Zinc and Magnesium Catalysts for the Hydrosilylation of Carbon Dioxide

Abstract

The terminal zinc and magnesium hydride compounds, [κ-Tism]ZnH and [Tism]MgH, which feature the tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl ligand, react with B(CF) to afford the ion pairs, {[Tism]M}[HB(CF)] (M = Zn, Mg), which are rare examples of these metals in trigonal monopyramidal coordination environments. Significantly, in combination with B(CF), {[Tism]M}-[HB(CF)] generates catalytic systems for the hydrosilylation of CO by RSiH to afford sequentially the bis(silyl)acetal, HC(OSiR), and CH (RSiH = PhSiH, EtSiH, and PhSiH). In contrast to many other catalysts for these transformations, both the zinc and magnesium catalytic systems are active at room temperature, and the latter provides the first example of catalytic hydrosilylation of CO involving a magnesium compound. Also of note, the selectivity of the catalytic systems may be controlled by the nature of the silane, with PhSiH favoring CH, and PhSiH favoring the bis(silyl)acetal, HC(OSiPh).

Heterolytic Si−H Bond Cleavage at a Molybdenum‐Oxido‐Based Lewis Pair

“…Whereas mechanisms involving such an initial formal hydroboration of the substrate are scarce, they have been described previously in FLP‐based CO 2 hydrogenation and alkyne hydroboration reactions, the latter also requiring substrate activation by a Lewis acid . A comparable mechanism has very recently been proposed for a Mg/Zn mediated CO 2 hydrosilylation reported by Parkin and co‐workers …”

Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex

“…Thus,it is surprising that only very few examples of zinc-catalyzed hydrosilylation of CO 2 have been reported:t wo cationic,Nheterocyclic carbene (NHC) stabilized zinc complexes,ad icationic NHC-stabilized zinc hydride cluster,a swell as the tris(thiopyridyl)methane based [Tptm]ZnH and the tris[(1isopropylbenzimidazol-2-yl)dimethylsilyl]methane based [Tism PriBenz ]ZnH complexes were shown to catalytically react with CO 2 in presence of silanes ( Figure 1). [11] Herein we show that the recently introduced [Tntm] system [13] allows the isolation of the terminal zinc hydride complex [Tntm]ZnH. [11] Herein we show that the recently introduced [Tntm] system [13] allows the isolation of the terminal zinc hydride complex [Tntm]ZnH.…”

“…[3] Thecatalytic reduction of CO 2 with silanes is well-known, mainly using ruthenium complexes with ac ombination of high CO 2 pressures (20-80 bar) and moderate to high temperatures (45-100 8 8C), [4] but also Cu, [5] Ir, [6] and Pd [7] complexes were found to catalyze this reaction under mild conditions.In terms of price,a bundance,a nd toxicity of the metal center, the use of zinc-based systems is of significant interest. [8][9][10][11][12] However,these systems require either high temperatures and high pressures or only show low to moderate turnover numbers and turnover frequencies.O nly the recently introduced [Tism PriBenz ]b ased system was found to catalyze the hydrosilylation of CO 2 under ambient conditions,albeit with the use of ab orane additive and with only low turnover frequencies. [8][9][10][11][12] However,these systems require either high temperatures and high pressures or only show low to moderate turnover numbers and turnover frequencies.O nly the recently introduced [Tism PriBenz ]b ased system was found to catalyze the hydrosilylation of CO 2 under ambient conditions,albeit with the use of ab orane additive and with only low turnover frequencies.…”

“…Indeed, we found [Tntm]ZnH to catalytically reduce CO 2 with trimethoxysilane at room temperature and under mild conditions.T his is the first zinc-based system capable of catalytically reducing CO 2 at room temperature without the need of any additive and is also the most active system up to date.T he intermediate formate complex [Tntm]Zn(O 2 CH) was isolated and fully characterized. [8][9][10][11][12] [Tntm]ZnH (2)was prepared by reaction of the respective zinc trimethylsilanolate complex [Tntm]Zn(OSiMe 3 )(1)with aslight excess of (MeO) 3 SiH in THF in 85 %yield, similar to apreviously described method. Reported zinc-based catalysts for the hydrosilylation of CO 2 .…”

Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex

“…[8][9][10][11][12] However,these systems require either high temperatures and high pressures or only show low to moderate turnover numbers and turnover frequencies.O nly the recently introduced [Tism PriBenz ]b ased system was found to catalyze the hydrosilylation of CO 2 under ambient conditions,albeit with the use of ab orane additive and with only low turnover frequencies. [11] Herein we show that the recently introduced [Tntm] system [13] allows the isolation of the terminal zinc hydride complex [Tntm]ZnH. Compared to the similar [Tptm]ZnH complex, the more electron deficient thiopyridazine heterocycles were expected to render the metal center more Lewis acidic and thus more reactive (Figure 1).…”