Generation of Stannabenzenes and Their Properties

A tin analogue of propadiene with cumulated C[double bond, length as m-dash]Sn double bonds

The synthesis, structure, and properties of a stable, linear 2-stannapropadiene are reported. The identical C[double bond, length as m-dash]Sn bonds in this 2-stannapropadiene are the shortest hitherto reported C-Sn bonds. This 2-stannapropadiene features a 119Sn NMR signal at 507 ppm for the central tin atom, indicative of an unsaturated Sn4+ oxidation state. Due to the inert-pair effect, the tin atom displays a pronounced preference for the +2 oxidation state over the +4 oxidation state. Nevertheless, by employing silyl substituents, it is possible to disrupt the inert-pair effect, leading to the formation of an isolable 2-stannapropadiene with a linear structure centered on a Sn4+ atom. Treatment of this 2-stannapropadiene with SnBr2·dioxane resulted in the formation of a novel four-membered cyclic 1,1-dibromo-1,3-distannetane, which was subsequently reduced to afford the corresponding stable four-membered cyclic bis(stannylene).

Recent progress in the chemistry of heavy aromatics

The aromaticity and synthetic application of "heavy benzenes", i.e., benzenes containing a heavier Group 14 element (Si, Ge, Sn, and Pb) in place of skeletal carbon, have been the targets of many theoretical and synthetic studies. Although the introduction of a sterically demanding substituent enabled us to synthesize and isolate heavy aromatic species as a stable compound by suppressing their high reactivity and tendency to polymerize, the existence of a protection group is an obstruction to the development of functional materials based on heavy aromatics. This review will delineate the most recent topics in the chemistry of heavy aromatics, i.e., the chemistry of "metallabenzenyl anions", which are the heavier Group 14 element analogs of phenyl anions stabilized by taking advantage of charge repulsion instead of steric protection.

Heavier element-containing aromatics of [4n+2]-electron systems

While the implication of the aromaticity concept has been dramatically expanded to date since its emergence in 1865, the classical [4n+2]/4n-electron counting protocol still plays an essential role in evaluating the aromatic nature of compounds. Over the last few decades, a variety of heavier heterocycles featuring the formal [4n+2] π-electron arrangements have been developed, which allows for assessing their aromatic nature. In this review, we present recent developments of the [4n+2]-electron systems of heavier heterocycles involving group 13-15 elements. The synthesis, spectroscopic data, structural parameters, computational data, and reactivity are introduced.

Metallaaromatic Chemistry: History and Development

Since the prediction of the existence of metallabenzenes in 1979, metallaaromatic chemistry has developed rapidly, due to its importance in both experimental and theoretical fields. Now six major types of metallaromatic compounds, metallabenzenes, metallabenzynes, heterometallaaromatics, dianion metalloles, metallapentalenes and metallapentalynes (also termed carbolongs), and spiro metalloles, have been reported and extensively studied. Their parent organic analogues may be aromatic, non-aromatic, or even anti-aromatic. These unique systems not only enrich the large family of aromatics, but they also broaden our understanding and extend the concept of aromaticity. This review provides a comprehensive overview of metallaaromatic chemistry. We have focused on not only the six major classes of metallaaromatics, including the main-group-metal-based metallaaromatics, but also other types, such as metallacyclobutadienes and metallacyclopropenes. The structures, synthetic methods, and reactivities are described, their applications are covered, and the challenges and future prospects of the area are discussed. The criteria commonly used to judge the aromaticity of metallaaromatics are presented.

Generation of stannabenzenes and their monomer–dimer equilibration

A combination of bulky aryl and t-butyl groups was found to suppress the dimerization of stannabenzene, giving a monomer/dimer equilibration mixture.

Recent Advances in Metallaaromatic Chemistry

Metallaaromatics can be broadly defined as aromatic compounds in which one of the ring atoms is a transition metal. The metallabenzenes are one important class of these compounds that has undergone extensive study recently. Closely related species such as fused-ring metallabenzenes, heterometallabenzenes, π-coordinated metallabenzenes and metallabenzynes have also attracted considerable attention. Although many metallaaromatics can be considered as metalla-analogues of classic organic aromatic compounds, this is not always the case. Recent seminal studies have shown that metallapentalenes and metallapentalynes, which are metalla-analogues of the anti-aromatic compounds pentalene and pentalyne, are in fact aromatic and highly stable. Very unusual spiro-metallaaromatic compounds have also recently been isolated. In this concepts article, key features of all these intriguing metallaaromatic compounds are discussed with reference to the structural, spectroscopic, reactivity and theoretical studies that have been undertaken. These compounds continue to generate much interest, not only because of the contributions they make to fundamental chemical understanding, but also because of the promise of possible practical applications.

Group 14 inorganic hydrocarbon analogues

This Review article deals with the synthesis and properties of inorganic hydrocarbon analogues: binary chemical species that contain heavier Group 14 elements (Si, Ge, Sn or Pb) and hydrogen as components. Rapid advances in our general knowledge of these species have enabled the development of industrially relevant processes such as the hydrosilylation of unsaturated substrates and the chemical vapor deposition of semi-conducting films.

Coordination chemistry of 9-sila- and 9-germa-phenanthrenes — unique coordination modes in their metallene complexes

Ligand exchange reactions of 9-sila- and 9-germa-phenathrenes with chromium carbonyl complexes, [Cr(CH3CN)3(CO)3] and [Cr(η6-benzene)(CO)3], were performed. Their reactions with [Cr(CH3CN)3(CO)3] afforded the corresponding η6-complexes, in which Cr(CO)3 moieties coordinated to the C6-rings. However, those with [Cr(η6-benzene)(CO)3] gave unique four-membered complexes bearing semibridging carbonyl ligands. All the structures of novel complexes were determined by NMR and X-ray crystallographic analysis.

Abnormally long-range diamagnetic anisotropy induced by cyclic d(δ)-p(π) π conjugation within a six-membered dimolybdenum/chalcogen ring

Incorporating two quadruply bonded dimolybdenum units [Mo(2)(DAniF)((3))](+) (ancillary ligand DAniF = N,N'-di-p-anisylformamidinate) with two hydroselenides (SeH(-)) gave rise to [Mo(2)(DAniF)(3)](2)(μ-SeH)(2) (1). With the molecular scaffold remaining unchanged, aerobic oxidation of 1, followed by autodeprotonation, generated [Mo(2)(DAniF)(3)](2)(μ-Se)(2) (2). The two complexes share a common cyclic six-membered Mo(2)/Se core, but compound 2 is distinct from 1 by having structural, electronic, and magnetic properties that correspond with aromaticity. Importantly, the aromatic behaviors for this non-carbon system are ascribable to the bonding analogy between the δ component in a Mo-Mo quadruple bond and the π component in a C-C double bond. Cyclic π delocalization via d(δ)-p(π) conjugation within the central unit, which involves six π electrons with one electron from each of the Mo(2) units and two electrons from each of the bridging atoms, has been confirmed in a previous work on the oxygen- and sulfur-bridged analogues (Fang, W.; et al. Chem.-Eur. J.2011, 17, 10288). Of the three members in this family, compound 2 exhibits an enhanced aromaticity because of the selenium bridges. The remote in-plane and out-of-plane methine (ArNCHNAr) protons resonate at chemical shifts (δ) 9.42 and 7.84 ppm, respectively. This NMR displacement, Δδ = 1.58 ppm, is larger than that for the oxygen-bridged (1.30 ppm) and sulfur-bridged (1.49 ppm) derivatives. The abnormally long-range shielding effects and the large diamagnetic anisotropy for this complex system can be rationalized by the induced ring currents circulating the Mo(2)/chalcogen core. By employment of the McConnell equation {Δσ = Δχ[(l - 3 cos 2θ)/3R(3)N]}, the magnetic anisotropy (Δχ = χ(⊥) - χ(||)) is estimated to be -414 ppm cgs, which is dramatically larger than -62.9 ppm cgs for benzene, the paradigm of aromaticity. In addition, it is found that the magnitude of Δχ is linearly related to the radius of the bridging atoms, with the selenium analogue having the largest value. This aromaticity sequence is in agreement with that for the chalcogen-containing aromatic family, e.g., furan < thiophene < selenophene.