Catalytic hydrogenation of carboxamides and esters by well-defined Cp*Ru complexes bearing a protic amine ligand

A novel catalytic method for the straightforward hydrogenation of carboxamides and esters to primary alcohols has been developed. Chiral modification in the ligand sphere of the well-defined Cp*Ru catalyst molecule opens up a new possibility for the development of an enantioselective hydrogenation of racemic substrates via dynamic kinetic resolution.     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

Dinuclear 3D metal complexes based on a carbacylamidophosphate ligand: redetermination of the ligand crystal structure

Dinuclear Ni(II), Co(II) and Zn(II) complexes of general formula $ \left[ {{\text{M}}_{ 2}^{\text{II}} {\text{Cl}}_{ 4} \left( {\text{HL}} \right)_{ 4} \left( {\text{i-PrOH}} \right)_{ 2} \cdot 2\left( {\text{i-PrOH}} \right)} \right] $ with a carbacylamidophosphate ligand, namely 2,2,2-trichloro-N-(dipiperidine-1-yl-phosphoryl)acetamide (CCl₃C(O)N(H)P(O)[N(CH₂)₅]₂), were synthesized and characterized by physicochemical and spectroscopic methods. Electronic absorption spectra of the nickel and cobalt complexes were measured at room temperature in toluene and in the solid state. The crystal structures of HL and [Ni₂Cl₄(HL)₄(i-PrOH)₂·2(i-PrOH)] have been determined by single-crystal XRD studies. Earlier, the structure of a monoclinic C2/c modification of HL was reported. In this paper, redetermination of the structure of HL with triclinic crystal system, P $ \overline{1} $ , was made. The nickel complex is a chloro-bridged dimer, in which the Ni(II) centers are in a distorted octahedral geometry and the neutral HL is coordinated via its phosphoryl oxygen atom. This coordination mode was determined for the first time for 3D metal carbacylamidophosphate complexes.     

Particle formation during oxidation catalysis with Cp* iridium complexes

Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir(III) precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO(4) as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*(2)Ir(2)(μ-OH)(3)]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (~580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously.     

Dinuclear cobalt(II) and copper(II) complexes with a Py2N4S2 macrocyclic ligand

The interaction between Co(II) and Cu(II) ions with a Py(2)N(4)S(2)-coordinating octadentate macrocyclic ligand (L) to afford dinuclear compounds has been investigated. The complexes were characterized by microanalysis, conductivity measurements, IR spectroscopy and liquid secondary ion mass spectrometry. The crystal structure of the compounds [H(4)L](NO(3))(4), [Cu(2)LCl(2)](NO(3))(2) (5), [Cu(2)L(NO(3))(2)](NO(3))(2) (6), and [Cu(2)L(μ-OH)](ClO(4))(3)·H(2)O (7) was also determined by single-crystal X-ray diffraction. The [H(4)L](4+) cation crystal structure presents two different conformations, planar and step, with intermolecular face-to-face π,π-stacking interactions between the pyridinic rings. Complexes 5 and 6 show the metal ions in a slightly distorted square-pyramidal coordination geometry. In the case of complex 7, the crystal structure presents the two metal ions joined by a μ-hydroxo bridge and the Cu(II) centers in a slightly distorted square plane or a tetragonally distorted octahedral geometry, taking into account weak interactions in axial positions. Electron paramagnetic resonance spectroscopy is in accordance with the dinuclear nature of the complexes, with an octahedral environment for the cobalt(II) compounds and square-pyramidal or tetragonally elongated octahedral geometries for the copper(II) compounds. The magnetic behavior is consistent with the existence of antiferromagnetic interactions between the ions for cobalt(II) and copper(II) complexes, while for the Co(II) ones, this behavior could also be explained by spin-orbit coupling.     

Dinuclear platinum complexes with biological relevance based on the 1,2-diaminocyclohexane carrier ligand

The synthesis of bifunctional dinuclear platinum complexes, [{PtCl(dach)}(2)-mu-Y](n+)Cl(n) (1-3; Y = H(2)N(CH(2))(3)NH(2)(CH(2))(4)NH(2), H(2)N(CH(2))(6)NH(2)(CH(2))(6)NH(2), and H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2), respectively; Figure 1) is reported. There was no labilization of the polyamine linker groups of the cis-1,2-diaminocyclohexane complexes in the presence of sulfur-containing species at physiological pH, in contrast to previous studies preformed on trans complexes. Metabolism reactions are somewhat dependent on the nature of the polyamine: at physiological pH, the spermidine complex 1 forms an inert (tetraamine)platinum species in which one platinum is chelated by a central and terminal amino group. The stability of cis-geometry complexes may make them viable second-generation polynuclear platinum clinical candidates.     

Synthesis and structural studies of arene ruthenium and Cp*Rh/Cp*Ir complexes containing pyridylpyrazole- and pyridylthiazole-based ligands

The reactions of [(arene)RuCl₂]₂ (arene = p-cymene or benzene) and [Cp*MCl₂]₂ (M = Rh or Ir) with N,N′-bidentate chelating ligands 2-[3-(2-pyridyl)pyrazolyl]pyrimidine (L1) and 4-phenyl-(2-pyridyl)thiazole (L2) leads to the formation of mononuclear complexes of general formula [(arene)/Cp*M(L)Cl]PF₆. Eight such complexes have been prepared and characterized by spectroscopic techniques. In addition, five of the complexes were also characterized by single-crystal X-ray diffraction. These complexes have typical piano-stool geometries around the metal center, with five-membered metellacycles in which L1 and L2 both act as N,N′-chelating ligands. Moreover, L1 prefers to coordinate through its pyrimidine and pyrazolyl nitrogen atoms, rather than the pyridine nitrogen.     

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

The crystal structures of [M₂(phen)₄(H₂O)₂(C₄O₄)]· C₄O₄· 8H₂O [M = Co²⁺ (1), Mn²⁺ (2); phen: 1,10-phenanthroline] complexes have been prepared and characterized by IR spectroscopy, thermal analysis and single X-ray diffraction techniques. Their structures consist of [Co₂(phen)₄(H₂O)₂(C₄O₄)]²⁺ (1) and [Mn₂(phen)₄(H₂O)₂(C₄O₄)]²⁺ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C₄O ₄ ^2? (SQ^2?) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the μ-1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M–M separation being 8.053(7) Å (1) and 8.175(4) Å (2), respectively, while the other squarate acts as a counter anion. The voltammetric behaviour of complexes (1) and (2) was investigated in DMSO (dimethylsulfoxide) solution by cyclic voltammetry using n-Bu₄NClO₄ as supporting electrolyte. The complexes exhibit both metal and ligand centred electroactivity in the potential ?±1.75 V versus Ag/AgCl reference electrode. The dianion SQ^2? is oxidized in two consecutive steps to the corresponding radical monoanion and neutral form.     

Imidazol-2-yl complexes of Cp*Ir as bifunctional ambident reactants

Loss of chloride ion from imidazol-2-yl complex 4a activates the H-H bond of dihydrogen or the C-H bond of acetylene, forming an Ir(III) N-heterocyclic carbene (NHC) complex (3b or 9). Deprotonation of Ir(III) hydride 4b gives one new species, formulated as Ir(I) carbene complex 5. Protonation or alkylation of 5 occurs at the metal, returning the Ir(III) core of 6a,b. Deprotonation of cationic NHC complex 3a gives neutral imidazol-2-yl analogue 4a; as seen by X-ray diffraction, the Ir-C bond in 3a is shorter than that in 4a. These and other comparisons and interconversions of NHC complexes with an NH function and related imidazol-2-yl species expand the potential of NHC complexes by showing their bifunctional character.     

Chemoselective transfer hydrodechlorination of aryl chlorides catalyzed by Cp*Rh complexes

An effective Cp*Rh catalyzed transfer hydrodechlorination of aryl chlorides was achieved with high tolerance towards a variety of functional groups using 2-butanol as a hydrogen source.     

Influence of ligand electronic effects on the structure of monovalent cobalt complexes

The syntheses, spectroscopic properties, and structures of the monovalent cobalt complexes, [PhTt (tBu)]Co(L), 1-L {PhTt (tBu) = phenyltris[( tert-butylthio)methyl]borate; L = PPh 3, PMe 3, PEt 3, PMe 2Ph, PMePh 2, P(OPh) 3, CNBu (t)}, are described. Complexes 1-L are prepared via the sodium amalgam reduction of [PhTt (tBu)]CoCl in the presence of L. The complexes display magnetic moments and paramagnetically shifted (1)H NMR spectra consistent with triplet, S = 1, ground states. The molecular geometries, determined by X-ray diffraction methods, reveal that some of the complexes display structures in which the L donor is moved off of the inherent 3-fold axis. In the most extreme cases (e.g., 1-P(OPh) 3 or 1-CNBu ( t )), the geometries can be described as cis-divacant octahedra. The origin of the geometric distortions is a consequence of the electronic characteristics of L as first deduced by Detrich et al. for [Tp (Np)]Co(L) ( J. Am. Chem. Soc. 1996, 118, 1703). The results establish a linear correlation between the magnitude of the structural distortion and the electronic parameter of the phosphine donor.     

Direct arylation of aromatic C-H bonds catalyzed by Cp*Ir complexes

The C-H bond of benzene was directly arylated by reaction with aryl iodides in the presence of a catalytic amount of a pentamethylcyclopentadienyliridium complex and potassium tert-butoxide.     

DNA-binding studies of mixed ligand cobalt(III) complexes

The DNA binding characteristics of mixed ligand complexes of the type [Co(en)₂(L)]Br₃ where en = N,N′-ethylenediamine and L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 1,10-phenanthroline-5,6-dione (phendione), dipyrido[3,2-a:2′,3′-c]phenazine (dppz) have been investigated by absorption titration, competitive binding fluorescence spectroscopy and viscosity measurements. The order of intercalative ability of the coordinated ligands is dppz > phen > phendione > bpy in this series of complexes.     

Dinuclear trivalent chromium,manganese, iron and cobalt complexes bridged by aromatic diamines

Summary Trivalent chromium, manganese, iron and cobalt salts react withm-phenylenediamine and acetylacetone to give complexes of the type [M(C₁₆H₁₈N₂O₂)X]: X = Cl, Br, NO₃ or NCS for M = chromium(III) and iron(III); X = Cl, Br, OAc or NCS for manganese(III); and X = OH for cobalt(III). Conductance measurements show the complexes to be nonelectrolytes. Molecular weights determined cryoscopically, show the iron complexes to be dinuclear. Magnetic measurements above 85 K reveal the presence of slight antiferromagnetic interactions. The complexes are dimeric five-coordinate square-pyramidal withm-phenylenediamine residues acting as bridges. The electronic spectra are interpreted in terms of the Normalised Spherical Harmonic Hamiltonian Theory and the DT/DQ values which indicate that chromium complexes are slightly distorted, whereas those of manganese are severely distorted.     

Dinuclear cobalt and nickel complexes of a mercaptoacetic acid substituted 1,2,4‐triazole ligand: syntheses,structures and urease inhibitory studies

Because of its versatile coordination modes and strong coordination ability, the mercaptoacetic acid substituted 1,2,4‐triazole 2‐{[5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl]sulfanyl}acetic acid ( H₂L ) was synthesized and characterized. Treatment of H₂L with cobalt and nickel acetate afforded the dinuclear complexes {μ‐3‐[(carboxylatomethyl)sulfanyl]‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐ido‐κ²N¹,N⁵:N²,O}bis[aqua(methanol‐κO)cobalt(II)] methanol disolvate, [Co₂(C₉H₆N₄O₂S)₂(CH₃OH)₂(H₂O)₂]·2CH₃OH ( 1 ), and {μ‐3‐[(carboxylatomethyl)sulfanyl]‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐ido‐κ²N¹,N⁵:N²,O}bis[diaquanickel(II)] methanol disolvate dihydrate, [Ni₂(C₉H₆N₄O₂S)₂(H₂O)₄]·2CH₃OH·2H₂O ( 2 ), respectively. Complex 1 crystallized in the monoclinic space group P2₁/c, while 2 crystallized in the tetragonal space group I4₁/a. Single‐crystal X‐ray diffraction studies revealed that H₂L is doubly deprotonated and acts as a tetradentate bridging ligand in complexes 1 and 2 . For both of the obtained complexes, extensive hydrogen‐bond interactions contribute to the formation of their three‐dimensional supermolecular structures. Hirshfeld surface analysis was used to illustrate the intermolecular interactions. Additionally, the urease inhibitory activities of 1 , 2 and H₂L were investigated against jack bean urease, where the two complexes revealed strong urease inhibition activities.     

Dinuclear asymmetric ruthenium complexes with 5-cyano-1,10-phenanthroline as a bridging ligand

New dinuclear asymmetric ruthenium complexes of the type [(bpy)(2)Ru(5-CNphen)Ru(NH(3))(5)](4+/5+) (bpy = 2,2'-bipyridine; 5-CNphen = 5-cyano-1,10-phenanthroline) have been synthesized and characterized by spectroscopic, electrochemical, and photophysical techniques. The structure of the cation [(bpy)(2)Ru(5-CNphen)Ru(NH(3))(5)](4+) has been determined by X-ray diffraction. The mononuclear precursor [Ru(bpy)(2)(5-CNphen)](2+) has also been prepared and studied; while its properties as a photosensitizer are similar to those of [Ru(bpy)(3)](2+), its luminescence at room temperature is quenched by a factor of 5 in the mixed-valent species [(bpy)(2)Ru(II)(5-CNphen)Ru(III)(NH(3))(5)](5+), pointing to the occurrence of intramolecular electron-transfer processes that follow light excitation. From spectral data for the metal-to-metal charge-transfer transition Ru(II) --> Ru(III) in this latter complex, a slight electronic interaction (H(AB) = 190 cm(-1)) is disclosed between both metallic centers through the bridging 5-CNphen.     

Multialkylation of aqueous ammonia with alcohols catalyzed by water-soluble Cp*Ir-ammine complexes

Novel water-soluble Cp*Ir-ammine complexes have been synthesized, and a new and highly atom-economical system for the synthesis of organic amines using aqueous ammonia as a nitrogen source has been developed. With a water-soluble and air-stable Cp*Ir-ammine catalyst, [Cp*Ir(NH(3))(3)][I](2), a variety of tertiary and secondary amines were synthesized by the multialkylation of aqueous ammonia with theoretical equivalents of primary and secondary alcohols. The catalyst could be recycled by a facile procedure maintaining high activity. A one-flask synthesis of quinolizidine starting with 1,5,9-nonanetriol was also demonstrated. This new catalytic system would provide a practical and environmentally benign methodology for the synthesis of various organic amines.