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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.

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 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)).

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 ...

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 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.

[see reaction]. Mild and highly selective one-pot procedures for obtaining phosphoranes that exhibit reversed (O-cis) apicophilicity are described. On the basis of the procedures, O-cis phosphorane bearing an aryl group (R = 2,4,6-tri-i-propylphenyl) could be isolated for the first time; the procedure is also applicable for alkyl derivatives. Particularly effective was the use of I2 as an oxidizing reagent.

A novel family of organochalcogens, Ph5TeX (X = Cl, Br), was readily obtained by the halogenation of Ph5TeLi, which was prepared by reaction of 5 equiv of PhLi with 1 equiv of TeCl4 or TeBr4; Ph5Te...

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

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. Copyright © 2008 American Chemical Society.

The oxidized octaethyltetraphenylporphyrin (1, OETPP) and the corresponding newly prepared octaisobutyltetraphenylporphyrin (3, OisoBuTPP) could be isolated from the reaction of OETPPLi2 (or OisoBuTPPLi2) with SOCl2. The X-ray analysis and the characteristic UV-vis spectra of 1 and 3 revealed that these are the first examples of 16 pi nonaromatic porphyrins.

An anti-apicophilic phosphorane bearing an oxaphosphetane ring, in which the ring carbon is apical and the ring oxygen is equatorial (C-apical), has been prepared as a thermally less stable stereoisomer of a phosphorane with an ordinary equatorial carbon-apical oxygen array in the oxaphosphetane ring (O-apical). This novel C-apical phosphorane, which could be considered to be a model compound of the reactive intermediate in the Wittig reaction, was fully characterized by NMR and X-ray structural analysis. The compound was found to easily isomerize to its more stable O-apical isomer, especially in the presence of proton sources, and the latter O-apical compound was found to furnish olefin at elevated temperatures.

Synthese des nicotinates du titre substitues en 1 par R (R=alcoxycarbonyl, acetyl ou dimethylcarbamoyl) par action d'enol ethers de silicium sur des chlorures de R-1 methoxycarbonyl-3 pyridiniums; leur addition de Diels Alder conduit (apres desulfonylation) aux R-1 dichloro-6,8 dihydro-1,4 oxo-2' alkyl-4 quinoleinecarboxylates-3. Stereochimie