Issue 37, 2016

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

Abstract

In an effort to mimic N-diaryl-β-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 [CY5NpNAr,Ar′]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 ([CY5NpNAr,Ar′]Fe)2(μ-N2) 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 [CY5NpNAr,Ar′]Fe[CY5NPAr] (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.

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

Supplementary files

Article information

Article type
Paper
Submitted
21 رجب 1437
Accepted
25 شعبان 1437
First published
25 شعبان 1437

Dalton Trans., 2016,45, 14697-14708

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

N. M. Hein, T. Suzuki, T. Ogawa and M. D. Fryzuk, Dalton Trans., 2016, 45, 14697 DOI: 10.1039/C6DT01673A

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