Chemistry Reference
In-Depth Information
3-
2-
Cl
Cl
oxidation
Cl
Cl
Cl
-e
+e
Cl
Cl
Cl
III
IV
[IrCl
6
]
3-
[IrCl
6
]
2-
Ir
Ir
(6.29)
Cl
Cl
Cl
Cl
reduction
Alternatively, the coordination number and/or the ligand set can change substantially in
an irreversible oxidation reaction. Any reduction reaction of the product will then not
regenerate the original complex.
Not only are oxidation reactions fairly common, but also one may employ reduction
reactions in simple synthetic paths, provided the reduced form is also in a stable oxidation
state. Two examples of reduction reactions, with the metal oxidation states included, are
given in (6.30) and (6.31).
IV
II
[Pt (en)
3
]Cl
4
[Pt Cl
2
(en)]
(+ 2 (en) + 2 Cl
-
)
4+
+2e
HN
NH
NH
(6.30)
IV
NH
2
Cl
Pt
II
Pt
NH
NH
HN
NH
2
Cl
Zn/HCl
III
[Mo Cl
5
O]
2-
[Mo Cl
6
]
3-
(+ OH
-
+ Zn
2+
)
2-
V
O
Cl
Cl
Cl
V
3-
Cl
(6.31)
Mo
Cl
Cl
Cl
Cl
III
Cl
Mo
Cl
Cl
Reduction reactions occurring along with substitution chemistry are also well known, and
the examples above are such cases. Another simple example involves the [IrCl
6
]
2
−
ion,
which undergoes both reduction (with hypophosphorous acid) and substitution in (6.32).
IV
III
III
[Ir Cl
6
]
2-
cis
-[Ir Cl
2
py
4
]
-
fac
-[Ir Cl
3
py
3
]
H
2
PO
2
2-
pyridine
boil, 30 min
boil, 6 hrs
1-
Cl
III
Cl
(6.32)
2-
Cl
N
N
Cl
N
N
N
III
Ir
Ir
Cl
Cl
Cl
IV
Ir
Cl
Cl
N
N
Cl
Cl
Because of the slow substitution chemistry of iridium, sequential reaction steps are well
separated in terms of reaction time, so that the initial product of the redox-substitution
reaction undergoes further simple substitution only with prolonged heating.
Where a reactive lower oxidation state results, a key concern is the necessary protection
of the reduced complex from air or other potential oxidants, as they are often readily re-
oxidized. Usually, this requires their handling in special apparatus such as inert-atmosphere
boxes or sealed glassware in the absence of oxygen. Where active metal reducing agents
(such as potassium) are employed, special care with choice of solvent is also necessary.
The nickel reduction reaction (6.33) can be performed in liquid ammonia as solvent, since
the strongly-bound cyanide ions are not substituted by this potential ligand.
[Ni (CN)
4
]
2-
+ 2 K
[Ni (CN)
4
]
4-
+ 2 K
+
0
II
liquid
NH
3
(6.33)
4-
2-
NC
CN
CN
NC
CN
CN
0
II
Ni
Ni
NC
NC
