Tetraalkoxyaluminates of Nickel(II), Copper(II), and Copper(I)

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2·2HOiPr, with nickel(II) in a distorted
octahedral oxygen environment, or Ni[Al(OiPr)4]2·py, with nickel(II) in a square-pyramidal O4N coordination sphere,
or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated
complex is Ni[(iPrO)3AlOAl(OiPr)3]·3py (with nickel(II) being sixfold-coordinated), which may also be described as
a “NiO” species trapped by two Al(OiPr)3 Lewis acid−base systems stabilized at nickel by three pyridine donors.
Copper(I) compounds have been isolated in three forms:  [(iPrO)4Al]Cu·2py, [(tBuO)4Al]Cu·2py, and Cu2[(tBuO)4Al]2.
In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted
N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell
[Cu−Cu 2.687(1) Å] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates
have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being
tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu·py (pentacoordinated copper similar to the nickel derivative). Finally,
a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by
dimerization, with the formula {[(tBuO)4Al]Cu(OH)·py}2. The formation of all of these isolated products is not always
straightforward because some of these compounds in solution are subject to decomposition or are involved in
equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize
the compounds.