2 Homometallic Alkoxides

334 Alkoxo and Aryloxo Derivatives of Metals
3.1 Alkali Metal Dimetallic Alkoxides
3.1.1 Lithium
Complexes of general formula [Li4K4⊲OSiMe3⊳8 x ⊲OBu t ⊳x ] have been prepared and
the structure of [Li4K4⊲OSiMe3⊳6.8⊲OBu t ⊳1.2] has been determined. The array of metals
comprises two orthogonal trigonal prisms fused at their base which consists of a
near square plane of potassium ions with two lithiums above and two below the
plane. The trimethylsiloxo or tert-butoxo ligands cap each of the four triangular
and four trapezoidal faces. 446 The lithiums are three-coordinated and the potassiums
four-coordinated. The lithium-bridged spirocyclic magnesiasiloxane complex
[f⊲py⊳2Lig2 -fOSi⊲Ph⊳2OSi⊲Ph⊳2OSi⊲Ph⊳2Og -fOSi⊲Ph⊳2OSi⊲Ph⊳2OgMg] has fourcoordinated
lithium and four-coordinated (distorted tetrahedral) magnesium 447
(Table 4.17, pp. 339–345).
Four-coordinated Li and pseudo-four-coordinated yttrium are found in [Li⊲thf⊳2⊲ -
OBu t ⊳2YfC5H4SiMe3g2]. 448 In the trinuclear complex [⊲thf⊳2Li⊲ -OBu t ⊳⊲ , 2 -
CH2SiMe2⊳Y⊲CH2SiMe3⊳⊲ -OBu t ⊳Li⊲thf⊳2] the four-coordinated lithiums are bridged
by Bu t O and Me2Si⊲CH2⊳2 ligands, giving the Y a distorted square pyramidal
configuration. 449 In the remarkable salt [f⊲thf⊳Lig4⊲ 4-OBu t ⊳4⊲ 4-
Cl⊳Y⊲CH2SiMe3⊳x ⊲OBu t ⊳1 x ] C [Y⊲CH2SiMe3⊳4] salt the pentanuclear cation has a
five-coordinated Y and four-coordinated Li. 450 Interestingly, the chloride ion is incorporated
into the same structure as the lithiums. The dinuclear complex
[⊲thf⊳Li⊲ -OBu t ⊳2YfCH⊲SiMe3⊳2g2] has three-coordinated (trigonal planar) Li and
four-coordinated (pseudo-tetrahedral) Y. 451 The [⊲thf⊳3Li⊲ -Cl⊳Y⊲OCBu t 3 ⊳3] complex
also has four-coordinated metals. 452
With titanium(IV) the tetranuclear compound [Li2⊲ 3-OPr i ⊳2⊲ -OPr i ⊳4Ti2⊲OPr i ⊳4]
has distorted tetrahedral Li and distorted TBP titanium. 453 In the tetranuclear mixed
ligand complex [f⊲thf⊳Lig2⊲ 3-OMe⊳2⊲ -OPr i ⊳4fTi⊲OPr i ⊳2g2] the lithium is fourcoordinated
and the Ti(IV) is octahedrally coordinated. 176
The bulky ligand Bu t 3 CO gave rise to the dinuclear complex [⊲Et2O⊳2Li⊲ -
Cl⊳ZrCl⊲OCBu t 3 ⊳2] with four-coordinated Li and the pseudo-trigonal bipyramidal
zirconium(IV). 454 In the heterometallasiloxane [⊲Me5C5⊳2Zr⊲ , 2 -OSiPh2O⊳⊲ -
OH⊳Li⊲ -OH⊳Li⊲ , 2 -OSiPh2O⊳Zr⊲C5Me5⊳2] another tetranuclear structure involves
three-coordinated Li and pseudo-four-coordinated zirconium. 455
In the hafnium complex [Li2⊲ 3-OPr i ⊳2⊲ -OPr i ⊳4Hf2⊲OPr i ⊳4] the hafniums are in
an edge-bridged bi-octahedral structure Hf2⊲OPr i ⊳10 which is bridged by two lithiums
in pyramidal three-coordinated configurations. 200 The corresponding Nb(V) complex
[⊲EtOLi⊳2⊲ 3-OEt⊳2⊲ -OEt⊳4Nb2⊲OEt⊳2⊲OH⊳2] has octahedral niobium and fourcoordinated
lithium. 456 However, in [Li⊲ -OEt⊳4Nb⊲OEt⊳2]n an infinite helical polymer
occurs owing to the cis configuration of the terminal Nb-OEt groups. 457 In the structure
of the tetranuclear [⊲Me3SiCH2O⊳3Nb⊲ 3-OCH2SiMe3⊳⊲ -OCH2SiMe3⊳2Li2⊲ 3-
OCH2SiMe3⊳⊲ -OCH2SiMe3⊳2Nb⊲OCH2SiMe3⊳3], the two niobium octahedra are
bridged by the two lithium atoms which are each bonded to four alkoxo groups.
In the lithiatantalasiloxane complex [⊲py⊳2Lif , 2 -O⊲SiPh2O⊳2g2f 2 -O⊲SiPh2O⊳2Tag]
the three tetraphenyl siloxanediolate ligands chelate the octahedral Ta(V) and two of them
bridge the lithium. 459