869368-15-0Relevant academic research and scientific papers
Bis(imino)pyridine iron alkyls containing β-hydrogens: Synthesis, evaluation of kinetic stability, and decomposition pathways involving chelate participation
Trovitch, Ryan J.,Lobkovsky, Emil,Chirik, Paul J.
, p. 11631 - 11640 (2009/05/30)
Bis(imino)pyridine iron alkyl complexes bearing β-hydrogens, ( iPrPDI)FeR ((iPrPDI = 2,6-(2,6-iPr 2-C6H3N=CMe)2C5H 3N; R = Et, nBu, iBu, CH2 cycloC5H9; 1-R), were synthesized either by direct alkylation of (iPrPDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, (iPrPDI)Fe(N 2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced (iPrPDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin ferrous compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found to produce a mixture of the corresponding alkane and alkene. The kinetic stability of the iron alkyl complexes was inversely correlated with the number of β-hydrogens present. For example, the iron ethyl complex, 1-Et, underwent clean loss of ethane over the course of three hours, whereas the corresponding 1-iBu compound had a half-life of over 12 h under identical conditions. The mechanism of the decomposition was studied with a series of deuterium labeling experiments and support a pathway involving initial β-hydrogen elimination followed by cyclometalation of an isopropyl methyl group, demonstrating an overall transfer hydrogenation pathway. The relevance of such pathways to chain transfer in bis(imino)pyridine iron catalyzed olefin polymerization reactions is also presented.
Carbon-oxygen bond cleavage by bis(imino)pyridine iron compounds: Catalyst deactivation pathways and observation of acyl C-O bond cleavage in esters
Trovitch, Ryan J.,Lobkovsky, Emil,Bouwkamp, Marco W.,Chirik, Paul J.
, p. 6264 - 6278 (2009/04/13)
Investigations into the substrate scope of bis(imino)pyridine iron-catalyzed hydrogenation and [2π + 2π] diene cyclization reactions identified C-O bond cleavage as a principal deactivation pathway. Addition of diallyl or allyl ethyl ether to the bis(imino)pyridine iron dinitrogen complex, (iPrPDI)Fe(N2)2 (iPrPDI = 2,6-(2,6-iPr2-C6H3N=CMe) 2C5H3N, 1-(N2)2), under a dinitrogen atmosphere resulted in facile cleavage of the C-O bond and yielded a mixture of the corresponding paramagnetic iron allyl and alkoxide complexes. For ethyl vinyl ether, clean and selective formation of the iron ethoxide was observed with concomitant loss of the vinyl fragment. In situ monitoring of the catalytic hydrogenation of trans-methyl cinnamate established ester C-O bond cleavage as a competing process. Stoichiometric reactions between 1-(N 2)2 and allyl and vinyl acetate also produced facile C-O oxidative addition. For the latter, a six coordinate diamagnetic bis(imino)pyridine acetatoxy iron vinyl compound was obtained and characterized by X-ray diffraction. Phenyl acetate undergoes exclusive acyl C-O bond cleavage, while alkyl-substituted esters such as ethyl, pentyl, benzyl, isopropyl, cyclohexyl, and tert-butyl acetate undergo competing ester and acyl C-O bond cleavage accompanied by iron-promoted decarbonylation. Deuterium labeling studies established that reversible C-H activation and chelate cyclometalation occur prior to, but are not a prerequisite for, carbon-oxygen bond oxidative addition of ethyl acetate. The molecular and electronic structures of the ether and ester C-O bond cleavage products have been established and demonstrate that ligand- rather than metal-based oxidation accompanies substrate activation.
Square planar bis(imino)pyridine iron halide and alkyl complexes
Bouwkamp, Marco W.,Bart, Suzanne C.,Hawrelak, Eric J.,Trovitch, Ryan J.,Lobkovsky, Emil,Chirik, Paul J.
, p. 3406 - 3408 (2007/10/03)
Square planar iron methyl complexes containing bis(imino)pyridine (PDI) ligands have been prepared by reductive alkylation of the corresponding ferrous dichloride; dialkylation is observed upon treatment with a larger alkyl lithium. The Royal Society of Chemistry 2005.
