A series of discrete chromium(III) precatalysts, {[Cr(κ3‐L1)] (1a.7H2O), {[Cr(κ3‐L2)] (2a.5H2O), {[Cr(κ3‐L3)] (3a.6H2O), {[Cr(κ3‐L4)] (4a.10H2O), {[Cr(κ3‐L5)] (5a.4H2O) and in‐situ‐generated chromium(III) precatalysts {[Cr(κ3‐L1)] (1b), {[Cr(κ3‐L2)] (2b), {[Cr(κ3‐L3)] (3b), {[Cr(κ3‐L4)] (4b), {[Cr(κ3‐L5)] (5b) bearing 2,4‐di‐tert‐butyl‐6‐{[2‐(1H‐imidazol‐4‐yl)‐ethylimino]‐methyl}‐phenol (L1), 2,4‐di‐tert‐butyl‐6‐{[2‐RR‐pyrazol‐1‐yl‐ethylimino]‐methyl}‐phenol, R = H (L2), Me (L3), Ph (L4), and 2,4‐di‐tert‐butyl‐6‐{[2‐pyrid‐2‐yl‐ethylimino]‐methyl}‐phenol (L5) are developed. The discrete precatalysts are characterized by IR spectroscopy, elemental analysis, and mass spectrometry. The in‐situ‐generated precatalysts afford a one‐step process for screening chromium(III) complexes as ethylene polymerization catalysts. Upon activation with EtAlCl2, both types of precatalysts exhibit high catalytic activities up to 1.71 × 105 g mol(Cr)−1 h−1 for the formation of high‐density polyethylene with molecular weights as high as 3.48 × 103 g mol−1. While the discrete precatalysts produce monomodal active catalysts at all conditions, the in‐situ‐generated precatalysts produce either monomodal or bimodal active catalysts, suggesting that, at certain conditions, two active catalysts are produced in the in situ reactions.