Jeong-Wook Hwang

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.

Group 4 complexes derived from o-carborane: synthesis, structures and ethylene polymerization properties

Abstract Nine thermally stable complexes (η5-Cp*)[η5-(C5H4)CMe2CB10H10CR]MCl2 (R=H and Me) and (η5-Cp*)[η5; η1-(C5H4)CMe2(CB10H10C)]MCl have been prepared via metathesis reactions of Cp*MCl3 (M=Ti, Zr and Hf, Cp*=pentamethylcyclopentadienyl) with monolithium salts of (C5H5)CMe2(CB10H10CR) (R=H and Me) and with dilithium salt of (C5H5)CMe2(CB10H10CH), respectively. These compounds have been fully characterized by various spectroscopic methods and elemental analyses. All of the compounds except (η5-Cp*)[η5-(C5H4)CMe2CB10H10CMe]HfCl2 were additionally characterized by a single crystal X-ray diffraction study, establishing their monomeric bent metallocene structural feature with carborane acting as a substituent or an ancillary ligand. The titanium and zirconium complexes produce high-density polyethylenes with the activity range of about 103–104 g PE per mol of M bar h in the presence of modified methylaluminoxane cocatalyst.

OXIDATION OF TRICARBONYLMOLYBDACARBORANE. 2. OXIDATIVE DECARBONYLATION WITH VARIOUS SULFUR DONORS

Abstract For the first time, the structure of the half-sandwich complex [(C 2 B 9 H 11 )Mo(CO) 3 ] 2− ( 1 ) has been determined. The addition of sulfur donor ligands, such as aldrithiol ((C 5 H 4 NS) 2 ) and tetraethylthiuram disulfide ((Et 2 NS) 2 S 2 ), leads to the partial oxidative decarbonylation of 1 producing mixed half-sandwich complexes, [(C 2 B 9 H 11 )Mo(CO) 2 (S 2 CNEt 2 )] · (PPN) ( 2 ·PPN) (PPN; bis-(triphenylphosphoranylidene)ammonium) and [(C 2 B 9 H 11 )Mo(CO) 2 (C 5 H 4 NS)] · (NMe 4 ) ( 3 ·NMe 4 ). These compounds were characterized both spectroscopically and structurally. Complexes 2 and 3 contain a Mo(II) center in a pseudo pyramidal geometry. Compound 1 · (NMe 4 ) 2 is fundamental in affording an entry into the chemistry of new molybdacarboranes with higher formal oxidation states.

Highly diastereoselective additions of methoxyallene and acetylenes to chiral α-keto amides

α-Keto amides bearing (S)-indoline chiral auxiliaries reacted with lithiated methoxyallene or lithium acetylides to produce the corresponding dihydrofuranones 7 through formation of the tertiary α-hydroxy allenes, or tertiary α-hydroxy acetylenes, respectively, at −78 °C with high diastereoselectivities (up to >99% de).

First tetrathiolate-bridged dinuclear molybdacarbaboranes: scission and formation of the C-C cluster bond during oxidation processes

Unprecedented tetrathiolate-bridged dinuclear ionic molybdacarbaboranes [(C 2 B 9 H 11 )Mo(SPh) 2 ] 2 n- (n = 2, 1) are prepared by successive oxidation of [(C 2 B 9 H 11 )Mo II - (CO) 2 (SPh) 2 ] 2- with diphenyl disulfide and iodosylbenzene: X-ray crystal structure determinations and NMR studies show unusual scission and reformation of the C–C carbaborane cage bond.