2 Homometallic Alkoxides

Metal Aryloxides 479
whereas R D Me produces a five-membered metallacycle. All of the metallated species
produce [W(OAr)(H)3(PMe3)4] under H2.
The addition of 4-methylphenol to the ruthenium species [Ru( 2 -Me2P-
CH2)(Me)(PMe3)4] produces the cyclometallated aryloxide [Ru⊲O- 1 -C6H4⊳⊲PMe3⊳4]. 209
Reaction with CO and CO2 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 2formylphenoxides.
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)2Cl] (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
t
[Ta(OC6H3Bu2-2,6) 2Cl3] [Ta(OC 6H 3Ph 2-2,6) 3Cl 2]
2Na/Hg, −2NaCl
−H2
2Na/Hg, −2NaCl
−H 2
Me
Me
Bu t
H2C O
Ta Cl
H2C O
But Me
Me
Ph
O Ph
Ta O
O Ph
Ph
(6.60)
The reaction probably proceeds via initial oxidative addition of the first CH bond
followed by subsequent activation and H2 elimination via -bond metathesis (see
below). Related reactivity is observed upon reduction (4 Na per W) of the tetrachloride
[W(OC6H3Ph2-2,6)2Cl4], although in this case an intermediate [W(OC6H3Ph- 6 -
C6H5)(OC6H3Ph2-2,6)(PMePh2)] could be isolated and shown to thermally convert to
the bis-cyclometallated product and H2. 29,216