VOLATILE FLUORINATED BETA-KETOIMINES AND ASSOCIATED METAL COMPLEXES

Abstract: Fluorinated β-ketoimine ligands and highly volatile β-ketoiminato metal complexes of the ligands are synthesized by silylating a fluorinated β-diketone to form a silylenolether, and subsequently reacting the silylenolether with a primary amine to form the desired ligand having the structural formula: wherein R₁ and R₂ are independently linear or branched perfluorinated, C₁-C₈ alkyl groups and R₃ is any organic functionality such as a C₁-C₈ alkyl, phenyl or hydroxyalkyl group, all of which can be partially or fully fluorinated. The corresponding metal complex is formed by treating the ligand with a metal halide.

Description: The present invention relates to fluorinated beta-ketoimines and volatile metal complexes formed therefrom. BACKGROUND OF THE INVENTION In the electronics industry there is a growing need for volatile sources of different metals to be used in the chemical vapor deposition (CVD) of metallic films, metal oxide films, metal silicide films, and the like. The key property required for such metal sources is that they readily evaporate or sublime to give a metal containing vapor or gas which can be decomposed in a controlled manner to deposit a film onto a target substrate. Examples of such materials which are commonly utilized in the microelectronics industry in the preparation of printed circuits and semiconductor devices include the complex H₃SiCo(CO)₄ complex which is pyrolyzed in the gas phase at 670-770°K to produce CoSi and dimethylzinc (1,4 dioxane) which is reacted with hydrogen selenide at 250-550°C to produce ZnSe. References teaching the above CVD methods are B. J. Aylett, et al in Vacuum, 35 p 435-439(1985) and P. J. Wright, et al., in a paper accepted for publication in J. of Crystal Growth, London (1986), respectively. Known fluorinated metal complexes that are chemically stable and easily volatized into the gas phase are the perfluorinated β-diketone metal coordination compounds along with their parent β-diketone precursor ligands, represented by the formulas: wherein R₁ is alkyl or fluoroalkyl, R₂ is fluoroalkyl, and M is a metal capable of forming a coordination compound. The volatility and gas phase stability of these compounds have been exploited for the gas chromatographic separation of various metals, the purification of uranium and the manufacture of specialty glasses. Decomposing such metal complexes by reaction with hydrogen in the gas phase to deposit thin metal films is taught in U.S. Patent 3,356,527. In the past, attempts have been made to condense primary amines or primary diamines with ligands similar to those having the above structure. In instances in which R₁ and R₂ are not both fluorocarbon groups, it was reported that an O atom could be replaced with a N atom from an amine by direct Schiff-base condensation between an appropriate β-diketone and an amine. Additionally, the corresponding metal complex could be synthesized by chelation to a metal ion. See A. E. Martell, et al J. Inorg. Chem. Vol. 5 pp 170-181 (1958). As reported by Sievers, et al in J. Inorg. Nucl. Chem. Vol. 32 pp 1895-1906 (1970), ligands in which R₁ and R₂ are both perfluoralkyl and in which an oxygen has been replaced with an amine have not been obtainable. It is believed that such methods have been unsuccessful because the perfluorinated β-diketones are of such high acidity that the amine used in the reaction becomes protonated, thereby forming a salt between the amine and the β-diketone rather than forming the desired ligand. Sievers, et al do report synthesizing a ligand having the structure: wherein R₁ = R₂ = CF₃ and R₃ = -CH₂CH₂-. This ligand was reportedly synthesized by sublimation of the salt [(CF₃C(O)CHC(O)CF₃)] - / 2 [NH₃-CH₂CH₂NH₃]⁺². The ligand was reported to be chemically unstable and hence impossible to isolate. Charles, U.S. Patent 3,594,216 discloses a process for depositing a metallic coating on a substrate by heating the substrate and contacting it with vaporized metal-organic beta-ketoamine chelates. The metal-organic beta-ketoamines were prepared by conventional synthesis techniques. While a wide range of metal chelates are disclosed generally, none of the examples or synthesis techniques specifically use perfluorinated metal chelates. Johnson, et al in Journal of Fluorine Chemistry, 27 pp 371-378 (1985) reported synthesizing a ligand in which R₁ and R₂ are perfluoroalkyl and oxygen was replaced with an ammonia nitrogen. The Cu⁺² complex was also prepared and was reported to be volatile. BRIEF SUMMARY OF THE INVENTION The present invention is a class of novel, β-ketoimine ligands and highly volatile metal complexes of the ligands and also a process for making the same. The β-ketoimine ligands of the present invention are those of the general structural formula: wherein R₁ and R₂ are independently linear or branched, perfluorinated, C₁-C₈ alkyl groups, and R₃ is a C₁-C₈ alkyl, phenyl or hydroxyalkyl group, which can be partially or fully fluorinated. The highly volatile β-ketoiminato metal complexes which are synthesized from these ligands have the structural formula: wherein R₁, R₂ and R₃ are as described above, and M is a metal, and n is 1, 2 or 3. The present invention is also a process for making both the β-ketoimine ligands and metal complexes described above. The ligands are synthesized by silylating a fluorinated β-diketone to form a silylenolether, and subsequently reacting the silylenolether with a primary amine to form the desired ligand. The corresponding metal complex is formed by treating the resulting ligand with potassium methoxide followed by treatment with a halide salt of the desired metal. DETAILED DESCRIPTION OF THE INVENTION The present invention is a class of heavily fluorinated β-ketoimine ligands and thermally volatilizable β-ketoiminato metal complexes of the ligands. The ligands are characterized in that they are highly fluorinated and contain oxygen and nitrogen donor atoms which can be covalently coordinated to a central metal atom to form the corresponding metal complex. This class of ligand as well as the corresponding metal complex, are chemically stable and easily volatized into the gas phase. The high fluorine content of the complex is believed to reduce the Van der Waals forces between individual molecules and hence lower the boiling or sublimination point of the compound. The heavily fluorinated β-ketoimine ligands of the present invention can be represented by the structural formula: wherein R₁ and R₂ are independently linear or branched, perfluorinated, C₁-C₈ alkyl groups, and R₃ is a C₁-C₈ alkyl, phenyl or hydroxylalkyl group, which can be partially or fully fluorinated. The highly volatile metal complexes which are synthesized from these ligands can be represented by the structural formula: wherein R₁, R₂ and R₃ are as described above, and M is a metal and n = 1, 2 or 3. These volatile complexes hold great potential for use as metal sources in Chemical Vapor Deposition (CVD) processes engaged in the art of depositing, for instance, metal films or metal oxide films. The ligands of structure I above are synthesized by treating a fluorinated β-diketone of the formula R₁COCH₂COR₂ with potassium hydride under anhydrous conditions to produce a compound of the formula R₁COCHCOR - / 2K⁺ and subsequently reacting the resultant R₁COCHCOR - / 2K⁺ with a silylchloride such as, t-butyldimethylsilylchloride, to produce a silylenolether having the general formula: wherein R₁ and R₂ are as described above, and each R₅ is an alkyl group. The silylenolether described above is then treated with a primary monoamine, R₃NH₂ wherein R₃ is as above to produce the desired β-ketoimine ligand of structural formula I; i.e. R₁COCH₂CN(R₃)R₂. To form the metal complex of the β-ketoimine ligand formed above, the ligand is initially treated with potassium methoxide to produce a compound of the formula R₁COCHCN(R₃)R - / 2K⁺, which is subsequently treated with a metal halide of the formula M +n (X) - / n, where n = 1, 2 or 3, and X is a halogen, to form the desired highly fluorinated β-ketoiminato complex of formula II above. The ligands of formula I produced in accordance with this invention can exist in two tautomeric forms, enol and keto, with the keto form being represented generally by formula I. Preferred ligands and metal complexes of the present invention include: Ligands . where R₁=R₂=CF₃, R₃=CH₂CF₃, R₁=CF₂CF₃, R₂=CF₃, R₃=CH₂CF₃ R₁=CF₂CF₂CF₃, R₂=CF₃, R₃=CH₂CF₃ R₁=R₂=CF₃, R₃=phenyl R₁=R₂=CF₃, R₃=CH₂CH₂OH Complexes . where R₁=R₂=CF₃, R₃=CH₂CF₃, M +n =Cu⁺² R₁=R₂=CF₃, R₃=CH₂CF₃, M +n =Co⁺² R₁=CF₂CF₃, R₂=CF₃, R₃=CH₂CF₃, M +n =Cu⁺² R₁=CF₂CF₂CF₃, R₂=CF₃, R₃=CH₂CF₃, M +n =Cu⁺² R₁=R₂=CF₃, R₃=CH₂CH₂OH, M +n =Cu⁺² Experimental In the following examples, temperatures are set forth uncorrected in degrees Celcius. Unless otherwise indicated, all parts and percentages are by weight. 1,1,1,5,5,5 hexafluoro-2,4-pentanedione, t-butyldimethylsilylchloride, potassium hydride, 2,2,2-trifluoroethylamine, ethylenediamine, ethanolamine, 1,3-propanediamine, 1,3-diamino-2-propanol and analine were obtained from Aldrich Chemical Co. (940 West St. Paul Ave. Milwaukee, Wis. 53233). 1,1,1,2,2,6,6,6-octafluoro-3,5-hexanedione and 1,1,1,2,2,3,3,7,7,7-decafluoro-4,6-heptanedione were obtained from Fairfield Chemical Company Inc. (P.O. Box 20, Blythewood, SC 29016). Solvents used are HPLC grade. Tetrahydrofuran (THF) was distilled from calcium hydride under nitrogen, methanol was distilled from Mg metal under nitrogen. All operations in the preparation of the free ligands or corresponding complexes are carried out using Standard Schlenk line techniques described by D. F. Shriver, "The Manipulation of Air Sensitive Compounds" McGraw-Hill Publishing Co. Microanalyses were performed by Schwarzkopf Microanalytical Laboratory, Woodside, NY or Research Services, Air Products and Chemicals, Inc. 'H, ¹⁹F and ¹³C spectra were recorded using an IBM SY-200 and a Bruker WH-200 NMR spectrometer. The chemical structure, along with both the IUPAC and abbreviated names of the ligands synthesized in the following examples are set out below. The corresponding metal complexes have the similar structure with an (H) being replaced by the metal (see formula II above). The charge on the metal complex must remain neutral, i.e., if the ligand is diprotonated one divalent metal atom such as Cu⁺² is required. 4-(2,2,2-trifluoroethyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanone 5-(2,2,2-trifluoroethyl)imino-1,1,1,2,2,6,6,6-octafluoro-3-hexanone 6-(2,2,2-trifluoroethyl)imino-1,1,1,2,2,3,3,7,7,7-decafluoro-4-heptanone 4-(2-hydroxyethyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanone 4-(phenyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanone Example 1 Synthesis of the silylenolethers of perfluorinated β-diketones The following represents a generic synthesis for the preparation of: (i) 4-(t-butyldimethylsiloxy)-1,1,1,5,5,5-hexafluoro-3-penten-2-one from 1,1,1,5,5,5-hexafluoro-2,4-pentanedione. (ii) 4-(T-butyldimethylsiloxy)-1,1,1,5,5,6,6,6 octafluoro-3-hexen-2-one (and its isomer 2-(t-butyldimethylisiloxy)-1,1,1,5,5,6,6,6-octafluoro-2-hexen-4-one) from 1,1,1,5,5,6,6,6-octafluoro-2,4-hexanedione. (iii) 4-(t-butyldimethylsiloxy)-1,1,1,5,5,6,6,7,7,7-decafluoro-3-hepten-2-one (and its isomer 2-(t-butyldimethylsiloxy)-1,1,1,5,5,6,6,7,7,7-decafluoro-2-hepten-4-one) from 1,1,1,5,5,6,6,7,7,7-decafluoro-2,4-heptanedione. Potassium hydride (20.0 g, 0.5 moles) is charged into a solid addition funnel which is fitted to a 1.01 reaction flask; the latter is also fitted with a rubber septum, an inlet for nitrogen, and a magnetic stir bar. Under an atmosphere of dry nitrogen THF (500 ml) is added to the flask which is subsequently cooled to -78°C. The perfluoro β-diketone (0.5 moles) is then added by syringe to the stirred THF at approx. 0.5 ml/min while also slowly adding potassium hydride at such a rate that it is consumed without an excess accumulating in the reaction flask. After adding all the reagents, the reaction is left to stir at room temperature until all traces of hydride are digested (up to 18 hrs). A reflux condenser and an addition funnel charged with t-butyldimethylsilylchloride (75.36 g. 0.5 moles) are fitted to the reaction flask, 150 ml THF is run into the addition funnel to dissolve the silylchloride. This solution is added dropwise over 30 mins to the stirring reaction mixture after which it is refluxed for 18 hrs. During this time a thick white precipitate of potassium chloride forms. The mixture is then filtered under nitrogen to give a pale brown or yellow filtrate. Approximately 500 ml of THF is then distilled off under nitrogen and the resulting concentrated silylenol ether solution left to cool, thereby precipitating further potassium chloride. This solution is then filtered as before then distilled under nitrogen to give the silylenolether as a moisture sensitive pale yellow liquid. NOTE: Care must be taken to not heat the distillation flask too near to dryness. As the residual brown colored liquid in the distillation flask evaporates down to ∼30 ml it may start to evolve thick yellow-grey fumes prior to rapidly decomposing and producing a surge of pressure within the apparatus. It is noted that two silylenolether isomers form when starting with unsymmetrical perfluoro β-diketones (i.e., 1,1,1,2,2,6,6,6-octafluoro-3,5-hexandione and 1,1,1,2,2,3,3,7,7,7-decafluoro-4,6-heptanedione. However, these are not separated in this distillation stage and are collected as one fraction composed of a mixture of two isomers. Each enolether is collected as one main fraction BPT 165-180°C. The yields and analytical data are reported in Table 1. Example 2 Preparation of solid Cu ⁺² (NONA-F[TFEA])₂, Cu ⁺² (UNDECA-F[TFEA])₂, Cu ⁺² (TRIDECA-F[TFEA])₂ The above metal complexes are obtained by reaction between 1,1,1-trifluoroethylamine and the silylenolethers of the perfluorinated β-diketones synthesized in Example 1, followed by treatment with copper bromide. Under a nitrogen atmosphere, 1,1,1-trifluoroethylamine (12.4 ml, 0.16 moles) is added over 5 mins to 0.16 moles of neat silylenol ether cooled to -78°C. This mixture is allowed to warm to room temperature and stirred for 1 hr then poured into 400 ml of methanol containing 0.16 moles of potassium methoxide and stirred for 10 minutes. To this bright yellow solution, copper bromide (17.1 g, 0.08 moles) is added and the mixture stirred for 1 hour. The potassium bromide precipitate is filtered off, solvent stripped away and the resultant solid twice sublimed under dynamic vacuum to give dark green needles of product complex. The yields and analytical data are reported in Table 2 below. Example 3 Preparation of ligands (H)NONA-F[TFEA], (H)UNDECA-F[TFEA], (H)TRIDECA-F[TFEA] A saturated solution of the appropriate parent copper complex (from example 2) in diethyl ether is prepared and washed with excess 50/50 concentrated HCl/H₂O. The ether layer is then extracted and treated with more acid until it holds no further green color. The organic layer is then washed with brine, dried over anhydrous sodium sulfate and distilled. Yields of 80-90% of isolated pure colorless ligand were realized. Analytical data is reported in Table 3 below. Example 4 Preparation of ligands (H)HEXA-F[EOA] Under a cover of nitrogen, a 100 ml reaction flask fitted with a reflux condenser, addition funnel and magnetic stir bar is charged with the t-butyl dimethylsilylenol ether of hexafluoro-2,4-pentadione (9.66 g, 3 x 10⁻² moles). The addition funnel is charged with ethanolamine (EOA) (1.83 g, 3.0 x 10⁻² moles) in 5ml THF and this solution is then added over 5 mins, with stirring, to the enolether after which the reaction mixture is refluxed 1.5 hrs. The reaction mixture is then poured into excess methanolic copper acetate solution, the entire mixture is extracted with methylene chloride (3 x 100 ml). The combined organic fractions are washed with water (3 x 100 ml) then dried over anhydrous sodium sulfate. Removal of solvent yields a blue oil which is chromatographically purified via a Chromatron® apparatus (Harrison Research, 840 Moana Court, Palo Alto, California) using Kieselgel 60 PF₂₅₄, and CH₂Cl₂ eluant) to yield a blue crystalline solid (ie. Cu⁺²(HEXA-F[EOA])₂, MPt 232°C). This is treated with HCl to yield (H)HEXA-F[EOA] as a colorless oil. Analytical data is reported in Table 4 below. Example 5 Preparation of ligand (H)HEXA-F[AN] Under nitrogen, a 50 ml reaction flask fitted with a reflux condenser is charged with the silylenolether of hexafluoro 2,4-pentanedione (9.66 g, 3 x 10⁻² moles) and aniline (2.79 g, 3 x 10⁻² moles) added. The mixture was then refluxed for 35 mins and distilled under vacuum to yield 8.0 g (H)HEXA-F[AN] at 140°C/10 torr as a yellow liquid. Yield = 94% NMR 'H CDCL₃ δ6.05(S, 1H ); δ7.25(m, 2H ); δ7.40(m, 3H ); δ11.90(bS, 1H ). ¹⁹F CDCL₃ δ-77.8(S); δ-64.1(S). ¹³C neat δ88.0(S); δ117.21(Q); δ119.82(Q); δ126.56(S); δ128.68(S); δ129.45(S); δ136.85(S); δ153.25(Q); δ180.51(Q). Elemental analysis Cal for C₇H₆NO₂F₆ % C 33.61; H 2.42; N 5.60; O 12.79; F 45.57 Found: % C 49.31; H 3.68; N 4.15; F 31.0 Example 6 Preparation of a metal complex of (H)NONA-F[TFEA] Under nitrogen, potassium methoxide (1.75 g, 0.025 moles) is dissolved in 150 ml dry methanol and 0.025 moles of a β-iminoketone ligand is added. The mixture is then stirred for 15 minutes to give a clear bright yellow solution. Solid metal dibromide (0.025 moles) is then added and the mixture stirred an additional 1 hour. The mixture is then filtered, the methanol evaporated off from the filtrate and the resultant solid redissolved in toluene (100 ml). This solution is filtered to remove residual potassium bromide and the filtrate evaporated to a solid that is then sublimed under a dynamic vacuum to yield the product complex. The analytical data is as follows: Metal Bromide = CoBr₂ Complex Formed = Co⁺²(NONA-F[TFEA])₂ Yield = 83% M.P. = 76-77°C Elemental Analysis Cal for C₁₄H₆N₂O₂F₁₈CO: % C 26.48; H 0.95; N 4.41; O 5.04; F 53.84; Co 9.28 Found: % C 25.99; H 0.52; N 4.35; O ; F 45.0; Co 9.51 Example 7 Relative volatility measurement of perfluoro β-ketoiminato complexes A standard weight loss experiment for each metal complex was conducted by heating a sample of approximately 50 mg at 10°C/min under a 100 cc/min flow of nitrogen using a Dupont Model No. 951. Thermal Gravimetric Analyzer in conjunction with a model No. 9900 Controller. Table 5 below indicates that all of the metal complexes tested in this way are clearly volatile, leaving as little as 0.34% residue at the end of an evaporation cycle. The data reported indicates that the evaporation of these complexes is a smooth process, i.e. a gradual and even transition from the solid to the gas phase. Volatility of Perfluoro β-ketoiminato Copper Complexes Complex Temperature T°C at which complex is completely vaporized Residual weight left at T°C Cu⁺²(TRIDECA-F[TFEA]₂ 162 0.342% Cu⁺²(UNDECA-F[TFEA]₂ 157 0.652% Cu⁺²(NONA-F[TFEA])₂ 150 1.81% Having thus described the present invention, what is now deemed appropriate for Letters Patent in set out in the following appended claims.

Claims: A chemically stable, β-ketoimine having the structural formula: wherein R₁ and R₂ are independently linear or branched, perfluorinated C₁-C₈ alkyl groups, and R₃ is an unfluorinated, partially or fully fluorinated phenyl or C₁-C₈ alkyl or hydroxyalkyl group. An imine in accordance with Claim 1 wherein R₁ and R₂ are both CF₃. An imine in accordance with Claim 1 wherein R₁ and R₂ are independently perfluorinated methyl, ethyl or propyl groups. An imine in accordance with Claim 3 wherein R₃ is CH₂CF₃. An imine in accordance with Claim 1 wherein said ligand is 4-(2,2,2-trifluoroethyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanone. An imine in accordance with Claim 1 wherein said ligand is 5-(2,2,2-trifluoroethyl)imino-1,1,1,2,2,6,6,6-octafluoro-3-hexanone. An imine in accordance with Claim 1 wherein said ligand is 6-(2,2,2-trifluoroethyl)imino-1,1,1,2,2,3,3,7,7,7-decafluoro-4-heptanone. A thermally volatilizable, β-ketoiminato metal complex having the structural formula: wherein R₁ and R₂ are independently linear or branched, perfluorinated, C₁-C₈ alkyl groups, R₃ is an unfluorinated, partially or fully fluorinated phenyl or C₁-C₈ alkyl or hydroxyalkyl group, M is a metal, and n=1, 2 or 3. A metal complex in accordance with Claim 8 wherein both R₁ and R₂ are CF₃. A metal complex in accordance with Claim 8 wherein R₁ and R₂ are independently perfluorinated methyl, ethyl or propyl groups. A metal complex in accordance with Claim 10 wherein R₃ is CH₂CF₃. A metal complex in accordance with Claim 8 wherein M +n is Cu⁺². A metal complex in accordance with Claim 8 wherein M +n is Co⁺². A process for making a stable, β-ketoimine as defined in claim 1 said process comprising: a) treating a β-diketone of the formula R₁COCH₂COR₂ with potassium hydride under anhydrous conditions to produce a compound of the formula R₁COCHCOR - / 2K;⁺ b) treating the resultant R₁COCHCOR - / 2K⁺ with a silylchloride of the formula (R₅)₃SiCl, wherein each R₅ is independently an alkyl group, to produce a silylenolether of the formula and (c) treating said silylenolether with a primary monoamine of the formula R₃NH₂, wherein R₁, R₂ and R₃ are as defined in claim 1. A process in accordance with Claim 14 wherein said silylchloride is t-butyldimethylsilylchloride. A process in accordance with Claim 14 wherein R₃ is a C₁-C₈ alkyl, phenyl or hydroxyalkyl group. A process in accordance with Claim 14, wherein the desired β-ketoimine produced in step (c) is treated with potassium methoxide to produce a compound of the formula R₁COCHCN(R₃)R - / 2K⁺ wherein R₁, R₂ and R₃ are as above, which is subsequently treated with a metal halide of the formula M +n (X) n , wherein N = 1, 2 or 3 and X is a halogen, to form a β-ketoiminato metal complex.

Inventors: NORMAN, JOHN ANTHONY THOMAS
Applicants: AIR PRODUCTS AND CHEMICALS, INC.
Application year: 1989
Main classification: C07C251
IPC codes: C07F7, C23C16, H01L21, C07C251, C07C249, C07F15, C07F1