Gas-phase C-H and N-H bond activation by a high valent nitrido-iron dication and NH-transfer to activated olefins.

A tetrapodal pentadentate nitrogen ligand (2,6-bis(1,1-di(aminomethyl)ethyl)pyridine, 1) is used for the synthesis of the azido-iron(III) complex [(1)Fe(N3)]X2 where X is either Br or PF6. By means of electrospray ionization mass spectrometry, the dication [(1)Fe(N3)]2+ can be transferred into the gas phase as an intact entity. Upon collisional activation, [(1)Fe(N3)]2+ undergoes an expulsion of molecular nitrogen to afford the dicationic nitrido-iron species [(1)FeN]2+ as an intermediate, which upon further activation can intramolecularly activate C-H- and N-H bonds of the chelating ligand 1 or can transfer an NH unit in bimolecular reactions with activated olefins. The precursor dication [(1)Fe(N3)]2+, the resulting nitrido species [(1)FeN]2+, and its possible isomers are investigated by mass spectrometric experiments, isotopic labeling, and complementary computational studies using density functional theory.

A non-heme dinuclear iron(II) complex containing a single, unsupported hydroxo bridge.

Complexation of the tetrapodal pentadentate NN4 ligand 2,6-C5H3N[CMe(CH2NH2)2]2 (I) with iron(II) perchlorate hydrate in methanol, in the presence of N-methylimidazole, produces a diferrous complex with a single, unsupported mu-OH ligand between two {(I)FeII} coordination modules.

Iron carbonyl, nitrosyl, and nitro complexes of a tetrapodal pentadentate amine ligand: synthesis, electronic structure, and nitrite reductase-like reactivity.

The tetrapodal pentaamine 2,6-C5H3N[CMe(CH2NH2)2]2 (pyN4, 1) forms a series of octahedral iron(II) complexes of general formula [Fe(L)(1)]Xn 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 = NO2-, 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, NOBF4, and NaNO2, 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 [Fe2[mu 2-(eta 1-N: eta 1-O)-NO2](1)2]Br2PF6 (7), whose bridging NO2- 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 NO2- 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.