摘要:

Preparation and reactivities of chiral manganese(@ and copper(@complexes of binaphthyl Schiff bases7Chun-Wah Ho,' Wing-Chi Cheng," Ming-Chuan ChengTb Shie-Ming Peng,b Kin-Fai Cheng *+I andChi-Ming Che *9'a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong KongDepartment of Chemistry, National Taiwan University, Taipei, TaiwanA series of chiral Schiff bases, 2,2'-bis(3-R'-5-R2-2-hydroxybenzylideneamino)-l, 1 '-binaphthyl H2L (R2 = C1,R' = CI, Me, Et or NO,; R2 = Me, R' = But; R2 = NO,, R' = H, Me, Et, Pr', But or Cl), and theircomplexes [CuL'] 1 and [Mn,L',(OMe),] 2 (R' = R2 = CI) have been prepared. The crystal structure of theracemic form of 1 has been determined. Complex 1 is an active catalyst for the oxidation of alkenes by tert-butyl hydroperoxide.On the contrary, 2 is inert towards alkene epoxidation by PhIO. However, upon mixingMn(O,CMe),-xH,O and H,L in acetonitrile a green solution was obtained which could effect asymmetricepoxidation of alkenes by PhTO. The effects of the steric and electronic effects of the R' and R2 substituents,temperature, and the addition of donors like N-methyl- and 2-methyl-imidazole and pyridine N-oxide on thecatalytic activity of the Mn"' + (S)-H,L systems towards alkene epoxidation have been investigated. WhenR' = Et and R2 = NO, the best enantiomeric excesses of 58 and 43% were found for epoxidation of cis-p-methylstyrene to ( 1 S,2R)-cis-P-methylstyrene oxide and 4-chlorostyrene to 4-(S)-chlorostyrene oxiderespectively.The design of new metal oxidative catalysts bearing opticallyactive auxiliary ligands plays an important role in thedevelopment of asymmetric organic oxidation.Successfulexamples in this context include the asymmetric epoxidation ofallylic alcohols by titanium(1v) alkoxide in the presence ofoptically active tartrate, cis dihydroxylation of unfunctional-ized alkenes by the OsO,-chiral alkaloid system' and morerecently the asymmetric epoxidation of unfunctionalizedalkenes catalysed by chiral manganese(rI1) Schiff-base com-p l e x e ~ . ~ Among the various chiral compounds employed inasymmetric metal catalysis, those containing C,-symmetricbinaphthyl group(s) have been widely ~ t u d i e d . ~ In some caseseffective asymmetric catalysis has been found. These include theuse of ruthenium complexes of 2,2'-bis(dipheny1phosphino)-1,1 '-binaphthyl (binap) in asymmetric hydrogenation andaluminium complexes of 1 ,l'-binaphthol' as catalysts inasymmetric Diels-Alder reactions.In addition, metallo-porphyrin complexes of iron and manganese incorporatingthe 1,l'-binaphthyl unit have also been shown to induceasymmetric epoxidation of simple alkenes by iodosylbenzene(PhIO).' Despite the effectiveness of this class of ligands, therehas been no study on the use of non-porphyrin metal complexesof binaphthylic ligands in organic oxidation. Herein wedescribe the preparation of chiral 2,2'-bis(salicy1ideneamino)-1 ,l'-binaphthyl derivatives H,L and their copper(I1) andmanganese(m) complexes, and the use of these chiralcomplexes in epoxidation of alkenes by tert-butyl hydroper-oxide and PhIO.ExperimentalInstrumentationThe TR spectra were recorded on a Shimadzu IR-470spectrometer, NMR spectra on a JEOL GSX-270 spectrometerin deuteriochloroform unless otherwise stated, with tetramethyl-silane as internal standard at ambient temperature, masst Non-SI unit employed: pe z 9.27 x J T-'.R'R' R24" 3"\R'H2L'H2L2H ~ L ~H,L~H ~ L ~H2L6H21'H2L8H ~ L ~H2L'OCIMeEtHMeEtBu'CIButp ispectra on a Finnigan MAT 95 high-resolution massspectrometer and UV spectra on a Perkin-Elmer UV/VIS/NIRLambda 19 spectrometer.Optical rotations were measuredat ambient temperature with an Optical Activity AA-1000automatic polarimeter (c in g per 100 cm3). Analytical HPLCwas performed on a Beckmann model 331 HPLC system with amodel 163 variable UV/VIS detector.Chiral HPLC measure-ments were performed on a commercial column (DaicelChemical Industries, Ltd., Chiralcel OJ). Analytical GC wasperformed on a Hewlett-Packard 5890 series TI system equippedwith a HP 5890A flame ionization detector and a HP 3395integrator. The measurements were performed on a commercialchiral column (J & W Scientific, Cyclodex-B, 30 m x 0.25 mminternal diameter, 0.25 mm film). The CD spectra weremeasured with a JASCO 720 spectrophotometer. Magneticsusceptibility was determined at ambient temperature by usingthe Evan's method with deuteriochloroform as solvent.J. Chem. Soc., Dalton Trans., 1996, Pages 405-414 40Materials Recrystallization from diethyl etherdichloromethane gave aproduct melting at 73-74 "C; 6,(90 MHz, CDC1,) 1.41 (9 H, s,m, H6), 9.78 (1 H, s, aldehyde) and 11.61 (1 H, s, OH); 6,(22.5MHz, CDCI,) 20.5 (5-Me), 29.3 [C(CH,),], 34.8 [C(CH,),],120.5, 128.1, 131.4, 135.4, 138.0, 159.2 (2-OH) and 197.0(aldehyde).The (R)- and (S)-2,2'-diamino-1 3 l'-binaphthyls were Obtained But), 2-30 (3 H, s, 5-Me), 7.15-7.17 (1 H, m, H4), 7.31-7.34 (1 H, from Fluka. A racemic sample was prepared according to theliterature procedure.* Various substituted salicylaldehydes usedin the syntheses were prepared by literature procedures.'Manganese(1n) acetate dihydrate from Aldrich was dried inuacuo before use. Iodosylbenzene was prepared by hydrolysisof iodobenzene diacetate (Aldrich) in NaOH solution.m-Chloroperoxybenzoic acid (50 or 70%) was obtained fromMerck. Dichloromethane and acetonitrile used for catalyticepoxidation were distilled from CaH, and stored over 4 8,molecular sieves in the dark. All olefinic substrates for catalyticepoxidation were from Aldrich or Fluka and were purifiedeither by vacuum distillation or by passing through activatedalumina. trans-Stilbene was recrystallized from ethanol anddried in uacuo. cis-P-Methylstyrene was prepared by hydrogena-tion of 1 -phenyl-1 -propyne (Aldrich) using Lindler catalyst. l oRacemic styrene oxide was obtained from Fluka and distilledbefore use, (S)-( -)-styrene oxide from Aldrich (used withoutfurther purification) and trans-P-methylstyrene oxide, cyclohex-ene oxide, cis- and trans-stilbene oxide from Aldrich (distilledor purified by silica gel chromatography before use).All otherepoxides required for determination of product yield andenantiomeric excess (e.e.) were independently prepared fromthe corresponding alkene and m-chloroperoxybenzoic acid indichloromethane. ''Preparations(S)-2,2'-Bis(3,5-dichloro-2-hydroxybenzylideneamino)-l, 1 '-binaphthyl, (S)-H2L1. A mixture of 3,5-dichlorosalicylaldehyde(0.32 g, 1.67 mmol) and (S)-2,2'-diamino-l, 1'-binaphthyl(O.2 g,0.7 mmol) in ethanol (10 cm3) was stirred at room temperaturefor 3 h during which the diimine formed was precipitated as anorange solid. The crude product was filtered off, washed withethanol and recrystallized from dichloromethane-diethyl etherto give an orange crystalline solid (0.36 g, 81.2%), m.p.174 "C(decomp.); [a]: + 674.6 (c 0.816, toluene); h,,,(MeCN)/nm 230 (log 4.87), 227 (4.61), 323 (4.38), 372 (4.33)and 470 (2.63); V(Nujol)/cmp' 3290-3650 (OH) and 1611(C=N); 6,(270 MHz, CDC1,) 7.08 [l H, d, J(H4"H6") 2.44,H4")], 7.18 (1 H, d, J 8.31, H5 or Ha), 7.26 [l H, d, J(H4"H6")2.44, H6"), 7.28-7.31 (1 H, m, H6 or H7), 7.44-7.50 (1 H, m, H6or H'), 7.59 [l H, d, J(H3H4) 8.79, H4], 7.97 (1 H, d, J8.06, H5or H8), 8.1 1 [I H, d, J(H3H4) 8.78 Hz, H3], 8.55 (1 H, s, CH=N)and 12.76 (1 H, s, OH); 6,(67.9 MHz, CDCI,) 116.8, 120.4,122.4, 123.1, 126.4, 126.5, 127.3, 128.5, 129.7, 130.5, 132.5,132.9, 133.1, 142.8, 155.4 and 160.4 (Found: C, 64.5; H, 3.40;N, 4.15.Calc. for C,,H,,C1,N,02: C, 64.8; H, 3.20; N, 4.45%).The compound (R)-H,L' was prepared by the same method.Starting with (R)-2,2'-diamino-l ,l'-binaphthyl (0.2 g, 0.7 mmol)and 3,5-dichlorosalicylaldehyde (0.32 g, 1.67 mmol), the desiredcompound was obtained after recrystallization fromdichloromethane-diethyl ether (0.34 g, 77%); [a]::$ - 670.9(c 0.812, toluene). It exhibits identical spectral properties tothose of its ( S ) isomer.3-tert-Butyl-5-methyIsalicylaldehyde. 2-tert-Butyl-4-methyl-phenol (3 g, 18.3 mmol) was dissolved in anhydrous toluene (1 0cm3) then stirred under a nitrogen atmosphere. Tin(1v) chloride(0.25 cm', 2.1 mmol) was added, followed by 2,6-dimethylpyr-idine (1 cm3, 8.6 mmol).The mixture was stirred at roomtemperature for 20 min and paraformaldehyde (1.1 g, 36.7mmol) added. The resulting mixture was heated at 100 "C for 8h. On cooling, it was poured into water (100 cm3), acidified topH 2 with HC1 and extracted with diethyl ether (2 x 50 cm3).The ether extracts were combined, washed with a saturatedNaCl solution, dried (Na,SO,) and concentrated. The yellowliquid so obtained was cooled in ice and the crystalline yellowsolid was filtered off and washed with cold hexane (3 g, 85%).2,2'-Bis( 3-tert-butyl-2-hydroxy-5-methylbenzylideneamino)-1,l'-binaphthyl, H2L'0. A mixture of 2,2'-diamino- 1,l '-binaph-thyl (20 mg, 0.07 mmol) and 3-tert-butyl-5-methylsalicylalde-hyde (30 mg, 0.16 mmol) in glacial acetic acid (6 cm3) washeated at 60 "C for 2 h.The acetic acid was removed in uacuo.Addition of diethyl ether to the residue induced precipitation ofthe required compound as a yellow solid (36 mg, 80%).Recrystallization from EtOH-CH2C12 afforded a pure product,m.p. > 210 "C; V(Nujol)/cm-' 3055 (OH) and 1622 (C=N);6,(270 MHz, CDC1,) 1.20 (9 H, s, But), 2.17 (3 H, s, 5"-Me),6.77 [l H, d, J(H4"H6") 1.71, H4"], 6.99 [l H, d, J(H4"H6")1.95, H6"], 7.27-7.46 (3 H, m), 7.53 [l H, d, J(H3H4) 8.79, H4],7.94 [l H, d, J8.30, H5 or H8], 8.03 [l H, d, J(H3H4) 8.79 Hz,H3], 8.50 (1 H, s, CH=N) and 12.64 (I H, s, OH); 6,(67.5 MHz,CDCl,) 20.6 (5"-Me), 29.1 [C(CH,),], 34.6 [C(CH,),], 117.3,118.7, 125.5, 126.3, 126.6, 126.8, 128.1, 129.0, 129.7, 130.1,130.9, 132.5, 133.3, 137.0, 144.2, 158.2 and 162.5 (Found: C,83.6; H, 7.10; N, 4.40.Calc. for C,,H4,N20,: C, 83.5; H, 7.00;N, 4.40%).The ( S ) isomer was prepared by the same method as itsracemic form starting with (S)-2,2'-diamino- 1,l '-binaphthyl(0. I g, 0.35 mmol) and 3-tert-butyl-5-methylsalicylaldehyde(0.15 g, 0.8 mmol). However, the product thus obtained wasvery soluble in diethyl ether, so instead of recrystallization thecrude product was purified by column chromatography usingalumina as absorbent and light petroleum (b.p. 40-60 "C)-diethyl ether (8 : 2 v/v) as eluent. The yellow waxy solid (0.21 g,94%) exhibited identical spectral properties to those of itsracemic form; [a];:d 301.6 (c 0.67, toluene).General procedure for (S)-2,2'-bis(3-alkyl-5-chloro-2-hydroxybenzylideneamin0)-1,l'-binaphthyl. 3-Alkyl-5-chloro-salicylaldehyde (0.8 mmol) and (S)-2,2'-diamino-l, 1'-binaph-thyl (0.1 g, 0.35 mmol) were dissolved in a mixture of absoluteethanol (7 cm3) and glacial acetic acid (1 cm3) and stirred atroom temperature under anhydrous conditions for 4 h.Theorange product was filtered off, washed with absolute ethanoland recrystallized from EtOH-CH,Cl,.(S)-2,2'- Bis(5-chlor0-3-ethyl-2-hydroxybenzylideneamino)-1,l'-binaphthyl, (S)-H2L3. Yield 0.16 g (74%). h,,,(MeCN)/nm276 (log 4.73), 321 (4.47) and 370 (4.42); V(Nujol)/cm '1604 and 1570 (C=N); 6,(270 MHz, CDCl,) 1.02 [3 H, t,J(H7"H8") 7.41, 3 H'"], 2.40 [2 H, q, J(H7"H8") 7.41, 2 H7"],6.93 [l H, d, J(H4"H6") 2.75, H4"], 7.01 [l H, d, J(H4"H6")2.75, H6"], 7.20-7.46(3H,m),7.52[1 H,d,J(H3H4)8.79, H4],7.93 (1 H, d, J8.24, H5 or H8), 8.04 [I H, d, J(H3H4) 8.79 Hz,H3], 8.46 (1 H, s, CH=N) and 12.28 (1 H, s, OH); 6,(67.9 MHz,CDCI,) 13.2 (C8"), 22.3 (C"'), 117.2, 119.2, 122.8, 125.9, 126.5,127.0, 128.2, 128.5, 129.0, 130.1, 131.7, 132.6, 133.2, 134.1,143.8, 157.4 and 161.4(Found: C, 73.95; H, 4.75; N, 4.35.Calc.for C,8H,oC12N20,: C, 73.9; H, 4.90; N, 4.50%).(S)-2,2'- Bis( 5-chloro-2-hydroxy-3-methylbenz~llideneamino)-1,l'-hinaphthyl, (S)-H2L2. Yield 0.18 g (87%). V(Nujol)/cmp'1603 and 1570 (C=N); 6,(270 MHz, CDCl,) 2.00 (1 H, s, Me),6.97-7.03 (2 H, m, H4" and H6"), 7.20-7.48 (3 H, m), 7.55 [l H,d, J(H3H4) 9.06, H4], 7.96 (1 H, d, J8.05, H5 or H8), 8.07 [l H,d, J(H3H4) 9.06 Hz, H3], 8.49 (1 H, s, CH=N) and 12.21 (1H, s, OH); 6,(67.9 MHz, CDCl,) 15.3 (Me), 117.2, 119.1,122.6, 125.9, 126.5, 127.1, 128.2, 128.3, 128.5, 129.0, 130.1,132.6, 133.2, 133.3, 143.8, 157.7 and 161.3 (Found: C, 72.9;N, 4.75%).H, 4.30; N, 4.50.Calc. for C,6H,6C12N,O2: C, 73.35; H, 4.45;406 J. Chem. SOC., Dalton Trans., 1996, Pages 40541General procedure for (S)-bis(lalky1- or (S)-bis(3-chloro-2-hydroxy-5-nibobenzylideneamino)-l,l'-binaphthyl. (S)-2,2'-Diamino-1 ,l'-binaphthyl (0.1 g, 0.35 mmol) and 3-alkyl-5-nitrosalicylaldehyde (0.80 mmol) were dissolved in a mixtureof absolute ethanol (7 cm3) and glacial acetic acid (1 cm3) andstirred under anhydrous conditions at room temperature for4 h. The crude yellow product was filtered off, washed withethanol and recrystallized from an appropriate solvent.(S)- Bis(2-hydroxy-3-methyl-5-nitrobenzylideneamino)- 1,l I -binaphthyl, (S)-H,L5.The crude product was recrystallizedfrom acetic acid-ethanolkdichloromethane (0.17 g, 79%);[x]5:$ + 642.7 (c 0.470, toluene); C(Nujol)/cm-' 2000-3500 (br,OH), 1603 (C=N), 15 10 and 1334 (NO,); 6,(270 MHz, CDCl,)2.07 (3 H, s, Me), 7.23 (1 H, d, J8.55, H5 or H'), 7.27-7.54(2 H,m, H6 and H7), 7.69 [l H, d, J(H3H4) 8.85, H4], 7.96 [l H, d,J(H4"H6") 2.75, H4"], 8.01 (1 H, d, J7.94, H5 or H8), 8.07 [l H,d, J(H4"H6") 2.74, H6"], 8.15 [l H, d, J(H3H4) 8.85 Hz, H3],8.75 (1 H, s, CH=N) and 13.38 (1 H, s, OH); 6,(67.5 MHz,CDCl,) 15.4 (Me), 116.4, 117.2, 125.9, 126.4, 126.6, 127.4,127.9, 128.2, 128.4, 129.9, 130.5, 132.9, 133.1, 139.1, 142.2,m/z, 610.1852).The (R) isomer was prepared by the same method.It exhibitsidentical spectral properties and gives an optical rotation of[a]::; - 640.6 (c 0.240, toluene).hinaphthyl, (S)-H,L6. The crude product was recrystallizedfrom acetic acid-ethanol-dichloromethane (0.17 g, 76%);[a]::$ + 573.3 (c 0.658, toluene); h,,,(MeCN)/nm 276 (logE,,, 4.78), 313 (4.68), 371 (4.49) and 456 (3.23); ?(Nujol)/cm-'2000-2570 (br, OH), 1602 (C=N), 1510 and 1330 (NO,); 6,(270MHz, CDCI,) 1.07 (3 H, t, J 7.33, CH,CH,), 2.46 (2 H, q, J7.33, CH,CH,), 7.23-7.53 (3 H, m), 7.68 [l H, d, J(H3H4) 8.85,H4], 7.96 [l H, d, J(H4"H6") 2.75, H4"], 8.00(1 H, d, J8.24, H5or H8), 8.06 [l H, d, J(H4"H6") 2.75, H6"], 8.15 [l H, d,J(H3H4) 8.85, H3"], 8.73 (1 H, s, CH=N) and 13.46 (1 H, s,116.4, 117.3, 125.9, 126.4, 126.5, 126.6, 127.4, 128.4, 129.8,130.5,133.0,133.1,133.7,139.3,142.2,160.3and164.7(Found:C,N, 8.75%).The (R) isomer was prepared by the same method.It exhibitsidentical spectral properties and gives an optical rotation of[a]:i$5 - 576.4 ( c 0.330, toluene).( S)- Bis( 2-lzydroxj~- 3 -isopropyl- 5 -nitro benzy1ideneamino)- I , 1 I -binuphthyf, ( S)-H2L7. The crude product was recrystallizedfrom acetic acid-ethanol-dichloromethane (0.14 g, 60%);[a]:;: + 502.1 (c 0.354, toluene); C(Nujol)/cm-' 2000-3495 (br,OH), 1582, 1602 (C=N), 1518 and 1333 (NO,); 6,(270 MHz,CDCl,) 1.08 [6 H, m, CH(CH,),], 3.06 [l H, m, CH(CH,),],7.26-7.52 (3 H, m), 7.67 [l H, d, J(H3H4) 8.85, H4], 7.99--8.01(2 H, m, H4" and H5 or H8), 8.06 [l H, d, J(H4"H6") 2.75,and 13.56 (1 H, s, OH); 6,(67.5 MHz, CDC1,) 21.7[CH(CH,),], 26.7 [CH(CH,),], 116.4, 117.4, 124.6, 125.8,126.4, 126.5, 127.5, 128.4, 129.8, 130.5, 133.1, 133.2, 138.2,139.5, 142.2, 160.4 and 164.4 (Found: m/z, 666.2479.C40H34N406 requires m/z, 666.2478).(S)-Bis( 3-tert-butyl-2-hydroxy-5-nitrobenzylideneamino)- 1,l I -hinaphthyl, ( S)-H,L8.The crude product was recrystallizedfrom ethanol-dichloromethane (0.15 g, 66%); [a];:$ + 238.0 (c 0.748, toluene); h,,,(MeCN)/nm 278 (log E, 4.72),314 (4.64), 372 (4.49) and 456 (3.45); C(Nujol)/cm-' 1980-3500(br, OH), 1602, 1582 (C=N), 1509 and 1324 (NO,); 6,(270MHz, CDCl,) 1.18 (9 H, s, Bu'), 7.34-7.54 (3 H, m, H5 or H8and H6 and H7), 7.71 [l H, d, J(H3H4) 8.85, H4], 8.00 (1 H, d, J8.24, H5 or H8), 8.07 (2 H, s, H4" and H6"), 8.15 [l H, d,J(H3H4) 8.85 Hz, H3], 8.75 (1 H, s, CH=N) and 14.21 (1 H, s,OH); 6,(67.5 MHz, CDCl,) 28.6 [C(CH,),], 35.0 [C(CH,),],115.8, 117.6, 125.1, 126.4, 126.5, 126.7, 127.6, 128.4, 130.3,160.2 and 164.9 (Found: m/Z, 610.1846.C36H26N406 requires(S)- Bis( 3-ethyl-2-hydroxy-5-nitrobenzylideneumino)- 1,l '-OH); 6J67.5 MHz, CDCI,) 12.8 (CH2CH3), 22.4 (CHZCH,),71.2; H, 4.65; N, 8.50. Calc. for C , ~ H , O N ~ O ~ : C, 71.45; H, 4.75;H6"], 8.15 [l H, d, J(H3H4) 8.85 Hz, H3], 8.74 (1 H, S, CH=N)130.5, 133.2, 133.3, 138.9, 139.3, 141.4, 159.7, and 166.4.(Found: c , 72.35; H, 5.50; N, 7.85. Calc. for C4,H,,N4O6: c ,72.60; H, 5.50; N, 8.05%).(S)-Bis(3-chloro-2-hydroxy-5-nitrobenzylideneumino)- 1,l '-binuphthyl, (S)-H2L9.The crude product was recrystallizedfrom acetic acid-ethanol-dichloromethane (0.16 g, 71%);[a]::; + 781.9 (c 0.252, toluene); T(Nujol)/crn-' 2000-3500(br, OH), 1621, 1564 (GN), 1525 and 1341 (NO2); 6,(270MHz, CDCI,) 7.17-8.17 (8 H, m), 8.73 (1 H, s, CH=N) and13.93 (1 H, s, OH); 6,(67.5 MHz, CDCl,) 116.1, 122.4, 126.5,127.0, 127.7, 128.3, 128.4, 128.6, 130.0, 131.0, 133.0, 133.2,136.2, 138. I , 141.5, 154.7 and 159.2 (Found: m/r, 650.0765.C34H20C12N406 requires m/z, 650.0756).(S)- Bis( 2- h ydroxy- 5-nit YO benzylideneumin0)- 1 , 1 '-binuph thy I,(S)-H2L4. The crude product was recrystallized from aceticacid&hanol (0.11 g, 54%); [a]::: +594.6 (c 0.326,toluene); C(Nujol)/cm-' 2020-3355 (br, OH), 1608, 1585 (GN),1519 and 1337 (NO,); 6,(270 MHz, CDCl,) 6.74 [I H, d,J(H3"H4") 9.23, H3"], 7.23 (1 H, d, J8.46, H5 or H'), 7.30-7.55(2H,m,H6andH7),7.74[1 H,d,J(H3H4)8.97,H4],8.02(1 H,d, J8.21, H5 or H'), 8.07 [l H, dd, J(H3"H4") 9.10, J(H4"H6")2.57, H4"], 8.19 [l H, d, J(H3H4) 8.98, H3], 8.24 [l H, d,J(H4"H6") 2.57 Hz, H6"], 8.81 (1 H, s, CH=N) and 13.19 (1 H,s, OH); 6,(67.5 MHz, CDCI,) 115.9, 118.1, 118.2, 126.4, 126.8,127.6, 128.1, 128.2, 128.5, 130.4, 130.6, 133.1, 139.7, 141.8,159.6, 166.3 (Found: C, 69.55; H, 3.80; N, 9.45.Calc. forC34H22N406: c, 70.1; H, 3.80; N, 9.60%).[CuL'] 1. A mixture of Cu(O,CMe), (0.1 g) and H,L'(0.25 g) in ethanol (50 cm3) was refluxed for 0.5 h to afforda green solution. The solvent was evaporated and the residueextracted with CH,Cl, (2 x 25 cm3).The volume of thecombined extracts was reduced to ca. 10 cm'. Addition of anexcess of methanol induced immediate precipitation of [CuL']as a green solid, which was recrystallized by slow evaporationof a CH,CI,-MeOH mixture (Found: C, 59.0; H, 2.70; N,4.10. Calc. for C,4H18C14CuN,0,: C, 59.0; €4,260; N, 4.05%).(S)-[Mn,L',(OMe),] 2. To a solution of (S)-H,L1 (0.1 g, 0.18mmol) in dichloromethane (20 cm3) was added a solution ofMn(02CMe),-2H,0 (0.08 g, 0.31 mmol) in methanol ( 5 cm3).The mixture was stirred at 40 "C for 1 h then allowed to stand atroom temperature. Upon slow evaporation of solvent, a darkgreen crystalline solid was deposited. The solid was filteredoff, washed with cold methanol and dried (0.1 1 g, 49%):h,,,(MeCN)/nm 266 (log E,,, 4.76), 350 (4.03) and 390 (3.82);C(Nujol)/cm-' 1601 ( E N ) , 1030 (Mn-0-Mn); peff 3.95 ps permanganese atom; m/z 1429 (M'), 1398 ( M + - OMe) and1366 (M+ - 20Me) (Found: C, 57.6; H, 3.10; N, 4.1.Calc. forC,5H21C14MnN,0,~H,0: C, 57.8; H, 3.15; N, 3.85%).CrystallographyCrystal data. (C,,H ,C14CuN,0,) ,-2H20CH , COCH , ,M = 1499.78, triclinic, space group P1, u = 12.844(5), b =14.748(6), c = 18.706(4) A, a = 107.89(3), p = 89.95(3), y =100.11(3)", U = 3314(2) A3, D, = 1.48 g ern-,, Z = 2,F(OO0) = 1500, p(Mo-Ka) = 10.2 cm-'.A crystal of dimensions 0.05 x 0.20 x 0.50 mm was used fordata collection on an Enraf-Nonius diffractometer (graphite-monochromatized Mo-Ka radiation, h = 0.7107 A) using the8-28 scan mode (28,,, = 45") at 298 K.Intensity data werecorrected for Lorentz and polarisation effects; empirical absorp-tions were based on w scans of five strong reflections. 8629Unique reflections were obtained, 4944 of which were consid-ered observed (IF,/ 3 2.0 olF,,I) and used in structure refinement.The structure was solved by Patterson and Fourier methodsand subsequent refinement by full-matrix least squares wasperformed using the NRCVAX program.12 There are twoindependent molecules of complex 1 per unit cell. The finalJ. Chem. SOC., Dalton Trans., 1996, Pages 405414 40Fig. 1 A perspective view of one of the enantiomers of [CuL'] 1least-squares refinement was calculated with 830 parametersand converged to R = 0.05, R' = 0.048 and S = 1.68 withweights based on counting statistics. The hydrogen atoms wereplaced in calculated positions and were not refined. The finaldifference map showed residual extrema in the range 0.680 to- 0.50 e k3.The atomiccoordinates of non-hydrogen atoms arelisted in Table 1 , selected bond distances and angles in Table 2.Alkene oxidationCatalysed by [CuL'] 1. In a typical run a mixture of organicsubstrate (0.2 g, ~2 mmol) and the oxidant Bu'0,H (80%, 2cm3) in dichloromethane (10 cm3) was stirred at 0 "C. Complex1 (25 mg, 0.05 mmol) was added and the mixture stirred for 8-12 h. A blank containing the same amount of solvent, substrateand But02H but without the metal catalyst was simultaneouslystirred under the same conditions. The reaction was quenchedby addition of a saturated solution of Na2S03 (10 cm3) at 0 "C.The organic product was extracted with diethyl ether, driedwith Na2S04 and filtered.The aliquot was then subjected toGC analyses, and the products quantified by the internalstandard method. The yield of the catalytic oxidation wascalculated based on the amount of substrate used.Catalysed by Mn"' + H,L. All catalytic oxidation reactionswere carried out at either 0 "C or room temperature under anargon atmosphere. In a typical run the olefinic substrate (0.85mmol), manganese(rr1) acetate dihydrate (4 mol%) and thecompound H,L (4 mol%) were mixed in acetonitrile ( 5 cm3).The mixture was stirred at room temperature for 20 min.Forreactions at 0 "C, the mixture was stirred at 0 "C for 15 minmore. Iodosylbenzene, PhIO (0.43 mmol), was added to thesubstrate-catalyst mixture and the system stirred until all ofit had dissolved. The epoxide product and iodobenzene formedwere quantified by gas chromatography using the internalstandard method and the epoxide yield for the PhIO epoxid-ation was based on the amount of iodobenzene formed. Theepoxide products of the catalytic oxidation of stilbenes wereanalysed by 'H NMR spectroscopy using 1 , 1-diphenylethyleneas internal standard.Enantiomeric excess of epoxide products. The enantiomericexcesses of the styrene oxide, 4-chlorostyrene oxide and cis-p-methylstyrene oxide products were determined on a commercialchiral GC column (J & W Scientific, Cyclodex-B, 30 m x 0.25mm internal diameter, 0.25 mm film).For trans-stilbene oxidethe e.e. was determined on a commercial chiral HPLC column(Daicel Industries Ltd., Chiralcel OJ). All other epoxideproducts, were first purified by column chromatography andtheir e.e.s determined by 'H NMR spectroscopy in the presenceof tris[3-(heptafluoropropylhydroxymethylene)-~-camphor-ato]europium(~~r) {camphor = (R)-( + )-I ,7,7-trimethylbicyclo-C2.2.13 heptan-2-one} [Eu(hfc),]. The absolute configurationof the enriched isomer in the styrene oxide product was deter-mined by comparison with an authentic sample, (S)-styreneoxide (Aldrich). The absolute configuration of the enrichedisomer in the 4-chlorostyrene oxide products was determinedby comparing the [Eu(hfc),]-shifted 'H NMR spectra of theproducts with a previously reported spectrum of a sampleenriched with (R)-6chlorostyrene oxide.l 3 For the cis-P-methyl-styrene oxide products the absolute configuration of theenriched enantiomer was determined by matching the orderof elution of the two enantiomers on the Cyclodex-B columnwith that provided by Professor Jacobsen:14 first peak, (1 R72S)-( + )-cis-P-methylstyrene oxide; second peak, (1 S,2R)-( -)-cis-P-methylstyrene oxide. The assignments of absolute configur-ation to the enriched enantiomer in the three types of epoxideproduct were further supported by optical rotation measure-ments.Relative reactivity of styrenes in epoxidation mediated byMn"' + H,L6 or H,L'.In a typical competition reaction,equimolar amounts of styrene and substituted styrene (0.3mmol each) were mixed in acetonitrile ( 5 cm3) containing theappropriate GC internal standards. The initial amounts ofthe two olefins were determined by GC. The compoundMn(02CMe),-2H20 and the compound H2L (4 mol %) wereadded to the solution and the mixture stirred at roomtemperature for 20 min. With H2L6 the substrate-catalystmixture was stirred at 0 "C for 15 min more. Iodosylbenzene(0.15 mmol) was then added and the mixture stirred until allof it had dissolved. The final amounts of the two olefins weredetermined by GC. The relative reactivity was calculatedaccording to equation (1) where Yi and Y, are the amounts ofk s t yrenesubstituted styrene before and after reaction and Xi and Xf arethe corresponding amounts of styrene.Results and DiscussionThe compound (R)- or (S)-H2L' was prepared by a one-potreaction of (R)- or (S)-2,2'-diamino-l, 1 '-binaphthyl respectivelywith 3,5-dichlorosalicylaldehyde in absolute ethanol at roomtemperature.The optically active forms are stable and nosignificant racemization was found to occur at temperaturesbelow 90 "C. Reaction of Cu(O,CMe), with H2L' in refluxingethanol afforded the complex [CuL'] 1 in high yield. Theoptically active forms of 1 were prepared from the pure R( -)and S( +) forms of H2L1. The structure of the racemic formof 1 has been established by X-ray crystal analysis. In eachasymmetric unit there are two independent molecules, A and B,a perspective view of one of which is shown in Fig.1. The ligandbehaves like other tetradentate salicylideneimine ligands. Theco-ordination geometry of Cu is distorted tetrahedral. The mostintriguing structural feature is the seven-membered twist-boatring formed from the two imine nitrogen atoms N( 1) and N(2),the two naphthalene rings and the copper atom. Importantly,the measured dihedral angles of 7531) (molecule A) and74.1( 1)" (B) between the two naphthalene rings are comparableto the values of 65.6" in [Ru(OCOCMe,),((S)-binap)] l 6 and87.59(5)" in the related 2,2'-bis(pyridine-2-carboxamido)- 1,l'-binaphthyl ligand. IReaction of a mixture of H2L' and Mn(02CMe),-2H20 in408 J. Chem. SOC., Dalton Trans., 1996, Pages 405-41Table 1 Atomic coordinates of non-hydrogen atoms of complex I (the atomic coordinates of the water and acetone molecules are not included)AtomCu( 1 A)N( 1 A)N(2A)O( 1 A)OVA)C(1A)C(2A)C(3A)C(4A)C(5A)C(6A)C(7A)C(8A)C(9A)C( I OA)C(11A)C( 12A)C( 13A)C( 14A)C( 15A)C( 16A)C( 17A)C( 18A)C( 19A)C(20A)C(21A)C( 22A)C( 23A)C( 24A)C( 25A)C(26A)C(27A)C(28A)C(29A)C(30A)C(3 1 A)C(32A)C(33A)C(34A)C1( 1 A)C1( 2A)C1( 3A)Cl(4A)x-0.249 12(8)0.325 3(4)0.164 2(4)0.250 5(4)0.262 l(4)0.362 5(6)0.472 O(6)0.509 O(6)0.438 O(6)0.475 O(6)0.404 l(7)0.296 3(7)0.258 O(6)0.329 l(6)0.290 5(5)0.174 5(5)0.124 7(6)0.182 3(6)0.132 7(7)0.035 4(6)0.014 5(6)0.045 O(6)0.002 9(6)0.1 13 2(6)0.359 O(6)0.340 9(6)0.377 5(6)0.371 2(6)0.327 l(7)0.293 l(6)0.297 4(6)0.138 4(6)0.165 6(5)0.131 4(6)0.147 8(6)0.196 7(6)0.231 6(6)0.218 5(5)0.295 2(2)0.239 O(2)0.416 4(2)0.022 7(7)0.101 O(2)Y0.017 79(6)0.027 2(4)0.006 4(3)0.153 2(3)-0.111 6(4)-0.057 7(5)-0.057 7(5)-0.139 2(5)- 0.226 O(5)-0.314 O(6)-0.396 7(6)-0.397 6(5)-0.314 3(5)- 0.225 7(5)- 0.I38 4(5)- 0.136 5(4)-0.143 6(5)-0.141 2(5)- 0.145 6(6)-0.150 4(6)-0.151 7(6)-0.147 5 ( 5 )-0.146 5 ( 5 )- 0. I38 O(5)- 0.130 8(4)0.107 6( 5 )0.201 6(4)0.277 7(5)0.370 8(5)0.390 O(5)0.317 7(5)0.219 3(5)- 0.173 7(5)- 0.159 5(5)-0.238 4(5)- 0.229 5 ( 5 )-0.142 5(5)- 0.064 9(5)- 0.069 9(5)-0.326 l(2)0.043 l(2)0.342 92( 15)0.463 58(16)Z0.488 74(5)0.581 8(3)0.470 6(3)0.385 3(3)0.512 l(3)0.586 2(4)0.586 l(4)0.582 2(4)0.576 9(4)0.566 l(4)0.557 3(5)0.558 5 ( 5 )0.569 3(4)0,578 l(4)0.585 5(3)0.591 5(4)0.658 2(4)0.722 9(4)0.786 8(4)0.788 9(4)0.728 3(4)0.661 5(4)0.599 3(4)0.535 7(4)0.534 l(3)0.635 6(4)0.637 2(4)0.703 9(4)0.708 l(5)0.648 7(5)0.584 4(4)0.574 9(4)0.405 l(4)0.334 4(4)0.269 6(4)0.200 7(4)0.192 2(4)0.254 4(4)0.328 2(4)0.243 5(1)0.1 19 5(1)0.509 6(2)0.790 4( 2)AtomCu( 1 B)N( 1 B)N(2B)0(1B)0(2B)C( 1 B)C(2B)C(3B)C(4B)C(5B)C(6B)C(7B)C(8B)C(9B)C( 1 OB)C(11B)C( 12B)C( 13B)C( 14B)C( 15B)C( 16B)C( 17B)C( 18B)C( 19B)C(20B)C(21B)C(22B)C(23B)C( 24B)C(25B)C(26B)C(27B)C(28B)C(29B)C( 30B)C(3 1 B)C(32B)C(33B)C(34B)C1( 1 B)Cl(2B)Cl(3B)Cl(4B)Y0.247 ll(8)0.186 6(4)0.340 7(4)0.235 2(4)0.226 5(4)0.156 O(5)0.047 l(6)0.014 5(6)0.087 O(6)0.054 2(6)0.126 4(7)0.233 3(7)0.268 8(6)0.196 3(6)0.230 9(5)0.346 9(5)0.404 2(5)0.355 7(6)0.414 6(7)0.523 7(6)0.572 7(6)0.515 5(6)0.564 5 ( 5 )0.508 9(6)0.399 5(5)0.156 8(6)0.163 8 ( 5 )0.129 6(6)0.126 O(6)0.155 5(6)0.189 3(6)0.196 3(6)0.367 2(6)0.329 3(6)0.360 l(6)0.335 4(7)0.278 8(7)0.247 9(6)0.268 9(6)0.175 60(2)0.374 9(2)0.225 l(2)0.081 5(2)Y0.474 99(6)0.495 4(4)0.601 2(4)0.457 O(3)0.338 7(3)0.587 8(4)0.590 7(5)0.676 9(5)0.763 7(5)0.856 5(5)0.940 3(5)0.938 5 ( 5 )0.851 8(5)0.762 3(5)0.669 6(5)0.666 5(4)0.695 3(5)0.715 7(5)0.738 O(6)0.743 4(6)0.725 4(6)0.700 O(5)0.674 7( 5 )0.643 5(5)0.639 O(5)0.427 7( 5 )0.327 3(5)0.268 3(5)0.170 7(5)0.129 O ( 5 )0.186 5(5)0.289 l(5)0.648 2(5)0.613 4(5)0.678 8(6)0.650 9(7)0.559 2(7)0.495 3(6)0.519 3(6)0.381 3(2)0.731 4(2)0.134 4(2)0.096 3( 1)Z1.004 41 (5)0.916 2(3)1.043 l(3)l.lOOO(3)0.959 6(3)0.926 5(4)0.925 8(4)0.944 O(4)0.966 5(4)0.992 3(4)1.015 l(5)1.012 6(4)0.987 5(4)0.964 6(4)0.942 4(4)0.938 7(4)0.881 6(4)0.821 5(4)0.766 6(4)0.768 3(4)0.824 O(4)0.882 l(4)0.939 l(4)0.990 9(4)0.989 7(4)0.853 6(4)0.835 8(4)0.762 4(4)0.743 4(4)0.795 4(4)0.866 6(4)0.890 8(4)1.175 2(4)1.248 4(4)1.309 7(4)1.302 5(4)1.232 O(4)1.164 9(4)1.223 6( 1)1.397 8(1)0.932 O( 1)0.653 5(1)I .113 5(4)Table 2 Selected bond distances (A) and angles (") of [CuL'] 1CU( 1 A)-N( 1 A)CU( 1 A)-N(2A)CU( 1 A)-O( 1 A)Cu( lA)-0(2A)N(lAFC(21A)N(2A)-C(28A)N( 1 A)-C( 1 A)1.953(5)1.954(4)1.89 1 (5)1.885(4)1.301(8)1.287(8)1.441(9)N( 1 A)-Cu( 1 A)-N(2A)N(2A)-Cu( 1 A)4( 1 A)N( 1 A)-C( 1 A)<( 1 OA)N( 1 B)-Cu( 1 B)-N(2B)N(2B)-Cu( 1 B)-O( 1 B)N( 1 B)-C( 1 B)-C( 1 OB)98.1(2)93.4(2)119.4(6)97.6(2)93.7(2)120.0(6)CU( 1 B)-N( 1 B)CU( 1 B)-N(2B)CU( 1 B)-O( 1 B)CU( 1 B)-0(2B)N(2B)-C(28B)N( 1 B)-C( 1 B)N( 1 B)-C(2 1 B)N( 1 A)-Cu( 1 A)-O( 1 A)N( 1 A)-Cu( 1 A)-0(2A)N(2A)-C(20A)-C( 1 1A)N( 1 B)-Cu( 1 B)-O( 1 B)N(2B)-C(20B)-C( 1 1 B)N( 1 B)-Cu( 1 B)4(2B)1.95 l(5)1.889(5)1.895(5)1.290(8)1.299(9)1.440(8)1.954(5)149.4(2)93.6(2)118.6(6)1 5 1.6(2)93.4( 2)119.5(6)methanol-dichloromethane at 50 "C afforded a deep greensolution, from which a dark green crystalline solid wasobtained.Both elemental analyses and the mass spectrumestablished the empirical formula of the green solid to be[Mn,L',(OMe),] 2. This empirical formula has also beeninferred from a partial X-ray crystal analysis of the dark greencrystals," although due to their poor quality a completestructural solution is not feasible. Complex 2 is paramagneticand has an effective magnetic moment of 3.95 pB per manganeseatom at room temperature.This value is lower than the spin-only value of 4.9 pB for high-spin Mn"'. It is likely that in themanganese(iI1) Schiff-base complexes dimer formation tends tolower the effective magnetic moment as a result of coupling.The two optically active forms were prepared from the R( -)and S( +) forms of H,L1. As shown in Fig. 2, their ORD curvesare mirror images but are different from that of the free H2L'.The UV/VIS absorption spectrum of 2 measured in acetonitrileis shown in Fig. 3.Catalytic alkene oxidation by [ CuL'] 1Complex 1 was found to catalyse alkene oxidation in thepresence of tert-butyl hydroperoxide and the results aresummarized in Table 3. Styrene was oxidized to a mixture ofJ.Chem. SOC., Dalton Trans., 1996, Pages 405-414 40-1002 5 750UnmFig. 2 The ORD spectra of the (R) and ( S ) forms of[Mn,L',(OMe),]. The insert shows the corresponding spectra of thetwo forms of H,L' in dichloromethane18 1.2s 2 0.8t ca e0.40.0200 300 400 500 600UnmFig. 3 The UV/VIS spectra of the green solution obtained fromMn(O2CMe,),-2H,O with (S)-H,L' in acetonitrilestyrene oxide and benzaldehyde in a ratio of 5 : 1 . Norbornene(bicyclo[2.2.l]hept-2-ene) was oxidized to exo-norborneneoxide exclusively. Oxidation of cyclohexene gave cyclohexen-2-one predominantly together with a small amount ofcyclohexene oxide. The oxidation reaction was non-stereo-specific as exemplified in stilbene oxidation where trans-stilbeneafforded trans-stilbene oxide, and cis-stilbene gave trans-stilbene oxide only.It should be noted that in the cis-stilbeneoxidation a significant amount of trans-stilbene was detected(entry 5 in Table 3). A similar finding was reported previouslyby Valentine and co-workers '' in the catalysis by simple metal410 J. Chem. SOC., Dalton Trans., 1996, Pages 405-414Table 3 Oxidation of alkenes by tert-butyl hydroperoxide catalysedby [CuL']Entry Substrate Product1 Styrene Styrene oxideBenzaldehyde2 Norbornene exo-Norbornene oxide3 C yclohexene Cyclohexene oxideC yclohex-2-enone4 trans-S ti1 bene trans-Stilbene oxideBenzaldeh yde5 cis-Stilbene trans-Stilbene oxideBenzaldehydetrans-Stilbene* Based on substrate consumed.Yield51115610325610161050(%I *Bub,)-i -Ph PhC-C bond rotation 1-Bu~o* B U t O p P h -Ph PhScheme 1salts (Mn"', Fe"', Co", Cu") of the oxidation of cis-stilbene byiodosylbenzene. These workers ascribed this result to the metal-catalysed isomerization of cis- to trans-stilbene.Given the lowyields of organic epoxides and non-stereospecific nature of thecis-stilbene oxidation, we rationalize the oxidation as involvingradical-chain reaction(s) arising from homolytic 0-0 bondcleavage induced by Cu". Thus reaction of cis-stilbene with thetert-butylperoxy radical would give the Bu'0,CHPhCHPh'intermediate which undergoes C-C bond rotation beforeexpulsion of Bu'O' (Scheme 1).With the use of chiral (S)-[CuL'] as the catalyst theoxidation of styrene with Bu'0,H gave styrene oxide (entry 1in Table 3) but there was no asymmetric induction.Other co-oxidants like PhIO, morpholine N-oxide and NaOCl in thepresence of 1 were found to be ineffective towards oxidation ofalkenes. For this reason, no detailed study of the Cu"-catalysedoxidation was undertaken.Catalytic alkene oxidation by manganese complexes of chiralComplex 2 is not a good catalyst for epoxidation of alkenes byiodosylbenzene. When a mixture of styrene (1 equivalent), 2(0.04 equivalent) and PhIO (0.5 equivalent) was stirred at roomtemperature under an argon atmosphere for 24 h no styreneoxide was detected. Changing the solvent to acetonitrile gavethe same result. We speculated that the poor catalytic activity of2 is due to the presence of co-ordinating methoxide ions whichhamper the interaction between PhIO and Mn"'.In order torender the system catalytic, an equimolar amount of (S)-H,L'and Mn(02CMe)3-2H,0 was allowed to react in acetonitrile atroom temperature. A dark green solution was obtained after 20min which displayed a similar UV/VIS absorption spectrum tothat of 2 (Fig. 3). The ORD curves of the green solutionsobtained from Mn(O2CMe),-2H,O with (S)- or (R)-H,L1 aresimilar to that of [Mn,{(S)-L'},(OMe),] and [Mn,{(R)-L'} ,(OMe),] respectively. However, unlike 2, the greensolution is active towards alkene epoxidation by PhIO. Wespeculate that the green species generated in situ is amanganese(rr1) dimer but without the co-ordinated methoxide.The results of PhIO oxidation of alkenes catalysed by theH Table 4 Alkene epoxidation catalysed by the Mn"' + (S)-H,L' systemEntry Substrate Producte.e.(%)*Yield (%)" (configuration)I Styrene Styrene oxide 79 25 ( S )2 cis-0-Methylstyrene cis-0-Methylstyrene oxide 46 34 (1 R,2S)4 4-Chlorostyrene 4-Chlorostyrene oxide 66 31 ( S )5 4-Methylstyrene 4-Methylstyrene oxide n.d.' 24 ( S )3 trans-0-Methylstyrene trans-0-Methylstyrene oxide 27 6 (n.d.)'6 Oct-I-ene Oct- 1 -ene oxide 18 0" Based on the amount of PhI formed. Determined by either 'H NMR spectroscopy in the presence of [Eu(hfc),] or chiral column GC. ' n.d. =Not determined.Mn"' + (S)-H2L1 system are summarized in Table 4. Thereaction usually took less than 30 min for completion.In allcases, epoxides are the major products. Styrene was oxidisedto (S)-styrene oxide with 25% e.e. When (R)-H,L' was usedin the preparation of the green solution styrene was oxidizedto (R)-styrene oxide with similar product yield but withz 25% e.e.Like the oxidation reactions mediated by other chiralmanganese Schiff-base complexes,20 cis-alkenes such as cis+methylstyrene reacted with higher yield and e.e. and are morereactive than the trans isomers (entries 2 and 3 in Table 4). Forexample, the reaction time required for trans-P-methylstyrene is2 h whereas that for the cis counterpart is just 10 min. The e.e. isaffected by electronic effects as found in the oxidation of a seriesof para-substituted styrenes.The electron-withdrawing chlorogroup enhances the e.e. by about 6%, whereas an electron-donating substituent decreases it slightly (entries 4 and 5 inTable 4). Oct-I-ene, an aliphatic terminal alkene, is a poorsubstrate in the present catalytic system.Optimization of the chiral inducing effect of the auxiliarybinaphthyl Schiff-base ligandsThe effect of changing the Mn(02CMe),*2H20: (S)-H,L' moleratio on the e.e. of the organic epoxide formed has beenexamined. With styrene as the substrate, changing the ratiofrom I to 2 : 1 had no significant effect on both the activity andenantioselectivity of the Mn"' + (S)-H,L' system. The e.e. ofthe (S)-styrene oxide was unaffected.Previously, Zhang and Jacobsen 2o reported that bulkysubstituents on the salicylidene ring of the Schiff-base ligandstrongly affect the chiral inducing power of the manganesecatalyst.In an attempt to improve the enantiodiscriminationeffect of the newly developed binaphthylic Schiff-base ligand,the chloro groups in H2L' were replaced by bulky alkylsubstituents to give (S)-H2L" (R' = But, R2 = Me). Disap-pointingly, the Mn"' + (S)-H,L" system in a molar ratio ofI : 1 was found to be a poor catalytic system under similarconditions as that used for Mn"' + (S)-H2L'. The former tooknearly 3 h for complete dissolution of PhIO and only a traceamount of racemic styrene oxide was formed. Attempts topromote the oxidation by first heating the reaction mixture didnot lead to any improvement in the catalytic properties.Asimilar result was found when R' = R2 = Me. Thus theinability of the dialkyl binaphthylic Schiff bases to activateMn"' is not solely due to the steric effect of the alkyl substituentsat the 3 position. The failure of the H,L (R' = R2 = Me)ligand to promote epoxidation led us to attach electron-withdrawing groups on the two phenoxy rings. Thus the twomethyl groups at the 5 positions were substituted with chlorosubstituents to give ligands which have different stericproperties in the vicinity of the manganese atom.Under similar conditions to those used in the Mn"' + (S)-H,L' catalysed epoxidation, the catalytic activities of theMn"' + (S)-H,L (R' = Me or Et, R2 = C1) systems wereexamined using 4-chlorostyrene as substrate. However, in allOH ?HNo,R dScheme 2 (i) (CH,O),, SnCI,, 2,6-dimethylpyridine, toluene; (ii)concentrated HNO,, MeC0,H; (iii) MeC0,H-EtOH (1 : 7), roomtemperature.dabn = 2,2'-Diamino-l , 1 '-binaphthylcases, a very low yield of racemic epoxide was found.Furthermore, the UV/VIS spectrum of a 1 : 1 mixture ofMn(0,CMe),-2H20 and (S)-H2L3 (R' = Et) in acetonitrile(stirred at 50 "C for 1 h) and that of free H,L3 are similar. Thus,the poor reactivity was attributed to the poor ability of (S)-H,L3 to co-ordinate to Mn"'.In order to improve the co-ordination ability of the Schiffbase, the compounds (S)-H,L (R' = H, alkyl or CI; R2 =NO,) were prepared (Scheme 2). The effect of (S)-H2LS(R' = Me), as a chiral auxiliary ligand has been examined.Stirring a mixture of 4-chlorostyrene (1 equivalent), Mn(0,-CMe),=2H2O (0.04 equivalent) and (S)-H,L5 (0.04 equivalent)in acetonitrile under an argon atmosphere for 30 min at roomtemperature resulted in the formation of a dark brown solution.Addition of PhIO (0.5 equivalent) gave 4-chlorostyrene oxide in61% yield and 37% e.e.and the reaction was completed within10 min. When cis-P-methylstyrene was employed as substratean even higher enantioselectivity of 47% was observed. Thisresult is better than that obtained with the Mn"' + (S)-H,L'system.The effect of varying the R' groups (Et, Pri, But, H or Cl) atthe 3 positions of (S)-H2L (R2 = NO2) on enantioselectivitywas examined. 4-Chlorostyrene and cis-p-methylstyrene wereused as the substrates and the results are listed in Table 5.When R' = Me, Et or Pr' the reactions were completedwithin 20 min, whereas when R' = But about 2-3 h wererequired for complete consumption of PhIO.This indicatesthat the bulky tert-butyl group adversely affects the catalyticactivity .With cis-P-methylstyrene there is a slight improvement in e.e.from 47 to 50% when the substituent R' changes from methyl toethyl (entries I and 2 in Table 5). However, when the bulkinessof the R' groups increase further the enantioselectivity drops asJ. Chem. SOC., Dalton Trans., 1996, Pages 405414 41Table 5 Epoxidation of cis-0-methylstyrene and 4-chlorostyrene with PhIO catalysed by the (S)-H,L (R2 = NO,) + Mn"' systems, at roomtemperature"cis-p-Methylstyrene oxide 4-Chlorostyrene oxideEntry R' Yield (%) e.e.PA)' Yield ( % ) b e.e. ( % ) d1 Me 51 47 61 372 Et 50 50 59 363 Pr' 49 33 52 194 Bute 14 2 16 05 c1 57 34 50 34a All reactions completed within 20 min.Chlorostyrene oxide was the major product. Reaction time 3 h.Based on amount of PhI formed. ' ( 1 R,2S)-cis-P-Methylstyrene oxide was the major product. (29-4-Table 6 Epoxidation of cis-P-methylstyrene and 4-chlorostyrene with PhIO catalysed by various (5')-H,L (R2 = NO,) + Mn"' systems at 0 OCacis-P-Methylstyrene oxide 4-Chlorostyrene oxideR' Yield (%) e.e. (%)' Yield (%)' e.e.H 35 45 45 35Me 37 47 50 41Et 38 54 56 43Pr' 41 35 42 24For all reactions, manganese(@ acetate, H,L and substrate were stirred at room temperature for 20 min and for 15 min at 0 "C before the additionof PhIO.All mixtures were stirred at 0 "C for 90 min after the addition of oxidant. Determined on the basis of the PhI formed. ' (lR,2S)-cis-P-Methylstyrene oxide was the major product. (S)-4-Chlorostyrene oxide was the major product.Table 7 Effect of donor ligand on the epoxidation of cis-P-methylstyrene with PhIO catalysed by the H2L6 + Mn"' catalytic system at 0 OC"Donor Amount H,L6 (equivalents) 'Nil 055102-Methylimidazole 1N-Methylimidazole 1Pyridine N-oxide 5Yield (%)'38372437314344e.e. (%)d54515151445454" Reactions were carried out in acetonitrile with 0.85 mmol of substrate, 0.43 mmol of PhIO and 4 molx catalyst. In all cases, manganese(n1) acetate,H,L7 and substrate were stirred at room temperature for 20 min, a calculated amount of donor was then added and the mixture stirred for 15 min at0 "C before addition of PhIO.Based on the amount of catalyst. Yields of cis-P-methylstyrene oxide formed are based on PhI formed. (1 R,2S)-cis-P-Methylstyrene oxide was the major product. Reaction time 1 h. Reaction time 2 h.illustrated by the 2% e.e. in the case of tert-butyl (entry 4 inTable 5).When R' was the electron-withdrawing chloro group, i.e.H,L9, lower e.e.s were found in the epoxidation of both 4-chlorostyrene and cis-P-methylstyrene (entry 5 in Table 5).The effect of decreasing the reaction temperature has alsobeen investigated. The results are listed in Table 6. As shown,the enantioselectivity increases with decreasing temperature.Epoxidation of cis-P-methylstyrene with the Mn"' + (5')-H2L6(R' = Et) system gave the best result with epoxide up to 54%e.e. at 0 "C and 58% at -20 "C.As far as the configuration of the organic epoxide isconcerned, epoxidation of styrene and cis-P-methylstyrene withMn"' + (S)-H2L6 gave (5')-styrene oxide and (1 S,2R)-cis-P-methylstyrene oxide, whereas with (R)-H2L6 the cis-P-methyl-styrene oxide was found in the 1R,2S configuration with54% e.e.Efforts have been made to characterize and/or isolate theactive intermediate responsible for the catalytic activity.However, no well characterized product was obtained uponheating an equimolar mixture of Mn(02CMe),-2H20 and (5')-H , L ~ in acetonitrile.Effect of donor ligands on the catalytic activities of themanganese complexesAs reported by Katsuki and co-workers,21 addition of a donorligand could improve the e.e.of alkene epoxidation catalysed bychiral manganese Schiff-base complexes. In this work the effectof three donor ligands, namely N-methylimidazole (1 -mim), 2-methylimidazole (2-mim) and pyridine N-oxide (pyo), on theMn"' + H,L6 catalytic system, for cis-P-methylstyrene oxid-ation has been examined and the results are shown in Table 7.Addition of 1-mim (1 and 5 equivalents) does not affect thecatalytic activity. The reaction was completed within 15 min butthere was a decrease in both the e.e. and yield of the epoxideproducts. On the other hand, addition of just 5 equivalents of2-mim was found to slow the reaction, which took about 90min for completion.Presumably, the excess of 2-mim woulddeactivate the catalyst through binding to Mn"'. Although theepoxide yield decreased considerably there was only a slightdecrease in e.e.Like 1-mim, pyo did not suppress the activity of the catalyst.All PhIO reacted within 15 min. Unlike the imidazole donor,the e.e. was not affected by the N-oxide additive and therewas a small improvement in the product yield (entries 6 and 7in Table 7).Epoxidation of various olefinic substrates by PhIO-Mn"'-H2L6systemThe results of PhIO epoxidation of various alkenes catalysed bythe Mn"' + H2L6 system are listed in Table 8. A similarselectivity pattern has been found with the Mn"' + H2L1system (Table 4).Electron-withdrawing substituents in meta-or para-substituted styrenes (Table 8, entries 2-4) give higher412 J. Chem. SOC., Dalton Trans., 1996, Pages 405-41Table 8 Epoxidation of alkenes by PhIO catalysed by the (S)-H2L6 + Mn"' catalytic system at 0 "C"r G.2-0.8 -0.6 -0.4 -0.2 0Entry13456789101 112133 I4-CIa 1 I '0 0.4SubstrateStyrene3-Chlorostyrene4-Chlorosty rene3-Nitrostyrene4-Methylstyrenecis-P-Methylstyrenecis-P-Methylstyrene 'gdtrans-0-Methylstyrenecis-Stil benetruns-Stilbened*'cis-Hept-2-enetr~ms-Oct-2-ene fC yclohexeneProductStyrene oxide3-Chlorostyrene oxide4-Chlorostyrene oxide3-Nitrostyrene oxide4-Methylstyrene oxidecis-P-Methylstyrene oxidecis-P-Methylstyrene oxidetrans- p- Met hy 1st yrene oxidecis-Stilbene oxidetrans-Stilbene oxidecis-Hept-2-ene oxidetrans-Oct-2-ene oxideCyclohexene oxideYield (%)596056n.d.bn.d.38(cis-epoxide : trans-epoxide34(cis-epoxide : trans-epoxide33(no cis-epoxide detected)65(cis-epoxide : trans-epoxide21(no cis-epoxide detected)871893e.e.(%) (configuration)36 ( S )46 ( S )43 ( S )49 (n.d.)35 ( S )54 ( 1 S,2R)58 ( I S,2R)3 (n.d.)= 10:l)= 9 : l )-= 6: 1)1 (n.d.1" Reactions were carried out in acetonitrile ( 5 cm3) with 0.85 mmol of alkene, 0.43 mmol of PhIO and 4 mol % of catalyst. All reactions were allowedto proceed for I h and the yields of epoxide determined by GC and reported based on the amount of PhI formed.' n.d. = Not determined. Reactionwas carried out at -20°C. dReaction for 2 h. 'Reaction was carried out at room temperature. Reaction for 3 h. g A small amount ofcyclohexanone was detected.Table 9catalysed by the H2L6 + Mn"' systemRelative reactivities of substituted styrenes in epoxidationSubstituted styrene log(ksubs:ituted styrenelkslyrene) IT+4-Chloro 0 0.1 13-Chloro -0.13 0.404-Methyl 0.3 1 - 0.3 14-Methoxy 0.62 - 0.78i-;u" nFig. 4 Hammett plot ClOg(ksubsti:uted styrenelkstyrene) US. o+I for thereaction of iodosylbenzene with substituted styrenes catalysed byMn"' + H,Lhe.e.s than unsubstituted styrenes, whereas an electron-donatinggroup (Table 8, entry 5 ) reduces the enantioselectivity slightly.cis-P-Methylstyrene remains the best substrate among thealkenes examined.The Mn"' + H2L6 system displays pooractivity towards trans alkenes. All the trans substrates werefound to react in a sluggish manner (about 2 h for completereaction) and epoxides were obtained with very low e.e. andpoor yield (Table 8, entries 8, 10 and 12).Besides aryl-substituted alkenes, several aliphatic alkeneshave also been tested (entries I 1-13, Table 8). fvans-Oct-2-eneafforded a low yield of epoxide. On the other hand, cis-hept-2-ene and cyclohexene were epoxidized in excellent yields. In thecase of cyclohexene a small amount of cyclohexenone (allylicoxidation product) was formed. Attempts to determine the e.e.of cis-hept-2-ene oxide and trans-oct-2-ene oxide productsfailed.In both cases addition of [Eu(hfc),] to a CDCl, solutionof the epoxide led to a set of overlapping multiplets and noresolved NMR signals from the two enantiomers.Oxidation of cis-P-methylstyrene at 0 "C gave a 9: 1 mixtureof cis- and trans-epoxides. Furthermore, in the epoxidation ofcis-hept-2-ene no trans-epoxide was detected. In the case ofcis-stilbene a mixture of cis- and trans-epoxides was formedin a ratio of only 6 : 1.The reactivities of a series of substituted styrenes (relative tostyrene) towards PhIO catalysed by the Mn"' + H2L6 systemwere studied by a competition method and the results are listedin Table 9. A Hammett plot of log(ksubstituted styrene/k,ty,e,e) us. 0'is shown in Fig. 4. A p+ value of - 0.65 was found. The uniformvariation of the ksubstituted styrene values with para substituentsindicates that a common mechanism is operating for allsubstituted styrenes studied.However, the p ' value is smallwhen compared with those for reactions which involve rate-determining formation of a carbocation intermediate (p' >-3).22 By comparison with p' values for concertedelectrophilic reactions, such as carbene insertion into alkenedouble bonds (p' = -0.62 to - 1.61)23 or epoxidation ofstilbene by peroxybenzoic acid (p' = - 1.2),24 it is probablethat oxygen insertion into the alkene double bond in the presentepoxidation reactions proceeds via a concerted pathway.ConclusionThe results obtained clearly demonstrate that the newlyprepared binaphthyl Schiff bases are capable of activating Cu"and Mn"' towards catalytic oxygen-atom transfer to alkenes.Enantioselective formation of organic epoxides from the PhIOoxidation of alkenes catalysed by the Mn"' + H2L system hasJ.Chem. SOC., Dalton Trans., 1996, Pages 405-414 41been demonstrated. The chiral inducing ability of the dinitro-substituted auxiliary ligands could be enhanced by attachingsmall alkyl groups at the 3 positions and the best ligand in thisrespect is H,L6 (R' = Et). Addition of donor ligands such assubstituted imidazole or pyridine N-oxide did not result in e.e.enhancement. The small p+ value obtained in the oxidation of aseries of substituted styrenes suggests a concerted pathway forthe Mn"' + H,L system.AcknowledgementsWe acknowledge support from The University of Hong Kongand The Hong Kong Research Grants Council.References1 T. Katsuki and K. B. Sharpless, J. Am. Chem. Soc., 1980,102, 5974;M. G. Finn and K. B. Sharpless, Asymmetric Synthesis, ed. J. D.Morrison, Academic Press, New York, 1985, vol. 5, p. 247.2 H. C. Kolb, M. S. VanNieuwenhze and K. B. Sharpless, Chem. Rev.,1995,94, 2483 and refs. therein.3 E. N. Jacobsen, Catalytic Asymmetric Synthesis, ed. 1. Ojima, VCH,New York, 1993, p. 159; T. Katsuki, Coord. Chem. Rev., 1995, 140,189.4 C. Rosini, L. Franzini, A. Raffaelli and P. Salvadori, Synthesis,1992,504.5 R. Noyori, Chem. Soc. Rev., 1989, 18, 187; R. Noyori andH. Takaya, Ace. Chem. Res., 1990,23,345 and refs. therein.6 K. Maruoka, T. Itoh, T. Shirasaka and H. Yamamoto, J. Am. Chem.Soc., 1988, 110, 310.7 J. T. Groves and R. S. Myres, J. Am. Chem. Soc., 1983, 105, 5791;Y . Naruta, F. Tani, N. Ishihara and K. Maruyama, J. Am. Chem.Soc., 1991, 113, 6865; S. O'Malley and T. Kodadek, J. Am. Chem.Soc., 1989, 111, 91 16.8 S. Miyano, M. Nawa, A. Mori and H. Hashimoto, Bull. Chem. Soc.Jpn., 1984, 57, 2171.9 S. J. Angyal, P. J. Morris, J. R. Tetaz and J. G. Wilson, J. Chem.Soc., 1950, 2141.10 H. Lindler and R. Dubuis, Org. Svnth., 1973, Coll. Vol. V, 880.1 1 L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, Wiley,12 E. J. Cabe, Y. Le Page, J. P. Charland, F. L. Lee and P. S. White,13 J. T. Groves and R. S. Myres, J. Am. Chem. Soc., 1983,105, 5791.14 W. Zhang, J. L. Leobach, S. R. Wilson and E. N. Jacobsen, J. Am.15 P. S. Skell and A. Y. Garner, J. Am. Chem. Soc., 1956,78, 5340.16 T. Ohta, H. Takaya and R. Noyori, Znorg. Chem., 1988,27,566.17 J . H. Lin, C. M. Che, T. F. Lai, C. K. Poon and Y. X. Cui, J. Chem.18 S. M. Peng and C. M. Che, unpublished work.19 R. B. VanAtta, C. C. Franklin and J. S. Valentine, Inorg. Chem.,20 W. Zhang and E. N. Jacobsen, J. Am. Chem. SOC., 1990,112,2801.21 R. Irie, Y. Ito and T. Katsuki, Synlett, 1991, 265.22 W. M. Schubert and J. R. Keeffe, J. Am. Chem. Soc., 1972,94,559;K. Yates, R. S. Mcdonald and S. A. Shapiro, J. Org. Chem., 1973,38,2460.23 R. A. Moss, Carbenes, eds. M. Jones, jun., and R. A. Moss, Wiley,New York, 1973, vol. 1, p. 268.24 Y. Ogata and I. Tabushi, J. Am. Chem. Soc., 1961,83,3440.New York, 1967, vol. 1, p. 137.J. Appl. Crystallogr., 1989, 22, 384.Chem. Soc., 1990,112,2801.Soc., Chem. Commun., 1991,468.1984,23,4121.Received 14th August 1995; Puper 5/05430C414 J. Chem. SOC., Dalton Trans., 1996, Pages 40541

ISSN:1477-9226    

DOI:10.1039/DT9960000405

出版商:RSC    

年代:1996

数据来源: RSC