Mechanism of Cu/Pd-Catalyzed Decarboxylative Cross-Couplings: A DFT Investigation

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1 Mechanism of Cu/Pd-Catalyzed Decarboxylative Cross-Couplings: A DFT Investigation Andreas Fromm, a Christoph van Wüllen, b Dagmar Hackenberger a and Lukas J. Gooßen* a a Fachbereich Chemie Organische Chemie Technische Universität Kaiserslautern Erwin-Schrödinger-Straße Geb. 54, Kaiserslautern, Germany Fax: (+49) , goossen@chemie.uni-kl.de b Fachbereich Chemie Theoretische Chemie Technische Universität Kaiserslautern Erwin-Schrödinger-Straße Geb. 52, Kaiserslautern, Germany Fax: (+49) , vanwullen@chemie.uni-kl.de Supporting Information Computational details Experimental studies Energy profile of the anion exchange step without the potassium counter-ion Electronic energies (with and without solvation) and Gibbs energies including solvation at different temperatures and pressures Empirical dispersion corrections and final Gibbs energies including solvation and empirical dispersion corrections Optimized Cartesian coordinates (Å) from B3LYP/6-31+G(d) calculations Literature S2 S3 S4 S5-S6 S7-S8 S9-S128 S129-S130 S1

2 Computational details All calculations were performed with the Gaussian 03 1 or the Gaussian 09 2 program package and the B3LYP density functional. 3 For the geometry optimizations, the atoms C, H, Br, F, K, N, O and P were described by the 6-31+G(d) basis, 4 while for Cu and Pd a scalar-relativistic effective core potential 5 was used to replace 10 (Cu) or 28 (Pd) core electrons, together with the valence basis sets 5 in double zeta quality. Spherical d and f functions were used in all cases (5D, 7F). All geometries of minima and transition states were fully optimized. Transition states were located from a relaxed potential energy surface scan in which the reaction coordinate was kept fixed at different distances, while all other degrees of freedom were optimized. After this linear transit search, transition states were located using the STQN (synchronous transit-guided quasi-newton) method. 6 The nature of all important transition states were verified by following the intrinsic reaction coordinates. 7 Harmonic force constants were calculated for the optimized geometries to characterize the stationary points either as minima or saddle points. Additional single point energy calculation were performed on all structures employing the G(2d,p) basis 8 for the atoms C, H, Br, F, K, N, O and P. For Cu and Pd the d functions of the basis sets were slightly decontracted from [411] to [3111], and a single set of f functions (taken from the def2-tzvp basis sets, 9 f (Cu) = 2.233, f (Pd) = ) was added for both elements. Single point solvent calculations were performed with the same basis set at the optimized gas-phase geometries for all of the intermediates and transition states, using the conductor-like polarizable continuum model 10 (CPCM) of Gaussian 09, which is an implementation of the conductor-like screening solvation model 11 (COSMO). N-Methyl-2-pyrrolidone (NMP) was chosen as the solvent (EPS = 32.55). To calculate the zero-point vibrational energies, the harmonic frequencies calculated (with the small basis) were scaled with a factor of as suggested by Wong. 12 The thermal corrections to the Gibbs energy can be calculated from the partition function, which practically cannot be calculated exactly for polyatomic molecules. The approximation used in the Gaussian program uses the ideal gas, harmonic oscillator and rigid rotator approximation for the translational, vibrational and rotational part of the partition function. Since the ideal gas approximation is used for the reaction mixture, the total Gibbs energy is the sum of the Gibbs energies of all components, which behave as a gas confined to the volume of the reaction mixture, and the translational partition function of each component depends on its concentration in the solution. Note that in the Gaussian program one has to specify the concentration as a pressure, using the ideal gas law p i = RTn i / V where p i is the pressure, R the gas constant, T the absolute temperature, n i the molar quantity and V the reaction volume. Typical experiments, as modeled in our calculations, involve approximately 1 mmol starting material and product in a reaction volume of 2 ml, which corresponds to a pressure of Pa (18.2 atm) at a reaction temperature of 443 K. The amount of catalyst is lower by a factor of 20, so that we used a pressure of Pa (1 atm) for all species involving Cu and/or Pd. The reaction product CO 2, which has a low solubility in NMP at the elevated temperatures and largely leaves the reaction mixture, was considered as follows. The experimental solubility data of CO 2 in NMP 13 show that under the experimental conditions, the molar fraction of CO 2 / NMP is clearly less than 0.01, most likely about when extrapolating temperature and pressure, which also amounts to a CO 2 concentration in NMP that corresponds to a partial pressure of Pa (1 atm) for an ideal gas. Because of the ideal gas approximation, the Gibbs energy for a given temperature T and pressure p was computed from the results for p 0 = 1 atm as G(T,p) = G(T,p 0 ) + RT ln(p / p 0 ). Additionally, empirical dispersion corrections that are not included in density functionals were calculated with Grimme s D3 parameters. 14 All ball and stick models were rendered with GaussView S2

3 Experimental studies Genaral methods Reactions were performed in oven-dried glassware under a nitrogen atmosphere containing a Teflon-coated stirrer bar and dry septum. For the exclusion of atmospheric oxygen from the reaction media, three freeze-pump-thaw cycles were preformed before the reagents were mixed. Solvents were purified by standard procedures prior to use. Potassium carboxylates 7, the triflate and ligand L1 L4 17 were synthesized according to the literature procedures. All reactions were monitored by GC using n-tetradecane as an internal standard. Response factors of the products with regard to n- tetradecane were obtained experimentally by analyzing known quantities of the substances. GC analyses were carried out using an HP-5 capillary column (Phenyl Methyl Siloxane 30 m , 100/ /3) and a time program beginning with 2 min at 60 C followed by 30 C/min ramp to 300 C and then 3 min at this temperature. General procedure for the decarboxylation study (Scheme 7) An oven-dried vessel was charged with the carboxylic acid 22a or b (1.00 mmol), copper(i) oxide (10.7 mg, mmol), 1,10-phenanthroline (27.0 mg, 0.15 mmol), and the appropriate amount of potassium bromide (10) (0 or 1.00 mmol, see Scheme 8). After the vessel was flushed with alternating vacuum and nitrogen purge cycles, degassed NMP (1.5 ml), degassed quinoline (0.5 ml) and n-tetradecane (50 µl) were added via syringe. The resulting mixture was stirred at 170 C for 6 h. Then the reaction mixture was allowed to cool to room temperature and was diluted with ethyl acetate (2 ml). A sample of the reaction mixture (0.25 ml) was dissolved in ethyl acetate (2 ml), washed with a saturated solution of bicarbonate (2 ml), dried over MgSO 4, and analyzed by GC. General procedure for the decarboxylation study (Table 1) An oven-dried vessel was charged with the carboxylic acid 22a d (0.50 mmol), copper(i) oxide (3.61 mg, mmol), 1,10-phenanthroline (9.10 mg, 0.05 mmol). After the vessel was flushed with alternating vacuum and nitrogen purge cycles, degassed NMP (2 ml) was added via syringe. The resulting mixture was stirred at 100 C for the given time. Then the reaction mixture was allowed to cool to room temperature, n-tetradecane (50 µl) was added via syringe and the mixture was diluted with ethyl acetate (4 ml). A sample of the reaction mixture (0.25 ml) was dissolved in ethyl acetate (2 ml), washed with a saturated solution of bicarbonate (2 ml), dried over MgSO 4, and analyzed by GC. General procedure for the decarboxylative cross-couplings (Table 2; entries 1, 2, 4 7) Inside the glovebox an oven-dried vessel was charged with the potassium carboxylate 7c or d (0.5 mmol), copper(i) oxide (3.61 mg, mmol), 1,10-phenanthroline (9.10 mg, 0.05 mmol), palladium(ii) iodide (3.61 mg, 0.01 mmol) and the appropriate ligand (0.03 mmol). NMP (2.00 ml) and the triflate 31 (1.0 mmol) were added to this vial and the resulting mixture was stirred at 100 C for 24 h outside the glovebox under a dry atmosphere of nitrogen. Then the reaction mixture was allowed to cool to room temperature, n-tetradecane (50 µl) was added via syringe and the mixture was diluted with ethyl acetate (4 ml). A sample of the reaction mixture (0.25 ml) was dissolved in ethyl acetate (2 ml) and washed with with aqueous HCl (1 M, 2 ml). The organic phase was filtered through a plug of NaHCO 3 / MgSO 4 and analyzed by GC. General procedure for the decarboxylative cross-coupling (Table 2; entry 8) Inside the glovebox an oven-dried vessel was charged with the potassium carboxylate 7c (0.75 mmol), copper(i) oxide (3.61 mg, mmol), 1,10-phenanthroline (9.10 mg, 0.05 mmol), palladium(ii) acetylacetonate (4.57 mg, mmol) and L (12.3 mg, 0.03 mmol). NMP (4.00 ml) and the triflate 31 (0.5 mmol) were added to this vial and the resulting mixture was stirred at 100 C for 24 h outside the glovebox under a dry atmosphere of nitrogen. Then the reaction mixture was allowed to cool to room temperature, n-tetradecane (50 µl) was added via syringe and the mixture was diluted with ethyl acetate (4 ml). A sample of the reaction mixture (0.25 ml) was dissolved in ethyl acetate (2 ml) and washed with with aqueous HCl (1 M, 2 ml). The organic phase was filtered through a plug of NaHCO 3 / MgSO 4 and analyzed by GC. S3

4 Energy profile of the anion exchange step without the potassium counter-ion Relative Energy (kcal mol 1 ) [29 15] [15 33] DEtot (2-F) DEtot (4-F) DGsov (2-F) DGDGsov (4-F) Figure S1. B3LYP/6-31+G(d) Optimized structures for the anion exchange of the 2-fluorobenzoate anion and phenanthroline copper(i) bromide, hydrogens are omitted for clarity. Energy and solution Gibbs energy profiles overlaid for 2- and 4-fluorobenzoate. Color code: C: black, Br: brown, Cu: orange, F: turquoise, N: blue, O: red. S4

5 Electronic energies (with and without solvation) and Gibbs energies including solvation at different temperatures and pressures Table S1. Electronic energies (E tot ), electronic energies including solvation (E sov ) and Gibbs energies including solvation (G sov ) at different temperatures and pressures. All energies are given in hartree. Structure E tot E sov G sov (298 K, 1 atm) G sov (443 K, 1 atm) G sov (443 K, 18.2 atm) Number of imaginary frequencies 1a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b [1a 2a] S5

6 [1b 2b] [12 24] [14a 28a] [14b 28b] [15a 16a] [15a 33a] [15b 16b] [15b 33b] [16b 25b] [19a 20a] [19b 20b] [20a 21a] [20b 21b] [24 13] [25a 26a] [25b 26b] [26a 14a] [26b 27] [27 14b] [28a 12a] [28b 12b] [29a 15a] [29b 15b] S6

7 Empirical dispersion corrections and final Gibbs energies including solvation and empirical dispersion corrections Table S2. Empirical dispersion corrections (E disp ) and final Gibbs energies including solvation at the temperature of 443 K at the given pressure and including empirical dispersion corrections (G sov ). All energies are given in hartree. Structure E disp G sov Pressure / atm Number of imaginary frequencies 1a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b [1a 2a] [1b 2b] S7

8 [12 24] [14a 28a] [14b 28b] [15a 16a] [15a 33a] [15b 16b] [15b 33b] [16b 25b] [19a 20a] [19b 20b] [20a 21a] [20b 21b] [24 13] [25a 26a] [25b 26b] [26a 14a] [26b 27] [27 14b] [28a 12a] [28b 12b] [29a 15a] [29b 15b] S8

9 Optimized Cartesian coordinates (Å) from B3LYP/6-31+G(d) calculations Structure 1a S9

10 N C C C C C C C C C C C C N Cu O C O C C C C C C F H H H H H H H H H H H H S10

11 Structure 1b S11

12 N C C C C C C C C C C C C N Cu O C O C C C C C C F H H H H H H H H H H H H S12

13 Structure 2a S13

14 C C C C C C Cu N C C C C C C C C C C C C N F H H H H H H H H H H H H S14

15 Structure 2b S15

N 0.000000 0.000000 0.000000 C 0.000000 0.000000 1.363418 C 1.201876 0.000000 2.119987 C 2.425007 0.002968 1.412475 C 2.410367 0.004864 0.030681 C 1.172483 0.003224-0.637025 C -1.273308-0.002560 2.

003888 1.305737 Cu -1.708253 0.010887-1.058250 C -3.048330 0.045982-2.417537 C -3.159944-0.938523-3.427330 C -4.169685-0.926509-4.400836 C -5.099042 0.103837-4.372337 C -5.052828 1.108224-3.

16 N C C C C C C C C C C C C N Cu C C C C C C F H H H H H H H H H H H H Structure 3 C O O S16

17 Structure 7a S17

18 C C O O K C C C C C H H H H F S18

19 Structure 7b S19

20 C C O O K C C C C C H H F H H S20

21 Structure 8 S21

22 Br C C C C C C H H H H H S22

23 Structure 9a S23

24 C C C C C C C F H H H H C C C C C H H H H H S24

25 Structure 9b S25

C 0.000000 0.000000-0.016982 C 0.000000 0.000000 1.469964 C 1.205515 0.038381-0.741073 C 1.215725 0.039608-2.137228 C 0.000000 0.000000-2.808897 C -1.215725-0.039608-2.137228 C -1.205515-0.038381-0.741073 H 2.

26 C C C C C C C H H F H H C C C C C H H H H H Structure 10 K Br S26

27 Structure 11 S27

28 C C N N C C C C H H C C H H C C H H C C H H Cu Br S28

29 Structure 12 C P C Pd Br C H H H H H H H H H S29

Structure 13 C -0.077087-0.158206 0.085372 P -0.085635-0.228198 1.936316 C 1.721650-0.083557 2.320261 Pd -1.217118-2.034722 3.080619 Br -1.955916-3.128656 0.935231 Br -0.501106-0.978741 5.271719 C -2.

30 Structure 13 C P C Pd Br Br C C H H H H H H H H H C C C C C H H H H H S30

31 Structure 14a S31

32 C C C C C C Pd C P C Br C C H H H H H H H H H H H H H H C C C C C H H H H F S32

33 Structure 14b S33

34 C C C C C C Pd C P C Br C C H H H H H H H H H H H H H H C C C C C H H F H H S34

35 Structure 15a S35

36 N C C C C C C C C C C C C N Cu O C O C C C C C C F H H H H H H H H H H H H Br S36

37 Structure 15b S37

38 N C C C C C C C C C C C C N Cu O C O C C C C C C H H F H H H H H H H H H H Br S38

39 Structure 16a S39

40 N C C C C C C C C C C C C N Cu Br C H H H H H H H H C C C C C F H H H H S40

41 Structure 16b S41

42 N C C C C C C C C C C C C N Cu Br C H H H H H H H H C C C C C H H F H H S42

43 Structure 17a S43

44 C C C C C C C O F O H H H H S44

45 Structure 17b S45

46 C C O O C C C C C H H F H H S46

47 Structure 19a S47

48 C C C C C C C O H O K C N C C C C C C C C C C C N Cu Br F H H H H H H H H H H H S48

49 Structure 19b S49

50 N C C C C C C C C C C C C N Cu Br O C O C C C C C C F K H H H H H H H H H H H H S50

51 Structure 20a S51

52 N C C C C C C C C C C C C N Cu Br O C O C C C C C C F K H H H H H H H H H H H H S52

53 Structure 20b S53

54 C C C C C C C O F O Cu Br N C C C C C C C C C C C C N K H H H H H H H H H H H H S54

55 Structure 21a S55

56 C C C C C C C O F O Cu Br N C C C C C C C C C C C C N K H H H H H H H H H H H H S56

57 Structure 21b S57

58 C C C C C C C O F O Cu N C C C C C C C C C C C C N K Br H H H H H H H H H H H H S58

59 Structure 24 S59

60 C C C C C C Pd Br Br P C C C H H H H H H H H H H H H H H S60

Structure 25a Pd -2.394126-0.467763-0.510193 P -2.939169 1.795022-1.177295 Br -4.770004-0.711529 0.296526 C -1.636258 2.875886-1.919489 H -2.036494 3.871006-2.154198 H -0.803558 2.971214-1.

61 Structure 25a Pd P Br C H H H C H H H C H S61

62 H H C Br Cu C C C C C C F H H H H N C C C C C H H H H H C C N C C C C C C C C C C H H H H H H H H S62

Structure 25b Pd -2.485088-0.570149-0.469569 P -3.112416 1.344409-1.819758 Br -4.791162-0.811424 0.483959 C -3.210644 0.946586-3.627101 H -3.449521 1.833765-4.228353 H -2.248521 0.535323-3.

63 Structure 25b Pd P Br C H H H C H H H C H H H S63

64 C Br Cu C C C C C C H H F H H N C C C C C H H H H H C C N C C C C C C C C C C H H H H H H H H S64

Structure 26a C -4.434388-1.658937 1.437112 N -3.889842-0.703660 0.691323 C -4.651269 0.366583 0.356106 C -6.006600 0.508311 0.760972 C -6.556247-0.523331 1.552590 C -5.766829-1.611032 1.891470 C -6.

65 Structure 26a C N C C C C C C C C C C C N Cu C C C C C C F Pd C S65

66 C C C C C P C Br C C Br H H H H H H H H H H H H H H H H H H H H H H H H H H S66

Structure 26b C -4.641847-0.883952 1.668460 N -3.725929-0.231897 0.950492 C -4.091522 0.937783 0.

672672 2.769209-0.116229 C -4.736244 3.412585-0.873128 C -3.430664 2.847398-1.075572 C -3.111461 1.

67 Structure 26b C N C C C C C C C C C C C S67

68 N Cu C C C C C C F Pd C C C C C C P C Br C C Br H H H H H H H H H H H H H H H H H H H H H H H H H H S68

69 Structure 27 S69

70 C C C N C C C C C C N C C C Cu Br Pd P C C C C C C C Br C C C C C C F C C H H H H H H H H H H H H H H H H H H H H H H S70

H 5.270976-4.046476 0.197640 H 3.043510-5.124256-0.298826 H 0.

71 H H H H Structure 28a S71

72 C C C C C C C C C C C C F Pd P C Br C C H H H H H H H H H H H H H H H H H H S72

73 Structure 28b S73

74 C C C C C C C C C C C C Pd P C F Br C C H H H H H H H H H H H H H H H H H H S74

75 Structure 29a S75

76 C C C C C C C O F O C C C C N C C C C C C C C N Cu Br H H H H H H H H H H H H S76

77 Structure 29b S77

78 C C C C C C C O F O C C C C N C C C C C C C C N Cu Br H H H H H H H H H H H H S78

79 Structure 33a S79

80 N C C C C C C C C C C C C N Cu O C O C C C C C C F Br H H H H H H H H H H H H S80

81 Structure 33b S81

82 N C C C C C C C C C C C C N Cu O C O C C C C C C F Br H H H H H H H H H H H H S82

83 Structure [1a 2a] S83

84 C C C C C C C C C N C C C N Cu C C C C C C F C O O H H H H H H H H H H H H S84

85 Structure [1b 2b] S85

86 C C C C C C C C C N C C C N Cu C O C C C C C C F O H H H H H H H H H H H H S86

87 Structure [12 24] S87

88 C C C C C C Pd P C Br Br C C H H H H H H H H H H H H H H S88

Structure [14a 28a] C 0.035687-0.194484 0.130822 C -0.127217 0.034636 1.518397 C 1.119581 0.085775 2.216028 C 2.356621-0.065534 1.593121 C 2.440979-0.270070 0.208867 C 1.248384-0.336123-0.

89 Structure [14a 28a] C C C C C C Pd Br F C C C C C C P C C C H H H H H H H H H H H H H H H H H H S89

90 Structure [14b 28b] S90

91 C C C C C C Pd Br H C C C C C C P C C C H H H H H H H H H H H H H H H H F H S91

92 Structure [15a 16a] S92

93 C C C C C C C C C N C C C N Cu C C C C C C F C O O H H H H H H H H H H H H Br S93

94 Structure [15a 33a] S94

95 N C C C C C C C C C C C C N Cu O C O C C C C C C F Br H H H H H H H H H H H H S95

96 Structure [15b 16b] S96

97 C C C C C C C C C N C C C N Cu C O C C C C C C F O H H H H H H H H H H H H Br S97

98 Structure [15b 33b] S98

99 N C C C C C C C C C C C C N Cu O C O C C C C C C F Br H H H H H H H H H H H H S99

Structure [16b 25b] C -2.796796 2.980901 0.567726 C -2.964723 1.664517 1.031871 C -3.317189 1.482935 2.380373 C -3.

100 Structure [16b 25b] C C C C C C Pd S100

101 Br P C C C Br H H H H H H H H H H H H H H Br Cu C C C C C C F N C C C C C C C C C C C C N H H H H H H H H H H H H S101

102 Structure [19a 20a] S102

103 C C C C C C C O F O Cu Br N C C C C C C C C C C C C N K H H H H H H H H H H H H S103

104 Structure [19b 20b] S104

105 C C C C C C C O F O K Cu Br N C C C C C C C C C C C C N H H H H H H H H H H H H S105

106 Structure [20a 21a] S106

107 N C C C C C C C C C C C C N Cu O C O C C C C C C F K Br H H H H H H H H H H H H S107

108 Structure [20b 21b] S108

109 N C C C C C C C C C C C C N Cu O C O C C C C C C H K Br H F H H H H H H H H H H S109

Structure [24 13] C 0.317296 0.438993-0.162576 C -0.152290 0.127928 1.135682 C 0.735229-0.380136 2.115511 C 2.110801-0.457077 1.820072 C 2.582895-0.104695 0.558536 C 1.675311 0.338907-0.429146 Pd -0.

110 Structure [24 13] C C C C C C Pd Br P C C C Br H H H H H H H H H H H H H H S110

Structure [25a 26a] C -3.973654-2.498169-0.186497 N -3.642183-1.208133-0.145292 C -4.646996-0.291320-0.114257 C -6.022665-0.647957-0.131732 C -6.336618-2.022692-0.178115 C -5.304760-2.950002-0.

111 Structure [25a 26a] C N C C C C C C C C C C C N Cu C C C C C C F Pd C C S111

112 C C C C P C Br C C Br H H H H H H H H H H H H H H H H H H H H H H H H H H S112

Structure [25b 26b] C -4.013510-2.592658-0.327158 N -3.683493-1.305630-0.197052 C -4.694846-0.400644-0.067874 C -6.066403-0.773174-0.030795 C -6.374579-2.144219-0.153521 C -5.338899-3.055840-0.

113 Structure [25b 26b] C N C C C C C C C C C C C N Cu C C C C C C H Pd C S113

114 C C C C C P C Br C C Br H H H H H H H H H H F H H H H H H H H H H H H H H H S114

Structure [26a 14a] C 3.267323 2.361166 1.746267 C 2.086337 1.999475 1.077994 C 0.991695 2.

115 Structure [26a 14a] C C C C C C S115

116 Pd Br C C C C C C Cu Br F N C C C C C C C C C N C C C P C C C H H H H H H H H H H H H H H H H H H H H H H H H H H S116

Structure [26b 27] C 3.258702 2.405494 1.786288 C 2.060491 1.999296 1.178458 C 0.903035 2.751417 1.429754 C 0.939058 3.872358 2.269850 C 2.136513 4.262495 2.878213 C 3.297262 3.521653 2.632605 Pd 2.

117 Structure [26b 27] C C C C C C Pd Br C C C C C S117

118 C Cu Br F N C C C C C C C C C N C C C P C C C H H H H H H H H H H H H H H H H H H H H H H H H H H S118

Structure [27 14b] C 0.844034 2.481273 2.432389 C 0.150154 1.403020 1.843684 C -0.823381 1.581854 0.823732 C -1.057065 2.932056 0.

119 Structure [27 14b] C C C C C C Cu Pd S119

120 Br F N C C C C C C C C C C C C N Br P C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H S120

121 Structure [28a 12] S121

122 C C C C C C C C C C C C Pd Br F P C C C H H H H H H H H H H H H H H H H H H S122

123 Structure [28b 12] S123

124 C C C C C C C C C C C C Pd Br F P C C C H H H H H H H H H H H H H H H H H H S124

125 Structure [29a 15a] S125

126 C C C C C C C O F O Cu Br N C C C C C C C C C C C C N H H H H H H H H H H H H S126

127 Structure [29b 15b] S127

Supporting Information

Supporting Information Decarboxylative Biaryl Synthesis from Aromatic Carboxylates and Aryl Triflates Lukas J. Gooßen*, Nuria Rodríguez, Christophe Linder B Chemie rganische Chemie, TU Kaiserslautern, Erwin-Schrödinger-Strasse,