Ruthenium-Catalyzed Site-Selective Intramolecular Silylation of Primary C–H Bonds for Synthesis of Sila-Heterocycles

Abstract

Incorporating the silicon element into bioactive organic molecules has received increasing attention in medicinal chemistry. Moreover, organosilanes are valuable synthetic intermediates for fine chemicals and materials. Transition metal-catalyzed C-H silylation has become an important strategy for C-Si bond formations. However, despite the great advances in aromatic C(sp)-H bond silylations, catalytic methods for aliphatic C(sp)-H bond silylations are relatively rare. Here we report a pincer ruthenium catalyst for intramolecular silylations of various primary C(sp)-H bonds adjacent to heteroatoms (O, N, Si, Ge), including the first intramolecular silylations of C-H bonds α to O, N, and Ge. This method provides a general, synthetically efficient approach to novel classes of Si-containing five-membered [1,3]-sila-heterocycles, including oxasilolanes, azasilolanes, disila-heterocycles, and germasilolane. The trend in the reactivity of five classes of C(sp)-H bonds toward the Ru-catalyzed silylation is elucidated. Mechanistic studies indicate that the rate-determining step is the C-H bond cleavage involving a ruthenium silyl complex as the key intermediate, while a η-silene ruthenium hydride species is determined to be an off-cycle intermediate.

Interconversion and reactivity of manganese silyl, silylene, and silene complexes

“…For example, they are thought to be active species in polycarbosilane synthesis from dichloromethylsilanes and sodium in the presence of [Cp 2 ZrCl 2 ], 9 13 in C 6 D 6 . Furthermore, silene complexes were recently proposed as off-cycle species in sila-heterocycle synthesis by intramolecular silylation of primary C-H bonds, 14 and free silenes play a key role in hot wire CVD of SiC using alkylsilanes. 15 Early examples of isolable transition metal complexes bearing a terminal silylene ligand featured Lewis base coordination to silicon, 16 and base-free terminal silylene complexes were not isolated until 1990.…”

“…28 Furthermore, many of the known silene complexes were synthesized by installation of a CH 2 SiR 2 H (R ¼ Me or Ph) or SiR 2 Me group, followed by b-hydride elimination. 14,28,29 These classes of reaction are combined in Scheme 2, highlighting the potential to interconvert between silylene, silyl, silene, and alkyl (CH 2 SiHR 2 ) complexes.…”

Consecutive β,β′‐Selective C(sp3)−H Silylation of Tertiary Amines with Dihydrosilanes Catalyzed by B(C6F5)3

“…Selective functionalization of C(sp 3 )ÀH bonds is an important goal in synthetic chemistry. [1] One way to achieve this is by transition-metal-catalyzed C(sp 3 ) À H silylation, [2,3] and recently selected boron Lewis acids also emerged as catalysts for this purpose. [4] For example, B(C 6 F 5 ) 3 has been shown to abstract hydride from a-C(sp 3 )ÀH bonds of amines to result in the formation of iminium ions and the borohydride; [5] that iminium ion is CÀH acidic and can be deprotonated by another molecule of the amine, affording the corresponding enamine along with the ammonium borohydride [6,7] (Scheme 1, gray box).…”

“…This process has already been employed for silylation, [8] alkylation, [9] deuteration, [10] and olefination [11] of the b-carbon atom of various (a)cyclic tertiary amines (Scheme 1, top). Of note, Park and Chang merged the C(sp 3 )ÀH silylation with a B(C 6 F 5 ) 3catalyzed intramolecular Friedel-Crafts-type silylation [12] for the synthesis of bridged silicon-containing nitrogen heterocycles starting from N-arylated piperidines. [8a] However, the undirected silylation of acyclic tertiary amines [3c] as well as their challenging two-fold C(sp 3 ) À H silylation are unprecedented.…”

Aufeinanderfolgende β,β′‐selektive C(sp3)‐H‐Silylierung von tertiären Aminen mit Dihydrosilanen katalysiert durch B(C6F5)3

“…Die Diarylsilane 2 b-e wiesen eine gute Reaktivität auf und lieferten die entsprechenden Produkte im gleichen Ausbeutebereich wie für 2 a gefunden (1 a!3 ab-ae; Tabelle 2, Nr. [1][2][3][4]. Mit dem sterisch gehinderten Dimesitylsilan (2 f) wurde keine Reaktion beobachtet (Tabelle 2, Nr.…”