Thiosemicarbazone complexes of the platinum metals. A story of variable coordination modes

Salicylaldehyde thiosemicarbazone (H2saltsc) reacts with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) to afford complexes of type [M(PPh3)2(Hsaltsc)2], in which the salicylaldehyde thiosemicarbazone ligand is coordinated to the metal as a bidentate N,S-donor forming a four-membered chelate ring. Reaction of benzaldehyde thiosemicarbazones (Hbztsc-R) with [M(PPh3)3X2] also affords complexes of similar type, viz. [M(PPh3)2(bztsc-R)2], in which the benzaldehyde thiosemicarbazones have also been found to coordinate the metal as a bidentate N,S-donor forming a four-membered chelate ring as before. Reaction of the Hbztsc-R ligands has also been carried out with [M(bpy)2X2] (M = Ru, Os; X = Cl, Br), which has afforded complexes of type [M(bpy)2(bztsc-R)]+, which have been isolated as perchlorate salts. Coordination mode of bztsc-R has been found to be the same as before. Structure of the Hbztsc-OMe ligand has been determined and some molecular modelling studies have been carried out determine the reason for the observed mode of coordination. Reaction of acetone thiosemicarbazone (Hactsc) has then been carried out with [M(bpy)2X2] to afford the [M(bpy)2(actsc)]ClO4complexes, in which the actsc ligand coordinates the metal as a bidentate N,S-donorformingafive-membered chelate ring. Reaction of H2saltsc has been carried out with [Ru(bpy)2Cl2] to prepare the [Ru(bpy)2(Hsaltsc)]ClO4 complex, which has then been reacted with one equivalent of nickel perchlorate to afford an octanuclear complex of type [Ru(bpy)2(saltsc-H)4Ni4](ClO4)4

Chemistry of 2-(phenylazo)pyridine complexes of osmium: synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Os(PPh3)3Br2] afforded a mixed ligand complex of the type [Os(PPh3)2(pap)Br2]. The structure of this complex was determined by X-ray crystallography. The PPh3 ligands are trans and the bromides are in cis positions. The pap ligand is coordinated to osmium as a bidentate N,N-donor forming a five-membered chelate ring. The complex is diamagnetic (low-spin d6, S=0) and in dichloromethane solution shows intense MLCT transitions in the visible region. The two bromides were replaced from the coordination sphere of [Os(PPh3)2(pap)Br2] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox), 1-nitroso-2-naphtholate (nn) and acetyl acetonate (acac)) to afford complexes of the type [Os(PPh3)2(pap)(L)]+, which were isolated and characterized as the perchlorate salt. The structure of the [Os(PPh3)2(pap)(acac)]ClO4 complex was determined by X-ray crystallography. The PPh3 ligands occupy trans positions and the acetylacetonate anion is coordinated to osmium as a bidentate O,O-donor forming a six-membered chelate ring. The [Os(PPh3)2(pap)(L)]+ complexes are diamagnetic and show multiple MLCT transitions in the visible region. [Os(PPh3)2(pap)Br2] shows an osmium(II)-osmium(III) oxidation at 0.49 V versus SCE. The same oxidation is displayed by the [Os(PPh3)2(pap)(L)]+ complexes within 0.69 to 0.96 V versus SCE. Two successive one-electron reductions of the coordinated pap ligand are also observed in all the complexes below -0.90 V versus SCE

Chemistry of ruthenium with some dioxime ligands. Syntheses, structures and reactivities

Reaction of two dioxime ligands, viz. dimethylglyoxime (H2dmg) and diphenylglyoxime (H2dpg), (abbreviated in general as H2L, where H stands for the oxime protons) with [Ru(PPh3)3Cl2] in 1¦1 mole ratio affords complexes of type [Ru(PPh3)2(H2L)Cl2]. Structure of the [Ru(PPh3)2(H2dpg)Cl2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N2P2Cl2 with the two PPh3 ligands in trans and the two chlorides in cis positions. Reaction of the dioxime ligands with [Ru(PPh3)3Cl2] in 2¦1 mole ratio in the presence of a base affords complexes of type [Ru(PPh3)2(HL)2]. Structure of the [Ru(PPh3)2(Hdmg)2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N4P2 with the two PPh3 ligands in trans positions. Reaction of the [Ru(PPh3)2(H2dpg)Cl2] complex with a group of bidentate acidic ligands, viz. picolinic acid (Hpic), quinolin-8-ol (Hq) and 1-nitroso-2-naphthol (Hnn), (abbreviated in general as HL′, where H stands for the acidic proton) in the presence of a base affords complexes of type [Ru(PPh3)2(H2dpg)(L′)]+ isolated as perchlorate salts. All the complexes are diamagnetic (low-spin d6, S=0) and in dichloromethane solution show several intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a reversible ruthenium(II)-ruthenium(III) oxidation within 0.36-0.98 V versus SCE followed by a quasi-reversible ruthenium(III)-ruthenium(IV) oxidation within 0.94-1.60 V versus SCE

Synthesis, structure and electrochemical properties of tris-picolinate complexes of rhodium and iridium

Reaction of picolinic acid (Hpic) with rhodium trichloride or iridium trichloride affords tris-picolinate complexes of the type [M(pic)3] (M = Rh, Ir). The crystal structures of both complexes have been determined by X-ray diffraction. In both complexes, the picolinate ligands are coordinated to the metal center as bidentate N,O-donors forming five-membered chelate rings. There is one molecule of water of crystallization per molecule of each [M(pic)3] complex. The water molecule is hydrogen bonded to the carboxylate fragments of two adjacent [M(pic)3] molecules and thus acts as a bridge between the individual complex molecules. The complexes are diamagnetic (low-spin d6, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry on the [M(pic)3] complexes shows a M(III)-M(IV) oxidation near 1.0 V versus SCE and a ligand-centered reductive response near -1.0 V versus SCE

Chemistry of some ruthenium phenolates: synthesis, structure and redox properties

Reaction of three phenolate ligands, viz. 2,4,6-tribromophenol (HL1, where H stands for the phenolic proton), 2-nitrophenol (HL2) and 2,4,6-trinitrophenol (HL3O), with [Ru(PPh3)3Cl2] in a 2¦1 molar ratio in the presence of a base gives complexes of type [Ru(PPh3)2(L)2] (L=L1, L2 and L3). The 2,4,6-tribromophenolate ligand (L1) binds to ruthenium as a bidentate O,Br-donor, while the 2-nitrophenolate ligand (L2) acts as a bidentate O,O-donor. 2,4,6-Trinitrophenol (HL3O) undergoes oxygen loss from one nitro group at the ortho position and coordinates to ruthenium in the 2-nitroso-4,6-dinitrophenolate (L3) form through the nitroso nitrogen and phenolate oxygen. The structures of the [Ru(PPh3)2(L1)2] and [Ru(PPh3)2(L3)2] complexes have been solved by X-ray crystallography. In [Ru(PPh3)2(L1)2] the coordination sphere around ruthenium is O2P2Br2 with a trans-cis-cis disposition of the three sets of donor atoms, respectively. In [Ru(PPh3)2(L3)2] ruthenium has a N2O2P2 coordination sphere with a cis-cis-trans arrangement of the three sets of donor atoms, respectively. The [Ru(PPh3)2(L)2] complexes are diamagnetic (low-spin d6, S=0) and in acetonitrile solution show intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru(PPh3)2(L)2] complexes shows a reversible ruthenium(II)-ruthenium(III) oxidation within 0.63-0.71 V versus SCE followed by an irreversible ruthenium(III)-ruthenium(IV) oxidation near 1.5 V versus SCE

Chemistry of ruthenium with some phenolic ligands: synthesis, structure and redox properties

Reaction of three phenolate ligands, viz. salicylaldehyde (HL1), 2-hydroxyacetophenone (HL2) and 2-hydroxynaphthylaldehyde (HL3), (abbreviated in general as HL, where H stands for the phenolic proton) with [Ru(PPh3)3Cl2] in 1¦1 mole ratio gives complexes of the type[Ru(PPh3)2(L)Cl2]. The structure of the [Ru(PPh3)2(L2)Cl2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium isO2P2Cl2 with a cis-trans-cis geometry, respectively. The [Ru(PPh3)2(L)Cl2] complexes are one-electron paramagnetic (low-spin d5, S=½) and show rhombic ESR spectra in 1¦1 dichloromethane-toluene solution at 77 K. In dichloromethane solution the [Ru(PPh3)2(L)Cl2] complexes show several intense LMCT transitions in the visible region. Reaction between the phenolic ligands and [Ru(PPh3)3Cl2] in 2¦1 mole ratio in the presence of a base affords the [Ru(PPh3)2(L)2] complexes in two isomeric forms. 1H NMR spectra of one isomer shows that it does not have any C2 symmetry and has the cis-cis-cis disposition of the three sets of donor atoms. 1H NMR spectra of the other isomer shows that it has C2 symmetry. The structure of the isomer of the [Ru(PPh3)2(L1)2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is O4P2 with a cis-trans-cis disposition of the carbonylic oxygens, phenolate oxygens and phosphorus atoms, respectively. The [Ru(PPh3)2(L)2] complexes are diamagnetic (low-spin d6, S=O) and show intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru(PPh3)2(L)Cl2] complexes shows a ruthenium(III)---ruthenium(II) reduction near -0.3 V versus SCE and a ruthenium(III)---ruthenium(IV) oxidation in the range 1.08-1.24 V versus SCE. Cyclic voltammetry on both isomers of the [Ru(PPh3)2(L)2] complexes shows a ruthenium(II)---ruthenium(III) oxidation within 0.09-0.41 V versus SCE, followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.31-1.52 V versus SCE

8-quinolinolate complexes of ruthenium(ii). Synthesis, characterization and electron transfer properties

Two stable 8-quinolinolate complexes of ruthenium(II), [Ru(bpy)(Q)]ClO4 and [Ru(tap)2(Q)]ClO4 [bpy = 2,2′-bipyridine, Q=8-quinolinolate anion, tap = 2-(m-tolylazo) pyridine] have been synthesized. The complexes are diamagnetic and show strong absorption near 1100 cm-1 in the IR spectra due to the presence of ClO-4. In acetonitrile solution they behave as 1¦1 electrolytes. The complexes display intense absorption bands in the visible region (400-700 nm) which are assigned to MLCT transitions. The formal potential (E0298), determined cyclic voltammetrically for the ruthenium(II)-ruthenium(III) oxidation, is 0.48 V vs SCE for [Ru(bpy)2(Q)]+. The same oxidation takes place irreversibly at 1.00 V vs SCE (Eρα value) in the case of [Ru(tap)2(Q)]+. Reductions of the bound bpy and tap ligands are also observed

Synthesis, characterization and reactivity of a ruthenium-quinone complex

A mixed ligand ruthenium-quinone complex, Ru(trpy)(DBQ)Cl [trpy = 2,2&#8242;: 6&#8242;,2&#8243;-terpyridine, DBQ = 3,5-di-tert-butylquinone] has been synthesized. The complex is paramagnetic (1 upe) and shows a sharp EPR signal at g &#8776; 2. A Ru<SUP>II</SUP>-DBSQ [DBSQ = semiquinonate form of DBQ] charge distribution is therefore assigned to this complex. It shows intense absorption bands in the visible and near-infrared regions which are assigned to allowed charge-transfer transitions. In dichloromethane solution it shows three reversible cyclic voltammetric responses, one ruthenium(II)-ruthenium(III) oxidation and the reductions of DBSQ and trpy ligands. The chloride ligand in Ru(trpy)(DBSQ)Cl can be replaced in aqueous medium by reacting it with Ag<SUP>+</SUP>to afford the [Ru(trpy)(DBSQ)(H<SUB>2</SUB>O]<SUP>+</SUP> ioin, which has been isolated and characterized as the perchlorate salt. This aquo complex is easily converted back to the parent chloro complex by reaction with the chloride ion

Synthesis, characterization, electron-transfer properties and reactivities of a group of ruthenium(ii) complexes with RuN<SUB>2</SUB>P<SUB>2</SUB>X<SUB>2</SUB>(X = Cl, Br) coordination spheres

Four dihaloruthenium(II) complexes of general formula Ru(PPh3)2(L)X2 [L = 2,2&#8242;-bipyridine (bpy), 1,10-phenanthroline (phen); X = Cl, Br] have been synthesized by the reaction of L with Ru(PPh3)3X2 in dichloromethane. The complexes are diamagnetic and show intense absorptions in the visible region which are assigned to the MLCT transitions. In dichloromethane solution they show a reversible ruthenium(II)-ruthenium-(III) oxidation near 0.4 vs SCE. Two [RuIII(PPh3)2(L)(Cl2)]+ ions have been generated in solution by electrochemical oxidation of RuII(PPh3)2(L)Cl2. Solutions of the oxidized complexes show LMCT transitions in the visible region and at 77 K show rhombic EPR spectra. The distortions from octahedral symmetry have been quantified, in these species, with the help of EPR data analysis. The axial distortion is much larger than the rhombic one. The two X- ligands are easily displaced from Ru(PPh3)2(L)X2 by its reaction with Ag+ in ethanol producing [Ru(PPh3)2(L)(EtOH)2]2+, which upon reacting with L&#8242; [L&#8242; = bpy, phen, acetylacetonate ion (acac-), oxalate ion (ox2-)] affords complexes of type [Ru)PPh3)2(L)(L&#8242;)n+ (n = 0, 1, 2). Five such complexes have been synthesized and characterized. They all are diamagnetic and show intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation is very sensitive to the nature of L&#8242;. The potential decreases in the order (of L&#8242;); bpy (or phen) gt; acac-gt; ox2-. Reductions of the coordinated bpy and phen are also observed

The chemistry of [Ru(trpy)(Q)X]n+ (trpy = 2,22-terpyridine; Q = the quinolin-8-olate anion; x = cl<SUP>-</SUP>, h<SUB>2</SUB>o, mecn and N<SUP>-_3</SUP>; n = 0 and 1)

Reaction of [Ru(trpy)Cl<SUB>3</SUB>] with quinolin-8-ol (HQ) yields [Ru(trpy)(Q)Cl]. Treatment of [Ru(trpy)(Q)Cl] with Ag<SUP>+</SUP> in Me<SUB>2</SUB>CO-H<SUB>2</SUB>O (3&#166;1) and MeCN gives [Ru(trpy)- (Q)(H<SUB>2</SUB>O)]<SUP>+</SUP> and [Ru(trpy)(Q)(MeCN)]<SUP>+</SUP>, respectively, which were isolated as their perchlorate salts. A similar reaction in EtOH, in the presence of N<SUB>a</SUB>N<SUB>3</SUB>, yields [Ru(trpy)(Q)(N<SUB>3</SUB>)]. All complexes are diamagnetic (low-spin, d<SUP>6</SUP>, S = 0) and show many intense m.l.c.t. transitions in the visible region. They display a reversible Ru<SUP>II</SUP>-Ru<SUP>III </SUP>oxidation in the -0.13-0.48 V versus s.c.e. range, followed by an irreversible Ru<SUP>III</SUP>-Ru<SUP>IV</SUP> oxidation in the 0.46-1.08V versus s.c.e. range and three trpy-based reductions on the negative side of s.c.e. Chemical oxidation of [Ru<SUP>II</SUP>(trpy)(Q)Cl] by Ce<SUP>4+</SUP> gives [Ru(trpy)-(Q)Cl]<SUP>+</SUP> which shows intense l.m.c.t. transitions in the visible region together with a weak ligand field transition in the lower energy region. The complex is one-electron paramagnetic (low-spin, d<SUP>5</SUP>, S=&#189;) and shows a rhombic e.s.r. spectrum in MeCN-PhMe (1&#166;1) solution at 77K. Chemical oxidation of [Ru(trpy)(Q)-(H<SUB>2</SUB>O)]<SUP>+</SUP> results in the formation of a &#181; -oxo dimer, [{Ru(trpy)(Q)}<SUB>2</SUB>O]<SUP>2</SUP><SUP>+</SUP>