Tris-Complexes of 3-Substituted Camphor

A question arises whether stereoselectivity would be shown in tris complexes with ligands forming planar chelate rings. One group of such ligands is the 3-substituted camphors (I). 

The formyl derivative (R = H) is hydroxymethylenecamphor (Hhmc) and the acetyl derivative (R = CH3) is 3-acetyl camphor (Hate). For a tris(3-substituted camphorato)cobalt(lll) complex, four diastereoisomers are possible A-wer, K-mer, b -fac and K-fac (Fig. 4.7). 

In 1966, Dunlop et al. reported on the tris-complexes of (H-)-hydroxymethylene-camphorate, [Co((- -)-hmc 3] they prepared this complex by the reaction of Na[Co(C03)j] 3 H2O and the ligand in a water—benzene mixture (see 2 4) and separated the product into the A-mer and A-/ac isomers in the ratio 85/15. This marked stereoselectivity was confirmed by similar studies on the [Co (—)-hmc 3] and [Co (-t-)-atc 3] complexes For the former complex, A-mer and A-fac isomers 

At about the same time. King and Everett also separated the four isomers of [Co (-f )-atc 3] by preparative thin-layer chromatography on silica gel. The relative amounts of the diastereomers were determined from each TLC band, dissolved in an organic solvent. The absorbances of the solutions resulted in 48.2,29.5,12.9 and 9.4 % for A-mer, A-mer, A-fac and A-fac, respectively. The stereoselectivities, A-mer j A-mer and A-fac j A-fac were calculated as 1.63 and 1.37, respectively. 

7 Complexes Containii Optically Active Tartaric Acid 

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