Youngkyu Do

Unusual Ferromagnetic Couplings in Single End‐to‐End Azide‐Bridged Cobalt(II) and Nickel(II) Chain Systems

Two new one-dimensional single azide-bridged metal(II) compounds [[M(5-methylpyrazole)4(N3)]n](ClO4)n(H2O)n [M = Co (1a), Ni (2a)] were prepared by treating an M(II) ion with stoichiometric amount of sodium azide in the presence of four equivalents of the 3(5)-methylpyrazole ligand. The isostructural compounds 1a and 2a crystallize in the monoclinic space group P2(1)/n. The azide bridging ligands have a unique end-to-end coordination mode that brings two neighboring metal centers into a cis-position with respect to the azide unit to form single end-to-end azide-bridged cobalt(II) and nickel(II) chains. The two neighboring metal atoms at inversion centers adopt octahedral environments with four equatorial 3(5)-methylpyrazole ligands and two axial azide bridges. Two adjacent equatorial least-squares planes form dihedral angles of 60.5 degrees and 60.6 degrees for Co and Ni, respectively. In addition, the metal-azide-metal units form large M-N3-M torsion angles, which are magnetically important geometrical parameters, of 71.6 degrees for M=Co and 75.7 degrees for M=Ni. It should also be noted that the M-N-N angles associated with end-to-end azide group, another magnetically important structural parameter, fall into the experimentally observed range of 120-140 degrees as 128.3(3) and 147.8(3) degrees for cobalt species and 128.4(2) and 146.1(3) degrees for nickel species; these values deviate from the theoretical value of around 164 degrees at which the incidental orthogonality is achieved under the torsion angle of 0 degrees. The compounds 1a and 2a have unique magnetic properties of ferromagnetism, zero-field splitting, and spin canting. The MO calculations indicate that the quasiorthogonality between the magnetic orbitals of metal ions and the p atomic orbitals of the bridging azide is possible in the observed structures and leads to the ferromagnetism. The spin canting related to the perturbation of ferromagnetism arises from the magnetic anisotropy and antisymmetric interactions judged by the structural parameters of the zero-field splitting and the tilted MN4 planes in a chain. The enhancement of magnetic interactions was accomplished by dehydrating the chain compounds to afford two soft magnets with critical temperature T(C) and coercive field of 2 K and 35 G for 1b and 2.3 K and 20 G for 2b, respectively.

Canted Ferromagnetism in a NiII Chain with a Single End-to-End Azido Bridge

Ferromagnetic coupling between metal centers and end-to-end coordination of the azido bridges were found together for the first time in the one-dimensional nickel(II) compound [{Ni(5-methylpyrazole)4(N3)}n](ClO4)n⋅n H2O (1; the structure in the unit cell is shown). The ferromagnetic coupling involving spin canting occurs between the two crystallographically distinct types of magnetic centers in 1 owing to a large Ni-N3-Ni torsion angle of 75.7° and a dihedral angle of 60.6° between two types of NiN4 least-squares planes.

Synthetic Utility of Ammonium Salts in a Cu-Catalyzed Three-Component Reaction as a Facile Coupling Partner

Ammonium salts were found to be a convenient and inexpensive reagent in the Cu-catalyzed three-component reaction with terminal alkynes and sulfonyl or phosphoryl azides leading to N-unprotected amidines. Thus obtained amidines bearing 2-bromobenzenesulfonyl moiety were efficiently cyclized by the Cu-catalyzed intramolecular N-arylation to give an important pharmacophore skeleton of 2H-1,2,4-benzothiadiazine 1,1-dioxides. Conveniently, two tandem catalytic procedures could be readily operated in one pot.

Synthesis, structures and electrochemical characterization of ferrocene-substituted porphyrin and porphodimethene

Abstract Condensation of ferrocenecarboxaldehyde and dipyrrolylmethane gave 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethyl-5,15-dihydroporphyrin (H21), and 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin (H22) in 31 and 49% yield, respectively. Structures of H21·CHCl3 and H22·0.5C6H5Me have been determined by X-ray diffraction. Compound H21 has syn-axial configuration and H22 has syn configuration of two ferrocenyl groups. Compound H21 was only proven to be an intermediate species of H22 in the photooxidation pathway. The large steric bulkiness of the ferrocenyl group permitted the isolation of compounds H21 and H22 directly from the oxidation reaction of 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrinogen. Porphodimethene H21 has exceptional stability toward air and light in the absence of acid. Electrochemically, ferrocene subunits of H21 are oxidized with a reversible two-electron transfer process (0.33 V), while those of H22 are oxidized with two reversible one-electron transfer processes (0.06 and 0.27 V).

Synthesis and polymerization behavior of various substituted indenyl titanium complexes as catalysts for syndiotactic polystyrene

Abstract Five substituted indenyltrichlorotitanium compounds have been synthesized and characterized by spectroscopic methods and their catalytic behavior for the polymerization of styrene was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. Substituted indenyl ligands include 1,3-dimethyl, 1-methyl, 1-ethyl, 1-isopropyl and 1-(trimethylsilyl)indenyl groups. All five compounds gave extremely pure syndiotactic polystyrene, with conversion rates of at least 95%, and their catalytic properties were compared with the data obtained from the ( η 5 -indenyl)trichlorotitanium-MAO system. The catalytic activity is enhanced by less bulky and better electron-releasing substituents of the indenyl ligand.

Synthesis, structure and ethylene polymerization behavior of zirconium complexes with chelating ketoiminate ligands

Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η5-Cp*){CH3C(O)CHC(NHR)CH3}{CH3C(O)CHC(NR)CH3}ZrCl2] (R=4-CF3Ph) (3) has been prepared in high yield by the reaction of one equivalent of 4-CF3-phenyl-β-ketoimine (1a) and one equivalent of lithium 4-CF3-phenyl-β-ketoiminate (2a) with one equivalent of Cp*ZrCl3 in Et2O. Bis(ketoiminate)zirconium dichloride complexes, 4 and 6, have been also prepared in high yield by the reaction of amine elimination of ketoimine ligands, respectively 1a and 1b, with Zr(NMe2)4 and followed by chlorination reaction with TMSCl. The X-ray crystallography reveals that the compound 3 is based on distorted octahedral geometry containing a ketoimine and a ketoiminate. The ketoiminate ligand coordinates to the zirconium as a bidentate ligand, leaving the metal center coordinatively unsaturated and thus leading to an additional binding of a ketoimine ligand to the metal to stabilize the complex 3. The zirconium complexes 3, 4 and 6 provide the moderate activity for the polymerization of ethylene in the presence of MMAO cocatalyst. Low molecular weight and high density polyethylene was obtained.

Aluminium–salen luminophores as new hole-blocking materials for phosphorescent OLEDs

The organic light-emitting diodes (OLEDs) employing complex [salen(tBu)4Al(OC6H4-p-C6H5)] (4) as a hole-blocking layer produced stable green EL emission of Ir(ppy)3 irrespective of changing current density and showed higher brightness and device efficiency than the BAlq-based device.

New half-sandwich metallocene catalysts for polyethylene and polystyrene

Abstract A new type of half-sandwich metallocene catalysts for the polymerization of ethylene and styrene, Cp*MCl(DEAR) (DEA=(OCH2CH2)2N, R=Me, M=Ti (1); R=Me, M=Zr (2); R=n-Bu, M=Ti (3)), was prepared by the reaction of corresponding N-alkyl-N,N-diethanolamine with Cp*MCl3 in the presence of triethylamine. Compounds 1–3 are slightly air-sensitive and thermally unstable. All catalyst systems show moderate activities in ethylene polymerization and especially the 2/MMAO system gives PE with broad molecular weight distribution at all polymerization temperatures. In addition, 1/MMAO and 3/MMAO show fairly good activities in sPS polymerization in the order 3/MMAO>1/MMAO.

New half-metallocene catalysts generating polyethylene with bimodal molecular weight distribution and syndiotactic polystyrene

A new type of half-metallocene catalyst for the polymerization of ethylene and styrene Cp * M((O) 3 O 9 Si 7 (c-C 5 H 9 ) 7 ) (M= Ti (1), Zr (2)) is prepared by the reaction of (HO) 3 O 9 Si 7 (c-C 5 H 9 ) 7 with Cp * MCl 3 in the presence of triethylamine. Complex 1 is stable to heat and air but heavier congener 2 is sligtly air sensitive. The catalytic systems 1/MMAO and 2/MMAO, in which MMAO is modified methylaluminoxane show good activities in ethylene polymerization, with that of 2/MMAO greater than that of 1/MMAO. Polyethylenes with bimodal molecular weight distributions were obtained. In addition, the catalytic system 1/MMAO shows fairly good activities for the syndiospecific polymerization of styrene.

Platinum(II) complexes of 3,3′-disubstituted-2,2′-bypyridines. Synthesis, structures, cytotoxic effect and unusual solvolysis in DMSO

Abstract The reaction of 3,3′-disubstituted-2,2′-bipyridines, 2,2′-bipyridyl-3,3′-dicarboxylic acid (H2BDC) and 3,3′-dimethylol-2,2′-bipyridine (DMB) with potassium tetrachloroplatinate(II) in water gives Pt(H2BDC)Cl2 (1) and Pt(DMB)Cl2 (2), respectively. Both complexes were characterized by elemental analysis and various spectroscopic techniques. The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. 1·2DMF: triclinic system, space group P 1 , α=8.089(9) A , b=9.707(8) A c=15.541(4) A , α=106.88(6)° , β=100.41(3)°, γ=94.39(8)°, V=1137.8(2) A 3 , Z=2 . 2: monoclinic system, space group P2, lc, α=7.849(5) A , b=16.125(3) A , c=21.613(5) A , β=94.10(2)°, V=2728.5(9) A 3 , Z=8 . X-ray structures indicate that two pyridine rings of the bipyridyl ligand in both compounds cannot attain the coplanar state owing to the steric bulkiness of the substituents in the 3,3′-positions. The solvolysis of 1 in DMSO. characterized by 1H, 13C and 195Pt NMR spectra, leads to the unprecedented example for the complete release of the free amine ligand H2BDC, yielding the formation of cis-[Pt(Me2SO)2Cl2]. No antitumor activity was observed for 1 and 2 against the leukemia L1210 cell line.