Cobalt(III) complexes with cyanide and the tetraamines 1,9-diamino-3,7-diazanonane and 1,10-diamino-4,7-diazadecane

Abstract

The reaction of trans-(dichloro)(1,9-diamino-3,7-diazanonane)cobalt(III) chloride and trans-(dichloro)(1,10-diamino-4,7-diazadecane)cobalt(III) chloride with sodium cyanide in aqueous solution is found to yield products with either trans or uns- cis stereochemistry depending on the reaction conditions. The stereochemistry of the products was determined by proton and carbon-13 NMR, electronic and vibrational spectroscopy. This is the first case where uns- cis diacido complexes with cobalt(III) and the tetraamines 1,9-diamino-3,7-diazanonane and 1,10-diamino-4,7-diazadecane have been prepared directly. Previous preparations of uns- cis complexes with these tetraamines have required an uns- cis complex with a chelating ligand as an intermediate. The stability of the uns- cis complexes is attributed to a greater degree of π bonding in the uns- cis complex compared with the corresponding trans complex. The difference in π bond energy must be greater than the 6 Kcal mol −1 difference in strain energy estimated from a molecular mechanics calculation.