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

Abstract

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 dimethylanilinesubstituted 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.

New o-methoxyphenylcyclopentadienylchromium (III) complexes: Synthesis, structures and catalytic properties for ethylene polymerization

“…1 H NMR spectroscopic analysis indicates that 2 exists as a mixture of three isomers. Similar behavior has been observed before for the N,N-dimethylaminophenyl-tetramethylcyclopentadiene ligand system [9] and the tetramethylcyclopentadienylphenol ligand system [12]. The same phenomenon was not found for ligand 1 which exists as one isomer.…”

“…Jolly et al [5][6][7] reported that half-sandwich type chromium complexes (a) shows good activity for the polymerization of ethylene to give polyethylenes with high molecular weights. Enders et al [8,9] described cyclopentadienylchromium(III) complexes (b and c) functionalized by quinolinyl or N,N-dimethylanilinyl group exhibit high catalytic activity for ethylene polymerization. Most recently, Huang et al [10] reported the bridged cyclopentadienylchromium complexes (d) as effective ethylene polymerization catalysts.…”

Synthesis and Reactivity of Cobalt Complexes with Pendant Nitrogen Functional Groups

“…[18] Considering that the alkyl ring of piperidine is an electron-releasing substituent, the nitrogen atom in the tethered side chain in 10 should be a stronger σ donor compared with that in 9 and 12 and the chelate bond in 10 would be expected to be the strongest one among the three analogues. However, the chelate bond in 10 was found to be the longest.…”

Chelate ring closing and opening behavior in cyclopentadienyl cobalt(III) complexes with pendant nitrogen functional group

“…As a d 6 metal, cobalt(III) has less electron density to feedback to CO and therefore the metal-CO bond is weaker than that in cobalt(I) complexes. However, monocarbonyl cobalt(III) compounds have been reported as stable complexes even when there is a weak competitive donor functional group such as ether, ester or multiple bonds in a pendant side chain [32][33][34][35][36][37][38][39][40]. When a nitrogen atom is included in the pendant side chain as in our case, since it is a better donor than oxygen or multiple bonds, the CO was thermally substituted by the amino functional group and metal chelators were formed under mild conditions.…”