Organosilicon and organogermanium compounds - Organometallic chemistry of p-block elements JEE Notes | EduRev

JEE : Organosilicon and organogermanium compounds - Organometallic chemistry of p-block elements JEE Notes | EduRev

 Page 1


Module 3 : Organometallic chemistry of p-block elements
Lecture 5 : Organosilicon and organogermanium compounds
 
   Objectives
   In this lecture you will learn the following
Organosilicon and organogermanium compounds.
Compounds with Si=Si and Ge=Ge bonds.
Organosilicon and organogermanium compounds
Organosilicon compounds are extensively studied due to the wide range of commercial applications as
water repellents, lubricants, and sealants.
Many oxo-bridged organosilicon compounds can be synthesized.
e.g. (CH
3
)
3
Si—O—Si(CH
3
)
3
 which is resistant to moisture and air.
The lone pairs on O are partially delocalized into vacant s*- orbitals of Si, as a result the directionality
of the Si-O bond is reduced making the structure more flexible. 
This flexibility permits silicone elastomers to remain rubber-like down to very low temperature. 
Delocalization also accounts for low basicity of an O atom attached to silicon as the electrons needed for
the O atom to act as a base are partially removed. 
The planarity of N(SiH
3
)
3
 is also explained by the delocalization of the lone pair on N which makes it
very weakly basic.
Si—C bonds are relatively strong (bond enthalpy is 318 kJ mol
-1
) and R
4
Si derivatives possess high
thermal stabilities. 
Et
4
Si on chlorination gives (ClCH
2
CH
2
)
4
Si, in contrast to the chlorination of R
4
Ge or R
4
Sn which yields
R
n
GeCl
4-n
 or R
n
SnCl
4-n
. 
Me
2
SiCl
2
 on hydrolysis produce silicones.
( ?
1
-C
5
Me
5
) 
2
SiBr
2 
on treatment with anthracene/potassium gives Cp*
2
Si 
Solid state structure of Cp*
2
Si consists of two independent molecules which differ in the relative
orientations of the Cp rings.
In one molecule, they are parallel and staggered whereas in the other, they are tilted with an angle of
167°at Si. 
The reaction between R
2
SiCl
2
 and alkali metal or alkali naphthalides give cyclo-(R
2
Si)
n
 by loss of Cl
-
and Si—Si bond formation. 
t
Page 2


Module 3 : Organometallic chemistry of p-block elements
Lecture 5 : Organosilicon and organogermanium compounds
 
   Objectives
   In this lecture you will learn the following
Organosilicon and organogermanium compounds.
Compounds with Si=Si and Ge=Ge bonds.
Organosilicon and organogermanium compounds
Organosilicon compounds are extensively studied due to the wide range of commercial applications as
water repellents, lubricants, and sealants.
Many oxo-bridged organosilicon compounds can be synthesized.
e.g. (CH
3
)
3
Si—O—Si(CH
3
)
3
 which is resistant to moisture and air.
The lone pairs on O are partially delocalized into vacant s*- orbitals of Si, as a result the directionality
of the Si-O bond is reduced making the structure more flexible. 
This flexibility permits silicone elastomers to remain rubber-like down to very low temperature. 
Delocalization also accounts for low basicity of an O atom attached to silicon as the electrons needed for
the O atom to act as a base are partially removed. 
The planarity of N(SiH
3
)
3
 is also explained by the delocalization of the lone pair on N which makes it
very weakly basic.
Si—C bonds are relatively strong (bond enthalpy is 318 kJ mol
-1
) and R
4
Si derivatives possess high
thermal stabilities. 
Et
4
Si on chlorination gives (ClCH
2
CH
2
)
4
Si, in contrast to the chlorination of R
4
Ge or R
4
Sn which yields
R
n
GeCl
4-n
 or R
n
SnCl
4-n
. 
Me
2
SiCl
2
 on hydrolysis produce silicones.
( ?
1
-C
5
Me
5
) 
2
SiBr
2 
on treatment with anthracene/potassium gives Cp*
2
Si 
Solid state structure of Cp*
2
Si consists of two independent molecules which differ in the relative
orientations of the Cp rings.
In one molecule, they are parallel and staggered whereas in the other, they are tilted with an angle of
167°at Si. 
The reaction between R
2
SiCl
2
 and alkali metal or alkali naphthalides give cyclo-(R
2
Si)
n
 by loss of Cl
-
and Si—Si bond formation. 
t
Bulky R groups favour small rings [e.g. (2,6-Me
2
C
6
H
3
)
6
Si
3
 and Bu
6
Si
3
] while smaller R groups
encourage the formation of large rings [Me
12
Si
6
, Me
14
Si
7
 and Me
32
Si
16
]
Bulky substituents stabilize R
2
Si=SiR
2
 compounds. The sterically demanding 2,4,6-
i
Pr
3
C
6
H
2
 provided
first example of compound containing conjugated Si=Si bonds. 
Has s-cis configuration in both solution and the solid state.
Similar germanium compounds are also known
*The spatial arrangement of two conjugated double bonds about the intervening single bond is
described as s- cis if synperiplanar and s-trans if antiperiplanar.
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