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The ligand coupling reaction (LCR) of hypervalent pentacoordinate antimony compounds (ArnTol5−nSb; Ar = p-trifluoromethylphenyl, Tol = p-methylphenyl; n = 0–5) was analyzed via the long-range-corre...

The ligand exchange reactions (LERs) of hypervalent compounds of antimony (R5Sb: R = Me, Ph) and tellurium (R4Te: R = Me, Ph) were analyzed via dispersion corrected density functional theory (DFT) and coupled cluster calculations. The dispersion force plays a key role in forming reactant/product complexes. For the phenyl ligand compounds, the pathway of the LER was predicted as being stepwise, while that for the methyl ligand compounds was predicted to be concerted. From the natural localized molecular orbital analysis for the reaction of Me4Te, it was found that the lone pair electrons of tellurium do not participate in LER. The LER of antimony compounds was elucidated to proceed along the mechanism similar to that of Me4Te. LER of a mixture of Me4Te and Me5Sb was shown to proceed more easily than that of each component.

A hexacoordinate hypervalent carbon compound with an ideal octahedral structure was proposed theoretically in a previous study (Chem. Phys. Lett. 2008, 460, 37). However, there is no report telling...

A series of the monocyclic organophosphorus compounds ([o-OC(CH3)2C6H4]PPh(CH2 Ph)X) bearing a halogen (X = F, Cl, and Br) or a tetrafluoroborate (X = BF4) were synthesized. The solid-state structures of the bromide, the tetrafluoroborate, and an analogous fluoride ([o-OC(CF3)2C6H4]PPh(CH2 Ph)F) were determined by single crystal X-ray crystallography. The geometry of the fluoride was almost an ideal trigonal bipyramid (TBP). On the other hand, the bromide and tetrafluoroborate were essentially phosphonium salts with phosphorane character to some extent for the former. In CD3 CN, the bromide, the chloride, and the tetrafluoroborate were found to exist as phosphonium salts. However, it was suggested that in CDCl3, the bromide and the chloride have structures rapidly equilibrating or averaged between the phosphorane and the phosphonium forms. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:523–530, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20717

The stereomutation rates between a pair of stable diastereomeric hydroxyphosphoranes (2c-exo and 2c-endo) were measured by monitoring the change in the relative diastereomeric ratios and by 19F NMR magnetization transfer. Analysis of the data gave averaged kinetic parameters of ΔH≠ = 15.7 kcal mol−1; ΔS ≠ = −19.3 eu; ΔG≠298 = 21.4 kcal mol−1 for interconversion in toluene-d8 and ΔH≠ = 18.9 kcal mol−1; ΔS≠ = 4.8 eu; ΔG≠298 = 20.4 kcal mol−1 for that in pyridine. These results suggested that the ring-opening of 2c to yield a phosphinate occurred and that the process involving the attack of the hydroxy group of this phosphinate to the phosphorus atom from the side opposite of a carbon atom was the rate-determining step. X-ray crystallographic analysis of their symmetric analog 2b was also carried out. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:491–499, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20712

The major studies of my research group in the University of Tokyo (1965–1980) and Hiroshima University (1980–2000) and some related research (2000–2010) are outlined briefly. The following themes are included mostly in chronological order: (1) phosphoranes and nitrosoimines, (2) synthetic work based on heteroaromatic cations and activation of imines, (3) bond switching at hypervalent sulfurane (10-S-3): energy of a hypervalent bond, (4) formation of the hypervalent bond, (5) edge inversion of antimony(III) and bismuth(III) compounds, (6) apicophilicity, pseudorotation, and ligand coupling, (7) freezing pseudorotation of phosphoranes and its effect, (8) hypervalent ate complexes of antimony and bismuth and their transition metal complexes, (9) hypervalent organotellurium compounds, (10) porphyrins of group 15 elements (phosphorus, arsenic, and antimony), and (11) synthesis and structure of hypervalent carbon species (10-C-5 and 12-C-6). © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:207–274, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20726

N-Ethoxycarbonylpyridinium chloride A was generated in solution (CH2Cl2 or CH3CN) from pyridine and ethyl chloroformate and reacted to tri-i-propyl phosphite, RCu·BF3, and silyl enol ethers at 4-position exclusively to afford 1,4-dihydropyridine derivatives containing the corresponding phosphonyl (2), R (6), and 2-oxoalkyl (11) groups in high yields. These were oxidized to the corresponding 4-substituted pyridines by oxygen. Methyl nicotinate was also quaternized by ethyl chloroformate to generate the nicotinium salt Din situ and silyl enol ethers and RCu·BF3 added at 4-position exclusively to give 1,4-dihydronicotinic esters 12, 13 in high yields. N-Methoxy-carbonylquinolinium chloride E was generated in situ and reacted to silyl enol ethers to give a mixture of 2- and 4-adducts. The major adducts 15, 1,2-dihydroquinolines having 2-oxoalkyl group at 2-position, were easily separated by flash column chromatography. Trialkyl phosphite reacted to E at 2-position exclusively to give the corresponding 1,2-dihydroquinoline-2-phosphonate 16, which was alkylated at 4-position exclusively after deprotonation by n-butyllithium. N-Ethoxycarbonyl-isoquinolinium chloride G was also generated in situ and reacted to silyl enol ethers at 1-position exclusively to afford the corresponding 1,2-dihydroisoquinolines 20. 20 was used as a precursor for stereoselective cyclization to benzo[a]qionolizine derivatives. Chromone and coumarin reacted neat with t-BuMe2SiOTf by heating and 4- (I) and 2-(K)-siloxybenzopyrylium salts were prepared. Both salts reacted with conjugated 2-siloxydienes and afforded [4+2] type cycloadducts 32 and 37 in one-pot process. The stereochemistry of annulation was cis for all the cycloadducts and the structure of the cycloadducts is discussed in detail based on 1H NMR.

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).

The present study theoretically investigated hypervalent bonding systems with the skeleton of pentalene. Geometries and energetics were examined by density functional theory calculations with tripl...

A hexacoordinate phosphoranate bearing two Martin ligands and two methyl groups was synthesized by the reaction of the monocyclic phosphorane bearing a hydroxy group with KH, and was crystallized in the presence of 18-crown-6 ether. The crystal structure of the phosphoranate could be regarded as an intermediate model in the reaction of the O-equatorial methylphosphorane with a methyl anion.

The existence of hexacoordinate hypervalent carbon compounds is discovered theoretically. Kohn–Sham orbitals related to three-center four-electron bonds are obtained for a compound, in which two 2,6-bis( p -methylphenyloxymethyl)phenyl groups are bonded to a carbon atom. Estimated bond energies confirm the existence of the hypervalent bond between carbon and oxygen atoms.

A diastereomeric pair of monocyclic apical H-phosphoranes (2-exo and 2-exo) has been prepared from a diastereomeric pair of bicyclic equatorial H-spirophosphoranes (1) with tBuLi. The thermal cyclization reaction of each diastereomeric apical H-phosphorane gave rise to different diastereomeric O-equatorial anti-apicophilic phosphoranes (3-exo and 3-endo, respectively) as single products. On the other hand, the oxidation reaction of each of these apical H-phosphoranes was complementary to the thermal reaction, affording the opposite diastereomeric anti-apicophilic phosphorane (3-endo and 3-exo, respectively) as a single product. The pseudorotation of each of these diastereomeric anti-apicophilic phosphoranes (3-exo and 3-endo) gave rise to different diastereomeric O-apical phosphoranes (4-exo and 4-endo, respectively) as single products.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Several organoboron compounds having a tridentate ligand based on 2,6-bis(p-tolyloxymethyl)benzene (5) were prepared. X-ray crystallography revealed that the distances between the central boron and both oxygen atoms of the tridentate ligand varied from 2.50 A to 3.16 A. The boron atom of the pinacolato derivative (5a) was found to be tricoordinated, whereas those of the diphenyl (5b) and the catecholato derivative (5c) were pentacoordinated, although these molecular structures were unsymmetrical. Compound 5c was found to have the strongest B[sbnd]O interactions among this series because the B[sbnd]O distances of 5c (av. 2.60 A) are shorter than those for 5b (av. 2.65 A), and this could mainly come from the electronic effect of the substituents at the boron atom.

Hypervalent bond (three center-four electron bond: 3c-4e) is the central feature of the structure and reactivity of hypervalent compounds. The SSS bond of thiathiophthene, the so-called no-bond resonance compound, is realized as one of the examples of 3c-4e bond centered at the sulfur atom (10-S-3). A variety of reactions such as cycloaddition-elimination, bond-switching rearrangement, and bond-switching equilibration of sulfur-containing heterocycles are exemplified to proceed through the presence of hypervalent 10-S-3 species. In the transition state of edge inversion, it is predicted that a vacant p-type orbital is perpendicular to the square planar species. Antimony(III) and bismuth(III) compounds bearing a bidentate Martin ligand and a phenyl, or 2-dimethylaminomethylphenyl, or 2,6-bis(dimethylaminomethyl)phenyl group were prepared. The rates of inversion of these compounds at the central atom of Sb or Bi were accelerated significantly by the coordination of the dimethylamino group and also of pyridine from the solvent, where 3c-4e bond is formed by the coordination to stabilize the transition state. Finally, the presence of rapid bond-switching equilibration between NB···N bond of 1,8-bis(dimethylamino)-9-(substituted)borylanthracenes was shown to proceed through 10-B-5 species at the transition state. It is concluded that the bond-switching equilibration takes place as a piston rod in the range of 1.32 A. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:161–175, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20326

The reaction of a chlorophosphorane (9-Cl) with primary amines produced anti-apicophilic spirophosphoranes (5, O-equatorial phosphoranes), which violate the apicophilicity concept, having an apical carbon-equatorial oxygen configuration, along with the ordinarily expected O-apical stereoisomers (6) with the apical oxygen-equatorial carbon configuration. Although the amino group is electronegative in nature, the O-equatorial phosphoranes were found to be stable at room temperature and could still be converted to their more stable O-apical pseudorotamers (6) when they were heated in solution. X-ray analysis implied that this remarkable stability of the O-equatorial isomers could be attributed to the orbital interaction between the lone-pair electrons of the nitrogen atom (n(N)) and the antibonding sigma(P-O) orbital in the equatorial plane. A kinetic study of the isomerization of 5 to 6 and that between diastereomeric O-apical phosphoranes 13b-exo and 13b-endo revealed that 5b bearing an n-propylamino substituent at the central phosphorus atom was found to be less stable than the corresponding isomeric 6b by ca. 7.5 kcal mol(-1). This value was smaller than the difference in energy (11.9 kcal mol(-1)) between the O-equatorial (1b) and the O-apical n-butylphosphorane (2b) by 4.4 kcal mol(-1). This value of 4.4 kcal mol(-1) can be regarded as the stabilization energy induced by the n(N) --sigma(P-O) interaction. The experimentally determined value was in excellent agreement with that derived from density functional theory (DFT) calculations at the B3PW91 level (4.0 kcal mol(-1)) between the nonsubstituted aminophosphoranes (5g is less stable than 6g by 10.1 kcal mol(-1)) and their P-methyl-substituted counterparts (1a is less stable than 2a by 14.1 kcal mol(-1)).

The invitation by the organizing committee of ISOCS-21, which was held in Madrid, July 2004, to address the memorial speech for the late Professor James C. Martin reminded me at once of his gentle and generous character and his great contributions to the chemistry of hypervalent molecules. Although he died in April 1999, I believe that it is still appropriate to do so and also I am heartily honored by the invitation. As a Japanese chemist, I do not know the formal European tradition of the memorial speech, the memoirs consists of two parts, that is, the first part is dedicated to his personal history and the second one describes short history and back ground of the chemistry of hypervalent compounds and is devoted mainly to the accomplishment of J. C. Martin. Here, all the materials I used for the speech are shown accompanied by some short comments.

P–H spirophosphorane 4 bearing two Martin ligands was converted to dianions (5a–n), bearing R groups, with excess organolithium reagents (RLi). Subsequent oxidation with I2 at ambient temperature gave anti-apicophilic (O-cis) spirophosphoranes 2a–n. All anti-apicophilic phosphoranes 2a–n isomerized irreversibly to the O-trans spirophosphoranes 3a–n, respectively. For 2,6-dialkylphenyl derivatives 2k–n, the barrier for pseudorotation between enantiomers 2-RP and 2-Sp was rather high, and thus the interconversion could not be observed on the NMR timescale. The activation parameters for the pseudorotation of the triisopropylphenyl (TIP) derivative 2n to 3n were almost identical with those of nBu derivative 2b to 3b, i.e., ΔH‡ = 21.3 kcal mol–1, ΔS‡ = –9.4 eu. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Monocyclic P-H a p i c a l phosphoranes 10 bearing a ring-opened Martin ligand are formed upon treatment of the P-H e q u a t o r i a l spirophosphorane 7 with more than 2 equiv. of alkyllithium compounds. A ligand-exchange process of these phosphoranes 10 involving the interconversion of the bidentate Martin ligand with the monodentate Martin ligand was found to proceed, probably through a hexacoordinate phosphorus atom. Heating of 10 in nondonating solvents furnished alkylspirophosphoranes 5, whereas heating of 10 in donor solvents led to the formation of anti-apicophilic phosphoranes 6, a new class of phosphoranes in which the less apicophilic carbon substituent occupies an apical position and the more apicophilic oxygen atom occupies an equatorial position. These phosphoranes 6 were found to completely convert into their energetically more stable C e q u a t o r i a l , O a p i c a l stereoisomers 5 upon heating. On the basis of kinetic examinations of the cyclization process of 10, the formation of 6 can be rationalized by the enhanced nucleophilicity of the hydroxy group in the donor solvents. The isomer 5b was estimated to be more stable than 6b (R = nBu) by 12 kcalmol - 1 from kinetic studies on the pseudorotation of 6b to 5b. This is in good agreement with theoretical calculations with analogous 5a and 6a (R = Me), which estimate the difference in energy to be 14.1 kcalmol - 1 .

A variety of hexaorganotellurium compounds, Ar6−n(CH3)nTe [Ar=4-CF3C6H4, n=0 (1 a), n=1 (3 a), n=2 (trans-4 a and cis-4 a), n=3 (mer-5 a), n=4 (trans-6 a); Ph, n=0 (1 b), n=1 (3 b), n=2 (trans-4 b); 4-CH3C6H4, n=0 (1 c), n=1 (3 c), n=2 (trans-4 c), n=4 (trans-6 c); 4-BrC6H4, n=0 (1 d)] and Ar5(R)Te [Ar=4-CF3C6H4, R=4-CH3OC6H4 (8); Ar=4-CF3C6H4, R=vinyl (9), Ar=Ph, R=vinyl (10), Ar=4-CF3C6H4, R=PhSCH2 (11), Ar=Ph, R=PhSCH2 (12), Ar=4-CF3C6H4, R=nBu (13)] and pentaorganotellurium halides, Ar5TeX [Ar=4-CF3C6H4, X=Cl (2 a-Cl), X=Br (2 a-Br); Ar=Ph, X=Cl (2 b-Cl), X=Br (2 b-Br); Ar=4-CH3C6H4, X=Cl (2 c-Cl), X=Br (2 c-Br); Ar=4-BrC6H4, X=Br (2 d-Br)] and (4-CF3C6H4)4(CH3)TeX [X=Cl (trans-7 a-Cl) and X=Br (trans-7 a-Br)] were synthesized by the following methods: 1) one-pot synthesis of 1 a, 2) the reaction of SO2Cl2 or Br2 with Ar5Te−Li+ generated from TeCl4 or TeBr4 with five equivalents of ArLi, 3) reductive cleavage of Ar6−m(CH3)mTe (m=0 or 2) with KC8 followed by treatment with CH3I, 4) valence expansion reaction from low-valent tellurium compounds by treatment with KC8 followed by reaction with CH3I, 5) nucleophilic substitution of Ar6−y−z(CH3)zTeXy−z (X=Cl, Br, OTf; z=0, 1; y=1, 2) with organolithium reagents. The scope and limitations and some details for each method are discussed and electrophilic halogenation of the hexaorganotellurium compounds is also described.

The enantiomers of the first optically active selenurane oxide ever reported, C2-symmetric 3,3,3′,3′-tetramethyl-1,1′-spirobi[3h,2,1]-benzoxaselenole oxide, were isolated via enantioselective liquid chromatography of the racemate or by spontaneous resolution that occurs during the slow evaporation of its acetonitrile solution or the slow crystallization from the same solvent. Chirality 16:598–601, 2004. © 2004 Wiley-Liss, Inc.

Various carbon and boron compounds bearing a 1, 8-disubstituted anthracene skeleton were synthesized and characterized by X-ray analysis. They showed three types of structures based on the kinds of substituents. The first one is symmetrical and is a loose pentacoordinate structure, which has the sp2 carbon or boron atom and the two weak apical interactions. The next one is an unsymmetrical tetracoordinate structure, which has the sp3 central atom. The last one is symmetrical and is a tight pentacoordinate structure, which resulted from the special feature of the fluorine substituents on the boron. The existence of hypervalent interaction was proved by the Atoms In Molecules Theory, experimental electron distribution analysis and a comparison among the structures of tight and loose pentacoordinate species. The synthesis and structures of hypervalent carbon compounds with a 2, 6-bis (aryloxymethyl) benzene ligand are also discussed.

All four diastereomers of β-hydroxy-α,β-diphenylethylspirophosphoranes bearing two Martin ligands were prepared from a P–H (equatorial) spirophosphorane. Treatment of these phosphoranes with t-BuOK or t-BuONa at low temperature (ca. −40°C) led to the formation of stilbene with complete stereospecificity. In half of the cases the reaction proceeded quantitatively, whereas the other half gave rise to retro-aldol reaction with the formation of varying amounts of benzaldehyde and benzylphosphorane. A kinetic examination revealed that of the four the quantitatively proceeding reaction that gives cis-stilbene was the fastest. Based on the experimental observations, a mechanistic rationale for the previously reported Wittig-type reaction of exceptionally high Z-selectivity using an ethoxycarbonylmethylspirophosphorane is presented.

Novel spirophosphoranes (O-cis) that exhibit reversed apicophilicity having an apical carbon−equatorial oxygen array in a five-membered ring showed enhanced reactivity toward nucleophiles such as n-Bu4N+F- or MeLi in comparison with the corresponding stable isomeric spirophosphoranes (O-trans) having an apical oxygen−equatorial carbon configuration. The enhanced reactivity of the O-cis isomer could be explained by the presence of a lower-lying σ*P-O(equatorial) orbital as the reacting orbital in the equatorial plane, whereas the corresponding orbital is a higher-lying σ*P-C(equatorial) in the O-trans isomer. Density functional theory (DFT) calculation on the actual compounds provided theoretical support for this assumption. In addition, we found that the benzylic anion α to the phosphorus atom in O-cis benzyl phosphorane is much more stable than that generated from the corresponding O-trans compounds. The experimental results were considered to be due to the nC → σ*P-O interaction in the O-cis anion, and ...

The enantiomers of a C2-symmetric spirobisalkoxyselenurane, 3,3,3′,3′-tetramethyl-1,1′-spirobi[3H,2,1]-benzoxaselenole, have been isolated for the first time via chromatographic resolution of the racemate using a chiral HPLC column. The isomers were further characterized by 1H NMR and CD spectroscopic measurements.

Antimony-121 Mössbauer spectra for hypervalent pentacoordinate antimony compounds having Sb-transition metal bond [Rf2SbMCp(CO)n {RfH = o-C6H4C(CF3)2OH- , M = Fe, Ru, Cr,Mo, W}, Rf2SbFeCp(CO)PPh3, Rf2SbFeCp(dppe)] and closely related compounds Rf2SbTol (Tol = p-CH3C6H4), Rf2SbX (X = Cl, Br) are described. The strong -donor power of the metal fragments is demonstrated by theM¨ossbauer parameters. The -donor power decreases in the order FeCp(dppe) > FeCp(CO)PPh3 > FeCp(CO)2 > RuCp(CO)2 > CrCp(CO)3 > MoCp(CO)3 > WCp(CO)3 ≫Tol. The essential trends in the molecular structure and the Berry pseudorotation are interpreted by this order. In addition, the e2qQ values for 32 hypervalent antimony compounds are successfully calculated using the additivity model for the e2qQ value. A unique electronic feature for Rf2SbX is clarified through the calculation

Solution and crystal structures of monocyclic pentacoordinate phosphoranes bearing two Martin ligands and two carbon substituents are described. When the two carbon substituents are different, relative apicophilicity of the two monodentate carbon substituents could be determined based on the equilibrium ratio of the pseudorotamers. In some cases, x-ray structural analysis could be carried out and the crystallized structure from CH 3 CN is consistent with the major pseudorotamer in solution (CD 3 CN). Furthermore, when the equilibrium ratio of pseudorotamers is almost unity, novel cocrystallization of two pseudorotamers in a single crystal was observed.

Effect of † * P--O orbital of C-apical O-equatorial (O-cis) spirophosphorane was investigated both experimentally and theoretically. O-cis phosphoranes revealed to be much more electrophilic on the phosphorus atom than O-trans isomers by experimental studies. Theoretically, the energy of the † * P--O orbital of O-cis phosphorane was calculated to be lower than that of the † * P--C orbital of O-trans phosphorane by 18.7 kcal/mol, and the result supports the enhanced electrophilicity of O-cis spirophosphoranes compared with O-trans isomer.

The electrochemistry of nine arsenic(V) octaethylporphyrins is reported in benzonitrile or dichloromethane containing 0.1 M tetra-n-butylammonium perchlorate as supporting electrolyte and the results compared to data for phosphorus and antimony porphyrins containing a similar set of σ-bonded and/or anionic axial ligands. The investigated compounds are divided into three groups based on the nature of the axial ligands and are represented as [( OEP ) As ( R )( R ')]+ (group I), [( OEP ) As ( R )( X )]+ (group II) and [( OEP ) As ( F )2]+ (group III) where R and R’ = CH 3 or C 2 H 5, X = OH −, OCH 3−, OC 2 H 5−, OC 3 H 7− or NHC 4 H 9− and OEP = the dianion of octaethylporphyrin. Each compound was characterized in its neutral, oxidized and reduced form by UV-visible and ESR spectroscopy. An X-ray crystallographic analysis of [( OEP ) As ( F )2]+ PF 6−, [( OEP ) As ( CH 3)( OCH 3)]+ ClO 4− and [( OEP ) As ( C 2 H 5)2]+ PF 6− is also presented.

The regioselective and stereospecific intramolecular ring closure reactions of o-ethynylbenzyl tellurols 5A and o-ethynylbenzyl selenols 5B, which were readily generated by the reaction of the o-ethynylbenzyl bromides 4 with sodium hydrogen telluride (NaHTe) or sodium hydrogen selenide (NaHSe), produced the isotellurochromenes 6A and isoselenochromenes 6B together with (Z)-1-methylidene-2-telluraindans 7A and (Z)-1-methylidene-2-selenaindans 7B, respectively. The obtained isochromenes 6A and 6B were transformed into the corresponding 2-benzotelluropyrylium tetrafluoroborates 9A and 2-benzoselenopyrylium tetrafluoroborates 9B by treatment with triphenylcarbenium tetrafluoroborate (Ph3C+BF4−) in excellent yields, respectively. An X-ray structural analysis of the tert-butyl derivatives 9Ac and 9Bc is also described.

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.

By freezing Berry pseudorotation of spirophosphoranes with recourse to the rigidity of the Martin bidentate ligand, we successfully prepared configurationally stable enantiomeric pairs of optically active phosphoranes, and could isolate “anti-apicophilic” C-apical O-equatorial (O-cis) phosphoranes. The effect of σ*PO orbital of the O-cis phosphorane was investigated both experimentally and theoretically. O-cis phosphoranes were revealed to be much more electrophilic at the phosphorus atom than O-trans isomers by experimental studies. The acidity of the α-proton of an O-cis benzylphosphorane was found to be higher than that of the corresponding O-trans isomer. By the reaction of the α-carbanion of an O-cis benzylphosphorane with PhCHO, we succeeded in the first isolation and full structural characterization of a 12-P-6 phosphate bearing an oxaphosphetane ring, the intermediate in the Wittig type reaction using a 10-P-5 phosphorane. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:390–396, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10072

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 Buchwald's 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).

Hypervalent 10-Sn-5 allyl and crotyl tin ate complexes bearing Martin ligands were prepared and found to be surprisingly stable in water. These compounds were found to react with aldehydes in the presence of weak Lewis acids such as LiBr to give the corresponding homoallyl alcohols. Product analysis of the reaction of the crotyl compounds indicated that the reaction occurred via a cyclic transition state unlike an acyclic transition state operative for widely utilized allyltrialkyltin reagents that are of ordinary valency. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:425–430, 2001

The reaction of pentaphenyltellurium chloride 2 with silver perchlorate afforded the pentaphenyltelluronium salt, Ph5Te+ClO, (1b), and treatment of 2 with silver triflate and sodium tetrakis{3,5-bis(trifluoromethyl)phenyl}borate provided Ph5Te+[3,5-(CF3)2C6H3]4B− (1c), which were isolated as stable yellow solids. X-ray crystallographic analyses of the hypervalent telluronium salts revealed square-pyramidal geometry around the tellurium, which are rare examples for penta-substituted main group element compounds. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:380–384, 2001

[(Por)M(R)(OOR′)]+Y− (Por: TPP [tetraphenylporphyrin], OEP [octaethylporphyrin]; M: Sb, As, P; R: Me, Et, Ph; R′: H, C(=O)m-ClC6H4, t-Bu) were prepared from [(Por)M(R)(X)]+Y− (X: OTf, Br). The reactivities of the peroxide porphyrins toward nucleophiles such as triphenylphosphine increased in the order of -OOt-Bu, m-CPBA, and -OOH derivatives. Phosphorus (P-OOH) and arsenic hydroperoxide (As-OOH) were much more reactive than the corresponding antimony hydroperoxide (Sb-OOH). The higher reactivity of phosphorus and arsenic peroxides can be explained by the stability of the M=O (M=P, As) bonding system in the intermediates of the oxidation reactions. An X-ray structural analysis of [(TPP)Sb-(Me)(OOt-Bu)]+PF6− is presented. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:431–443, 2001

Diastereomeric pentacoordinate hypervalent stiboranes with an Sb−Fe bond {4a and 4b: RfRfm*Sb*FeCp(CO)2 {Rf = o-C6H4C(CF3)2O-, Rfm* = o-C6H4C*(CF3)(Me)O-} were synthesized by the reaction of stiboranide anion, RfRfm*Sb*-Li+ (3-Li), with CpFeI(CO)2 in the presence of AgBF4. The carbonyl group of 4 was replaced with triphenylphosphine by irradiation with a tungten lamp to give a mixture of four diastereomers {5a−5d: RfRfm*Sb*Fe*Cp(CO)(PPh3)}. Each of the diastereomers was separated by TLC, and the relative stereochemistry was determined by X-ray crystallographic analysis. The thermal equilibration from the pure diastereomer of 5 indicated that the isomerization took place through inversion (pseudorotation) at the central antimony atom. The pseudorotational barriers of 5 were much higher than those of Rf2Sb*Cl and RfRfm*Sb*(p-CH3C6H4). These results are consistent with the electron-donating properties of the group 8 transition metal fragment. Hypervalent stiboranes {6, Rf2Sb*Fe*Cp(CO)(PMe3); 7, Rf2Sb*Fe*Cp...

Hypervalent pentacoordinate stiboranes with an Sb−group 6 element bond [Rf2Sb*MCp(CO)3 {Rf = o-C6H4C(CF3)2O-, M = Cr (2), Mo (3), W (4)}] were synthesized by the reaction of Rf2Sb*-Li+ (1-Li) with [CpM(CO)3]+BF4-. X-ray crystallographic analysis of 2−4 showed that the geometry about the antimony atom is a distorted TBP structure with the CpM(CO)3 fragment at the equatorial site of the TBP. Diastereomeric antimony compounds RfRfm*Sb*MCp(CO)3 {Rfm* = o-C6H4C*(CF3)(Me)O-, M = Cr (10a,b), Mo (11a,b), W (12a,b)} were synthesized by similar procedures. Each of the diastereomers could be separated by flash column chromatography, and the relative stereochemistry was determined by X-ray analysis. The pseudorotational barrier of 11a at the central antimony atom was found to be very high (31.3 kcal/mol at 110 °C), showing the strong equatophilicity of the Mo fragment.

A variety of Group 15 element porphyrins bearing element–carbon bond(s) were synthesized mainly by use of R 3 Al as an alkylating reagent. The synthetic methods, X-ray crystallographic structures, some spectral data ( 1 H-NMR), and some reactions of the porphyrins were surveyed. One of the most important properties of these compounds is the formation of the element–oxygen double bond in the phosphorus and arsenic porphyrins. The bond formation was confirmed by X-ray crystallographic analysis of (OEP)P(Et)(O). The PO bond length of [(OEP)P(Et)(OH)] + Cl − and (OEP)P(Et)(O) was 1.636(4) and 1.484(9) A, respectively (cf. PO bond length of Ph 3 PO is 1.483 A). Since (OEP)P(Et)(O) was stabilized by the formation of the PO bond, the OH proton of [(OEP)PEt(OH)] + Cl − was acidic (p K a ca. 7–8). Although the similar formation of the double bond was not observed in the corresponding antimony compounds, the corresponding AsO formation was observed in newly synthesized (OEP)As(R)(O). The relatively high acidity of the OH protons in [(OEP)M(R)(OH)] + X − (M=P, As) {and the stability of the (OEP)M(R)(O)} would be the main reason for the relatively high reactivity of phosphorus and arsenic porphyrins, [(OEP)M(R)(OH)] + X − , toward (OEP)Al(Me) to give μ-oxobridged dinuclear porphyrins and the high reactivity of phosphorus and arsenic porphyrins bearing a OOH group toward triphenylphosphine. In addition, X-ray analysis of a variety of phosphorus(V), arsenic(V), antimony(V) octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) derivatives showed the effect of the axial ligand(s) on the distortion of the porphyrin core from the plane.

The synthesis of (S,S)-1,2-bis(3,5-di-tert-butylphenyl)ethane-1,2-diol (98.6% ee), which should be useful as a chiral ligand of catalysts in asymmetric inductions, is described.

A new Rh(III) complex bearing a hypervalent phosphorus(V) ligand, Rf 2 PRh(Cp*)Cl ( 4 ) (Rf=Martin ligand; o -C 6 H 4 C(CF 3 ) 2 O), was obtained by the reaction of Rf 2 P − Li + generated in situ with [Cp*RhCl 2 ] 2 . X-ray structural analysis of 4 showed that the hypervalent phosphorus ligand Rf 2 P acted as a bidentate ligand coordinating to the Rh center through the phosphorus and one oxygen atom of a Martin ligand. The Rh center became coordinatively saturated and was stabilized by the additional coordination of the oxygen atom. However, in solution the equilibrium between the bidentate ( 4A ) and the monodentate ( 4B ) species was observed ( 4A : 4B =6:1 in C 6 H 6 , 4:1 in CHCl 3 , 2:1 in THF, 1.6:1 in CH 2 Cl 2 ), and the monodentate species 4B became predominant in polar solvents ( 4A : 4B =1:2 in CH 3 CN, 1:2.5 in CH 3 NO 2 , 1:3 in DMSO). Therefore, the strong Lewis acidic Rh center can be regarded as masked in the solid state but in solution it becomes unmasked to 4B , in which a solvent is coordinating to the Rh center.

The following nine unsymmetrically axially substituted antimony(V) tetraphenylporphyrins with an antimony–carbon bond or an antimony–fluorine bond were synthesized: [(TPP)Sb(Me)(OEt)]+ClO4− (1-ClO4), [(TPP)Sb(Me)(OC6H4CH3-p)]+ClO4− (2-ClO4), [(TPP)Sb(Me)(SC6H4CH3-p)]+ClO4− (3-ClO4), [(TPP)Sb(Me)(NHC6H4CH3-p)]+ClO4− (4-ClO4), [(TPP)Sb(Me)(NHCH2C6H5)]+ClO4− (5-ClO4), [(TPP)Sb(Me)(OC(=O)C6H4Cl-m)]+PF6− (6-PF6), [(TPP)Sb(Me)(Et)]+PF6− (7-PF6), [(TPP)Sb(Me)(CH2CHMe2)]+PF6− (8-PF6), and [(TPP)Sb(F)(OH)]+ClO4− (9-ClO4). All nine compounds were stable towards atmospheric moisture. X-Ray crystallographic analysis of 6-PF6 revealed that the antimony atom lies at 0.182 A out-of-plane of the four nitrogens (Δ4N) toward the carbon atom; 6-PF6: space group P21/n, a = 25.49(2), b = 11.27(1), c = 16.58(1) A, β = 96.74(5)°, R = 0.064.

Anti-apicophilic pseudorotamers bearing a Martin ligand with equatorial-O and apical-C, that isO-cis isomer, were prepared selectively. Kinetic study of BPR of O-cis isomer to O-trans isomer is discussed.

Te(C6H4-4-CF3)6 1a was obtained by the unique one-pot reaction of LiC6H4-4-CF3 with TeCl4, where oxidation of Te(IV) to Te(VI) occurred. Compound 1a is extremely thermally stable and not light sensitive unlike tetraorganotellurium compounds. Thermolysis and some reactions of 1a are described. ClTe(C6H4-4-CF3)5, synthesized by chlorination of LiTe(C6H4-4-CF3)5, reacted with LiC6H4-4-CF3 to give 1a. Bond dissociation energies of Te(CH3)n (n = 2, 4, 6) were calculated in order to explain the stability of Te(VI) compounds.

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.

Deprotonation of PH spirophosphorane 4 bearing Martin ligands with n -BuLi followed by reaction with trans -stilbene oxide gave a pair of anti - β -hydroxy-α,β-diphenylethylspirophosphoranes 5-S P ∗ R ∗ S ∗ and 5-S P ∗ S ∗ R ∗ , whereas treatment with cis -stilbene oxide yielded syn - β -hydroxy-α,β-diphenylethylspirophosphoranes 5-S P ∗ S ∗ S ∗ . The remaining diastereomer 5-S P ∗ R ∗ R ∗ was obtained selectively by α-benzoylation of benzylspirophosphorane 3 followed by reduction with LiBH 4 . Deprotonation of the diastereomers with t -BuOK or t -BuONa lead to the stereospecific formation of stilbenes. The anti diastereomers gave cis -stilbene ( Z : E =99:1) and the syn diastereomers furnished trans -stilbene ( Z : E =1:99).