Complexes Containing Aminoalcoholate Ion

Aminoalcohols such as 2-aminoethanol(ethanolamine, Heta) and 2-amino-1-pro-panol(propanolamine, Hpra) have been known to combine as a neutral bidentate or as a deprotonated aminoalcoholate In 1973, Ogino et al. communicated CD spectral studies of [Co(en)2(Heta)p and [Co(en)2(L-Hpra)fthe complexes were prepared from frans-[Co8r2(en)2] and the Ugands via [Co8r(en)2(Ham)] (Ham = Heta or L-Hpra) according to 8uckingham et al. Each complex was separated into two diastereoisomers by Sephadex chromatography. 

Okazaki and Shibata reported on the [Co(Heta or S-Hpra)(N)2(0)2]-type complexes in which the (N)2(0)2 moiety denotes two glycinate, two P-alaninate, ethylenediamine plus oxalate, or two ammonia plus oxalate. For a [Co(Heta)-(N)2(0)2]-type complex, the possible geometrical isomers are illustrated in Fig. 5.7, 

These complexes were prepared from carbonato complexes such as [Co(C03)-(am)2] (am = gly or p-ala), [Co(C03)(ox)(en)] , ds-[Co(C03)(ox)(NH3)2] as the starting materials. For the isolation of the geometrical isomers, each reaction mixture was first chromatographed on a cation-exchange resin in Na form using an aqueous NaCl as eluent, and then rechromatographed under alkaline condition, using water as eluent. 

The absorption spa tra measured at pH ca. 2.0 and pH ca. 8.0 are shown in Figs. 5.8 and 5.9, respectively. Each of the deprotonated complexes exhibits a spectrum quite different from that of the corresponding protonated complexes. 

The trans(H- isomer of each of [Co(gly)2(eta)] and [Co(P-ala)2(cla)] exhibits recognizable splitting in the T2g band and no splitting in the Tj, band. Furthermore, in the spectrum of c s,cis-[Co(gly)2(eta)], the T2g band exhibits a broad maximum, and the Tjg band shows explicit splitting. The intense CD peak at ca. 25(XX)cm was observed in the CD spectrum for c-[Co(gly)2(eta)]. From the polarized crystal spectra and the results of X-ray analysis of the isomers of [Co(eta)(gly)2], the a- and K-antibonding parameters for the alcoholate O atom were estimated by the Angular Overlap Model and found to be comparable with those for the OH ligand. 

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