Provided herein are compounds useful for the treatment of cancer.

An organometallic complex represented by Formula 1-1 or Formula 1-2 is provided: ##STR00001##
wherein in Formulae 1-1 and 1-2, descriptions of R.sub.1 to R.sub.7, X.sub.1, X.sub.2, Y.sub.1 to Y.sub.4, rings A, B, C, and a to e are understood by referring to the description provided herein. An organic light-emitting device includes a first electrode, a second electrode facing the first electrode, and an organic layer that is disposed between the first electrode and the second electrode and includes an emission layer, wherein the organic layer includes at least one organometallic complex represented by Formula 1-1 or Formula 1-2.

An organometallic complex represented by Formula 1-1 or Formula 1-2 is provided: ##STR00001##
wherein in Formulae 1-1 and 1-2, descriptions of R.sub.1 to R.sub.7, X.sub.1, X.sub.2, Y.sub.1 to Y.sub.4, rings A, B, C, and a to e are understood by referring to the description provided herein. An organic light-emitting device includes a first electrode, a second electrode facing the first electrode, and an organic layer that is disposed between the first electrode and the second electrode and includes an emission layer, wherein the organic layer includes at least one organometallic complex represented by Formula 1-1 or Formula 1-2.

A catalyst composition and a process for di-, tri- and/or tetramerization of ethylene, wherein the catalyst composition comprises a chromium compound, a ligand of the general structure R.sub.1R.sub.2PN(R.sub.3)P(R.sub.4)N(R.sub.5)PR.sub.6R.sub.7, or any cyclic derivatives thereof, wherein at least one of the P or N atoms of the PNPNP-unit is member of a ring system, the ring system being formed from one or more constituent compounds of the ligand by substitution, and a co-catalyst or activator.

A catalyst composition and a process for di-, tri- and/or tetramerization of ethylene, wherein the catalyst composition comprises a chromium compound, a ligand of the general structure R.sub.1R.sub.2PN(R.sub.3)P(R.sub.4)N(R.sub.5)PR.sub.6R.sub.7, or any cyclic derivatives thereof, wherein at least one of the P or N atoms of the PNPNP-unit is member of a ring system, the ring system being formed from one or more constituent compounds of the ligand by substitution, and a co-catalyst or activator.