Abstract: Coated fluorescent semiconductor nanoparticles having an organic surface layer of multi-functional surface ligands that include a nanocrystal binding center and one or more covalently attached functional groups or reactive functional groups are described as well as water-dispersible nanoparticles having an organic surface layer or multi-functional surface ligands and methods for the preparation and use of such coated nanoparticles.

Abstract: Catalysts suitable for asymmetric hydrogenation reactions are described comprising the reaction product of a group 8 transition metal compound, a chiral phosphine and a chiral diamine of formula (I) in which R1, R2, R3 and R4 are independently hydrogen, a saturated or unsaturated alkyl or cycloalkyl group, an aryl group or a urethane or sulphonyl group and R5, R6, R7 and R8 are independently hydrogen, a saturated or unsaturated alkyl or cycloalkyl group, or an aryl group, at least one of R1, R2, R3 and R4 is hydrogen and A is a linking group comprising one or two substituted or unsubstituted carbon atoms.

Abstract: In one aspect, the present invention provides a contrast enhancement agent comprising an iron chelate having structure I and salts thereof wherein R1 is independently at each occurrence a hydroxy group, a C1-C3 hydroxyalkyl group, or a C1-C3 alkyl group, and b is 0-4; R2-R7 are independently at each occurrence hydrogen, a C1-C3 hydroxyalkyl group, or a C1-C3 alkyl group, with the proviso that at least one of R1-R7 is a hydroxy group or a C1-C3 hydroxyalkyl group; and wherein Q is one or more charge balancing counterions. Also provided are a metal chelating ligand having structure IX and medical formulations comprising the contrast enhancement agent I.

Abstract: Transition metal complexes of selected monoanionic phosphine ligands, which also contain a selected Group 15 or 16 (IUPAC) element and which are coordinated to a Group 3 to 11 (IUPAC) transition metal or a lanthanide metal, are polymerization catalysts for the (co)polymerization of olefins such as ethylene and ?-olefins, and the copolymerization of such olefins with polar group-containing olefins. These and other nickel complexes of neutral and monoanionic bidentate ligands copolymerize ethylene and polar comonomers, especially acrylates, at relatively high ethylene pressures and surprisingly high temperatures, and give good incorporation of the polar comonomers and good polymer productivity. These copolymers are often unique structures, which are described.

Abstract: The present invention relates to a kind of novel carbene ligands and ruthenium catalysts, which is highly active and selective for ROMP and RCM reactions, respectively. It discloses the significant electronic and steric effect of different substituted carbene ligands on the catalytic activity and stability of corresponding carbene ruthenium complexes; some of novel ruthenium complexes in the invention can be broadly used as catalysts highly effectively and selective for ROMP and RCM reactions. The invention also relates to preparation of new ruthenium catalysts and the uses in metathesis. Moreover, the invention also provides effective methods of making various functional polymers by ROMP reaction in the presence of new ruthenium catalysts.

Abstract: An anchor group anchors organic dielectric compounds used in the production of organically based capacitors. The capacitors referred to are those that can be produced in a parallel process on a prepeg or other common printed circuit board substrate without additional metallisation on copper. The pre-fabricated capacitor layer can then be built into the printed circuit board, thereby gaining on space and cost for the surface of the printed circuit board.

Abstract: A process for producing a crosslinked type or non-crosslinked type layered metal phosphonate compound including a reaction step of reacting two or more members selected from organic diphosphonic acids or monophosphonic acids, or derivatives thereof having predetermined conditions and a metal source capable of forming an ion of a hexacoordinate metal atom as a central atom (M) of a metal oxide octahedron upon reaction under the presence of a sulfuric acid catalyst, a crosslinked or non-crosslinked metal phosphonate compound obtained by the process, as well as a stock solution used for the synthesis of the crosslinked or non-crosslinked type layered metal phosphonate compound described above.

Abstract: A light emitting device comprising an anode, a cathode, a light emissive layer located between the anode and the cathode, said light emissive layer comprising a compound for emitting light, said compound comprising a metal complex and X, said metal complex containing a metal (M) and a phosphorous atom that is coordinated directly to M, and an aryl or heteroaryl group Ars that is directly bonded to the phosphorous atom, where Ars is substituted with X, and characterized in the X comprises an aryl or heteroaryl group.

Abstract: The present invention concerns a metallocene-based phosphine ligand for use in enantioselective catalysis, the ligand having the Formula (I): Wherein M is a metal; Z is P or As; L is a suitable linker; R1 is selected from alkyl, alkoxy, alkylamino, cycloalkyl, cycloalkoxy, cycloalkylamino carbocyclic aryl, substituted and unsubstituted carbocyclic aryloxy, heteroaryl, heteroaryloxy, carbocyclic arylamino and heteroarylamino; X* is selected from (II): Wherein R, R2 and R3 are independently selected from optionally substituted branched- and straight-chain alkyl, cycloalkyl, heterocycloalkyl, carbocyclic aryl, and heteroaryl.

Abstract: A substituted paracyclophane is described of formula (I) wherein X1 and X2 are linking groups comprising between 2 to 4 carbon atoms, Y1 and Y2 are selected from the group consisting of hydrogen, halide, oxygen, nitrogen, alkyl, cycloalkyl, aryl or heteroaryl and Z is a substituted or unsubstituted alkyl group, aryl group or heteroaryl group. Preferably X1 and X2 are —(C2H4)— and Z is a substituted aryl group. The substituted paracyclophane provides transition metal catalysts that are useful in C—C and C—N bond formation and asymmetric hydrogenation reactions.

Abstract: The invention relates to a compound of the formula (I) or the formula (II) in which: W is an oxygen atom or a radical of the formula NH; X is hydrogen or an alkaline cation or a C1-C8 alkyl or a —(CH2)n3—C(R4)(R5)(R6) radical; X and R on the one hand and X and R1 on the other hand may independently form an optionally substituted cycle with 5, 6 or 7 links. The invention also relates to complexes of said compounds with at least one metal selected from the group comprising copper, palladium, ruthenium, iridium and rhodium, and to a method for the synthesis of these compounds. These compounds and complexes can be used in various asymmetrical catalysis methods.

Abstract: The invention relates to a process for the preparation of a hydrocarbylated metal organic compound, comprising a hydrocarbyl group, a spectator ligand and optionally a ligand, by contacting a metal-organic reagent with a spectator ligand in the presence of at least 2 equivalents of a hydrocarbylating agent.

Abstract: Disclosed are a novel cyclotriphosphazene-platinum(II) complex conjugate anticancer agent, showing high selectivity to tumor tissues due to the enhanced permeability and retention effect in tumor tissues and a preparation method thereof.

Abstract: The invention relates to a process for modifying an inorganic substrate, directed toward giving it antimicrobial properties, said process consisting in grafting in one or more steps onto a surface of said substrate groups with intrinsic antimicrobial properties or groups capable of releasing species with antimicrobial properties. The grafting is performed by means of an organophosphorus coupling agent. A subject of the invention is similarly a substrate obtained by this process, as well as diverse uses of such a substrate.

Abstract: Mixed metal phosphonates are generally provided. The mixed metal phosphonate can generally have the composition: AB(RPO3)3, where A is Mg2+, Ca2+, Sr2+, Ba2+, Pb2+, La3+, or combinations thereof; B is Ti4+, Zr4+, Al3+, or combinations thereof; and R is an organic group (e.g., aryl group, an alkyl group, an alkenyl group, etc.). The mixed metal phosphonate can be combined with a polymeric material to form a polymeric film. Methods of making the mixed metal phosphonate by combining and reacting a metal oxide and an organophosphonic acid are also provided.

Abstract: Coordination complexes having at least two structural conformations are disclosed. The coordination complexes contain at least one metal center and at least one hemi-labile ligand, and change structural conformations due to the presence or absence of allosteric effectors. Methods of detecting an analyte using the coordination complexes are also disclosed.

Abstract: Tetraphosphorous ligands are combined with transition metal salts to form catalysts for use in hydroformylation, isomerization-hydroformylation, hydrocarboxylation, hydrocyan-ation, isomerization-formylation, hydroaminomethylation and similar related reactions.

Abstract: The present invention relates to biarylbisphosphines and intermediates thereof. Furthermore, the scope of the invention encompasses catalysts which can be prepared from the bisarylphosphines and their use in asymmetric syntheses.

Abstract: The present invention provides a novel mononuclear transition metal compound, a novel binuclear transition metal compound, a novel organic amine or phosphorous compound, and a method for preparing the same. The mononuclear transition metal compound according to the present invention is configured such that a cyclopentadienyl group and an amido or phosphorous group are bridged via a phenylene bridge. The binuclear transition metal compound according to the present invention is configured such that the two bridged mononuclear transition metal compounds configured such that a cyclopentadienyl group and an amido or phosphorous group are bridged via a phenylene bridge are linked via a bridging group located at the phenylene bridge. According to the present invention, the mononuclear transition metal compound, the binuclear transition metal compound, the organic amine or phosphorous compound can be prepared in a simple manner by using suzuki-coupling reaction with a high yield.

Abstract: Dopant-group substituted (cyclo)silane compounds, liquid-phase compositions containing such compounds, and methods for making the same. Such compounds (and/or ink compositions containing the same) are useful for printing or spin coating a doped silane film onto a substrate that can easily be converted into a doped amorphous or polycrystalline silicon film suitable for electronic devices. Thus, the present invention advantageously provides commercial qualities and quantities of doped semiconductor films from a doped “liquid silicon” composition.

Abstract: The present invention can provide a cyanation catalyst represented by the general formula (I): (in the formula (I), R1 through R4 are each an optionally substituted hydrocarbon group; R1 and R2 and/or R3 and R4 may form an optionally substituted carbon chain ring; R5 through R8 are each a hydrogen atom, or an optionally substituted hydrocarbon group; R5 and R6 and/or R7 and R8 may form an optionally substituted carbon chain ring; R9 and R10 are each a hydrogen atom, or an optionally substituted hydrocarbon group; W, X and Y each represent an optionally substituted binding chain; X and/or Y may be non-existent; M represents a metal or a metal ion; and ligands of M may each be located at any position).

Abstract: The invention concerns metal complexes and their preparation, in particular a metal complex MLnXm, where M is a metal of group 8, 9 or 10 and X is a halide, HCO3—, NO3—, CO32— or carboxylate. n is a number equal to or less than the coordination number of the metal and m is 1 or 2 and is equal to the oxidation state of the metal. The ligand L may be a bidentate phosphine of formula (I), (II), (III) or (IV) as set out herein. The process of production comprises reacting an ammine compound of metal M with a complexing compound, which is preferably a phosphine.

Abstract: A process for extractively removing nickel(0) complexes having phosphorus ligands from a reaction effluent of a hydrocyanation of unsaturated mononitriles to dinitriles by extraction by means of a hydrocarbon, a phase separation of the hydrocarbon and of the nitrile-containing solution into two phases being effected, by feeding at least one polar additive to the hydrocyanation effluent (feedstream) and/or to the extraction stage.

Abstract: Tetraphosphorous ligands are combined with transition metal salts to form catalysts for use in hydroformylation, isomerization-hydroformylation, hydrocarboxylation, hydrocyan-ation, isomerization-formylation, hydroaminomethylation and similar related reactions.

Abstract: Process for stereoselective hydrogenation by reacting racemic aldehydes or ketones having a stereogenic carbon atom in the position relative to the C(O) group and containing the structural element —(O)C—C—CH— by means of hydrogen in the presence of a base and a ruthenium complex containing a bidentate ligand having coordinating P and N atoms, a monophosphine ligand and anionic and/or uncharged ligands as homogeneous catalyst, with the charge being balanced by one or two monovalent acid anions or a divalent acid anion when uncharged ligands are present.

Abstract: A process for producing a crosslinked type or non-crosslinked type layered metal phosphonate compound including a reaction step of reacting two or more members selected from organic diphosphonic acids or monophosphonic acids, or derivatives thereof having predetermined conditions and a metal source capable of forming an ion of a hexacoordinate metal atom as a central atom (M) of a metal oxide octahedron upon reaction under the presence of a sulfuric acid catalyst, a crosslinked or non-crosslinked metal phosphonate compound obtained by the process, as well as a stock solution used for the synthesis of the crosslinked or non-crosslinked type layered metal phosphonate compound described above.

Abstract: Process for preparing halide metallocene compounds comprising the step of reacting the dialkyl derivative with a halogenating agent of formula R3xTLw wherein: L is chlorine, iodine or bromine; R3 is hydrogen or a hydrocarbon group; T is a metal of groups 2-14 of the periodic table of the elements; and x is ?1 so that x+w is equal to the oxidation state of the metal T.

Abstract: A ring-opening metathesis polymerisation (ROMP) reaction is disclosed in which a cyclic alkene compound is subjected to ROMP using a transition metal ROMP catalyst which has an alkyl moiety which is connected to the metal centre thereof through a double bond. The process includes the step of adding sufficient of an acyclic alkene having a carbon-carbon double bond capable of reacting with the catalytic metal moieties attached to the living end of each of the polymer chains generated in the ROMP reaction to end cap the polymer chains and to generate a stable olefin metathesis catalyst.

Abstract: Coordination complexes having at least two structural conformations are disclosed. The coordination complexes contain at least one metal center and at least one hemi-labile ligand, and change structural conformations due to the presence or absence of allosteric effectors. Methods of detecting an analyte using the coordination complexes are also disclosed.

Abstract: The present invention relates to the use of copper(I) complexes of the formula I where X is nitrogen or a C—R group, R is alkyl or aryl, Ar is phenyl or naphthyl, each of which is optionally substituted by from one to three radicals selected from the group consisting of alkoxy, alkylthio, alkylamino, dialkylamino, alkoxycarbonyl, alkoxysulfonyl, halogen, cyano, carboxyl, hydroxysulfonyl and nitro, and the two optionally substituted phenyl or naphthyl radicals may be joined to one another by a chemical single bond via the carbon atoms in the ?- and ??-position relative to the phosphorus atom, n is 1, 2 or 3, and Y is halogen, cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino, in organic light-emitting diodes (OLEDs), The present invention further relates to light-emitting layers which comprise at least one copper(I) complex of the formula I, to OLEDs which comprise at least one copper(I) complex of the formula I or an inventive light-emitti

Abstract: The present invention relates to ligands of the general formula (I). In addition, a process for the production thereof and the use thereof are demonstrated.

Abstract: Stable rare earth tris (organophosphate) solutions comprise a rare earth tris (organophosphate) and a hydrocarbon solvent. From about 2% to about 10% rare earth element, preferably from about 3% to about 8%, is present in the solutions. The rare earth tris (organophosphate) solutions are stable from precipitation of the rare earth tris (organophosphate) for at least about fifteen (15) days, preferably for at least about twenty (20) days and most preferably at least about thirty (30) days. A process for preparing these solutions is described herein. A stabilizing additive, acid, glycol or mixtures thereof, is utilized to inhibit precipitation. The molar ratios of free acid, glycol and/or water to the rare earth element are controlled to inhibit precipitation.

Abstract: A compound of the formula Ia or Ib; where, in the formula Ia, E1 is O, S, Se, Te, NR, CR2, or PR; E2, E3 are each CR, N, or P; E4 is N, or P; E5 is OH, SH, NHR, OR?, SR?, or NRR?; E6 is NH, PH, NR?, or PR?; R5, R6 are each hydrogen or a linear, branched or cyclic alkyl radical or an aryl radical; R1, R2, R3, R4 are each hydrogen, a linear, branched or cyclic alkyl radical, an aryl radical, a halogen or a nitro group; R is hydrogen, a linear, branched or cyclic alkyl radical; R? is a linear, branched or cyclic alkyl radical; where at least one of the groups E5 and E6 contains a hydrogen atom; and in the formula Ib, the symbols E1, E4, E5, E6, R5, R6, R1, R2, R3, R4, R and R? are as defined in formula Ia; and E?2 and E?3 are each O, S, Se, Te, NR, CR2, or PR.

Abstract: Phosphinines of formula (I) can be combined with metal salts to prepare hydroformylation catalysts. The phosphinine complexes have two phosphorus centers that may be substituted with a variety of hetero atoms or alkyl substituents to modify the ligand characteristics of the phosphinine. Phosphinine metal complexes are employed under normal hydroformylation reaction conditions. The preparatory routes to the phosphinine ligands of formula (I) allow for their convenient synthesis.

Abstract: This invention relates to metallocene compounds represented by formula: wherein M is a group 3, 4, 5 or 6 transition metal atom, or a lanthanide metal atom, or actinide metal atom; E is a substituted or unsubstituted indenyl ligand that is bonded to Y through the two position of the indenyl ring; A is bonded to Y, and is a substituted or unsubstituted cyclopentadienyl ligand, a substituted or unsubstituted heterocyclopentadienyl ligand, a substituted or unsubstituted indenyl ligand, a substituted or unsubstituted heteroindenyl ligand, a substituted or unsubstituted fluorenyl ligand, a substituted or unsubstituted heterofluorenyl ligand, or other mono-anionic ligand, or A may, independently, be defined as E; Y is a phosphorus containing group that is bonded to both E and A, and is bonded via the phosphorus atom to E; and X are, independently, univalent anionic ligands, or both X are joined and bound to the metal atom to form a metallocycle ring, or both X join to form a chelating ligand, a diene ligand, o

Abstract: There are disclosed a phosphorus-containing carboxylic acid derivative which has a group containing phosphorus atom and has in its molecule, a group represented by the following formula (1): wherein R1, R2 and R3 are each hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, and Y is oxygen atom or sulfur atom; a process for producing the derivative; and a flame retardant comprising the foregoing derivative as an effective ingredient. The present invention can provide the phosphorus-containing carboxylic acid derivative and a flame retardant which are each excellent in solubility in an organic solvent, compatibility with a variety of resins, stability and flame retardancy.

Abstract: A process for preparing dihalide or monohalide metallocene compounds comprising contacting a compound of formula (II) (Cp)(ZR1m)n(A)rML?y (II) wherein Cp is a cyclopentadienyl radical; (ZR1m)n is a divalent bridging group between Cp and A; A is a cyclopentadienyl radical or O, S, NR2, PR2 wherein R2 is an hydrocarbon radical, M is zirconium, titanium or hafnium.

Abstract: 2-Decarboxy-2-phosphinico prostaglandin derivatives are disclosed. These derivatives comprise a modified ?-chain and an ?-chain bonded to a ring structure. The modified ?-chain has a 2-decarboxy-2-phosphinico group. The derivatives can be used to treat a variety of pharmaceutical and cosmetic conditions.

Abstract: The present invention provides compounds of the formula wherein R is optionally substituted lower alkyl, cycloalkyl or aryl; R? is alkyl or aryl; n is zero or an integer of 1 or 2; or an enantiomer thereof; or an enantiomeric mixture thereof. The compounds of formula (I) are bridged C2-symmetric biphenyldiphosphine analogs and, thus, may be employed as ligands to generate chiral transition metal catalysts which may be applied in a variety of asymmetric reactions. The compounds of the present invention are easily accessible in high diastereomeric and optical purity according to the methods disclosed herein.

Abstract: Group 4 metal constrained geometry complexes comprising tricyclic 4-arylsubstituted indenyl ligands, especially 1,5,6,7-tetrahydro-4-aryl-s-indacen-1-yl ligands, catalytic derivatives thereof, processes for preparing the same and their use as components of olefin polymerization catalysts are disclosed.

Abstract: The invention relates to phosphinites I of formulae (1) or (2), in which R1, R2, R5, R6, R7, R8, R9 independently represent hydrogen, an alkyl or alkylene group having 1 to 8 carbon atoms or an alkoxy group having 1 to 8 carbon atoms; R3 is H or methyl; R4 is i-propyl or t-butyl; X is F, Cl or CF3 and n is 1 or 2

Abstract: Phosphonites I of the formula 1 or 2 where R1, R2 are each, independently of one another, hydrogen, an alkyl or alkylene group having from 1 to 8 carbon atoms or an alkoxy group having from 1 to 8 carbon atoms, with the proviso that R1 and R2 are not simultaneously H, R3 is H or methyl, R4 is t-butyl, R5, R6, R7, R8, R9 are each, independently of one another, H or an alkyl or alkylene group having from 1 to 8 carbon atoms.

Abstract: Chiral organometallic compounds are provided which comprise certain non-symmetrically substituted cyclopentadiene complexed to a transition metal. The cyclopentadiene has a second coordinating group which also complexes the transition metal and is attached to the cyclopentadiene by means of a chiral connecting chain. Preferred transition metals include rhodium, ruthenium, iridium, cobalt, iron, manganese, chromium, tungsten, molybdenum, nickel, palladium, or platinum. These chiral organometallic compounds find use in asymmetric synthesis to produce chiral compounds.

Abstract: A process for preparing dihalide or monohalide metallocene compounds comprising contacting a compound of formula (II) (Cp)(ZR1m)n(A)rML?y (II) wherein Cp is a cyclopentadienyl radical; (ZR1m)n is a divalent bridging group between Cp and A; A is a cyclopentadienyl radical or O, S, NR2, PR2 wherein R2 is an hydrocarbon radical, M is zirconium, titanium or hafnium, L? is an hydrocarbon radical, r ranges from 0 to 2 and y is equal to 4; with an halogenating agent selected from the group consisting of: T1Lw1 wherein T1 is a metal of groups 3–13 of the periodic table; L is halogen and w1 is equal to the oxidation state of the metal T1; T2Lw2 wherein T2 is a nonmetal element of groups 13–16 of the periodic table (new IUPAC version); and w2 is equal to the oxidation state of the element T2; O=T3Lw3 where T3 is a selected from the group consisting of C, P and S; O is an oxygen atom bonded to T3 trough a double bond; and w3 is equal to the oxidation state of the element T3 minus 2; R6C(O)L, wherein R6 is an hydrocarbon

Abstract: 2-Decarboxy-2-phosphinico prostaglandin derivatives are disclosed. These derivatives comprise a modified ?-chain and an ?-chain bonded to a ring structure. The modified ?-chain has a 2-decarboxy-2-phosphinico group. The derivatives can be used to treat a variety of pharmaceutical and cosmetic conditions.

Abstract: 3,3?-Substituted chiral biaryl phosphine and phosphinite ligands and metal complexes based on such chiral ligands useful in asymmetric catalysis are disclosed. The metal complexes are useful as catalysts in asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition, epoxidation, kinetic resolution and [m+n] cycloaddition. The metal complexes are particularly effective in Ru-catalyzed asymmetric hydrogenation of beta-ketoesters to beta-hydroxyesters and Ru-catalyzed asymmetric hydrogenation of enamides to beta amino acids.

Abstract: A monocyclopentadienyl or substituted monocyclopentadienyl metal complex containing compound useful as a polymerization catalyst corresponding to the formula: CpMXn+A− wherein: Cp is an &eegr;5-substituted cyclopentadienyl group optionally covalently bonded to M through a substituent, said Cp being substituted in at least one occurrence with an alkoxy or aryloxy group; M is a metal of Group 3-10 or the Lanthanide Series of the Periodic Table bound in an &eegr;hu 5 bonding mode to the cyclopentadienyl or substituted cyclopentadienyl group; X each occurrence independently is selected from the group consisting of hydride, halo, alkyl, aryl, silyl, germyl, aryloxy, alkoxy, amide, siloxy, neutral Lewis base ligands and combinations thereof having up to 20 non-hydrogen atoms, and optionally one X together with Cp forms a metallocycle with M; R is alkyl or aryl of up to 10 carbons; n is one or two depending on the valence of M; and A is a noncoordinating, compatible anion of a Bronsted acid salt.

Abstract: Metal compounds of the formula I, where M is selected from among Ni and Pd in the oxidation state +II can be used for the polymerization or copolymerization of olefins. Supported catalysts for the polymerization and copolymerization of olefins can be obtained by application of one or more of the above-described ionic metal compounds to a support.

Abstract: The novel metallocenes of the formula I in which, preferably, M1 is Zr or Hf, R1 and R2 are alkyl or halogen, R3 and R4 are hydrogen, R5 and R6 are alkyl or haloalkyl, —(CR8R9)m—R7—(CR8R9)n— is a single- or multi-membered chain in which R7 may also be a (substituted) hetero atom, m+n is zero or 1, and R10 is hydrogen, form, together with aluminoxanes as cocatalysts, a very effective catalyst system for the preparation of polyolefins of high stereospecificity and high melting point.

Abstract: The novel metallocenes of the formula I in which, preferably, M1 is Zr or Hf, R1 and R2 are alkyl or halogen, R3 and R4 are hydrogen, R5 and R6 are alkyl or haloalkyl, —(CR8R9)m—R7—(CR8R9)n— is a single- or multi-membered chain in which R7 may also be a (substituted) hetero atom, m+n is zero or 1, and R10 is hydrogen, form, together with aluminoxanes as cocatalysts, a very effective catalyst system for the preparation of polyolefins of high stereospecificity and high melting point.