Page 51 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

1.17 OXIDATIVE ADDITIONS AND REDUCTIVE ELIMINATIONS 31
Quite a variety of mechanisms are possible for the two processes, including radical
pathways. We’ll focus here, however, on just a couple of polar mechanisms. A concerted,
one-step mechanism may be written as follows:

X
X
E E (1.52)
Y
Y

Another common pathway involves a two-step polar addition. As written below, the overall
process may be viewed as a tandem S 2–A process:
N

X
2 +
S N A
E X Y − E X E (1.53)
Y
Y

The following chlorination reactions are good examples of oxidative addition involving
main-group elements:

PCl + Cl → PCl 5 (1.54)
3
2
ICl + Cl → ICl 3 (1.55)
2

As in the case of many main-group reactions, the mechanisms have not been investigated for
these two reactions. Given that Cl is a good electrophile, either of the above mechanisms
2
seems quite reasonable.
For reductive elimination, we may envision the reverse of the above two pathways. A
concerted, one-step reductive elimination may be depicted as follows:

X
X
E E + (1.56)
Y
Y

Alternatively, we may envision a D–S 2 sequence:
N

X −
+ Y
D S 2
N
E E X E + X Y (1.57)
Y