Organometallics Study Meeting Part 4. Reactions of Organometallic Complexes
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1 rganometallics Study eeting art 4. eactions of rganometallic Complexes 1. asics 2011/4/28 oshino(d1) igand Exchange Dissosiative echanism ' n n-1 ' n-1 Fe(C) 5 (18e):hoto-promoteddissociationofigand Associative echanism Commonind 8 squareplanar16ecomplex(() 4 etc.) eactionratedoesnotdependonthe[']. T X T X X T retention TransEffect:EffectofTonrateofligandexchange C,CN,C 2 4 > 3, >C 3 >C 6 5, >r, >N 3, 2 Trans nfluence: arameter indicating how weak T makes -X bond,c 3,C 6 5 > 3,CN >C,C 2 4 >,r > >N 3, 2 Evaluated using t() complex -onding ligands show strong trans effect by stabillizing 5-coordinated structure. X Transmetallation n -X-' n -'X = transition metal '=gr,' 2,Sn' 3, 2 Zretc. X=halides,Acetc xidative Addition General A xidation number increases by 2. n (m)a- n (m) Coordination number increases by 2. ow valent, coordinatively unsaturated, electron rich complexes are active in oxidative addition. Vaska'scomplex[trans-r(C)(h 3 ) 2,r(),] 2 [Ni(0),(0),t(0),d 10,14e] xidativeadditionto 2 t 2 t t energy level increases when -t- bond bends(upto90 ). t U (6s, 6p) rbital nteractiion t (5d) identate phosphine ligand improve reactivity of oxidative addition. 1 *
2 xidative Addition to C-, C-C ond t C 2 C(C 3 ) 3 C(C 3 ) 4 t horc 4 t =h,c3 t(), t(0),d 10,14e t(), * h e 3 h(), h 2 * h e 3 h(), * h e 3 h(), xidativeadditiontoc-xondthroughs N 2echanism n -X n X [ n -] X etal:(0),t(c 3 ) 2,r()etc. alides:alkyl-x,allyl-x(sp 3 C-X) (0),d 10,14e D r Even18ecomplexcanreactthtoughS N 2mechanism. r r(),d 8,18e C C 3 D r C C 3 r(), r r h 3 D h 3 Stereo nversion at C Center. Trans Addition Allyl-X shows higher reactivity and -ally-complex is formed. Cy 3 Cy 3 (0),d 10,14e Ac Cy 3 Cy 3 (0),d 10,16e Ac Cy 3 Cy 3 Ac (), Cy 3 Cy 3 Ac (), xidativeadditiontosp 2 C-Xbond X X X trans isomer (0),d 10,14e eactivity X:>r>> : Electron Withdrawing Group > Electron Donating Group Alkenyl-X gives stereo-retained product. xidativeadditionthroughadicalechanism Alkyl-rt(Et 3 ) 2
3 1-3. eductive Elimination General A etro reaction of oxidative addition. n (m) n (m)a- 3-membered transition state. eactivity: Complex with lower d-orbital energy level shows higher reactivity. high Co(), h() Ni(), () are good species for reaductive elimination. low eactivity(igands) Alkyl(e<Et<nr<nu)<Aryl,Alkenyl< nly cis-ligands undergoes reductive elimination. Elimination of alkyl group requires strained TS. n Aryl, Alkenyl: -orbital can particilate n the formation of 3-membered TS. < < ydride() has spherical symmetry and form TS without strain, eductive Elimination from Group 10 metal() Complex ' (a) Dissociation path -' '(14e) are difficult to generate, but highly reactive to reductive elimination. cis- 2 -(alkyl) 2 ' (b) Direct path -' 2 ost complexes ' (c) Assosiation path Niiseasytoform 5 coordinated complexes. -' 3 ostnicomplexes 1-4. nsertion and Elimination C nsertion and Elimination n C n C n andcmustbecis. eversible process. Attackof toc'su. 3
4 CdoesnotmoveandrearrangetoCgroup. C C 3 C C CC 3 C CC 3 n n n C C C C C C C C C n(), n(),d 6,16e n(), =Cor 3 ore -donating, nucleophilic group have large K. C h h3 h(), K C h h3 h(),d 6,16e Electronwithdrawing ligand more strongly coodinate to. Espcially, - bond is far stronger than -C bond. Also C insertion to -C bond cannot proceed. Et,nr,n hc 2 C 2 C 3 pc 6 4 C 2 h C 2, K >50 ~17 3.4± <0.05 <0.02 nsertion of Alkene, Alkyne and -ydride Elimination A n C A D nsertion A D C -Elimination n nsertion A These processes are reversible. Alkyl complexes are easy to undergo -elimination. n -Elimination n Co Co Co e 3 CD 3 CD CD 3 3 CD CD 3 3 e 3 CD 3 D 3 C CD 3 Co(), Co(),d 6,16e Co(), Co(),d 8,18e Co nly -hydride eliminated product was observed. echanism * Nb * Nb(),d 2,18e * * Nb * Nb * Nb(),d 2,16e eaction with () Complex C 3 h 3 (), h 3 C 3 eactionproceededdissociatively.cationic(dppe)(ac)(c 3 CN) complexshowshigherreactivity. C 3 4
5 1-5. Cycloaddition Cycloaddition of Schrock Carbene e Ti Al e Ti(V),d 0,16e DA Ti C 2 Ti(V),d 0,16e Tebbe eagent Schrock Carbene [2 2 ] Ti Ti(V),d 0,16e The same reversible process is the key for olefin methathesis. Ti Ti(V),d 0,16e 2 C 2 Ti= xidative Cyclization ±C 2 4 Zr Zr h h Zr(V),d 0,16e Zr(),d 2,16e h h Zr Zr(V),d 0,16e ow valent alkene, alkyne complexes undergo this reaction eactions at igands cleophilic Attack to etal-alkene Complexes n 2 to 1 ()-alkene complexes have been well studied. : Alcohols, Amines, Enolates n cleophilic attack occured on opposite face to metal. cleophilic attack occured at more substituted carbon. etal with high oxidation state eactions of Allyl igands 1 -AllylComplexesshownucleophilicreactivity. h 2 h h 2 2 C 6 F 5 C 6 F C 6 F 5 5 h 2 h 2 h 2 (), (), (), 5
6 3 -AllylComplexesshowelectrophilicreactivity. (b) (a) n n : alonates, Amines n (c) (b) n n : Grignard eagents (a) (c) n Example of ath(c) ow valent (0) is unstabilized by -donating N ligand. e 2 N h N e 2 h e 2 N NaC(CN)(C 3 ) 2 N e 2 h h C(CN)(C 3 ) 2 ardnucleophiles,ei,,favorpath(c). etals which disfavor low valent states, Zr(V), W(V), t(), tend to react through path(c). eactions of C igands n C n The weaker -backdonation, the higher reactivity of C group. h 3 base h 3 t C t t t h 3 h 3 t(), t(), t(), = alcohols, amines emovalofcbytan Fe(C) 5 (C 3 ) 3 N Fe(0),d 8,18e (C) 4 Fe ( 3 C) 3 N Fe(0),d 8,18e C 2 Fe(C)4 N(C 3 ) 3 Fe(0),d 8,18e 2. omogenious Catalysis 2-1. somerization of lefin h() 2 N 2 N S h S reductive elimination N 2 h N2 2 N ligand exchange 2 N Takasago's enthol Synthesis NEt 2 Catalytic Cycle 96-99% ee [((S)-NA)h ] NEt 2 N 2 h N2 oxidative addition toc-bond N 2 h N2 6
7 2-2. ydrogenation h(h 3 ) oxidative addition h h3 S ligand exchange S h h3 h catalyzed hydrogenation proceeds through dihydride mechanism h S h3 reductive elimination Catalytic Cycle h h3 S nsertion h h3 S 2-3. ydroformylation Coorucat. C/ 2 C C inear product is more valuable. h-h 3 systemgivesgoodselectivity. rocessusingh 3 assolventexist. 2 h C 2 C 2 C 3 C 2 oxidative addition C C 2 C 2 C 3 2 h C insertion h(c) 2 reductive elimination Catalytic Cycle 2 h C C 2 C 2 C 3 C d 8,18e 2 h C d 8,18e insertion C 2 C 2 C 3 2 h C C 7
8 2-4. oechst-wacker xidation 2 (cat) Cu 2 (cat) 2 21/2 2 2, 2 2Cu 2 2Cu (0) () Catalytic Cycle () 2 2 roposal athways to Give roduct FromC 2 () C FromA () () A () (0) 3 () 2 (0) 3 eactionusingd 2 insteadof 2 gavenodeuteratedaldehyde. So pathway of non--catalyzed isomerization from was denied Carbonylation of ethanol C 3 h cat.,c C 3 C C 3 C 3 C C 3 C non-metallic cycle C C C h C h C oxidative addition reductive elimination rganometallic Cycle C CC 3 h C insertion CC 3 h C d 6,16e C 2-6. ther eactions eck eaction, Cross Coupling, lefin ethathesis etc. 8
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