Recent advances in homogeneous catalysis via metal–ligand cooperation involving aromatization and dearomatization

Recently, an increasing number of metal complex catalysts have been developed to achieve the activation or transformation of substrates based on cooperation between the metal atom and its ligands. In such “cooperative catalysis, ” the ligand not only is bound to the metal, where it exerts steric and electronic effects, but also functionally varies its structure during the elementary processes of the catalytic reaction. In this review article, we focus on metal–ligand cooperation involving aromatization and dearomatization of the ligand, thus introducing the newest developments and examples of homogeneous catalytic reactions

含窒素複素環化合物合成を指向した, 遲移金属を用いたオキシムエステルのN-O結合切断をきっかけとする変換反応に関する研究

京都大学0048新制・課程博士博士(工学)甲第21120号工博第4484号新制||工||1697(附属図書館)京都大学大学院工学研究科物質エネルギー化学専攻(主査)教授 大江 浩一, 教授 辻 康之, 教授 中尾 佳亮学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDGA

Dehydrogenative transformation of alcoholic substrates in aqueous media catalyzed by an iridium complex having a functional ligand with α-Hydroxypyridine and 4,5-Dihydro-1H-imidazol-2-yl Moieties

A new catalytic system that employs water as an environmentally friendly solvent for the dehydrogenative oxidation of alcohols and lactonization of diols has been developed. In this catalytic system, a water-soluble dicationic iridium complex having a functional ligand that comprises α-hydroxypyridine and 4, 5-dihydro-1H-imidazol-2-yl moieties exhibits high catalytic performance. For example, the catalytic dehydrogenative oxidation of 1-phenylethanol in the presence of 0.25 mol % of the iridium catalyst and base under reflux in water proceeded to give acetophenone in 92% yield. Additionally, under similar reaction conditions, the iridium-catalyzed dehydrogenative lactonization of 1, 2-benzenedimethanol gave phthalide in 98% yield

Effect of a Substituent in Cyclopentadienyl Ligand on Iridium-Catalyzed Acceptorless Dehydrogenation of Alcohols and 2-Methyl-1,2,3,4-tetrahydroquinoline

New iridium(III)-bipyridonate complexes having cyclopentadienyl ligands with a series of alkyl substituents were synthesized for the purpose of tuning the catalytic activity for acceptorless dehydrogenation reactions. A comparison of the catalytic activity was performed for the reaction of alcoholic substrates such as 1-phenylethanol, 2-octanol, and benzyl alcohol. The 1-t-butyl-2,3,4,5-tetramethylcyclopentadienyl iridium complex exhibited the best performance, which surpassed that of the 1,2,3,4,5-pentamethylcyclopentadienyl (Cp*) iridium catalyst in the dehydrogenation reaction of alcohols. The catalytic activity in the dehydrogenation of 2-methyl-1,2,3,4-tetrahydroquinoline was also examined. The highest efficiency was obtained in the reaction catalyzed by the same t-butyl-substituted cyclopentadienyl iridium complex

C–H Activation Induced by Oxidative Addition of N–O Bonds in Oxime Esters: Formation of Rhodacycles and Cycloaddition with Alkynes

The reaction of oxime esters with a rhodium­(I) precursor to form five-membered rhodacycles via N–O bond cleavage followed by C–H bond activation has been investigated by isolating these complexes. Kinetic studies on the formation of rhodacycles show that the reversible oxidative addition of the N–O bond in the oxime ester to RhCl­(PPh₃)₃ occurs at room temperature. The <i>E</i>-isomer of the oxime ester was found to undergo rhodacycle formation faster than the <i>Z</i>-isomer, which suggests that the geometry of the oxime esters reflects the geometry of intermediates during C–H activation. The rhodacycle reacted with an alkyne to construct an isoquinoline ring in both stoichiometric and catalytic conditions, despite its basic stability in air, in moisture, and even during heating, which demonstrates the potential of the rhodacycle as an intermediate for further catalytic transformation of oxime esters

Iridium-catalyzed transfer hydrogenation of ketones and aldehydes using glucose as a sustainable hydrogen donor

A new catalytic system for transfer hydrogenation of carbonyl compounds using glucose as a hydrogen donor was developed. Various ketones and aldehydes were efficiently converted to corresponding alcohols with two equivalents of glucose in the presence of a small amount (0.1 to 1.0 mol%) of iridium catalyst that had a functional ligand. In this catalytic system, transfer hydrogenation reactions proceeded based on the cooperativity of iridium and a functional ligand. It should be noted that environmentally benign water could have been used as a solvent in the present catalytic system for the reduction of various carbonyl substrates. Furthermore, the reaction scope could be extended by using N, N-dimethylacetamide as a reaction solvent

Facile Construction of Tetrahydropyrrolizines by Iron-Catalyzed Double Cyclization of Alkene-Tethered Oxime Esters with 1,2-Disubstituted Alkenes

The iron-catalyzed cycloaddition reaction of alkene-tethered oxime esters with 1,2-disubstituted alkenes afforded tetrahydro­pyrrolizines, the structural motif often seen in bicyclic alkaloids. The reaction proceeds through consecutive cycloaddition reactions. These include, first, <i>intramolecular</i> cyclization, followed by <i>intermolecular</i> cyclization with a 1,2-disubstituted alkene in a regioselective manner where an imine moiety first generated plays a pivotal role

Indium-Catalyzed [2 + 2] Cycloaddition of Allylsilanes to Internal Alkynones

We have developed an indium-catalyzed [2 + 2] cycloaddition of allylsilanes to alkynones leading to selective cyclobutenone formation. The resulting cyclobutenones were readily converted to the oxidized products by Tamao–Fleming oxidation or the ring-opened products by an electrocyclic reaction

Divergent Catalytic Approach from Cyclic Oxime Esters to Nitrogen-Containing Heterocycles with Group 9 Metal Catalysts

We report the divergent catalytic transformation of alkene-tethered isoxazol-5­(4<i>H</i>)-ones by using rhodium and cobalt catalysts to afford 2<i>H</i>-pyrroles (with Rh catalyst) and azabicyclic cyclopropanes (with Co catalyst). The rhodium-catalyzed 2<i>H</i>-pyrrole formation involving hydrogen shift is supported by deuterium-labeling experiments. The control experiments in the cobalt-catalyzed reaction indicate that the bicyclic aziridines as the primary product undergo a skeletal rearrangement assisted by metal iodide salts