Chromium complexes camphorates

Equilibrium studies have shown that the first formation constant of the chromium(iii)-ethylenediamine system is < 10, over 10 -fold smaller than the value (10 ) previously reported. [Cr(en)3 (tn) ] (x = 0—3 and tn = tri-methylenediamine) complexes have been prepared and resolved using nitro-(-f )D-camphor. These mixed complexes have the same absolute configuration, A, as the pure [Cr(en)3] and [Cr(tn)3] species. Selective intervention of an optically active counterion in the relaxation processes of excited enantiomeric complexes can lead to partial resolution. This has been achieved for [Cr(phen)3] using D-tartrate. ... 

Camphorate complexes of chromium (III) have been studied. The four possible isomers of the tris complex of (+ )-3-acetylcamphorate (173) were isolated,752,753 and absolute configurations were tentatively assigned. The photoisomerization of these complexes has been investigated 754 quantum yields of the order of 10-3 were obtained with visible or ultraviolet radiation at temperatures around 100 °C. Bond-breaking processes were held to be important in the reactivity of cis isomers. 

The tris(ethylenediamine) chromium (III) ion was first resolved by Werner6 by means of sodium 3-nitro-(+)-camphor. What has been said concerning the resolution of the corresponding rhodium compound holds true of the chromium compound, except that for the chromium compound the solubility difference of the diastereoisomeric chloride (+)-tartrates is so small that a resolution via these diastereoisomers has not been achieved.5,6 The method reported here is essentially the same as the one described for the rhodium complex but with minor alterations... 

Phenol chromium tricarbonyl complex, n-butyllithium (2,mols) tertramethylethylenediamine (3 mols.) in THF at 60C for 3h. Benzaldehyde added and after oxidative decomplexation by addn. of Ij and camphor sulphonic acid in 10%HC/THF l-(3-hydroxyphenyl)benzyl slcohol obtained. 

In another example, the hydrogenation of the azapenam (55,6/ )-6-methoxy-2,2,6-trimethyl-l,4-diazabicyclo[3.2.0]heptan-7-one (154), prepared by reaction of a pentacarbonyl chromium carbene complex with liV-Boc-4,4-dimethylimidazoline, in the presence of 1.1 equiv. of racemic camphor sulfonic acid resulted in the cleavage of the Boc group and ring expansion of the azapenam to hexahydro-3,3,6-trimethyl-6-methoxy-5//-l,4-diazepin-5-one (155) in 71% yield <92JA5010>. It was pointed out that the ready availability of a variety of substituted chromium carbene complexes and imidazolines would make this a general route to this class of diazepine. 

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