2 Homometallic Alkoxides

Heterometallic Alkoxides 221
Heterometallic alkoxides of subvalent main group metals (ns 2 configuration) located
at the apices of one or two (fused) trigonal bipyramids are able to function as excellent
electron donors to various transition metal carbonyls as illustrated 163 in two typical
examples (3-V) and (3-VI)
(OC)5Cr
Sn
R
O
R
O
O
R
(3-V)
(OC) 5Cr Sn
R
O
R
O
O
R
In Cr(CO) 4
(3-VI)
In
In
Fe(CO)4
R
O
R
O
O
R
Sn
Cr(CO) 5
In these carbonyl adducts the reactivity sequences are In I × Ge II > Sn II > Tl I ¾ Pb II
and Ni⊲CO⊳4 > Fe⊲CO⊳5 > Mo⊲CO⊳6 > Cr⊲CO⊳6 > W⊲CO⊳6.
Purdy and George 127 obtained two interesting alkali (Na, K) tritertiarybutoxozincates
by the 1:3 molar reaction of ZnCl2 with alkali tertiary butoxide:
ZnCl2 C 3M⊲OCMe3⊳ ! 1
2 [fMZn⊲OCMe3⊳3g2] C 2MCl ⊲3.128⊳
Both these zincates are soluble in hydrocarbon solvents and are volatile (Na and
K derivatives start to sublime at 50ŽC and 90ŽC, respectively, under vacuum).Their
structures are centrosymmetric, with alkali metal atoms positioned above and below
the Zn2O2 plane.
For other chelating ligands, a few examples are mentioned below by the formulae of
the derivatives: KSb⊲OBut⊳4, fKBi⊲OBut⊳4gn, K2Sb⊲OBut⊳5.C4H8O2, 59 M2Sb4⊲OEt⊳16
(M D Mn, Ni), 111,112 MSb⊲OR⊳6 (M D Li, Na, K; R D Me, Prn ,Pri ,Bun ,But ), 232 and
YBa2⊲OBut⊳7⊲ButOH⊳. 233
3.6 Higher Heterometal Alkoxides and Single-source Precursors
Synthesis (by metathetic reactions) of a large number of hetero-tri and tetrametallic
alkoxides of a number of metals has been reported since 1985 (Section 2.3 and
Table 3.4(c)) mainly from the research school of Mehrotra 7–9,17,101,149–159 and the
potentiality of their applications as “single-source” precursors 12,20,22,24,25,43 for highpurity
heterometallic-oxide ceramic materials has been emphasized since 1988.
However, the lingering scepticism about these novel and stable (as depicted by
their volatility) coordination systems has been allayed only since 1996 when the
crystal structure of the first heterotrimetallic derivative [fCd⊲OPr i ⊳3gBafZr2⊲OPr i ⊳9g]