Reduction of N-Cyanomethyl Groups on a Macrocyclic Nickel(II) Complex Using Sodium Borohydride: Synthesis of a Complex Bearing Two N-(2-Aminoethyl) Pendant Arms

The stepwise protonation constants for [NiL2]2+ were determined by a spectrophotometric titration.17 The approximate pKa1 value (ca. 3.6) was found to be somewhat larger than the pKa2 value (ca. 2.4), as usual. The low pKa1 and pKa2 values may be result from the relatively strong interactions between the functional groups and the central metal of the complex. NaBH4 is an efficient reagent for the reduction of [NiL1]2+ in the presence of methanol, even though the N-CH2CN groups are not involved in coordination. The stepwise protonation constants for [NiL2]2+ indicate that the pendant amino groups-central metal interactions are relatively strong