2 Homometallic Alkoxides

518 Alkoxo and Aryloxo Derivatives of Metals
Table 6.17 Strontium aryloxides
Bond Bond
length ( ˚A) angle ( Ž )
Compound Aryloxide M–O M–O–Ar Ref.
[Sr4⊲OAr⊳8⊲HOAr⊳2⊲THF⊳6]
6-coord. Sr
[Sr(OAr) 2⊲THF⊳3]
OC6H5
2-OC6H5
3-OC6H5
OC6H2Bu
2.450 (7)
2.404 (7)–2.495 (7)
2.512 (7)–2.558 (6)
i
t tbp, equatorial OAr
3-2,4,6 2.306 (5)
2.323 (5)
175
176
ii
[Sr3⊲OAr⊳6⊲HMPA⊳5]
[Ba2Sr6⊲OAr⊳14⊲O⊳2⊲H⊳2⊲HMPA⊳6]
two fused Sr3Ba2 square
pyramids with 5-O, 6-coord.
Sr and 6- and 8-coord. Ba
OC6H5
2-OC6H5
3-OC6H5
2-OC6H5
3-OC6H5
2.34 (3)
2.38 (3)–2.53 (2)
2.52 (2)–2.65 (2)
2.52 (3)–2.62 (4)
2.44 (3)–2.71 (3)
169 iii
iv
[Sr(OAr) 2].5H2O
8-coord. Sr, polymeric structure
2-OC6H2⊲NO2⊳3-
2,4,6
2.604 (4), 2.843 (4) v
i S.R. Drake, W.E. Streib, M.H. Chisholm, and K.G. Caulton, Inorg. Chem., 29, 2707 (1990).
ii S.R. Drake, D.J. Otway, M.B. Hursthouse, and K.M.A. Malik, Polyhedron, 11, 1995 (1992).
iii K.G. Caulton, M.H. Chisholm, S.R. Drake, K. Folting, J.C. Huffman, and W.E. Streib, Inorg.
Chem., 32, 1970 (1993).
iv K.G. Caulton, M.H. Chisholm, S.R. Drake, K. Folting, and J.C. Huffman, Inorg. Chem., 32,
816 (1993).
v J.M. Harrowfield, B.W. Skelton, and A.H. White, Aust. J. Chem., 48, 1311 (1995).
6.2.3 Group 3 Metal and Lanthanide Aryloxides
The synthesis of group 3 metal and lanthanide aryloxides can be achieved utilizing
metal halide substrates reacted with alkali metal aryloxides. Homoleptic, basefree
metal(III) aryloxides can be formed by this method when the aryloxide is
bulky, e.g. [Sc(OC6H2Bu t 2 -2,6-Me-4)3], 289 [M(OC6H3Bu t 2 -2,6)3](MD La, Sm), 290 and
[Ce(OC6H3Bu t 2 -2,6)3] 291 (which is also obtained via [CefN⊲SiMe3⊳2g3]. 292 However, in
a number of homoleptic derivatives there exists association via -interaction with the
phenoxide nucleus and adjacent metal centres, e.g. [(ArO)2M( 2-O- 6 -OAr)2M(OAr)2]
(M D La, Sm, Nd; ArO D OC6H3Pr i 2 -2,6) (Table 6.19).293 The reaction of substrates
such as [SmfCH⊲SiMe3⊳2g3] (itself prepared from a homoleptic aryloxide) [Cp3Ln]
(Ln D Nd, Yb), 91 [Cp Ł 2 Sm(thf)2], 294 and [ScfN⊲SiMe3⊳2g2⊲THF⊳3] with phenols has
been shown to yield corresponding metal(II) and (III) aryloxides. 295 An important
alternative synthetic strategy involves reaction of the lanthanide metal itself with the
phenol. This can occur in the presence of aryl-mercury reagents (Eq. 6.12). 296,297 Direct
reaction of europium 298 and ytterbium 299 with 2,6-dialkylphenols in liquid ammonia
has been reported. Recently N-methylimidazole and acetonitrile have been shown to
be suitable solvents for the production of europium aryloxides from the metal. 300 The
conversion of ytterbium(III) aryloxides to the corresponding bis-aryloxide has been
achieved using Yb metal as the reducing agent.
In the case of 2,6-diphenylphenoxide ancillary ligands, chelation to the electrondeficient
metal via -interactions with ortho-phenyl rings has been observed in a large
number of cases (Table 6.19). In some compounds only a fraction of the arene ring