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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

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)

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)).

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.

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 ...

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 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).

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.

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).

The stereomutation barriers of diastereomeric spirophosphoranes, [o- O(CF 3 )(CH 3 )C ∗ C 6 H 4 ][o- O(CF 3 ) 2 C 6 H 4 ] P ∗ X (X=OMe, SMe) were determined to be high enough to freeze the mutation at ambient temperatures [ ΔG ≠ (298K)=25.0, 30.4 kcal mol −1 ; respectively]. The nucleophilic substitution reaction of SMe compounds with alkyllithium reagents resulted in inversion of configuration, whereas that of OMe compounds gave various ratios of inversion and retention products depending on the stereochemistry of the diastereomeric reactant phosphoranes and solvent. However, the use of OCH 2 CH 2 NMe 2 as substituent lead to almost exclusive formation of the retention product regardless of these conditions.

Trans-2,6-disubstituted-4-piperidones were synthesized by [4+2]type cycloaddition of chiral aldimines (5) with 2-silyloxy-1,3-butadiene (3) in the presence of Lewis acids. In the cycloaddition, only two 2,6-trans isomers (chelation and nonchelation products) were observed and no cis compounds were detected regardless of the Lewis acid used. Chelation-controlled products 6b, 8b, and 9b were obtained selectively by the use of TiCl4-i-PrCN and 6a was obtained with high selectivity when TMSOTf or Zn(OTf)2 was used as a Lewis acid at 4°C. The scope of the reaction is also described.

Mechanism of ligand coupling reaction (LCR) of hypervalent pentaarylantimony compounds was investigated in benzene and in vapor phase (flash vacuum thermolysis). All the experimental results could be interpreted consistently by the idea invoking that the apical-apical coupling is the sole reaction path in the presence of stereoisomers which are inevitably generated by very fast Berry pseudorotation (BPR). In order to obtain the above conclusion, the following experiments were carried out carefully: i) synthetic methods of pure mixed pentaarylantimony compounds were developed. ii) the structures of all T~lg-~SbAr, were determined as TBP by X-ray analysis and were investigated in solution by using 13C-chemical shifts of ipso-carbons of To1 and Ar groups. iii) ligand exchange (LE) was found to take place in benzene at 60 "C before any LCR started and relative stability (Si) of all the compounds was determined. iv) products of LCR in solution and in vapor phase were determined quantitatively. Ab initio calculation for LCR of SbH5 is also described.

Diastereomeric phosphoranes (o-OC(CF3)2C6H4)2P*CH2CO2-(−)-menthyl (3-RP and 3-SP) of which absolute stereochemistry was determined were treated with LiAlH4 to give (o-OC(CF3)2C6H4)2P*CH2CH2OH (4-RP and 4-SP) as the first optically active pair of enantiomeric phosphoranes of rigid stereochemistry with asymmetry only upon the pentacoordinate phosphorus atom. The high enantiomeric purities of the alcohols were confirmed by converting them to their (+)-MTPA esters. Furthermore, when diastereomeric phosphoranes (o-OC(CF3)2C6H4)2P*CH2NHC*HCH3Ph (10-RP and 10-SP) of which absolute stereochemistry was also determined were treated with MeLi the first optically active pair of enantiomeric P–H phosphoranes (o-OC(CF3)2C6H4)2P*H (2-RP and 2-SP) with asymmetry only upon the pentacoordinate phosphorus atom could be obtained. The high enantiomeric purities of the P–H phosphoranes were confirmed by converting each of them to their corresponding (−)-menthyl esters 3-RP and 3-SP.

The permutation of [o- OC ∗ (CH 3 )(CF 3 )C 6 H 4 ][o- OC(CF 3 ) 2 C 6 H 4 ]PH was found to be a non-dissociative process with activation parameters of ΔH≠=ca.24.5 kcal mol−1 and ΔS≠=ca.−4 eu. The reaction of its conjugate base, phosphoranide [o- OC ∗ (CH 3 )(CF 3 )C 6 H 4 ][o- OC(CF 3 ) 2 C 6 H 4 ]P − , with ethyl chloroacetate was found to proceed with full retention of configuration.

By treating diastereomeric [o-OC(CF3)2C6H4]2PCH2CO2(−)menthyl] (2-(R)P and 2-(S)P) with LiAlH4, a pair of enantiomerically pure phosphoranes, [o-OC(CF3)2C6H4]2PCH2C2HOH (3-(R)P and 3-(S)P), having asymmetry only at phosphorus were obtained.

The crystal and molecular structures of [2-(2-methoxy-2-propyl)phenyl-C ~](2-phenyl-2-propanolatoC,O)bismuth (I), [2-(2-hydroxy-2-propylphenyl-CI)](2-phenyl-2-propanolato-C~,O)bismuth (II) and tetraethylammonium bis(2-phenyl-2-hexafluoropropanolato-C~,O)bismuthate monohydrate (III) were determined by the X-ray method. Crystal data: (I), [Bi(CI9H2302)], Mr = 492.37, monoclinic, P21/n, a = 11.635 (3), b = 8.837 (2), c= 18.149 (4) A,, /3 = 103.17(3) ° , V= 1817.0(7)A 3, Z=4, Dx = 1.800 Mg m -3, a(Mo Ka) = 0.71069 A,, # = 9.680 mm-~, F(000) = 944, T = 298 K, R = 0.046, wR=0.061 for 3033 observed reflections. (II), [Bi(CtsH2102)], Mr = 478.34, monoclinic, C2/c, a = 19.902 (4), b = 18.353 (2), c = 17.303 (2) A,, /3 = 109.69(2) °, V=5951(1) A, 3, Z=12, Dx=1.602, Dm= 1.663 Mg m -3, ,~(Mo Ka) = 0.71069 A,, /z = 8.865 mm-i, F(000) = 2736, T= 298 K, R = 0.070, wR=0.096 for 3609 observed reflections. (III), [N(C2Hs)4][Bi(C,sH8F,202)].H20, Mr = 841.49, monoclinic, P21/n, a = 15.547 (2), b = 15.900 (2), c = 11.996.(2) A,, /3 = 90.19 (2) °, V = 2965.4 (8) A 3, Z = 4, Dx = 1.885, Dm = 1.896Mgm --3, A(MoKa)=

The mechanism we propose for the cyclopentane annulation is the following one. The allylic reagent (5D) attacks the siloxypyrylium salts (2a,b) at the C2 position, giving the intermediate carbocation (B) which is stabilized by the trimethylsilyl and the methyl group. Attack by the emerging enolate at C 3 , forms the five-membered ring compound (8a,b). Generally, electrophiles attack allylic silanes anti to the silyl group. Since there is undoubtedly interaction with the silicon in the transition state, the stereochemistry of the bridged intermediate (B) should be trans geometry due to stereoelectronic effect and allylic 1,3-strain. In the reaction of 2a, the favored pathway is cyclization. However, competition between cyclization and desilylation was observed in 2b due to steric hindrance between the two methyl groups at the step of cyclization

The anionic 10-Bi-4 species ( 2a , 2b ) were synthesized by the reaction of BiCl 3 with 2 equiv of lithium 2-(2-lithiophenyl)-2-propoxide derivatives ( 1a , 1b ). The X-ray crystallographic analysis showed 2a- Et 4 N + to be distorted pseudotrigonal bipyramid in geometry. Reaction of dimethyl-substituted 2b- Li + with methyl iodide took place exclusively not at the bismuth but at the oxygen to give an ether 4 .

A series of 10-S-3 type sulfuranes, tetraazathiapentalenes (10a-i, 11a-f, 12, and 17) fused with pyrimidine ring and/or pyridine ring, were prepared by oxidation of the corresponding thioureas. The restricted internal rotation of the pyrimidine ring was observed by temperature dependent 1H NMR spectrum which gave the kinetic parameters of ΔG298_??_=16.6kcal/mol, ΔH=15.9kcal/mol, and ΔS_??_=-2.4 eu at 25°C for the rotational barrier in 10a. The substituent effect to the kinetic data can be reasonably explained in terms of electronic balance of the N-S-N hypervalent bond or the different degree of contribution of resonance canonical structures. Comparison of the rotational barrier of 10a with that of model compounds (18 and 24) suggests that hypervalent N-S-N stabilization in 10a is more than 6kcal/mol. Methylation of these 10-S-3 type sulfuranes (10a, 10d, and 11a) was investigated to clarify the electronic effect in these molecules. The crystal structure of the neutral symmetric sulfurane 10a reveals to be a planar molecule in which the sulfur atom was found to be in the same plane of the two pyrimidine rings. The S-N bond lengths 1.948(3) and 1.938(3) A are longer than the sum of the covalent bond radii, consistent with a bond order less than unity. The crystal structures of the dicationic symmetric sulfurane 17 and the unsymmetrical sulfurane 11a also show to be planar molecules. The S-N distances in 11a were different each other due to the electronic imbalance between the apical ligands. Semi-empirical calculation (AM 1) of these systems (10a and 17) indicate the expected electronic features of the hypervalent molecules (10-S-3 sulfuranes) and the small contribution of π-overlapping in the N-S-N bonds.

A series of neutral (8−10), monomethylated (12−14), and dimethylated (17) 10-S-3 sulfuranes, derivatives of tetraazathiapentalenes fused with pyrimidine and/or pyridine ring, were prepared. These molecules are planar, and bond energies of the hypervalent N−S−N bond were evaluated by the temperature dependent restricted rotation of the pyrimidine ring caused by cleavage of one of the S−N bonds. The bond length is longer, and the energy is lower for the S−N bond fused with more electron-withdrawing heterocycles.

Te(C6H4-4-CF3)61a was obtained by the unique one-pot reaction of LiC6H4-4-CF3 with TeCl4. The Te atom resides in the highest oxidation state (TeVI) having six C Te bonds in 1a. Compound 1a is extremely thermally stable and not light sensitive unlike tetraorganotellurium compounds. The X-ray crystallographic analysis of 1a revealed a rare example of approximately Th molecular symmetry.

A 10-Sb-4 type organoantimony ate complex was prepared from hexafluorocumyl alcohol and SbCl3 as an air and water stable compound. Its X-ray structural analysis revealed a distorted pseudo-trigonal bipyamidal structure. The compound reacted with both alkyl halides and organolithium reagents to yield neutral 10-Sb-5 compounds.

Stable anionic 10-Sn-51) species, tetraalkylammonium bis[α,α-bis(trifluoromethyl)benzenemethanolato(2−)-C2,O]alkylstannates(1−) [2a (R = Ph), 2b (R = p-CH3C6H4), 2c (R = n-Bu), and 2d (R = Me)], were prepared. Reaction of 2a and 2b with sulfuryl chloride gave chlorostannate (3a), which could be converted to fluorostannate (3b). 3a and 3b reacted with organolithium reagents to give 2. The X-ray crystallographic analysis of 3b-n-Bu4N+ revealed a distorted trigonal bipyramidal structure.

New title dibenzobicyclic stiboranes and related phosphoranes were prepared by means of tridentate 2,2′-diphenolamines. Coordination number of the central pnictogen atoms (Sb and P) changed from three into five during the reaction.

Symmetrical 10-S-3 sulfuranes ( 1a - c ) fused with two pyrimidine rings and their unsymmetrically substituted ones ( 1d , e ) were synthesized by oxidation of the corresponding thioureas. Substituent effect on the kinetic data of the restricted rotation was explained in terms of the balance of electron-withdrawing ability of the ligand in the NSN hypervalent bond.

X-ray analysis of bis(p-fluorophenyl)methyl cation bearing a 2,6-bis(p-tolyloxymethyl)benzene ligand showed a symmetrical structure (10-C-5) where the two C-O distances are identical, although the distance (2.690(4) A) is longer than those (2.43(1) and 2.45(1) A) of 1,8-dimethoxy-9-dimethoxymethylanthracene monocation, which was recently reported by us. However, X-ray analysis of the more stable aromatic xanthylium cation with the same benzene ligand showed the tetracoordinate carbon structure where only one of the two oxygen ligands is coordinated with the central carbon atom. These results clearly indicate that the carbocations (10-C-5) bearing the sterically flexible benzene ligand were quite sensitive to the electronic effect on the central carbon atom. The electron distribution analysis by accurate X-ray measurements and the density functional calculation on the initially mentioned bis(p-fluorophenyl)methyl cation clearly show that the central carbon atom and the two oxygen atoms are bonded even if the bond is weak and ionic based on the small value of the electron density (rho(r)) and the small positive Laplacian value (nabla(2)rho(r)) at the bond critical points.

Pentacoordinate and tetracoordinate carbon and boron compounds (27, 38, 50-52, 56-61) bearing an anthracene skeleton with two oxygen or nitrogen atoms at the 1,8-positions were synthesized by the use of four newly synthesized tridentate ligand precursors. Several carbon and boron compounds were characterized by X-ray crystallographic analysis, showing that compounds 27, 56-59 bearing an oxygen-donating anthracene skeleton had a trigonal bipyramidal (TBP) pentacoordinate structure with relatively long apical distances (ca. 2.38-2.46 A). Despite the relatively long apical distances, DFT calculation of carbon species 27 and boron species 56 and experimental accurate X-ray electron density distribution analysis of 56 supported the existence of the apical hypervalent bond even though the nature of the hypervalent interaction between the central carbon (or boron) and the donating oxygen atom was relatively weak and ionic. On the other hand, X-ray analysis of compounds 50-52 bearing a nitrogen-donating anthracene skeleton showed unsymmetrical tetracoordinate carbon or boron atom with coordination by only one of the two nitrogen-donating groups. It is interesting to note that, with an oxygen-donating skeleton, the compound 61 having two chlorine atoms on the central boron atom showed a tetracoordinate structure, although the corresponding compound 60 with two fluorine atoms showed a pentacoordinate structure. The B-O distances (av 2.29 A) in 60 were relatively short in comparison with those (av 2.44 A) in 59 having two methoxy groups on the central boron atom, indicating that the B-O interaction became stronger due to the electron-withdrawing nature of the fluorine atoms.

A variety of phosphorus(V) octaethylporphyrin derivatives of the type [P(OEP)(X)(Y)](+)Z(-) (OEP: octaethylporphyrin) (X = CH(3), CH(2)CH(3), C(6)H(5), F; Y = CH(3), CH(2)CH(3), OH, OCH(3), OCH(2)CH(3), On-Pr, Oi-Pr, Osec-Bu, NHBu, NEt(2), Cl, F, O(-); Z = ClO(4), PF(6)) were prepared. X-ray crystallographic analysis of eleven compounds reveals that the degree of ruffling of the porphyrin core becomes greater and the average P-N bond distance becomes shorter as the axial ligands become more electronegative. Therefore, the electronic effect of the axial substituents plays a major role in determining the degree of ruffling although the steric effect of the substituents plays some role. A comparison of the (1)H NMR chemical shifts for the series of [P(OEP)(CH(2)CH(3))(Y)](+)Z(-) complexes with those of the corresponding arsenic porphyrins, which possess a planar core, indicates a much smaller ring current effect of the porphyrin core in the severely ruffled phosphorus porphyrins. The electrochemistry, spectroelectrochemistry and ESR spectroscopy of the singly reduced compounds are also discussed. The OH protons of [P(OEP)(X)(OH)](+) are acidic enough to generate P(OEP)(X)(O) by treatment with aq dilute NaOH. X-ray analysis of P(OEP)(CH(2)CH(3))(O) reveals that the PO bond length is very short (1.475(7) A) and is comparable to that in triphenylphosphine oxide (1.483 A). The features of the quite unique hexacoordinate hypervalent compounds are investigated by density functional calculation of a model (Por)P(CH(2)CH(3))(O) and (Por)P(F)(O) (Por: unsubstituted porphyrin).

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.