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Iron Carbonyl, Nitrosyl, and Nitro Complexes of a Tetrapodal Pentadentate Amine Ligand: Synthesis, Electronic Structure, and Nitrite Reductase‐like Reactivity
Author(s) -
Pitarch López Jesús,
Heinemann Frank W.,
Prakash Raju,
Hess Bernd A.,
Horner Olivier,
Jeandey Claudine,
Oddou JeanLouis,
Latour JeanMarc,
Grohmann Andreas
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021216)8:24<5709::aid-chem5709>3.0.co;2-i
Subject(s) - chemistry , ligand (biochemistry) , coordination sphere , crystallography , homoleptic , unpaired electron , amine gas treating , stereochemistry , medicinal chemistry , octahedron , reactivity (psychology) , osmium , molecule , metal , crystal structure , organic chemistry , ruthenium , biochemistry , receptor , medicine , alternative medicine , pathology , catalysis
The tetrapodal pentaamine 2,6‐C 5 H 3 N[CMe(CH 2 NH 2 ) 2 ] 2 (pyN 4 , 1 ) forms a series of octahedral iron( II ) complexes of general formula [Fe(L)( 1 )]X n with a variety of small‐molecule ligands L at the sixth coordination site (L=X=Br, n =1 ( 2 ); L=CO, X=Br, n =2 ( 3 ); L=NO, X=Br, n =2 ( 4 ); L=NO + , X=Br, n =3 ( 5 ); L=NO 2 − , X=Br, n =1 ( 6 )). The bromo complex, which is remarkably stable towards hydrolysis and oxidation, serves as the precursor for all other complexes, which may be obtained by ligand exchange, employing CO, NO, NOBF 4 , and NaNO 2 , respectively. All complexes have been fully characterised, including solid‐state structures in most cases. Attempts to obtain single crystals of 6 produced the dinuclear complex [Fe 2 { μ 2 ‐( η 1 ‐ N : η 1 ‐ O )‐NO 2 }( 1 ) 2 ]Br 2 PF 6 ( 7 ), whose bridging NO 2 − unit, which is unsupported by bracketing ligands, is without precedent in the coordination chemistry of iron. Compound 2 has a high‐spin electronic configuration with four unpaired electrons ( S =2), while the carbonyl complex 3 is low‐spin ( S =0), as are complexes 5, 6 and 7 ( S =0 in all cases); the 19 valence electron nitrosyl complex 4 has S =1/2. Complex 4 and its oxidation product, 5 ({Fe(NO)} 7 and {Fe(NO)} 6 in the Feltham–Enemark notation) may be interconverted by a one‐electron redox process. Both complexes are also accessible from the mononuclear nitro complex 6 : Treatment with acid produces the 18 valence electron NO + complex 5 , whereas hydrolysis in the absence of added protons (in methanolic solution) gives the 19 valence electron NO . complex 4 , with formal reduction of the NO 2 − ligand. This reactivity mimicks the function of certain heme‐dependent nitrite reductases. Density functional calculations for complexes 3, 4 and 5 provide a description of the electronic structures and are compatible with the formulation of iron( II ) in all cases; this is derived from the careful analysis of the combined IR, ESR and Mössbauer spectroscopic data, as well as structural parameters.