Nitrogen-Functionalized Cyclopentadienyl Ligands with a Rigid Framework: Complexation Behavior and Properties of Cobalt(I), -(II), and -(III) Half-Sandwich Complexes

Reaction of 2-lithio- N, N -dimethylaniline with 2,3,4,5-tetramethylcyclopentenone yields 1-[2-( N, N -dimethylaminophenyl)-2,3,4,5-tetramethylcyclopentadiene ( 2 ). As in 1-(8-quinolyl)-2,3,4,5-tetramethylcyclopentadiene ( 1 ), the N-donor is connected to the Cp ring by a rigid C 2 spacer. Co 2 (CO) 8 reacts with 1 or 2 to give the Co I -dicarbonyl half-sandwich complexes 7 and 3, respectively. Irradiation leads to the binuclear complexes 4 and 8 with a Co−Co double bond. Oxidation of 3 or 7a is possible with iodine. Whereas 7a directly forms the Co III complex 9 with coordination of the quinoline to the metal, 3 yields the monocarbonyldiiodo complex 5 . Upon gentle heating in dichloromethane, 5 loses carbon monoxide to give the cobalt complex 6, displaying intramolecular nitrogen coordination. Reaction of the dimethylaniline-substituted cyclopentadienide 10 with CoCl 2 yields the Co II complex 11 . The Co III complex 6 and the Co II complex 11 were treated with methylaluminoxane (MAO) and gave low-activity catalysts for the polymerization of ethylene.