Studies on chemistry of silicon-silicon triple bond species : synthesis, characterization, and reactivity

Thesis (Ph. D. in Science)--University of Tsukuba, (A), no. 4234, 2007.3.23Includes bibliographical reference

How to install Boron into aromatic scaffolds: chemistry of diazadiborinines

The concept of aromaticity has been of paramount significance in myriad fields of chemistry. To modulate the intrinsic electronic nature of aromatic molecules, partial incorporation of heteroatoms into the benzene scaffold represents a useful strategy in modern inorganic chemistry. This account presents how to incorporate boron into aromatic six‒membered scaffolds, leading to hybrid organic/inorganic benzenes, namely diazadiborinines. In addition, their reactivity towards a variety of substrates are summarized.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityThese works were supported by Nanyang Technological University, the Singapore Ministry of Education (MOE2013-T2-1-005, MOE2015-T2-2-032, MOE2018-T2-2-048(S)), and A*Star (Agency for Science, Technology and Research of Singapore (PSF/SERC 1321202066)

An inorganic Huisgen reaction between a 1,2-diboraallene and an azide to access a diboratriazole

Regioselective Huisgen cycloaddition reaction between 1,2-diboraallene and azide proceeds under catalyst-free and mild conditions to furnish a diboratriazole (2). X-ray diffraction analysis and computational studies confirmed the delocalization of π electrons over the B2 N3 five-membered ring of (2), indicating its aromatic features. Molecule (2) spontaneously releases N2 to form the 2,3-dibora-4-aza-1,3-butenyne derivative (3). The mechanism of a whole reaction profile was extensively investigated by density functional theory (DFT) calculations.Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionWe are grateful to Nanyang Technological University (NTU) and the Singapore Ministry of Education (MOE2018-T2-2-048(S)) for financial support

Boron-based catalysts for C − C bond‐formation reactions

Because the construction of the C−C bond is one of the most significant reactions in organic chemistry, the development of an efficient strategy has attracted much attention throughout the synthetic community. Among various protocols to form C−C bonds, organoboron compounds are not just limited to stoichiometric reagents, but have also made great achievements as catalysts because of the easy modification of the electronic and steric impacts on the boron center. This review presents recent developments of boron‐based catalysts applied in the field of C−C bond‐formation reactions, which are classified into four kinds on the basis of the type of boron catalyst: 1) highly Lewis acidic borane, B(C6F5)3; 2) organoboron acids, RB(OH)2, and their ester derivatives; 3) borenium ions, (R2BL)X; and 4) other miscellaneous kinds.MOE (Min. of Education, S’pore

Fragmentation of White Phosphorus by a Cyclic (Alkyl)(Amino)Alumanyl Anion

The stable cyclic (alkyl)(amino)alumanyl anion (CAAAl) 3 reacts with white phosphorus (P4) under ambient conditions, in which P4is fragmented into a P1unit to afford the bis(alumanyl)phosphide 2, demonstrating the direct formation of a P anion from an Al anion. Structural and electronic features of the latter were fully characterized by standard spectroscopic means, X-ray diffraction analysis, and computational studies, which revealed that 2 bears highly polarized Al (δ+) and P (δ-) and relatively short Al-P bonds, indicative of the σ-donating and π-accepting nature of CAAAl groups.Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionWe are grateful to Nanyang Technological University (NTU) and the Singapore Ministry of Education (MOE2018-T2-2- 048(S)) for financial support

Zero-valent species of group 13–15 elements

This perspective describes the development of zero-valent species En(0) of group 13–15 elements. Computational studies providing reinterpretation of bonding involved in well-known molecules, such as carbodiphosphorane, have opened up the area. Employment of Lewis bases to form donor-acceptor interactions with the elemental fragments in the zero oxidation state is the key to stabilizing such species. Because of the diversity of Lewis bases available, En(0) derivatives with a variety of bonding and structural motifs are isolable. The monoatomic E1(0) species of group 13 and 15 elements, middle-size En(0) clusters (n = 4–6) of group 13 and 14 elements, and the heavier group 13 cousins have been much less explored. The end of the article outlines one of the potential future directions of zero-valent main-group chemistry, which is an exploration of the allotrope chemistry relevant to materials science.Ministry of Education (MOE)Submitted/Accepted versionThis work was supported by the Singapore Ministry of Education (MOE2018-T2-2- 048 (S))

Construction of σ-aromatic AlB₂ ring via borane coupling with a dicoordinate cyclic (alkyl)(amino)aluminyl anion

Since the groundbreaking discovery in 2018 that the synthesis of a bottleable nucleophilic aluminyl anion is feasible, a handful of derivatives have been developed to date, which are, however, limited to diamino- and dialkyl-substituted species. Herein, we report the synthesis of a cyclic (alkyl)(amino)aluminyl anion based on a five-membered framework. The dicoordinate aluminum center features both a lone pair of electrons and an unoccupied 3p orbital, thus genuinely making it isoelectronic with carbenes. We show the bond formation and bond activation at the Al sphere: thus, not only does it undergo electron redistribution with borane to furnish a heteroatomic group 13 ring exhibiting a σ-aromatic nature concomitant with a three-center two-electron AlB₂ bond but also the ambiphilic nature allows for oxidative addition of Si-H, N-H, and even C-C bonds at the aluminum center.Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionWe are grateful to Nanyang Technological University (NTU) and the Singapore Ministry of Education (MOE2018-T2-2-048(S)) for financial support

A highly strained Al-Al σ-bond in dianionic aluminum analog of oxirane for molecule activation

Since aluminum is the most electropositive element among the p-block elements, the construction of molecules bearing a dianionic Al-Al σ-bond is inherently highly challenging. Herein, we report the first synthesis of a dianionic dialane(6) 2 based on the Al2O three-membered ring scaffold, namely, an aluminum analog of oxirane. The structure of 2 has been unambiguously ascertained by spectroscopic analysis as well as X-ray crystallography, and computational studies revealed that 2 bears a highly strained Al-Al σ-bond. 2 readily reacts with the unsaturated substrates such as isocyanide, ethylene, and ketone, concomitant with the cleavage of the Al-Al σ-bond under mild conditions, leading to the four- and five-membered heterocycles 3-5. Furthermore, the reaction of 2 with two molecules of benzonitrile (PhCN) furnishes a seven-membered heterocycle 6, resulting from the C-C coupling reaction of PhCN. We further delineate that 2 selectively activates an arene ring C-C bond of biphenylene, rendering a di-Al-substituted benzo[8]annulene derivative 7. Preliminary computational studies propose that the stepwise reaction mechanism involves the Al-Al σ-bond cleavage, dearomative Al-C bond formation, subsequent sigmatropic [1,3]shifts, and a pericyclic reaction.Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionWe are grateful to Nanyang Technological University (NTU) and the Singapore Ministry of Education (MOE2018-T2-2-048(S)) for financial support

Open questions in boron species with globally 4n π systems

The Hückel rule defines that monocyclic and planar conjugated systems containing [4n + 2] π electrons are aromatic. Here, the authors highlight boron species that feature a globally 4n π system, defying the Hückel rule, but nonetheless exhibit aromaticityMinistry of Education (MOE)Nanyang Technological UniversityPublished versionThe authors gratefully acknowledge financial support from Nanyang Technological University and The Singapore Ministry of Education (MOE2018-T2-2-048(S))

A Cyclic (Alkyl)(boryl)germylene Derived from a Cyclic (Alkyl)(amino)germylene

A cyclic (alkyl)(amino)germylene undergoes a ring expansion reaction with dibromomesitylborane (MesBBr2 ) to afford a six-membered dibromogermane derivative. In the presence of Lewis bases (PMe3 or Me NHC), reduction of the latter with two equivalents of potassium graphite (KC8 ) gives rise to cyclic (alkyl)(boryl)germylene-Lewis base adducts. Upon heating, the germylene-PMe3 adduct reacts with H2 to yield a germane, probably via a base-free germylene featuring a small HOMO-LUMO gap.Ministry of Education (MOE)Nanyang Technological UniversityAccepted versionWe are grateful to Nanyang Technological University (NTU) and the Singapore Ministry of Education (MOE2017-T1-002-031) for financial support