Organometallics 1995,14, 561-563
561
Influence of Different 4,7=Substituted 1,10-PhenanthrolineLigands on Reactivity and Regioand Stereocontrol in Tungsten-CatalyzedAllylic Alkylations Hdkan Frise11 and Bjorn Hikermark* Department of Organic Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden Received February 8, 1994@
Scheme 1
Summary: The substitution of allylic carbonate using tetracarbonyl(1,10-phenunthroline)tungsten(O)complexes as catalysts was found to give products with high retention of configuration (>go%) with both (E)- and (2)substrates.
Introduction Metal-catalyzed nucleophilic substitution of allylic leaving groups, in principle, offers the possibility to convert allyl alcohols and related compounds into substituted alkenes of specified stereochemistry.' For example, a (2)-product 7 could be obtained from an (E)acetate or -carbonate 1 as illustrated in Scheme 1. Several conditions have to be fulfilled in this specific case. (i) syn-anti isomerization (2 3) has to be fast relative to nucleophilic addition. (ii) The product between the concentration and the rate of the reaction with the nucleophile has to be greater for the anti isomer. (iii) The nucleophilic attack has to take place preferentially at the least substituted terminus of the intermediate (q3-allyl)system. We have recently found that if a palladium catalyst with 1,lO-phenanthroline as ligand is used, either a (2)substrate 4 or an (E)-substrate 1 can be converted selectively into an (E)-product.2 In this case, all of the conditions i-iii are evidently fulfilled. During work toward developing a procedure for converting an (E)substrate into a (2)-product, we have earlier shown that in (v3-allyl)palladium systems, ligands such as 2,9dimethyl-1,lO-phenanthroline(dmphen) are able to induce a preference for the anti configuration 3.3 Unfortunately, the continued work has shown that synanti isomerization becomes slow with this type of ligand. Furthermore, the regioselectivity is dramatically decreased, and a ca. 1:l mixture of the two regioisomers 6 and 7 is generally obtained. In order to see if it is possible to overcome these problems, we have started a broad investigation of systems based on other metals and also other ligands. The pioneering studies by Trost and his co-workers using tris(acetonitrile)tungsten(O) tricarbonyl and auxillary bipyridine and related ligands
-
Abstract published in Advance ACS Abstracts, December 1,1994. (1)(a) Trost, B. M.; Verhoeven, T. R. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, 1982; Vol. 8, pp 799-938. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (c) Trost, B.; Lautens, M. Tetrahedron 1987,43, 4817. (d) Trost, B. M.; Lautens, M. J.Am. Chem. Soc. 1982,104,5543. (2)Sjogren, M.;Hansson, S.; h e r m a r k , B.; Vitagliano, A. Organometallics 1994,13, 1963. (3)(a) Hansson, S.;Vitagliano, A.; h e r m a r k , B. J.Am. Chem. SOC. 1990,112,4587.(b) Sjogren, M.; Hansson, S.; Norrby, P. 0.; Cucciolita, M. E.; Vitagliano, A.; h e r m a r k , B. Organometallics 1992,11, 3954. @
L
N
2
3
suggest a preference for attack of the more substituted terminus of the intermediate q3-allyl system^.^ However, we recently observed that, depending on the substitution pattern, 1,lO-phenanthroline type ligands induced a wide variation in selectivity in reactions involving (q3-allyl)palladium systems.2 We therefore decided to study the reaction of (2)-ethyl hexenyl carbonate 4 (R= C3H7, Fi' = OEt) with sodium dimethyl methylmalonate using tungsten(0) tetracarbonyl coordinated to a series of 1,lO-phenanthroline ligands. Here we would like to report some results, which show that a (2)-substrate 4 may indeed be converted in to a (2)product 7 with high selectivity and with an efficiency that is strongly dependent on the phenanthroline substituents.
Results and Discussion Five different catalysts were prepared by refluxing the appropriate phenanthroline with tungsten hexacarbonyl for 20 h a t 110 "C in toluene. Tetracarbonyl[4,7-bis(hexanoy1oxy)-l,lO-phenanthrolineltungsten(0) (8),tetracarbonyl-( 1,lO-phenanthroline)tungsten(O) (9), tetracarbonyl( 2,9-dimethyl-l,lO-phenanthroline)tungsten(0) (lo),tetracarbony1(4,7-dimethyl-l,lO-phenanthroline)tungsten(O)(111, and tetracarbonyl(4,7-dibutoxy(4)(a)Trost, B.M.; Hung, M.-H. J.Am. Chem. SOC.1983,105,7757. (b) b a t , B. M.; Tometzki, G. B.; Hung, M.-H. J.Am. Chem. Soc. 1987, 109,2176.
0276-733319512314-0561$09.0010 0 1995 American Chemical Society
Notes
562 Organometallics, Vol. 14,No. 1, 1995
Figure 1. Table 1. Product Pattern from Tungsten-Catalyzed Alkylations of @)-Ethyl 2-Hexen-l-yl Carbonate (Entries 1-8), @)-Ethyl 2-Hexen-l-yl Carbonate (Entries 9-11), and Ethyl l-Hexen-3-yl Carbonate (Entry 12) Entry 1 2 3 4 5
6 7 8 9
IO II 12
Catalyst W(C0)6 8 9 9 10 10 11 12 9 11 12 12
-
98 93 89 90 91 91 88 92 0 0 0 4
Nu
&
% Yield'
1 6
1
23
1
2 1 2 2 2 1 91 84 80 13
9 9
38 43 48b
Nu - N ~
7 1
45
10
61
I
lood
9
33 49
16
20 23
54c
62
85
The standard reaction conditions arc 110°C. 10 mol% of the catalyst and 200 mol% of sodium dimethyl methyl malonate. a GC yields after 20 h reaction time, Nu= dimthyl methylmalonate. b 20 mol% of I,lO-phenanthroline was added. c 20 mol% of 2,g-dimethyl1,lO-phenanthroline was added. d Reaction was finished within 60 min.
1,lO-phenanthroline)tungsten(O)(12) (see Figure 1). These were reacted with Wethy1 hexenyl carbonate in toluene at 110 "C with 200 mol % of sodium dimethyl methylmalonate (10 mol % of catalyst). In all cases, high preference was observed for attack at the least substituted terminus of the intermediate r3-allyl system, leading to ca. 90% selectivity for the desired (2)product 7 (see entries 1-8, Table 1). A remarkable difference in reactivity among the catalysts was observed. While tungsten hexacarbonyl itself was essentially inactive as catalyst, the phenanthroline catalyst 9 gave ca. 40% and the 4,7-dmphen catalyst 11 a 70% yield of product after 20 h. In bright contrast, the 4,7-dibutoxyphenanthrolinecatalyst 12 led to complete reaction after 1h. The reason for this strong influence of the ligands is not clear. A possible explanation is that we are seeing the result of a balance between oxidative addition, which could then lead to the desired product and decomposition of the catalyst. This is supported by the fact that addition of 20% excess ligand (which would be expected to increase the stability of the catalyst) to catalysts 9 and 10 leads to 10-20% increase in yield. The importance of the oxidative addition step is also shown by the fact that allylic acetates fail to react. In order to define the limits for the activity of the catalyst 12,experiments with only 1%catalyst were performed. After 1 h ca. 30% yield was obtained, but the catalyst degenerates and the yield levels off to become ca. 40% after 20 h. Experiments were also done a t lower temperatures and at 80 "C (10 mol % catalyst), the reaction is considerably slower and only ca. 60% yield was obtianed after 20 h. However, a t this temperature, the catalyst seems stable and there is no leveling off in the yield, which continues to increase on further reaction. Also the structure of the substrate has a strong influence on the reactivity. While ethyl l-hexen-3-yl
carbonate was essentially as reactive as the (2)-isomer (entry 121, the (E)-isomer was considerably less reactive (entries 9-11). It is interesting t o compare the results from the reactions of @ðyl and (E)-ethyl hexenyl carbonates and tungsten catalyst with those from (2)and (E)-hexenyl acetates and palladium-dmphen as catalyst. In both cases, the stereochemistry is preserved. With the palladium catalyst, (E)-substrate 1 gave exclusively reaction at the less substituted q3-allyl terminus while (2)-substrate gave a mixture (3/2) of the two products 6 and 7. By contrast, the tungsten catalyst gave a mixture of (E)-product and terminal alkene 6 from the (E)-substrate but exclusively the (Z)-product 7 from (2)-substrate. Thus the two different catalysts are nicely complementary. A few exploratory experiments were finally performed, using the most active catalyst 12. With (2)-ethyl hexenyl carbonate, reaction with a P-keto ester enolate, sodium ethyl 2-methylacetoacetate, gave the (2)-product exclusively, but the reaction was fairly slow (ca. 60% yield after 20 h). No reaction was observed with bis(phenylsulfonyUmethy1 anion, perhaps due to steric effects. In order to compare the phenanthroline based catalyst 12 with (CH3CN3)W(C0)3tb (E)-cinnamyl ethyl carbonate was reacted with sodium diethyl methylmalonate. While (CH3CN3)W(C0)3gave exclusive reaction at the more substituted allyl terminustbthe catalyst 12 gave a mixture of products from internal reaction (68%)and (2)-(24%) and (E)-(8%)products from reaction at the less substituted allyl terminus. The regiocontrol thus clearly depends on the substrates, but it is clear that simple (2)-substrates can be converted cleanly to (2)-products, using phenanthroline substituted tungsten carbonyl catalysts.
Experimental Section General. All reactions were performed in oven-dried glassware. Melting points (uncorrected) were determined by using a Biichi SMP-20 melting point apparatus. lH and 13C NMR were recorded on a 400 MHz (Bruker Model AM4001 and a 250 MHz (Bruker Model AC250) instrument a t 298 K in CDC4 (unless otherwise indicated), using CHC13 (6 7.26 ppm) and CDCl3 (6 77.0 ppm) as internal references for 'H and 13C, respectively. The following abbreviations are used in descriptions of NMR multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broadened and J = coupling constant. IR spectra were recorded on a PerkinElmer 1725X FTIR instrument. Gas chromatographic determination of yields and product patterns were performed using a Varian Model 3700 spectrometer equipped with a 15 m x 0.15 mm dimethylpolysiloxane(100%)capillary column and a Varian 4290 integrator. Elemental analyses were performed by Analytische Laboratorien, Gummersbach, Germany. All solvents and reagents were purchased from commercial sources and dried and purified by standard techniques. General Procedure for Tungsten-Catalyzed Alkylation. Toluene (10 mL) was added to a flask containing sodium hydride (48 mg, 2 mmol) under argon. Dimethyl methylmalonate (321 mg, 2.2 "01) was added with a syringe. After stirring for 45 min at ambient temperature, ethyl hexenyl carbonate (172 mg, 1mmol) and the internal standard dodecane (70 mg) was added followed by the catalyst (0.1 mmol). The contents of the flask were heated to reflux. The reaction was monitored by GC a t regular time intervals (1,2, 5 , and 20 h). Results are presented in Table 1.
Organometallics, Vol. 14, No. 1, 1995 563
Notes
4,7-Dibuto~y-l,l0-phenanthroline.~ To a mixture of 47dihydroxy-1,lO-phenanthroline(0.20 g, 0.94 "01) in DMF (10 mL) was added NaH (0.67 g, 2.82 mmol) with stirring under argon at room temperature. After 20 min, n - B a r (0.64 g, 4.67 mmol) was added to the reaction flask and the mixture was stirred at 100 "C for 10 h. The resulting clear, brown solution was cooled down to room temperature. Water (50mL) was added to obtain a precipitate, which was extracted with CHzClz and dried over MgSO4. The pure product (0.25 mg, 80%, mp 131-132 "C) was obtained by chromatography on silica gel (MeOWCH2C12, 1/20). lH NMR (CDZC12, 250 MHz): 6 8.90 (d, J = 5.28 Hz, 2H), 8.19 (s, 2H), 6.99 (d, J = 5.77 Hz, 2H), 4.25 (t, J = 6.36 Hz, 4H), 1.96 (m, 4H), 1.62 (m, 4H), 1.04 (t, J = 7.37 Hz, 6H). 13C(CD&12,62,5MHz) 6 151.3,119.2,103.7, 66.7, 31.4, 19.7, 14.0. Anal. Calcd for CleHdJzOz: C, 74.0; H, 7.5; N, 8.6. Found: C, 73.5; H, 7.3; N, 8.5. Tetracarbonyl[4,7-bis(dihexanoyloxy)-l,lO-phenanthroline] tungsten(0)(8). To a mixture of 4,7-dihydroxy1,lO-phenanthroline (0.30 g, 1.41 mmol) in DMF (20 mL) was added NaH (0.10 g, 4.23 mmol) with stirring under argon at room temperature. After 20 min, the solution was cooled down to 0 "C and hexanoyl chloride (0.95 g, 7.05 mmol) was added slowly and was then stirred at room temperature overnight. The reaction product was then filtered off and DMF removed under reduced pressure at 60 "C, giving yellow-brown crystals. Crude yield, 0.50 g (87%). The crystals was used in the following synthesis of 8 without further purification. Tungsten hexacarbonyl (0.084 g, 0.24 m o l ) and 4,7-bis(hexanoy1oxy)-1,lO-phenanthroline(0.10 g, 0.24 mmol) were dissolved and refluxed in dry toluene (50mL) overnight under argon atmosphere. The deep red crystals that were formed upon cooling were washed with toluene and dried in vacuo. Yield, 0.15 g (89%). lH NMR (400 MHz) 6 9.43 (d, J = 5.7 Hz, 2 H), 8.07 (9, 2 H), 7.71 (d, J = 5.8 Hz, 2 H), 2.82 (t, J = 7.5 Hz, 4 H, CHz), 1.2 (m, 12 H, CHz), 0.98 (t, J = 7.6 Hz, 6H, CH3). 13C NMR (100 MHz) 6 222.7 (CO), 204.8 (CO), 170.3, 154.4, 153.8, 147.7, 123.8, 120.7, 116.9, 34.5, 29.7, 24.5, 22.3, 13.9 IR (KBr): 1886 (C=O, broad). Tetracarbonyl(1,lO-phenanthroline)tungsten(O) Tungsten hexacarbonyl (1.0 g, 2.80 mmol) and 1.10-phenanthroline (0.50 g, 2.80 mmol) were dissolved and refluxed in dry toluene (50 mL) overnight under argon atmosphere. The deep red crystals that were formed upon cooling were washed with toluene and dried in uacuo. Yield, 1.0 g (75%). Mp 190195 "C dec. lH NMR (400 MHz) 6 9.62 (dd, Ji= 5.1 Hz, JZ = 3.76 Hz, 2 H), 8.49 (dd, J1 = 8.1 Hz, Jz = 6.78 Hz, 2 H), 8.00 (9, 2 H), 7.78 (dd, J1 = 8.1 Hz, Jz = 5.1 Hz, 2 H). 13C NMR (100 MHz) 6 215.6 (CO), 201.2 (CO), 152.9,147.3,136.1,130.4, 127.3, 125.0. IR (KBr): 1997 (C=O), 1846 (C=O, broad). Anal. Calcd for C16H8WNzO4: C, 40.36; H, 1.69. Found: C, 40.28; H, 1.77. ( 5 ) Procedure for this ligand synthesis was extracted from:
Miikela, M. Licentiate thesis, 1992. Department of Organic Chemistry, Royal Institute of Technology, Sweden.
Tetracarbonyl(2,9-dimethyl-l, 10-phenanthroline)tungTungsten hexacarbonyl(l.0 g, 2.80 mmol) and sten(0) 2,9-dimethyl-l,lO-phenanthroline (0.58 g, 2.80 mmol) were dissolved and refluxed in dry toluene (50 mL) overnight under argon atmosphere. The deep red crystals that were formed upon cooling were washed with toluene and dried in vacuo. Yield, 1.20 g (85%). Mp 150-155 "C dec. 'H NMR (400 MHz) 6 8.26 (d, J = 8.2 Hz, 2 H), 7.85 (s, 2 H), 7.71 (d, J = 8.3 Hz, 2 H), 3.34 (s,6 H, CH3). 13CNMR (62 MHz, DMSO-&) 6 214.3 (CO), 199.0 (CO), 163.5,147.0, 138.3, 128.3, 126.6, 126.3 31.0. IR (KBr): 2005 (C=O), 1875 (C=O), 1854 (CEO), 1808 (C=O). Anal. Calcd for Cl!&ZWNZ04: C, 42.88; H, 2.40. Found: C, 42.65; H, 2.31.
Tetracarbonyl(4,7-~ethyl-l,lO-phen~thro~e)~sten(0)(11). Tungsten hexacarbonyl(O.50 g, 1.42 mmol) and 4,7-dimethyl-l,lO-phenanthroline (0.45 g, 1.42 mmol) were dissolved and refluxed in dry toluene (50mL) overnight under argon atmosphere. After cooling, the toluene was removed by distillation under reduced pressure. The residue was then dissolved in CH2C12. Deep red crystals were formed upon slow addition of pentane. The precipitate was filtered off and dried in vacuo. Yield, 0.49 g (65%). Mp 205-210 "C dec. 'H NMR (400MHz)69,44(d, J = 5 . 2 H z , 2 H ) , 8 . 1 5 ( ~ , 2 H ) , 7 . 5 6 ( dJ, = 5.2 Hz, 2 H), 2.91 ( ~ , H, 6 CH3). 13CNMR (62 MHz, DMSOd~)6219.5,202.0,152.6,147.9,146.0,129.7,126.5, 123.9, 18.7. IR (KBr): 2003 (C=O), 1866 (C=O, broad), 1812 (C=O). Anal. Calcd for C18H12wN204: C, 42.88; H, 2.40. Found: C, 42.87; H, 2.51.
Tetracarbonyl(4,7-dibut~xy-l,l0-phenanthroline)~gsten(0)(12). Tungsten hexacarbonyl(O.11 g, 0.31 mmol) and 4,7-dibutoxy-l,lO-phenanthroline (0.10 g, 0.31 mmol) were dissolved and refluxed in dry toluene (50 mL) overnight under argon atmosphere. m e r cooling, the toluene was removed by distillation under reduced pressure. The residue was then dissolved in CH2C12. Deep red crystals were formed upon slow addition of pentane. The precipitate was filtered off and dried in vacuo. Yield, 0.17 g (88%).Mp 150-155 "C dec. 'H NMR (400 MHz) 6 9.29 (d, J = 6.1 Hz, 2 H), 8.25 (s, 2 H), 7.06 (d, J = 6.1 Hz, 2 HI, 4.34 (t, J = 6.4 Hz, 4 H, CHd, 2.00 (m, 4 H, CHz), 1.54 (m, 4 H, CHz), 1.06 (t, J = 7.4 Hz, 6H, CH3). 13C NMR (100 MHz) 6 215.5 (CO), 202.4 (CO), 162.2, 154.1,147.9, 122.7, 119.9, 105.4, 69.6, 30.7, 19.3, 13.8 IR. (KBr): 2004 (C=O), 1814 (C-0, broad). Anal. Calcd for C ~ ~ H Z ~ W NC, ZO~: 46.47; H, 3.90. Found: C, 46.23; H, 3.87.
Acknowledgment. We thank TFR (Swedish Research Council for Engineering Sciences) and the foundation "Bengt Lundqvists minne" for financial support. We also thank Dr Joachim Persson and Dr Per-Ola Norrby for valuable comments on this work. OM9401014 (6)Pardo, M. P.; Cano, M. J. Organomet. Chem. 1984,260,81.
