π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements

This review is essentially an update of one entitled “πBonding and The Lone Pair Effect in Multiple Bonds Between Heavier Main Group Elements” which was published more than 10 years ago in this journal.1 The coverage of that survey was focused on the synthesis, structure, and bonding of stable compounds2 of heavier main group elements that correspond to the skeletal drawings reproduced in Tables 1 and 2. A row of numbers is listed at the bottom of each column in these tables. This refers to the number of stable complexes from each class that are currently known. The numbers in parentheses refer to the number of stable species that were known at the time of the previous review. Clearly, many of the compound classes listed have undergone considerable expansion although some remain stubbornly rare. The most significant developments for each class will be discussed in detail under the respective sections. As will be seen, there are also a limited number of multiple bonded heavier main group species that do not fit neatly in the classifications in Tables 1 and 2. However, to keep the review to a manageable length, the limits and exclusions, which parallel those used earlier, are summarized as follows: (i) discussion is mainly confined to compounds where experimental data on stable, isolated species have been obtained, (ii) stable compounds having multiple bonding between heavier main group elements and transition metals are not generally discussed, (iii) compounds in which a multiple bonded heavier main group element is incorporated within a ring are generally not covered, and (iv) hypervalent main group compounds that may incorporate faux multiple bonding are generally excluded. Such compounds are distinguished from those in Tables 1 and 2 in that they apparently require the use of more than four valence bonding orbitals at one or more of the bonded atoms. The remainder of this review is organized in a similar manner to that of the previous one wherein the compounds to be discussed are classified according to those summarized in Tables 1 and 2. The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.3 Since the previous review was published in 1999, several review articles that cover parts of the subject matter have appeared.4

π-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium

The reaction of 2,2,3,3-tetrabromo-1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasilane with four equivalents of potassium graphite (KC 8 ) in tetrahydrofuran produces 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne, a stable compound with a silicon-silicon triple bond, which can be isolated as emerald green crystals stable up to 100°C in the absence of air. The SiSi triple-bond length (and its estimated standard deviation) is 2.0622(9) angstroms, which shows half the magnitude of the bond shortening of alkynes compared with that of alkenes. Unlike alkynes, the substituents at the SiSi group are not arranged in a linear fashion, but are trans-bent with a bond angle of 137.44(4)°.

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A stable compound containing a silicon-silicon triple bond.

Oligomeric and Polymeric Systems with a Cross-conjugated π-Framework†

Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms

Stable Tetrakis(trialkylsilyl)disilenes; Synthesis, X-Ray Structures, and UV/VIS Spectra

Chemistry of organosilicon compounds. 263. Synthesis, properties, and molecular structure of highly distorted hexakis(trimethylsilyl)benzene

The first nonconjugated mononuclear benzene dianion. Isolation and characterization of bis[(tetrahydrofuran)lithium(I)] hexakis(trimethylsilyl)benzenide

Keisuke Ebata

Papers

Stable Tetrakis(trialkylsilyl)disilenes; Synthesis, X-Ray Structures, and UV/VIS Spectra

Chemistry of organosilicon compounds. 263. Synthesis, properties, and molecular structure of highly distorted hexakis(trimethylsilyl)benzene

The first nonconjugated mononuclear benzene dianion. Isolation and characterization of bis[(tetrahydrofuran)lithium(I)] hexakis(trimethylsilyl)benzenide

Bis[(dimethoxyethane)lithium(I)] 1,2,4,5-tetrakis(trimethylsilyl)benzenide. The first 6C-8.pi. antiaromatic benzene dianion

Lithium pentakis(dimethylsilyl)cyclopentadienide and formation of isolable coordination complexes with ketones : [(R2C=O)Li.{C5(SiMe2H)5]