A family of rhodium(i) NHC chelates featuring O-containing tethers for catalytic tandem alkene isomerization–hydrosilylation

Abstract

The catalytic performances in hydrosilylation of alkenes strongly depend on the structure of O-functionalized NHC Rh(i) complexes.

Mn2(CO)10 and UV light: a promising combination for regioselective alkene hydrosilylation at low temperature

“…It is worth noting that no trace of alkene isomerization nor dehydrogenative silylation products were detected, which are commonly observed side reaction products. 24–26 Increasing the alkene : silane ratio from 1 : 2 to 1 : 1 and 2 : 1 (entries 5 and 6, respectively) led to reasonable decrease of the hydrosilylation yields (from 94% to 78% for the 1 : 1 ratio and 86% for the 2 : 1 ratio) and minimal increase of octene isomerization (1% for the 1 : 1 ratio and 3% for the 2 : 1 ratio).…”

Rh(I)/(III)‐N‐Heterocyclic Carbene Complexes: Effect of Steric Confinement Upon Immobilization on Regio‐ and Stereoselectivity in the Hydrosilylation of Alkynes

“…Complexes Rh1-Rh5 were stable as solids under atmospheric conditions and were obtained as yellow to orangecoloured solids after recrystallization from CH 2 Cl 2 /diethyl ether. The 13 C NMR spectra displayed one doublet signal for the NHC's C 2 -carbon in the range of 173-184 ppm (J Rh-C = 52 Hz) for complexes Rh1-Rh7, which is in the usual range for Rh(I)À NHC complexes. [14c] In Rh3 and Rh4, the pyridine fragment of the hemilabile NHCs coordinates to the metal.…”

“…[12a] Rh(I) NHC complexes provide high anti-Markovnikov selectivity in the hydrosilylation of alkenes. [13] Despite the vast number of catalysts including Rh NHC complexes, [14] there is still need for the development of catalysts that allow for high stereo-and regioselectivity. [4,6b,15] Also, while substantial efforts have been dedicated to the immobilization of organometallic catalysts over the last decades, [2b,16] still few examples of Rh-catalysed alkyne hydrosilylations by supported catalysts with high regio-and stereoselectivity exist.…”

“…Detailed studies on Co(III) bis(NHC) complexes also revealed that bulky NHCs favour the formation of the anti ‐Markovnikov products in alkene hydrosilylation [12a] . Rh(I) NHC complexes provide high anti ‐Markovnikov selectivity in the hydrosilylation of alkenes [13] …”

Rh(I) Complexes in Catalysis: A Five-Year Trend

“…The catalyst produced the E-vinylsylane in excellent yields and high selectivity [56] (Scheme 6, Figure 2). Hydrosilylation and tandem isomerization-hydrosilylation of alkenes, on the other hand, were successfully performed by a family of rhodium complexes bearing an NHC ligand with an oxygen-containing pendant arm and differing for the derivatization on the O-donor [57] (Figure 2). The results showed the efficacy of O,C-hemilabile species in this kind of process, but also that the catalytic performances can be significantly affected by slight changes in the stereo-electronic properties of the ligand.…”