Renate Gross

Koordinationsambivalenz und Elektronenstruktur ein- und zweikerniger Methylcyclopentadienyldicarbonylmangan-Komplexe der Cyanpyridine und Terephthalsäuredinitrile

Abstract The ambident cyanopyridine ligands form N(pyridine) and N′(nitrile) coordinated mono- and binuclear complexes with the (C 5 H 4 CH 3 )(CO) 2 Mn fragment. All three possible forms for 4-cyanopyridine could be isolated, whereas mononuclear compounds were obtained as most stable species in N 1 -coordinated form with 3-cyanopyridine and in CN 2 -coordinated form with the 2-isomer. IR, NMR, and UV/VIS spectroscopy as well as electrochemistry and ESR spectroscopy of the anion radicals demonstrate superior π back-bonding via the pyridine nitrogen centers, the isolation of nitrile coordinated complexes is attributed to the kinetic stability of the CNMn bond. While terephthalonitrile was found to form exclusively mononuclear neutral complexes, its anion radical prefers to coordinate to a second metal fragment, illustrating the excellent coordination properties of reduced nitriles. A neutral binuclear complex could be isolated with the stronger π-acceptor, tetrafluoroterephthalonitrile.

Electron Transfer Induced Metal Addition and Ligand Exchange in Organometallic Anion Radical Complexes

Transition metal complexes containing anion radical ligands display a strong tendency towards full coordinative saturation at the singly reduced ligand and towards substitutional activation of coligands at the metal center. Examples involving metal carbonyls show how both of these reactivities can be employed either separately or in a combined fashion for electron transfer catalyzed substitution processes and for the construction of new polynuclear complexes with unusual properties.

Bridging the fields of organometallic and classical coordination chemistry: localized and delocalized bonding in polynuclear complexes of (C5R5)(CO)2Mn

Abstract The capability of the title fragment to undergo efficient π back bonding, to exist in two kinetically stable neighboring oxidation states, and to exhibit a relatively small ligand field splitting have allowed the formation of unusual coordination compounds. Several mono- and polynuclear examples with an odd or even electron count and different degrees and direction of electron delocalization between ligand and metal fragment(s) will be discussed.

Electron spin resonance and electronic spectroscopy of low-spin manganese(II) complexes (C5R5)(CO)2(L)Mn with L = hydrazido(1-), arylamido, anionic nitrile and purine-type ligands

The low-spin manganese(II) oxidation state is stabilized in complexes (C5R5)(CO)2(L)Mn, R = H, CH3, with the negatively charged and π-electron-rich nitrogen bases L = imidazolate, benzimidazolate, benzotriazolate, purinate, adeninate, 8-aza-adeninate, indolate, 4-pyridylamide, anilide, 4-tolylamide, p-phenylenediamide(1-), N,N-dimethyl-p-phenylenediamide(1-), 1,1-diphenylhydrazide(1-), dicyanamide, deprotonated malonodinitrile and t-butylmalonodinitrile. The paramagnetic compounds were obtained by synergistic oxidative deprotonation of diamagnetic manganese(I) complexes of amines. Increasing σ and π donor strength of the various anionic ligands L results in facilitated oxidative deprotonation, a considerable bathochromic shift of the ligand-to-metal charge-transfer (LMCT, dâ†�πN) absorption band across the visible region of the spectrum, and in growing metal-to-ligand spin delocalization, as evident from diminished g factors and a(55Mn) hyperfine coupling constants in the e.s.r. spectra. Resolved 14N and 1H superhyperfine splitting was observed in a few instances. Electronic structures, coordination sites and molecular conformations are inferred from experimental data and from their correlation with MO calculations.

Three compounds from the reaction between dicarbonyl(methylcyclopentadienyl)(tetrahydrofuran)-manganese and 4-cyanopyridine

Abstract The isolation and characterization of two mononuclear complexes and one binuclear compound from the reaction between dicarbonyl(methylcyclopentadienyl) (tetrahydrofuran)manganese and 4-cyanopyridine are reported. The competition between the pyridine and nitrile nitrogen centers for coordination with the (η 5 -C 5 H 4 CH 3 )Mn(CO) 2 fragment results in the formation of two mononuclear complexes, of which the N 1 -coordinated isomer is more stable.

Persistent cation radicals containing carboxamide and thiophosphinic amide functions. The one electron oxidation of acceptor stabilized 1,4-dihydropyrazines

Even when it is N,N′-disubstituted by the acceptor groups C(O)Me and P(S) Me2, the 1,4-dihydropyrazine system remains sufficiently electron rich to undergo facile one-electron oxidation to give persistent radical cations with acetamide and thiophosphinic amide functionality.