Homogeneous Catalytic Hydrosilylation of Pyridines

Abstract

The color change from yellow to violet allows the formation of the intermediate [Cp Ti(SiHMePh)(pyridine)] to be monitored in the reaction of PhMeSiH with a pyridine in the presence of the precatalyst [Cp TiMe ] [Eq. (a)]; the hydride [Cp TiH] is postulated to be the key intermediate in the catalytic cycle. The regioselective hydrosilylation of pyridine and also substituted pyridines can be catalyzed by the titanocene [Cp TiMe ]. R=Me, CO Et.

Magnesium hydrides and the dearomatisation of pyridine and quinoline derivatives

“…In this case a [Cp 2 TiMe 2 ]/PhMeSiH 2 system was reported -3 -to effect the transformation of a variety of 3-and 4-substituted and 3,5-disubstituted pyridines to the N-silylated 1,2-and 1,4-dihydropyridines or, dependent upon substitution patterns, the corresponding tetrahydropyridine products. 5 This process was reasoned to proceed via a Ti-H pyridine coordination/insertion and silane metathesis mechanism (Scheme 1) and an inability to dearomatise pyridines with 2-or 6-substitution patterns was attributed to the substrate steric demands. Although similar limitations have been observed in very recent work described by Nikonov and coworkers, in this case the catalytic ability of the cationic ruthenium complex [Cp( i Pr 3 P)Ru(NCCH 3 )]PF 6 to effect hydrosilylation of 3-and 5-substituted pyridines to the dihydropyridines was not compromised by the concomitant reduction of these products to tetrahydropyridines.…”

“…8 Scheme 1: Proposed mechanism for the titanocene-catalysed hydrosilylation of pyridine. 5 Our own interest in this area derives from our attempts to develop a catalytic and stoichiometric reaction chemistry for the abundant and environmentally benign group 2 elements heavier than beryllium that takes them beyond their traditional applications -4 -as, for example, Grignard reagents or Hauser bases. 9 Much of this initial work has explored the reactivity of the redox-inactive divalent cations of these elements by analogy with chemical behaviour previously observed for similarly d 0 complexes of early transition elements or lanthanides in their highest and trivalent oxidation states respectively.…”

Selective partial reduction of quinolines: Hydrosilylation vs. transfer hydrogenation

“…Hydrosilylation of imines, although still challenging, has been reported with rhodium [19], zinc [20], titanium [21], iridium [22], and palladium [23] catalysts. Reduction of pyridines via hydrosilylation has also been reported using palladium [24] and titanium [25] catalysts. We have now screened catalysts for imine hydrosilylation and then applied the best ones to aromatic heterocycles such as quinolines.…”

Amine synthesis via transition metal homogeneous catalysed hydrosilylation

“…136 Thus, pyridine derivatives in the presence of 2 equiv. of PhMeSiH 2 in neat conditions at 80 °C led to the silylated dihydropyridine compounds in 70-99% NMR-yields.…”