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A new amidinato-diolefin ligand is presented along with its sodium salt as a starting point for the preparation of iron(II) compounds. Rational synthetic approaches to cationic and dinuclear iron species have been established and allowed for the first isolation of an amidinato stabilized cationic Fe species. The versatility of the potentially tetradentate ligand system is mirrored by structural authentification of three different binding modes. These include rare examples of Fe(II)–olefin interactions in neutral compounds. A set of iron compounds was shown to be active as precatalysts in the synthesis of poly silylethers by dehydrogenative alcoholysis of PhSiH3. The most active catalyst was generated from a dinuclear iron compound. Characterization techniques include NMR, IR, and Mossbauer spectroscopy, single crystal X-ray analysis, magnetic susceptibility measurements, and mass spectrometry.

A diolefin ether, trop2O (2), and a diolefin thioether, trop2S (3), have been investigated as ligand analogues of the well-established diolefin amine, trop2NH (1). Compounds 2 and 3 form different conformers in solution and in the solid state. Whereas 2 could be coordinated to Ni(0), 3 was found to be more suited for coordination to Rh(I). The coordination chemistry, electrochemical properties, and ligand exchange phenomena of the resulting complexes, [Ni(trop2O)(PPh3)] (5) and [Rh(trop2S)(L)n][OTf] (6: L = NCMe, n = 2; 7: L = 2,2′-bipy, n = 1) were investigated by analytical techniques including NMR spectroscopy, single crystal X-ray analysis, and cyclic voltammetry. The results were compared with those obtained for the amine analogues of 5, 6, and 7.

(Chemical Equation Presented) Rh steps into the ring: The radical cation shown is best described as a rhodaazacyclopropane (A) rather than as a Rh I iminium ion complex (B). EPR and DFT data indicate that the delocalization of the unpaired electron into the ligand framework contributes to the stability of A (see plot of the singly occupied molecular orbital). © 2006 Wiley-VCH Verlag GmbH and Co. KGaA.

H2bruderlich aufgeteilt: Mit neuartigen vierfach-koordinierten Rhodium(I)-amiden gelingt die effiziente heterolytische Spaltung von H2. Die Reaktion ist reversibel, und DFT-Rechnungen zeigen, dass sie als Einstufenprozess uber eine relative niedrige Aktivierungsbarriere verlauft. Die Amidkomplexe katalysieren die Hydrierung von Ketonen und Iminen ohne weitere Zusatze.

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(troppPh)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(troppPh)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(troppPh)ethane was separated by fractional crystallisation and reacted with [Ir(cod)2]OTf (cod=cylcooctadiene, OTf−=CF3SO3 −) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(troppPh)ethane)(cod)]+, where the bis(troppPh)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(troppPh)ethane)(cod)]+: k

Complexes of the type [Ru(H2bibzim)(R-bpy)2X2·nH2O (R = H, 2,2′-bipyridine, bpy, X = CF3SO3−1; R = Me, 4,4′-dimethyl-2,2′-bipyridine, dmbpy, X = PF6−2; R = tert-butyl, 4,4′-di-tert-butyl-2,2′-bipyridine, tbbpy, X = Cl−3; H2bibzim = 1,1′-bibenzimidazole) containing two NH functions acting as hydrogen bond donors formed different spatially highly organised supramolecular assemblies with water. X-Ray investigation revealed that the nature of the counter ion influences the hydrogen bonding pattern and extent of spatial organisation. In 2 one dimensional chains of hydrogen bonded water could be found. In the deprotonated complex [Ru(bibzim)(tbbpy)2] 4 water molecules serve as hydrogen bond donors. The diastereomeric forms 5a/5b of the homodinuclear ruthenium complex [{Ru(tbbpy)2}2(bibzim)][PF6]2 could be separated. No differences in their photophysical properties could be detected. The X-ray investigation of 5a and [{Ru(bpy)2}2(bibzim)][PF6]26 showed little influence of peripheral substitution on structural properties. Complexes 3–5 exhibit activity in electrochemical CO2 reduction which can be tuned by variation of the degree of protonation of the bibenzimidazole.

The chlorido-bridged dimeric complex [Rh 2 (μ-Cl) 2 (trop 2 -NH) 2 ] [trop 2 NH =bis(benzo[a,d]cycloheptenyl)amine] or the acetonitrile complexes [Rh(trop 2 NH)(MeCN) 2 ] + (CF 3 SO 3 - ) and [IrCl(MeCN)(trop2NH)] are well-suited precursor complexes for phenanthroline-type complexes [M(trop2NH)(R,R-phen)] + A - (M = Rh, Ir; R = H, Me, Ph substituents in the 4,7-or 5,6-positions of the phen ligand, A - = CF 3 SΟ 3 - , PF 6 - ). These complexes contain 18-valence-electron configured metal centers in a trigonal-bipyramidal coordination sphere with the amino (NH) group in an axial position and each of the olefinic C=C trop units is in an equatorial position. The cationic amino complexes [M(trop 2 NH)(R,R-phen)] + are sufficiently acidic (pK a in dmso: 18.2-19.0) to be quantitatively deprotonated by one equivalent of KOtBu to give neutral amido complexes [M(trop2N)(R,R-phen)] (M = Rh, Ir). These can be easily oxidized to give aminyl radical complexes [M(trop 2 N - )(R,R-phen)] + A - , which for M = Rh can be isolated as green crystals. The iridium complex [Ir(trop 2 N . )(phen)] + is unstable. High-resolution pulse EPR spectroscopy was used to gain insight into the electronic structure of the aminyl radical complexes. Remarkably, the rhodium and iridium complexes have a very similar electronic structure, as revealed by their EPR parameters ([Rh(trop 2 N . ](phen)] + : g 1,2,3 = 2.084(2), 2.049(2), 2.027(2); lA iso l = 45.4 (N1), 10.4 (N 2 ), 3.1 (N3) 27.0 (Rh) MHz; [Ir(trop 2 N . )(phen)] + : g 1,2,3 = 2.140(2), 2.107(2), 2.015(2); lA iso l = 47 (N1), 7.9 (N2), 3.5 (N3), 26.8 (Ir) MHz} and these show that about 60 % of the spin population is localized on the nitrogen center (N1) of the trop 2 N ligand. In reactions with stannanes (R 3 SnH) and thiols (RSH), H-atom transfer to the trop 2 N nitrogen atom is observed, [M(trop 2 N . ](phen)] + + EH→ [M(trop 2 NH)(phen)] + + 1/2HE-EH.

Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic oxidations. We report that transition metal coordination also supports an aminyl radical, resulting in a stable crystalline complex: [Rh(I)(trop 2 N . )(bipy)] + OTf – (where trop is 5-H-dibenzo[a,d]cycloheptene-5-yl, bipy is 2,2′-bipyridyl, OTf – is trifluorosulfonate). It is accessible under mild conditions by one-electron oxidation of the amide complex [Rh(I)(trop 2 N)(bipy)], at a potential of –0.55 volt versus ferrocene/ferrocenium. Both electron paramagnetic resonance spectroscopy and density functional theory support 57% localization of the unpaired spin at N. In reactions with H-atom donors, the Rh-coordinated aminyl behaves as a nucleophilic radical.

A split decision: Efficient heterolytic hydrogen splitting is achieved with novel tetracoordinate rhodium(I) amides. This reaction is reversible, and DFT calculations imply that the cleavage is a one-step process with a relatively low activation barrier. Ketones and imines are hydrogenated by the amide complexes without the need for further additives.

The luminescence of a ruthenium bibenzimidazole complex can be switched on by the presence of Zn(II), Mg(II), and Cu(I) compounds. Complexation of these metals to the ruthenium center is confirmed by electrospray mass spectrometry.

A combination of the rigid bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine (trop(2)NH) and 5-amino-5H-dibenzo[a,d]cycloheptene (tropNH(2)) ligand allowed the synthesis of the stable pentacoordinated 18 electron amine olefin rhodium(i) complex [Rh(trop(2)NH)(tropNH(2))]O(3)SCF(3)(); this complex can be cleanly deprotonated [pK(a)(DMSO) = 20.6(1)] to the corresponding amide [Rh(trop(2)N)(tropNH(2))](6) which is reversibly oxidised at -0.466 V (vs. Fc/Fc(+)). The coordinated NH bond strength in is estimated to be 379 +/- 10 kJ mol(-1).