N-heterocyclic carbene analogues with low-valent group 13 and group 14 elements: syntheses, structures, and reactivities of a new generation of multitalented ligands.

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC–main group element adducts, and might be...

NHCs in Main Group Chemistry.

Zwitterionic and Donor-Stabilized N-Heterocyclic Silylenes (NHSis) for Metal-Free Activation of Small Molecules

Recent developments in stereoselective 1,2-cis glycosylation that have emerged during the past decade are surveyed herein. For detailed coverage of the previous achievements in the field the reader is referred to our earlier reviews: A. V. Demchenko, Curr. Org. Chem., 2003, 7, 35–79 and Synlett, 2003, 1225–1240.

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Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms

Convenient Access to Monosilicon Epoxides with Pentacoordinate Silicon

The reactions of silylenes with organic azides are quite diverse, depending on the substituents of the silylene center and on the nature of the azide employed. Elusive silaimine with three-coordinate silicon atom L1SiN(2,6-Triip2-C6H3) (5) {L1 = CH[(C═CH2)(CMe)(2,6-iPr2C6H3N)2] and Triip = 2,4,6-triisopropylphenyl} was synthesized by treatment of the silylene L1Si (1) with a sterically demanding 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide (2,6-Triip2C6H3N3). The reaction of Lewis base-stabilized dichlorosilylene L2SiCl2 (2) {L2 = 1,3-bis(2,6-iPr2C6H3)imidazol-2-ylidene} with Ph3SiN3 afforded four-coordinate silaimine L2(Cl2)SiNSiPh3 (6). Treatment of 2,6-Triip2C6H3N3 with L3SiCl (3) (L3 = PhC(NtBu)2) yielded silaimine L3(Cl)SiN(2,6-Triip2-C6H3) (7) possessing a four-coordinate silicon atom. The reactions of L3SiN(SiMe3)2 (4) with adamantyl and trimethylsilyl azide furnished silaimine compounds with a four-coordinate silicon atom L3(N(Ad)SiMe3)SiN(SiMe3) (8) (Ad = adamantyl) and L3(N(SiMe3)2)SiN(SiMe3) (...

Stable silaimines with three- and four-coordinate silicon atoms.

Reaction of IPr x SiCl(2) (1) [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] with 1-azidoadamantane leads to functionalized N-heterocyclic carbene (NHC) 2. Silyl-substituted NHC 2 reacts easily with 1-azidoadamantane to form triazene 3, in which the exocyclic C=N bond is slightly shorter than those of regular NHC-derived triazines. 2 could serve as a promising ligand for transition metals.

A Facile Route to Functionalized N-Heterocyclic Carbenes (NHCs) with NHC Base-Stabilized Dichlorosilylene

Phenalenyl in action: The cationic state of the phenalenyl system can be used to design Lewis acidic catalysts. The phenalenyl backbone can tune the energy of the lowest unoccupied molecular orbital (LUMO) of the molecule, which in turn controls the catalytic activity in the ring-opening polymerization of cyclic esters.

Markus Granitzka

Papers

Convenient Access to Monosilicon Epoxides with Pentacoordinate Silicon

Stable silaimines with three- and four-coordinate silicon atoms.

A Facile Route to Functionalized N-Heterocyclic Carbenes (NHCs) with NHC Base-Stabilized Dichlorosilylene

Phenalenyl-based molecules: tuning the lowest unoccupied molecular orbital to design a catalyst.

N-Heterocyclic Carbene Stabilized Dichlorosilaimine IPr·Cl2Si═NR