Ari Lehtonen

cis-Dioxomolybdenum(VI) complexes with tridentate and tetradentate Schiff base ligands. Preparation, structures and inhibition of aerial oxidation of aldehydes

Abstract The synthesis and characterisation of four monomeric cis -dioxomolybdenum(VI) complexes involving Schiff base ligands is described. Ligands were obtained by condensation of salicylaldehyde with substituted aminoethanols. [MoO 2 (acac) 2 ] reacted with the prepared ligands forming six-coordinated cis -dioxoMo(VI) complexes. X-ray diffraction studies confirmed that ligands act in a tridentate manner and the sixth coordination site around Mo(VI) is occupied by methanol used as solvent. The complexes act as inhibitors in the oxidation of aldehydes by oxygen.

Synthesis and crystal structures of bis(2,3-dimethyl-2,3-butanediolato) (1,2-ethanediolato)tungsten(VI) and tris(2,3-dimethyl-2,3-butanediolato)tungsten(VI)

Abstract Neutral tungsten(VI) complexes [W(eg) (pin)2] (2) and [W(pin)3] (3) (eg = 1,2-ethanediolato ligand, pin = 2,3-dimethyl-2,3-butanediolato ligand) were prepared from [W(eg)3] (1) and H2pin by a diol exchange reaction. The X-ray crystal structures of the compounds were determined. In both complexes, the central tungsten atom of the monomer is octahedrally coordinated by six oxygen atoms of three diolato ligands.

rac-[Ethylenebis(2-(thexyldimethylsiloxy)indenyl)]zirconium dichloride: Synthesis, molecular structure and olefin polymerization catalysis

Abstract The synthesis and molecular structure of rac -[ethylenebis(2-(thexyldimethylsiloxy)indenyl)]zirconium dichloride ( 4 ), is reported. In combination with methylaluminoxane (MAO), 4 forms an active catalyst system for homogeneous polymerization of ethylene and propylene. The high activity of 4 /MAO is retained at low [Al]:[Zr] ratios [(150–250):1]. Decreasing polymerization temperature or the [Al]:[Zr] ratio results in production of polyethylene having a high molecular weight shoulder in its molecular weight distribution (MWD). Deconvolution of the MWDs into a series of calculated Flory-distribution curves indicates that with this catalyst system ethylene is polymerized by three different types of active sites, whereas propylene is predominantly polymerized by two active sites. Complex 4 crystallizes in the indenyl-backward conformation. The ligand backbone adopts the expected C 2 symmetry.

Oxomolybdenum(VI) complexes with glycine bisphenol [O,N,O,O′] ligand: synthesis and catalytic studies

The oxomolybdenum(VI) complex [MoOCl(L)] with a tetradentate glycine bisphenol ligand (H3L) was prepared by reaction of [MoO2Cl2(DMSO)2] with a ligand precursor in hot toluene. The product was isolated in moderate yield as separable cis and trans isomers along with the third minor component, [MoO2(HL)]. The solid-state structure of trans-[MoOCl(L)] was determined by X-ray diffraction. The ligand has tetradentate coordination through three oxygens and one nitrogen, which is located trans to the terminal oxo whereas the sixth coordination site is occupied by a chloride. Both cis and trans isomers of [MoOCl(L)] are active catalysts for epoxidation of cis-cyclooctene and sulfoxidation of tolyl methyl sulfide. The cis isomer gave higher activity in epoxidation and sulfoxidation reactions at room temperature than the trans isomer but they performed identically at 50 °C. Graphical Abstract

SYNTHESIS AND CHARACTERIZATION OF ETHYLENE-BRIDGED 1-TERT-BUTYLDIMETHYLSILOXY-SUBSTITUTED BIS(INDENYL) AND BIS(TETRAHYDROINDENYL)ZIRCONIUM DICHLORIDES

The synthesis and characterization of three siloxy-substituted zirconocene complexes rac - and meso -ethylenebis[1-( tert -butyldimethylsiloxy)indenyl]zirconium dichlorides ( 3a , 3b ) and rac -ethylenebis[1-( tert -butyldimethylsiloxy)-4,5,6,7-tetrahydroindenyl]zirconium dichloride ( 4 ) are reported. The molecular structures of 3b and 4 have been determined and reveal that 3b crystallizes in a chiral staggered meso -conformation, whereas 4 adopts the expected C 2 symmetric bent metallocene structure with indenyl-forward conformation of the ligand backbone. In both complexes 3b and 4 the intramolecular oxygen-chlorine distances (3.15–3.30 A) are close to the sum of their van der Waals radii (3.20 A).

Synthesis and crystal structures of dinuclear oxotungsten(VI) diolato complexes

Dinuclear complexes [W2O3L2(HL)2][H2L = 2,3-dimiethylbutane-2,3-diol (H2pin), trans-cycloheptane-1,2-diol (H2chpd) or trans-cyclooctane-1,2-diol (H2cocd)] were prepared in high yield by hydrolysis of [W(eg)(pin)2](H2eg = ethane-1,2-diolate), [W(chpd)3] and [W(cocd)3] in alcoholic solution. X-Ray diffraction studies showed that each tungsten(VI) ion is bonded to one diolate, one hydrogendiolate, one terminal and one bridging oxide ligand. Two tungsten-centred units are also linked together by intramolecular O ⋯ H–O hydrogen bonds between the diolate and hydrogendiolate ligands. The geometry of the dinuclear unit is dependent on the nature of the diolate ligands.

Reactions of tris (1,2-ethanediolato)tungsten (VI) with phenyl acetates. X-ray structures of three products

Abstract Tungsten (VI) complex [W(eg)3] (eg=ethanediolate dianion) reacts with phenyl acetates leading to the displacement of one or three diolato ligands. Two types of phenoxides, [W(O–C6H4R-4)6] (R=H, Me, Cl) and [W(eg)2 (OC6H3R2′-2,6)2] (R′=Me, i Pr) are formed, depending on the nature of phenyl group. The X-ray crystal structure determinations of [W(OC6H5)6], [W(eg)2 (OC6H3Me2-2,6)2] and [W(eg)2 (OC6H3i Pr2-2,6)2] confirmed the nature of the compounds.

Bis(triisopropylsiloxyindenyl) zirconocenes

Abstract The synthesis and characterization of 1- and 2-triisopropylsiloxy substituted bis(indenyl) zirconocenes is reported. The molecular structures of rac-[ethylenebis(2-(triisopropylsiloxy)-1-indenyl)]zirconium dichloride (6) and rac-[ethylenebis(2-(triisopropylsiloxy)-4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride (8) have been determined and reveal that complex (6) crystallizes in the indenyl-forward (Π) conformation while (8) adopts the indenyl-backward (Y) conformation.

Preparation and crystal structures of new phenoxide derivatives of tungsten(VI) oxytetrachloride

Two oxotungsten(VI) complexes of the type [WOCl2(OAr)2] (OAr= OC6H3 t Bu-2-Me-6 or OC6H2 t Bu-2-Br-4-Me-6) were prepared by the reaction of WOCl4 with 2 equiv. of phenolic ligand precursors in a refluxing toluene solution. Both compounds form monomeric units, in which the tungsten ion has adopted a square pyramidal coordination geometry with the oxo ligand in the apical position and phenoxide groups bound in a trans orientation.

Mononuclear tungsten(VI) complexes with bis(phenolato) ligands: syntheses, characterisations and activity in ROMP reaction

The reaction of bulky ligand precursor 2,2?-methylenebis(4-methyl-6-tert -butylphenol) (H2mbp) or 2,2?-ethylidenebis(4,6-di-tert butylphenol) (H2ebp) with trisdiolatotungsten(VI) complex [W(eg)3] 1 (eg � /ethanediolate dianion) provides heteroleptic complexes [W(mbp)(eg)2] 2 or [W(ebp)(eg)2] 3, respectively. Sterically less hindered 2,2?-dihydroxy-1,1?-dinaphtylmethane (H2dinap) forms heteroleptic disubstituted complex [W(dinap)2(eg)] 4. The X-ray crystal structure determinations confirmed that the isolated compounds are made of monomeric tris(diolato)tungsten(VI) molecules in which the central tungsten atom is bonded to six oxygen atoms forming a distorted octahedral coordination sphere around the metal ion. Complexes 2 and 3 catalyse the ring opening metathesis reaction of norbornene when activated by Et2AlCl. # 2002 Elsevier Science Ltd. All rights reserved.