Volume 85, Issue 4

The International Conference on Heteroatom Chemistry (ICHAC) is an established international forum for the presentation and discussion of research results in the diverse fields of heteroatom chemistry. Previous ICHAC meetings have been held in different countries: 1987 (Kobe, Japan); 1989 (Albany, NY, USA); 1992 (Riccione, Italy); 1995 (Seoul, Korea); 1998 (London, Ontario, Canada); 2001 (Łódź, Poland); 2004 (Shanghai, China); 2007 (Riverside, CA, USA); and 2009 (Oviedo, Spain). To celebrate its 10th anniversary, ICHAC returned to Japan, the first ICHAC host country. The ICHAC series has been organized mostly every three years, but now is a biennial event beginning with ICHAC-9 in Spain. Continuing the successful ICHAC series, ICHAC-10 covered many areas around the central topic of heteroatom chemistry. Following the long tradition of these conferences, ICHAC-10 was a major scientific event, bringing together organic and inorganic chemists all over the world to share their interests in the different areas of heteroatom chemistry. As usual, this conference served as a professional forum to disseminate scientific knowledge. Synthesis, structure, and reactivity, including catalysis, theoretical methods, and material aspects, constituted the major themes of ICHAC-10. This issue of Pure and Applied Chemistry presents the selected plenary, invited, and commemorative lectures at ICHAC-10. ICHAC-10 was held 20-25 May 2012 at Uji Obaku Plaza, Kyoto University, and the conference program consisted of 7 plenary and 17 invited lectures, 3 memorial lectures celebrating the 10th event in the ICHAC series, as well as 43 short communications and 154 poster presentations. We had 371 participants (92 from abroad) from 28 countries. All the participants may have found a fruitful environment at ICHAC-10 for personal contact and scientific exchange, and experienced useful interactions between chemists of different areas. As for the poster presentations by students, the organizing committee selected 9 posters for the student poster awards, and the best 3 of them were awarded as IUPAC poster awards in ICHAC-10. Although ICHAC-10 was originally scheduled to take place in the summer of 2011, we postponed it to 2012 owing to the effects of the earthquake and tsunami on 11 March 2011 and the following accident in the Fukushima nuclear power plant. On this occasion, I would like to express our sincere thanks for the worldwide support and sympathy given to the victims of this unprecedented disaster and also for the patience and cooperation concerning the postponing of ICHAC-10. As a chair of ICHAC-10, I would like to express my sincere thanks to the kind support by IUPAC, the Chemical Society of Japan, the Society of Silicon Chemistry Japan, the Kinki Chemical Society Japan, and the Institute for Chemical Research, Kyoto University, and also the great assistance and contribution from many foundations and companies related to heteroatom chemistry. ICHAC-11 will be held in Caen (France) in June 2014 and will be hosted by Prof. Annie-Claude Gaumont of ENSICAEN-Université de Caen Basse-Normandie. Norihiro Tokitoh Conference Editor

Nitrogen-bridged bidentate phosphaalkenes reveal several exceptional properties as a new class of P=C-unsaturated diphosphinoamine (PNP) ligands: N–Si bond cleavage of the first N -silylimino-bridged bis-phosphaalkene (R 2 C=P) 2 NSiMe 3 (R = i PrMe 2 Si) with chlorides of Ag I , Au I , and Rh I leads to complexes of the 5c-6π-heteropentadienide imidobisphosphaalkene anion; double Cl – transfer from PtCl 2 and PdCl 2 to coordinated phosphaalkene phosphorus atoms of P -diphenylphosphanylamino phosphaalkenes R 2 C=PN(R')PPh 2 (R' = Me 3 Si or i PrMe 2 Si; R = t Bu, 1-Ada) furnishes unprecedented bis-chelate P -chloroylid complexes M[R 2 CP(Cl)N(R')PPh 2 ] 2 (M = Pd, Pt); CO- and Rh I -induced coupling of two P -diphenylphosphanylamino phosphaalkenes under disilylketene elimination provides trigonal–bipyramidal Rh III complexes with novel tetradentate dianionic “PNP–C–PNP” ligands R 2 C[P (–) N(R')PPh 2 ] 2 .

The heaviest analogues of alkynes are investigated to realize a short triple bond between Pb atoms. For a short double bond between Pb atoms, the Pb 2 molecule stabilized by dative N -heterocyclic carbenes is investigated. For unsupported and supported short bonds between transition metals, two-coordinate transition-metal and bicyclic four-membered ring complexes are investigated.

This article highlights the achievements in the chemistry of supercarboranes (carboranes with more than 12 vertices) in the past decade and the future perspectives. The chemistry of boron clusters has been dominated by 12-vertex carboranes for several decades. Only in recent years has significant progress been made in the chemistry of supercarboranes. Such a breakthrough relies on the use of CAd (carbon-atoms-adjacent) 12-vertex nido -carborane anions as starting materials. A series of 13- and 14-vertex carboranes as well as their corresponding 14- and 15-vertex metallacarboranes have been prepared and structurally characterized. Reactions of supercarboranes with reducing agents, electrophiles, and nucleophiles are studied, which reveal a more diverse and richer reaction chemistry than their icosahedral cousins.

In order to elucidate the electronic nature of our recently reported first hexacoordinated carbon (12-C-6), density functional theory (DFT) calculations of sulfide precursor, sulfone derivative, and S + -F derivative were carried out and compared with those of the reported S + -Me hexacoordinated carbon. Computations on the hexacoordinated carbon, indicating that four attractive C–O interactions with the central hexacoordinate carbon atom exist, also revealed that the interactions consist of two different types of three-center four-electron bonds, which can be regarded as electron donation by the lone pairs of the oxygen atoms to the empty low-lying π*-orbitals of the allene. The optimized structures of the sulfide, sulfone, S + -F, and the original S + -Me suggested that the introduction of electron-withdrawing groups at the sulfur atoms would make the C–O attractive interactions stronger by a larger contribution of the carbon dication resonance structure. Thus, allene compounds (sulfide, sulfone, sulfonium) with two different thioxanthene ligands (one with 1,8-dimethoxy groups as in the S + -Me compound and the other with 1,8-diphenoxy groups) were synthesized to confirm the predicted substituent effects on the C(central)–O interactions. Electron-withdrawing substituents at the sulfur atoms were found to give rise to strong C(central)–O attractive interactions; the average values of the four C–O distances were smaller as the electron-withdrawing ability of the sulfur atoms rose. Additionally, C(central)···OMe distances were shorter than the corresponding C(central)···OPh distances, reflecting the higher electron-donating ability of the oxygen atoms at these 1,8-positions of the thioxanthene skeleton.

The contribution of Asian chemists to the International Conference on Heteroatom Chemistry (ICHAC) meetings, several topics in low- and high-coordination main group element chemistry mainly in Japan, and our contributions to heteroatom chemistry are described. Other important compounds from other countries will also be presented.

This contribution contains a representative sampling from the Padwa laboratory of the conjugate addition of oximes with 2,3- bis (phenylsulfonyl)-1,3-butadiene followed by a subsequent dipolar cycloaddition cascade to produce a variety of alkaloids. The resulting cycloadducts are cleaved reductively to provide azapolycyclic scaffolds with strategically placed functionality for further manipulation of the target compounds.

Selected examples from previous work on iodonium-triggered approaches for the functionalization of unsaturated systems, which summarize innovative transformations, are presented. This section is mostly focused on C–C bond-forming processes from alkynes that are directly bonded to relevant heteroatoms, such as iodine, silicon, or sulfur. Besides, recent advances related to iodonium-promoted C–H functionalization reactions are briefly outlined. A second section shows representative examples of our current research activity on electrophilic reactions aimed at the activation of unsaturated systems, which now are built upon the potential offered by the so-called carbophilic catalysis. More specifically, a new catalytic cyclopentannulation sequence from N -tosylimines and propargyl tosylates and novel C–H functionalization processes from related tosylates are studied. Likewise, representative examples for the intermolecular Au(I)-catalyzed [2 + 2] cycloaddition reaction of sulfonylallenamides with activated alkenes are given, including the first enantioselective reaction of this type, which is also among the first examples of an intermolecular asymmetric gold-catalyzed reaction. The discussion of the reported iodonium and gold chemistry emphasizes a search for new intermolecular processes, although intramolecular reactions are also pursued and developed.

Aziridinyl imines are well-known carbene equivalents because they are precursors of diazo compounds from which reactive intermediates can be produced. These carbene equivalents can be utilized as zwitterionic species, diradicals, or 4π system for cycloaddition reactions. Thus, the intermediates derived from aziridinyl imines have been used in the sulfur-ylide-mediated epoxide formation, tandem free-radical reactions, or cyclopropanation reaction via carbene intermediates to form trimethylenemethane (TMM) diyls, which undergo [2 + 3] cycloaddition reactions to form cyclopentanoids. Diazo compounds generated from aziridinyl imines also react with allenes to form TMM diyls. This reaction was utilized in tandem cycloaddition reactions of linear substrates to form polyquinanes. These tandem reaction strategies were successfully applied to the total synthesis of various cyclopentanoid natural products.

The development of an intramolecular vicinal diamination protocol using metal-free conditions is discussed. The reaction uses a bromide source to generate a Br(I) catalyst in situ from a benign terminal oxidant such as sodium chlorite. The reaction is of great scope and surpasses the transition-metal catalyses developed so far for these types of reactions.

Multimetal complexes provide a variety of interesting structures, unique properties, and functions. Such sophisticated functions are often produced by synergistic and cooperative interactions among the metal ions accumulated in the restricted small area of the multimetal systems. We describe novel three strategies (i.e., macrocyclic, C-shape, and multimetal template) for the preparation of the multimetal supramolecular systems by the cooperative metal binding of a multi-Schiff-base and multi-oxime ligands, and their characteristic structures and functions. The three approaches are versatile and effective because the employed coordination reactions smoothly and quickly proceeded under mild conditions to quantitatively form the desired coordination structures. The multimetal supramolecular systems obtained here exhibit the synergistic and cooperative functions for ion recognition, magnetic properties, helicity control, and modulation of reaction selectivity. These types of multimetal complexes could be developed for a cascade functional supramolecular system that shows highly synergistic properties, integrated multifunctions, and function amplification.

We describe the design and synthesis of ferrocene dimers and trimers bridged by an oligothiophene spacer as both cathodic and anodic multiple redox-active organic–organometallic hybrid molecules. The electrochemical properties of all compounds were examined by cyclic voltammetry (CV). The voltammograms showed different multi-step, multi-electron redox reactions derived from multi-ferrocene fragments and the organic spacer. The results indicate that a number of thiophene rings in the spacer can be attuned to the redox potentials and the electron-transfer processes.

Photoinduced cyclization of o -alkenylaryl isocyanides with (PhS) 2 in the presence of (PhTe) 2 affords the corresponding bisthiolated indene derivatives in good yields via radical cyclization process by thio radical. The procedure can be applied to the construction of tetracyclic systems by using bis( o -aminophenyl) disulfides in place of (PhS) 2 . In sharp contrast, when o -alkynylaryl isocyanides are employed as the substrates, novel electrocyclic reactions take place upon photoirradiation or heating at 40~80 °C to generate quinoline 2,4-biradical species, which are trapped with organic diselenides, ditellurides, and molecular iodine to give the corresponding 2,4-diseleno-, ditelluro-, and diiodo-quinoline derivatives, respectively, in good yields. The obtained quinoline derivatives are useful synthetic intermediates; for example, cross-coupling reactions using 2,4-diiodoquinolines lead to the preparation of functionalized quinoline derivatives.

Phosphaalkenes (RP=CR 2 ) and diphosphenes (RP=PR) are main group analogues of alkenes (R 2 C=CR 2 ). Molecules featuring such multiply bonded phosphorus functionalities often display structural features and chemical reactivities that mimic their purely organic counterparts, lending credence to the claim that these compounds are “carbon copies”. We have been expanding this analogy to include oligomers and polymers with extended conjugation that directly involve P=C and P=P units. Many of these materials, however, display little or no photoluminescence (PL). This article summarizes our efforts to understand P=C and P=P photobehavior and to produce materials having significant PL that mimic or “photocopy” the PL properties of the phosphorus-free systems. Recent materials based on benzoxaphospholes (BOPs), benzobisoxaphospholes (BBOPs), and higher analogues having significant fluorescence quantum yields are covered.

Organophosphorus chemistry plays a key role in the modern synthesis of organic compounds. The formation of phosphine oxides from phosphines often drives reactions to completion. However, these oxides also result in waste and purification issues. Organophosphorus catalysis aims to address these problems, and in this paper we present our progress in developing and utilizing new organophosphorus catalysts. More specifically, the in situ reduction of a range of cyclic phosphine oxides was explored, leading to the development of dibenzophospholes as new organophosphorus catalysts and the application thereof in the phosphorus-mediated substitution of alcohols by halides, which is also known as the Appel reaction. We show that the electronic fine-tuning of the catalyst is crucial for the success of the reaction and that the development of reactions using the in situ reduction protocol all depends on finding the right balance in the reactivities of the reaction components. This balance has been successfully found for the bromination of alcohols, and significant progress has been made for the chlorination reactions.

An approach to novel P -functional chloroformylphosphane complexes is described using the synthetic potential of lithium/halogeno phosphinidenoid tungsten(0) complexes. Similarly to transition-metal-free chloroformylphosphanes, the obtained complexes tend to eliminate CO via P–C bond cleavage to give the corresponding P -chlorophosphane complex derivatives. Nevertheless, this method allowed the isolation of the first complex derivatives, which will open new synthetic perspectives in organophosphorus chemistry.

A new concept for photodegradable cross-linked polymers utilizing characteristics of rotaxane cross-links and aromatic disulfides is proposed. The cross-linked polymer is obtained by the radical polymerization of a vinyl monomer in the presence of a [3]rotaxane-type cross-linker having two radically polymerizable groups. The [3]rotaxane-type cross-linker was prepared in 93 % yield by the typical rotaxane-forming reaction using a dumbbell-shaped aromatic disulfide possessing a bis(ammonium salt) moiety and a crown ether wheel tethered by a hydroxymethyl group (96 %) and the subsequent vinyl group-endowment (80 %). The radical polymerization of methyl methacrylate (MMA) in the presence of the cross-linker (0.1 mol %) at 60 °C afforded solvent-insoluble polymer in 90 % yield. When the polymer was swollen to a gel in dimethylformamide (DMF) and a small part of the gel was UV-irradiated, the gel was promptly solubilized, probably via the photochemical scission of the S–S linkage of the interlocked aromatic disulfide, causing the efficient decomposition of the rotaxane cross-links. The recovered poly(methyl methacrylate) bearing a small amount of crown ether moiety has a molecular weight of M n 170 kg/mol ( M w / M n 2.1) that indicated the occurrence of the site-selective photodegradation.

Highly enantioselective hydrogenation of substituted dibenzo[ b , f ][1,4]thiazepines was achieved with up to 96 % ee (enantiomeric excess) using [Ir(COD)Cl] 2 /( R )-SynPhos complex as catalyst in the presence of iodine. This method provides an efficient access to optically active 11-substituted-10,11-dihydrodibenzo[ b , f ][1,4]thiazepines.

This document represents the final report of discussions and conclusions arising from the workshop on Developments in Science and Technology Relevant to the Chemical Weapons Convention, held in Spiez, Switzerland in February 2012.