Robust Chromium Precursors for Catalysis: Isolation and Structure of a Single-Component Ethylene Tetramerization Precatalyst

We
have introduced a new class of stable organometallic Cr reagents
(compounds 1–4) that are readily
prepared, yet reactive enough to serve as precursors. They were used
for ethylene tetramerization catalysis following stoichiometric activation
by in situ protonation. This study highlights the importance of balancing
stability with reactivity in generating an organometallic precursor
that is useful in catalysis. Moreover, precursor 4 allowed
for the isolation and crystallographic characterization of a room-temperature
stable cationic species, (PNP)­CrR2+ (R = o-C6H4(CH2)2OMe, PNP = iPrN­(PPh2)2). This complex (5) may be used as a single component
precatalyst, without any alkylaluminum reagents. This result provides
an unprecedented level of insight into the kind of structures that
must be produced from more complicated activation processes.