HYDROSILYLABLE MIXTURE INCLUDING STRONG ELECTRON DONORS, AS CATALYST ADDITIVE

Abstract

A hydrolysable mixture M contains a) at least one compound A with at least one hydrogen atom directly bonded to a silicon atom, b) at least one compound B that contains at least one carbon-carbon multiple bond, c) at least one hydrosilylation catalyst, and d) at least one strong electron donor, as a catalyst additive.

Claims

1-15. (canceled)

16. An N-heterocyclic germylene of general formula (I), ##STR00008## wherein the following applies for the radicals R.sup.1 and R.sup.2: (a) the radicals R.sup.1 and R.sup.2 are independently selected from substituted or unsubstituted alkyl-attached alkylheteroaryl radicals having a total of 1-30 carbon atoms and at least one heteroatom selected from nitrogen, sulfur, and oxygen; where substituted means that at least one hydrogen atom of the alkylaryl or alkylheteroaryl radical has been replaced by a C.sub.1-C.sub.10 hydrocarbon radical. or (b) the radical R.sup.1 is an unsubstituted or substituted pyridin-2-ylmethyl radical, where substituted means that at least one hydrogen atom of the pyridine ring has been replaced by a C.sub.1-C.sub.10 hydrocarbon radical, and the radical R.sup.2 is a neopentyl radical.

17. The N-heterocyclic germylene as claimed in claim 16, wherein the following applies for the radicals R.sup.1 and R.sup.2: (a) the radicals R.sup.1 and R.sup.2 are independently selected from substituted or unsubstituted alkyl-attached alkylheteroaryl radicals having a total of 1-30 carbon atoms and at least one nitrogen atom; where substituted means that at least one hydrogen atom of the alkylheteroaryl radical has been replaced by a C.sub.1-C.sub.10 hydrocarbon radical.

18. The N-heterocyclic germylene as claimed in claim 17, wherein the following applies for the radicals R.sup.1 and R.sup.2: a) the radicals R.sup.1 and R.sup.2 are identical and an unsubstituted or substituted pyridin-2-ylmethyl radical, where substituted means that at least one hydrogen atom of the pyridine ring has been replaced by a C.sub.1-C.sub.10 hydrocarbon radical.

19. The N-heterocyclic germylene as claimed in claim 16, wherein these are selected from the compounds below ##STR00009##

20. A hydrosilylable mixture M comprising a) at least one compound A having at least one hydrogen atom attached directly to a silicon atom, b) at least one compound B that contains at least one carbon-carbon multiple bond, c) at least one hydrosilylation catalyst, and d) at least one strong electron donor as a catalyst additive.

21. The hydrosilylable mixture M as claimed in claim 20, wherein the strong electron donor is selected from the group consisting of phosphines, carbenes, silylenes, and germylenes.

22. The hydrosilylable mixture M as claimed in claim 20, wherein the strong electron donor is selected from N-heterocyclic germylenes of general formula (I′) ##STR00010## where the radicals R.sup.1 and R.sup.2 are independently a substituted or unsubstituted hydrocarbon radical having 1-30 carbon atoms, where substituted means that at least one carbon atom has been replaced by a heteroatom selected from nitrogen, sulfur, and oxygen.

23. The hydrosilylable mixture M as claimed in claim 22, wherein the strong electron donor is selected from N-heterocyclic germylenes of claims 1-4.

24. The hydrosilylable mixture M as claimed in claim 20, wherein the hydrosilylation catalyst is a Pt(0) species.

25. The hydrosilylable mixture M as claimed in claim 22, wherein the hydrosilylation catalyst is a Pt(0) species and the molar ratio of hydrosilylation catalyst to N-heterocyclic germylene is within a range from 1:0.1 to 1:10.

26. The hydrosilylable mixture M as claimed in claim 25, wherein the molar ratio of hydrosilylation catalyst to N-heterocyclic germylene is within a range from 1:1 to 1:5.

27. A method for preparing siloxanes, comprising the following steps: a) preparing a hydrosilylable mixture M as claimed in claim 20 by contacting the individual components with one another, b) reacting the hydrosilylable mixture M at a temperature within a range from 25° C. to 200° C.

28. The method as claimed in claim 27, wherein the reaction is carried out at a temperature within the range 80-150° C.

29. The use of phosphines, carbenes, silylenes, and germylenes as catalyst additives in noble metal-catalyzed hydrosilylation, especially in platinum(0)-catalyzed hydrosilylation.

30. The use as claimed in claim 29, wherein the germylene is an N-heterocyclic germylene of general formula (I′) ##STR00011## where the radicals R.sup.1 and R.sup.2 are independently a substituted or unsubstituted hydrocarbon radical having 1-30 carbon atoms, where substituted means that at least one carbon atom has been replaced by a heteroatom selected from nitrogen, sulfur, and oxygen.

Description

EXAMPLES

[0079] The method of the invention is what is known as an additive catalysis. This means that strong electron donors are added to the hydrosilylation catalyst (e.g. Pt(0) species such as Karstedt's catalyst) in the reaction mixture solely as additives, thereby influencing the reaction characteristics such as rate, selectivity or yield. It is not necessary to synthesize and isolate a catalyst-donor complex in order to use it as the catalytically active species.

##STR00006##

[0080] FIG. 2: N-Heterocyclic germylenes used as an additive.

[0081] The Pt(0) species most commonly used for hydrosilylation is Karstedt's catalyst. When using Karstedt's catalyst, a significant adverse effect on product yield arises through the formation and agglomeration of colloidal platinum during the catalytic reaction. The formation of the latter can be suppressed by using coordinating ligands. The compounds shown in FIG. 1 above benefit from this effect. It should also be mentioned that the use of additionally coordinating elements in the ligand system (multiply coordinating, chelating ligands) can additionally enhance the stability of a coordination compound. On the other hand, it should be noted that overloading the catalytic system with electron-donating compounds can lead to a significant slowing of the reaction or almost complete loss of catalytic activity.

[0082] As well as carbenes and silylenes, various N-heterocyclic germylenes have been tested as additives in hydrosilylation together with Karstedt's catalyst.

[0083] In all the compounds investigated, the catalytically active species must first be formed from the coordinatively stabilized platinum complexes. If a ligand coordinates strongly/if the coordination compound is strongly stabilized, substantial initiation phases can occur. The use of N-heterocyclic germylenes having variable side branches permits high electronic flexibility at the metal center and thus rapid and selective catalysis. As shown below, very high selectivities can be achieved in the catalytic hydrosilylation with Karstedt's catalyst when using strong electron donors and in particular NHGe as an additive, even at elevated temperatures. This represents a significant improvement, since a high yield is achieved in a relatively short time.

1. Preparation of N-Heterocyclic Dermylenes (NHGe)

A) N3Ge

2,2-Dichloro-N,N′-neopentyl(pyridin-2-ylmethyl)benzimidazoline-2-germanium

[0084] N,N′-Neopentyl(pyridin-2-ylmethyl)-1,2-diaminobenzene (912 mg, 3.39 mmol, 1.0 equiv.), and DABCO (399 mg, 3.55 mmol, 1.1 equiv.) are dissolved in 15 mL of dry and degassed THF under an inert atmosphere. GeCl.sub.4 (402 μl, 755 mg, 3.52 mmol, 1.1 equiv.) is added, whereupon a light yellow suspension immediately forms. The reaction is stirred at room temperature for 20 hours, filtered through a filter pad, and reduced to approx. 6 mL. 12 mL of dry and degassed pentane is added and the solution is stored at −30° C. After 1 day, a large quantity of green crystals suitable for single-crystal X-ray diffractometry has formed. The crystals are filtered off, washed with dry and degassed pentane (2×5 mL) and dried under reduced pressure. The product is isolated as a green crystalline solid. Yield: 81% (1.12 g, 2.73 mmol).

[0085] .sup.1H NMR (C.sub.6D.sub.6): δ=8.63 (dt, .sup.3J=5.6, .sup.4J=1.4, 1H, CH-1), 7.14-7.03 (m, 2H, CH-12; 13), 6.96 (td, .sup.3J=7.6, .sup.4J=1.4, 1H, CH-11), 6.65 (td, .sup.3J=7.6, .sup.4J=1.4, 1H, CH-3), 6.54 (dd, .sup.3J=7.6, .sup.4J=1.3, 1H, CH-10), 6.38 (ddd, .sup.3J=7.3, 5.6, .sup.4J=1.2, 1H, CH-2), 6.02 (dt, .sup.3J=7.6, 1H, CH-4), 3.89 (br, 2H, CH-17), 3.75 (s, 2H, CH-7), 1.34 (s, 9H, CH-19; 20; 21).

[0086] .sup.13C NMR (C.sub.6D.sub.6): δ=150.7 (C-5), 143.5 (C-1), 141.2 (C-9), 139.1 (C-3), 133.6 (C-14), 123.7 (C-2), 122.0 (C-4), 119.2 (C-12), 116.1 (C-11), 109.3 (C-13), 108.6 (C-10), 57.4 (C-17), 44.3 (C-7), 34.3 (C-18), 30.2 (C-19-21).

[0087] HRMS (LIFDI, toluene): m/z=411.0242[32].sup.+ (calculated C.sub.17H.sub.21N.sub.3GeCl.sub.2: 411.04320).

[0088] Elemental analysis: calculated for N3GeCl.sub.2 (%): C, 49.69, H, 5.15, N, 10.23; found=C, 49.95, H, 5.25, N, 9.92.

N,N′-Neopentyl(pyridin-2-ylmethyl)benzimidazoline-2-germylene (N3Ge)

[0089] 10 mL of dry and degassed THF is added to a mixture of 2,2-dichloro-N,N′-neopentyl(pyridin-2-ylmethyl)benzimidazoline-2-germanium (224 mg, 545 μmol, 1.0 equiv.) and KC.sub.8 (147 mg, 1.09 mmol, 2.0 equiv.) at −78° C. under an inert atmosphere. The suspension turns yellow on warming to room temperature and is stirred for a further 20 hours. The resulting suspension is filtered, evaporated to dryness, dissolved in 2 mL of dry and degassed diethyl ether, and filtered again. The solution is stored at −32° C. for 24 hours, whereupon a large quantity of solid, crystal-containing crystals suitable for single-crystal X-ray diffractometry is formed. The crystals are filtered off, washed with dry and degassed pentane (2×5 mL) and dried under reduced pressure. The product is isolated as a yellow crystalline solid. Yield: 69% (128 mg, 376 μmol)

[0090] .sup.1H NMR (C.sub.6D.sub.6): δ=8.47 (ddd, .sup.3J=4.9, .sup.4J=1.8, .sup.5J=0.9, 1 H, CH-1), 7.10-6.99 (m, 3H, CH-10; 11; 12), 6.96-6.90 (m, 1H, CH-13), 6.87 (td, .sup.3J=7.7, .sup.4J=1.8, 1H, CH-3), 6.76 (d, .sup.3J=7.7, 1H, CH-4), 6.54 (ddd, .sup.3J=7.7, 4.9, .sup.4J=1.3, 1H, CH-2), 5.29 (s, 2H, CH-7), 3.74 (s, 2H, CH-17), 0.87 (s, 9H, CH-19; 20; 21).

[0091] .sup.13C NMR (C.sub.6D.sub.6): δ=160.2 (C-5), 149.5 (C-1), 144.1 (C-14), 142.1 (C-9), 136.3 (C-3), 121.9 (C-2), 121.1 (C-4), 118.6 (C-10/13), 118.2 (C-10/13), 110.6 (C-11/12), 110.5 (C-11/12), 56.8 (C-17), 52.0 (C-7), 33.0 (C-18), 28.6 (C-19; 20; 21).

[0092] HRMS (LIFDI, toluene): m/z=341.0976[33].sup.+ (calculated for C.sub.17H.sub.21N.sub.3Ge: 341.0950).

[0093] Elemental analysis: Calculated for N3Ge (%): C, 60.05, H, 6.23, N, 12.36; found: C, 59.77, H, 6.30, N, 12.28.

b) N4Ge

[0094] 702 mg of N,N′-di(pyridin-2-ylmethyl)-1,2-diaminobenzene (2.42 mmol, 1.0 equiv.) is dissolved in 10 mL of THF (dry, degassed) and a solution of Ge[N(SiMe.sub.3).sub.2].sub.2 (952 mg, 2.42 mmol, 10 equiv.) in 2 mL of THF (dry, degassed) slowly added under an inert atmosphere. The reaction mixture is heated to reflux for 3 days, after which the solvent is removed under reduced pressure (10.sup.−8 bar). The crude product can be purified by distillation under high vacuum at 250° C. Crystals can be grown from a THF solution at −32° C. Yield: 80% (697 mg, 1.94 mmol).

[0095] .sup.1H NMR (THF-d.sub.8): δ=8.53 (dd, .sup.3J=4.8, .sup.4J=1.7, 2H), 7.52 (td, .sup.3J=7.7, .sup.4J=1.8, 2H), 7.21-7.11 (m, 4H), 6.87 (m, 2H), 6.73-6.67 (m, 2H), 5.35 (s, 4H).

[0096] .sup.13C NMR (THF-d.sub.8): δ=161.2, 150.3, 143.8, 137.6, 123.1, 122.3, 119.1, 110.8, 52.7.

[0097] HRMS (LIFDI, THF): M/z=361.9556 [N4Ge].sup.+ (calculated: C.sub.18H.sub.16N.sub.4Ge: 362.0590).

[0098] Elemental analysis: Calculated for N4Ge (%): C, 59.89, H, 4.47, N, 15.52; found: C, 59.43, H, 4.78, N, 15.54.

2. Catalysis Reactions

[0099] The experiments are catalysis reactions in which strong electron donors are added to the catalyst solely as an additive. This simplifies process control, since isolation of the transition metal compound is not necessary.

[0100] As well as the NHGe already shown above (FIG. 2), the ligands known from the literature that are shown in FIG. 3 were also employed as additives for comparison. The investigations below are divided into 4 sections.

##STR00007##

[0101] FIG. 3: Alternatively employed additives in platinum-catalyzed olefin hydrosilylation.

a) Screening of Different Additives

[0102] The catalytic reaction is the hydrosilylation of 1-octene (375 mg, 3.34 mmol, 1.65 equivalents) with heptamethyltrisiloxane (450 mg, 2.03 mmol, 1.0 equivalent) in 4 mL of p-xylene (0.5 M HSi). All of the following experiments were carried out in heated glass apparatus under inert gas. The results of the reactions were monitored via gas chromatography using n-decane (405 mg) as internal standard, and the selectivity of the reaction was determined.

[0103] To prepare the catalyst solutions, 6.41 mg of Pt.sub.2(dvtms).sub.3 (0.096 mmol) was dissolved in 19.0 mL of p-xylene and optionally mixed with 0.096 mmol of additive (solution in 1 mL of p-xylene) (1.98 mg .sup.iPNHC, 4.26 mg .sup.DIPPNHC; 2.54 mg PPh.sub.3; 3.08 mg NeoGe; 3.28 mg N3Ge). If no additive was added, the solution was instead diluted with 1.0 mL of p-xylene. These catalyst solutions were stirred for 3 hours at the relevant temperature for the experiment and, in accordance with the experimental details, 0.15 mL (50 ppm [Pt]) or 0.2 mL (66 ppm [Pt]) or 0.4 mL (133 ppm [Pt]) added to the thermally equilibrated substrate mixture.

[0104] The use of .sup.iPNHC, .sup.DIPPNHC, and PPh.sub.3 results in initiation phases of varying length; the maximum TOFs (TOF=turnover frequency) vary less strongly. A point to note is the very long initiation phase when using the sterically very demanding .sup.DIPPNHC (complete conversion after approx. 15 hours). The reactions using NeoGe and N3Ge proceed with significantly greater rapidity. Complete conversion is achieved after no later than 100 minutes. All reactions with additive show a higher yield than with Karstedt's catalyst alone.

[0105] The results of the reactions with 50 ppm [Pt] are shown in Table 1.

TABLE-US-00001 TABLE 1 Conversion and yield of reactions using different additives. 50 ppm of [Pt] was used in all cases. Conversion Yield Experiment Catalytic system [%] [%] 1 Karstedt catalyst 100 83 2 +1 equiv. iPr-NHC 100 84 3 +1 equiv. DiPP-NHC 100 89 4 +1 equiv. PPh.sub.3 100 87 5 +1 equiv. NeoGe 100 93 6 +1 equiv. N3Ge 100 95

[0106] The conversion and the product yield were calculated by means of gas chromatography with n-decane as internal standard. In all reactions, complete conversion of the H-silane used was observed. The product yields achieved are shown in Table 1. The product yields achieved for the ligands known from the literature (cf. FIG. 3, experiments 2-4) are in the region of the values presented in the literature for the corresponding isolated (ligand)Pt(dvtms) complexes.

[0107] It is noticeable that the reactions with NeoGe and N3Ge achieve significantly higher yields despite the more rapid reaction (experiments 5/6: 93%/95%).

b) Stoichiometric Addition of Additive Versus Excess Additive

[0108] To prepare the catalyst solutions, 6.41 mg of Pt.sub.2(dvtms).sub.3 (0.096 mmol) was dissolved in 19.0 mL of p-xylene and optionally mixed with 0.192 mmol of additive (solution in 1 mL of p-xylene) (3.96 mg .sup.iPNHC, 8.52 mg .sup.DIPPNHC, 3.19 mg .sup.tBuNHSi, 6.16 mg NeoGe; 6.56 mg N3Ge; 6.98 mg N4Ge). If no additive was added, the solution was instead diluted with 1.0 mL of p-xylene. These catalyst solutions were stirred for 3 hours at the relevant temperature for the experiment and, in accordance with the experimental details, 0.15 mL (50 ppm [Pt]) or 0.2 mL (66 ppm [Pt]) or 0.4 mL (133 ppm [Pt]) added to the thermally equilibrated substrate mixture.

[0109] If there is an excess of NHGe, the initiation phase is significantly prolonged. After 180 minutes, a conversion of approx. 15% is observed, with complete conversion of the starting material (H-silane) subsequently achieved (complete conversion after no later than 15 hours, not shown). This is accompanied by an improvement in the selectivity of the reaction by approx. 3 percentage points (Table 2, experiments 2/5: 96%/98%). Increasing the temperature by 30° C. in turn significantly shortens the initiation phase despite the excess of NHGe. The selectivity decreases accordingly (Table 2, experiments 3/6: 89%/93%).

TABLE-US-00002 TABLE 2 Conversions and yields of the reactions using different additives. Yield Yield Catalytic system, Conversion [%] [%] Experiment 50 ppm [Pt] [%] 70° C. 100° C. 1 1 equiv. NeoGe 100 93 2 2 equiv. NeoGe 100 96 3 2 equiv. NeoGe.sup.[a] 100 89 4 1 equiv. N3Ge 100 95 5 2 equiv. N3Ge 100 98 6 2 equiv. N3Ge.sup.[a] 100 95 (.sup.[a]= 133 ppm [Pt])
c) Catalytic Reactions with Excess Additive at 100° C.

[0110] To investigate the effect of an additional pyridine donor as a side branch on the germylene, further catalytic experiments were carried out at 100° C. and with an excess of NHGe and compared with conventional ligands. To improve the comparability of the reaction profiles, runs with a higher loading (133 ppm [Pt], 0.4 mL of catalyst solution, 100° C.) were carried out.

[0111] The results of the reactions are shown in Table 3.

[0112] In the reaction profile, it can be seen that the potentially additional donor in N3Ge results in a prolongation of the initiation phase of the catalysis compared to the pyridine-free NeoGe. The additional donor in N4Ge reinforces this effect further. The yields achieved in each case are shown in Table 3. The reaction with .sup.DIPPNHC (experiment 2) is slower.

TABLE-US-00003 TABLE 3 Conversion and yield of the catalysis using various additives (2 equivalents) at 100° C. and 133 ppm [Pt]. Conversion Yield Experiment Catalytic system [%] [%] 1 Karstedt catalyst (KC) 100 83 2 KC + 2 equiv. .sup.DIPPNHC 100 90 3 KC + 2 equiv. .sup.tBuNHSi 100 93 4 KC + 2 equiv. NeoGe 100 89 5 KC + 2 equiv. N3Ge 100 95 6 KC + 2 equiv. N4Ge 100 97

[0113] As can be seen from Table 3, the addition of a strong electron donor as a catalyst additive considerably increases the yield compared to Karstedt's catalyst alone.

[0114] Whereas catalysis with Karstedt's catalyst shows a selectivity of only 83% in the absence of further additives, the use of .sup.DIPPNHC (sterically large side branches, very slow reaction) increases this selectivity to 90% (experiments 1 and 2). When using the known ligand .sup.tBuNHSi, a maximum selectivity of 93% is achieved (experiment 3; the ligand .sup.tBuNHSi is a donor-stabilized silylene with strong electron donor properties). The use of chelating germylene additives under the same conditions allows a selectivity of up to 97% to be achieved (experiment 6, 2 equivalents of N4Ge). The progress of the reaction when using the non-chelating and more weakly donating NeoGe is considerably more rapid than the reaction with .sup.tBuNHSi, the yield is accordingly 89%. The use of the additive N3Ge allows a selectivity of 95% to be achieved, the reaction proceeding with greater rapidity than with N4Ge. This is due to the lower chelating capacity of the N3Ge ligand.

d) Catalytic Experiments with 2 Equivalents of N3Ge and 2 Equivalents of N4Ge as Additive at 70° C., 100° C., and 130° C.

[0115] The catalyst solutions with excess additive were prepared as described in section b), with 0.2 mL (66 ppm [Pt]; Table 4) used each time.

[0116] The catalytic reactions were carried out at a loading of 66 ppm [Pt]. In the reaction profile it can be seen that the initiation phase can be considerably shortened by increasing the temperature. Complete conversion is achieved after no later than 3 hours. The use of NHGe additives is characterized by the ability to at the same time achieve very high selectivity (Table 4).

TABLE-US-00004 TABLE 4 Yield of catalysis using 2 equivalents of N3Ge and N4Ge at 70° C., 100° C., and 130° C. Yield Yield Yield Catalytic system, [%] [%] [%] Experiment 66 ppm [Pt] 70° C. 100° C. 130° C. 1 Karstedt catalyst (KC) 82 79 78 2 KC + 2 equiv. N3Ge 95 93 93 3 KC + 2 equiv. N4Ge 98 97 94

[0117] Despite the high temperatures and thus very rapid reactions, high to very high selectivities can still be achieved.

[0118] In summary, when using stoichiometric amounts of NHGe additive to the platinum(0) species, complete conversion is achieved much more rapidly than with the other additives. Significantly higher selectivities are also achieved here. The use of additive in a molar excess can result in a significant prolongation of the initiation phase, while the selectivity is improved further. Increasing the temperature has a significant influence on the initiation phase, with high selectivities still achievable by using chelating NHGes. The influence of the pyridine side branch can be clearly seen in section c). Whereas a significant slowing of the reaction occurs, the additional donor improves the selectivity of the catalysis.

[0119] The experiments show that a higher temperature accelerates the reaction, but at the same time worsens the selectivity.

[0120] The addition of the N-heterocyclic germylenes as a catalyst additive slows the reaction, but also increases the selectivity. The addition of more additive intensifies this effect further.

[0121] The reaction conditions, in this case temperature and addition of catalyst additive, more particularly N-heterocyclic germylenes, can be freely combined in order to optimize reaction conditions for the hydrosilylation.