Sandra Bogdanovic

Carbohydrate-substituted phosphines as new ligands for two-phase catalysis – synthesis and application

Abstract The synthesis and catalytic application of a new class of polar hydrophilic phosphines for two-phase catalysis is described in full detail. Contrary to the well-known sulfonated phosphines the hydrophilic character of the ligands is attributed to a neutral carbohydrate moiety. Two general routes for the synthesis of monosaccharide substituted triarylphosphines are presented. In the first procedure protected halopyranoses and OH-substituted triphenylphosphines were combined under phase transfer conditions to generate carbohydrate-substituted phosphines. In a second more efficient protocol, the palladium-catalyzed coupling of suitable haloaryl glycosides with diphenylphosphine constitutes a new access to these ligands. The properties of the ligands in terms of solubility, surfactant activity, and partition between two non-miscible phases are discussed. In addition, superior catalytic performance compared to ionic hydrophilic ligands was demonstrated for important C–C coupling reactions such as the Suzuki, Heck, and hydroformylation reactions.

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: CX 1. Methylierte Nitridomolybdän(VI)-Komplexe

Methylation of the nitridomolybdenum(VI) complex NMo(O-t-C4H9)3 2, obtained from NMoCl3· THF (1), is achieved by use of dimethylzinc, resulting in the formation of the novel tetranuclear products [N Mo(CH3)2(O-t-C4H9) · 12py]4 (3) (py = 4-t-butylpyridine). A single-crystal X-ray diffraction study reveals four NMo(CH3)2 units being connected through the nitrogen atoms, thereby forming unsymmetrical, linear MoN-Mo units. The cubane-type zinc complex [CH3ZnO-t-C4H9]4 (4; X-ray diffraction study) is also formed.

Molecular structures of the sixth period metal pentachlorides,MCl5 (M = Ta, W or Re), determined by gaselectron diffraction; is Jahn–Teller distortion of WCl5quenched by spin–orbit coupling?

The molecular structure of TaCl 5 has been optimised under D 3h symmetry by density-functional theory calculations. Calculation of the molecular force field and vibrational frequencies showed that the optimised structure corresponds to a minimum on the full potential energy surface. Gas electron diffraction data of MCl 5 (M = Ta, W or Re), recorded with nozzle temperatures ranging from 130 to 210 °C, showed that WCl 5 and ReCl 5 are trigonal bipyramidal like TaCl 5 . Structure refinements based on molecular models of D 3h symmetry lead to satisfactory agreement between experimental and calculated intensities for each compound and yield the M–Cl bond distances (ax/eq): Ta 231.3(5)/226.6(4); W 229.1(4)/224.1(5); Re 226.2(12)/223.7(7) pm. Tungsten pentachloride is a d 1 compound and might have exhibited dynamic or static Jahn–Teller distortion from D 3h symmetry; it has been suggested that such distortion is quenched by strong spin–orbit coupling.