A chromium complex [2-(NHCH2PPh2)C5H4N]CrCl3 center dot 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)(3)Al, an unprecedented divalent polyhydride chromium cluster mu,kappa(1),kappa(2),kappa(3)-N,N,P-{[2-(NCH2PPh2)C5H4N]-Cr(mu-H)}(4)[(mu-Cl)Cr(mu-Cl)Al(i-Bu)(2)Cl](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.