The preparation and characterisation of chromium(III) complexes of C-meso-5, 12-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane (LM). Aquation and base hydrolysis kinetics ofcis- andtrans-[CrLMCl2]+ |
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Authors: | Robert W Hay Mahesh P Pujari Ramesh Bembi Bakir Jeragh Paul R Norman |
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Institution: | (1) Chemistry Department, University of Stirling, FK9 4LA Stirling, U.K.;(2) Present address: Chemistry Department, University of St. Andrews, KY16 9ST St. Andrews, U.K. |
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Abstract: | Summary The reaction of CrCl3(DMF)3] with C-meso-5, 12-dimethyl-1, 4, 8, 11-tetra-azacyclotetradecane(LM) in DMF gives a mixture ofcis-CrLMCl2]Cl (ca. 90%) andtrans-CrLMCl2]Cl (ca. 10%). These complexes are readily separated, as thecis-isomer is insoluble in warm methanol while thetrans-isomer is soluble. Using the dichlorocomplexes as precursors it has been possible to prepare a range ofcis-CrLMX2]+ complexes (X=Br–, NO
3
–
, N
3
–
, NCS– and X2=bidentate oxalate) and alsotrans-CrLMX2]+ complexes (X=Br–, H2O or NCS–). The spectroscopic properties and detailed stereochemistry of the complexes are discussed.The aquation and base hydrolysis kinetics ofcis- andtrans-CrLMCl2]+ have been studied at 25° C. Base hydrolysis of thecis-complex is extremely rapid with KOH =1.46×105 dm3 mol–1 at 25° C. This unusual reactivity appears to be associated with thetrans II stereochemistry of thesec-NH centres of the macrocycle. Base hydrolysis of thetrans complex with thetrans III chiral nitrogen stereochemistry is quite normal with kOH =1.1 dm3 mol–1 s–1 at 25° C. |
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