Yohsuke Yamamoto

Synthesis of B/Si Bidentate Lewis Acids, o-(Fluorosilyl)(dimesitylboryl)benzenes, and Their Fluoride Ion Affinity

o-(Fluorosilyl)(dimesitylboryl)benzenes have been prepared as colorless crystals by reacting fluorodimesitylborane with o-(fluorodimethylsilyl)phenyllithium and o-(fluorodiphenylsilyl)phenyllithium. The o-(fluorosilyl)(dimesitylboryl)benzenes serve as B/Si bidentate Lewis acid and efficiently capture fluoride ion from potassium fluoride in the presence of [2.2.2]cryptand or 18-crown-6 in toluene, giving the corresponding mu-fluoro bridged products. The structures were characterized by X-ray crystal structure analysis and multinuclear NMR spectroscopy. Fluoride ion affinities of the o-(fluorosilyl)(dimesitylboryl)benzenes were evaluated in comparison with non-silylated triarylborane.

Synthesis and structure of a hexacoordinate carbon compound

In an exploration of six coordination and hypervalence in carbon compounds, steric constraints have been employed to bring four ether O atoms in close proximity to an allenic carbon atom. The dimethylated dication 2 is confirmed to have hexacoordinate carbon by experimental charge density analysis and DFT calculations and is arguably hypervalent.

A structure-activity relationship for pincer palladium(II) complexes: influence of ring-size of metallacycles on the activity in allylic alkylation

A series of new palladium(II) complexes derived from the well-known pincer complex [PdCl{(C 6 H 3 )(OP i Pr 2 ) 2 -2,6}] were synthesised: [PdX{(C 6 H 3 )(OP i Pr 2 ) 2 -2,6}] (X=Br − , I − , OAc − , OTf − ). A novel PCP′ pincer ligand 1-( i Pr 2 PO)-3-( i Pr 2 POCH 2 )(C 6 H 4 ) was prepared and complexed to palladium(II) to give [PdX{(C 6 H 3 )(OP i Pr 2 )-2-(CH 2 OP i Pr 2 )-6}] (X=Cl − , I − , OAc − , OTf − , BF 4 − ). The X-ray structure of [PdCl{(C 6 H 3 )(OP i Pr 2 )-2-(CH 2 OP i Pr 2 )-6}] was solved and is discussed. These complexes were applied to the catalytic reaction of cinnamyl acetate with sodium dimethyl malonate in order to evaluate the influence of the ligand structure and co-ordinating or non-co-ordinating anions on the regioselectivity. A detailed analysis shows that palladium(II) complexes of the unsymmetrical PCP′ bis(phosphinito) ligand are much more active when compared to related complexes of the symmetrical PCP bis(phosphinito) ligand. The origin of this difference in activity is discussed.

Synthesis, Reactions, and Electronic Properties of 16 π-Electron Octaisobutyltetraphenylporphyrin

The reaction of the doubly oxidized beta-octaisobutyl-meso-tetraphenylporphyrin (OiBTPP, 4), which has a 16 pi-electronic structure at the porphyrin core, with a variety of metal reagents was investigated. The reaction of 4 with SnCl(2) followed by ethanolysis afforded an 18 pi-electron tin complex, (OiBTPP)Sn(OEt)(2) (5), in a redox manner. No reactions were observed using zerovalent metals (Zn, Cu, and Pd). However, the reaction of 16pi [(OiBTPP)Li](+)[BF(4)](-) (6), which was easily derived from 4, with Zn, Cu, and Pd(2)(dba)(3) gave the corresponding 18pi metalloporphyrins (OiBTPP)M (7, M = Zn(EtOH); 8, M = Cu; and 9, M = Pd). One-electron oxidation of the copper complex 8 by AgSbF(6) afforded a 17 pi-electron cation radical complex, [(OiBTPP)Cu](*+)[SbF(6)](-) (10). The UV-visible and electron spin resonance spectra of 10 were quite similar to those of previously reported beta-octaethyl-meso-tetraphenylporphyrin (OETPP) derivatives, [(OETPP)Cu](*+)X(-) (X = ClO(4), I). In contrast to the reaction of 6 with Zn to give the 18pi complex 7, the reaction of 4 with divalent ZnCl(2) enabled us to isolate a new 16pi porphyrin-zinc(II) complex, [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11), in 92% yield. The solid-state structures of 5 and 7-11 were unambiguously determined by single-crystal X-ray crystallography. The porphyrin cores of 10 (17pi) and 11 (16pi) are much more distorted than those of the 18pi derivatives 5 and 7-9. Furthermore, the bond distances of 10 and 11 clearly showed the presence of bond alternation in contrast to aromatic 18pi species 8 and 7, respectively. Nucleus-independent chemical shift calculations of 4 and some metalated porphyrins indicated that the highly distorted 16pi porphyrins are essentially nonaromatic, with only weak antiaromaticity. Magnetic circular dichroism studies in conjunction with ZINDO/S calculations assisted in identifying the electronic transitions of the UV-vis spectra of key porphyrins. Electrochemical and thin-layer UV-vis spectroelectrochemical experiments on 4 (16pi) and 11 (16pi) indicated that both compounds can be electroreduced to give the 18pi species, with the 16pi/18pi transition being reversible in the case of [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11).

Intramolecular cyclization of o-silylbenzyl alcohols with elimination of hydrocarbon via hypervalent silicon intermediates: Effect of structure on the selectivity for elimination

Abstract o-Silylbenzyl alcohols (1a–1e) cyclized with elimination of hydrocarbon to give cyclic silanes (2) in quantitative yield. The cyclization took place only in aprotic polar solvents such as acetonitrile, indicating that the intermediate of the cyclization was 10-Si-5 zwitterion B . The selectivity for the elimination of substituents was found as the following order, i.e., Ph>Me>t-Bu, and structure of zwitterions was found to play a key role to determine the selectivity.

Stereomutation and apicophilicity of diastereomeric spirophosphoranes (10-P-5)

Abstract The apicophilicity for a series of monodentate groups were determined by deducing activation parameters of equilibration between diastereomeric spirophosphoranes bearing a Martin ligand and a modified Martin ligand. The equilibration was shown to be an intramolecular process and the order of apicophilicity of the groups turned out to be OMe≈H>COMe≈SMe>NMe2>Me>n-Bu on the basis of activation enthalpy. The involvement of π-conjugation type interactions was revealed by X-ray structures of symmetric analogs bearing COMe (acceptor) and NMe2 (donor) groups.

Anti-Aromatic 16π Porphyrin–Metal Complexes with meso-Alkyl Substituents

In recent years, investigations on anti-aromatic porpyrACHTUNGTRENNUNGinoids including expanded porphyrins and hetero porphyrins have rapidly increased and properties unique to them have been revealed. As for compounds bearing the basic porphyrin core, however, reports on 16pand 20p-electron species are still scarce, owing to their unstable nature. While twenty years have passed since the first doubly reduced species (20p-electron state) was structurally characterized, the doubly oxidized species (16p-electron state) have been reported only rather recently, by us and Vaid s group (Figure 1). Therefore, it would be worthwhile and challenging to further explore the chemistry of 16p porphyrins.

Novel cationic titanium(IV) Lewis acids and their use in asymmetric aldol reactions

Abstract Novel cationic Lewis acids were generated by the addition of silver hexafluoroantimonate to titanium complexes 7 (TiCl4·(R,R)-1,2-diphenylethane-1,2-diol dialkyl ether) or 8 (TiCl3(OR)·(R,R)-1,2-diphenylethane-1,2-diol dialkyl ether) at −20 °C. Interestingly, the titanium complexes 7 or 8 could be isolated and the structures of 7c (TiCl4·(R,R)-1,2-diphenylethane-1,2-dioldi-n-propyl ether) and 8a (TiCl3(O-i-Pr)·(R,R)-1,2-diphenylethane-1,2-diol dimethyl ether) were determined by X-ray analysis. Asymmetric aldol reaction using the cationic Lewis acids is also described.

Synthesis of a novel potential tridentate anthracene ligand, 1,8-bis(dimethylamino)-9-bromoanthracene, and its application as chelate ligand for synthesis of the corresponding boron and palladium compounds.

A novel potential tridentate ligand, 1,8-bis(dimethylamino)-9-bromoanthracene, was synthesized. The key steps are as follows: 1) dimethylamination of 1,8-dibromo-9-methoxyanthracene by a modified Buchwalds method to afford 1,8-bis(dimethylamino)-9-methoxyanthracene, and 2) reduction of the methoxy group by LDBB (lithium di-tert-butylbiphenylide) followed by treatment with BrCF2CF2Br. The corresponding 1,8-bis(dimethylamino)-9-lithioanthracene, which should be a useful versatile tridentate ligand, could be generated by treatment of the bromide with one equivalent of nBuLi. The lithioanthracene reacted with B-chloroborane derivatives to give three 9-boryl derivatives. Although we recently reported that the crystal structure of 1,8-dimethoxy-9-B-catecholateborylanthracene was a symmetrical compound with the almost identical two O-B distances (2.379(2) and 2.441(2) A), the newly prepared 1,8-bis(dimethylamino)-9-borylanthracene derivatives clearly have unsymmetrical structures with coordination of only one NMe2 group toward the central boron atom. However, the energy difference between the unsymmetrical and symmeterical structures was found to be very small based on 1H NMR measurements, in which symmetrical anthracene patterns in the aromatic region (two kinds of doublets and a triplet) and a sharp singlet signal of the two NMe2 groups were observed even at -80 degrees C. 1,8-Bis(dimethylamino)-9-bromoanthracene itself can be a versatile ligand for transition metal compounds. In fact, direct palladation of the bromide took place by the reaction with [Pd2(dba)3].CHCl3 in THF to give the 9-palladated product. X-ray crystallographic analysis of the Pd compound showed that the square planar palladium atom was coordinated in a symmetrical fashion by both NMe2 groups (Pd-N bonds are 2.138(5) and 2.146(5) A).

Stereoselective synthesis of 1,2-Amino alcohols by addition of organocuprate·BF3 complexes and organolithium reagents to an α-silyloxyaldimine derived from (S)-ethyl lactate

Abstract 1,2-Amino alcohols were synthesized by addition of organocuprate·BF3 2 (R=n-Bu, n-octyl, Me, phenethyl, Ph), organocopper·BF3 3 (R=Me, n-Bu), and organolithiums (R=n-Bu, n-octyl, Me, phenethyl, Ph) to an α-silyloxyaldimine 1 derived from commercially available (S)-ethyl lactate. The reactions with organocuprate·BF3 2 and organocopper·BF3 3 led to the anti isomers almost exclusively (anti:syn=>98: