_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

The main Groups IV and V
Dimethyltin difluoride is tetragonal, a= 42 5 and c = 710 pm. Positions for
non-hydrogen atoms have been determined as follows:
Sn (0,0,0)
F (O.î.O) and (Î.O.O)
C (O,O,z) and (O, O,- z) z = 0.29
Describe the crystal structure of (CH 3 ) 2 SnF 2 , calculating the Sn-F and Sn-C
bond distances.
(CH 3 ) 2 SnF 2 decomposes without melting at ca 400°C, whilst (CH 3 ) 2 SnCl 2 and
(CH 3 ) 2 SnBr 2 melt at ca 90oC and 75°C respectively. Suggest a possible reason for
this difference in behaviour.
(University of Edinburgh).
5. Triethylphosphite (C 2 Hp) 3 P and benzyl chloride were heated together and
gave a compound A (C 11 H 17 0 3 P). When A (in toluene) was treated sequentially
with sodium hydride, benzaldehyde, and then dilute aqueous hydrogen chloride,
the product B (C 14 H 1 J was obtained.
Formulate A and B and suggest a mechanism for the formation of each.
(Vniversity of Strathclyde).
6. A chemical method of detecting dati ve n-bonding to Group IV elements is to
measure the relative donor properties of compounds in which such bonding is
suspected. A guide to the Lewis basicity of such derivatives is provided by the shift
(./\ v) which they cause in the infrared spectrum of CDCl 3 through C-D .... O or
C-D ... N hydrogen bonding. Discuss the results in the Table on the basis of
inductive effects (electronegativities) of the Group IV elements and of their
capacity to form (p-d)n bonds with N, O or S. How is the extent of n-bonding
reflected in the structures of the compounds?
Base
(Me 3 M) 3 N
(Me 3 M) 2 0
(Me 3 MLS
c
100
33
40
Si
o
13
29
Ge
72
55
38
Sn
106
84
43
Pb
SI
Relative donor properties of some organometallic bases . .!\ v / cm- 1 for v( C-D) of
CDCl 3
7. When dichlorodimethylsilane is treated with alkali metals in tetrahydrofuran,
the main product X is a crystalline solid of composition, C, 41.4; H, 1 0.3; Si,
48.3 %. and molecular weight 2 90. The proton n.m.r. spectrum of X measured in
benzene consists of a single band. Compound X reacts with bromine to give a
compound Y which contains 35.5% Br; and, when Y is allowed to react with
sodium and chlorotrimethylsilane in toluene o ne of the products formed is a liquid
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