Synthesis and redox properties of dinuclear rhodium(II) carboxylates with 2,6-di-tert-butylphenol moieties

By exploiting the peculiar reactivity of [Rh₂(μ-O₂CBu^t)₄(H₂O)₂] (1) the examples of dinuclear rhodium(II) carboxylates containing N-donor axial ligands (2, 3) [Rh₂(μ-O₂CBu^t)₄L₂] [where L = benzonitrile (2), 3,5-di-tert-butyl-4-hydroxybenzonitrile (3)] were synthesized and characterized by elemental analysis, IR, multinuclear NMR spectroscopy, MALDI-TOF mass spectrometry. It was found by X-ray diffraction that pairs of 3 in crystals are associated through H atoms of phenol groups to produce a dimer of dimers. The chemical oxidation of dirhodium complexes with 2,6-di-tert-butyl-4-cyanоphenol pendants studied by means of ESR method in solutions leads to the formation of phenoxyl radicals 3′ in dirhodium system. The ESR data show the interaction of the unpaired electron with ligand nuclei (¹H, ¹⁴N) and ¹⁰³Rh. The stability of radical complexes with phenoxyl fragments in axial position is influenced by the temperature. The enthalpy of the 3′ decomposition followed by the formation of cyanophenoxyl radical as 20 ± 1 kJ/mol was estimated. Redox transformations in dirhodium system including both metal and axial ligands were investigated by electrochemistry. CV experiments confirm the assumption of the metal oxidation (Rh^II→Rh^III) as the first step following by the oxidation of the ligand.     

Hypoglycemic effect of copper(II) acetate imidazole complexes

The effect of copper(II) complexes on glucose metabolism was studied in normal and streptozotocin-induced diabetic rats. The copper(II) complexes used were bis(acetato)tetrakis(imidazole) copper (II), [Cu(OAc)₂(Im)₄], bis(acetato)bis(2-methylimidazole) copper(II), [Cu(OAc)₂(1,2dmIm)₂], and bis)acetato)bis(μ-acetato)tetrakis(N-methylimidazole) copper(II) hexaaquo, [Cu₂(OAc)₄-(NmIm)₄]·6H₂O. Intramuscular administration of various doses of Cu(OAc)₂(Im)₄ ranging from 10 to 100 mg/kg body mass to overnight fasted rats decreased blood glucose levels in a dose-dependent manner. Maximum hypoglycemic effect was observed 3 h after administration and lasted for at least 6 h. Treatment with 100 mg/kg body mass of Cu(OAc)₂(Im)4 caused hypoglycemic shock, which was irreversible and even lethal. Blood insulin levels were reduced sharply during this hypoglycemic shock. Similar changes in blood glucose level were achieved using Cu(OAc)₂)2mIm)₂. The same pattern of hypoglycemia, although less pronouned, was observed for Cu₂(OAc)₄(NmIm)₄·6H₂O and Cu (OAc)₂(1,2dmIm)₂. Binary copper(II) acetate complex, the ligand imidazole, and the inorganic form of copper, such as copper(II) chloride, had no significant effect on blood glucose level. These results indicate that the hypoglycemic activity of these complexes varies with the imidazole ligand and structure of the complex. Intramuscular administration of Cu(OAc)₂(Im)₄ to diabetic rats caused a reduction in blood glucose levels and improved their tolerance for glucose.     

Oligonuclear nickel(II) complexes sustained by intermolecular hydrogen-bonding

Reaction of Ni(OAc)₂ with the symmetric `end-off' compartmental proligand 2,6-[N,N^′-bis(2-hydroxy-phenylmethyl)-N,N^′-bis(2-pyridylmethyl)aminomethyl]-4-methylphenol (H₃L) in the presence of NaPF₆ has been found to generate a homotetranuclear nickel(II) complex [(Ni₄HL)(L)(OAc)₂(H₂O)₂(HOAc)₂]PF₆. The crystal structure of the complex reveals that the complex is donor asymmetric and that the extended supra-ligand periphery is maintained by a tight hydrogen-bond between two pendant phenol/phenoxy groups of adjacent ligands and by further tight hydrogen-bonds between coordinated acetic acid molecules and the remaining pendant phenols of the ligand, generating a double acid salt of the type [CH₃COO?H?LH?L?H?OOCCH₃]⁵⁻. Reaction of H₃L with Ni(OAc)₂ and NaClO₄ in methanol gave the complex [Ni₂(HL)(OAc)₂(OH₂)₂][ClO₄]. The structure was determined by X-ray diffraction and showed that the complex exists as a dimer promoted by intermolecular hydrogen-bonding.     

Dinuclear Rh(II) complexes with one polypyridyl ligand, structure, properties and antitumor activity

Rhodium(II) complexes [Rh₂(μ-OAc)₂(OAc)(bpy)(H₂O)₂]PF₆ (1), [Rh₂(μ-OAc)₂(OAc)(phen)(H₂O)₂](PF₆)·H₂O (2), [Rh₂(μ-OOCCH₃)₃(OOCCH₃)(phen)] (3) and [Rh₂(μ-O₂CCH₃)₃(O₂CCH₃)(Ph₂phen)] (4) (Ph₂phen = 4,7-diphenyl-1,10-phenanthroline) have been synthesized and characterized by means of NMR, IR and UV-Vis spectroscopic methods. X-ray structure of complex 4·1.5(CH₃COCH₃) has been determined and its geometry and electronic structure has been elucidated using OPBE and B3LYP DFT methods. The compounds are active cytostatic agents against tumor cells.     

Syntheses and structures of photochromic molybdenum(II) and rhodium(II) complexes with 1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Four novel Mo(II) and Rh(II) complexes with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe were synthesized and characterized. Employing [M(O₂CCF₃)₄] (M = Mo, Rh) with cis-dbe or closed-dbe afforded complex [Mo₂(O₂CCF₃)₄(cis-dbe)](benzene) (1), [Rh₂(O₂CCF₃)₄(cis-dbe)](benzene) (2), [{Mo₂(O₂CCF₃)₄}₂(closed-dbe)] (3), and [Rh₂(O₂CCF₃)₄(closed-dbe)](p-xylene) (4). The structures of four metal complexes were revealed by X-ray crystallographic analyses and the correlation between the crystal structures and the photochromic performance was discussed. In all complexes, two cyano groups of the ligand bridged two dimetal carboxylates to give a 1-D zigzag infinite chain structure. Upon irradiation with 405 nm light, complex 1 turned into reddish purple from yellow, and the color reverted to initial yellow on exposure to 563 nm light, indicating the reversible cyclization/ring-opening reaction in the crystalline phase. However, the Rh(II) complex 2 did not display similarities in reaction induced by light, which is attributable to the lower ratio of photoactive anti-parallel conformers compared with complex 1 and coordination effect of metal ions on photochromism of diarylethenes. The complexes of Rh(II) ions did not exhibit the expected reversible photoinduced behavior.     

Synthesis,spectral characterisation and cytotoxic effect of metal complexes of 2-(2-(4-carboxyphenyl)guanidino) acetic acid ligand

Abstract

A new series of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Sr(II), Hg(II), Ag(I), Tl(I) and UO₂(II) complexes of 2-(2-(4-carboxyphenyl)guanidino)acetic acid ligand have been synthesised and characterised by elemental analyses, IR, UV-Vis spectra, mass spectra (ligand and its zinc(II) complex), ¹H NMR spectra (ligand and its mercury(II) complex), magnetic moments, conductances, thermal analyses (DTA and TGA) and ESR measurements. The IR data show that, the ligand behaves as neutral tridentate, (2), [(H_{2 L}L)_{3 C}Cu_{2 (}(OAc)_{4 (}(H_{2 O}O)_{2 ]} ], neutral bidentate, (3), [(H_2LL)Cu(OAc)_2]].1/2H_2OO, (13), [(HL)_2CCuCl₂₍(H_2OO)_2]], (17), [(H_2LL)Cu(OOSO₂₎)(H_2OO)J,dibasic hexadentate, (4), [(L) Ni₄₍(OAc)₆₍(H_2OO)J.4H_2OO, (5), [(L)Mn4(OAc)6(H2O)10]. 4H2O, (6), [(L)Co4(OAc)6(H2O)10] . 4H2O, monobasic bidentate, (7), [(HL)(UO2)(OAc)(H2O)3], (12), [(HL)2Cu], (15), [(HL)2Fe2(Cl4)(H2O)2]. 7H2O, (16), [(HL)2Cr2(Cl4)(H2O)2]. 7H2O, (21 ), [(H2L)Cd (OOSO2)(H2O)3]. 2H2O, monobasic tridentate, (8), [(L)_2HHg₂₍(OAc)₂ (H2O)6].H2O, (9), [(L)2Zn2(OAc)2(H2O)6].H2O, (10), [(L) _2ZZn₂₍(OAc)₂₍(H_2OO)_6]].H_2OO, (11), [(L)Tl4(OAc)3 (H2O)6], (18), [(HL)(OH)Cr2(SO4)2(H2O)5]. H2O, (19), [(HL)3Ag3NO3], or dibasic tridentate, (14), [(L) Sr(Cl)_{20 (}(H_{2 O}O)_{24 ]}], (20), [(L)_{3 C}Cu (H_{2 O}O)_{2 ]} ]. Molar conductances in DMF indicate that, the complexes are non-electrolyte. The ESR spectra of Cu(II) complexes (2), (3) and (20) at room temperature show axial type symmetry with g_// > g_-> 2.00, indicating a d_(x2-y2) ground state with significant covalent bond character in an octahedral or square planar geometry. However, Cu(II) complexes (12) and (13) show isotropic type, indicating square planar and octahedral structure. Complexes Mn(II) (5) and Co(II) (6) show broad signals in the low field region indicating spin exchange interaction take place between metal(II) ion. Hg(II) complex (9), Tl(I) complex (11), Cr(III) complex (16), Cu(II) complex (17) and Cd(II) complex (21) showed potential antiproliferative activity where they showed inhibitory effect on breast carcinoma (MCF-7 cell line) in comparing with the standard drug.     

Dynamic properties of the fluxional Rh2H(μ-PPh2)2(PPh3)3 complex

The rhodium dimer [Rh₂H(PPh₂)₂(PPh₃)₃]⁻ was prepared from RhCl(PPh₃)₃ and K₄Sn₉ in the presence of 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-crypt)]⁺ salt was isolated and characterized via NMR and X-ray diffraction studies. The solid state structure reveals a binuclear, diphenylphosphido-bridged, 32 electron Rh(I)-Rh(I) complex with edge-shared tetrahedral and square planar Rh centers with overall C_s point symmetry. 1-D and 2-D ¹H, ³¹P, and ³¹P{¹H} NMR experiments were used to characterize the complex.     

Efficiency, error and yield in light-directed maskless synthesis of DNA microarrays

Background

Rhodium (II) citrate (Rh₂(H₂cit)₄) has significant antitumor, cytotoxic, and cytostatic activity on Ehrlich ascite tumor. Although toxic to normal cells, its lower toxicity when compared to carboxylate analogues of rhodium (II) indicates Rh₂(H₂cit)₄ as a promising agent for chemotherapy. Nevertheless, few studies have been performed to explore this potential. Superparamagnetic particles of iron oxide (SPIOs) represent an attractive platform as carriers in drug delivery systems (DDS) because they can present greater specificity to tumor cells than normal cells. Thus, the association between Rh₂(H₂cit)₄ and SPIOs can represent a strategy to enhance the former's therapeutic action. In this work, we report the cytotoxicity of free rhodium (II) citrate (Rh₂(H₂cit)₄) and rhodium (II) citrate-loaded maghemite nanoparticles or magnetoliposomes, used as drug delivery systems, on both normal and carcinoma breast cell cultures.

Results

Treatment with free Rh₂(H₂cit)₄ induced cytotoxicity that was dependent on dose, time, and cell line. The IC₅₀ values showed that this effect was more intense on breast normal cells (MCF-10A) than on breast carcinoma cells (MCF-7 and 4T1). However, the treatment with 50 μM Rh₂(H₂cit)₄-loaded maghemite nanoparticles (Magh-Rh₂(H₂cit)₄) and Rh₂(H₂cit)₄-loaded magnetoliposomes (Lip-Magh-Rh₂(H₂cit)₄) induced a higher cytotoxicity on MCF-7 and 4T1 than on MCF-10A (p < 0.05). These treatments enhanced cytotoxicity up to 4.6 times. These cytotoxic effects, induced by free Rh₂(H₂cit)₄, were evidenced by morphological alterations such as nuclear fragmentation, membrane blebbing and phosphatidylserine exposure, reduction of actin filaments, mitochondrial condensation and an increase in number of vacuoles, suggesting that Rh₂(H₂cit)₄ induces cell death by apoptosis.

Conclusions

The treatment with rhodium (II) citrate-loaded maghemite nanoparticles and magnetoliposomes induced more specific cytotoxicity on breast carcinoma cells than on breast normal cells, which is the opposite of the results observed with free Rh₂(H₂cit)₄ treatment. Thus, magnetic nanoparticles represent an attractive platform as carriers in Rh₂(H₂cit)₄ delivery systems, since they can act preferentially in tumor cells. Therefore, these nanopaticulate systems may be explored as a potential tool for chemotherapy drug development.     

Structural variations in dinuclear model hydrolases and hydroxamate inhibitor models: synthetic, spectroscopic and structural studies

Reactions of the structural model hydrolases [M₂(OAc)₄(H₂O)(Im)₄]; M=Mn (E^′); M=Co (D^′); M=Ni (B^′) and [M₂(OPiv)₄(H₂O)(tmen)₂]; M=Mn (E″); M=Co (D″); M=Ni (B″) with a number of hydroxamic acids, RHA (aceto- (R=CH₃), benzo- (R = C₆H₅) and N-phenylacetohydroxamic acid (NPhAHA)) gave a series of hydroxamate dibridged complexes [M₂(OAc)(RA)₂(Im)₄][OTf] and [M₂(OPiv)(RA)₂(tmen)₂][OTf]; M=Co, Ni, in which the bridging hydroxamates exhibit a novel bonding mode in which the deprotonated hydroxamate hydroxyl bridges the two metal centres only. The formation of this type of structure by NPhAHA is the first example involving a secondary hydroxamic acid. These complexes are good structural models of the acetohydroxamate-inhibited C³¹⁹A variant of Klebsiella aerogenes urease (KAU) and their structures are close to those previously reported for complexes containing tmen capping ligands. Reaction with glutarodihydroxamic acid leads to hydroxylamine elimination and formation of a dimer containing deprotonated N-hydroxyglutarimide as bridging ligand but in this case the structure contains pentacoordinated Co(II) and only one bridging acetate in contrast to the tmen-based series where the analogous complex contains hexacoordinated Co(II) and two bridging acetates. Reaction of [Mn₂(OAc)₂(μ-OAc)₂(μ-H₂O)(tmen)₂] with acetohydroxamic acid (AHA) gave the first structurally characterized manganese hydroxamate, [Mn₂(OAc)₃(AA)(tmen)₂] with the same bridging/chelating mode of hydroxamate bonding as in the analogous cobalt and nickel complexes, although only one bridging hydroxamate occurs in the manganese complex in contrast to the two bridging hydroxamates in the cobalt and nickel complexes. The isolation of the dimanganese hydroxamate bridged complex suggests that hydroxamic acids may also inhibit the dimanganese based metallohydrolase, arginase.     

Mixed-ligand compounds incorporating quadruply bonded dimolybdenum(II) core: Syntheses, structures and reactivity studies

Reaction of cis-[Mo₂(OAc)₂(CH₃CN)₆][BF₄]₂ with NP-Et,Me (2-ethyl-3-methyl-1,8-naphthyridine) in acetonitrile provides trans-[Mo₂(NP-Et,Me)₂(OAc)₂(CH₃CN)][BF₄]₂ (1). Partial protonation of 1 by HBF₄·Et₂O in acetonitrile leads to trans-[Mo₂(NP-Et,Me)₂(OAc)(CH₃CN)₃][BF₄]₃ (2). In both compounds, NP-R ligands are arranged in a head-to-head (HH) fashion leaving one of the axial sites vacant. Substitution of acetonitriles by NP-Me (3-methyl-1,8-naphthyridine) in trans-[Mo₂(NP-tz)₂(OAc)(CH₃CN)₂][BF₄]₃ provides trans-[Mo₂(NP-tz)₂(OAc)(NP-Me)][BF₄]₃ (3) with retention of configuration. Fully solvated dimolybdenum(II) compound reacts with NP-NH₂ to provide [Mo₂(NP-NH₂)₂(NP-NH)(CH₃CN)₂][BF₄]₃ (4) in which the NP-NH₂ ligands are trans and arranged in a HH fashion. The deprotonated ligand (NP-NH⁻) binds the dimetal unit utilizing naphthyridine nitrogen and amido nitrogen. Treatment of [Mo₂(NP-tz)₂(CH₃CN)₄][CF₃SO₃]₄ with bpym (2,2′-bipyrimidine) followed by crystallization in air provided an oxo complex [Mo₂(NP-tz)₂(μ₂-O)₂(bpym)₂][CF₃SO₃]₄ (5). Compounds 1-5 have been characterized by a variety of spectroscopic techniques and by X-ray crystallography. The reactivity pattern is rationalized based on ligand labilities and thermodynamic stabilities.     

Studies on the characterization of the Rho(D) antigen

The Rh_o(D) antigen of red cell membranes was solubilized using ethylenediamine tetraacetic acid (EDTA) and 2-mercaptoethanol. The solubilized antigen was partially separated from other solubilized membrane components using molecular filtration. The antigen was treated with various enzymes to learn some of the chemical characteristics. It was found that the activity of the antigen, as measured by hemagglutination inhibition, was not affected by bee venom phospholipase A, Clostridium welchii phospholipase C, calf-intestinal alkaline phosphatase, Vibrio cholerae neuraminidase, pig kidney leucine aminopeptidase, bovine pancreatic carboxypeptidase A, a pig pancreatic carboxypeptidase B. However, the proteolytic enzymes, pronase, trypsin, chymotrypsin and papain, did destroy Rh_o(D) activity as measured by hemagglutination inhibition. These results indicate that protein is an important part of the active determinant of the Rh_o(D) antigen. The experiments by other investigators have shown that lipid is important to maintain the Rh_o(D) activity in the intact membrane; lipid probably helps to maintain the structural conformation of the Rh_o(D) molecule in its natural environment. The solubilized Rh_o(D) molecules are apparently not dependent on lipid for their Rh_o(D) activity.     

Metal cluster topology. 4. Rhodium carbonyl clusters having fused polyhedra

Previously discussed topological models of metal cluster bonding are now extended to the treatment of anionic rhodium carbonyl clusters having structures consisting of fused polyhedra. Examples of such rhodium carbonyl clusters built from fused octahedra include the ‘biphenyl analogue’ [Rh₁₂(CO)₃₀]⁻², the ‘face-sharing naphthalene analogue’ [Rh₉- (CO)₁₉]³⁻, and the ‘perinaphthene analogue’, [Rh₁₁- (CO)₂₃]³⁻. More complicated anionic rhodium carbonyl clusters treated in this paper include the [Rh₁₃(CO)₂₄H_5−q]^q− anions (q = 2, 3, 4) having an Rh₁₃ centered cuboctahedron, the [Rh₁₄(CO)₂₅- H_4−q]^q− (q = 3,4) and [Rh₁₄(CO)₂₆]²⁻ anions based on a centered pentacapped cube, the [Rh₁₅- (CO)₃₀]³⁻ anion having an Rh₁₅ centered 14-vertex deltahedron, the [Rh₁₅(CO)₂₇]³⁻ anion having a tricapped centered 11-vertex polyhedron, the [Rh₁₇- (CO)₃₀]³⁻ anion having a tetracapped centered cuboctahedron, and the [Rh₂₂(CO)₃₇]⁴⁻ anion having a hexacapped centered cuboctahedron fused to an octahedron so that the octahedron and the cuboctahedron share a triangular face. Analyses of the bonding topologies in [Rh₉(CO)₁₉]³⁻, [Rh₁₇- (CO)₃₀]³⁻, and [Rh₂₂(CO)₃₇]⁴⁻ indicate that a polyhedral network containing several fused globally delocalized polyhedral chambers will not necessarily have a multicenter core bond in the center of each such polyhedral chamber. This observation is of potential importance in extending topological models of metal cluster bonding to bulk metals.     

Mono-, di-, and tri-ruthenium complexes with the ligand 2,2′-dipyridylamide (dpa): insights into the formation of extended metal atom chains

Reactions between Hdpa (2,2′-dipyridylamine) and either RuCl₃ · xH₂O and Ru₂(OAc)₄Cl produce mono-, di-, and tri-ruthenium complexes under various conditions. The ligand Hdpa and RuCl₃ · xH₂O react in boiling DMF to form the ionic species [Ru(Hdpa)₂Cl₂]Cl (1). Reaction of Ru₂(OAc)₄Cl with molten Hdpa leads to scission of the Ru-Ru bond and formation of the vertex-sharing bioctahedral complex Ru₂(dpa)₃(OAc)_0.64Cl_1.36 (2). A mixture of both of these species results from the reaction of Ru₂(OAc)₄Cl with Hdpa and LiCl in refluxing o-dichlorobenzene/EtOH mixtures. This mixture of compounds reacts further with KOBu^t and n-butanol in refluxing naphthalene to give low yields of the extended metal atom chain (EMAC) complex Ru₃(dpa)₄Cl₂ (I).     

Kinetics of CO substitution in Co4(CO)12 and Rh4(CO)12

The kinetics of rapid CO substitution by PPh₃ in Co₄(CO)₁₂ and Rh₄(CO)₁₂ have been examined by stopped-flow and low temperature FT-IR methods. In Co₄(CO)₁₂ rapid (k_obs ∼ 1.8 s⁻¹) substitution of CO occurs after a 1–15 s induction period at 28 °C in C₆H₅Cl solvent by a catalytic process. Addition of PPh₃ to Rh₄(CO)₁₂ yields Rh₄(CO)₁₁(PPh₃) according to a predominantly second order rate law k₁[Rh₄- (CO)₁₂] + k₂[Rh₄(CO)₁₂][PPh₃] with k₁ = 25 ± 11 s⁻¹ and k₂ = 2.97 ± 0.27 X 10⁴ M⁻¹ s⁻¹ at 28 °C. Substitution of a second CO ligand also occurs rapidly with k₁ = 0.15 ± 0.09 s⁻¹ and k₂ = 6.54 ± 0.07 X 10² M⁻¹ s⁻¹ at 28 °C. The reactivity of Rh₄(CO)₁₂ toward associative substitution is 10⁴– 10¹¹ faster than for the Co and Ir analogues, In Rh₄(CO)₁₁(PPh₃) the increase in CO substitution rates over Co and Rh analogues is 10²–10⁷. The ordering of associative substitution rates Co << Rh >>> Ir in these clusters exaggerates the trend seen in mononuclear metal complexes.     

Water replacement on the decaaqua-di-rhodium(II) cation; synthesis of superoxo and peroxo rhodium(III) complexes with N-donor ligands

The decaaqua-di-rhodium(II) cation has been found to be an interesting starting material in the preparation of dioxygen complexes with different N-donor ligands. Treatment of aqueous HClO₄ solution of [Rh₂(H₂O)₁₀]⁴⁺ with NH₄OH/NH₃, py and/or en results in water exchange and the formation of corresponding [Rh₂^II(H₂O)_10−m(base)_n(OH)_m]^(4−m)+ derivatives. Reaction of the latter with dioxygen afforded superoxo and/or peroxo complexes, depending on reaction conditions: [Rh₂^III(O₂ ⁻)(NH₃)₈(OH)₂](ClO₄)₃ (1), [Rh₂^III(O₂ ⁻)(NH₃)₈(OH)(H₂O)](ClO₄)₄ (2), [Rh₂^III(O₂ ²⁻)(NH₃)₁₀](ClO₄)₄ · 6H₂O (3), [Rh₂^III(O₂ ⁻)(py)₈(H₂O)₂](ClO₄)₅ (4), [Rh₂^III(O₂ ²⁻)(en)₄(H₂O)₂](ClO₄)₄ (5) and [Rh₂^III(O₂ ⁻)(en)₄(H₂O)₂](ClO₄)₅ (6). All the obtained complexes were characterized by elemental analysis, mass spectrometry, UV-Vis, IR and ESR spectroscopies and magnetic measurements.     

Structure of binuclear Rh(II) carboxylato complexes with 2,2-bipyridine and an unprecedented rhodium wire with Rh4 core

Structures of rhodium(II) binuclear complexes [Rh₂(OOCCH₃)₂(bpy)₂(H₂O){(CH₃)₂CHOH}][B(C₆H₅)₄]₂ · H₂O (1), [Rh₂Cl₂(OOCCH₃)₂(bpy)₂] · 2H₂O (2), [Rh₂Br₂(OOCCH₃)₂(bpy)₂] · 3H₂O (3), and [Rh₂I₂(OOCCH₃)₂(bpy)₂] (4), as well as an unprecedented wire with infinite Rh-Rh chain, {[Rh₄(μ-OOCH)₄(bpy)₄](BF₄)}_n · 0.5nC₄H₈O₂ (5), have been determined and discussed. Mass spectra of complexes [Rh₂(OOCMe)₂(bpy)₂(H₂O)₂](MeCOO)₂ and [Rh₂(OOCMe)₂(phen)₂(H₂O)₂](MeCOO)₂ have showed stability of polynuclear cations with rhodium in oxidation states in the range +1.25 to +1.75.     

The preparation and crystal structure of acetatobis(l-arginine)zinc(II) acetate trihydrate, the first reported X-ray structure of a zinc(II)-arginine complex

The synthesis and X-ray crystal structure of acetatobis(l-arginine)zinc(II) acetate trihydrate, [Zn(OAc)(l-Arg)₂]OAc·3H₂O is reported. In this structure, the first of a zinc(II)-arginine complex to be reported, the geometry around zinc(II) is distorted square-pyramidal containing two trans-N,O chelated l-Arg ligands in the basal plane and the acetato ligand in an axial position. The structure contains a second acetate which is salt-bridged to the δ and ω NH groups of the guanidinium side chain of an arginine ligand and also contains three hydrogen bonded water molecules.     

3(5)-Pyrazolyl substituted triphenylphosphines as ligands for the palladium catalyzed Heck reaction

3(5)-Pyrazolyl substituted triphenylphosphines have been investigated as ligands for the palladium catalyzed Heck reaction of aryl halides with styrene. Catalysts formed in situ from those phosphines and Pd^II(OAc)₂ are comparable in activity and selectivity with the corresponding pre-synthesized Pd(II) complexes, while Pd₂(dba)₃ has turned out to be a less suitable palladium source. Among the ligands investigated, the bidentate P,N-ligand 2-[3(5)-pyrazolylphenyl]diphenylphosphine has shown the highest activities for the coupling of bromobenzene with styrene in the presence of Pd^II(OAc)₂. In the presence of 1 equiv. of nBu₄NI as the additive, unreactive 4-chloroacetophenone also undergoes Heck coupling with styrene.     

Secondary bonding in a six-coordinate Mn(II) complex as a model of associative substitution

The new hexadentate, bis-pincer ligand, (dipyCH₂)MeNCH₂CH₂NMe(CH₂dipy) (dipy = 2,2′-dipyridyl-6-yl) forms a crystallographically characterized Mn(II) complex in which each half of the ligand binds a separate Mn(OAc)₂ unit. The structure consists of a distorted N₃Mn(η²-OAc)(η¹-OAc) core with six normal coordinate bonds and a long (2.85 Å) secondary bond to a seventh ligand atom, an oxygen of the η¹-acetate. In addition to demonstrating an interesting coordination mode, the structure also mimics a predicted transition state in the associative ligand exchange of octahedral Mn(II) complexes.     

X-ray structure and spectroscopic characterization of divalent dinuclear cobalt complexes containing carboxylate- and phosphodiester- auxiliary bridges

Two dinuclear spin-coupled divalent cobalt complexes, [Co₂(P1-O)(μ₂-OAc)](ClO₄)₂, (1) and [Co₂(P1-O)(μ₂-BNPP)](ClO₄)₂, (2) containing μ-1,3 acetate (OAc) and bis(4-nitrophenyl)phosphate (BNPP) auxiliary bridges, respectively, were synthesized by the reaction of a classic dinucleating ligand, P1-OH with cobalt(II) perchlorate in presence of acetic acid/bis(4-nitrophenyl)phosphate. They were characterized by single crystal X-ray diffraction, to show a trigonal bipyramidal geometry around each cobalt center and the intervening bridging atoms that are responsible for spin-transfer between the two divalent cobalt centers; the alkoxo oxygen donor occupies an equatorial position, and the auxiliary ligand oxygens (OAc/BNPP) occupy the axial positions. Solution state magnetic moment measurement together with UV-Vis/NIR spectra revealed a high-spin ground state (S = 3/2) for Co(II) in these compounds. Complexes 1 and 2 show interesting ¹H NMR spectral features of resonances with relatively narrower linewidths in conjunction with a sizable chemical shift dispersion of −5 and 265 ppm. Complex 2 containing the bis(4-nitrophenyl)phosphate auxiliary bridge showed narrower spectral window than complex 1 that has the acetate auxiliary bridge.