Chemistry Reference
In-Depth Information
whereas R D Me produces a five-membered metallacycle. All of the metallated species
produce [W(OAr)(H)
3
(PMe
3
)
4
] under H
2
.
The addition of 4-methylphenol to the ruthenium species [Ru(
2
-Me
2
P-
CH
2
)(Me)(PMe
3
)
4
] produces the cyclometallated aryloxide [Ru
O-
1
-C
6
H
4
PMe
3
4
].
209
Reaction with CO and CO
2
was found to lead to insertion into the metal - aryl bond to
produce five- and six-membered metallacycles respectively.
210
The overall ortho-metallation of the phenoxide nucleus can also take place with 2-
formylphenoxides. The intermediate, chelated acyl formed
via
activation of the formyl
CH bond,
211
,
212
undergoes decarbonylation (typically at Ru or Os metal centres) to
produce the four membered metalacycle.
213
,
214
A variety of low valent aryloxide derivatives of the early transition metals undergo
intramolecular CH bond activation. Attempts to isolate the d
2
-species [M(OAr)
3
]or
[M(OAr)
2
Cl] (OAr D 2,6-di-
tert
-butylphenoxide or 2,6-di-phenylphenoxide; M D Nb,
Ta) by reduction of the corresponding d
0
-chloride leads instead to bis-cyclometallated
compounds (Eq. 6.60).
215
Me
Bu
t
Me
O
H
2
C
2Na/Hg, −2NaCl
t
[Ta(OC
6
H
3
Bu
2
-2,6)
2
Cl
3
]
Ta
Cl
−H
2
O
H
2
C
Bu
t
Me
Me
(6.60)
Ph
Ph
O
2Na/Hg,
−
2NaCl
[Ta(OC
6
H
3
Ph
2
-2,6)
3
Cl
2
]
Ta
O
−
H
2
O
Ph
Ph
The reaction probably proceeds
via
initial oxidative addition of the first CH bond
followed by subsequent activation and H
2
elimination via
-bond metathesis (see
below). Related reactivity is observed upon reduction (4 Na per W) of the tetrachlo-
ride [W(OC
6
H
3
Ph
2
-2,6)
2
Cl
4
], although in this case an intermediate [W(OC
6
H
3
Ph-
6
-
C
6
H
5
)(OC
6
H
3
Ph
2
-2,6)(PMePh
2
)] could be isolated and shown to thermally convert to
the bis-cyclometallated product and H
2
.
29
,
216
