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This article deals with a class of ruthenium-BIAN-derived complexes, [Ru-II(tpm)(R-BIAN)Cl]ClO4 (tpm = tris(1-pyrazolyl)methane, R-BIAN = bis(arylimino)acenaphthene, R = 4-OMe ([1a]ClO4), 4-F ([1b]ClO4), 4-Cl ([1c]ClO4), 4-NO2 ([1d]ClO4)) and [Ru-II(tpm)(OMe-BIAN)H2O](2+) ([3a](ClO4)2). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([N-(phenyl)imino]acenapthenone)-derived complex [Ru-II(tpm)(BIAO)Cl]ClO4 ([2]ClO4). The redox-sensitive bond parameters involving -N=C-C=N- or -N=C-C=O of BIAN or BIAO in the crystals of representative [1a]ClO4, [3a](PF6)(2), or [2]ClO4 establish its unreduced form. The chloro derivatives 1a(+)-1d(+) and 2(+) exhibit one oxidation and successive reduction processes in CH3CN within the potential limit of +/- 2.0 V versus SCE, and the redox potentials follow the order 1a(+) < 1b(+) < 1c(+) < 1d(+) approximate to 2(+). The electronic structural aspects of 1a(n)-1d(n) and 2(n) (n = +2, +1, 0, -1, -2, -3) have been assessed by UV-vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru-II -> Ru-III) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex 3a(2+) undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru-II-H2O}/{Ru-III-OH} and {Ru-III-OH}/{Ru-IV=O}, respectively. The chloro (1a(+)-1d(+)) and aqua (3a(2+)) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI(OAc)(2) as oxidant in CH2Cl2 at 298 K, though the analogous 2(+) remains virtually inactive. The detailed experimental analysis with the representative precatalyst 1a(+) suggests the involvement of the active {Ru-IV=O} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations.

An intramolecular dehydrogenative (sp(3))C-O bond formation in salicylamides can be initiated by an active Cu/O-2 species to generate pharamaceutically relevant dihydro-oxazinones. Experimental findings suggest that stereoelectronic parameters in both coupling partners are controlling factors for site selectivity in bond formation. Mechanistic investigations including isotope labeling, kinetic studies helped to propose a catalytic cycle. The method provides a convenient synthesis of an investigational new medicine CX-614, which has potential in finding treatment for Parkinson's and Alzheimer's diseases.

The varying coordination modes of the ambidentate ligand 2,2'-bipyridine-3,3'-diol (H2L) in a set of ruthenium complexes were demonstrated with special reference to the electronic features of the coligands, including sigma-donating acac(-) (= acetylacetonate) in Ru-III(acac)(2)(HL-) (1), strongly pi-accepting pap (= 2-phenylazopyridine) in Ru-II(pap)(2)(L2-) (2)/[(pap)(2)Ru-II(mu-L2-)Ru-II(pap)(2)](ClO4)(2) ([4](ClO4)(2)), and reported moderately pi-accepting bpy (= 2,2'-bypiridine) in [Ru-II(bpy)(2)(HL-)]PF6 ([5]PF6)/[(bpy)(2)Ru(mu-L2-)Ru(bpy)(2)](PF6)(2) ([7] (PF6)(2)). The single-crystal X-ray structures reveal that, in paramagnetic and electron paramagnetic resonance active 1 and reported diamagnetic [5]PF6, nearly planar monoanionic HL- coordinates to the metal ion via the N,N donors forming a five-membered chelate ring with hydrogen-bonded O-H center dot center dot center dot O function at the backbone of the ligand framework, as has also been reported in other metal complexes. However, structurally characterized diamagnetic 2 represents O-,O- bonded seven-membered chelate of fully deprotonated but twisted L2-. The nonplanarity of the coordinated L2- in 2 does not permit the second metal fragment {Ru(pap)(2)} or {Ru(bpy)(2)} or {Ru(acac)(2)} to bind with the available N,N donors at the back face of L2-. Further, the deprotonated form of the model ligand 2,2'-biphenol (H2L') yields Ru-II(pap)(2)(L'(2-)) (3); its crystal structure establishes the expected O-,O- bonded seven-membered chelate of nonplanar L'(2-) as in reported Ru-II(bpy)(2)(L'(2-)) (6), although {Ru(acac)(2)} metal precursor altogether fails to react with H2L'. All attempts to make diruthenium complex from {Ru(acac)(2)} and H2L failed; however, the corresponding {Ru(pap)(2)(2+)} derived dimeric [4](ClO4)(2) was structurally characterized. It establishes the symmetric N,O-/N,O- bridging mode of nonplanar L2- as in reported [7](PF6)(2). Besides structural and spectroscopic characterization of the newly developed complexes, the ligand (HL-, L2-, L'(2-), pap)-, metal-, or mixed metal-ligand-based accessible redox processes in 1(n) (n = +2, +1, 0, -1), 2(n)/3(n) (n = +2, +1, 0, -1, -2), and 4(n) (n = +4, +3, +2, +1, 0, -1) were analyzed in conjunction with density functional theory calculations.

Microwave irradiation of a toluene solution of the diyne FcC(2)C(2)Ph and Ru-3(CO)(12) yields the [Ru(CO)(3)(eta(4)-ruthenole)] derivatives 1a-f, which differ in relative positions of the uncoordinated alkyne group. Upon treatment with Pt(PPh3)(2)C2H4, the ruthenoles 1a-c, containing a single free C equivalent to C unit at the a position with respect to the ring Ru metal, yield the novel allene-coordinated, phosphido-bridged Ru2Pt clusters 3a-c along with their phosphine-substituted derivatives 4a-c. Under similar reaction conditions, isomers 1d,e, which are devoid of any free C equivalent to C unit at the alpha position, and If, having free C equivalent to C units at both alpha positions, form only their phosphine-substituted derivatives 4d-f. The formation of Ru2Pt clusters from ruthenole complexes involves cleavage of the P-C bond of the phosphine and migration of the resulting phenyl group onto the free alkyne, which leads to enyne to allene transformation.

Oxidative addition of diaryldichalcogen ligands (REER) to ruthenium carbonyl (Ru-3(CO)(12)) followed by the addition of halogen (X-2) afforded chalcogen-bridged Ru(II)-based metallacycles of general formula [X(CO)(3)Ru(mu-ER)(2)Ru-(CO)(3)X] (1-10), where E = S, Se, and Te; R = phenyl, tolyl, and benzyl; and X = Br and I. Compounds 1-10 were characterized using IR, UV-vis, and NMR spectroscopic techniques. Molecular structures of the metallacycles have been elucidated by single-crystal X-ray diffraction methods that confirm the dimeric nature of metallacycles, wherein the two Ru(CO)(3)X moieties are held together by the bridging aryl chalcogenide ligands.

The Rauhut-Currier reaction between nitroalkenes and vinyl sulfones has been successfully carried out for the first time. The reaction proceeds in the presence of an imidazole/LiCl catalyst system in dioxane to provide the adducts possessing a synthetically useful 1-bis-sulfonyl-3-nitroalkene moiety in good to excellent yield. A one-pot transformation of the products to beta-sulfonyl-alpha,beta-unsaturated ketoximes has also been demonstrated.

A novel cage-annulated (bis-homocubyl) vinylidenecarbene has been generated and successfully trapped without any intermediacy of its cycloalkyne isomer. The greater kinetic and thermodynamic stability of the vinylidenecarbene vis-a-vis its cycloalkyne isomer has been predicted by DFT B3LYP/6-31G* calculations. The calculated results suggest the prospects of the cycloalkyne becoming amenable for trapping, if generated under suitable experimental conditions, owing to the substantial kinetic energy barrier associated with its possible ring contraction via 1,2-shift to the vinylidenecarbene isomer and marginal ground state energy difference. However, all of our attempts to directly generate and trap the cycloalkyne yielded unsatisfactory results. Attempted generation and trapping of a C2-symmetric bis-vinylidenecarbene from a bis-vinylidenedibromide met with unexpected failure.

The redox systems [Ru(L)(bpy)(2)](k), [Ru(L)(2)(bpy)](m), and [Ru(L)(3)](n) containing the potentially redox-active ligand 9-oxidophenalenone = L- were investigated by spectroelectrochemistry (UV-vis-near-IR and electron paramagnetic resonance) in conjunction with density functional theory (DFT) calculations. Compounds [Ru(L-)(bpy)(2)]ClO4 ([1]ClO4) and [Ru(L-)(2)(bpy)]ClO4 ([2]ClO4) were structurally characterized. In addition to establishing electron-transfer processes involving the Ru-II/Ru-III/Ru-IV. and bpy(0)/bpy(center dot-) couples, evidence for the noninnocent behavior of L- was obtained from [Ru-IV(L-center dot)(L-)(bpy)](3+), which exhibits strong near-IR absorption due to ligand-to-ligand charge transfer. In contrast, the lability of the electrogenerated anion [Ru(L)(2)(bpy)](-) attributed to a resonance situation [Ru-II(L center dot 2-)(L-)(bpy)](-)/[Ru-II(L-)(2) (bpy(center dot-))](-), as suggested by DFT calculations.

The diruthenium(III) complex [(acac)(2)Ru(mu-L(2-))Ru(acac)(2)] (1) with acac(-) = acetylacetonato = 2,4-pentanedionato and a 2,5-pyrazine-dicarboxylato bridge, L(2-), has been obtained and structurally characterized as the rac (Delta Delta,Lambda Lambda) diastereomer. The Ru(III)Ru(III) configuration in 1 (d(Ru-au) = 6.799 angstrom) results in a triplet ground state (mu = 2.82/2 mu(B) at 300 K) with a density functional theory (DFT) calculated triplet-singlet gap of 10840 cm-and the metal ions as the primary spin-bearing centers (Mulliken spin densities: Ru, 1.711; L, 0.105; acac, 0.184). The paramagnetic 1 exhibits :broad, upfield shifted (1)H NMR signals with delta values ranging from -10 to -65 -65 ppm and an anisotropic electron paramagnetic resonance (EPR), spectrum (< g > = 2.133, g(1) - g(3) = Delta g = 0.512), accompanied by a weak half-field signal at g = 4.420 in glassy frozen acetonitrile at 4 K Compound 1 displays two closely spaced oxidation steps to yield labile cations. In contrast, two well separated reversible reduction steps of 1 signify appreciable electrochemical metal-metal interaction in the Run Rum mixed-valent state 1(-) (K(c) approximate to 10(7)). The intermediate 1(-) shows a weak, broad Ru(II)-> Ru(III) intervalence charge transfer (IVCT) band at about 1040 nm (epsilon = 380 M(-1) cm(-1)); the DFT approach for 1(-) yielded Mulliken spin densities of 0.460 and 0.685 for the two metal centers. The monitoring of the frequencies of the uncoordinated C=O groups of L(2-) in 1" by IR spectroelectrochemistry suggests valence averaging (Ru(2.5)Ru(2.5)) in 1(-) on the vibrational time scale. The mixed-valent 1(-) displays a rhombic EPR signal (< g > = 2.239 and Delta g = 0.32) which reveals non-negligible contributions from the bridging ligand, reflecting a partial hole-transfer mechanism and being confirmed by the DFT-calculated spin distribution (Mulliken spin density of -0.241 for L in 1(-)). The major low energy electronic transitions in 1(n) (n = 0,-,2-) have been assigned as charge transfer processes with the support of TD-DFT analysis.

Reaction of [Cp*MoCl(4)], 1 (Cp*= eta(5)-C(5)Me(5)), with [LiBH(4) center dot thf] in toluene at -70 degrees C, followed by pyrolysis with excess dichalcogenides RE-ER (R = Ph, CH(2)Ph, 2,6-((t)Bu)(2)-C(6)H(2)OH, (CH(3))(3)C=(t)Bu); E=S, Se) yielded a new class of hybrid clusters, 3-8: (3, [(Cp*Mo)(2)(mu-eta(1)-SPh)(2)(mu(3)-S)(H(2)BSPh)]; 4, [(CP*Mo)(2)B(5)H(8)(SPh)]; 5, [(CP*Mo)(2)B(6)H(8)(SePh)]; 6, [(CP*Mo)(2)B(2)S(2)H(2)(mu-eta(1)-S)]; 7, [(CP*Mo)(2)B(2)H(5)(BSR)(2)(mu-eta(1)-SR)], (R = 2,6-((t)Bu)(2)-C(6)H(2)OH); and 8, [(Cp*Mo)(2)B(2)H(5)(BSePh)(2)(mu-eta(1)-SePh)]. Compounds 3-8 have been isolated in modest yields as green or brown crystalline solids. In parallel with 3-8, [(CP*Mo)(2)B(5)H(9)] was isolated as a major product in all cases. The isolation and structural characterization of compounds 3 and 6-8 provided the first direct evidence of the existence of [(Cp*Mo)(2)B(4)H(8)], 2, an intermediate in the formation of [(Cp*Mo)(2)B(5)H(9)]. These new compounds have been characterized in solution by mass spectrometry, (1)H, (11)B, (13)C NMR, and IR spectroscopy, and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 3-8.

The complexes meso- and rac-[(acac)(2)Ru(mu-L)Ru(acac)(2)](n), 1 and 2, where L(2-) = 1,4-dioxido-2,3-bis(3,5-dimethylpyrazol-1'-yl)benzene and acac = 2,4-pentanedionato. were characterized structurally, magnetically, electrochemically, and spectroscopically as well as spectroelectrochemically (UV-vis-NIR, EPR) in the accessible redox states (n = 0, +, -, 2-). Due to steric interference, the neutral compounds contain a severely twisted L(2) bridging ligand with 43-48 degrees dihedral angles between the planes of the hydroquinone dianion and those of the ortho positioned pyrazolyl substituents. The difference between meso and rac isomers is rather pronounced in terms of the redox potentials (easier oxidation and reduction of the rac form 2) and with respect to the absorption spectra of the oxidized states. Susceptibility and EPR measurements confirm the {Ru(III)(mu-L(2))Ru(III)} configuration of the neutral species, showing J values of -37 and 21 cm (1) for the spin-spin interaction between the ca. 7.75 angstrom separated metal centers in 1 and 2, respectively. Two-step reduction involves the metals and produces Ru(III)Ru(II) mixed-valent monoanions with comproportionation constants of ca. 10(4), with Ru(III)-type EPR signals, and with broad intervalence charge transfer bands at about 1200-1500 nm absorption maximum, suggesting localized valence (class 11). Oxidation produces intense near-infrared absorption at 892 (1(+)) or 1027 nm (2(+)) and narrow isotropic EPR spectra at g approximate to 2.005, signifying unprecedented spin localization at the p-semiquinone bridge. These results are not compatible with an (L(2))-bridged {Ru(IV)Ru(III}) situation nor with an {Ru(III)(mu-L(center dot))Ru(III)} three-spin arrangement with up-down-up spin configuration in the ground state, which would result in metal-centered spin through antiferromagnetic coupling between the adjacent individual spins. Only the {Ru(III)(mu-L(center dot))Ru(III)} situation, with up-up-down spin configuration, leads to ligand-centered resulting spin through the strong antiferromagnetic coupling between the remote metal spins, an unusual situation which is favored here because of weakened metal-radical coupling resulting from the pyrazolyl/p-semiquinone twist.

Mononuclear [Ru-II(tptz)(acac:)(CH3CN)]ClO4 ((ClO4)-Cl-[1]) and mixed-valent dinuclear [(acac)(2)Ru-III{(mu-tptz-H+)(-)}Ru-II(acac)(CH3CN)]ClO4 ([5]ClO4; acac = acetylacetonate) complexes have been synthesized via the reactions of Ru-II(acac)2(CH3CN)(2) and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO4, tptz binds with the Ru-II ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz: bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the Ru-II center and cyclometalated N,C- state with the Ru-III site (motif F). The activation of the coordinated nitrile function in [1]ClO4 and [5]ClO4 in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives, respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H-----O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the (RuI)-I-I state in both the mononuclear {[(acac)(tptz)Ru-II-N=-C-CH3]ClO4 ([1]ClO4) >> [(acac)(tptz)Ru-II-NH=C(CH3)-OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)(RuNH2)-N-II-C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)Ru-II-NH=C(CH3)-NHC2H5]ClO4 ([4]ClO4)} and dinuclear {[(acac)(2)Ru-III-{mu-tptz-H+)(-)}Ru-II(acac)(N equivalent to C-CH3)]ClO4 {(mu-tptz-H+)(-)}Ru-II(acac)(N equivalent to C-CH3)]ClO4 ([5]ClO4), [(acac)(2)Ru-III[(mu-tptz-H+(N-O ([6]ClO4), [(acac)(2)Ru-III{(mu-tptz-H+)(-)}Ru-II(acac)(NH=C(CH3)-OC2H5)]ClO4([7]ClO4), and [(acac)(2)Ru-III{(mu-tptz-H+)(-)}Ru-II(acac)(NC4H4N)]ClO4 ([8]ClO4), complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the Ru-III center in the dinuclear complexes remain more or less invariant. The mixed-valent (RuRuIII)-Ru-II species ([5]ClO4-[8]ClO4) exhibits high comproportionation constant (K-c) values of 1.1 X 10(12)-2 x 109, with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display Ru-II- and Ru-III-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high K, values for [5]ClO4[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the tpical near-IR region up to 2000 nm. The paramagnetic (RuRuIII)-Ru-II species ([5]ClO4-[8]ClO4) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (< g > similar to 2.15 and Delta g similar to 0.5), typical of a low-spin Ru-III ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [RuII(tptz center dot-)(acac)(CH3CN)] (1) and [(acac)(2)Ru-III{mu-tptz-H+)(center dot 2-)}-Ru-II(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.