The synthesis, hydrolysis kinetics and structures of nickel(II) and cobalt(III) complexes of meso and racemic 1,2-diaminocyclohexane

Commercial samples of 1,2-diaminocyclohexane (chxn) are available as approximately equal mixtures of the cis-meso-RS- and trans-racemic-RR,SS-isomers. The two forms of the ligand can be separated via their Ni(II) salts (R. Saito and Y. Kidani, Chem. Lett., (1976) 123) to give yellow square planar C-2h delta,lambda-[Ni(cis-RS-chxn)(2)]Cl-2 (1) and blue octahedral delta,lambda-[Ni(trans-RR-chxn)(trans-SS-chxn)(OH2)(2)]Cl-2 (2) as confirmed by their single crystal X-ray structures. A transmetalation reaction of 2 with CoCl2.6H(2)O in methanol and air bubbling gives two distinct isomeric forms of trans-[CoCl2(chxn)(2)](+), 3 and 4, as the chloride (3) and perchlorate (4) salts, respectively. These have been assigned trans-[CoCl2(RR-chxn)(SS-chxn)]ClO4 (4) and {trans-[CoCl2(RR-chxn)(2)]Cl plus trans-[CoCl2(SS-chxn)(2)]Cl} (3), respectively, on the basis of a sequence of chiral interconversions, as only 3 can be separated into chiral forms. Acid hydrolysis rates (k(H)(1),s(-1)) and activation parameters (Delta H-not equal, kJ mol(-1); Delta S-not equal, J K-1 mol(-1)) for the loss of the first chloro ligand and the Hg2+-assisted chloride release rates (k(Hg)(2), M-1 s(-1)) for the loss of the second chloro ligand from isomers 3 and 4, are: 3, 10(5) k(H)(1)=10.6 s(-1), Delta H-not equal=103+/-3, Delta S-not equal=+23+/-6; 10(3) k(Hg)(2)=27.9 M-1 s(-1), Delta H-not equal=103+/-3, Delta S-not equal=+70+/-6; 4: 10(5) k(H)(1) s(-1)=11.3, Delta H-not equal=97+3 Delta S-not equal=+5+/-6; 10(3) k(Hg)(2)=34.1 M-1 s(-1), Delta H-not equal=91.1+/-2, Delta S-not equal=+32.6+/-4.