C-H Bond Activation Using Homogeneous Transition Metal Catalysts

Transcription

1 C- Bond Activation Using omogeneous Transition tal Catalysts Kevin Campos March 1, 1996 Reviews: R. Bergman, Acc. Chem. Res., 1995, 28, 154 R. Crabtree, Chem. Rev., 1985, 245 M. Brookhart, J. rganomet. Chem., 1983, 250, /29/96 4:25 PM

2 Some Interesting Early Examples Co 2 (C) 8, 238 C, C Ph S. oriie,bull. Chem. Soc. Jpn. 1960, 23, 247 i(cp) 2, 135 C i Ph Cp J. Kilman, M. ubeck, JACS 1963, 85, /29/96 4:30 PM

3 Early Examples of xidative Addition P 2 P 2 P Ru 2 P Ru 2 P P2 2 P P2 d 8, 16 e - d 6, 18 e - P 2 P 2 2 P Ru 2 P Ru 2 P P2 2 P P2 J. Chatt, J. avidson, JCS 1965, 843 P 2 P Ru 2 P = P2 2 P P 2 P Ru Ru 2 P P P2 P 2 P 2 Intramolecular cyclometallated product determined to be a dimer by X-ray crystallography F. Cotton, JCS CC, 1974, /29/96 4:32 PM

4 Intramolecular C- Bond Activation PPh 3 Cl d 8, 16 e -, C 6 12 Cl PPh 2 d 6, 18 e - M. Bennet, JCS CC 1967, 581 Et 3 P Et 3 P Pt C 2 C 3 C 2 C 3 - C 4 Et 3 P Et 3 P d 8, 16 e - d 8, 16 e - Pt G.M. Whitesides, rganomet. 1982, 1, 13 Cl d 6, 18 e - t-bu P P t-bu t-bu t-bu Et t-bu P P t-bu Cl t-bu t-bu d 6, 16 e t-bu P P t-bu Cl t-bu t-bu d 8, 16 e - C. Crocker, JCS CC 1979, 498 (PPh 3 ) 3 (d 8, 16 e - ) TF, - 2 PPh 2 C 3 PPh 2 P h2 P PPh /29/96 5:07 PM PPh 3 d 8, 16 e - Cl Cl Ph 2 P PPh 2 3 C PPh 3 d 6, 18 e -. Milstein, ature, 1993, 364, 699

5 Intramolecular C- Bond Activation C- agostic interaction observed in X-ray structure of iridium-methylquinoline complex: (cod)(pph 3 ) 2 d 8, 16 e - C 3 2, 25 C C PPh 3 2 d 6, 18 e - R. Crabtree, Inorganic Chem 1985, 24, 1986 xidative addition was observed in X-ray structure when benzoquinoline was used: (cod)(pph 3 ) 2 2, 25 C 2 PPh 3 d 6, 18 e - R. Crabtree, JCS CC 1985, /29/96 5:15 PM

6 Potential ifficulties in Intermolecular C- Bond Activation Cp 2 W 2 d 2, 18 e - hυ, C 6 6 Cp 2 W Cp 2 W(Ph)() d 4, 16 e - d 2, 18 e - Cp 2 W 2 hυ 4 Si Cp W W Cp C 2 Si 3 Cp 2 W 2 hυ Alkanes Cp W W Cp xidative addition into a variety of aryl C- bonds was observed Stronger C- bonds were unreactive, causing oxidative additon into Cp- Green, JCS CC 1972, 1114 Green, JCS alton Trans. 1979, /29/96 5:18 PM

7 ehydrogenation of Alkanes Transfer dehydrogenation of alkanes: 2 S 2 (PPh 3 ) t-bu L L d 7, 19 e - d 7, 19 e t-bu C 3 R.. Crabtree, JACS 1979, 101, 7738 R.. Crabtree, JACS 1982, 104, 6994 Catalytic dehydrogenation of alkanes: hυ, 7 days! 2 (F 3 CC 2 )(PCy 3 ) mol% PCy 3 F 3 C PCy 3 hυ F 3 C PCy 3 PCy 3 d 6, 18 e - d 8, 16 e - Reaction may proceed via coordinatively unsaturated iridium complex 07 2/29/96 5:22 PM R.. Crabtree, JCS CC 1985, 1829 R.. Crabtree, JACS 1987,109, 8025

8 σ-bond tathesis Proposed for Some rganolanthanide Complexes C 2 -C 4 C 4 Lu * Lu C 3 * C 4 C 4 Lu * C 3 3 C 3 C Lu Lu 3 C C * * 3 ther straight-chain alkanes were also added, but quickly decomposed to yield the alkene and metal hydride 08 2/7/96 11:22 PM G.Parshall, P. Watson, Acc. Chem. Res. 1985, 18, 51

9 Intermolecular xidative Additions via Photochemically Induced Complex [( 5 C 5 ) Cl 2 ] 2 1) PPh 3 2) LiEt 3 B hυ, C 6 6 hυ, C 3 C Ph 2 P R. Bergman, JACS 1982, 104, P hυ 3 P d6, 18 e - d8, 16 e - 2 radiation to coordinatively unsaturated complex 09 2/8/96 8:13 AM Similar photolysis/oxidative addition has been reported for Cp * (C) 2 - W. Graham, JACS 1982, 104, 3723

10 chanistic Studies [( 5 C 5 ) Cl 2 ] 2 1) P 3 2) LiEt 3 B 3 P hυ, R- R R = Ph, c-ex, neopentyl Characterization of complexes by MR -18 ppm) and mass spectrometry Ruling out Free Radical chanisms:. R + Cp*(PR 3 ) 2. + R Cp*(PR 3 ) Cp*(PR 3 ) R. Cp*(PR 3 )()(R). o () exchange observed between iridium-hydride and C P hυ, C 6 12 C 6 11 R. Bergman, JACS 1983, 105, /29/96 6:47 PM

11 chanistic Studies: Lending Proof Against a Free Radical chanism Cp*(PR 3 ). Cp*(PR 3 ) 2 R + Cp*(PR 3 ) Cp*(PR 3 ) + R R +. Cp*(PR 3 ) Cp*(PR 3 )()(R) idium complex reacts three times as fast with Ar- than with Ar-C 3 3 P hυ C 3 3 C C 3 2 C C 3 3 C 5.5 : /29/96 6:48 PM R. Bergman, JACS 1982, 104, 352

12 chanistic Studies: Lending Proof Against a Free Radical chanism Ruling out Free Radical chanisms: Cp*(PR 3 ). R + Cp*(PR 3 ) 2 + R Cp*(PR 3 ) Cp*(PR 3 ). R + Cp*(PR 3 ) Cp*(PR 3 )()(R) o crossover observed between deuterated and non-deuterated hydrocarbons 3 P hυ Cyclohexane-d 12 (C 3 ) 4 C 3 P C 2 C(C 3 ) P C 6 11 R. Bergman, JACS 1983, 105, /8/96 8:34 AM

13 Relative Rates of Reaction with Various ydrocarbons 3 P hυ, R- R ydrocarbon Benzene Cyclopropane Cyclopentane eopentane Cyclohexane Cyclodecane Cyclooctane Ethylene Propane (1 :2 ) Pentane (1 :2 ) Rel. Rate () : 1 10 : 1 Rel. Rate () : 1 59 : 1 R. Bergman, JACS 1983, 105, /8/96 8:38 AM

14 Little Kinetic Selectivity, But igh Thermodynamic Selectivity 3 P hυ C 5 12, 6 C Cp * Cp * 110 C / C 5 12 R. Bergman, JACS 1983, 105, /8/96 8:40 AM

15 We Can Activate the C- Bond, But Can We Functionalize the Alkane? 3 P hυ, R- R CBr 3 Br R gcl 2 RBr Br 2 RgCl Br Cl R. Bergman, JACS 1983, 105, /29/96 5:23 PM

16 Can We Activate thane? xidative Additon Reversible at 140 C: 3 P C K eq = P + Applications Towards Activation of thane: 3 P 20 atm C 4 c-c 8 16, 145 C 3 P C 3 Thermodynamic sink R. Bergman, Science 1984, 223, /8/96 8:47 AM

17 Similar Chemistry bserved With odium 3 P hυ, R- CBr 3 Br 2 R Br R Br Br RBr The Advantages igher selectivities for 1 vs 2 C- bonds observed irect conversion to alkylhalides from haloalkyl complexes by treatment with Br 2 The isadvantages ydridoalkyl complexes only stable at temperatures below -20 C 17 2/8/96 8:55 AM R. Bergman, Pure & Appl. Chem. 1984, 56, 13

18 An Interesting () Exchange bserved in Alkyliridiumdeuterides 130 C C 6 6, + euterium exchange was observed between hydride position and α-position of cyclohexane As the reaction progressed, the rate of combined disappearance of cyclohexyl complexes decreased For reductive elimination, k obs (C 6 11 ) / k obs (C 6 11 ) = 0.7 (Inverse Isotope effect) Similar scrambling was observed in hydridomethyl iridium complex 18 2/8/96 9:12 AM R. Bergman, JACS 1986, 108, 1537

19 Inverse Isotope Effect? PPh 3 PPh 3 k 2 C 6 6 Reductive elimination/oxidative addition consistent with observed kinetic data except for inverse isotope effect Intermediate σ-complex postulated to explain both inverse isotope effect A deuterium exchange Inverse isotope effect observed for various alkyl/aryl hydride complexes 19 2/8/96 9:21 AM W.. Jones, JACS 1985, 107, 620 J. orton, JACS 1989, 111, eineky, JACS 1989, 111, 5502 R. Bergman, JACS 1986, 108, 1537

20 Attempts to Identify the Intermediate in α-c- Exchange 2 : 1 mixture of diastereomers at rhodium at -60 C -50 C 2 : 1 mixture of diastereomers retained! -30 C 1 : 1 mixture of diastereomers obtained after equilibration Proposed explanation for stereospecific exchange R. Bergman, JACS 1986, 108, /8/96 9:31 AM

21 Can We bserve β-c- Exchange? * C 3-80 C * C 3-30 C C 2 * -80 C * C 3-30 C C 2 * C 2 * Reactions run at 0.025M in toluene-d 8 Perdeuterated ethyl deuteride complex was doped with ethane in toluene-d 8 to show no ethyl hydride Perdeuterated ethyl deuteride complex and ethyl hydride complex mixed together showed no crossover products 21 2/8/96 9:43 AM R. Bergman, JACS 1986, 108, 7332

22 Transient tal-alkane σ-complex bserved Using IR Flash Kineitc Spectroscopy C C hυ, Kr K C Kr C 4 C C 3 I.R. C cm -1 σ-complex 1946 cm -1 C C cm -1 C C hυ, Kr K C Kr C(C 3 ) 4 C 1946 cm -1 σ-complex 1947 cm -1 C(C 3 ) 3 C C(C 3 ) cm -1 tal-alkane intermediate grows at a rate equal to the decay of the metal-krypton complex Intermediate decays at a rate equal to the decay of the metal-krypton complex and growth of the product k / k = 25 C for oxidative addition K eq () / K eq () = 0.1 Similar results observed for cyclohexane-d 0, d /29/96 5:44 PM R. Bergman, JACS 1994, 116,

23 C- Bond Activation of Alkenes C 2 C=C 2 C 2 C 2 2 C 66 : 34 C C Benzene C 2 2 C 66 : 34 represents a kinetic product ratio of coordinatively unsaturated iridium complex with ethylene η 2 -ethylene complex is thermodynamic product of the reaction η 2 -ethylene complex cannot be an intermediate to the formation of the C- inserted complex The reaction proceeds without reversion to ethylene and the reactive iridium intermediate The η 2 -ethylene complex and the C- inserted complex are formed through unique transition states Interconversion between the two complexes proceeds through a third unique transition state 23 2/8/96 9:51 AM R. Bergman, JACS 1985, 107, 4581

24 Similar Kinetic Results Were bserved with ther tal Systems Re PPh 3 d 6, 18e - hυ, 20 C PPh 3 10 : 1 Re 2 C=C 2 d 4, 16e - C 2 Equilibration at 30 C Re 2 C d 6, 16e - C 2 R. Bergman, JACS 1986, 108, P 2 P P 2 Fe P 2 hυ, 80 C 2 C=C 2 2 P 2 P P 2 Fe C 2 P 2 9 : 1 2 P 2 P P 2 Fe P 2 C 2 C 2 d 6, 18e - d 6, 18e - d 8, 18e - Equilibration at 30 C M. Baker, L. Field, JACS 1986, 108, /29/96 5:43 PM

25 Two istinct chanisms are Proposed C 2 C 2 C C C 2 C 2 C 2 2 C C 2 C R. Bergman, JACS 1985, 107, /8/96 10:21 AM

26 Isotope Studies to efine chanism 2 C=C 2 k / k = C=C 2 () C 2 ( 2 ) () k / k = 1.38 (Cyclohexane) k / k = 1.05 (Benzene) 2 C=C 2 k / k = C=C 2 C 2 ( 2 ) ( 2 ) 2 C 2 C=C 2 C 2 vs C 2 k / k = 1.20 R. Bergman, JACS 1988, 110, /8/96 10:26 AM

27 Revised chanism Based on Isotope Studies C 2 C 2 C 2 C 2 C 2 C 2 2 C R. Bergman, JACS 1988, 110, /8/96 10:29 AM

28 An Interesting Contrast to Bergman's Ethylene Activation Studies [1,2] shift observed in rhodium aryl hydride complex: -13 C k / k = 0.37 W. Jones, JACS 1984, 106, /8/96 10:32 AM

29 η 2 - Arene Postulated as the Intermediate in Aryl- xidative Addition Two examples of an η 2 -arene-metal complex C 7 13 t-bu -20 C t-bu t-bu t-bu -12 C C 6 6 Proposed mechanism for Ar- activation based on experimental results: C 6 5 W. Jones, JACS 1984, 106, /8/96 10:39 AM

30 Isotope Studies Lend Proof Toward an η 2 -Arene Intermediate hυ, 10 C C 6 6, C 6 6 C k /k = 1.05 C 6 5 hυ, -40 C + k /k = 1.4 () 51.2 C, C () k /k = /8/96 10:44 AM W. Jones, JACS 1986, 108, 4814

31 C- Activation Using Imidozirconocene Complexes Zr t-bu Ph- Zr t-bu Ph (t-bu) 3 Si (t-bu) 3 Si d 0, 16 e - d 0, 16 e - Zr Si(t-Bu) 3 C 6 6 R. Bergman, JACS, 1988, 110, 8729 (t-bu) 3 Si Zr Si(t-Bu) 3 (t-bu) 3 Si C 6 5 C 4, 3 atm, C 6 12 (t-bu) 3 Si (t-bu) 3 Si Zr Si(t-Bu) Zr 3 (t-bu) 3 Si C (t-bu) 3 Si C C 3 Si(t-Bu) 3 Extrusion of alkane correlates with C- bond strength k (C 3 ) / k ( 3 /C 3 = 7.3), k (C 3 ) / k ( 3 /C 3 ) = 1.32 thane binding not detected in this system Standard β-elimination mechanism? C. Cummins, P. Wolczanski, JACS 1988, 110, 8731 C. Cummins, P. Wolczanski, JACS 1991, 113, 2985 P. Wolczanski, JACS 1994, 116, /29/96 5:50 PM

32 Intermolecular ydroacylation: C- Bond Activation / C-C Bond Formation 3 P Cl 3 P P 3 d 8, 16 e - 3 P 3 P 3 P P Cl 3 3 P Cl d 6, 18 e - d 6, 18 e - 3 P 3 P Cl d 6, 18 e - Sakai, Tet. Lett. 1972, Milstein, JCS CC, 1982, 1357 C C, C 2 4 (1000 psi). Milstein, rganomet., 1988, /29/96 6:03 PM

33 C- Bond Activation Using omogeneous Transition tal Catalysts R (S-Binap)(B) Cl 4, 2 5 min. C 2 Cl 2 or Acetone R R e.e. Ph t-bu 3 Si C(C 3 ) 2 PhC() t-buc() EtC() t-bu vs Favored t-bu isfavored B. Bosnich, JACS, 1994, 116, /29/96 6:06 PM

34 irected Functionalization of Aromatic C- Bonds Using Catalytic Ruthenium R 2 R 1 C Ru PPh 3 Toluene reflux 2-5 mol % R 2 Ru R 1 Y R 2 R % yld Y Si(Et) 3 C 3 C 3 Si(Et) 3 C 3 Si(Et) 3 S Si(Et) 3 Si(Et) 3 Murai, ature, 1993, 366, /8/96 11:02 AM

35 Shinji Murai oes It Again Ru 3 (C) 12 Toluene, 20 atm C 160 C, 20 h (C) 3 Ru (C) 4 Ru Ru(C) 3 Y R 42-95% yld 99:1 regioselectivity Ph Ph t-bu t-bu Murai, JACS, 1996, 118, /8/96 11:57 AM

36 Trends in the (II) Catalyzed C- Insertion Y 2 Y Y C 3 C 3 C 3 R 1 R 1 R 1 2 (X) 4 R 1 Y Ratio 2 (Ac) 4 2 (Ac) 4 2 (Cap) 4 2 (Ac) 4 2 (Cap) 4 Ac : 1 1 : 8 1 : 30 1 : : > 2 ~ Ar- > 1 Alkyl > allyl ~ aryl C- α to heteroatoms are activated towards C- insertion C- α and β to electron withdrawing groups are deactivated towards C- insertion More hindered sites undergo slower rates of C- insertion The reaction proceeds with retention of configuration at the reacting site Five-member rings are preferentially formed More basic ligands on rhodium will increase the afformentioned selectivity 36 2/9/96 10:49 AM J. Adams, Tet. Letters, 1989, 30, 1749 G. Stork, Tet. Letters, 1988, 29, 2283 M. oyle, Tet. Letters, 1989, 30, 7001 J. Adams, JACS, 1994, 116, 3296

37 chanism of (II) Catalyzed C- Insertion C 3 C 3 C 3 R E 3 C C 3 C 3 R E + 2 C 3 II Ac C 3 II R E II Ac C 3 C 3 III C 3 I 3 C C 3 III C 3 C 3 C 3 R E E III Ac R C 3 C 3 III R - E III Ac C 3 C 3 III 37 2/9/96 5:27 PM Speculation by K. Campos based on J. Adams, Tetrahedron, 1991, 47, 1765

38 C- Insertion Reactions: Applications to Synthesis C 2 C 3 C 3 (II) cat. C 3 C 3 C 3 C 3 C 2 2 (Ac) 4 C 3 1) LA 2) I C 3 3 C 1) Ts 2 2) C 3 Li C 3 3 C (+)-albene C 3 3 C 1) 2 C 3 2) PCl 2) i-pr-br, PPh 5 3 C 1) ibal C 3 (-)-β-santalene. Sonawa, J. rg. Chem. 1991, 56, /8/96 9:19 PM

39 Asymmetric C- Insertion Reactions: Applications to Synthesis endrobatid Alkaloid (251F) 3 C C 3 octanoate (cat.) 2 C 2 C 3 2 C 3 C C 3 C 3 1) LiAl 4 2) a, BnBr 3) +, 2 4) TsCl, pyr. Bn Ts C 3 Et 2 C C 3 K 2 C 3, Toluene cat. Bu 4 I, 66% 3 C C 3 3 C 3 C C 2 Et Bn 1) BsCl 2) LiMS 53% C 2 Et C 3 Bn 1) LiAl 4 2) PhSSPh / PPh 3 3) a / 3 66% C 3 C 3. Taber, JACS, 1995, 5757 C /9/96 10:56 AM Some insight on the stereochemical outcome. Taber, JACS, 1996, 118, 547

40 Asymmetric C- Insertion Reactions: Synthesis of ibenzylbutyrolactone Lignans 2 C 2 R C 2 Cl 2 R = Et Bn R 91% e.e. 89% e.e. 87% e.e. M. oyle, JACS 1991, 113, 8982 Ph 2 2 C C 2 Cl 2 63% yld. 93% e.e. (-) - enterolactone M. oyle, J. rg. Chem. 1995, 60, /9/96 5:00 PM

41 Asymmetric C- Insertion Reactions: Synthesis of eoxyxylolactone 2 C 2 Bn Bn mol%, C 2 Cl % Bn Bn Bn Bn 93% 7% 94% e.e. 45% e.e. R R vs R Favored R isfavored Postulated Conformation Leading to bserved Product 41 2/9/96 5:29 PM M. oyle, A. yatkin, J. Tedrow, Tet. Letters, 1994, 35, 3853

42 Asymmetric C- Insertion Reactions: More oyle Results A 2 C 2 C 2 Cl 2 A= C 2 C()C 3 55% (96% e.e.) 75% (97% e.e.) 99% (97% e.e.) 45% (95% e.e.) 25% (91% e.e.) 1% (65% e.e.) vs Favored isfavored Postulated Conformation Leading to bserved iastereomer 42 2/9/96 5:30 PM M. oyle, JACS 1994, 116, 4507

43 Asymmetric C- Insertion Reactions: ouble Stereodifferentiation bserved A 2 C 2 C 2 Cl 2 A= C 2 C()C 3 99% (98% e.e.) 98% (98% e.e.) 99% (98% e.e.) <1% 2% (84% e.e.) <1% A 2 C 2 C 2 Cl 2 A= C 2 C()C 3 10% (68% e.e.) 15% (82% e.e.) 63% (93% e.e.) 90% (95% e.e.) 85% (91% e.e.) 37% (57% e.e.) 43 2/9/96 5:56 PM M. oyle, JACS 1994, 116, 4507

44 Asymmetric C- Insertion Reactions: More oyle Results vs Very Favored Very isfavored The Matched Case vs isfavored Favored The Mismatched Case 44 2/9/96 5:46 PM M. oyle, JACS 1994, 116, 4507

45 Asymmetric C- Insertion Reactions: Insertion α to itrogen 2 2 (5S-MEPY) 4 C 2 Cl 2, 67% 97% e.e. M. oyle C 2 C 3 2 C 3 C 3 3 C C 3 R CuTf C 2 Cl 2 R C 2 C 3 A C 3 C 3 C 2 C 3 B C 3 C 3 Catalyst 2 (Ac) 4 2 (5(S)-MEPY) 4 CuTf, R = ipr CuTf, R = t-bu CuTf, R = Ph %A (trans : cis) 50% (3:1) 38% (5:95) 33% (1:1) 33% (9:1) 33% (13:1) %B (trans : cis) 50% (10:1) 62% (5:95) 67% (2:1) 67% (1:1) 67% (1:2) 45 2/9/96 4:54 PM G. Sulikowski, J. rg. Chem. 1995, 60, 2326