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Valence tautomerism involving coupled Cu+/2+ and quinone−\./2− redox systems has been observed for the first time outside an enzymatic situation (amine oxidases) with chelates L as CuI and CuII affine coligands. Even slight variations of the quinone substitution pattern suffice to shift the valence tautomer equilibrium completely. [(L)CuII(Q−II)] ⇌ [(L)CuI(Q−I)]

2-Ammoniobutenynyl Ru-complexes trans-[Cl(dppm) 2 Ru-CtC-C(NR 2 R′)dCH 2 ] + PF 6 -(3ag) have been prepared in a one-pot procedure from cis-[RuCl 2 (dppm) 2 ], excess butadiyne, and various tertairy amines, whereas 4-(dimethylamino)pyridine binds to the unsaturated carbon ligand via the pyridine nitrogen to give 3h. These results may be rationalized by envoking the butatrienylidene complex trans-[Cl(dppm) 2 RudCdCdCdCH 2 ] + as the reactive intermediate. Amine complexes cis-[Ru(dppm) 2 Cl(NR 2 R′)] + are frequently formed as side products and the 4-dimethylaminopyridine derivative cis-[Ru(dppm) 2 Cl(4-DMAP)] + was obtained in high yield in the absence of butadiyne but under otherwise identical reaction conditions. Complexes 3 have been characterized by various spectroscopic and electrochemical techniques including cyclic and square wave voltammetry and, in the case of the NEt 3 derivative 3a, also by X-ray crystallography. Most complexes 3 undergo a fully reversible one-electron oxidation at half-wave potentials that depend on the amine substituent. This provides evidence for delocalization over the conjugated C 3 bridge. EPR spectroscopic investigations of the oxidized forms of the NEt 3 and PhCH 2 NMe 2 derived complexes 3a and 3f point to Ru-centered radical dications. The irreversible reduction of complexes 3 occurs in two closely spaced, poorly defined waves and ultimately releases the respective free amine, which itself is reactive toward the Ru(III) oxidation product. Following the oxidation of 3a and 3f by UV/vis and IR spectroelectrochemistry revealed a blue shift of the prominent absorption band and a bleaching of the CtC stretch.

Coordinatively stabilized C n ligands of higher chain lengths built exclusively from sp-hybridized carbon atoms are not only appealing synthetic goals but also interesting materials with unusual physical and material properties. They serve as model compounds for "molecular wires" 1 or high-spin materials, 2 and some representatives have been found to exhibit nonlinear optical 3 or liquid crystalline properties. 4 Within this context, alkynyl-and alkenylidene ligands have to be distinguished. Allenylidene 5 and pentatetraenylidene complexes 6 are the first members of the latter family with an odd number of carbon atoms within the unsaturated chain. Reports about corresponding systems with an even number of carbon atoms are still quite scarce and restricted to the butatrienylidene ligand. 7,8 While this work was in progress, Bruce et al. showed this ligand to regioselectively add phosphorus nucleophiles, 7b to add protic nucleophiles to the terminal CdC bond leading to functionalized allenylidene complexes, or to engage in cycloaddition reactions with aromatic imines. 7c Coordinatively unsaturated 16 valence electron ruthenium cations are able to isomerize terminal alkynes RCtCH to cationic vinylidene complexes [{Ru}dCdCHR] + . These are the conjugate acids of neutral alkynyl complexes [{Ru}sCtCR], and many cases are known where such transformations have successfully been performed in the presence of a base. 3b,5a,9 Substitution of the simple alkynes RCtCH for diynes RCtCsCtCH is thus expected to give diynyl compounds [{Ru}sCtCsCtCR via butatrienylidene intermediates [{Ru}dCdCdCdCHR] + . An appropriate choice of R should render these diynyl complexes valuable starting materials for the construction of C 4 or C 8 bridged dimetal compounds, 1b,10 which deserve special attention for their unusual electronic properties. For this purpose, butadiyne (R ) H) should be an ideal starting material.In our initial studies, we chose [ClRu(dppm 2 ) 2 ] + (1a, dppm ) bis(diphenylphosphino)methane) as the ruthenium complex fragment. The latter species is generated in situ from the corresponding cis-dichloro compound in the presence of NaPF 6 . When KO t Bu or DBU was added to the dark green solutions obtained after treating 1a with excess butadiyne in dichloromethane or THF, complex product mixtures were produced from which no pure materials could be isolated.The tertiary amines NEt 3 and NPr 3 , however, were found to selectively add to the electrophilic C γ atom of the proposed butatrienylidene intermediate 2a (see Scheme 1). After chromatographic workup, the ammoniobutenynyl adducts trans-[RuCl(dppm) 2 sCtCsC-(NR 3 )dCH 2 ] + PF 6 -(3a, R ) Et; 3b, R ) Pr) were isolated Clays, K.; Persoons, A. Cadernio, V.; Gamasa, M. P.; Gimeno, J. Organometallics 1996, 15, 5266.(4) (a) Takahashi S.; Takai, Y.; Morimoto, H.; Sonogashira, K.; Hagihara, N. Mol. Cryst. Liq. Cryst. 1982, 82, 139. (b) Takahashi, S.; Takai, Y.; Morimoto, H.; Sonogashira, K. J. Chem. Soc., Chem. Commun. 1984, 3. (c) Kaharu, T.; Matsubara, H.; Takahashi, S. J. M...

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The pyrazine-bridged diosmium(II) complex {(μ-C4H4N2)[Os(CN)5]2}6- has been synthesized as the hexapotassium salt and was converted to the hexakis(tetrabutylammonium) compound by ion exchange. Its stepwise oxidation to the Os2 IIIOsII and Os2 IIIOsIII states was monitored spectroelectrochemically in acetonitrile/0.1 M Bu4NPF6 in the UV−vis−NIR and IR regions and by EPR. The OsII 2 species exhibits long-wavelength solvatochromic MLCT bands at 14 800 and 18 480 cm-1. The pentaanionic mixed-valent ion has a comproportionation constant K c of 105.8 and is distinguished by several electronic absorptions in the IR region. The bands at 1972, 2480, 4000, 5000, 7170, and 11 900 cm-1 are similar but appreciably lower in energy than those reported for the analogous complex {(μ-C4H4N2)[Os(NH3)5]2}5+. In addition to CN vibrational stretching features shifted on electron transfer there is an additional sharp band only for the 5− ion at 1582 cm-1 which is attributed to a pyrazine ring vibration. The intensity of this band suggests an unsymmetrical situation and thus valence localization on the vibrational time scale. The EPR signals at g ⊥ = 2.0563 and g ∥ = 1.761 point toward excited states lying close to the doublet ground state and to significant metal/cyanide interaction. Compared to the Creutz−Taube ion {(μ-C4H4N2)[Ru(NH3)5]2}5+ and its osmium homologue, the 5− ion described here exhibits a lower degree of metal−metal coupling.

The complexes [(DMA)Cu(PPh3)2](BF4) (1) (DMA = 1,3-dimethylalloxazine), [(DMA)Ru(bpy)2](PF6)2 (2), and (DMA)WO2Cl2 (3) were obtained as O4-N5-chelated species, as evident from an X-ray crystal structure analysis for 3 and from spectroscopy (NMR, IR, and UV-vis spectroelectrochemistry) for 1 and 2. The tungsten(VI) center in 3 has its oxide ligands in a cis/equatorial position and the chloride ligands in a trans/axial position; it also exhibits a relatively short bond to O4 (2.232(3) A) and a very long bond to N5 (2.462(3) A). Comparison with the new structurally characterized compound (BIK)WO2Cl2 (4) (BIK = bis(1-methylimidazol-2-yl)ketone), which has W-N bonds of about 2.30 A, confirms the unusual length of the W-N bond in 3, probably caused by repulsion between one of the oxo ligands and the peri-hydrogen atom (H6) of DMA. One-electron reduction of the complexes occurs reversibly at room temperature in THF (1, 2) or at 198 K in CH2Cl2 (3). EPR spectroscopy reveals that this process is ligand-centered for 1 and 2 but metal-centered for 3. Density functional methods and ab initio methodology are used to illustrate the correspondence in spin distribution between the radical anion pi systems of alloxazine and isoalloxazine ("flavosemiquinone").

Two hydrido ruthenium complexes could be isolated from the reaction between RuCl 2 (DMSO) 4 (DMSO) dimethyl sulfoxide) and the chelating 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and [BPh 4 ]-. These are [RuH-(dcpe) 2 ] + [BPh 4 ]-with a five-coordinate, 16 valence electron cation and the neutral zwitterionic 18 valence electron compound {(η 6-C 6 H 5)BPh 3 }RuH(dcpe). The relative amounts of these products depend on the reaction conditions. If NaBPh 4 is replaced by NH 4 PF 6 or added after the reaction with the diphosphine has gone to completion, the 16 valence electron species [RuH(dcpe) 2 ] + is the only product. Reducing the size of the diphosphine chelate to 1,1-bis(dicyclohexylphosphino)methane (dcpm) has a large effect on the reaction course. Either trans-RuHCl-(dcpm) 2 or trans-RuCl 2 (dcpm) 2 is formed, depending on the conditions. X-ray structures of [RuH(dcpe) 2 ] + [BPh 4 ]-(monoclinic, P2/c, a) 24.936(5) Å, b) 12.633(3) Å, c) 25.801(5) Å,) 102.86(3)°, V) 7924(3) Å 3 , Z) 4, R) 0.062, R w) 0.1694) and {(η 6-C 6 H 5)BPh 3 }RuH(dcpe) (monoclinic, P2 1 /n, a) 14.321(5) Å, b) 19.716-(7) Å, c) 17.100(5) Å,) 107.60°, V) 4602(3) Å 3 , Z) 4, R) 0.0648, R w) 0.1873) have been determined. A nearly planar arrangement of the four P atoms exists around Ru in the five-coordinate cation, implying a distorted square pyramid. This structural motif has not been observed previously for a d 6 RuL 5 system with a P 4 X donor set. {(η 6-C 6 H 5)BPh 3 }RuH(dcpe) represents an example for the noninnocent behavior of the "noncoordinating" [BPh 4 ]-anion. The coordinated six-membered ring displays a boatlike distortion with the BPh 3 "substituent" and the para-carbon of the coordinated ring displaced away from the metal.