Naokazu Kano

The first hypervalent compounds bearing both a pentacoordinate silicon atom and a pentacoordinate phosphorus atom were synthesized by the cooperative three. component reaction of a phosphoranide a silane, and THF.

The first hypervalent compounds containing both a pentacoordinated silicon atom and a pentacoordinated phosphorus atom were synthesized by the cooperative three-component reaction of a phosphoranide, a silane, and THF accompanying the ring opening of THF, or by the nucleophilic addition of phosphoranylalkoxides to a silane. Hydrolysis of the phosphoranyloxysilicate and phosphoranylalkoxysilicates gave the hydroxysilicate and the corresponding phosphoranes.

A pentacoordinate (E,E)-1,1,3,3-tetrahydrodisiloxane bearing two azo groups gave hydrazobenzene in the fluoride ion-induced hydrolysis involving hydrosilylation of the azo groups followed by cleavage of the Si-C bonds, while a tetracoordinate (E,E)-forms formed by its photoirradiation gave an octaarylsilsesquioxane without cleavage of the Si-C bonds. (c) 2007 Elsevier Ltd. All rights reserved.

A boron-substituted azobenzene, (E)-[2-(4-methoxyphenylazo)phenyl] bis(pentafluorophenyl) borane, presented the most intense fluorescence among the azobenzene derivatives.

Pentacoordinate allylsilanes bearing an azobenzene moiety were synthesized and their structures were elucidated. The reaction of allyldifluorosilane (E)-7a with BF3 center dot OEt2 did not proceed, but (E)-7a was allowed to react with a fluoride ion to give tetrafluorosilicate 8a via intramolecular allyl-migration from the silicon atom onto the azo group. Activation of both the nucleophilic and electrophilic parts by the Si center dot center dot center dot N interaction was found to be important for promotion of the allyl-migration reaction. The azobenzene moiety of the allylsilane was reversibly isomerized by photoirradiation. The (Z)-7a formed by photoirradiation of (E)-7a is in a tetracoordinate state in contrast to the (E)-7a, and it did not react with a fluoride ion at all under the conditions where (E)-7a reacted quantitatively. The reactivity was successfully controlled without changing any conditions other than the change of the coordination number of the silicon atom induced by photoirradiation. (c) 2006 Elsevier B.V. All rights reserved.

Thermolysis of a pentacoordinate 1 lambda(6),2-thiazetidine, which was synthesized for the first time and characterized by X-ray crystallographic analysis, gave the corresponding aziridine and a cyclic sulfinate almost quantitatively. The potential intermediacy of a 1 lambda(6),2-thiazetidine was suggested in the aza-Corey-Chaykovsky reaction.

Hydrazobenzenes 3-5 bearing a chalcogenophosphoryl group were synthesized by palladium-catalyzed cross-coupling reactions. Their X-ray crystallographic analyses and NMR and IR spectra showed the presence of intramolecular hydrogen bonds between the N-H protons and the chalcogenophosphoryl groups. The intermolecular hydrogen bonds in phosphine oxide 3 and selenide 5 were observed in the solid state. Phosphine oxide 3, sulfide 4, and selenide 5 constructed a dimeric structure, a discrete monomeric structure, and a chain structure, respectively. As the chalcogen atom changed, the crystalline structures of the 2-chalcogenophosphorylhydrazobenzenes also changed. The hydrogen bonds affected the oxidation reactions of the hydrazobenzenes, and oxidation of hydrazobenzenes bearing a lighter chalcogen atom was more difficult. For azobenzenes bearing a chalcogenophosphoryl group, X-ray crystallographic analyses and NMR spectra showed little interaction between the azo group and the chalcogenophosphoryl groups. However, in the UV-vis spectra, the red shifts of the absorption maxima due to the n -> pi(*) transitions indicated intramolecular interactions in the excited state, in contrast to the corresponding 4-substituted azobenzenes. In addition, photoirradiation of phosphine oxide (E)-7 gave (Z)-7, whereas that of phosphine sulfide (E)-8 and phosphine selenide (E)-9 did not give (Z)-8 and (Z)-9, suggesting that heavy chalcogen atoms quench excited states by through-space interactions. Introduction of a chalcogenophosphoryl group at the 2-position had a significant effect on the structure, spectral properties, and reactivity of hydrazobenzenes and azobenzenes. Although azobenzene (E)-10 bearing a hydroxyphosphoryl group at the 2-position did not show hydrogen bonding in the crystalline state, its optical properties and photoisomerization ratio were different from those of (E)-7.

The synthesis, reactivity, and bonding properties of several pentacoordinate P-phenyl- substituted 1H-phosphirenes are discussed. X-ray crystallographic analysis of one of them reveals a highly distorted square pyramidal (SP) arrangement around the phosphorus. NMR studies confirm that they retain the SP structure in solution and demonstrate that the endocyclic P-C bonds in the three-membered ring have a very high degree of p character, which results from their being both basal bonds in the SP structure and endocyclic bonds of the three- membered ring. Structural parameters of the three- membered ring of the pentacoordinate phosphirenes obtained by experiment and theoretical calculations are very close to those of a tetracoordinate phosphirenium cation. Thus, by analogy with tetracoordinate phosphirenium cations, it can be considered that sigma*-d interaction between the sigma* orbital of the apical bond and the pi orbital of the C = C bond in the three- membered ring is operative in pentacoordinate phosphirenes. The sigma*-pi interaction is found to lower the reactivity of the CdC bond of the three- membered ring. The reactivities of the pentacoordinate phosphirenes are also affected by the substituent on the carbon atom in the threemembered ring.

Several organosilicon compounds bearing a 2-(phenylazo) phenyl group were synthesized from the corresponding chlorosilanes and 2-lithioazobenzene prepared by halogen-lithium transmetalation of 2-iodoazobenzene. Their structures were determined by H-1, C-13, F-19, and Si-29 NMR spectra, UV-vis spectra, and X-ray crystallographic analyses. In the UV-vis spectra, silyl groups caused red shifts of both the n-pi* and pi-pi* transitions of the azo group compared with the transitions of the unsubstituted azobenzene. The E-isomers of the fluorosilanes showed an intramolecular interaction between a nitrogen atom of the azo group and the silicon atom, leading their intermediate structures between a distorted trigonal bipyramidal structure and a tetrahedral structure around the silicon atoms, which were revealed by the X-ray crystallographic analyses and the NMR spectra. On the other hand, silanes without fluorine atoms showed tetrahedral structures in the absence of such an interaction. The photoirradiation of the E-isomers of the fluorosilanes afforded reversibly the corresponding Z-isomers in good yields. The silicon atoms of the Z-isomers were found to be tetracoordinate in the absence of Si-N interactions by the Si-29 NMR spectra. The coordination numbers of the silicon atom of the fluorosilanes were reversibly switched between four and five by photoirradiation. These properties were compared to those of a tetrafluoro[2-(phenylazo)phenyl]-silicate.

[GRAPHICS] Pentacoordinate 1,2-oxastibetanes 14a-d, which are formal [2 + 2]-cycloadducts of the reactions of stibonium ylides with carbonyl compounds, were successfully synthesized by the reactions of the corresponding bromo-2-hydroxyalkylstiboranes with NaH. The crystal structures of 14a and 14c were established by X-ray crystallographic analyses, showing their distorted trigonal bipyramidal structures and smaller C-Sb-O angles of the four-membered ring around antimony than the C-P-O angle of pentacoordinate 1,2-oxaphosphetane 3. The H-1, C-13, and F-19 NMR spectra of 14a-d are consistent with the trigonal bipyramidal structure in the solution state. Although 14a did not decompose at all at 220 degrees C in o-xylene-d(10), the thermolyses of 3-phenyl-1,2-oxastibetane 14c were carried out at 220 degrees C in o-xylene-d(10) and at 140 degrees C in acetonitrile-d(3) to give the corresponding oxirane 28 with retention of configuration and cyclic stibinite 25. The formation of 28 is explained by apical-equatorial ligand coupling around antimony via a polar transition state, which is more favorable than olefin formation. In contrast, the thermolyses of 14c in the presence of LiBr and LiBPb4 gave oxirane 29 with inversion of configuration and the olefin 30, respectively. The formation of 29 and 30 is considered to proceed via an anti-betaine-type intermediate and hexacoordinate 1,2-oxastibetanide 36, respectively. Selective formation of 28, 29, and 30 in the thermolyses of 14c, which is regarded as an intermediate in the reaction of an alpha-phenyl-substituted stibonium ylide with a carbonyl compound, showed that the change of the reaction conditions controls the reactivity of a 1,2-oxastibetane compound.

Photoisomerization of a catecholborane bearing a 2-(phenylazo)phenyl group with an N-B dative bond caused photoswitching of the coordination number of boron between 3 and 4. The Lewis acidity of the catecholborane was switched by photoirradiation, and the complexation ability of the (E)- and the (Z)-isomers of the catecholborane with pyridine differs by more than a factor of 300.

Disilanes bearing four carboxylate ligands have a trigonal bipyramidal geometry around each silicon atom with two bridging carboxylate ligands with the apical Si-O axes, which are parallel to each other, in the crystalline state, while such a structure is in equilibrium with a tetrahedral structure in solution.

In this chapter, we review dithiocarboxylic acid salts. Methods of synthesizing these salts are reviewed, such as insertion of carbon disulfide into the metal-carbon bond, reaction of a dithiocarboxylic acid with a transition metal salt in the presence or absence of a base, ligand exchange of dithiocarboxylato metal or ammonium salts with another metal complex bearing a leaving group, and so on. The dithiocarboxylic acid complexes exhibit a variety of coordination styles that have been characterized by X-ray crystallographic analysis. Spectroscopic (IR, (13)C, and UV-Vis) properties of the salts are summarized. The reactivities, structures, properties, characteristics and applications of each salt are discussed in detail for the salts of most elements (except for carbon).

The reaction of a phosphorus ylide with elemental sulfur gave a pentacoordinate thiaphosphirane, which was characterized by X-ray crystallographic analysis, and it was allowed to react with elemental sulfur resulting in a thiophosphinate.

A tetracoordinate 1,2-iodoxetane was prepared by the fluorination of a tricoordinate 1,2-iodoxetane with xenon difluoride followed by hydrolysis. The tetracoordinate 1,2-iodoxetane oxidized alcohols and a sulfide to the corresponding aldehydes and ketones, and a sulfoxide, respectively, in good to moderate yields under mild conditions. (C) 2004 Elsevier Ltd. All rights reserved.

Pentacoordinate 1,2-oxastibetanes have been synthesized and characterized by x-ray crystallographic analysis and NMR spectroscopy. Thermolyses of a pentacoordinate 1,2-oxastibetane were carried out under various conditions to give the corresponding oxirane with retention of configuration, the oxirane with inversion of configuration and the olefin respectively.

An E,E-1,1,3,3-tetrafluoro-1,3-bis[2-(phenylazo)phenyl]-1,3-disiloxane (E,E-2) was synthesized by hydrolysis of E-trifluoro[2-(phenylazo)phenyl]silane (E-1). Its structure was characterized by H-1-, C-13- F-19-, and Si-29-NMR spectroscopy and X-ray crystallographic analysis showing two pentacoordinate silicon atoms with Si-N interactions. Photoirradiation of E,E-2 caused both isomerization of the azo group and formation of the corresponding Z-1 in a short time, while upon standing in the dark the E-1 was formed very slowly. (C) 2003 Elsevier B.V. All rights reserved.

A novel heterocyclic compound, 1,3,2,5-ox-azaphosphagermolidin-2-ium-5-uide, was synthesized by sequential treatment of HMPA with t-BuLi and a hydrogermane, and its crystal structure was established by X-ray crystallographic analysis.

The first 1,5-dioxa-4lambda(4)-telluraspiro[3.3]heptane was synthesized and its structure was determined by X-ray analysis. This tellurane gave the corresponding oxirane and olefin, as well as alcohol, upon heating, which were shown to be formed via a radical pathway. (C) 2002 Elsevier Science Ltd. All rights reserved.

Recently, the first heptacoordinate disilane [(MesCS(2))(2)MeSi](2) 1 was synthesized and shown to have a unique structure by X-ray analysis. Each of the silicon atoms is surrounded by three nonbonded thiobenzoylthio groups. We theoretically investigated the origins of the unusual geometry of 1 containing multiple hypercoordinations. The model compound [(HCS2)(2)MeSi](2) 2a shows both the H-C-Si-Si eclipsed conformation and the C-Si-Si-C eclipsed conformation. The dihedral angle of H-C Si-Si is calculated to be 24.6degrees at the RHF/6-31G* level (25.7degrees at the RHF/LANL2DZ+p level). Each of the carbon atoms of the methyl groups is also surrounded by three nonbonded thioformylthio groups. After the bond model analyses, We found that hypercoordination to the saturated carbon atom is essential for this unique geometry, as confirmed by scrutinizing the X-ray data of 1. (C) 2002 Elsevier Science Ltd. All rights reserved.

The phosphonium cations bearing the Martin ligand abstracted a fluoride ion from their counter anion, tetrafiuoroborate, and the corresponding fluorophosphoranes were obtained in good yields.

Reactions of an iminophosphorane bearing the Martin ligand (2,4,6-Pr3C6H2)(-C6H4-2-C(CF3)(2)O-)P=NPh 1 with carbonyl compounds and phenyl isothiocyanate gave the corresponding [2 + 2]-cycloadducts, 1,3,2lambda(5)-oxazaphosphetidine 2a and 1,3,2lambda(5)-diazaphosphetidine-4-thione 8a, respectively, whose structures were characterized by X-ray crystallographic analyses. Thermolysis of cycloadduct 2a, which is considered as an intermediate of the aza-Wittig reaction, showed two reactivities giving cyclic phosphinate 4 and imine 5 as well as I and ketone 3, respectively. Thermolysis of 8a afforded not only 1 and phenyl isothiocyanate 7a, but also cyclic thiophosphinate 10 and diphenylcarbodiimide 11a. The formation of 10 and 11a suggests the bond recombination around phosphorus atom of 8a. (C) 2002 Elsevier Science Ltd. All rights reserved.

The nonbenzenoid aromatic D6h and enediolate C2v valence tautomers of the relatively unstable rhodizonate dianion (see picture) have been generated in situ and stabilized by hydrogen bonding with (3-hydroxyphenyl)urea and 1,1′-ethylenediurea, respectively, in two novel crystalline inclusion compounds.

Oxidation of beta -aminoalkyl selenide 4a with an excess amount of mCPBA gave 1,2 lambda (4),5-oxaselenazolidine 1, a novel heterocyclic compound with an Se-O-N linkage. Its X-ray crystallographic analysis revealed that the oxaselenazolidine ring has an envelope conformation.

Hydrolysis of 6-tert-butyl-1-p-tolylbenzoxabismole (1) followed by self-condensation of hydroxybismuthine (3) gave the corresponding dibismuth oxide 2, which was found by X-ray crystallographic analysis to exhibit a dimeric form with a novel ladder type by both inter- and intramolecular Bi-O interactions.

Azobenzenes, 2-(R2RMC6H4N)-R-1-M-2=NPh (M = Si (1a-c), Ge (7), and Sn (8)), were synthesized by reactions of 2-lithioazobenzene (6) with the corresponding chloro compounds, (R2RMCl)-R-1-M-2, respectively, in good to moderate yields. The crystal structure of 1c was established by the X-ray crystallographic analysis.

Equation presented The first tetracoordinate 1λ4,2-selenazetidines were synthesized by taking advantage of the Martin ligand and characterized by X-ray crystallographic analysis. The selenazetidines gave the corresponding aziridine and the cyclic selenenate on their thermolysis, which indicates the possibiliy that a highly coordinate 1,2-heterachalcogenetane may provide the corresponding heteracyclopropane regardless of the heteroatoms.

Oxidation of beta -aminoalkyl selenides bearing the Martin ligand with neCPBA gave tetracoordinate 1,2-selenazetidines or a tetracoordinate 1,2,5-oxaselenazolidine as stable colorless crystals. The thermolysis of 1,2-selenazetidines afforded the corresponding aziridine and cyclic selenenate.

The title compound was successfully synthesized as yellow crystals by oxidative cyclization of the corresponding 3-iodo-3-hexene-2,5-diol with t-BuOCl. The NMR spectral data was consistent with a T-shape structure, which was confirmed by X-ray crystallographic analysis. Strong intermolecular interaction between the iodine atom and the oxygen atom of the four-membered ring was observed in the solid state.

Reaction of an iminophosphorane 2 bearing the Martin ligand with dimethyl acetylenedicarboxylate, followed by a ring opening reaction of a [2 + 2]-cycloadduct between them, gave the corresponding alpha -iminoalkylidenephosphorane 3, which was hydrolyzed to afford 1,2 lambda (5)-oxaphosphol-5(2H)-one 4. The structure of the novel five-membered ring compound 4 was established by X-ray crystallographic analysis. (C) 2001 John Wiley & Sons, Inc.

Cycloaddition reaction of an iminophosphorane bearing the Martin ligand with an alkyne gave the first stable 1,2 lambda (5)-azaphosphetine, whose structure was determined by X-ray crystallographic analysis, and variable temperature NMR spectroscopy revealed the existence of equilibrium with the corresponding alpha -iminoalkylidenephosphorane.

1,3,2 lambda(5)-Oxazaphosphetidines bearing the Martin ligand were synthesized by the reaction of the corresponding iminophosphorane and carbonyl compounds and characterized by X-ray crystallographic analysis. Thermolysis of the oxazaphosphetidine gave the cyclic phosphinate and the corresponding imine, indicating that the oxazaphosphetidine is an intermediate of the aza-Wittig reaction. (C) 2000 Elsevier Science Ltd. All rights reserved.

Divalent organolead compounds (plumbylenes Tip2Pb (6 Tip = 2,4,6-triisopropylphenyl) and Tbt(R)Pb (7a, R = Tbt Tb, R = Ttm 7c, R = Tip 7d, R = Dis Tbt = 2,4,6-tris[bis-(trimethylsilyl)methyl]phenyl, Ttm = 2,4,6-tris[(trimethylsilyl)methyl]phenyl, and Dis = bis-(trimethylsilyl)methyl)) were synthesized by taking advantage of kinetic stabilization afforded by bulky substituents and characterized by UV/vis and 207Pb NMR spectroscopy. X-ray structural analysis revealed that plumbylene 7a has a V-shaped, monomeric structure. Reactions of these plumbylenes with methyl iodide, carbon tetrabromide, diphenyl disulfide, diphenyl diselenide, and elemental sulfur are described. New methods for the synthesis of plumbylenes from tetravalent organolead compounds, by reductive debromination of dibromoplumbanes and exhaustive desulfurization of tetrathiaplumbolanes, were developed. © 1999 American Chemical Society.

Reaction of beta-styrylpentamethyldisilane (1a) with Ru-3(CO)(12) afforded beta-styryltrimethylsilane (2a) with elimination of a dimethylsilylene unit, while under similar conditions alpha-isomer 1b yielded 2a together with 1a. Studies on these reactions suggest the formation of silapropenyl and silylene ruthenium complexes as key intermediates.

Synthesis, structure, and some reactivities of kinetically stabilized plumbylenes are described. The reaction of an extremely hindered plumbylene Tbt(2)Pb: (Tbt= 2,4,6-tris[bis(trimethylsilyl)methyl]pheyl with elemental sulfur gave Tbt(TbtS)Pb: via an interesting 1,2-aryl migration of the intermediary plumbanethione, Tbt(2)Pb=S. The reactions of overcrowded aryl(arylthio)plumbylenes and bis(arylthio)-plumbylenes with carbon disulfide are also described.

Divalent organolead compounds (plumbylenes) and lead-sulfur double-bond compounds (plumbanethiones) were synthesized by taking advantage of the kinetic stabilization method and their crystal structures, spectroscopic properties and reactivities were investigated. Thermal reaction of a plumbanethione afforded an aryl(arylthio)plumbylene via 1,2-aryl migration.