Cationic Phosphine-Gold(I) Catalysis for C-C Forming Reaction with C C ~ Can relativistic effects rationalize its reactivity? ~

Transcription

1 iterature Seminar (D2 part) (wed) Wataru Itano (D2) page 1 Cationic Phosphine-Gold(I) Catalysis for C-C Forming eaction with C C ~ Can relativistic effects rationalize its reactivity? Carbometallation is powerful C-C bond formation although stoichiometric metal is needed. M M (M = i, MgX, Cu, Zr etc.) outstanding example MDS. TF/tol 1/1, -78 C; tbui (4 eq); AcO 30-40% A.G. Myers et al. (JACS 2006 Catalytic variant of this transformation is highly attractive cat. M lectorophilic late transion-metals (easily forming -complex) might be suitable for addition. But standard carbon (enolate etc.) is difficult to apply (oxi./red. stable but electrophic metal is desirable) problem : oxidative coupling of substrate etc. ecently some transition metal catalysts (In III, I or III, Pd II etc) are realized for this carbon addition. Among them, [ 3 P- I ] is one of the most powerful catalysts. F. Dean Toste B.Sc. and M.Sc. / University of Toronto, Canada (Prof. Ian W. J. Still) Ph.D. / Stanford University (Prof. Barry M. Trost) asymmetric alkylation (Pd), cycloisomerization (Cpu + ), some total syntheses 21 papers (17 JACS! ) Post-Doctoral Fellow / Caltech (Prof. obert. Grubbs) Assistant Professor / University of California, Berkeley Associate Professor / University of California, Berkeley e utilizes relativistic effect to explain unique reactivities of gold.?? D. J. Gorin and F. D. Toste (Nature 2007, 446, ) < Contents > 0. Preface (p2) 1. Thoretical chemistry of Gold 1-1. elativistic effects (p3) 1-2. Other theoretical aspects (p4) 2. addition toward C=C 2-1. eteroatom (discovery of [ 3 P(I)] + ) 2-2. Theoretical chemistry of cationic phosphinegold(i) 2-3. Carbon ((I) vs (III)) 3. eaction after addition (via carbenoid) 3-1. Generation of cationic intermediates 3-2. Investigation of cationic intermediate (p5) (p6) (p7-8) (p9) (p10)

2 0. Preface > (Z = 79) I (d10) --- [Xe] 4f 14 5d 10 6s 1 ( I --- [Xe] 4f 14 5d 10 6s 0 ) (π-acceptor) I X? linear, two-coordinate > intrinsically -electrophilic 14e (σ-donator) first recognized in heterogeneous catalyst Period 6 Group 11 Cu Ag Ir Pt g III III X 16e (d8) X X planar, tetra-coordinate page 2 G. J. utchings (J. Cat. 1985, 96, 292.) then extend homogeneous catalyst (-O, -N, -Ar) (Na[Cl 4 ], Cl 3, Cl) O O = O [] = cationic phosphine-gold(i) (Toste`s initial work on Gold) (is understanding from experiments) 3 P I X 1. strong ewis acidity (compared with other -electrophilic late transition-metals) 2. potential to stabilize cationic intermediate > elativistic effect should be considered when investigating (calculating) the electronic structure of heavy atoms (> 5th-row) In (Z = 79), relativistically expected 1. contracted 6s orbitals 2. expanded 5d orbitals (stabilized energically) UMO explains these characters. in (I) (destabilized energically) > To simplify Toste`s work OMO in (I) (with alkyne) "alkynophilic acid" relativistic 6s contraction explains ewis acidity relativistic 5d expansion might stabilize further intermediate (hopefully) generation of further intermediate; functionalization (see section 3) (-carbenoid?) direct addition of carbon to alkyne (functionalization of carbenoid) product (see section 2)

3 1. Theoritical chemistry of Gold 1-1 elativistic effects > quantum mechanics + special relativity Schrodinger`s equation (speed of light : c is infinite) molecular orbital calculation structure of electrons page 3 the average radial v of the 1s electrons v = Z au Z: atomic number (c = 137 au) In heavy atom (Z > 4-50), v has significant value relative to c consideration of special relativity Dirac`s equation (c is finite) > one basic consequense of special relativity The term "relativistic effects" refers to any phenomenon resulting from the need to consider velocity as significant relative to the speed of light. m m: corrected mass m 0 : non-relativistic (rest) mass mass increases towards infinity as a body's v approaches c > effects ffect 1: The elativistic Contraction Bohr radius: (supported by caclulation) (expected r for valence s) Cu(4s) Ag(5s) r [au] (6s) 3 P. Pyykko et al. (Acc. Chem. es. 1979, 276.) P. S. BAGUS (Chem. Phys. ett. 1975, 408.) contraction of the 1s and all s and p orbitals. why so contracted around Z ~80? Stabilization of orbital energies Practically, contraction is only significant for elements in which the 4f and 5d orbitals are filled 78Pt 80g electrons are closer to the nucleus; have greater ionization energies. (supported by caclulation) F (non relativistic) DF (relativistic) ps (non lanthanide) (experimental values)

4 ffect 2: The elativistic Self-Consistent xpansion The d and f orbitals are not contracted. (higher angular momentum, seldom descend to nucleus) better shielded by contracted s and p orbitals Instead, see a weaker nuclear attraction page 4 xpansion of d and f orbitals Destabilization of orbital energies ffect 3: The Spin-Orbit splitting relativistic effects 6s orbitals contracted 5d orbitals expanded stabilizing destabilizing (and spliting) > these effects are reflected in MO calculation P. Pyykko et al. (Acc. Chem. es. 1979, 276.) 1-2 Other theoretical aspects > aurophilicity the tendency for interactions to be stabilizing on the order of hydrogen bonds (might be important for neutral complex (AgX etc..)) > [Me 2 I ] not particularly nucleophilic relative to the corresponding Cu I (and Ag I ) complexes.. Nakamura et al. (J. Am. Chem. Soc. 2005, 127, 1446.) > Me 2 III ( = Me or allyl, = PMe 3 ) reductive elimination is relatively disfavoured as well. I and III complexes do not readily cycle between oxidation states. (of course exception exists) ( + from experiments) tolerate both oxygen and acidic With its unique properties strongly influenced by relativistic effects, theoretical chemists have much attention to gold. review (pp 4424) P. Pyykko (Angew. Chem. Int. d. 2004, 43, 4412.) one can regard the moiety [P 3 ] + as a σ-acceptor in analogy to +.

5 2. addition toward C C quite a lot! review page 5 A. S. K. ashmi (Angew. Chem. Int. d. 2005, 44, ) A. S. K. ashmi and G. J. utchings (Angew. Chem. Int. d. 2006, 45, ) A. S. K. ashmi (Chem. ev. 2007, 107, ) D. J. Gorin and F. D. Toste (Nature 2007, 446, ) 2-1 eteroatom > initially III halide (intramolecular) (intermolecular) (anhydrous) Pd II unsatisfactory results > cationic phosphine I Utimoto. K. et al. (eterocycle. 1987, 96, internal --- regio mixture, terminal --- K[(CN) 2 ] is Na[Cl 4 ] quickly reduced to metalic (TON >50) Utimoto. K. et al. (J. Org. Chem. 1991, 96, 292.) J.. Teles et al. (Angew. Chem. Int. d. 1998, 37, 1415) in situ generation of [- I ] + Me + MeO (continuous streaming) (1 eq) Ph 3 PMe (X mol%) MeSO 3 (10X mol%) C MeO OMe < terminal alkyne > less steric hinderance for (Markovnikov) TON up to 50000! ( mol%), TOF up to 5400 h -1 (cf g II quickly reduced to metalic g (TON ~100)) [- I ] + the initial TOFs [h -1 ] : Ph 3 As (430) < t 3 P (550) < Ph 3 P (610) < (4-F-C 6 4 ) 3 P (640) < (MeO) 3 P (1200) < (PhO) 3 P (1500) electron-poor ligands lead to an increase in activity, but the stability decreases. [Ph 3 P I X] the initial TOFs [h -1 ] : I - (2) < Cl - (7) < NO -3 ~ CF 3 COO - ~ C 3 SO -3 (700) progresses from soft to hard anions + < internal alkyne > less steric hinderance for Ab initio experimental data cis-auration intuitively trans-auration acceptable 1,3 hydrogen migration; bond rotation theoretically cis-auration

6 2-2 Theoretical chemistry of cationic phosphinegold(i) page 6 > [ 3 P I ] + + P 3 far more covalent robust 1) [ I 3 P ] in reaction 2nd P 3 is 2) P 3 (I) + is a large, diffuse cation sharing positive charge with the phosphine ligand, one might expect orbital rather than charge interactions in binding a second ligand. "soft" 6s orbital of [ 3 P I ] + can further accept electrons keep strong ewis acidity (contracted 6s) Cl [X 2 III ] + + P3 not investigated P. Schwerdtfeger et al. (Inorg. Chem. 2003, 42, 1334.) > Stability of [ 3 P I ] + + 1) with several ligand stability [kj/mol]: [Me 3 P I ] + + C 2 Cl 2 (+63) < 2 O (+44) < acetylene (+38) < MeO ~ 1,4-dioxane (+24) < propyne (+18) < TF (+2) < 2-butyne (0) < Me 2 S (-18 ) < Ph 3 P (- 114) carbophilic rather than oxophilic J.. Teles et al. (Angew. Chem. Int. d. 1998, 37, 1415) substituted alkynes are better ligands than MeO or dioxane 2) alkyne vs alkene xperimentally, reactivity of is > W. Koch et al. (J. Phys. Chem. 1996, 100, 12253) V. M. ayon et al. (J. Phys. Chem. A 2004, 108, 3134) but theoretical stability is inverse ( + -alkyne) < ( + -alkene) (~10 kcal/mol) alkynes UMOs intrinsically lower than alkenes (~0.5eV) That is important for addition. > Backdonation from [ 3 P I ] + 1) to alkyne /alkene (by calculation) Backbonding to antibinding orbital (of alkene / alkyne) is poor (smaller than Cu) render alkyne / alkene more electron deficient 2) to carbene (their explanation, not by calculation?) Backbonding to antibinding orbital also might be poor but backbonding (from I 5d) to lower-energy (than antibonding) non-bonding p-orbitals (of carbene) might be suitable relativistically expanding (destabilizing) This can stabilize carbenoid intermediate in the I catalyzed reaction

7 2-3 carbon > ( = β-keto ester) page 7 (J. Am. Chem. Soc. 2004, 126, 4526) 5-exo-dig terminal alkyne only #1 [Ag I ] + weak ewis acidity #2 [ 3 PAg I ] + insufficient #3 [ III X 3 ] sufficient ewis acidity (?) but undesired path #4 [ 3 P I X ] insufficient #5 [ 3 P I ] + sufficient ewis acidity #6 [(NC) 2 I ] + insufficient cationic - I - mono-phosphine? vs Ag --- relativistic contraction of s orbital? [ I ] + vs I --- aurophilicity (?)? I vs III --- unknown (for regio, see ( = Ar-))? vs Pt --- not mentioned (possible?) nucleophilic attack on a (I)-alkyne complex by enol trans-auration formation of a -enolate followed by a cis-carboauration cis-auration D [] D [] Trans-auration (mechanism A) Now generally accepted. MeO 2 C 5-endo-dig (Angew. Chem. Int. d. 2004, 43, 5350) (1,5-enyne) Me O [ I ] + 5-endo-dig MeO 2 C Me O internal alkyne OK > usually prepared in situ 3 P I Cl + Ag I X [ 3 P I ] X 3 P I Me + X (X = OTf, SbF 6, BF 4 etc) [( 3 P I ) 3 O]X + X ( = 3 P)

8 > ( = Ar-) page egioselectivity is inversed between (I) and (III) with terminal alkyne, (only intrinsical regio?) M. T. eertz et al. (ur. J. Org. Chem. 2003, 3485) (10 eq) [(III)] n+ [(I)] + (10 eq) + (Z/ = 100/0) Ph 3 PCl/AgBF 4 ineffective Cl 3 / 3AgBF 4 (5 mol%) 37 (~60%) + 39 (10%) 60 C, 16h (Z/ = Ar-[] might be unlikely instead of electrophilic activation of alkyne (III) slightly activate carbonyl? (2 eq) [Cl 3 ] 2 2,6-lutidine Ph unstable TF 50 C, 5h 82-94% > I vs III ( = -C=O) Y. Fuchita et al. (J. Chem. Soc., Dalton. Trans. 2001, They said "oxophilic III species" and "π-philic I species" (or Cl 3 + TF) [(III)] [(I)]X 1,2 hydride shift via gold carbenoid V. Gevorgyan et al. (J. Am. Chem. Soc. 2005, 127, 10500) (my opinion) Basically both (I) and (III) are π-philic But (III) is slightly more oxophilic than (I) (summary so far) 2 7 a lot! ow to generate vinyl- ( 1 = ) ( 2 = ) (endo/exo) (endo/exo) same position several electrophiles same position 12 9 This section ( = N, O, C, = ) ( = S, = allyl, silyl etc.) Y. Yamamoto et al. (Angew. Int. 2006, 45, 4473.) (O. 2007, 9, 4081.) ( = O, = benzyl, iminium). Zhang (JACS 2005, 127, 16804) F. D. Toste et al. intramolecular carboalkoxylation (JACS. 2006, 128, 12062) different position Next section (Toste`s plan) new reaction? relativistically expanding 5d orbitals of might stabilize cationic intermediate by backdonation

9 3. eaction after addition (via carbenoid) page 9 different position Generation of cationic I -NC complexes are known can catalyze cyclopropanation of styrene with ethyldiazoacetate S. P. Nolan et al. (Angew. Chem. Int. d. 2005, 44, vinyl species was proposed to have significant carbene character on the basis of NM, X-ray, and calculations ( ---> Cr(CO) 5 ) cationic intermediate [5 6] might exists. G. aubenheimer et al. (Organometallics 2002, 21, 3173) different position 13 endo ,2- -migration initial work of Toste (J. Am. Chem. Soc. 2004, 126, 10858) same intermediates (14-16) was proposed with I Nieto-Oberhuber, C. et al. (Angew. Chem. Int. d. 2004, 43, 2402) (Chem. ur. J. 2006, 12, 1677.) Furstner, A. et al. (J. Am. Chem. Soc. 2004, 126, 8654) complete conversion, but substantial amount of decomposition. 5% Cl3 with 15% AgOTf pseudoeqatrial (16) (14 15) stereospecific might lower the barrier to cationic intermediate by backbonding. "expanded 5d" With (III), analogous intermediates were proposed. Pt(II) shows similar reactivity(relativistic effect also influense Pt) activation of alkynes Anyway... carbenoid or cationic? cationic (I) --- even in the presence of strongly donating ligands, such as phosphines Pt(II) --- simple salts or CO complex reactivity tuning, stereoselectivity

10 3-2 Investigation of cationic intermediate different position page 10 O 5-exo O O O C-C bond formation (J. Am. Chem. Soc. 2005, 127, 5802) Original autenstrauch rearr. (J. Org. Chem. 1984, 49, 950) metal carbene intermediate proposed "a method for generation of metal-carbenoid" Toste`s case chirality transfer not -carbene (21) A.. de era (J. Am. Chem. Soc. 2006, 128, 2434) DFT calculation predicts helically chiral intermediate = (19) (20) = Nazarov like cyclization cyclization from cationic vinyl- (9 or 11) might predominate carbenoid or cationic? cationic = (19) on a fast time scale (intramolecular reaction) = (21) toward highly carbenoid character (J. Am. Chem. Soc. 2005, 127, 18002) cis favored 1) stereochemical information was not conserved. "carbenoid" might be concerted mechanism

11 PivO ' 2) page 11 3) Ar' Anyway... carbenoid character might dominates Ar' high ee even linear geometry of I further reaction would be developed. X mono cationic? Ar PivO ' bifunctional? dicationic? > to conquar demerit of linear coodination geometry of I for ee (Science. 2007, 317, 496) standard chiral phosphine poor ee (<10%ee) (+ + : known as chiral Bronsted acid only PPh 3 Cl or Ag-6 or : no dinuclear I less polar solvent best ee depends on the proximity of the counteranion to the cationic gold match-mismatch pairing between chiral phosphine and chiral counteranion observed in other systems. might extend standard transition metal catalysed process cf) hydroamination of allene with chiral phosphine gold (J. Am. Chem. Soc. 2007, 129, 2452) < summary > I 6s contraction 5d expansion strong ewis acidity (Nature 2007, 446, ) backdonation for carbenoid (with alkyne) carbon Conia-ne (JACS 2004, 126, 4526) (Angew 2004, 43, 5350) Silyl-enol (Angew 2006, 45, 5991) ow to generate propalgyl claisen. (JACS 2004, 126, 15978) ring expansition (JACS 2005, 127, 9708) etc. 4 carbon alkoxycarbolation (JACS 2006, 128, 12062) 2 3 ow to proceed cycloisomerization (JACS 2004, 126, 10858) autenstrauch rearr.(jacs 2005, 127, 5802) different mode 5 ow to generate acetylenic Schmidt (JACS 2005, 127, 11260) cyclopropanation (JACS 2005, 127, 18002) 6 1,2-shift, cyclization rearrangement etc.. product oxidative trap (JACS 2007, 129, 5838) other works about (with allene) (cycloaddition) (asymmetric variants)