Take-aki Koizumi

Aerobic Oxidative Dehydrogenation of 2‐Substituted Imidazolines Promoted by a Cyclometalated Ruthenium Catalyst

Imidazole derivatives are chemically and pharmaceutically very important. The oxidative dehydrogenation of imidazolines is a general and reliable method of synthesizing 2-substituted imidazoles; metal salts serving as oxidants are generally employed. However, these reagents often suffer from limitations such as toxicity, explosibility, and harsh reaction conditions, and the use of large amounts of the oxidants produces serious disposal problems. Therefore, the development of a synthetic method employing aerial oxygen without the need for a co-oxidant is highly desired. In terms of catalytic oxidation, the oxidative dehydrogenation of amines and alcohols is promoted by their coordination to transition metal complexes, and there are a number of reports on the aerobic oxidation of alcohols and amines promoted by ruthenium catalysts. 5] However, to our knowledge, the transition-metal-catalyzed aerobic oxidation of imidazolines has, to date, not been achieved. We previously reported a pincer ruthenium complex incorporating a kNCN pincer ligand with imidazoline units that exhibited the oxidative dehydrogenation of the coordinated imidazoline unit with aerial oxygen to give an imidazole-ligated pincer complex. The s-donor character of the cyclometalated ligand was considered to assist the ruthenium-promoted aerobic oxidation of the coordinated imidazoline moiety. This observation persuaded us to explore the ruthenium-catalyzed oxidation of imidazolines with aerial oxygen. Several cyclometalated ruthenium complexes are known to be active catalysts in the base-cocatalyzed transfer hydrogenation of ketones, whereas no example of a cyclometalated ruthenium complex that efficiently catalyzes the oxidative dehydrogenation of 2substituted imidazolines has been reported. We report herein that a cyclometalated ruthenium complex, [RuCl(ppy)(tpy)][PF6] 1 a (ppy = 2-phenylpyridine; tpy = 2,2’:6’,2’’-terpyridine) is an excellent catalyst for the aerobic oxidative dehydrogenation of 2-substituted imidazolines, affording the corresponding imidazoles under mild conditions. In preliminary studies, the oxidation of 2-phenylimidazoline (2 a) using 1 a in methanol at 55 8C in air without an added oxidant was investigated, monitored by H NMR spectroscopy. The aerobic oxidation of 2 a was achieved by employing 1 a as the catalyst (Table 1, entry 1). The reaction proceeded much faster using molecular oxygen (101 325 Pa, balloon), whereas the same reaction under a nitrogen atmosphere gave only a

A Symmetrically Bridging Triarylsilyl Ligand in a Dinuclear Rhodium Complex: Synthesis and Structure of [LRh(H)(µ‐Cl)(µ‐SiAr2)(µ‐SiAr3)Rh(H)L] (Ar=Ph, p‐FC6H4; L=PiPr3)

Simply warming solutions of the dinuclear complexes 1 provides novel complexes 2 [Eq. (a); Ar = Ph, p-FC6 H4 ; L = PiPr3 ], which contain a bridging triarylsilyl ligand and show unusual thermal stability. Compounds with this type of symmetric structure are of interest as models of the transition state for the migration of tertiary silyl groups in a bimetallic framework.

DIBROMIDES OF BOC-PROTECTED 1-AMINOPYRROLE AND 4-AMINO-1,2,4-TRIAZOLE : SYNTHESIS, X-RAY MOLECULAR STRUCTURE, AND NMR BEHAVIOR

α-Dibromides of BOC-protected 1-aminopyrrole and 4-amino-l,2,4-triazole have been prepared and their molecular structures have been confirmed by X-ray crystallography. They can be used for polymer synthesis.

New rhodacyclopentane with phenylvinylidene substituents,mer-[Rh{CH2C(CHPh)C(CHPh)CH2}Cl(PMe3)3]. Structureand formation through concerted cycloaddition of phenylallene molecules to[RhCl(PMe3)3]

[RhCl(PMe 3 ) 3 ] reacts with an excess of phenylallene to give a new rhodacyclopentane, mer-[Rh{CH 2 C(CHPh)C(CHPh )CH 2 }Cl(PMe 3 ) 3 ] 1, which is not obtained via the reaction of [RhCl(η 2 -CH 2 CCHPh)(PMe 3 ) 3 ] 2 with phenylallene.

Crystal structure of 1,13,14-tri­aza­dibenz[a,j]anthracene 1,1,2,2-tetra­chloro­ethane monosolvate

The crystal structure of 1,1,2,2-tetrachloroethane (TCE)-solvated 1,13,14-triazadibenz[a,j]anthracene (dibenzo[c,h]-1.9,10-anthyridine, dbanth) was determined by X-ray diffraction study. Two H atoms in the solvated TCE molecule form intermolecular C—H⋯(N,N) hydrogen bonds with three N atoms in dbanth. π–π interactions link the dbanth molecules to form a one-dimensional columnar structure.

Cross-Coupling Polymerization

Organometallic cross-coupling reactions directed toward the synthesis of aromatic polymers are reviewed. The progress of this methodology has made the syntheses of numerous functional polymers possible, which includes the synthesis of well-defined π-conjugated polymers and buildup molecular architectures. The polycondensation has been spread out to material areas ranging from optical and electronic materials to biological sensing materials. The use of organometallic direct arylation and carbon-heteroatom bond formation for the synthesis of functional polymers has also been dealt with.