61702-08-7Relevant academic research and scientific papers
Spin Crossover and Valence Tautomerism in Neutral Homoleptic Iron Complexes of Bis(pyridylimino)isoindolines
Scheja, Anne,Baabe, Dirk,Menzel, Dirk,Pietzonka, Clemens,Schweyen, Peter,Br?ring, Martin
, p. 14196 - 14204 (2015/09/28)
Homoleptic iron complexes of six bis(pyridylimino)isoindoline (bpi) ligands with different substituents (H, Me, Et, tBu, OMe, NMe2) at the 4-positions of the pyridine moieties have been prepared and studied with regard to temperature-dependent spin and redox states by a combination of 57Fe M?ssbauer spectroscopy, SQUID magnetometry, single-crystal X-ray diffraction analysis, X-band EPR, and 1H NMR spectroscopy. While the H-, methyl-, and ethyl-substituted complexes remain in a pure high-spin state irrespective of the temperature, the 4-tert-butyl-substituted derivative shows spin-crossover behavior. The methoxy- and dimethylamino-substituted compounds were found to easily undergo oxidation. In the crystalline state, valence tautomeric behavior was observed for the methoxy derivative as a thermally activated charge-transfer transition, accompanied by a spin crossover above 200 K. The valence tautomerism leads to a chelate with one of the bpi ligands as a dianion radical L2-. and with an effective spin of S=2.
Living radical polymerization of acrylates mediated by 1,3-bis(2- pyridylimino)isoindolatocobalt(II) complexes: Monitoring the chain growth at the metal
Langlotz, Bjoern K.,Fillol, Julio Lloret,Gross, Juergen H.,Wadepohl, Hubert,Gade, Lutz H.
experimental part, p. 10267 - 10279 (2009/10/10)
A new type of mediator for cobalt(II)-mediated radical polymerization is reported which is based on 1,3-bis(2-pyridylimino)isoindolate (bpi) as ancillary ligand. The modular synthesis of the bis(pyridylimino)isoindoles (bpiH) employed in this work is based on the condensation of 2-aminopyridines with phthalodinitriles. Reaction of the bpiH protio-ligands with a twofold excess of cobalt(II) acetate or cobalt(II) acetylacetonate in methanol gave [Co(bpi)(OAc)], which crystallize as coordination polymers, and a series of [Co(acac)(bpi)(MeOH)], which are mononuclear octahedral complexes. Upon heating the [Co(acac)(bpi)(MeOH)] compounds to 100°C under high vacuum, the coordinated methanol was removed to give the five-coordinate complexes [Co(acac)(bpi)]. The polymerization of methyl acrylate at 60°C was investigated by using one molar equivalent of the relatively short-lived radical source 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as initiator (monomer/catalyst/V-70: 600:1:1). The low solubility of the acetato complexes inhibits their significant activity as mediators in this reaction, whereas the acetylacetonate complexes control the radical polymerization of methyl acrylate more effectively. The radical polymerizations of the hexacoordinate complexes did not show a linear increase in number-average molecular weight (Mn) with conversion; however, the polydispersities were relatively low (PDI= 1.12-1.40). By using the pentacoordinate complexes [Co(acac)(bpi)] as mediators, a linear increase in Mn values with conversion, which were very close to the theoretical values for living systems, and very low polydispersities (PDI n-R] (MA: methyl acrylate; R: C(CH3)(CH2C(CH3) 2OCH3)CN), a notion also confirmed by NMR end-group analysis.
