Abstract
We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn–alkyl bond to yield an acyl intermediate which undergoes rapid Si–H bond cleavage of the silane HSiR3 forming the active 16e– Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficiently and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data and DFT calculations revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor.
Highlights
Organosilane-based compounds are widely employed in a broad variety of commercial products such as coating materials, paints, or medicinal applicants, which is attributed to high chemical and thermal stability as well as to their low toxicity.[1]
We describe the activity of fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-isopropylphosphino) (1) and fac-[Mn(dpre)(CO)3(CH2CH2CH3)] (dpre = 1,2-bis(din-propylphosphino) (2) as precatalysts for the Dehydrogenative silylation (DS) of alkenes to afford selectively E-vinylsilanes. This is a rare example of a base-metal catalyzed DS of alkenes which proceeds at room temperature following two parallel catalytic cycles: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as a sacrificial hydrogen acceptor
The atom efficiency is lowered by the fact that an excess of substrate or addition of sacrificial agents is typically required
Summary
Organosilane-based compounds are widely employed in a broad variety of commercial products such as coating materials, paints, or medicinal applicants, which is attributed to high chemical and thermal stability as well as to their low toxicity.[1]. Dehydrogenative silylation (DS) of alkenes displays an interesting alternative to that Noble metals such as Rh,[8] Ir, or Ru10 are commonly used in DS reactions. Xu and co-workers reported on an elegant photoredox induced hydrogen-atom transfer (HAT) cascade in combination with cobalt catalysis for the ADS of alkenes yielding allylsilanes in high selectivity. We describe the activity of fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-isopropylphosphino) (1) and fac-[Mn(dpre)(CO)3(CH2CH2CH3)] (dpre = 1,2-bis(din-propylphosphino) (2) as precatalysts for the DS of alkenes to afford selectively E-vinylsilanes This is a rare example of a base-metal catalyzed DS of alkenes which proceeds at room temperature following two parallel catalytic cycles: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as a sacrificial hydrogen acceptor
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