Crystal structures and electrochemical properties of nickel(II) complexes with N,N',N'',S-tetra-dentate Schiff base ligands.

The thiol-ate nickel complexes {2-[({2-[(2-amino-ethyl-κN)(meth-yl)amino-κN]eth-yl}imino-κN)meth-yl]benzene-thiol-ato-κS}nickel(II) chloride, [Ni(C12H18N3S)]Cl (1), and [2-({[2-(piperazin-1-yl-κ2 N 1,N 4)eth-yl]imino-κN}meth-yl)benzene-thiol-ato-κS]nickel(II) hexa-fluoro-phosphate di-chloro-methane monosolvate, [Ni(C13H18N3S)]PF6·CH2Cl2 (2), were synthesized by the reactions of 2-(tert-butyl-thio)-benzaldehyde, tri-amines, and nickel(II) salts. Both complexes have a nickel ion surrounded by an N,N',N'',S-tetra-dentate ligand, forming a square-planar geometry. The terminal N,N-chelating moiety is N,N-di-alkyl-ethane-1,2-di-amine for 1 and 1-alkyl-piperazine for 2. The N-Ni-N bite angle in the terminal N,N-chelate ring in 2 [76.05 (10)°] is much smaller than that in 1 [86.16 (6)°]. Cyclic voltammograms of 1 and 2 in aqueous media indicated that the reduction and oxidation potentials of 2 are more positive than those of 1. The smaller bite angle of the terminal piperazine chelate in 2 reduces the electron-donating ability of the tetra-dentate ligand, resulting in a positive shift of the redox potentials. Both complexes exhibit catalytic activity for proton reduction, and the piperazine moiety in 2 is effective in reducing the overpotential.

Tetra- and dinuclear manganese complexes of xanthene-bridged O,N,O-Schiff bases with 3-hydroxypropyl or 2-hydroxybenzyl groups: ligand substitution at a triply bridging site.

Complexation properties of U-shaped ligands, L1 and L2, which are Schiff bases of 5,5'-(9,9-dimethylxanthene-4,5-diyl)bis(salicylaldehyde) (H2xansal) with 3-amino-1-propanol or 2-hydroxybenzylamine, respectively, were investigated to construct polynuclear manganese complexes. In these ligands, two O,N,O-Schiff bases are bridged by a xanthene backbone. The reactions of H4L1 or H4L2 with manganese salts afforded tetra- and dinuclear manganese complexes, including the tetramanganese(ii,ii,iii,iii) complex [Mn4(L1)2(µ-OAc)2] with a Mn4O6 core exhibiting an incomplete double-cubane structure. In the Mn4O6 core, phenolate and alkoxide O atoms bridge the manganese ions. Deprotonated 3-hydroxypropyl groups were crucial to the assembly of four manganese ions because the phenolate-bridged dimanganese(iii,iii) complex [Mn2(H2L1)2]2+ was obtained in the absence of a base, and H4L2, which has 2-hydroxybenzyl groups instead of 3-hydroxypropyl groups in H4L1, afforded the cyclic dimanganese(iv,iv) complex [Mn2(L2)2]. We disclosed that [Mn4(L1)2(µ-OAc)2] was converted to the oxo-bridged tetramanganese(iii,iii,iii,iii) complex [Mn4(L1)(HL1)(µ3-O)(µ-OAc)2]+ by treating with NH4PF6 or NH4BF4: a triply bridging alkoxide was protonated and replaced by an oxide ligand. The cyclic voltammograms of [Mn4(L1)(HL1)(µ3-O)(µ-OAc)2]+ suggested that the reverse reaction forming [Mn4(L1)2(µ-OAc)2] occurred in the electrochemical processes and was assisted by protonation.

CO Release from N,C,S-Pincer Iron(III) Carbonyl Complexes Induced by Visible-to-NIR Light Irradiation: Mechanistic Insight into Effects of Axial Phosphorus Ligands.

Light-induced CO release from newly synthesized N,C,S-pincer iron(III) carbonyl complexes with two phosphorus ligands- trans-[Fe(L-κ3 N,C,S)(CO)(PR2R')2]PF6 ([1]PF6, R = Me, R' = Ph; [2]PF6, R = R' = Me; [3]PF6, R = R' = OEt)-were investigated. All the iron(III) carbonyl complexes were stable in solution and showed light-inducible CO release under ambient conditions. Studies on the wavelength dependence of photoreaction revealed that the phosphite complex [3]PF6 exhibited the most extended photosensitivity including all visible and a part of near-IR light (390-800 nm wavelengths). The phosphine complexes [1]PF6 and [2]PF6 showed sensitivity to only the higher-energy region of visible light (390-450 nm). Quantum-chemical calculations and spectroscopic data suggested that all complexes [1]PF6-[3]PF6 have dπ-dπ excitation modes to depopulate Fe-C(carbonyl) bonding and potentially induce the CO release by irradiation of light in the near-IR region, although moderately weakened Fe-C(carbonyl) bonding due to stronger π-backbonding by the phosphite ligand rendered the excitation effective on the CO release exclusively in [3]PF6.

Visible-light-induced release of CO by thiolate iron(iii) carbonyl complexes bearing N,C,S-pincer ligands.

Iron(iii) carbonyl complexes are stabilized by a pincer ligand containing pyridine-N, phenyl-C and thiolate-S donors and two axial phosphine ligands. The N,C,S-pincer iron(iii) carbonyl complexes show CO-releasing properties induced by visible light.

Fluorescence behaviour of an anthracene-BODIPY system affected by spin states of a dioxolene-cobalt centre.

Dioxolene cobalt complexes, [Co(L)(TPA)]PF6 () and [Co(L)(Me3TPA)]PF6 (), were synthesized using a catechol with anthracene and boron-dipyrromethene (BODIPY), H2L, and tris(pyridin-2-ylmethyl)amine (TPA) or tris[(6-methylpyridin-2-yl)methyl]amine (Me3TPA) and characterised by UV-vis absorption, IR and NMR spectroscopy. Complexes and are a low-spin cobalt(iii) catecholate form and a high-spin cobalt(ii) semiquinonate form, respectively, in CH3CN at room temperature. The effect of the spin states of the dioxolene-cobalt centre on fluorescence was investigated in CH3CN at room temperature. The fluorescence intensity of was clearly lower than that of , although both complexes showed weaker fluorescence compared with that of H2L. The difference in the intensity between and is mainly due to the enhancement of nonradiative decay processes based on the stronger metal-ligand interactions for the cobalt(iii) catecholate form of compared with the cobalt(ii) semiquinonate form of .

Formation, reactivity and redox properties of carbon- and sulfur-bridged diiron complexes derived from dibenzothienyl Schiff bases: effect of N,N- and N,P-chelating moieties.

Dibenzothienyl Schiff bases, DBT-NN and DBT-NP, were derived from condensation of 4-formyldibenzothiophene with N,N-dimethylethylenediamine and 2-(diphenylphosphino)ethylamine, respectively. A photochemical reaction of [Fe(CO)5] with DBT-NN produced diiron complexes, [Fe2(µ-DBT-NN)(CO)6] (1) and [{Fe(µ-BPT-NN-κ(3)S,C,N)(CO)2}Fe(CO)3] (2). Complex 1 has π coordination of a Schiff base C=N bond and an N,N-chelate, while 2 has an S,C,N-tridentate ligand having an uncoordinated dimethylamino group. The corresponding reaction with DBT-NP produced a diiron complex of an S,C,N,P-tetradentate ligand, [{Fe(µ-BPT-NP-κ(4)S,C,N,P)(CO)}Fe(CO)3] (3), which has an N,P-chelate, via the DBT-NP complex [Fe(DBT-NP-κP)(CO)4] (4). Reactions of 2 and 3 with one equivalent of PMe2Ph gave the monosubstituted complexes [{Fe(µ-BPT-NN-κ(3)S,C,N)(CO)2}Fe(CO)2(PMe2Ph)] (5) and [{Fe(µ-BPT-NP-κ(4)S,C,N,P)(CO)}Fe(CO)2(PMe2Ph)] (6), respectively. The corresponding reactions with an excess of PMe2Ph produced mononuclear complexes, trans-[Fe(BPT-NN-κ(3)S,C,N)(CO)(PMe2Ph)2] (7) and [Fe(BPT-NP-κ(4)S,C,N,P)(CO)(PMe2Ph)] (8), respectively. Complexes 1-3 and 5-8 were structurally characterized by X-ray crystallography. Complexes 2, 3, 5 and 6 have similar dinuclear structures with different carbonyl/phosphine substitution patterns. Cyclic voltammograms of 2, 3 and 5 showed two one-electron reduction processes, and more negative potentials were observed for 6. The shift of the redox potentials are rationalized by the electron-donating character of the phosphine ligands, which suggests that the reduction occurs at the asymmetrically bridged diiron core.

Synthesis, magnetic properties and dynamic behavior of cobalt complexes with an anthracene-containing dioxolene ligand.

The anthracene-functionalized cobalt complexes [Co(L)(TPA)]PF6 (1) and [Co(L)(Me(n)TPA)]PF6 (2, n = 1; 3, n = 2; 4, n = 3) were synthesized by the combination of 9-(3,4-dihydroxyphenyl)anthracene (H2L) and tris(2-pyridylmethyl)amine (TPA) or its derivatives (Me(n)TPA, n = 1, 2, 3). Characterization of complexes 1-4 was performed by UV-vis absorption, IR, (1)H NMR, and magnetic susceptibility measurements. In the solid state, the variable-temperature magnetic susceptibility data showed that complex 1 is low-spin cobalt(III) catecholate (Co(III)(LS)-Cat), while complex 4 is high-spin cobalt(II) semiquinonate (Co(II)(HS)-SQ) in the range 4.5-400 K. The susceptibility data of complexes 2 and 3 suggested valence tautomerism between the Co(III)(LS)-Cat and Co(II)(HS)-SQ forms. Light-induced valence tautomerism was observed in complexes 2 and 3 at 5 K by photo-irradiation. In solution, the temperature dependence of (1)H NMR spectra of 1 and 2 showed an equilibrium between their geometrical isomers.

Fine-tuning the energy barrier for metal-mediated dinitrogen N≡N bond cleavage.

Experimental data support a mechanism for N≡N bond cleavage within a series of group 5 bimetallic dinitrogen complexes of general formula, {Cp*M[N((i)Pr)C(R)N((i)Pr)]}2(µ-N2) (Cp* = η(5)-C5Me5) (M = Nb, Ta), that proceeds in solution through an intramolecular "end-on-bridged" (µ-η(1):η(1)-N2) to "side-on-bridged" (µ-η(2):η(2)-N2) isomerization process to quantitatively provide the corresponding bimetallic bis(µ-nitrido) complexes, {Cp*M[N((i)Pr)C(R)N((i)Pr)](µ-N)}2. It is further demonstrated that subtle changes in the steric and electronic features of the distal R-substituent, where R = Me, Ph and NMe2, can serve to modulate the magnitude of the free energy barrier height for N≡N bond cleavage as assessed by kinetic studies and experimentally derived activation parameters. The origin of the contrasting kinetic stability of the first-row congener, {Cp*V[N((i)Pr)C(Me)N((i)Pr)]}2(µ-η(1):η(1)-N2) toward N≡N bond cleavage is rationalized in terms of a ground-state electronic structure that favors a significantly less-reduced µ-N2 fragment.

Titanium and manganese complexes supported by a xanthene-bridged bis(tripodal N2O2) ligand: isomerization, intramolecular hydrogen bonding and metal-binding ability.

A new bis(N2O2) ligand, L(4-), in which two tripodal diamine-bis(phenolate) moieties are bridged by a xanthene backbone, was prepared. The reaction of H4L with 2 equiv. of [Ti(O(i)Pr)4] produced C2 and Cs symmetrical isomers of the dititanium(IV,IV) complex [Ti2(L)(O(i)Pr)4]. The isolated C2 isomer was slowly converted to the Cs isomer via Ti-N bond cleavage to form a 3 : 2 mixture in equilibrium. A similar dimanganese(III,III) complex [Mn2(L)(OMe)2(MeOH)2] was synthesized from a 1 : 2 mixture of H4L and manganese(II) perchlorate in the presence of triethylamine. An X-ray analysis of [Mn2(L)(OMe)2(MeOH)2] revealed that two Mn-N2O4 octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene bridge to form a C2 symmetrical structure. The dimanganese(III,III) complex further reacted with manganese(II) acetate to form the mixed-valence trimanganese(III,II,III) complex [Mn3(L)(µ-OMe)2(µ-OAc)2]. Electrochemical data of the trimanganese(III,II,III) complex indicated that the xanthene-bridged dimanganese(III,III) unit effectively binds a Mn(II) ion in solution.

Design, synthesis, magnetic properties of a π-radical ligand with photo-excited high-spin state and its Fe(II) complex. The first stage of a new strategy for LIESST materials.

A π-radical ligand (9-[4-(6-oxo-1,5-dimethylverdazyl)phenyl]-10-[5-(2,2'-bipyridyl)ethynyl]anthracene, L1) with a photo-excited high-spin quartet state (S = 3/2) and its iron(II) complex [Fe(L1){H(2)B(Pz)(2)}(2)] (1) {H(2)B(Pz)(2)(-) = dihydrobis(1-pyrazolyl)borate} were synthesized as a candidate for a new strategy for spin-crossover compounds exhibiting light-induced excited spin state trapping (LIESST), which is via the photo-excited high-spin state of the π-conjugated aromatic system. Control compounds, ligand L2 and [Fe(L2){H(2)B(Pz)(2)}(2)] (2), in which the verdazyl radical moiety in L1 was removed, were also synthesized. The photo-excited quartet state of the π-radical ligand L1 was confirmed by the time-resolved ESR technique. Temperature dependence of the magnetic behaviors of 1 and 2 were investigated from 5 K to 350 K, showing spin-crossover transition at T(c) = 222 K and at T(c) = 162 K for complexes 1 and 2, respectively. The transition enthalpies and entropies were determined to be ΔH = 8.09 kJ mol(-1) and ΔS = 36.4 J K(-1) mol(-1) for 1 and to be ΔH = 22.39 kJ mol(-1) and ΔS = 138 J K(-1) mol(-1) for 2. LIESST phenomena were also observed below ca. 50 K for both complexes. The effects of the attachment of radical moiety are discussed based on the results.

Bis(µ(2)-4,7-dimethyl-4,7-diazadecane-1,10-dithiolato)trinickel(II) bis(perchlorate).

In the title compound, [Ni(3)(C(10)H(22)N(2)S(2))(2)](ClO(4))(2), the complex cation consists of a nickel(II) ion and two [Ni(C(10)H(22)N(2)S(2))] units with an N(2)S(2) tetra-dentate ligand, 3,3'-[1,2-ethane-diylbis(methyl-imino)]bis-(1-propane-thiol-ate). The central Ni(II) ion is located on a crystallographic inversion centre and is bound to the four S atoms of the two [Ni(C(10)H(22)N(2)S(2))] units to form a linear sulfur-bridged trimetallic moiety. The dihedral angle between the central NiS(4) plane and the terminal NiN(2)S(2) plane is 145.71 (5)°. In the [Ni(C(10)H(22)N(2)S(2))] unit, the two methyl groups on the chelating N atoms are cis to each other, and the two six-membered N,S-chelate rings adopt a chair conformation. The Ni-S bond lengths and the S-Ni-S bite angles in the central NiS(4) group are similar to those in the [Ni(C(10)H(22)N(2)S(2))] unit.

Anion-controlled assembly of four manganese ions: structural, magnetic, and electrochemical properties of tetramanganese complexes stabilized by xanthene-bridged Schiff base ligands.

The reaction of manganese(II) acetate with a xanthene-bridged bis[3-(salicylideneamino)-1-propanol] ligand, H(4)L, afforded the tetramanganese(II,II,III,III) complex [Mn(4)(L)(2)(µ-OAc)(2)], which has an incomplete double-cubane structure. The corresponding reaction using manganese(II) chloride in the presence of a base gave the tetramanganese(III,III,III,III) complex [Mn(4)(L)(2)Cl(3)(µ(4)-Cl)(OH(2))], in which four Mn ions are bridged by a Cl(-) ion. A pair of L ligands has a propensity to incorporate four Mn ions, the arrangement and oxidation states of which are dependent on the coexistent anions.

Redox-controlled, reversible rearrangement of a tris(2-pyridylthio)methyl ligand on nickel to an isomer with an "N,S-confused" 2-pyridylthiolate arm.

Interchange between the nickel +2 and +3 oxidation states precisely controls the reversible rearrangement of the tris(2-pyridylthio)methanide (tptm) ligand in the organometallic nickel(II) complex [{Ni(µ-Br)-(tptm)}(2)] (2). Oxidation of 2 first gives the corresponding Ni(III) complex [{Ni(µ-Br)(tptm)}(2)][PF(6)](2) (4). However, in solution the tptm ligand in 4 slowly undergoes a rearrangement, in which the N and S atoms of one of the pyridylthiolate arms exchange Ni and C bonding partners, thereby resulting in an "N,S-confused" isomer of tptm in the product, [NiBr(bpttpm)]PF(6) (5; bpttpm= bis(2-pyridylthio)(2-thiopyridinium)-methyl). Reduction of 5 reverses this ligand rearrangement and 2 is reformed quantitatively. The individual steps involved in these unusual ligand rearrangements were investigated by a number of methods, including voltammetric analysis, and a mechanism for this process is proposed. X-ray crystal structure determinations of the key compounds 2, 4 and 5 have been obtained.

Carbon-sulfur bond cleavage reactions of dibenzothiophene derivatives mediated by iron and ruthenium carbonyls.

A thermal reaction of 6-(4''-dibenzothienyl)-2,2'-bipyridine (bpyDBT) with [Ru(3)(CO)(12)] produced a sulfur-bridged triruthenium complex via double carbon-sulfur bond cleavage and CO insertion, while a diiron(I,I) complex containing a thiametallacycle was obtained by a photochemical reaction of bpyDBT with [Fe(CO)(5)].

Carbene-carbanion equilibrium for tris(2-pyridylthio)methanido Fe(II) complexes.

A reaction of FeCl(2) with tris(2-pyridylthio)methane (tptmH) produced the carbanion complex [Fe(tptm)(CH(3)CN)(2)](FeCl(4)){(C(2)H(5))(3)NH}. When FeI(2) was used instead of FeCl(2), the carbene complex [FeI(pyt)(bptmd)] (pyt = 2-pyridinethiolate, bptmd = bis(2-pyridylthio)methylidene) was isolated. The carbene forms [FeX(pyt)(bptmd)](n+) (n = 1 for X = CH(3)CN, n = 0 for X = I) were observed for [Fe(tptm)(CH(3)CN)(2)](FeCl(4)){(C(2)H(5))(3)NH} and [FeI(pyt)(bptmd)] in chloroform, whereas the carbene-carbanion equilibrium was observed in acetonitrile by NMR measurements. The thermodynamic parameters were evaluated by variable temperature (1)H NMR measurements using the diamagnetic salt [Fe(tptm)(CH(3)CN)(2)]PF(6) for [Fe(tptm)(CH(3)CN)(2)](+)⇆ [Fe(pyt)(bptmd)(CH(3)CN)](+) + CH(3)CN (ΔH = 23 kJ mol(-1), ΔS = 55 J mol(-1) K(-1)).

(η-Benzene){2-[2-(tert-butyl-sulfan-yl)phenyl]pyridine-κN,S}chlorido-ruthenium(II) hexa-fluorido-phosphate.

In the title compound, [RuCl(C(6)H(6))(C(15)H(17)NS)]PF(6), the cation adopts a three-legged piano-stool structure around the Ru(II) atom with an η(6)-benzene ligand, a chloride ligand and a 2-[2-(tert-butyl-sulfan-yl)phen-yl]pyridine (btppy) ligand. The btppy ligand acts as a N,S-bidentate ligand, forming a six-membered ring, which has an envelope conformation. The S-Ru-N bite angle is 86.76 (9)°, and the dihedral angle between the pyridine and benzene rings in btppy is 39.8 (2)°. The unit cell contains two pairs of racemic diastereomers with (S(Ru),S(S)) and (R(Ru),R(S)) configurations, in which the tert-butyl group on the coordin-ated S atom is distant from the η(6)-benzene ligand.

Synthesis and characterization of xanthene-bridged Schiff-base dimanganese(III) complexes: bimetallic catalysts for asymmetric oxidation of sulfides.

Dimanganese(III) complexes of salen-type ligands anchored by 9,9-dimethylxanthene-4,5-diyl spacers were synthesized. Two types of structures, cyclic and acyclic forms, are presented. The 2 + 2 Schiff-base condensation of 5,5'-(9,9-dimethylxanthene-4,5-diyl)bis(salicylaldehyde) and 1,2-diaminobenzene gave a macrocyclic ligand, from which a cyclic dimanganese(III) complex was synthesized. A similar dimanganese(III) complex with stereogenic centers was synthesized by the metal-assisted condensation reaction using (1R,2R)-1,2-diaminocyclohexane. Acyclic dimanganese(III) complexes anchored by one xanthene spacer were obtained by metal-assisted stepwise condensation reactions using the xanthene-bridged bis(salicylaldehyde), (1R,2R)-1,2-diaminocyclohexane monohydrochloride, and salicylaldehydes. X-Ray crystal structure analysis confirmed that both cyclic and acyclic complexes have two cofacially oriented salen-type manganese(III) units in a complex cation, showing an Mn...Mn distance of ca. 5.1 A. Asymmetric oxidation of sulfides was performed by using the chiral dimeric complexes as catalysts, which showed enantiomeric excesses ranging from 5 to 19%. The addition of 4-(dimethylamino)pyridine to the reaction system improved the enantioselectivity up to 39% ee. This effect was not observed for the corresponding mononuclear catalyst.

Steric, geometrical and solvent effects on redox potentials in salen-type copper(II) complexes.

Two diastereomers of the Schiff base ligand [N,N'-bis(2'-hydroxyphenyl)phenylmethylidene]-1,2-diamino-1,2-diphenylethane (H(2)L) were used for the analyses of the redox behaviour of the copper(ii) complexes [Cu(L(R,R/S,S))] (rac-) and [Cu(L(R,S))] (meso-). Both complexes were structurally characterised by X-ray crystallographic studies and showed square planar geometries. The reduction potential of Cu(II) to Cu(I) for meso- was higher than that for rac-. This is due to the steric effect of the phenyl substituents and the geometrical change in the copper(i) state, which is supported by DFT calculations. A red shift of the absorption spectrum was observed for meso- in the visible region by the change of solvent from dichloromethane to pyridine, while rac- did not show a significant change. The effect of solvent on the reduction potential was found to be relatively small. The geometrical effect is more important for understanding the electrochemical behaviour in this system.