F), by various routes. All of the tungsten(II) complexes underwent deprotonation at the amine site of the PHNP ligand when triethylamine was added, resulting in neutral seven-coordinate complexes. Variable temperature 1H, 31P{1H}, and 13C{1H} NMR spectroscopy showed fluxional behavior for all the seven-coordinate complexes reported here. Analysis of IR and NMR spectroscopic data showed trends through the series of coordinated halides. Crystal structures of tetracarbonyl 1, meridional tricarbonyl 3, and cationic hydride 4 were determined to confirm the coordination mode of the PHNP ligand.

Seeking a mechanistic analogue of the water-gas shift reaction: carboxamido ligand formation and isocyanate elimination from complexes containing the Tp'PtMe fragment.

Abstract: A series of stable, isolable Tp′Pt(IV) carboxamido complexes of the type Tp′PtMe2(C(O)NHR) (R = Et, nPr, iPr, tBu, Bn, Ph) has been synthesized by addition of amide nucleophiles to the carbonyl ligand in Tp′Pt(Me)(CO) followed by trapping of the Pt(II) intermediate with methyl iodide as the methylating reagent. These compounds mimic elusive intermediates resulting from hydroxide addition to platinum-bound CO in the Water–Gas Shift Reaction (WGSR). Seeking parallels to WGSR chemistry, we find that deprotonation of the carboxamido NH initiates elimination and the isocyanate-derived products form; the resulting platinum fragment can be protonated to reoxidize the metal center and generate Tp′PtMe2H, the synthetic precursor to Tp′Pt(Me)(CO). Mechanistic studies on the formation of and elimination from Tp′PtMe2(C(O)NHR) suggest a stepwise process with deprotonation from a Pt(IV) species as the key step prompting elimination.