Transformation and Structural Discrimination between the Neutral {Fe(NO)₂}¹⁰ Dinitrosyliron Complexes (DNICs) and the Anionic/Cationic {Fe(NO)₂}⁹ DNICs

Abstract

Reaction of Fe(CO)2(NO)2 and sparteine/tetramethylethylenediamine (TMEDA) in tetrahydrofuran afforded the electron paramagnetic resonance (EPR)-silent, neutral {Fe(NO)2}10 dinitrosyliron complexes (DNICs) [(sparteine)Fe(NO)2] (1) and [(TMEDA)Fe(NO)2] (2), respectively. The stable and isolable anionic {Fe(NO)2}9 DNIC [(S(CH2)3S)Fe(NO)2]- (4), with a bidentate alkylthiolate coordinated to a {Fe(NO)(2)} motif, was prepared by the reaction of [S(CH2)3S]2- and the cationic {Fe(NO)2}9 [(sparteine)Fe(NO)2]+ (3) obtained from the reaction of complex 1 and [NO][BF4] in CH(3)CN. Transformation from the neutral complex 1 to the anionic complex 4 was verified via the cationic complex 3. Here complex 3 acts as an {Fe(NO)2}-donor reagent in the presence of thiolates. The EPR spectra of complexes 3 and 4 exhibit an isotropic signal with g = 2.032 and 2.031 at 298 K, respectively, the characteristic g value of {Fe(NO)2}9 DNICs. On the basis of N-O/Fe-N(O) bond lengths of the single-crystal X-ray structures of the {Fe(NO)2}9/{Fe(NO)2}10 DNICs, the oxidation level of the {Fe(NO)2} core of DNICs can be unambiguously assigned. The mean N-O distances falling in the range of 1.214(6)-1.189(4) A and the Fe-N(O) bond distances in the range of 1.650(7)-1.638(3) A are assigned as the neutral {Fe(NO)(2)}(10) DNICs. In contrast, the mean N-O bond distances ranging from 1.178(3) to 1.160(6) A and the mean Fe-N(O) bond distances ranging from 1.695(3) to 1.661(4) A are assigned as the anionic/neutral/cationic {Fe(NO)2}9 DNICs. In addition, an EPR spectrum in combination with the IR nu(NO) (the relative position of the nu(NO) stretching frequencies and their difference Deltanu(NO)) spectrum may serve as an efficient tool for discrimination of the existence of the anionic/cationic/neutral {Fe(NO)2}9 DNICs and the neutral {Fe(NO)2}10 DNICs.

Synthesis, Structures, Spectroscopic and Electrochemical Properties of Dinitrosyl Iron Complexes with Bipyridine, Terpyridine, and 1,10-Phenathroline

“…The peaks close to 1619 cm −1 , 1621 cm −1 and 1614 cm −1 in complexes 1 – 3 are assigned to the coordinated bidentate ligands by comparing them with the IR spectra of the free ligands. The characteristic nitrosyl stretching frequencies are similar to the reported values 1673 cm −1 , 1616 cm −1 for the mononuclear metal complex Fe(NO) 2 (sparteine)10 and 1679 cm −1 , 1622 cm −1 for Fe(NO) 2 (1-MeIm) 2 9a; but clearly lower than the values 1774 cm −1 , 1712 cm −1 for the anionic complex9c [Fe(NO) 2 (Im-H) 2 ] − , and 1796 cm −1 , 1726 cm −1 for the tetranuclear iron complex9b [Fe(NO) 2 (Im-H)] 4 . The results show that the NO stretching frequencies are related to the oxidation levels of dinitrosyl iron complexes and the observed ν NO s’ in complexes 1 – 3 make them {Fe(NO) 2 }10 according to the Enemark-Feltham notation 20…”

“…Each iron center is connected to four nitrogen atoms, which include two from the nitrosyls and two nitrogen atoms from the bipy ligands, with a pseudo-tetrahedral geometry. The average Fe-N( NO ) bond distance of 1.650 Å is similar to those reported in mononuclear complexes Fe(NO) 2 (sparteine) (average value: 1.646 Å),10 [(MeIm) 2 Fe(NO) 2 ] (MeIm = 1-methylimidazole) (average value: 1.649 Å)9a and [(DAD)Fe(NO) 2 ] (DAD = diazadiene) (average value: 1.641 Å), 7d but clearly shorter than those found in the tetranuclear [Fe(NO) 2 (Im-H)] 4 (Im = imidazole) (average value: 1.694 Å)9b and the dinuclear complexes, [(N 2 C 5 H 7 )Fe(NO) 2 ] 2 (N 2 C 5 H 7 = 3,5-dimethylpyrazolyl) (average value: 1.696 Å),22 in which the iron is considered to carry one positive charge in order to balance the negative charge on the nitrogen-contained ligands due to deprotonation. This positive Fe center would have less electrons available for back-donation to the nitrosyl ligands, resulting in weaker Fe-N bonds.…”

“…In rare cases, it can be replaced by nitrogen-contained ligands 9,10. In order to prepare and isolate new class of DINC containing N,N′-chelating ligands and to investigate their properties, a series of dinitrosyl iron complexes [Fe(NO) 2 (bipy)], [Fe(NO) 2 (terpy)], and [Fe(NO) 2 (phen)] were prepared, as shown in Scheme 1, by the reaction of Fe(NO) 2 (CO) 2 with the appropriate ligand in THF at ambient temperature.…”

The Preparation, Structural Characteristics, and Physical Chemical Properties of Metal-Nitrosyl Complexes

“…Earlier work includes: a reaction of [Fe(NO) 2 Cl] 2 with 1,4,-diaza-1,3-butadiene, which yielded a DNIC with N,N′-chelation [49], a salt [Fe(bipy) 3 ][Fe(NO) 2 Cl 2 ] 2 , which was isolated by using large excess of bipy vs. [Fe(NO) 2 Cl] 2 (10:0.75) [50], and [(spartiene)Fe(NO) 2 ] was prepared by reacting spartiene with Fe(CO) 2 (NO) 2 [51]. …”

Quantum-chemical study of the Fe(NO)2 fragment in the cation of mononuclear nitrosyl iron complex [Fe(SC(NH2)2)2(NO)2]Сl·H2O

“…This complex has been recently obtained by the authors [13,14] and studied to compare it with neutral mononuclear DNICs insoluble in water and physiologic solutions [15][16][17] and water soluble anionic [18][19][20][21][22][23][24][25][26][27] ones with various sulfur containing ligands.…”