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”.