Jin Wook Han

Modification of Chiral Monodentate Phosphine Ligands (MOP) for Palladium-Catalyzed Asymmetric Hydrosilylation of Cyclic 1,3-Dienes

Several MOP ligands 5 containing aryl groups at 2′ position of (R)-2-(diphenylphosphino)-1,1′-binaphthyl skeleton were prepared and used for palladium-catalyzed asymmetric hydrosilylation of cyclic 1,3-dienes 6 with trichlorosilane. Highest enantioselectivity was observed in the reaction of 1,3-cyclopentadiene (6a) catalyzed by a palladium complex (0.25 mol %) coordinated with (R)-2-(diphenylphosphino)-2′-(3,5-dimethyl-4-methoxyphenyl)-1,1′-binaphthyl (5f), which gave (S)-3-(trichlorosilyl)cyclopentene of 90% ee.

Role of the planar chirality of imine–phosphine hybrid ligands bearing chromium tricarbonyl in the palladium-catalyzed asymmetric allylic alkylation

Optically active Cr-complexed imine–phosphine hybrid ligands having only a planar chirality showed excellent enantioselectivity for the palladium-catalyzed allylic alkylation with predictable absolute configuration.

Direct dehydrative esterification of alcohols and carboxylic acids with a macroporous polymeric acid catalyst.

A macroporous polymeric acid catalyst was prepared for the direct esterification of carboxylic acids and alcohols that proceeded at 50-80 °C without removal of water to give the corresponding esters with high yield. Flow esterification for the synthesis of biodiesel fuel was also achieved by using a column-packed macroporous acid catalyst under mild conditions without removal of water.

New planar chiral P,N-ligands containing tricarbonyl(arene)chromium for enantioselective asymmetric hydroboration of styrenes

Abstract Optically active (1,2-disubstituted arene) chromium tricarbonyl complexes 2A–2D with a pyridyl and a phosphorus group in the two ortho benzylic positions have been stereoselectively synthesized from a commercially available (+)-(4,6-O-benzylidene)methyl-α- d -glucopyranoside. These chromium complexes have been used as chiral ligands in the preparation of rhodium catalysts for the hydroboration of styrene derivatives. High enantioselectivities were observed in the hydroboration of vinylarenes.

Synthesis and use in palladium-catalyzed asymmetric allylic alkylation of new planar chiral chromium complexes of 1,2-disubstituted arenes having pyridine and aryl phosphine groups

Abstract Optically active (1,2-disubstituted arene)chromium tricarbonyl complexes 4 – 7 having pyridine and aryl phosphorus groups were synthesized from ( o -disubstituted benzaldehyde)tricarbonylchromium. These chromium complexes have been used as chiral ligands in the asymmetric allylic alkylation of rac -1,3-diphenyl-2-propenyl acetate 8 catalyzed by (η 3 -allyl)palladium complex. The enantioselectivity increases as the number of electron-withdrawing substituents in the aryl phosphine increases. Significant solvent effects on the enantioselectivity were observed for 4 and 7 . By the judicious choice of the planar chiral ligand, high enantioselectivities (90% R , 93% S at 0°C) were observed.

Enhanced catalytic activity in asymmetric hydrosilylation of 1,3-dienes with a soluble palladium catalyst

Abstract A new MOP ligand 8 containing two n-octyl groups at the 6 and 6′ positions of the (R)-2-(diphenylphosphino)-2′-aryl-1,1′-binaphthyl skeleton was prepared and used for the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes with trichlorosilane. The introduction of the n-octyl groups made the palladium–phosphine catalyst soluble in the reaction system, realizing high catalytic activity at a low reaction temperature. As a result, ligand 8 showed highest enantioselectivity for both cyclic and linear 1,3-dienes.

Synthesis of titanium trichloride complexes of 1,2,3-trisubstituted cyclopentadienyls and their use in styrene polymerization

Abstract The synthesis, characterization and styrene polymerization properties of titanium trichloride compounds (5, 1,3-dimethyl-2-n-butylcyclopentadienyl; 6, 1,3-dimethyl-2-t-butylcyclopentadienyl; 13, 1,3-diphenyl-2-n-butylcyclopentadienyl; 14, 1,3-dimethyl-2-phenylcyclopentadienyl; 15, 1,2,3-triphenylcyclopentadienyl) containing 1,2,3-trisubstituted cyclopentadienyl ligands are reported. Reactions of lithiated cyclopentadienide with Me3SiCl followed by addition of TiCl4 gave new titanium trichloride compounds 5 and 6, respectively, in reasonable yields, and reactions of cyclopentadiene with Ti(NMe2)4 followed by Me3SiCl or Me2SiCl2 gave new titanium trichloride compounds 13–15, respectively, in reasonable yields. Compound 14 has been characterized by single crystal X-ray diffraction studies: monoclinic space group P21/c; a=15.893(2), b=7.199(1), c=12.812(2) A, β=108.394(7)°, Z=4 and V=1390.9(3) A3. The catalytic behavior of the new titanium compounds in styrene polymerization has been studied in the presence of excess methylaluminoxane.

Preparation and application of polymer-supported π-allylpalladium complex as a chiral catalyst in the asymmetric allylic alkylation

Abstract Chiral ferrocenylphosphine-imines A–D were synthesized and grafted to polystyrene to afford polymeric ligands PA–PD. Ligands A–D and PA–PD were used as ligands in the palladium-catalyzed asymmetric allylic alkylation. In the homogeneous reactions, the best result was obtained when the ligand A was used (99% yield and 82% ee). In the heterogeneous reactions, the highest ee value (73%) in the first run was obtained when PA was used as a ligand. Considering the enantioselectivity and reusability, the best result was obtained in the case of PC. The recycling of the polymer-supported π-allylpalladium catalyst gave unsatisfactory results: it can be reused three times with moderate enantioselectivities (60–70% ee).

Synthesis of bis(1,2,3-substituted cyclopentadienyl)zirconium dichloride derivatives and their use in ethylene polymerization

Catalytic Pauson‐Khand reaction products with norbornadiene could be effectively transformed to trisubstituted cyclopentadienes, which have been used to synthesize a series of unbridged bis(1-R%-2-R-3-R%-trisubstituted cyclopentadienyl)zirconium dichlorides 3 (RR%Ph), 4(RPh, R%Me), 21(Rn-Bu, R% Me), 22(R t-Bu, R% Me), 23(R (CH2)4OMe), R%Me), and 24(Rn-Bu, R%Ph). The crystal structure of 24 was determined by X-ray crystallography. These zirconium complexes in the presence of methylaluminoxane (MAO) show activities for the polymerization of ethylene. The activities are in the following order: 21\4\2223Cp2ZrCl2\324. The activity of 21 is four times higher than that of Cp2ZrCl2 under similar conditions.

A water-soluble rhodium complex as a catalyst precursor for the hydroformylation of olefins

Abstract The first synthesis of a water-soluble cationic (sugar-substituted arene)rhodium complex has been described. The water-soluble cationic rhodium complex was synthesized by the reaction of an ethanol solution of [Rh(COD)Cl] 2 with AgBF 4 and then with phenyl- β - d -glucopyranoside. This water-soluble rhodium complex acts as a catalyst precursor for the hydroformylation of olefins in a two-phase (water and hexane) system and displays high regioselectivity and high conversion to branched-chain aldehydes.