Carboxylic esters as ligands

Abstract

Only four papers have been published on carboxylic esters as ligands. M.F.Lappert, J.Chem., 817 (1961). R.W.Hay, Aust. J.Chem., 17, 759 (l964). M.P.Springer and C.Curran, Inorg.Chem., 2, 1270 (1963). R.P.Houghton and D.J.Pointer, J.Chem.Soc, 3302 (1964). Boron halides form 1:1 complexes with ethyl acetate M.F.Lappert, J.Chera., 817 (1961), which have been shown by infrared spectroscopy to be coordination compounds having the carbonyl-oxygen acting as donor atom, [Structure (I)]: the C=0 stretching frequency is significantly lower for the 1:1 complexes than for the ester. The extent of this shift gives a quantitative measure of the strength of the Lewis acid (with ethyl acetate as the reference base), and the relative strengths of the boron halides are Bbr3> BC13> BF3. It has also been shown that hydrogen chloride is associated with ethyl acetate by protonation of the acyl-oxygen atom [Structure (II)] and not the alkyl-oxygen atom, and this has a bearing on the mechanisms of acid-catalysed carboxyl reactions, eg., acid catalysed hydrolysis of carboxylic esters.