N-Heterocyclic silylenes as ambiphilic activators and ligands

Abstract

Recent developments of the use of N-heterocyclic silylenes (NHSis), higher homologues of Arduengo-carbenes, as ambiphilic activators and ligands are highlighted and a comparison of NHSi ligands with NHC and phosphine ligands is provided.

Activation of CO Using a 1,2‐Disilylene: Facile Synthesis of an Abnormal N‐Heterocyclic Silylene

“…The order of those MOs is reversed with respect to the related π‐HOMO and σ‐HOMO−2 in 2 , as might be expected based on the inert pair effect. This situation is similar to what has been calculated for the comparative σ/π‐character of the carbene or silylene centered HOMO and HOMO−1 of NHCs vs. N‐heterocyclic silylenes (NHSi) [18] . The LUMO of 2 is essentially ligand based, while the LUMO+1 closely resembles the LUMO of Bertrand's a NHC A , in that it possesses significant π‐character located on the N C N carbon of the five‐membered ring [10, 11] .…”

“…This situation is similar to what has been calculated for the comparative σ/π-character of the carbene or silylene centered HOMO and HOMOÀ 1 of NHCs vs. N-heterocyclic silylenes (NHSi). [18] The LUMO of 2 is essentially ligand based, while the LUMO + 1 closely resembles the LUMO of Bertrand's aNHC A, in that it possesses significant π-character located on the NCN carbon of the five-membered ring. [10,11] Finally, further evidence for the zwitterionic formulation of the five-membered silylene ring comes from the natural charge on its silicon center which is negative (-0.107), in comparison to a positive charge (+ 0.456) on the other silylene Si center.…”

Tetrylenes: Electronic Structure, Stability, Reactivity, and Ligand Properties—A Comparative DFT Study

“…Scheme shows a number of tetrylenes that are not considered in this article, but worth noting: sterically shielded diorgano tetrylenes XI , , XII (Tip = 2,4,6-triisopropylphenyl, Tb = 2,4,6-tris­[bis­(trimethylsilyl)­methyl]­phenyl), , and XIII (Dipp = 2,6-diisopropylphenyl); tetrylenes stabilized by a combination of heteroatom and extensive steric bulk XIV ; Lappert’s diamido compounds XV ; , Veith’s cyclic diamido compounds XVI ; various amidinates XVII ; and diiminates XVIII . Chemistry and various applications of heavier tetrylenes as bond activators, ligands, and building blocks for the construction of new chemical entities was extensively reviewed recently. − …”

Amidinatoamidosilylene–Dibromodiborene

“…Silylenes of composition [R 2 Si:] (R = supporting substituents) have a lone pair of electrons and a vacant orbital on the Si atoms (Figure ). These electronic properties enable them to possess both nucleophilic and electrophilic character. To enhance the stability and ease of isolation, the vacant p orbital of silylenes can be stabilized by coordinating with a Lewis base donor to form base-stabilized derivatives [R 2 (L)­Si:] (L = Lewis base donor).…”

“…To enhance the stability and ease of isolation, the vacant p orbital of silylenes can be stabilized by coordinating with a Lewis base donor to form base-stabilized derivatives [R 2 (L)­Si:] (L = Lewis base donor). The silylenes [R 2 Si:] and [R 2 (L)­Si:] show fruitful chemistry toward small-molecule activation . In the case of boron compounds, silylenes typically donate their lone pair of electrons to the vacant p orbital of boranes, particularly BH 3 and BPh 3 , to form Lewis acid–base adducts .…”