Palladium-catalyzed silyl C(sp3)–H bond activation

Abstract

The first transition-metal-catalyzed activation of silyl C(sp(3))-H bond was realized and synthetically applied. A variety of organic skeletons substituted with SiMe(3) groups could undergo the Pd-catalyzed intramolecular coupling reaction, resulting in an unprecedented synthetic method for yielding six-membered silacycles. It was found that the adjacent Si atom played an essential role for the activation of the C(sp(3))-H bond of the SiMe(3) group; no activation reaction of the C(sp(3))-H bond of the CMe(3) group took place under the same reaction conditions.

Mechanism, reactivity, and selectivity of the iridium-catalyzed C(sp3)–H borylation of chlorosilanes

“…Namely, the reaction takes place at the methyl group adjacent to a chlorosilyl moiety, thus generating compounds containing 1-silyl-1-boryl-substituted methylene. 11 Both the boronate functionality introduced in the reaction and the silyl group are synthetically very useful, 10 as they can be employed in, for instance, Suzuki 12 and Hiyama 13 couplings, respectively. Since the silyl substituent is compatible with the conditions of the Suzuki reaction, 14 a sequential application of these transformations opens access to non-symmetrical gem -difunctionalized methylenes.…”

Key Mechanistic Features in Palladium-Catalyzed Methylcyclopropanation of Norbornenes With Vinyl Bromides: Insights From DFT Calculations

“…The calculations showed the relative Gibbs free energy of this complex is very high with a value of 68.1 kcal/mol (Figure 4), thus we exclude this possibility. Alternatively, we investigate the key role of base in deprotonation, which has been confirmed in previous experiments (Wasa et al, 2009; Liang et al, 2012) and calculations (Biswas et al, 2000; Davies et al, 2005; Lafrance et al, 2007; Ess et al, 2008; Kefalidis et al, 2010; Figg et al, 2013; Xie et al, 2013c, 2016). However, it is interesting to note that the γ-H 1 in complex 8 is far away from palladium center with the Pd–H 1 distance of 5.268 Å (Figure 4), therefore, it is very difficult to activate this C–H 1 bond.…”

Access to Silylated Pyrazole Derivatives by Palladium‐Catalyzed C−H Activation of a TMS group

“…Our experimental conditions and the results presented in the Supporting Information tables suggest that this reaction does not rely on a proton abstraction mechanism, as in Xi's case (strong bases such as t BuOK do not work), but rather on a concerted metalation–deprotonation mechanism, as proposed by Fagnou (Figure ). Indeed, the mild base employed (cesium carbonate) and the acceleration of the reaction induced by the addition of pivaloic acid are in good agreement with a CMD mechanism.…”

“…When the precursor 4 aa was treated under Xi′s conditions, the sila ring closing failed, providing only the desilylated bromopyrazole 11 a (Figure ). In his paper, Xi insisted on the critical importance of trialkylphosphines as ligand for the Pd 0 but also on the sensitivity of the C−H activation to the base employed, t BuONa being essential to the success of their process.…”

“…Our interest for silylated heterocycles and their applications in medicinal chemistry led us to pay particular attention to striking results from Xi et al This group has indeed shown that silyl C(sp 3 )−H bonds in trialkylsilyl groups such as SiMe 3 could be triggered by Pd(PPh 3 ) 4 , in the presence of ( t Bu) 3 P as ligand, in toluene at 120 °C (Figure a) …”