Recent Advances in Silylene Chemistry: Small Molecule Activation En-Route Towards Metal-Free Catalysis

Abstract

*2 Si: (Cp* ¼ η 5 -C 5 Me 5 ), the first isolable Si(II) compound, and later in 1994 with the discovery of the first N-heterocyclic silylene by West and Denk, heralding the beginning of a bourgeoning era in low-valent silicon chemistry. Since these and other key discoveries, massive advances have been made in understanding and elucidating the nature of these reactive compounds, and their ability, for example, to activate small molecules, or behave as ligands in transition metal complexes which can perform a variety of catalytic or stoichiometric transformations. In this chapter, recent advances in silylene chemistry will be presented, with a particular focus on developments in the last 10 years approximately. A key emphasis will rest on the reactivity of isolable silylenes, including their coordination towards metals, with respect to small molecule bond activation, and potential catalytic transformations. Although metalcoordinated silylene complexes have been shown to be catalytically useful in a variety of transformations, metal-free catalysis with silylenes is still a target.

Advances in Phosphasilene Chemistry

“…A similar reactivity towards H 2 S, NH 3 , and amines (1,1‐addition reactions) was observed for N ‐heterocyclic silylene 86 …”

NHCs in Main Group Chemistry

“…Nowadays it is widely recognized that some classes of low-valent main group element compounds possess properties similar to those of transition metals regarding some aspects of their bonding nature and chemical reactivity. − In fact, representatives of singlet carbenes and related main group element compounds can activate small molecules under mild conditions, catalyze organic reactions, and act as ligands in transition metal catalysis. − …”

1,4‐Dehydrogenation with a Two‐Coordinate Cyclic (Alkyl)(amino)silylene

“…Furthermore, owing to the intrinsic Lewis basicity (lone‐pair electrons) and Lewis acidity (vacant 3 p orbital) of the divalent silicon atom, a number of small‐molecule activations with either transient or isolable silylenes have been reported. Such discoveries have brought attention to the application of silylenes as potential reagents for the transformation of organic molecules in organic chemistry –. For example, Woerpel and co‐workers took advantage of the nature of silylenes in reversible [1+2] cycloaddition reactions with alkenes, for example, in the addition of di‐ tert ‐butylsilylene, generated from the cyclohexene adduct A , to various alkenes to afford the corresponding silacyclopropanes B (Scheme ) .…”