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Reactions of octahedral complexes: the stereochemical consequences. Stereochemistry of a dissociation reaction at an O h complex. X is cis to A, and A is a donor. vacant metal d 2 sp 3 orbital. donation stabilises the square pyramidal intermediate. - PowerPoint PPT Presentation
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Reactions of octahedral complexes:the stereochemical consequences
Stereochemistry of a dissociation reaction at an Oh complex
A
X
A A
Y
A
Y
Y
Y
Y
Y
A
A
Y
Berry pseudo rotation
100% trans
cis transcis:trans 2:1
The nature of A will control the nature of the intermediate, and hence the stereochemistry of the products
• X is cis to A, and A is a donor A
+ X-
Hence get retention of stereochemistry – close to 100% cis
A Y
Avacant metal d2sp3 orbital
donation stabilises the square pyramidal intermediate
trans product
• X is trans to A, and A is a donor
A
Y
A
A
Xviewed down the z axis Y
YYA
A
donation stabilises the trigonal bipyramidal intermediateLeads to a mixture
of cis and trans
The better the donor ability of A, the more the trigonal bipyramidal structure is formed, and the more of the cis product will be produced.
e
f
ba
d
c
e
f
ba
d
c
Racemisation of tris-chelate complexes
Three pathways
Bailar twist
a
e
b
f
cd
lambda isom er
a
e
b
f
cd
a
eb
fc
d
a
e
b
f
c
d
a
e
b
f
c
d
e
f
b
a
d
c
delta isom er
Ray-Dutt twist
f
a
d c
delta isom er
f
a
d c
f
ad
c
f
a
d c
f
a
d c
lambda isom er
Dissociation/Reformation