A process comprising a) contacting (i) ethylene, (ii) a catalyst system comprising 1) a heteroatomic ligand iron salt complex, or a heteroatomic ligand and an iron salt, (iii) hydrogen, and (iv) optionally an organic reaction medium; and b) forming an oligomer product wherein 1) the oligomer product has a Schulz-Flory K value from 0.4 to 0.8 and 2) the oligomer product comprises (a) less than 1 wt. % of polymer, (b) less than 1 wt. % compounds having greater than 70 carbon atoms, (c) less than 1 wt. % compounds having a weight average molecular weight of greater than 1000 g/mol, or (d) any combination thereof wherein the weight percentage is based on the total weight of the oligomer product.