WO1996037536A1

WO1996037536A1 - Chelate-metal complexes bridged by a single atom

Info

Publication number: WO1996037536A1
Application number: PCT/EP1996/001963
Authority: WO
Inventors: Ferdinand Lippert; Arthur Höhn; Peter Hofmann
Original assignee: Basf Aktiengesellschaft
Priority date: 1995-05-22
Filing date: 1996-05-09
Publication date: 1996-11-28
Also published as: CN1185167A; JPH11505812A; EP0827520A1

Abstract

Metal complexes having general formula (I) are useful to copolymerise carbon monoxide with olefinically unsaturated compounds. In said formula, the substituents and indexes have the following meanings: M is a metal of group VIIB of the periodic table of elements; E1, E2 stand for an element of group VA of the periodic table of elements; Z stands for a structural unit with a bridging atom selected among the elements of groups IVA, VA or VIA of the periodic table of elements; R1 to R4 stand for substituents selected in the group that consists of C¿1?-C20 organic carbon residues and C3-C30 organic silicium residues and at least one of these four residues is a non-aromatic residue; L?1, L2¿ stand for formally charged or neutral ligands; X stand for monovalent or polyvalent anions; p equals 0, 1 or 2; m, n equal 0, 1 or 2, whereas p = m x n.

Description

Chelated metal complexes bridged by one atom

description

The present invention relates to metal complexes of the general formula (I) which are suitable for the copolymerization of carbon monoxide with olefinically unsaturated compounds

in which the substituents and indices have the following meaning:

M is a metal from Group VIIIB of the Periodic Table of the Elements

E ¹ , E ² an element from group VA of the periodic table of the

Elements, a structural unit with a bridging atom selected from the elements of group IVA, VA or VIA of the periodic table of the elements,

R ¹ to R ⁴ substituents selected from the group consisting of C ₁ to C ₂₀ organic carbon and C ₃ to C ₃₀ organosilicon radicals, at least one of the four radicals being a non-aromatic radical,

L ¹ , L ² formally charged or neutral ligands X formally mono- or polyvalent anions

P 0, 1 or 2 m, n 0, 1 or 2 where p = mx n. In addition, the present invention relates to a process for the preparation of such metal complexes and the use of the metal complexes as catalysts for the copolymerization of carbon monoxide with olefinically unsaturated compounds.

The present invention further relates to chelate ligands of the general formula (II)

and their use for the preparation of metal complexes of the general formula (I).

Carbon monoxide / olefin copolymers, also called polyketones, which are built up alternately from the structural element of an olefin and carbon monoxide, are e.g. from the Journal of Organometallic Chemistry, 417 (1991) 235, and Adv. Polym. Sci., 73/74 (1986) 125ff.

The polymers are produced by the monomers in the presence of a, composed of several components,

Catalyst system.

The components consist essentially of a transition metal compound of subgroup VIII of the Periodic Table of the Elements, phosphine ligands and acids, as described, for example, in EP-A 121 965.

The constituents of the catalyst system are generally mixed with one another before the polymerization or directly in the polymerization reactor by metering in the individual components, the active catalyst being formed.

However, it is expensive to meter the individual components in a reproducible manner in optimal proportions. The dosing process with different dosing devices and the stocking of the various catalyst components is also economically disadvantageous. No. 5,338,825 describes a process for the production of carbon monoxide / olefin copolymers using single positively charged metal complexes which, inter alia, must have a ligand which stabilizes the complex.

The preparative accessibility and the polymerization activity of the catalysts leave something to be desired.

US Pat. No. 5,352,767 describes alternating, elastomeric copolymers of carbon monoxide and .alpha.-olefins which have been produced using a catalyst system which contains cationic metal complexes from the Villa group of the Periodic Table of the Elements and activators. For the preparation of the copolymers, however, only α-olefins have been described as comonomers and the polymerization activity of the catalysts is in need of improvement.

It was therefore an object of the present invention to provide metal complexes which do not have the disadvantages mentioned, or which have them only to a minor extent, have high productivity, are easily accessible and are easy to meter. Another object of the present invention was to provide a method for producing these metal complexes. Accordingly, the metal complexes (I) defined at the outset were found.

In addition, a process for the preparation of the metal complexes (I) defined at the outset and the use of the defined metal complexes (I) as catalysts for the copolymerization of carbon monoxide with olefinically unsaturated compounds were found. Furthermore, the chelate ligands (II) defined at the outset and their use for the preparation of metal complexes (I) were found.

Suitable metals M of the metal complexes of the general formula (I) are the metals from Group VIIIB of the Periodic Table of the Elements, i.e. in addition to iron, cobalt and nickel, primarily the platinum metals such as ruthenium, rhodium, osmium, iridium and platinum and very particularly palladium. The metals in the complexes can be formally uncharged, formally single positively charged, or preferably formally double positively charged.

The elements E ¹ and E ^{2 of} the chelating ligand are the elements of the 5th main group of the periodic table of the elements (group VA), that is to say nitrogen, phosphorus, arsenic, antimony or bismuth. Nitrogen or phosphorus, in particular phosphorus, are particularly suitable. The chelating ligand can contain different elements E ¹ and E ² , for example nitrogen and phosphorus. The bridging structural unit Z is an atomic grouping that connects the two elements E ¹ and E ^{2 to} one another. An atom from group IVA, VA or VIA of the Periodic Table of the Elements forms the connecting bridge between E ¹ and E ² . Free valences of these bridge atoms can be saturated in a variety of ways, for example by substitution with hydrogen, elements from group IVA, VA, VIA or VIIA of the periodic table of the elements. These substituents can also form a ring with one another or with the bridge atom. Particularly suitable bridging structural units are those with only one bridging atom from group IVA of the Periodic Table of the Elements, such as -CR ⁵ R ⁶ - or -SiR ⁵ R ⁶ - in which R ⁵ and R ^{6 are} hydrogen and C ₁ - to Cio- Carbon-organic residue stands. R ⁵ and R ⁶ can also form a 3- to 10-membered ring together with the bridge atom. Examples of structural units bridging one atom are methylene (-CH ₂ -), ethylidene (CH ₃ (H) C =), 2-propylidene ((CH ₃ ) ₂ C =), diphenylmethylene ((C ₆ H ₅ ) ₂ C = ), Dialkylsilylene, such as dimethylsilylene ((CH ₃ ) ₂ Si =), diphenylsilylene ((C ₆ H ₅ ) ₂ Si =); furthermore as cyclic bridge members cyclopropylidene, cyclobutylidene, cyclopentylidene, cyclohexylidene. Preferred bridging structural units are methylene (-CH ₂ -), ethylidene (CH ₃ (H) C =), 2-propylidene ((CH ₃ ) ₂ C =), dimethylsilylene, diphenylsilylene, especially methylene. Suitable organic carbon radicals R ¹ to R ⁴ are aliphatic, cycloaliphatic and aromatic radicals having 1 to 20 carbon atoms, for example the methyl, ethyl, 1-propyl,

1-butyl, 1-pentyl, 1-hexyl and 1-octyl group. Linear arylalkyl groups with 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical are also suitable, such as benzyl and aryl radicals such as phenyl, tolyl and other substituted phenyl groups, at least one of the four radicals R ¹ until R ^{4 is} a non-aromatic radical. The radicals R ¹ to R ⁴ should preferably be sufficiently space-filling that the central atom, for example the palladium atom, with which the atoms E ¹ and E ^{2 form} the active complex, is largely shielded. Residues which meet this requirement are, for example, cycloaliphatic radicals and branched aliphatic radicals, including in particular those with branching in the α position. Suitable cycloaliphatic radicals are C ₃ - to Cio-monocyclic radicals such as, for example, the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl groups and menthyl groups, and bicyclic radicals such as the norbornyl, pinanyl, bornyl group and bicyclononyl group in any combination of the ring structure with the atoms E ¹ and E ² into consideration. The cycloaliphatic radicals preferably contain a total of 5 to 20 carbon atoms; cyclohexyl and menthyl are very particularly preferred. Suitable branched aliphatic radicals are C ₃ - to C ₂₀ -, preferably C ₃ - to C ₁₂ -alkyl radicals, such as, for example, the isopropyl, isobutyl, sec-butyl, neopentyl and tert .-Butyl group, further alkylaryl each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical.

Particularly suitable branched aliphatic radicals are the tert-butyl group, the iso-propyl group and the sec-butyl group.

Alkyl groups with branching located further outside are also suitable as substituents R ¹ to R ⁴ , such as the isobutyl, 3-methyl-but-2-yl and 4-methylpentyl group.

The chemical nature of the radicals R ¹ to R ⁴ is not of decisive importance according to the observations to date, ie the radicals can also contain atoms from the group IVA, VA, VIA or VIIA of the periodic system of the elements, such as, for example, halogen, Oxygen, sulfur, nitrogen, silicon, here for example the bis (trimethylsilyl) methyl group. Functional groups such as hydroxy, alkoxy and cyano, which are inert under the polymerization conditions, can also be considered in this context.

Preferred hetero substituents R ¹ to R ⁴ are C ₃ - to

C ₃ o-organosilicon radicals, that is to say tetravalent silicon atoms which are bonded to E ¹ or E ² on the one hand and the rest thereof

Valences are saturated with three carbon-organic radicals, the sum of the carbon atoms of these three silicon-bonded radicals being in the range from three to thirty. Examples include the trimethylsilyl, tert-butyldimethylsilyl or triphenylsilyl group, in particular the trimethylsilyl group.

Diphosphines bridged with a methylene group are preferably used as the chelating ligand, such as, for example, [(di-tert-butylphosphino) (diphenylphosphino)] methane, particularly preferably one uses with C ₃ -C ₁₀ -cycloaliphatic or branched C ₃ -C ₂₀ - aliphatic radicals R ¹ to R ⁴ substituted methylene-bridged diphosphines, such as, for example, bis (di-tert-butyl- phosphino) methane, [(di-tert.-butylph-sphino) (di-cyclohexylphosphino)] methane, bis (di-cyclohexylphosphino) methane or [(di-tert.-butylphosphino) (dirntenthylphosphino)] methane, their suitability for the process according to the invention, the methylene linkage of the two phosphorus atoms and the large space-consuming structure of the radicals R ¹ to R ^{4 are} currently attributed.

Very particularly preferred compounds as the chelating ligand are bis (di-tert-butylphosphino) methane, [(di-tert-butylphosphino) (di-cyclohexylphosphino)] methane, bis (di-cyclohexylphosphino) methane, [(Di -tert.-butylphosphino) (diphenylphosphino)] methane or [(di-tert.-butylphosphino) (dimenthylphosphino)] methane.

Depending on the formal oxidation state of the central metal M, the ligands L ¹ , L ² carry one or two formally negative charges, or if the metal is formally uncharged, the ligands L ¹ , L ^{2 are} also formally uncharged.

The chemical nature of the ligands is not critical. According to the current state of knowledge, they have the function of stabilizing the rest of the metal complex against decomposition, for example deposition of the metal or non-specific reactions, for example aggregation of the complex fragments. Suitable formally charged inorganic ligands L ¹ , L ² are hydride, halides, sulfates, phosphates or nitrates.

Halides such as chlorides, bromides, iodides and in particular chlorides are preferably used.

Suitable formally charged organic ligands L ¹ , L ² are C ¹ -C ₂₀ -aliphatic, C ₃ - to C ₃₀ -cycloaliphatic, C ₇ - bis

C ₂₀ aralkyl radicals with C ₆ to C ₁₀ aryl radical and C ₁ to C ₁₀ alkyl radical, C ₆ to C ₂₀ aromatic radicals, such as, for example, methyl, ethyl propyl, isopropyl, tert-butyl , neo-pentyl, cyclohexyl, benzyl, neophyl, phenyl and aliphatic or aromatic substituted phenyl radicals.

Also suitable as formally charged organic ligands are L ¹ , L ² C ₁ - to C ₂₀ -carboxylates such as acetate, propionate, oxalate, benzoate, citrate and salts of organic sulfonic acids such as methyl sulfonate, trifluoromethyl sulfonate, p-toluenesulfonate.

C ₁ to C ₇ carboxylates, sulfonic acid derivatives and in particular acetate and p-toluenesulfonate are preferably used. Lewis bases, ie compounds with at least one lone pair of electrons, are generally suitable as formally uncharged ligands L ¹ , L ² . Lewis bases whose free electron pair or whose free electron pairs are located on a nitrogen or oxygen atom are particularly suitable, for example nitriles, R-CN, ketones, ethers, alcohols. C ₁ to C ₁₀ nitriles such as acetonitrile, propionitrile, benzonitrile or C ₂ to C ₁₀ ketones such as acetone, acetylacetone or C ₂ to bis are preferably used

C ₁₀ ether, such as dimethyl ether, diethyl ether, tetrahydrofuran. In particular, acetonitrile or tetrahydrofuran is used.

Depending on the formal charge of the complex fragment containing the metal M, the metal complex (I) contains anions X. If the M-containing complex fragment is formally uncharged, the complex according to the invention does not contain any anion X.

The chemical nature of the anions X is not critical. According to the current state of knowledge, however, it is advantageous if they are as little nucleophilic as possible, i.e. have as little tendency as possible to form a chemical bond with the central metal M.

Suitable anions X are, for example, perchlorate, sulfate,

Phosphate, nitrate and carboxylates, such as, for example, acetate, trifluoroacetate, trichloroacetate, propionate, oxalate, citrate, benzoate, and conjugated anions of organosulfonic acids, such as, for example, methyl sulfonate, trifluoromethyl sulfonate and para-toluenesulfonate, furthermore tetrafluoroborate, tetraphethenophenyl, tetraphenylphenol ) borate, hexafluorophosphate, hexafluoroarsenate or hexafluoroantimonate. Perchlorate, trifluoroacetate, sulfonates such as methyl sulfonate, trifluoromethyl sulfonate, p-toluenesulfonate, tetrafluoroborate or hexafluorophosphate and in particular trifluoromethyl sulfonate, trifluoroacetate, perchlorate or p-toluenesulfonate are preferably used. The new chelate phosphines (II) can be prepared as described, for example, in DE-A 41 34 772 (in particular example). In general, diorganophosphinomethanides are therefore reacted with diorganohalophosphanes in inert aprotic solvents, for example tetrahydrofuran, at temperatures in the range from (-) 100 to 25 ° C.

The metal complexes of the general formula (I) are prepared for the neutral chelal complexes by exchanging weakly coordinating ligands, such as, for example, 1,5-cyclooctadiene, benzonitrile or tetramethylethylenediamine, which are attached to the corresponding transition metal compounds, for example transition metal halides, transition metal (alkyl ) (Halides), Transition metal diorganyls are bound against the chelate ligands according to the invention [R ¹ R ² E ¹ ] -Z- [R ³ R ⁴ E ² ] whose substituents have already been defined. The reaction is generally carried out in a solvent such as dichloromethane at temperatures in the range of (-) 78 to 40 ° C.

A further synthesis method is the implementation of the chelate complexes of the general formula (I) with organometallic compounds from groups IA, IIA, IVA and IIB, for example 0χ - to C ₆ -alkyls of the metals lithium, aluminum, magnesium, zinc, formally charged inorganic ligands L ¹ , L ² as previously defined, are exchanged for formally charged aliphatic, cycloaliphatic or aromatic ligands L ¹ , L ² as also previously defined. The reaction is generally carried out in a solvent such as diethyl ether or tetrahydrofuran at temperatures in the range from (-) 78 to 65 ° C.

Monocation complexes of the general formula (I) are converted by reaction of (chelate ligand) metal (halogeno) (organo) complexes of the general formula (I) in which L ¹ halogen and L ² formally defined organic ligands (excluding the anions) organic acids) mean formed with metal salts M'X. The reaction is generally carried out in coordinating solvents such as acetonitrile or tetrahydrofuran at temperatures in the range from (-) 78 to 65 ° C.

It is advantageous if the metal salts M'X meet the following criteria. The metal M 'should preferably form poorly soluble metal chlorides, such as silver. The salt anion should preferably be a non-nucleophilic anion X, as previously defined.

Well-suited salts for the formation of cationic complexes are silver tetrafluoroborate, silver hexafluorophosphate, silver trifluoromethanesulfonate, silver perchlorate, silver paratoluenesulfonate.

The dicationic complexes (II) are prepared analogously to the monocationic complexes, except that now instead of the (chelate ligand) metal (halogeno) (organo) complexes, the (chelate ligand) metal (di-halogeno) complexes of the general formula ( I) (L ¹ and L ² means halogen) can be used as a precursor.

Another reaction for the preparation of the dicationic complexes (I) is the reaction of [Y ₄ M] X ₂ with the chelate ligands [R ¹ R ² E ¹ ] -Z- [R ³ R ⁴ E ² ] defined at the beginning . Here, Y means the same or different weak ligands as in for example acetonitrile, benzonitrile or 1, 5-cyclooctadiene, M and X have the previously defined meaning.

A preferred method for producing the metal complexes of the general formula (I) is the reaction of the dihalometal precursor complexes with silver salts with non-coordinating anions.

The metal complexes (I) according to the invention can be used as catalysts for the preparation of copolymers from carbon monoxide and olefinically unsaturated compounds.

The monomers are generally incorporated alternately in the copolymer.

In principle, all monomers of this class of compounds can be considered as olefinically unsaturated compounds.

Preference is given to ethylene and C ₃ -C ₁₀ -alk-1-enes, such as mainly propene, butadiene, and also cycloolefins, such as cyclopentene, cyclohexene, norbornene and norbornadiene and his

Derivatives.

Among the olefinically unsaturated aromatic monomers, styrene and α-methylstyrene are primarily mentioned.

Also of particular importance are acrylic acid and methacrylic acid and their derivatives, including in particular the nitriles, the amides and the C ₁ -C ₆ -alkyl esters, such as, for example, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, methyl methacrylate.

Other suitable monomers are vinyl chloride, vinyl acetate, vinyl propionate, maleic anhydride and N-vinyl pyrrolidone. Mixtures of different monomers can of course also be used, the mixing ratio generally not being critical.

The molar ratio of the olefinically unsaturated compound to carbon monoxide can be chosen largely freely and is preferably between 0.1: 1 to 10: 1, preferably in the vicinity of 1: 1.

The polymerizations for producing the carbon monoxide copolymers can be carried out batchwise or continuously. Pressures of 100 to 500,000 kPa, preferably 200 to 350,000 kPa and in particular 500 to 30,000 kPa, temperatures of (-50) to 400 ° C, preferably 20 to 250 ° C and in particular 40 to 150 ° C have proven to be suitable.

Polymerization reactions using the metal complexes (I) defined at the outset can be carried out in the gas phase, in suspension, in liquid and in supercritical monomers and in solvents which are inert under the polymerization conditions.

Suitable inert solvents are alcohols such as methanol,

Ethanol, propanol, i-propanol, 1-butanol and tert. Butanol,

Sulfoxides and sulfones, for example dimethyl sulfoxide, esters such as ethyl acetate and butyrolactone, ethers such as tetrahydrofuran, dimethyl ethylene glycol and

Diisopropyl ether and aromatic solvents such as benzene, toluene, ethylbenzene or chlorobenzene or mixtures thereof. The molecular weight of the polymers according to the invention can be varied by varying the polymerization temperature

protic compounds such as alcohols, for example methanol, ethanol, tert. -Butanol, preferably methanol and by the addition of hydrogen in a manner known to those skilled in the art. In general, a high concentration of regulating substances and / or a high polymerization temperature results in a relatively low molecular weight and vice versa.

Examples

Abbreviations

bcpm [(di-tert-butylphosphino) (di-cyclohexylphosphino)] methane dtbpm bis (di-tert-butylphosphino) methane

tbppm [(di-tert-butylphosphino) (diphenylphosphino)] methane tmeda tetramethylethylenediamine

COD 1,5-cyclooctadiene

MeCN acetonitrile, CH ₃ -CN

PhCN benzonitrile, C ₆ H ₅ -CN Example 1

Preparation of [(di-tert.-butylphosphino) (dicyclohexylphosphino)] methane (bcpm) To a suspension sipon of 5.35 g of lithium di-tert.-butyl methanide (32 mmol) in 150 ml of tetrahydrofuran were at (-) 78 ° C 7.7 g of dicyclohexyl-chlorophospan (33 mmol) metered in and the resulting reak tion mixture was warmed to room temperature over the course of 15 hours with constant stirring, then the tetrahydrofuran was distilled off, the remaining gray suspension was mixed with 80 ml of a 4% strength by weight solution of ammonium chloride in water, then extracted with 100 ml of pentane, the pentane extract was dried and the pentane evaporates. The residue was dried in a high vacuum. Yield 4.7 g (41%) of a yellow oil, which can be used without further purification and over which

Metal complex, see Example 10, can be characterized.

Examples 2 to 6

General regulation for the production of cationic complexes

The metal dihalide chelal complex (A) was dissolved in 20 ml of acetonitrile. The silver salt (B) was then added, the mixture was stirred at room temperature for 2 hours, the precipitate formed was filtered off and the product was precipitated from the filtrate by concentrating and adding diethyl ether, isolated, dried under high vacuum and characterized. The NMR spectroscopic data of all complexes can be found in the table according to Example 12. Production of dication complexes

Examples 7 to 10

Preparation of neutral complexes The precursor complex (C) was dissolved in 50 ml dichloromethane and then the chelate ligand (D) was added and the mixture was stirred at room temperature for 4 h. The chelate metal complex was precipitated with pentane, isolated and dried in a high vacuum.

Examples 11 and 12

Polymerization experiments

General polymerization conditions

100 ml of methanol and the corresponding palladium compound were placed in a 0.3 l autoclave. A mixture of ethylene and carbon monoxide in a molar ratio of 1: 1 was then injected to the desired total pressure at the selected reaction temperature. The polymerization was carried out for 5 hours. The temperature and the partial pressures of the monomers were kept constant throughout the reaction. The polymerization was stopped by reducing the pressure to ambient pressure, the reaction mixture was filtered and the residue was dried.

Example 11: Polymerization with [(bcpm) Pd (MeCN) ₂ ] (CF ₃ SO ₃ ) ₂ temperature: 85 ° C

Pressure: 6000 kPa

[(bcpm) Pd (MeCN) ₂ ] (CF ₃ SO ₃ ) ₂ : 60 mg, 0.07 mmol

Yield: 40.1 g. Example 12: Polymerization with [(tbppm) PdCl ₂ ]

Temperature: 85 ° C

Pressure: 6000 kPa

[(tbppm) PdCl ₂ ]: 52 mg, 0.1 mmol

Yield: 2.1 g

Claims

claims

1. Metal complexes of the general formula (I) which are suitable for the copolymerization of carbon monoxide with olefinically unsaturated compounds

in which the substituents and indices have the following meaning:

M is a metal from Group VIIIB of the Periodic Table of the Elements

E ¹ , E ² an element from group VA of the periodic table of the elements, a structural unit with a bridging atom selected from the elements of group IVA, VA or VIA of the periodic table of the elements,

L ¹ , L ² formally charged or neutral ligands

X formally monovalent or multivalent anions

0, 1 or 2 m, n 0, 1 or 2 where p = mx n.

2. Metal complexes according to claim 1, wherein Z is a structural unit with a bridging atom selected from the elements of group IVA of the periodic table of the elements.

3. Metal complexes according to claims 1 to 2, wherein Z is -CR ⁵ R ⁶ - or -SiR ⁵ R ⁶ - and R ⁵ and R ^{6 are} hydrogen, C ₁ - to C ₁₀ -carbon organic radical.

4. Metal complexes according to claims 1 to 3, wherein E ¹ and E ^{2 is} phosphorus.

5. Metal complexes according to claims 1 to 4, wherein R ¹ to R ^{4 is} C ₁ - to C ₂₀ -aliphatic or C ₃ - to C ₂₀ -cycloaliphatic radical.

6. A process for the preparation of metal complexes of the general formula (I) according to Claims 1 to 5 by ligand exchange reactions in metal complexes and, if appropriate, subsequent conversion of the metal complex formed into the cation complex, characterized in that the ligand exchange reaction with the chelate ligands of the general formula (Ia)

is carried out in which the substituents and indices have the following meaning:

E ¹ , E ² an element from group VA of the periodic table of the elements, Z a structural unit with a bridging one

Atom selected from the elements of group IVA, VA or VIA of the periodic table of the elements, R ¹ to R ⁴ substituents, selected from the group consisting of C ₁ to C ₂₀ organic carbon and C ₃ to C ₃₀ organosilicon radicals, wherein at least one of the four residues is a non-aromatic residue.

7. Chelating ligand of the general formula (II)

in which the substituents and indices have the following meaning:

R ⁷ , R ⁸ tert-butyl

R ⁹ , R ¹⁰ cyclo-hexyl, menthyl

Z is a structural unit with a bridging atom selected from group IVA of the periodic table

Elements.

8. Use of chelate ligands according to claim 7 for the production of metal complexes (I).

9. Use of metal complexes (I) according to claims 1 to 5 as catalysts for the copolymerization of carbon monoxide with olefinically unsaturated compounds.