Small Molecule Activation by Two‐Coordinate Acyclic Silylenes

Abstract

In recent decades, the chemistry of stable silylenes (R2Si:) has evolved significantly. The first major development in this chemistry was the isolation of a silicocene which is stabilized by the Cp* (Cp* = η5‐C5Me5) ligand in 1986 and subsequently the isolation of a first N‐heterocyclic silylene (NHSi:) in 1994. Since the groundbreaking discoveries, a large number of isolable cyclic silylenes and higher coordinated silylenes, i.e. Si(II) compounds with coordination number greater than two, have been prepared and the properties investigated. However, the first isolable two‐coordinate acyclic silylene was finally reported in 2012. The achievements in the synthesis of acyclic silylenes have allowed for the utilization of silylenes in small molecule activation including inert H2 activation, a process previously exclusive to transition metals. This minireview highlights the developments in silylene chemistry, specifically two‐coordinate acyclic silylenes, including experimental and computational studies which investigate the extremely high reactivity of the acyclic silylenes.

Generation of Bis(ferrocenyl)silylenes from Siliranes

“…Although single crystals suitable for an X-ray diffraction (XRD) analysis could not be obtained due to partial hydrolysis that furnished Fc*FcSi(OH)2 [45], 4 was characterized by spectroscopic techniques. As the reduction of diorganodichlorosilanes represents an efficient method for the generation of silylenes [4,33], we speculated that the reduction of bis(ferrocenyl)dichlorosilane 4 might furnish silylene 1. However, the generation of 1 by the reduction of 4 was not observed when common metal reductants such as KC8, Na, or Li were employed, and only complex mixtures including Fc*H were As the reduction of diorganodichlorosilanes represents an efficient method for the generation of silylenes [4,33], we speculated that the reduction of bis(ferrocenyl)dichlorosilane 4 might furnish silylene 1.…”

“…As the reduction of diorganodichlorosilanes represents an efficient method for the generation of silylenes [4,33], we speculated that the reduction of bis(ferrocenyl)dichlorosilane 4 might furnish silylene 1. However, the generation of 1 by the reduction of 4 was not observed when common metal reductants such as KC8, Na, or Li were employed, and only complex mixtures including Fc*H were As the reduction of diorganodichlorosilanes represents an efficient method for the generation of silylenes [4,33], we speculated that the reduction of bis(ferrocenyl)dichlorosilane 4 might furnish silylene 1. However, the generation of 1 by the reduction of 4 was not observed when common metal reductants such as KC 8 , Na, or Li were employed, and only complex mixtures including Fc*H were obtained [41].…”

“…Silylenes, i.e., divalent silicon analogues of carbenes, represent highly attractive reactive intermediates due to their considerable potential as building blocks for organosilicon compounds [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. There are several examples of stable silylenes, which are usually stabilized thermodynamically by introduction of heteroatom-based substituents such as amino groups.…”

Main Group Multiple Bonds for Bond Activations and Catalysis

“…The ability to control this equilibrium provides a new route to access to the more reactive silylsilylene species. Two‐coordinate acyclic silylenes are highly reactive species as they contain a vacant coordination site and a lone pair, and as such have shown facile bond activations towards small molecules and a variety of substrates [24, 28, 105–107] . It could be envisaged that new catalytic cycles, based on the ability to control this equilibrium, could be achieved in a somewhat similar fashion to that depicted in Scheme 1 B.…”

“…In addition to main group multiple bonds, low oxidation state and/or coordinate main group complexes have also undergone a renaissance in recent years. With several new breakthroughs revealing new classes of compounds, such as nucleophilic aluminyls, [21, 22] as well as advances in bond activations and catalysis [23–28] . The synthesis and bonding nature of main group multiple bonds have been reviewed recently [5, 6, 29–33] .…”