Bimetallic Borate Derivatives of the Salen Ligands

A series of bimetallic borate derivatives of the Salen
ligands have been prepared. They are of the general
formula
Salen{B(OR)2}2 (where Salen =
(N,N‘-1,n-alkylenebis(salicylideneimine);
alkylene = ethylene [R = Me (1), Et
(6)], propylene [Me (2), Et (7)],
butylene [Me (3), Et (8)], pentylene [Me
(4), Et (9)], and hexylene [Me (5),
Et
(10)]) and the analogous Salen(tBu)
derivatives (where Salen(tBu) =
N,N‘-1,n-alkylenebis(3,5-di-tert-butylsalicylideneimine); alkylene = ethylene [R = Me (11), Et
(16)], propylene [Me (12), Et
(17)], butylene [Me (13), Et
(18)], pentylene [Me (14), Et
(19)], and hexylene [Me (15), Et
(20)]). All of the compounds were
characterized
by spectroscopic (1H NMR, IR) and physical (mp, analyses)
techniques. X-ray crystallographic data are presented
for 1, 4, 7, 10,
12, and 16. Differences among these
structures were found to be dependent upon the length of
the ligand alkylene “backbone”.