Takanori Nishioka

Syntheses, NMR (1H, 31P) spectroscopy and crystal structures of complexes of copper(I) halides with isatin-3-thiosemicarbazones

Isatin-3-thiosemicarbazones (H2itsc) react with copper(I) bromide or iodide in a 1 : 1 mol ratio in acetonitrile in the presence of two moles of Ph3P to form tetrahedral monomeric complexes of composition [CuX(η1-S-H2itsc)(Ph3P)2], X = Br (1), I (2). These complexes, which have been characterized by single-crystal structure determinations, are unlike the iodo-bridged dinuclear complex of copper(I) iodide of pyrrole-2-carbaldehydethiosemicarbazone (Hptsc), namely [Cu2(μ-I)2(η1-S-Hptsc)2(PPh3)2] (3). In both 1 and 2, the geometry around Cu is distorted tetrahedral with P–Cu–P bond angles being 121.97(3) (1) and 124.09(5)° (2). Proton NMR confirms that thiosemicarbazone coordinates to the Cu atom as a neutral ligand, and 31P NMR shows that there is no dissociation of the complexes in solution; coordination shift values suggest that Ph3P stabilizes the Cu(I) oxidation state.

Photochromism of an organorhodium dithionite complex in the crystalline-state: molecular motion of pentamethylcyclopentadienyl ligands coupled to atom rearrangement in a dithionite ligand.

In the crystalline state, the rhodium dinuclear complex [(RhCp*)(2)(mu-CH(2))(2)(mu-O(2)SSO(2))] (1) with a photoresponsive dithionite group (mu-O(2)SSO(2)) and two pentamethylcyclopentadienyl ligands (Cp* = eta(5)-C(5)Me(5)) undergoes a 100% reversible unimolecular type T inverse photochromism upon interconversion to [(RhCp*)(2)(mu-CH(2))(2)(mu-O(2)SOSO)] (2). The photochromism can be followed directly by using stepwise crystal structure analysis (Angew. Chem., Int. Ed. 2006, 45, 6473). In this study, we found that the photoreaction of 1 was triggered by absorption of the 510 nm light (charge transfer band from sigma(S-S) to sigma*(S-S) and sigma*(Rh-Rh) orbitals assigned by DFT calculation) and included two important processes: kinetically controlled oxygen-atom transfer to produce four stereoisomers of 2 and thermodynamically controlled isomerization between the four stereoisomers of 2 to afford the most stable isomer. Although the formation rate of the four stereoisomer products was kinetically controlled and the population of the four stereoisomers produced in the system was thermodynamically controlled, both processes were regulated by the steric hindrance between the mu-O(2)SSO(2) or mu-O(2)SOSO ligand and the reaction cavity formed by the Cp* ligands. The cooperation of both processes achieved an intriguing stereospecific oxygen-atom rearrangement to produce only one stereoisomer of 2 at the final stage of the photoreaction at room temperature. We also determined the effect of the oxygen-atom rearrangement on the rotational motion of the two crystallographically independent Cp* ligands (parallel and perpendicular arrangement). Using variable-temperature (13)C CP/MAS NMR and quadrupolar echo solid-state (2)H NMR spectroscopies, before photoirradiation, the activation energies for the rotation of the parallel and perpendicular Cp* ligands in 1 were determined to be 33 +/- 3 and 7.8 +/- 1 kJ/mol, respectively, and after photoirradiation, in 2, they were much lower than those in 1 (21 +/- 2 and 4.7 +/- 0.5 kJ/mol, respectively). The large decrease in the activation energy for the parallel Cp* in 2 is attributed to the relaxation of molecular stress via a stereospecific oxygen-atom rearrangement, which suggests that the rotational motion of the Cp* ligands is coupled to the photochromism.

Remarkable decrease in overpotential of oxalate formation in electrochemical CO2 reduction by a metal–sulfide cluster

Triangular metal–sulfide clusters, [{Ir(C5Me5)}3(µ3-S)2]2+ and [{Co(C5H4Me)}3(µ3-S)2]2+, catalyse the electrochemical CO2 reduction to selectively produce oxalate at –1.30 and –0.70 V (vs. Ag/AgCl), respectively, in MeCN.

Syntheses, Characterization, and Antitumor Activities of Platinum(II) and Palladium(II) Complexes with Sugar-Conjugated Triazole Ligands

Four platinum(II) and palladium(II) complexes with sugar‐conjugated bipyridine‐type triazole ligands, [PtIICl2(AcGlc‐pyta)] (3), [PdIICl2(AcGlc‐pyta)] (4), [PtIICl2(Glc‐pyta)] (5), and [PdIICl2(Glc‐pyta)] (6), were prepared and characterized by mass spectrometry, elemental analysis, 1H‐ and 13C‐NMR, IR as well as UV/VIS spectroscopy, where AcGlc‐pyta and Glc‐pyta denote 2‐[4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl]ethyl 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranoside (1) and 2‐[4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl]ethyl β‐D‐glucopyranoside (2), respectively. The solid‐state structure of complex 6 was determined by single‐crystal X‐ray‐diffraction analysis. These complexes exhibited in vitro cytotoxicity against human cervix tumor cells (HeLa) though weaker than that of cisplatin.

Thia-calix[n]pyridines, synthesis and coordination to Cu(i,ii) ions with both N and S donor atomsElectronic supplementary information (ESI) available: emission spectra of compound 1. See http://www.rsc.org/suppdata/cc/b2/b203540e/

The novel thia-calix[n]pyridines (n = 3, 4, 6) coordinated to copper ions through nitrogen and sulfur atoms to give multinuclear complexes whose structures have been determined by X-ray crystallography and NMR spectra.

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)).

Steric control of tritolylphosphines on the nuclearity of Cu(I) complexes: Syntheses and structures of the iodo-bridged [Cu4(μ3-I)4(p-tolyl3P)4] cubane and the [Cu2(μ-I)2(o-tolyl3P)2] dimer

The preparation and crystal structures of copper(I) iodide complexes with tri-o-tolylphosphine (o-tolyl3P) and tri-p-tolylphosphine (p-tolyl3P) are described. While p-tolyl3P forms an iodo-bridged cubane, [Cu4I4(p-tolyl3P)4], 1, o-tolyl3P forms a dimer, [Cu2I2(o-tolyl3P)2], 2. In 1, each Cu is bonded to one P atom of p-tolyl3P {Cu–P, 2.248(2), 2.243(5) Å} and three iodide ligands {Cu–I, 2.690(1), 2.686(2), 2.663(2) Å}. I–Cu–I bond angles are in the range 67–70° and Cu–I–Cu vary between 106 and 112°. In 2, the central unit, Cu(μ-I)2Cu, forms a parallelogram with unequal Cu–I distances {Cu–I, 2.601(1), 2.579(1) Å} and bond angles {Cu–I–Cu, 74.42(3), I–Cu–I, 105.58(3)°}. Each Cu atom is further bonded to one P atom of o-tolyl3P {Cu–P, 2.246(2) Å}.

Laser photolysis studies on CuI complexes of thia-calix[3]pyridine. Phosphorescence from the intramolecular charge-transfer excited state

Abstract Copper(I) complexes of thia-calix[3]pyridine in dichloromethane exhibit phosphorescence from the MLCT triplet states at room temperature. The phosphorescence spectrum shifts to red on going from 300 to 180 K. The laser photolysis study carried out in the temperature range 300–180 K reveals that phosphorescence originates from the two triplet states, T H and T L , which are in thermal equilibrium with the energy difference of ca. 5 kcal mol −1 .

π-Back-Bonding Interaction Depending on the Bridging Chain Lengths of Chelated N-Heterocyclic Carbene Platinum Units in Heterometallic Trinuclear Complexes Affecting Their Electrochemical Property

Newly synthesized heterometallic trinuclear M2Pt complexes (M = Rh, Ir) containing a platinum moiety having a chelated bis-N-heterocyclic carbene (bisNHC) ligand with a variety of alkylene chain lengths of the bridging part showed two reversible reduction waves in cyclic voltammetry. Only the second reduction potentials were affected by the alkyl chain lengths, which afforded different dihedral angles between the imidazolylidene rings and the platinum coordination plane resulting in the variation of π-back-donation from the platinum center to the carbene carbon atoms.

Copper-sulfur interactions: synthesis and structure of a trigonal planar copper(I) complex with bis(diphenylthiophosphinyl)methane, [CuI(dppmS2)]·MeCN

Reaction of copper(I) iodide with 1,1-bis(diphenylthiophosphinyl)methane (dppmS2) in a 1:1 mol ratio in acetonitrile yielded a complex of stoichiometry [CuI(dppmS2)]·CH3CN (1) whose X-ray structure determination has shown that the geometry around the copper center is nearly trigonal planar. Acetonitrile is nonbonded. Copper–sulfur bond distances are 2.2470(7) and 2.2591(7) Å, while the copper–iodide bond distance is 2.4937(5) Å. IR and NMR spectroscopic data also show the formation of copper–sulfur bonds. Lack of bridging by iodide led to the formation of a three-coordinate copper complex, as against the expected iodo-bridged dimeric complex with chelating dppmS2.