Download or read book Transition Metal Complexes of Oxazolinylboranes and Cyclopentadienyl bis oxazolinyl borates written by and published by . This book was released on 2012 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: The research presented and discussed in this dissertation involves the synthesis of transition metal complexes of oxazolinylboranes and cyclopentadienyl-bis(oxazolinyl)borates, and their application in catalytic enantioselective olefin hydroamination and acceptorless alcohol decarbonylation. Neutral oxazolinylboranes are excellent synthetic intermediates for preparing new borate ligands and also developing organometallic complexes. Achiral and optically active bis(oxazolinyl)phenylboranes are synthesized by reaction of 2-lithio-2-oxazolide and 0.50 equiv of dichlorophenylborane. These bis(oxazolinyl)phenylboranes are oligomeric species in solid state resulting from the coordination of an oxazoline to the boron center of another borane monomer. The treatment of chiral bis(oxazolinyl)phenylboranes with sodium cyclopentadienide provide optically active cyclopentadienyl-bis(oxazolinyl)borates H[PhB(C5H5)(OxR)2] [OxR = Ox4S-iPr, Me2, Ox4R-iPr, Me2, Ox4S-tBu]. These optically active proligands react with an equivalent of M(NMe2)4 (M = Ti, Zr, Hf) to afford corresponding cyclopentadienyl-bis(oxazolinyl)borato group 4 complexes {PhB(C5H4)(OxR)2}M(NMe2)2 in high yields. These group 4 compounds catalyze cyclization of aminoalkenes at room temperature or below, providing pyrrolidine, piperidine, and azepane with enantiomeric excesses up to 99%. Our mechanistic investigations suggest a non-insertive mechanism involving concerted C-N/C-H bond formation in the turnover limiting step of the catalytic cycle. Among cyclopentadienyl-bis(oxazolinyl)borato group 4 catalysts, the zirconium complex {PhB(C5H4)(Ox4S-iPr, Me2)2}Zr(NMe2)2 ({S-2}Zr(NMe2)2) displays highest activity and enantioselectivity. Interestingly, S-2Zr(NMe2)2 also desymmetrizes olefin moieties of achiral non-conjugated aminodienes and aminodiynes during cyclization. The cyclization of aminodienes catalyzed by S-2Zr(NMe2)2 affords diastereomeric mixture of cis and trans cylic amines with high diasteromeric ratios and excellent enantiomeric excesses. Similarly, the desymmetrization of alkyne moieties in S-2Zr(NMe2)2-catalyzed cyclization of aminodiynes provides corresponding cyclic imines bearing quaternary stereocenters with enantiomeric excesses up to 93%. These stereoselective desymmetrization reactions are significantly affected by concentration of the substrate, temperature, and the presence of a noncyclizable primary amine. In addition, both the diastereomeric ratios and enantiomeric excesses of the products are markedly enhanced by N-deuteration of the substrates. Notably, the cationic zirconium-monoamide complex [S-2Zr(NMe2)][B(C6F5)4] obtained from neutral S-2Zr(NMe2)2 cyclizes primary aminopentenes providing pyrrolidines with S-configuration; whereas S-2Zr(NMe2)2 provides R-configured pyrrolidines. The yttrium complex S-2YCH2SiMe3 also affords S-configured pyrrolidines by cyclization of aminopentenes, however the enantiomeric excesses of products are low. An alternative optically active yttrium complex {PhB(C5H4)(Ox4S-tBu)2}YCH2SiMe3 ({S-3}YCH2SiMe3) is synthesized, which displays highly enantioselective in the cyclization of aminoalkenes at room temperature affording S-configured cyclic amines with enantiomeric excesses up to 96%. A noninsertive mechanism involving a six-membered transition state by a concerted C-N bond formation and N-H bond cleavage is proposed for {S-3}YCH

Download or read book Bifunctional Molecular Catalysis written by Takao Ikariya and published by Springer Science & Business Media. This book was released on 2011-06-26 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: Masakatsu Shibasaki, Motomu Kanai, Shigeki Matsunaga, and Naoya Kumagai: Multimetallic Multifunctional Catalysts for Asymmetric Reactions.- Takao Ikariya: Bifunctional transition metal-based molecular catalysts for asymmetric syntheses.- Chidambaram Gunanathan and David Milstein: Bond Activation by Metal-Ligand Cooperation: Design of ”Green” Catalytic Reactions Based on Aromatization-Dearomatization of Pincer Complexes.- Madeleine C. Warner, Charles P. Casey, and Jan-E. Bäckvall: Shvo’s Catalyst in Hydrogen Transfer Reactions.- Noritaka Mizuno, Keigo Kamata, and Kazuya Yamaguchi: Liquid-Phase Selective Oxidation by Multimetallic Active Sites of Polyoxometalate-Based Molecular Catalysts.- Pingfan Li and Hisashi Yamamoto: Bifunctional Acid Catalysts for Organic Synthesis.- Jun-ichi Ito, Hisao Nishiyama: Bifunctional Phebox Complexes for Asymmetric Catalysis.