main group om part 1 2005
TRANSCRIPT
-
8/8/2019 Main Group OM Part 1 2005
1/49
Main-Group Organometallics
MH+ - CH-
carbanionic in character
susceptible to attack by electrophilessusceptible to nucleophilic attack
Stability M-C is weak compared to M-N, M-O or M-Hal p use for organometallics
in synthesis
M-Cbondenergies cover wide range
within a main-group
decrease with increasing
atomic number
-
8/8/2019 Main Group OM Part 1 2005
2/49
Main-Group Organometallics
Lability thermal decomposition Pb(C2H5)4 Pb + C2H5
p Pb, EtH, C2H4, C4H10.
F-elimination
R2C CR2
H
R2C CR2
H
R2C CR2H
E F
Facilitated by vacant orbital at metal to accommodate metal-hydrogen bond pair
(Group I-III)
Stabilisation by adduct formation of Lewis base e.g. (bipy)BeEt2
BeEt2 inflames, (bipy)BeEt2 stable 10-15 min in air
-
8/8/2019 Main Group OM Part 1 2005
3/49
Main-Group Organometallics
Reactivitytowards O2 and H2O highest for organometallics with free electron pair,low lying empty orbitals and/or high polarity of M-C
bond
InMe3 pyrophoric/hydrolysed vacant orbital on In, moderate bond polarity
SiMe4 inert/not hydrolysed Si shielded well, low bond polarity
eactivity of M-C bonds may also be controlled by use of sterically demanding
substituents, e.g., (Me3Si)3C, mesityl p kinetic stabilisation
c.f. Zn(CH3)2 Zn{C(SiMe3)3}2
Pyrophoric, explodes with water Stable in air, steam
-
8/8/2019 Main Group OM Part 1 2005
4/49
Main Structural Types of Organometallic
Compounds
Li
1.0
Be
1.6
B
2.0
C
2.5
N
3.0
O
3.4
F
4.0
Na
0.9
Mg
1.3
Al
1.6
Si
1.9
P
2.2
S
2.6
Cl
3.1
K
0.8
Ca
1.0
Sc
1.3
Ti
1.5
V
1.6
Cr
1.6
Mn
1.6
Fe
1.8
Co
1.9
Ni
1.9
Cu
1.9
Zn
1.7
Ga
1.8
Ge
2.0
As
2.2
Se
2.6
Br
2.9
b
0.8
Sr
1.0
Y
1.2
Zr
1.3
Nb
1.6
Mo
2.1
Tc
1.9
u
2.2
h
2.3
Pd
2.2
Ag
1.9
Cd
1.7
In
1.8
Sn
1.8
Sb
2.0
Te
2.1
I
2.6
Cs
0.8
Ba
0.9
La
1.1
Hf
1.3
Ta
1.5
W
2.3
e
1.9
Os
2.2
Ir
2.2
Pt
2.3
Au
2.5
Hg
2.0
Tl
1.6
Pb
1.9
Bi
2.0
Po
2.0
At
2.2
metals with a strong tendency to form
alkyl- or aryl-bridged species;
covalent, multicenter bonds
metals that
form ionic
derivatives
transition metals
T-complexes tend to
predominate
metals and metalloids that
form volatile, covalent
organo derivatives
mainly M-C W-bonds
rarely M-C T-bonds
non-metals
-
8/8/2019 Main Group OM Part 1 2005
5/49
Synthesis
DirectSynthesis 2 M + n X nM + MXn (or nMXn)
2 Li + C4H9Br C4H9Li + LiBr
Mg + C6H5Br C6H5MgBr
2 Na + Hg + 2 CH3Br (CH3)2Hg + 2 NaBr4 NaPb + 4 C2H5Cl (C2H5)4Pb + 3 Pb + 4 NaCl
Mixed Metal
Synthesis
not fore.g. Hg or Pb
Transmetallation M + M M + M
Zn + (CH3)2Hg (CH3)2Zn + Hg
favourable when M is higher in electrochemical
series than M
slow
2 Al + 3 MeCl Me3Al2Cl3
-
8/8/2019 Main Group OM Part 1 2005
6/49
Synthesis
Metathesis M + MX X + M
Li Mg Al Zn
Electronegativity: 0.98 1.31 1.61 1.65
Si B As P
1.90 2.04 2.18 2.19
Li4(CH3)4 + SiCl4 4 LiCl + Si(CH3)4
Al2(CH3)6 + 2 BF3 2 AlF3 + 2 B(CH3)3
Hydrometallation M-H + C C C CHM M = B, Al, Si, Zr, e.g.
(C2H5)2AlH + C2H4 (C2H5)3Al
everse ofF-elimination
-
8/8/2019 Main Group OM Part 1 2005
7/49
Reaction Pattern
Oxidation - potential reducing agents; for electropositive elements very strong reducing
agents- componds of electropositive metals have unfilled valence orbitals,
or readily dissociate to fragments with unfilled orbitals - pyrophoric
Nucleophilic(carbanion) Character
-organic group at electropositive
- metal has partial negative charge
- strong nucleophile and Lewis base
- most commonly used carbanion
reagents LiR and RMgX
-
8/8/2019 Main Group OM Part 1 2005
8/49
Reaction Pattern
Protolysis Reaction
Ga Et
Et
Et
Ga O
Et
EtEt
CH3
H
Ga OCH3
Et
Et
CH3OH
- C2H6
Al2(CH3)6 + 6 C2H5OH 2 Al(OC2H5)3 + 6 CH4
Lewis Acidity presence of unoccupied orbitals on metal, electron-deficient
B(C6H5)3 + Li(C6H5) Li[B(C6H5)4]
Al2(CH3)6 + 2 N(C2H5)3 2 (CH3)3AlN(C2H5)3
-
8/8/2019 Main Group OM Part 1 2005
9/49
Alkali Metal Organometallics Method of Synthesis
DirectSynthesis - organic halide + metal
Transmetallation - using Hg organyls
MetalExchange - PhLi + (CH2=CH)
4Sn 4 (CH
2=CH)Li + Ph
4Sn
(good yields of vinyllithium)
Metal-HalExchange - BunLi + PhX BunX + PhLi (practicable only for ArX; competingreaction Wurtz coupling)
MetallationofC-HAcid- Na + C5H6 C5H5Na + 1/2H2
-
8/8/2019 Main Group OM Part 1 2005
10/49
Alkali Metal Organometallics Method of Synthesis
Forheavieralkalimetal organometallics widely used method metathesis of
organolithium reagent and an alkoxide
e.g., BunLi + KOBut LiOBut + BunK
in hydrocarbons, easy to separate the MR product, e.g. BunK
CH3CH2OCH2CH3 + KC4H9 C4H10 +
KOC2H5 + H2C=CH2
[CH-O-C2H5]
CH3
K
Ether Cleavage
-
8/8/2019 Main Group OM Part 1 2005
11/49
Organolithium Structures
i
i
i
i
i
i i
i
i
i i
i
s
i grouor itals
O iagram for one of the four e c on s in R i
hh
ii
i
h
h
i
.O t
.O t
t O.
t O.Ten ency to form
oligomers through
multicentre on s
e i tetramer
-
8/8/2019 Main Group OM Part 1 2005
12/49
Organolithium Structures
Hexamer of BunLiButLi tetramer
-
8/8/2019 Main Group OM Part 1 2005
13/49
Organolithium Structures
LiR Solvent Aggregation
MeLi thf, Et2O
Me2CH2CH2NMe2
(tmeda)
tetramer
(Li4 tetrahedron
monomer, dimer
BunLi cyclohexane
Et2O
hexamer
tetramer
ButLi hydrocarbons
thf
tetramer
monomer
LiCH2Ph thf, Et2O monomer
LiC3H5 (allyl) Et2O
thf
columnar structure
dimer
Ph
Ph
Ph
Ph
Li
Li
Li
OEt2
OEt2
Et2O
-
8/8/2019 Main Group OM Part 1 2005
14/49
Organolithium Structures
(n- i)tme a
i-
Degree of association strongly epen ent on nature of solvent
Affects structures an reactivity by increasing polarity of i- bon
Rates of metallation by Ph i excee those of 3 i by factor of 0 , although
3- stronger base as Ph -
omplexation of i ; polarisation of i- bon ;
carbanionic character of butyl group increase
-
8/8/2019 Main Group OM Part 1 2005
15/49
Reactions of Organolithium Compounds
Metallation ofC-H, N-H, O-Hacids R-Li + E-H R-H + E-Li
when E-H is stronger acid than R-H
H HLi
+
+ uHu
nLi
HHLi
unLi
+ uH
Reactions with Main-GroupandTransition-metalHalides
RLi + M-X M-R + LiX
-
8/8/2019 Main Group OM Part 1 2005
16/49
Reactions of Organolithium Compounds
C NR C NLiR
R'
C NHR
R'
C OR
R'R'Li hydrolysis hydrolysis
C
O
NR'2
H R CH
OLi
NR'2 CO
H
RRLi hydrolysis
W
OC
OC CO
CO
CO
CO
W
OC
OC CO
CO
CO
C
R O-Li+
W
OC
OC CO
CO
CO
C
R OCH3
LiR [(CH3)3O]BF4
Additions to Multiple Bonds
-
8/8/2019 Main Group OM Part 1 2005
17/49
Radical Anion Salts
Na + C10H8(thf) Na[C10H8](thf) sodium naphthalenide
+ ArH+
+ ArH . + ArH + + ArH -
( e5C5) SiBrK, anthracene
- KBrSi
-
8/8/2019 Main Group OM Part 1 2005
18/49
Radical Anion Salts
-
-.
-
non lanar
nTelectr
ti r tic
pl r
( n+1) T-electr
pl r
( n+2) T-electr
r tic
-
8/8/2019 Main Group OM Part 1 2005
19/49
Organomagnesium Compounds
DirectSynthesis Mg + RX RMgX(OR2)n
Transmetallation Mg + R2Hg R2Mg + Hg
MetallationR
-C|CH + EtMgBrR
-C|CMgBr + EtH
SchlenkEquilibrium 2 RMgX + 2 dioxane R2Mg + MgX2(dioxane)2
-
8/8/2019 Main Group OM Part 1 2005
20/49
Organomagnesium Compounds
RX
Mg Mg Mg
RX R MgX
R RMgX
. .
.
Mgacti eMgCl2K, t f
C 17Mg %!C 17F
r.t.,
Formation
Acti ation of Mg: I2, CCl4, 1,2-dibromoet ane
Riecke magnesium:
-
8/8/2019 Main Group OM Part 1 2005
21/49
Organomagnesium Compounds
2 R g R2Mg + Mg 2
I IIIII I
Mg Mg
R
R
Mg Mg
R R
sol ent it donor properties, usuall et er
Dominant forms: I et er solution of lo concentration
II in Et3N, it dioxane onl MgR2 in solution,precipitation ofMgCl2(dioxane)2
III and I in ig er concentration and it more basic t f
Schlenkequilibrium
-
8/8/2019 Main Group OM Part 1 2005
22/49
Organomagnesium Compounds
Structure
Generally polymeric/oligomeric structures, where halide (2e2c) bridges are preferred
over2e3calkyl bridges
Exception: [(Me3Si)3C]Mg is monomeric
due to bulky substituents
Al
Mg
Al
-
8/8/2019 Main Group OM Part 1 2005
23/49
Organomagnesium Compounds
Reactivity
RMgX + R'C|N R C R'
O
RMgX + R'CHO RR'CH-OH
Use in organic synthesis, e.g.
Alkylating/arylating reagents for main group and transition metals halides
l + Mg ( )
Mg
- Mg l
compared to LiR, RMg reagents - less reactive (do not form ate complexes)
- less reducing with transition metal halides
-
8/8/2019 Main Group OM Part 1 2005
24/49
Organomagnesium Compounds
Magnesium-ate-complexes MxMgyR
z (M = group 1,2 and 13);
the less EP metal usually in ate-complex anion
MgMe2+ iMeEt2O
iMgMe3(Et2O)ntmeda
lithium magnesiate
Me i
-
8/8/2019 Main Group OM Part 1 2005
25/49
Organometallics of Calcium, Strontium and Barium
Synthesis
Highly reactive due to predominantly ionic character of metal-ligand bond
increased lability complicates synthetic access; unstable and/or sparingly soluble
Transamination M[N(SiMe3)2]2 + 2 HR
MR
2 + 2 HN(SiMe3)2
Direct metallation 2 HR + activated M MR2 + H2
Transmetallation/ HgR2 + activated M MR2 + Hg
Metal exchange
2 LiR + M(OR)2 MR2 + 2 LiOR
M[N(SiMe3)2]2 + 2 LiR MR2 + 2 LiN(SiMe3)2
M[N(SiMe3)2]2 + 2 LiCH2Ph M(CH2Ph)2 + 2 LiN(SiMe3)2
MI2 + 2 LiCp* Cp*2M + 2 LiI
-
8/8/2019 Main Group OM Part 1 2005
26/49
Organometallics of Calcium, Strontium and Barium
Most intensively studied are the cyclopentadienyl systems
Magnesocene is useful reagent for introduction of C5H5 groups
Cp2Mg Cp*2Ca
M E,
MCp*2
Mg 180
Ca 154
Sr 149Ba 148
M2+ HH
Sterically should be parallel, however explained
by polarisable ion model bending due to dipole induced
on large central cation (also Yb(II), Eu(I) analogues)
maximises electrostatic bonding
-
8/8/2019 Main Group OM Part 1 2005
27/49
Organometallics of Calcium, Strontium and Barium
purelyW
-bonded ligands - scarce
[Ca{CH(SiMe3)2}2(1,4-dioxane)2] Ca[C(SiMe3)3]2
CCaC 150r
Lappert, 1991 Eaborn/Smith, 1997
-
8/8/2019 Main Group OM Part 1 2005
28/49
Tris(trimethylsilyl)methylmagnesium and -calcium
-
8/8/2019 Main Group OM Part 1 2005
29/49
Organoaluminium Compounds
Synthesis
Transmetallation 3 Ph2Hg + 2 Al 2 AlPh3 + 3 Hg
Metathesis (RLi orRMgX) AlCl3 + 3 ButLi AlBut3 + 3 LiCl
Hydroalumination 3 RCH=CH2 + AlH3.OEt2 (RCH2CH2)3Al
.OEt2
Direct synthesis 2Al + 3RX 2 R3Al2X3 sesquihalide
Properties
Alkyls are usually colourless liquids that react violently with air and water; short
chain lengths pyrophoric
Lewis acidic (6 valence electrons) marked effects on structure and reactivity
-
8/8/2019 Main Group OM Part 1 2005
30/49
Organoaluminium Compounds
Applications
Aufbau reaction (growth reaction) - multiple insertion of ethylene into the Al-C bond
e.g. AlC2H5 + C2H4 p AlC4H10 etc (Ziegler)
- produces 1-alkenes and (after reaction with
dioxygen and hydrolysis) unbranched C16 C20
primary alcohols for detergent industry
Catalytic dimerisation of propene basis for production of isoprene
(-synthetic rubber)
Olefin polymerisation Ziegler-Natta low-pressure process with mixed
catalysts like Et3Al/TiCl4
-
8/8/2019 Main Group OM Part 1 2005
31/49
Organoaluminium Compounds
CCatalytic dimerisation of propene
CH2=CHCH3Pr3Al Pr2AlCH2CHMePr
CH2=CHCH3
Pr2AlH + CH2=CMeCH2CH2CH3
cracking
CH2=CMeCH=CH2 + CH4
isoprene
-
8/8/2019 Main Group OM Part 1 2005
32/49
Organoaluminium Compounds
Structure andbonding
Al Al
C
C
109.5 Al Al 120
C
C
C
Al
C
AlAl CAl Al
AlC
AlAl
(2e3c) (2e3c) (2e2c) (2e4c)+ +
a b
Al(sp3) Al(sp2)
Al
H3C
H3C
Al
CH3
CH3
H3C
CH3
75
260 pm
214 pm
123
197 pm
H
H
Al2(CH3)6
Al2Cl6 d(Al-Al) 340 pm with Al-X-Al bridges
rcov Al = 252 pm [rcov(Al) = 146 pm]
-
8/8/2019 Main Group OM Part 1 2005
33/49
Organoaluminium Compounds
l l
a
l l76
270 pm
218 pm
115
196 pm
114 sp2 120
l l
c
spsp
109.5
Q- 6H5 Q- 6H5
Structure andbonding Al2(C6H5)6
-
8/8/2019 Main Group OM Part 1 2005
34/49
Organoaluminium Compounds
Associationin solution Al-C-Al bridging persists in non-polar solvents with
fast Al-Me exchange
50 rC + 20 rC
0.5 6.5 0.3
a R = Me b R = Ph
Al
R
R
R
R
R
R
Al Al
R
R
R
R
R
R
Al Al
R
R
R
R
R
R
Al Al
R
R
R
R
R
R
Al
**
*
*
a
b
-
8/8/2019 Main Group OM Part 1 2005
35/49
Organoaluminium Compounds
R2AlX and RAlX2 (X = halide) are most conveniently prepared by redistribution
of trialkyls and trihalides in correct stoichiometry. Reactions occur readily at RT.
2 R3Al + AlCl3 3 R2AlCl
R3Al + 2 AlCl3 3 RAlCl2
X
Al
X
Al
Me Me
Me Me
usually oligomers, formed by Al-X-Al bridging
(interaction with heteroatom lone pair favoured over Al-C-Al)
Al-Me-M bridges also formed with other acidic metal centres, e.g.
AlMe3 + Cp2Yb
-
8/8/2019 Main Group OM Part 1 2005
36/49
Organoaluminium Compounds
Reactivity
Organoaluminium compounds are hardacids and readily form adducts with bases
such as thf and amines
Mes3
Al + thf
Reactions with protic reagents gives access to wide variety of organoaluminium
compounds
AlR3-n + nROH R3-nAl(OR)n
-
8/8/2019 Main Group OM Part 1 2005
37/49
Organoaluminium Compounds
Formation of ate-complexes AlR3 + LiR Li[AlR4]
Carbalumination
Hydroalumination
H2C CHR
Et2Al Et
Et3Al(Et
3Al)
2
CH2=CHR H2C CHR
Et2Al Et
1/2
+
H2C CHR
Et2Al H
-
8/8/2019 Main Group OM Part 1 2005
38/49
Organometallics of Ga, In and Tl
Synthesis
R3M may be prepared by same methods as forR3Al metathesis orRLi/MgX with MX3
- transmetallation with organomercurials
Halides RnMX3-n most readily prepared by redistribution reactions
Structure R3Ga and R3In monomeric Lewis acidity less than that of AlMe3Ga very important ion semiconductor industry more inflammable
than dimeric Me3Al
ReactivityLess reactive than aluminium compounds so possible to get e.g.Me2GaOH easily
-
8/8/2019 Main Group OM Part 1 2005
39/49
Organometallics of Ga, In and Tl
X
GaX
Ga
R R
R R
InCl
In Cl
Cl In
[Me2InCl]n
in R2MX compound the larger In can adopt coordination numberes > 4
leads to coordination polymers in solid state
-
8/8/2019 Main Group OM Part 1 2005
40/49
Group 14 Organometallics
E Thermal stability Bond energy
E(E-C) in kJ/mol
Bond length
d(E-C) in pm
Bond polarity
EH+ - CH-EN
C 358 154 2.5
Si 311 188 1.9
Ge 249 195 2.0
Sn 217 217 1.8
Pb 152 224 1.9
Common oxidation state of +4 with increasing stability of +2 as group is descended
In contrast to group 13 derivatives R4M derivatives show lower bond polarity of the E-C bond,
have an octet configuration and reactivity towards nucleophiles is diminished,
ie. ER4 species are usually water-stable and often air-stable
-
8/8/2019 Main Group OM Part 1 2005
41/49
Group 14 Organometallics
Chlorination of ER4
species: for E = C and Si chlorination of organic part but for
E = Ge, Sn or Pb cleavage of the E-C bond
CEH
+ H-
u El
nucleophilic
attac
electrophilic
attac
Availability of empty nd orbitals at E renders associative
Mechanism of substitution possible by extending
the C to 5
Successive replacement ofR by more E groups X in
RnEX4-n increases affinity of E for attacking nucleophiles
Me4Sn inert towards H2O and [SnMe6]2- unknown, but
Me2SnCl2 hydrolyses and [Me2SnCl4]2- can be prepared
-
8/8/2019 Main Group OM Part 1 2005
42/49
Organosilicon Derivatives
Preparation
Metathesis withR
Li,R
MgX orR
3Al SiX4 + nLiR
SiX4-nR
n + nLiX
3 SiX4 + 4 AlR3 3 SiR4 + 4 AlX3
Hydrosilylation (anti-Markovnikov) R3SiH + CH2=CHR R3SiCH2CH2R
Industrially, prepared by 2 RCl + Si/Cu R2SiCl2 (ca. 70%)
Organosilanes -properties
R4Si are H2O and O2 stable because of low bond polarity, heterolytic cleavage does
not occur readily
Si-C bonds are thermally stable and do not decompose before ca. 700C
Leads to use in silicon polymers from hydrolysis of chlorosilanes now a very mature
industry
Chlorosilanes are commonest precursor for wide range of organosilanes
Rochowprocess
-
8/8/2019 Main Group OM Part 1 2005
43/49
Organosilicon derivatives
R2SiCl2 + H2O / catalyst p (R2SiO)n + ClR2Si(OSiR2)nOSiR2Cl
cyclics linear
D4 predominates
Mainly R = Me 106 tonnes/year
Thermal stability up to 350 rC Unzipping rate less when R = Ph
Low temperature coefficient of viscosity Tg < 120 rC
SiOSi ca 145 rC easy rotation
Good insulator
Hydrophobicity coatings, waxes, sealants
Many variations in pendant groups - copolymers
Si O
SiO
Si O
SiO
-
8/8/2019 Main Group OM Part 1 2005
44/49
Organosilicon Derivatives
SelectedReactions of organohalosilanes
R i l
R iOH
R i H2 (R i)2NH
R i H (R i)2S
(R Si)2O
R SiR'
R SiH
R Si-SiR
R SiSRR SiOR'
R'Li
Li lH4
Li
RSNa
R'OH
H2S
NH3H2O
-H2O
-NH3
-H2S
-
8/8/2019 Main Group OM Part 1 2005
45/49
Organo(germanium), -tin and (-lead) derivatives, RnMX4-n
Preparation ofR4M most commonly by metathesis of MX4 with RLi, RMgX and R3Al
derivatives
other methods similar to those employed for organosilanes
Preparation of the most important routes involve redistribution of tetraalkyl
RnMX4-n derivatives with tetrahalides; in contrast to group 13 derivatives
these reactions generally involve elevated temperatures
(ca. 170 C)
Structure/ R4Sn simple tetrahedral (sp3) coordination is encountered inproperties tetraalkyls which are air/moisture stable
R3SnX with more electronegative groups attached the Lewis acidity
increases and higher coordinate derivatives result from coordination
by bases in absence of external bases polymeric structures are
common
R
SnR
R
Me SnMe
MeCl
N
Me
Sn
MeMe
Me
Sn
MeMe
F
Me
Sn
MeMe
F
F
Me3SnF, 1 polymer with tbp Sn (5 coordinate)
-
8/8/2019 Main Group OM Part 1 2005
46/49
Organotin Derivatives
R3Sn l
R3SnOH
R3SnN'R2
(R3Sn)2O
R3SiR'
R3SnH
R3Sn-SnR3
R3SnMn( O)5
R3SnOR'
R'Li
Li lH 4
Na
NaMn( O)5
R'OH, R3N
LiNR'2
H2O
R3Sn 5H5
Na 5H5
SelectedReactions of organohalostananes
ompounds containing R3S
n are toxic and must be handled with great care
-
8/8/2019 Main Group OM Part 1 2005
47/49
Organotin Hydrides
RnSnX4-n RnSnH4-nLiAlH4, Et2O
HC
HC C
O
PhH
H2C
H2C C
O
PhH
+ Bun3SnH
1. cat. (Ph3P)4Pd,
thf, 20 C
2. H2O
Et3SnH + CH2=CH-CH=CH2 Et3SnCH2-CH=CH-CH3AIBN
in absence of Lewis acids or radical forming reagents polar double bonds like C=O or
C=N are not attackedwell-suited forchemoselective hydrogenation of activated C=C bonds
in presence of AIBN 1,4-addition to conjugated dienes occurs
Sn H + A B Sn A B HHydrostannation
-
8/8/2019 Main Group OM Part 1 2005
48/49
Organotin Hydrides
R'3Sn-H R'3Sn. + H
.
R'3Sn. + R R'3Sn + R
.
R. + R'3SnH RH + R'3Sn.
(start)
(propagation)
Sn H + X Y Sn Y + HXHydrostannolysis
R3Sn-H + Me OOH R3SnOO Me + H2 H-
4 R3Sn-H + i(NR'2)4 (R3Sn)4Ti + 4 HNR'2 H+
2 R3Sn-H + R'2Hg (R3Sn)2Hg + 2 R'H H.
R3SnH transfer
R6Sn2R =Me, -10
R = , +100
-Hg
low polarity ofSn-H bond R3SnH may act as a source of H-, H+ or H.,
depending on nature of attacking agent
-
8/8/2019 Main Group OM Part 1 2005
49/49
Organotin Hydrides
Me2 Br2 Me2
Br
Me2 H2
But3SnH
hY
But3SnH
hY
most convenient methods for conversion R-X to R-H
e.g., selective reduction of geminal dihalides in presence of other sensitive
groups