Transition metal catalyzed carbon‐silicon bond forming reactions using chlorosilanes promoted by Grignard reagents

Abstract

New catalytic C--Si bond-forming reactions using chlorosilanes are described. These reactions proceed efficiently under mild conditions by the combined use of Grignard reagents and transition metal catalysts, such as Ti, Zr, Ni, and Pd. It is proposed that ate complex intermediates formed by the reaction of transition metals with Grignard reagents play important roles as the active catalytic species. The present study demonstrates the practical use of chlorosilanes in transition metal catalyzed silylation reactions providing convenient methods for allyl- or vinylsilane synthesis. The reaction pathways of these transformations as well as the scope and limitations are discussed.

Integrated Palladium‐Catalyzed Arylation of Heavier Group 14 Hydrides

“…[3] The conventional chemical routes to these compounds have predominantly involved nucleophilic substitution with Grignard or organolithium reagents. [4,5] These methods have limited applications because compounds that contain functional groups sensitive to organometallic reagents are only accessible in multiple steps. Consequently, more general synthetically useful methods for the preparation of functionalized Group 14 compounds remain in great demand.…”

Synthesis of Structurally Complex Silicon Frameworks through the First Sila‐Aldol Reaction

“…[9] Forsilicon-based compounds,however, such siliconcarbon bond-forming reactions have not been reported, although they must be considered as ap owerful alternative to standard coupling techniques,s uch as the Wurtz reaction and related methods, [10] hydrosilylation, [11] as well as transition-metal-catalyzed silicon-carbon coupling reactions. [12] Consequently,w es et out to explore the applicability of the sila-aldol reaction as an ovel synthetic method for the synthesis of complex silicon-carbon frameworks.B ased on this sila-aldol strategy,w hich induced an anionic rearrangement cascade,w ea chieved the selective formation of 2-oxahexasilabicyclo[3.2.1]octan-8-ide 1 (Scheme 1).We considered the intramolecular sila-aldol reaction as an optimal starting point for the development of this trans-formation as it should be entropically favored and employs highly symmetric starting materials.H owever,t he synthesis and isolation of such compounds,f or example, a,w-bis-(acyl)silanes,were previously not possible.Given our ongoing interest in the formation of cyclic acylsilanes, [13] we were now able to accomplish the synthesis of 1,4-bis-(acyl)cyclohexasilane 2 by reacting 1,4-dipotassium-1,4-bis-(trimethylsilyl)cyclohexasilane (3) [14] with two equivalents of mesitoyl chloride (MesCOCl) in diethyl ether (Et 2 O) at À78 8 8C. This reaction resulted in the clean formation of airstable and crystalline 1,4-bis(mesitoyl)cyclohexasilane (2)a s a1 :1 mixture of the trans and cis isomers in 72 %y ield (Scheme 2), an optimal and highly promising precursor molecule for our subsequent studies.T he analytical data were consistent with the proposed structure,w ith one resonance in the 29 Si NMR spectrum for the magnetically equivalent endocyclic SiMe 2 groups near À37 ppm, one Scheme 1.…”

Synthesis of Structurally Complex Silicon Frameworks through the First Sila‐Aldol Reaction

“…Its structure was confirmed by NMR spectroscopya nd X-ray crystallography,a nd it displays ad istinctive chargetransfer transition. [12] Consequently,w es et out to explore the applicability of the sila-aldol reaction as an ovel synthetic method for the synthesis of complex silicon-carbon frameworks.B ased on this sila-aldol strategy,w hich induced an anionic rearrangement cascade,w ea chieved the selective formation of 2-oxahexasilabicyclo[3.2.1]octan-8-ide 1 (Scheme 1).We considered the intramolecular sila-aldol reaction as an optimal starting point for the development of this trans-formation as it should be entropically favored and employs highly symmetric starting materials.H owever,t he synthesis and isolation of such compounds,f or example, a,w-bis-(acyl)silanes,were previously not possible.Given our ongoing interest in the formation of cyclic acylsilanes, [13] we were now able to accomplish the synthesis of 1,4-bis-(acyl)cyclohexasilane 2 by reacting 1,4-dipotassium-1,4-bis-(trimethylsilyl)cyclohexasilane (3) [14] with two equivalents of mesitoyl chloride (MesCOCl) in diethyl ether (Et 2 O) at À78 8 8C. [1] On the basis of this general strategy,namely the merging of two carbonyl compounds,s ynthetic chemists have put al ot of emphasis on stereoselective aldol reactions over the last couple of centuries to accomplish results comparable to those achieved by organisms and enzymes in nature.…”

“…[1] On the basis of this general strategy,namely the merging of two carbonyl compounds,s ynthetic chemists have put al ot of emphasis on stereoselective aldol reactions over the last couple of centuries to accomplish results comparable to those achieved by organisms and enzymes in nature. [12] Consequently,w es et out to explore the applicability of the sila-aldol reaction as an ovel synthetic method for the synthesis of complex silicon-carbon frameworks.B ased on this sila-aldol strategy,w hich induced an anionic rearrangement cascade,w ea chieved the selective formation of 2-oxahexasilabicyclo[3.2.1]octan-8-ide 1 (Scheme 1). [9] Forsilicon-based compounds,however, such siliconcarbon bond-forming reactions have not been reported, although they must be considered as ap owerful alternative to standard coupling techniques,s uch as the Wurtz reaction and related methods, [10] hydrosilylation, [11] as well as transition-metal-catalyzed silicon-carbon coupling reactions.…”

“…[2][3][4][5] These synthetic approaches include,f or example, the use of organocatalysts (amine-based systems), [4,6] chiral auxiliaries (Evans oxazolidinone route), [7] as well as chiral Lewis acids (e.g., Zn, Ag, Pd, and Cu complexes) [4,5,8] and bases. [12] Consequently,w es et out to explore the applicability of the sila-aldol reaction as an ovel synthetic method for the synthesis of complex silicon-carbon frameworks.B ased on this sila-aldol strategy,w hich induced an anionic rearrangement cascade,w ea chieved the selective formation of 2-oxahexasilabicyclo[3.2.1]octan-8-ide 1 (Scheme 1). [12] Consequently,w es et out to explore the applicability of the sila-aldol reaction as an ovel synthetic method for the synthesis of complex silicon-carbon frameworks.B ased on this sila-aldol strategy,w hich induced an anionic rearrangement cascade,w ea chieved the selective formation of 2-oxahexasilabicyclo[3.2.1]octan-8-ide 1 (Scheme 1).…”