2 Homometallic Alkoxides

Metal Aryloxides 533
carbon atoms approach the metal centre. 301 The -interactions not only occupy vacant
sites around the metal centres but can also control the geometries adopted. 302
A large number of monomeric, Lewis base (typically O-donor) adducts of the
bis and tris aryloxides have now been isolated and studied (Table 6.19). With the
bulkiest ligands, only four-coordinate adducts such as [Yb(OC6H2Bu t 3
-2,4,6)3(THF)] 303
and [Yb(OC6H2But 2-2,6-Me-4)2(thf)2] 92 are generated. With intermediate sized
aryloxides or donor ligands a large number of five-coordinate adducts have been
obtained, e.g. [M(OAr)3(THF)2] (M D La, 304 Pr, 305 Sm, 306 Eu, 307 Gd, Lu308 ) and
[Yb(OC6H3Ph2-2,6)2(THF)3]. 309 Higher coordination numbers are common for very
small or chelating donor ligands, e.g. six-coordinate [Eu(OC6H3Bu t 2
-2,6)2(NCMe)4] 310
and [Yb(OC6H3Ph2-2,6)2(DME)2] 309 as well as seven-coordinate [La(OC6H3Pri 2- 2,6)3(NH3)4] 293 and eight-coordinate [La(OC6H3Me2-2,6)3(tetraglyme)]. 311
It is also common that mixed metal derivatives of the lanthanides and group 1
metals are the products of synthesis. This can occur for small aryloxides leading to
clusters, e.g. [La2Na3( 4-OAr)3( 2-OAr)6(dioxane)5] (OAr D OC6H4Me-4), 312 as well
as in the generation of more discrete species with bulkier aryloxides, e.g. [(thf)Li( 2-
OAr)2La(OAr)2(THF)] (OAr D OC6H3Pri 2-2,6).313 In some situations the alkali metal
interacts with the aryloxide -nucleus, e.g. [Cs( -Ar-O)2La(OAr)2] (OAr D OC6H3Pri 2- 2,6). 314 In an unusual reaction, anhydrous [LnCl3] (LnDNd or Er) was reacted with
[NaOC6H3Ph2-2,6] in 1,3,5-tri-tert-butylbenzene at 300ŽC to generate [NaLn(OAr)4]
which reacts with DME to form the discrete tetra-aryloxide anions. 315
Aryloxide derivatives can be valuable precursors for the synthesis of lanthanide
alkyl compounds. The first homoleptic alkyls, [MfCH⊲SiMe3⊳2g3] (MDLa, Sm) were
prepared by treatment of [M(OC6H3But 2-2,6)3] with [LifCH⊲SiMe3⊳2g]. 290 However,
only partial substitution of aryloxide ligands occurs in most cases and mixed alkyl,
aryloxides can be generated. For example the corresponding tris-aryloxides are a good
starting material for the synthesis of [CpŁM(OC6H3But 2-2,6)2] which can be converted to
[CpŁCM(OC6H3But 2-2,6)fCH⊲SiMe3⊳2g] (MD Ce, 291 Y316,317 ). The yttrium compound
undergoes hydrogenolysis to the dimeric hydride [CpŁ (ArO)Y( -H)]2 which has an
extensive olefin chemistry, including formation of polymers via [CpŁ (ArO)Y( -H)( -
R)Y(OAr)CpŁ ] intermediates. 317 Neither of the methyl compounds [CpŁ (ArO)Y( -
Me)]2 (ArO D OC6H3But 2-2,6) or [CpŁ (Me)Sc( -OAr)]2 (ArO D OC6H3But 2-3,5)318 react with olefins. 317
The alkylation of precursors [Y(OSiButAr2)(OC6H3But 2-2,6)2] (obtained from
the precursor [Y(OSiButAr2)ffN⊲SiMe3⊳2g2]g with [LiCH2SiMe3] yields the
salt complexes [LiY(OSiButAr2)(OC6H3But 2-2,6)(CH2SiMe3)2] 319 and [(THF)Li( 2-
OAr)2Sm(CH2SiMe3)( 2-OAr)( 2-CH2SiMe3)Li(THF)] 320 (ArO D OC6H3Pri 2-2,6) showing that elimination of LiOAr is sometimes not facile.
6.2.4 Actinide Aryloxides
The metals thorium and uranium (as with the chemistry in general of these elements)
dominate actinide aryloxide chemistry. Synthetic strategies normally focus on the halides
reacting with group 1 metal aryloxides or reaction of metal amides with phenols. 321,322
An important piece of early work was the demonstrated interconversion of eightcoordinate
[UMe4(dmpe)2] and [M(OPh)4(dmpe)2](MD Th, U: Table 6.20) by addition
of phenol or MeLi to each substrate respectively. 323 The reaction of the cyclometallated