Chelated Borates: Synthesis, Reactivity, and Cation Formation

The ligands N-salicylidene-o-aminophenol (LH(2)), N-(5-chlorosalicylidene)-o-aminophenol (L(Cl)H(2)), and N-(5-bromosalicylidene)-o-aminophenol (L(Br)H(2)) were used to prepare a series of borates having the formulas LBOR (R = Me (1), Et (2), (n)Pr (3), (n)Bu (4)), L(Cl)BOR (R = Me (5), Et (6), (n)Pr (7), (n)Bu (8)), and L(Br)BOR (R = Me (9), Et (10), (n)Pr (11), (n)Bu (12)). Either 1-4 or 9-12 could be combined with HOSiPh(3), to form unique compounds possessing a single B-O-Si linkage, LBOSiPh(3) (13) and L(Br)BOSiPh(3) (14), respectively. The charged species, [LB(thf)](+)OTf(-) (15) forms when 1 is combined with HOTf. It can be used as a catalyst for the oligomerization of propylene oxide. By comparison, [(n)Bu(2)B](+)OTf(-) effects the oligomerization to the same extent as 15, but the neutral species, 1-4, 13, and 14 do not, even under forcing conditions. All of the compounds were characterized by melting point, (1)H NMR, IR, elemental analyses, and, in the case of 13, by X-ray crystallography.