Hypervalent Silicates:Properties and Synthetic Utility

A Scheidt Group Literature Presentation

Robert B. Lettan IISeptember 21, 2004

Leading Reference: Chult, C.; Corriu, R. J. P.; Reye. C.; Young, J. C. Chem. Rev. 1993, 93, 1371-1448.

Si Si Si

Outline

I. Introduction

II. Preparation of Hypercoordinate Silicon Compounds

A. Pentacoordinate Compounds B. Hexacoordinate Compounds

III. Structures of Hypervalent Silicon Compounds

IV. Stereochemical Nonrigidity of Hypervalent Silicon Compounds

V. Reactivity of Silicon Compounds

A. Pentacoordinate Compounds B. Hexacoordinate Compounds

VI. Synthetic Methods Involving Hypervalent Silicon Intermediates

VII. Conclusion

Introduction

Silicon compounds with a coordination number higher than four have been know since the beginning of the 19th century.

SiFF F

F

F

F

2-

SiFF F

F

NH2

NH2

2-

1. Gay-Lussac, J. L.; Thenard, L. J. Mémoires de Physique et de Chimie de la Société d' Arcueil 1809, 2, 317.2. Davy, J. Phil. Trans. Roy. Soc. London 1812, 102, 352.

3. Colvin, E. W. Silicon in Organic Synthesis; Butterworths: London, 1981.4. Wbere, W. P. Silicon Reagents for Organic Synthesis; Springer-Verlag: Berlin, 1983.5. Fleming, I. Comprehensive Organic Chemistry; Jones, N., Ed; Pergamon Press: Oxford, 1979, Vol. 3, p. 554.6. Corriu, R. J. P.; Perz, R.; Reyé, C. Tetrahedron 1983, 39, 999.7. Müller, R. Organometal. Chem. Rev. 1966, 1, 359.8. Müller, R. Z. Chem. 1984, 24, 41.9. Kumada, M.; Tamao, K. Yoshida, J. J. Organomet. Chem. 1982, 239, 115.

In the past thirty years considerable interest has been paid to the distinctive reactivity of hypervalent silicon compounds

1) Nucleophilic activation and catalysis in the application of of organosilicon compounds as intermediates in organic synthesis.3-6

2) Formation and reactivity of organofluorosilicates [RSiF5]2-.7-9

Preparation of Pentacoordinate Silicon Compounds

There are three general methods:

1) Anion Addition to Tetracoordinate Silicon Compounds

RnSiX4-n + X- [RnSiX5-n]-

2) Inter- or Intramolecular Coordination of a Neutal Donor to Silicon

SiR4

N

3) Substitution of a Trifunctional Organosilane

a) By use of a Bidentate Ligand (i.e. catechol)

b) By use of trialkanolamines, N[(CH2)nOH]3 or tris-(2-aminoethyl)amine N[(CH2)nNHR]3 to give silatranes or triazasilatranes respectively.

Anion CoordinationFluoride Donation

SiF2R1R2

R1=F,Me,PhR2=F,Ph

FSiF2R1R2R4N+F-

NMR1and vibrational spectroscopic data2 suggest a pentacoordinate silicon.

18-crown-6 allowed isolation of the salt/crystal structure3

Hydride Donation4

HSi(OR)3 [H2Si(OR)3] + [HSi(OR)4]

R = Et, Pri, Bun, Bus, c-C6H11

4[H2Si(OR)3]-K+ 3[HSi(OR)4]-K+ + SiH4 + KH

R = Me, Et, Bun

KH

KH

a b

a:b increases as steric bulk of R increases

Alkoxide Donation5

PhnSi(OMe)4-n + KOMe/ 18-c-6 [PhnSi(OMe)5-n]-[K,18-c-6]+

MePhSi(OEt)2 + KOEt/ 18-c-6 [MeSi(OEt)4]-[K,18-c-6]+

THF or

DME29Si = 80-100 120-135HSi(OR)3 + KOR [HSi(OR)4]-K+

1. Klanberg, F. Muetterties, E. L. Inorg. Chem. 1968, 7, 155.2. Ault, B. S. Inorg. Chem., 1979, 18, 3339.3. Harland, J. J.; Payne, J. S.; Day, R. O.; Holmes, R. R.; Inorg. Chem. 1987, 26, 760. 4.Corriu, R. J. P.; Guérin, C.; Henner, B. J. L.; Wang, Q. Organometallics, 1991, 10, 3574.5.Damrauer, R.; Danahey, S. E. Organometallics 1986, 5, 1490.

Neutral Donors

Intermolecular Donation

Me2SiHCl NMI SiNMIMe

H

Me

NMI

Most cases of intermolecular donation areeither to weak to interact, or results in completeanionic dissociation (i.e. a new tetravalantcomplex). For complexation to work, morethan one electronegative ligand must beattached, or hydrogen must be a ligand as well,as in the example above, which wasconfirmed by X-ray structural analysis.1

Intramolecular Donation

Me2N Si FF F

NNSi F

F F

R

Me2N SiXYZ

OAr

O Si FF F

Me

O

SiClMe2

Si ClMe Me

N

O Si FMe Me

Although rigid and favorable geometries help allowinteractions, intramolecular coordination is moredependent on the remaining substituents on silicon.Bond distances and hypervalency confirmed by X-rayanalysis.2

1. Hensen, K.; Zengerly, T.; Pickel, P.; Z. Anorg. Allg. Chem. 1988, 558, 21.2. Onan, K. D.; McPhall, A. T.; Yoder, C. H.; Hillyard, R. W. J. Chem. Soc., Chem. Commun. 1978, 209.

Substitution in a Trifunctional OrganosilaneBy a Bidentate Ligand1-3

OH

OH2

R-Si(OMe)3

Et3N

( R = Ph)

Me4N+OH-

MeOM

MeOH

OSi

OPh

2

OSi

OR

2

OSi

OR

2

Et3NH+

Me4N+

M+

OHOH

2O

SiO

RO

2

BunNH3+

Si(OR)4

BunNH2

Li

F3C OLiF3C

RSi

O

O

F3C CF3

F3C CF3

RSiCl3Li+

Trialkanolamines and Tris(2-aminoethyl)amines4,5

RSi(NMe2)3 N NH2 3HN Si

NH

NH

N

R

RSi(OR')3 N OH3

O SiOO

N

R

Silatrane Azasilatrane

1. Frye, C. L. J. Am. Chem. Soc. 1964, 86, 3170.2. Frye, C. L. J. Am. Chem. Soc. 1970, 92, 1205.3. Perozzi, E. F.; Martin, J. C. J. Am. Chem. Soc. 1979, 101, 1591.4. Frye, C. L.; Vogel, G. E.; Hall, J. A. J. Am. Chem. Soc. 1961, 83, 996.5. Lukevics, E.; Zelchans, G.; Solomennikova, I. I.; Liepins, E. E.; Jankovska, I.; Mazeika, I. Chem. Abstr. 1977, 86, 171536j.

Hexacoordinate Silicon CompoundsFluoride Donation1 Intermolecular Coordination2

Intramolecular Coordination3 Bidentate Ligand Substitution4,5

RSiX3

X = Cl, Br, I, OR

SiRF F

F

F

FK

KF (excess)

H2O, 0 °C N

N

SiCl4

SiXYI2

Si2Br6

N

NSiCl4

N

NSi

N

NSi

X

Y2

3

2+

4+

2I-

4Br-

N

N= 2,2' bypyridine or 1,10-phenanthroline

Si XX

NMe2

Me2NX = H, F

SiX4

X = Cl, ORY = O, NR

O

Y

O

YSi

3

R2SiX2

X = Cl, ORY = O, NR

O

Y

O

YR2Si

2

Ligand Examples:

OOSi

Z

Z

Z = O, NMe

N

HO OH

OH

1. Tamao, K.; Yoshida, J.; Yamamato, H.; Kakui, T.; Matsumoto, H.; Takahashi, M.; Kuritam A.; Murata, M.; Kumada, M. Organometallics, 1982, 1, 355.2. Hensen, K.; Busch, R. Z. Naturforsch. 1982, 37B, 1174.3. Brelière, C.; Carré, F.; Corriu, R. J. P.; Poirier, M.; Royo, G.; Zwecker, J. Organometallics 1989, 8, 1831.4. Dilthey, W. Chem. Ber. 1903, 36, 923.

Structures of Hypervalent Silicon CompoundsPentaflurosilicates

F SiRR

F

F

R = F, organic groups

Organic groups occupy theequatorial positions.

Axial Si-F bond lengths are alwaysgreater than equatorial Si-F bonds.

Si-F bond lengths increase with increasing steric bulk of organic groups as well as with thediminishing number of electronegative atoms.

Pentacoordinate Bicyclic Silicates

Si

Si

vs.

trigonal bypyramid(TBP)

rectangular pyramid(RP)

RO SiOO

O

O

RP TBPInc. Steric Bulk of R

SiO

O O

O

Ph

97.6% RP

Intramolecular Coordination

R SiOO

HN

X

SiMeMe

Y

N

O

LessEWX

MoreEWX

Inc. Bond

LengthΣ rvw(N-Si) = 3.5AN-Si above = 2.0-2.2 A

o

o

Y = Cl, Br, I

Si-Y B.L.

Si-O Dist.Cl I

The heavier the halogen, thelonger the Si-Y bond, and the closer the Si-O distance.

Hexacoordinate Silicon

SiClCl N

N

R

R

N-Si interactions are always opposite to chlorine atoms.

BondN-SiCl-SiMe-Si

Oct. length (A)1.95-2.202.15-2.40

1.90

Tet. length (A)-

1.90-2.101.90

Stereochemical Nonrigidity

SiMeF

F

N Me

MeMe H

4 NMe2 peaks in 1H NMR spectra2 peaks in 19F DNMR spectra

Intramolecular F ligand exchange 2 NMe2 peaks in 1H NMR (ΔG‡ = 9.4kcal/mol)1 peak in 19F DNMR spectra (ΔG‡ = 9.3kcal/mol)

Si-N opening/ rotation/ inversion1 NMe2 peak in 1H NMR (ΔG‡ = 11.8kcal/mol)

[SiF5]- and [RSiF4]-

[R2SiF3]-

Exchange Extremely FastSingle 19F Resonance at LT

Axial and equatorial fluorine atomsdistinguished at LT 19F NMR (ΔG‡ = 9 -12 kcal/mol)

Inc. ΔG‡StrongerEWG

WeakerEWG

Pentavalent Silicon1,2

Hexacoordinate Silicon3

SiR

RR

NR2

R

Si-N coordinate bond < 6 kcal/molΔG‡ < 7 kcal/molVery Fluxional

1. Damrauer, R.; O'Connell, B.; Danahey, S. E.; Simon, R. Organometllics 1989, 8, 1167.2. Corriu, R. J. P.; Kpoton, A.; Poirier, M.; Royo, G.; Corey, J. Y. J. Organomet. Chem. 1984, 277, C25.3. Kessler, H. Angew. Chem., Int. Ed. Engl. 1970, 9, 219.

Incr

easin

g Te

mpe

ratu

re

Reactivity of Pentacoordinate Silicon Compounds

R1R2R3Si-Cl Nu R3SiR2R1

Cl

Nu

R3SiR2R1

Nu

Nu

Cl-

+

SiR2R1 Cl

R3

O

Nu

SiR2R1 Cl

R3

Nu

Nu

H H

Racemisation

R1R2R3Si-OH

Nu

H2O

v = krac [R1R2R3Si-Cl] [Nu]2

vrac = k [R1R2R3Si-Cl] [H2O] [Nu]

H2O

H2O

ΔS‡ = -40 to -60 e.u.ΔH‡ < 3 kcal/mol

Indicate a MechanismControlled by ΔS‡

Step 1: Initial and reversible attack of activating nucleophilic catalyst on substrate.

Step 2: Rate-determining step. A second Nu must attack. Pentacoordinate species must be more reactivethan tetracoordinate silane. RDS involves attack on pentacoordinate Si, so must result in hexacoordinateintermediate (or Transition State)Large negative values of ΔS‡ are consistent

with a highly organized transition state

1. Corriu, R. J. P.; Dabosi, G.; Martineau, M. J. Organomet. Chem. 1978, 150, 27.2. Corriu, R. J. P.; Dabosi, G.; Martineau, M. J. Organomet. Chem. 1980, 186, 25.

Spillover Effect

1. Voronkov, M. Top. Curr. Chem. 1986, 131, 99.2. Michael, F. Evans Group Seminar 1998-99.

XSi

X XX X Si

XX

X

X

SiXX X

X

X

X

2+ X- + X-

All B.O. = 1

Formal Charges:X = 0Si = 0

B.O. = 0.83

B.O. = 0.75

All B.O. = 2/3

Formal Charges:X = -0.33Si = 0

Formal Charges:Xax = -0.25Xeq = -0.17Si = 0

Ab initio study:

Species

SiH4SiH5

-

SiH3FSiH3F2

-

SiF4SiF4 NH3

SiF4 2NH3

Si Charge

+0.63+0.84

+1.10+1.26

+1.434+1.470+1.463

Ligand Charge

-0.16-0.29(eq), -0.49(ax)

-0.15(H), -0.67(F)-0.26(H), -0.74(F)

-0.358-0.397(F,eq), -0.385(F,ax), -0.084(NH3)-0.463(F), +0.196(NH3)

Formal charge does not change, but the number of electronegative substituentsincreases with increasing coordination.

Pentacoordinate Alkyl- and ArylsilicatesFluoro- and Methoxyorganosilicates

[R2SiX3]- [K, 18 Crown 6]+

R2SiH2

R2Si(OMe)2

R2SiMe2

R2Si

R2SiR'2

FBut

LiAlH4

NaOMe

R'Li

ButMgX

MeMgX

Rel. React.(penta/ tetra)

> 100:1

Ar-X + [(CH3)3SiF2]- Ar-CH3(η3-C3H5PdCl)2

Cross-Coupling Reactions( X = F, OMe)

Bis(1,2-benzenediolato)organosilicates

OSi

OR

2

-

K+O

O

R'2RSi

Ph CMgBr

R'2RSiC CPh

LAHR'

2RSiH

R'2RSiSiPh3

R'2RSiCl

R'2RSiOMe

2MeOLiMeOH

R'2RSi

Ph3SiLi

HClMgBr2

2 eq. R'Li

OSi

O 2

-

LAHEt2O

excessR'Li/ R'MgBr

BF3

Et2O

RSiH3

RSiR'3

R3MgBr

Cp2TiCl2

R2MgBr

Cp2TiCl2

OSi

OB

2

-

K+

R3RSiH2

R2RSiH2

R2 = primary grignard reagentR3 = secondary grignard reagent

Et3NH+ + Ar-X Ar[Pd]

Pentacoordinate HydridosilicatesAlkoxyhydridosilicates

[HSi(OEt)4]- K+ Cp(CO)2FeI

Ag + KBF4 + 0.5H2 + Si(OEt)4

0.5 [Cp(CO)2Fe]2 + KI + 0.5H2 + Si(OEt)4

R3SiH

Si(OR)4 + H2

3 RMgBr

RYCORCH3OH

RCO2EtRCHO

RCONMe2RCHO

ROH

AgBF4

single electron transfer

reductions

RXRH alkyl halide reductions

alcoholysis

Grignard Additions

Bis(diolato)hydridosilicates

Y = H, R

OSi

OH

2

-

Li+

Can also reduce aldehydes andketones, but not esters or amides.

H3C OLi

OLiH3C

OLi

OLi

PhH2CO

PhH2CO

OLi

OLi

H3CO

H3CO PhH2C NHLi

OLiOLiOLi

Ligands for Enantioselective Reductions (20-90 %ee)1,2

1. Kohra, S.; Hayashida, H.; Tominga, Y.; Hosomi, A. Tetrahedron Lett. 1988, 29, 89.2. Schiffers, R.; Kagan, H. B. Synlett 1997, 1175.

Pentacoordinate AllylsilicatesBis(1,2-benzenediolato)allylsilicates

SiOO

2

-

Me4N+

R R'(H)

O

KF, NaOMe,

or KOMe

ketones or aldehydes

(H)R'R OH

Ketones are less reactive, need alkoxide base to promote. Selectivealdehyde addition possible in presence of ketones.

(MeO)3Si

In presence of KF, cleavage of Si-O bond occurs, and crotonization or a Cannizzaroreaction is favored.

R2

R1

Fluoroallylsilicates Mechanism

SiF3

R2

R1

hydroxy compound

Et3N, CH2Cl2

R H

O

R

OH

R1 R2

R2R1

O

O

O

OOH

RR2

R1

High regio- and stereo-selectivity

Silatranes and Azasilatranes

Silatranes

O SiOO

N

R

R = H: Can reduce alkyl halides, acid chlorides and ketones, but with a much lower reacivity than hydridosilicates. Need long reaction times and heat.

R = I:

R = aryl: Can reduce with LAH. Can alkylate with R'Li.

R = vinyl: R'Li yields If R' is sterically bulky (i.e. t-Bu) substitution to the silane doesn't occur.

R = allyl: Need L.A. TiCl4 seems to work best. Allows addition to aldehydes. Will also add to allyl group to vinyl esters, yielding

Reactant(Me3Si)2OR'C CHR'R"HgR'OR"

MeCO2EtMeCHO

ProductR = Me3SiO R = C CR'R = R' or R"

R= OR' or OR"R = MeCO2

R = MeCHIO

SiR'3R'

CO2Et

Azasilatranes

HN SiNH

NH

N

R

1. R'Me2SiCl as a reactant: If R = H , OEt, or Me silylation of 2 of the equatorial NH groups occurs with NEt3. Silylation of all 3 amines proceeds readily with NEt3 when R = OEt. Silylation of the third amine when R = Me requires nBuLi. Following this silylation, it is possible to methylate the Nax with CF3SO3Me, yielding

2. MeOH as a reactant: If R = H , OEt, or Me, solvolysis gives RSi(OMe)3

N SiNN

N

MeSiMe2R

SiMe2RRMe2Si

Me

Neutral Pentacoordinate Silicon DerivativesSilicon Hydrides

Carboxylic Acids and Acid Chloridesto Aldehydes.

Isocyanates to formamides.

Thioisocyanates to N-acylthioformamides

PhN=C=X

(X = O,S)Si

NH

Ph

NMe2

X

HPh

R'COClN HR'

O X

Ph

alkylcarbodiimides (R-N=C=N-R)Reductions:

SiNH

Ph

NMe2

p-tolN

p-tol

Si HPh

NMe2

R' = Pri, c-C6H11

HCO2H

R"COCl

R"COCl

N"R

O

p-tolN

p-tol

HN N

RR

"RNH

NR'R'

O

Diaminosilanes

SiNMe2

NMe2

R

NMe2

CS2 (10 equiv.)

CS2 (1 equiv.)

Me2N NMe2

S

NMe2S

NMe2

S

S

Ph-N=C=X

(X = O,S)

CO2, Δ

Me2N NMe2

O

SiHH

R

N

SiNNMe2

R

N

NHR'

NR'

Ph

X

NMe2

SiXNMe2

R

NNPh

NMe2

1,3-migrationΔ

Me2N NMe2

NPh

Reactivity of Anionic Hexacoordinate Silicon Compounds

Organopentafluorosilicates

RR

SiF5

2M+AgI/ CuI

homocoupling

RR

RR

2

2CuX2

oxidation

RR

XE+ + CuII

Si-C bond cleavage

RR

E

C-C bond formation

EWG

RR

EWG

CO + ROH

carbonylation

RR

CO2R

NBS or X2RR

X

MCPBA

oxidative cleavage

RR

OH+ Pd(OAc)2

Heptacoordination at Silicon

Si

Me2N

Me2N NMe2

F

OSi

O2

NMe2

NMe2

PPN+

NMR Evidence:

29Si NMR spectrum has the chemical shift d = -129.8ppm, which is upfield in comparison to the monoaminehexacoordinate variant (d = 121.2ppm)

1H NMR spectrum shows one NMe2 peak at RT. Since it is assumed that the silicon atom is at least hexacoordinated,the equivalence must be due to reversible attack of the freeNMe2 group on the the silicon atom, with displacement of the chelated one. OR, nucleophilic attack on a hexacoordinate silicon species, which could occur via a heptacoordinate transition state.

Crystal Structure Evidence:

Basic tetrahedral geometry (tricapped tetrahedral) ofthe fluorosilane is retained.

Lone pairs of three NMe2 groups are oriented toward the silicon atom, even though there is no geometric constraint to force this, since the NMe2 groups in the benzylic positions are free to rotate.

N-Si bond distances vary from 3.00-3.49A,corresponding to weak intramolecular interactions. System prefers three weak interactions, as comparedto a single one (pentacoordination at silicon), or two(hexacoordination).

F Si

NMe2 3

Synthetic Methods Involving Hypervalent Silicon Intermediates

Activation of the Si-H Bond

ROH ROSiR1R2R3HSiR1R2R3

CsF/Im/DMF

RR'OSiR1R2R3HSiR1R2R3

TBAF/HMPA/RTR R'

O H3O+

RR'OH

primary>secondary>tertiary

mild reduction

R Z

O (EtO)3SiH, KF/CsF

Z = H, R, OR R

OH

Z

Can reduce in presence of olefins, bromo, nitro,or amido groups.

Can also selectively reduce aldehydes over ketones, and ketones over esters.

Mechanism

R1R2R3SiH R3SiR2R1

H

F

SiR2R1 O

R3

H

F

SiR2R1 O

R3

H

F

HR4

R4

R5

F-

R4OH

R4R5CO

F-

F-

R4OSiR1R2R3

R4R5CHOSiR1R2R3

Silicon-Oxygen Activation

OSiMe3

RX, F-

OR

OSiMe3

1)PhCHO, TBAF

2)H2O

O

Ph

OH

O

2Si(OR)4, KF/CsF

O

OSiMe3

PhO

CsF

silyl enol ethersO

Ph

O

RCOCH2R'

Me

CONH2

Si(OMe)4

CsF R

O

R' Me

CONH2

HN

OMe

RR'

OOSiMe3

OMeH3C

O

CO2Me

CH3

F-

Silyl Enol Ethers

Aldol Rxns

MIchael Rxns

Silyl Ketene AcetalsMechanistic Example

SiH3CH3C

CH3

O

F

R1

R3R2

OR

H

Silicon-Carbon Bond Activation

H3C

H3C SiMe3

X

TBAF or

KF, 18-crown-6 H3C

H3Cα-Elimination

Cl Cl

SiMe3

CsF ClO

Ph

Ph

O

Cl

Ph

Ph

β-Elimination

Elimination Rxns

NMe2

SiMe3

O

H3C

H

MeOCH3

H

CH3

H H

OCH3

CH3

H1) MeI

2)CsF MeCN

1,4-Elimination

Allylsilanes

Z3Si 1) F-,

2) H3O+

(Z = R, F)

R R'

Y

OH

R R'

Addition to Carbonyls and Imines

Also works with Michael Acceptors

SiMe3

CO2CH3

TBAF

CO2CH3

Alkynyl-, Propargyl-, and Benzyl-, Aryl-, and Alkenylsilanes

Activated with fluoride or alkoxide promoters,and applications in additions to carbonylcompounds.

Oxiranyl- Cyclopropylsilanes

X

(X = O, CH2)

EWGSiMe3

F- + E+ X EWGE

H3C

H3C

Silicon-Carbon Bond Activation: TMS derivatives with Anion-Stabilizing Groups in the α-Position

Anion Equivalents

SiMe3

H ClCl

1) F-, RCHO

2) H3O+ R CHCl2

O

Ph CH2SiMe3

OCsF

PhCHO

PhCH2Br

OPhCOCH=CHPh

PhCOCH2CH2Ph

O

CH2COPh

Ylide Equivalents

Ph3P CH2SiMe3 TfO-CsF

CH3CN

Wittig reaction

CH2

Ph

Me3SiH2C P(OMe)2

O

Ph

CsF, R1R2OCHPh

R2

R1

Horner-Emmonstype reaction

O

SPh

O

SPhCH2SiMe3

TMSCh2OTf

O

SPh

CsF

CH3CN

TfO-

Sulfur Ylides

NSR

SiMe3N

SR

SiMe3H3C

I-

MeI CsF

EWG EWG

NCH3

CO2CH3

H3CO2C

Azomethine Ylides

Acylsilanes

XSiMe3

O CsF or KF/18c6

PhCHO(X = O, S, NMe)

XO

Ph

OH

O

Ph

Palladium-Catalyzed Cross-Coupling Reactions

RX

R1SiZ3

F-

X = Br, I, OTfSiZ3 = SiMe2(OEt) SiMe(OEt)2 SiMe(OEt)3

RR1

E,Z retained

Vinylsilanes Arylsilanes

R1SiRF2

R2I

R2R1

KF/DMF

(η3-C3H5PdCl)2

CO insertions also possible

Alkynylsilanes

R SiMe3

BrPh

TAS TMSF2

(η3-C3H5PdCl)2

Ph

R

Alkyltrifluorsilanes

R1TfO

TBAF

(PPh3)4PdRSiF3

R1R

Allylsilanes

SiMe3

TAS TMSF2/ (η3-C3H5PdCl)2

TAS TMSF2/ (η3-C3H5PdCl)2

BrPh

PhBr

H3CPh

Ph

RI

SiMe3H3C

CH3 TBAF

(PPh3)4Pd R

CH3H3C

More Recent Advances in Silicon ChemistryRing Opening Halosilyations1

O

n

n = 1,2,3Also Applicable

to Lactones

XOSiR3

X = Br, IR = Me, Et

EtSiH/ MeI/ PdCl2 or

Me3SiNEt2/ MeI

1. Kunai, A.; Oshita, J. J. Organomet. Chem. 2003, 686, 3.2. Bassindale, A. R.; Parker, D. J.; Patel, P.; Taylor, P. G. Tetrahedron Lett. 2000, 41, 4933.3. Kirpichenko, S. V.; Suslova, E. N.; Albanov, A. I.; Shainyan, B. A. Tetrahedron Lett. 1999, 40, 185.

O

Y Me3SiNEt2/ MeI

Y = O, NMe

YOSiMe3

n

Chemoselective Methylation2

R NR'

O (Me3Si)2NH

ClCH2SiMe2Cl SiCH3

CH3

O

Cl

R'N

R

R NR'

O

CH3

CsF

Works with a variety of straight chain, cyclic, conjugated,and aromatic R groups.

Works with both primary and secondary amides.

72-85%Y

Sila-Pummerer Rearrangement3

Me2Si SO

Δ

THF

Me2SiS

O

Si S

O

H3C

CH3Si S

OH3C

CH3

SiH2C

SO

H3C

CH3

Me2SiS

O

Aldol Reaction

Kobayashi, J.; Nakamura, M.; Mori, Y.; Yamashita, Y.; Kobayashi, S. J. Am. Chem. Soc. 2004, 126, 9192.

NF3C

OSiMe3

OMe

OSiMe3

R H

O chiral Zr cat., tBuOMe

[(R)-binol]

78/22 - 90/10 ani/syn85-95 % ee (anti)

R OMe

O

NHCOCF3

OH

TBDPSOH

O

A

A, chiral Zr (10 mol%)

tBuOMe, toluene-20 °C, 95% Y

80/20 anti/syn, 97%ee

TBDPSOOH

OMe

O

NHCOCF3

O O

NHCOCF3

PMP

OTBDPS

1) NaBH4, MeOH

2) PMPCH(OMe)2, TsOH, DMF

OHNH2

OHTBSO 1) TBAF, THF

2) Ac2O, DMAP, pyr3) C12H25MgBr, Li2CuCl4

1) 2N NaOH-EtOH

2) 1N HCl-THF

62 %Y

51 %Y

O O

NHCOCF3

C13H27

PMP

74 %YL-erythro -sphingosine

Allylations

Ar

O

HSiCl3

N N

H3CH3C

CH3CH3

O

PINDOX

-60 °C

40-85%Y77-98 %ee

Ar

OH

*

SiO

NO

Cl

ClH

Ar

CH3

CH3

NCH3

H3C

1. Malkov, A. V.; Orsini, M.; Pernazza, D.; Muir, K. W.; Langer, V.; Meghani, P.; Kocovsky, P. Org. Lett. 2002, 4, 1047.2. (a) Chemler, S. R.; Roush, W. R. J. Org. Chem. 2003, 68, 1319. (b) Chemler, S. R.; Roush, W. R. Tetrahedron Lett. 1999, 40, 4643.

Chiral Ligands1

Chiral Aldehydes2

RMe

O

H

OH MeSiF3

i -Pr2NEtCH2Cl2, 0 °C

SiO

O F

FF

R

Me

H

Me

R3NHR

OH

CH3

OH

CH3

Other reactions

ROSi(H)R'2

"Pt"/ "Ru"H

R SiO

R' R'

ArXPd(dba)2

TBAF

THF, rt

H

R Ar

OH

Silicon Assisted/ Directed Cross-Coupling Reactions1

1. (a) Denmark, S. E.; Pan, W. Org. Lett. 2001, 3 , 61. (b) Denmark, S. E.; Pan, W. Org. Lett. 2002, 4, 4163.2. Lambert, J. B.; Singer, S. R. J. Organomet. Chem. 2004, 689, 2293.

Self-Assembled Macrocycles2

SiOO

O

ONHSi

OO

O

O NH

SiO O

OO

NH

New Materials with possibilities for usein ion exchange, sensor applications, molecular or chiral recognition, catalysis,environmental remediation, and drug discovery.

Conclusion

Silicon has the ability to go pentavalent and hypercoordinate, as demonstrated bynumerous NMR and X-ray experiments.

The "Spill Over" effect lends reasoning to the increasing electrophilicity of silicon, even as more ligands are appended to it.

Numerous synthetic reactions are made possible by the hypervalent transition statesof silicon compounds.

There are many areas left to be understood, explored, and improved upon in the area of hypervalent silicon chemistry.