Synthesis and Characterization of Oxybis(diacetoxyborane) Complexes of Bifunctional Tridentate Sulphur Donor Benzothiazolines

Abstract

Condensation reactions of salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 2-hydroxyacetophenone and 2,4-pentanedione with o-aminobenzenethiol lead to ring closure with the formation of heterocyclic compounds, i.e. benzothiazolines. These, however, remain in equilibrium with the azomethine form in the solution state. On reacting oxybis(diacetoxyborane), [(AcO)₂B]₂O, with these benzothiazolines in presence of anhydrous toluene, the stepwise replacement of the acetoxygroups with the azomethine moiety takes place and the equilibrium is shifted towards the formation of azomethine derivatives of boron. The 1:1 and 1:2 (metal:ligand) molar reactions yield (ONS)B-O-B(OAc)₂ and (ONS)B-O-B(ONS) (where ONSH₂ represents the ligand molecule) types of complexes, respectively. The 1:1 complexes undergo exchange reactions with 1, 2-dihydroxybenzene and 2-methylpentane-2, 4-diol. Possible structures are suggested on the basis of elemental analysis, molecular weight determinations, conductance measurements and electronic, infrared and proton magnetic resonance spectral studies.