Isolation of a Hexanuclear Chromium Cluster with a Tetrahedral Hydridic Core and Its Catalytic Behavior for Ethylene Oligomerization

A chromium complex
[2-(NHCH2PPh2)­C5H4N]­CrCl3·THF2 (1) of the ligand
PyNHCH2PPh2 has been synthesized, characterized,
and examined for its catalytic behavior toward ethylene oligomerization.
When complex 1 was treated with (i-Bu)3Al, an unprecedented divalent polyhydride chromium cluster
μ,κ1,κ2,κ3-N,N,P-{[2-(NCH2PPh2)­C5H4N]­Cr­(μ-H)}4­[(μ-Cl)­Cr­(μ-Cl)­Al­(i-Bu)2Cl]2 (2) was obtained.
The complex contains a Cr4H4 core, which is
expected to be diamagnetic, and which remains coordinated to two additional
divalent high-spin Cr atoms via bridging interactions. Two aluminate
residues remain bonded to the peripheral chromium atoms. The structure,
magnetism, and electronic configuration are herein discussed.