M.C. White, Chem 153 Silylformylation -209 Week of octo ber 29. 2002 terminal alkane Silylformylation of alkynes terminal sp C is selectively silylated Chaco)12(1 mol%) Formal product of MepPhSiH(I eq) SiMezph OHC H terminal alkynes with NEt(I eg), Co(29 atm opposite regioselectivity rises from isomerization under th arbon lation conditions CHr=Me RhgCo)2( mol%o ). C Em Other substituents tested: Ph, CO,R. OHC SiMe?Ph NEty(I eq), CO(29 atm OHC H sp c bearing the h,100C 85% yield ZE(70:30) When R3Si-D was used 且 Rhy(co)1 metal co clusters decompose to lower Bm时 alkenal deuterated at the R SiH CO complexes under CO pressure formyl carbon was produced >98% When deuterated alkyne was used, alkenal CO (CO武 RheSis3 as selectively (CO)3 SiR3)Rh (CO)3RhHSiR3 Rssi RasA (CO)aHh ( CO)4Rh OM1997(16)4327
M.C. White, Chem 153 Silylformylation -209- Week of October 29, 2002 Silylformylation of alkynes Me H Me H OHC SiMe2Ph CsF EtOH Me H OHC H C3H7 Me C3H7 Me OHC SiMe2Ph CsF EtOH C3H7 Me OHC H Rh4(CO)12 (1 mol%) Me2PhSiH (1 eq) NEt3 (1 eq), CO (29 atm) 2h, 100oC terminal sp C is selectively silylated 99% yield Z:E (80:20) Z-isomer is the kinetic product. E-isomer arises from isomerization under the carbonylation conditions. terminal alkynes: internal alkynes: Formal product of hydroformylation of terminal alkynes with opposite regioselectivity. Rh4(CO)12 (1 mol%) Me2PhSiH (1 eq) NEt3 (1 eq), CO (29 atm) 2h, 100oC 85% yield Z:E (70:30) sp C bearing the bulkier substituent is selectively formylated tri-substituted olefin Other substituents tested: Ph, CO2R. Matsuda JACS 1989 (111) 2332. Matsuda OM 1997 (16) 4327. Rh4(CO)12 metal CO clusters are known to decompose to lower nuclearity metal R CO complexes under CO pressure 3SiH (CO)4Rh(I) SiR3 (CO)3Rh(I ) SiR3 R' (CO)4Rh(I) R' R3Si (CO)3Rh(I) O R' R3Si (CO)3(SiR3)Rh(III) O R' R3Si H R' H OHC SiR3 CO CO R3SiH oxidative addition migratory insertion migratory insertion When R3Si-D was used, alkenal deuterated at the formyl carbon was produced >98%. When deuterated alkyne was used, alkenal deuterated at the vinyl carbon was selectively isolated (>94%)
M.C. White Chem 153 Silylformylation-210 Week of october 29, 2002 Silylformylation of epoxides cO AOSiMe2Ph note: I-methylpyrazole is essential to HSIMe2 Ph(1.2 eq), Co (50 atm) ring-opening silylformylation. w/out it n=0.1 cyclopentanol silyl ether is the main 0,1 Coco)s was also product observed. Although NEt, was tried; however yields ffective at promoting the rxn with nIng. no cIs cyclohexene, l-methylpyrazole was lower(51% based product observed. 1.82% uniquely effective at promoting silane ing-opening sily formylation over epoxide which was wide range of substrates(other amines used in 3-fold excess) CHo tried: pyridine, pyrrole, DBU failed).It I mol% that I-methylpyrazole OSiMe? Ph promotes CO incorporation, however HSIMe2Ph(1.2 eq), CO (50 atm no discussion of it's mechanism of OSiMe?Ph action is presented(perhaps it's act N 40 mol% as a ligand to the rh) CHO Murai Joc1993(58)4187 60% yield linear: branched(77: 23) Proposed mechanism CO CIRhFSiR3 exact structure HSiR3 not known AOSiMe,Ph Rh h OSiR3 epoxide ring tion CO Muria Inlet 1996414 While C
M.C. White, Chem 153 Silylformylation -210- Week of October 29, 2002 Silylformylation of epoxides Murai JOC 1993 (58) 4187. OC Rh OC Cl Cl Rh CO CO Cl[Rh] SiR3 H HSiR3 exact structure not known O O SiR3 + [RhI II] OSiR3 RhIII OSiR3 H H O RhIII H Cl Cl Cl CO [RhI]Cl HSiR3 OSiMe2Ph CHO nucleophilic epoxide ring opening stereospecific migratory insertion Proposed mechanism: O n= 0,1 OC Rh OC Cl Cl Rh CO CO 1 mol% HSiMe2Ph (1.2 eq), CO (50 atm) N N 40 mol% n= 0,1 OSiMe2Ph O H Stereospecific epoxide ring opening: no cis product observed. n = 0, 72% 1, 82% O OC Rh OC Cl Cl Rh CO CO 1 mol% HSiMe2Ph (1.2 eq), CO (50 atm) N N 40 mol% CHO OSiMe2Ph + OSiMe2Ph CHO 60% yield linear: branched (77:23) note: 1-methylpyrazole is essential to ring-opening silylformylation. w/out it cyclopentanol silyl ether is the main product observed. Although NEt3 was effective at promoting the rxn with cyclohexene, 1-methylpyrazole was uniquely effective at promoting ring-opening silylformylation over a wide range of substrates (other amines tried: pyridine, pyrrole, DBU failed).It is suggested that 1-methylpyrazole promotes CO incorporation, however no discussion of it's mechanism of action is presented (perhaps it's acting as a ligand to the Rh). Co2(CO)8 was also tried; however yields were significantly lower (51% based on silane, 17% based on epoxide which was used in 3-fold excess). Muria Synlett 1996 414
M C. White Chem 153 Silylformylation-211 Week of octo ber 29. 2002 Silylformylation" of alkenes Desired sily/formylation product CO, R]i-H acetate aldol equivalent Observed product: silyl enol ether of formylated alkene near alkenes OSiEt,Me Similar product distributions were obtained RhCI(PPh3)3(1.3 mol%) with CO(CO) Ru(CO)12 however the CHe CHH HSiEt2Me(1 eq) Meet,so overall yields were lower(57% and 40% espectively) Et3 N (3 mol%), CO(x atm) linear: Z: 56% E. 23% branched. Z: 18% E: 13% nzene. 140 C 20h Murai ACIEE 1977(16)881 cv OSiEt,Me OSiEr Me product appears if rxn carried out at higher HSiEt Me(l eq) temperatures or with a high concentration of CO(X atm) benzene. 140%C 20h Murai ACIEE 1977(16)174
M.C. White, Chem 153 Silylformylation -211- Week of October 29, 2002 “Silylformylation” of alkenes Observed product: silyl enol ether of formylated alkene C4H9 RhCl(PPh3)3 (1.3 mol%) HSiEt2Me (1 eq) Et3N (3 mol%), CO (x atm), benzene, 140oC, 20h C4H9 OSiEt2Me 88% linear:Z: 56%; E: 23% + C4H9 MeEt2SiO branched:Z: 18%; E: 13% linear alkenes cyclic alkenes Similar product ditributions were obtained with CO2(CO)8, Ru3(CO)12; however the overall yields were lower (57% and 40% respectively). Murai ACIEE 1977 (16) 881. Co2(CO)8 (0.7 mol%) HSiEt2Me (1 eq) CO (X atm) benzene, 140oC, 20h OSiEt2Me 89% OSiEt2Me product appears if rxn carried out at higher temperatures or with a high concentration of catalyst Murai ACIEE 1977 (16) 174. Desired silylformylation product: R catalyst* CO, R3Si-H R O H SiR3 R O H OH * Tamao * oxidation acetate aldol equivalent polyacetate polyol
M. C. White Chem 153 Silylformylation-212 Week of octo ber 29. 2002 Mechanism OSiEt, Me CofCO) (0.7 mol%) DSiEt2Me (1 eg) D 91% incorporation of the benzene,40°C.20h Proposed mechanism: (OC)cAcO(CO)3 (OC) Co-Co(CO)4 (OC)4Cp…9o(CO)4 DCo(CO)4t RySiCo(CO)4 a-bond metathesis It catalytic cycle SIeTe DCo(CO)4 D-SiEt Me co(X atm)HCo(Co) 4+ OSiR3 HCO(CO)4 Co(cO) Co(CO)4 R3Sr-Co(CO)4 Co(cO)4 Co(co)3 Muria ACIEE 1979(18)837
M.C.White Chem 153 Silylformylation -212- Week of October 29, 2002 Mechanism OSiEt2Me D Co2(CO)8 (0.7 mol%) DSiEt2Me (1 eq) CO (X atm) benzene, 140oC, 20h 91% incorporation of the deuterium in the vinylic position Proposed mechanism: (OC)3Co Co(CO)3 C C O O (OC)4Co Co(CO)4 D SiR3 (OC)4Co Co(CO)4 σ-bond metathesis D-SiEt2Me DCo(CO)4 + R3SiCo(CO)4 catalyst activation: 1st catalytic cycle: DCo(CO)4 D-SiEt2Me HCo(CO)4 OSiEt2Me D D + CO (X atm) + catalytic cycle: HCo(I )(CO)4 H Co(CO)4 O Co(CO)3 O Co(III)SiR3(CO)3 D O D R3Si Co(CO)4 Co(CO)4 SiR3 O D OSiR3 Co(CO)4 D H OSiEt2Me D + DSiR3 Muria ACIEE 1979 (18) 837
M.C. White Chem 153 Silylformylation-213- Week of october 29, 2002 Intramolecular alkene sily formylation -SiPh2 Alkyl 1000 psi CO, allyl, 64%, 4: FPr.79%.6:1 in this system, hydrosilylation -CH, CHOTBS cH, CH otBs. 60%.4: 1 Interestingly, when phenyl homoallylic alcohol are used as substrates, phenyl substituted silanes lead to hydrosilylation whereas diisopropyl silanes result in silylformylated products cO I mol% 1000 pSi CO R groups on Si in conjunction w/R'may dictate which olefin binding mode is preferable. Binding perpendicular to Rh-Si bond results in poor orbital H alignment with Rh-Si but good orbital reductive Rh( CO R入mR时 asertion of H that results in hydrosilylated product. oxidative R2S R R Rh(n H H CO R2Si silane migratory H leighton JACS 1997(119)12416
M.C. White, Chem 153 Silylformylation -213- Week of October 29, 2002 Intramolecular alkene silylformylation Alkyl O Si Ph Ph H Alkyl O SiPh2 O H O Rh O (I)CO CO alkyl = Me allyl i-Pr -CH2CH2OTBS alkyl = Me, 67%, 4.5:1 (cis: trans) allyl, 64%, 4:1 i-Pr, 79%, 6:1 -CH2CH2OTBS, 60%, 4:1 1 mol% 1000 psi CO, benzene, 60o C i-Pr O Si i-Pr i-Pr H O Rh(I) O CO CO 1 mol% i-Pr CH3 O SiPh2 1000 psi CO, benzene, 60o C Silylformylation reactivity depends on the nature of the silicon substituents. If isopropyl is replaced for Ph in this system, hydrosilylation results. Interestingly, when phenyl homoallylic alcohols are used as substrates, phenyl substituted silanes lead to hydrosilylation whereas diisopropyl silanes result in silylformylated products. R groups on Si in conjunction w/R' may dictate which olefin binding mode is preferable. Binding perpendicular to Rh-Si bond results in poor orbital alignment with Rh-Si but good orbital alignment w/Rh-H. This may lead to preferential migratory insertion of H that results in hydrosilylated product. Leighton JACS 1997 (119) 12416. Proposed mechanism: R' O Si R R H O Rh O (I) CO CO O Rh(Iii) O H CO R2Si O R' O Rh(Iii) O H CO CO O R2Si R' O Rh(Iii) O H CO O R2Si R' O R' O SiR2 O H silane migratory insertion oxidative addition CO migratory insertion reductive elimination O Rh(Iii) O H CO R2Si O R' or i-Pr CH3 O SiPh2