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Low coordinate iron derivatives stabilized by a beta-diketiminate mimic. Synthesis and coordination chemistry of enamidophosphinimine scaffolds to generate diiron dinitrogen complexes

TitleLow coordinate iron derivatives stabilized by a beta-diketiminate mimic. Synthesis and coordination chemistry of enamidophosphinimine scaffolds to generate diiron dinitrogen complexes
Publication TypeJournal Article
Year of Publication2016
AuthorsHein, NM, Suzuki, T, Ogawa, T, Fryzuk, MD
JournalDALTON TRANSACTIONS
Volume45
Pagination14697-14708
ISSN1477-9226
Abstract

In an effort to mimic N-diaryl-beta-diketiminate ligands (Nacnac), we have converted N-arylimine phosphine ligands to enamine-phosphinimines via the Staudinger reaction. By varying the aryl azide, one can access enamine-phosphinimine ligands with the same or different N-aryl substituents on both the enamine and phosphinimine units, which allows this intrinsically unsymmetrical bidentate donor set to present variable steric effects at the metal center. The enamine-phosphinimine was deprotonated and used in metathetical reactions with Fe(II) bromide precursors to generate low coordinate complexes of the empirical formula {[}(NpNAr,Ar')-Np-CY5]FeBr (where CY5 = cyclopentenyl; Ar,Ar' = 2,6-diisopropylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl). Depending on the substituents, these bromide derivatives can be monomeric or dimeric via bromide bridges. Reduction under dinitrogen using potassium graphite generates the dinitrogen complexes ({[}(NpNAr,Ar')-Np-CY5]Fe)(2)(mu-N-2) for Ar,Ar' = 2,6-diisopropylphenyl, and Ar = 2,6-dimethylphenyl, Ar' = 2,4,6-trimethylphenyl. However, for the former, a unsymmetrical side product can be isolated that has a bridging N-2,6-diisopropylphenylimide unit with one enamido-phosphine ligand bound to one iron and the other iron stabilized with an intact enamido-phosphinimine. When the steric bulk is reduced on both nitrogen donors, a complicated product mixture is obtained after reduction from which a small amount of {[}(NpNAr,Ar')-Np-CY5]Fe{[}(NPAr)-N-CY5] (Ar,Ar' = 2,6-dimethylphenyl) could be isolated. All of these complexes are paramagnetic and have been characterized by elemental analysis, magnetic studies and X-ray crystallography.

DOI10.1039/c6dt01673a