Dissociation of CuH+ and ZnH+ complexes of ethylenediamine and their N-methylated homologues: Family and neighbours, but not the same

Upon collisional activation, complexes of CuH+ and ZnH+ with H2NCH2CH2NH2 eliminate Cu(0) and Zn(0) to produce protonated ethylenediamine H2NCH2CH2NH3+ via a proton transfer. Variable collision energy experiments and model chemistry calculations (CBS-QB3 method) indicate that (i) the energy requirement for this process is significantly larger for the zinc complex than for the copper complex; and (ii) the transition-state for the proton transfer is rate-determining for dissociation of the zinc complex, whereas the same process in the copper complex is essentially barrierless. The large activation energy for the zinc complex opens up a competing fragmentation process, viz. loss of NH3, which does not occur in the copper complex.N-methyl substitution has no effect for the CuH+ complex ions: Cu(0) is lost from the complex (CH3)2NCH2CH2N(CH3)2⋯CuH+. However, a different situation obtains for the complex with ZnH+, which predominantly loses ZnH2. Experiment and theory indicate that loss of ZnH2 is more energy demanding than loss of Zn(0), but that ZnH2 loss prevails at elevated collision energies.