Preparation of Allyl and Vinyl Silanes by the Palladium‐Catalyzed Silylation of Terminal Olefins: A Silyl‐Heck Reaction

Abstract

A high-yielding protocol for the palladium-catalyzed silylation of terminal alkenes using silyl halides is reported. This method allows facile conversion of styrenes to E-β-silyl styrenes using either TMSI or TMSCl/LiI. Terminal allyl silanes with good E:Z ratios are also readily accessed from α-olefins by this method. When combined with existing technology, this transformation provides a powerful strategy to selectively functionalize the vinyl or allylic position of terminal alkenes.

Structure and reactivity of [(L·Pd) n ·(1,5-cyclooctadiene)] ( n = 1–2) complexes bearing biaryl phosphine ligands

“…The BrettPhos ( 15 ) used in this work was received as a gift from Sigma Aldrich, for which we are grateful. [(1,5-cyclooctadiene)Pd(CH 2 TMS) 2 ] was prepared according to the literature [12] or using a modification of this procedure [1] and was stored at −20 °C in a nitrogen-filled glovebox when not in use. All other reagents were purchased from commercial sources and used without further purification.…”

The first example of nickel-catalyzed silyl-Heck reactions: direct activation of silyl triflates without iodide additives

“…1 Recently, we have established the silyl-Heck reaction as a novel route to access both allyl and vinyl silanes. 2,3 This general method allows for the direct silylation of terminal alkenes using silyl halides and transition metal catalysts, in a reaction that we believe is analogous to classical Heck arylation (Figure 1). 4 …”

Palladium-Catalyzed Cross-Coupling of Monochlorosilanes and Grignard Reagents

“…Earlier this year, as part of our study of transition metal-catalyzed cross-couplings of silicon electrophiles, 10 we demonstrated that linear and α-branched silanes could be prepared via the cross-coupling of silyl iodides and alkyl zinc halides using palladium catalysis (Figure 1, top). 11 This “silyl-Negishi” strategy represents the natural polarity of the Si–C bond and takes advantage of the natural electrophilicity of silicon centers.…”

“…While modest in yield, the only other example of tert -butyldimethylsilyl halide (TBS–X) activation is through the use of more reactive TBS–OTf under nickel catalysis. 10c …”

“…From a mechanistic standpoint, however, considering that both the Grignard reagent and the palladium pre-catalysts introduce heavier halides (bromide and iodide) to the reaction, we cannot rule out the possibility that the reactions in Schemes 2–4 are proceeding via initial halogen exchange at the silicon center. 10a, 34 To better understand the role of the various halides in the reaction, we investigated reaction conditions that excluded heavier halogens. Using isopropyl magnesium chloride and the palladium chloride precatalyst (DrewPhos) 2 PdCl 2 , the alkylation of Me 2 PhSiCl was investigated (Table 2).…”