Chemoselective Hydrosilylation of Olefin/Ketone Catalyzed by Iminobipyridine Fe and Co complexes

Abstract

The chemoselective hydrosilylation of olefins and ketones catalyzed by Fe and Co complexes bearing an iminobipyridine derivative ligand was investigated. The reaction of a 1 : 1 mixture of styrene and acetophenone over the Fe catalyst achieved selective hydrosilylation of acetophenone. In contrast, the corresponding Co complex showed the opposite selectivitystyrene-selective hydrosilylation. The reaction of 3-acetylstyrene with both olefin and ketone moieties in the molecule showed that the Co complex catalyzed olefin-selective hydrosilylation. In contrast, the addition of pyridine to the Co-catalyzed system showed the opposite chemoselectivity, affording the ketone hydrosilylated product. The chemoselectivity of olefin/ketone hydrosilylation was switched by replacing the central metal of the complex with the iminobipyridine derivative ligand and by changing the simple reaction conditions (absence or presence of pyridine) using an identical Co complex.Hydrosilylation is widely used to obtain organosilane compounds, and many catalysts for hydrosilylation have been developed to date. Recent studies in this field involve the development of catalysts that facilitate hydrosilylation at olefin or carbonyl moieties while excluding other functional groups, such as halides and hydroxy groups from the reaction. These chemoselective hydrosilylation reactions have been reported for olefin bearing halogen, [1,2,[3][4][5][6] hydroxy, [4,7] carbonyl, [3,[7][8][9] epoxy, [1,3,5,7,10] amino, [1,3,6,11] and sulfide [5,12] substituents. Hydrosilylation reactions of unsaturated organic compounds such as olefins and ketones (aldehydes) are commonly and widely used in the industry. However, the chemoselective hydrosilylation of olefins and ketones is challenging. For compounds containing both olefin and ketone moieties, several reactions have demonstrated olefin [1,[7][8][9] and ketone selectivity [13] . To exhibit selectivity, each catalyst has its own distinctive ligand; however, catalysts with selectivity for olefin/ketone hydrosilylation that can be converted by simply changing the reaction conditions have not been reported to date.Recently, iron complexes with an iminobipyridine derivative ligand (Figure 1) have been reported to exhibit high catalytic activity for hydrosilylation of olefin [14] and ketone [15] with a much higher catalytic activity for ketone than that for olefin. [15] In addition, the addition of pyridine to the iron-catalyzed system accelerated ketone hydrosilylation, whereas it suppressed the olefin hydrosilylation. [15] These results suggest that a transition metal complex with higher catalytic activity for olefins than that for ketones could be developed. Moreover, the catalytic activity for ketones could be enhanced and that for olefins suppressed by the addition of a pyridine, similar to the iron system. Moreover, the chemoselectivity of olefin/ketone hydrosilylation could be switched by the simple addition of pyridine using the same catalyst.This paper reports (i) the preparation of novel Co complexes be...

Cobalt bis(2‐ethylhexanoate) and terpyridine derivatives as catalysts for the hydrosilylation of olefins

“…Gas chromatography: Trace DSQ GC Column, split = 50:1, flow = 1.1 ml min −1 constant flow, inlet temperature = 250 C, column temperature = 55 C (held for 1 min), then 15 C min −1 up to 120 C, then 20 C min −1 up to 200 C, and then 15 C min −1 up to 280 C, (held for 5 min). 1 H NMR (400 MHz) and 13 C NMR (100.6 MHz) spectra were recorded on a Bruker Advance spectrometer. The data of NMR were listed in the Supporting Information.…”

“…Data are available in article supplementary material: copies of 1 H NMR, 13 C NMR, and the data of single crystal of products.…”

“…These cobalt NNN complexes showed high activity and selectivity in the hydrosilylation of alkynes and 1,3‐diyne with Ph 2 SiH 2 . [ 13 ] The hydrosilylation of internal allene with Ph 2 SiH 2 conducted with cobalt‐dppf complex produced the allylsilanes with high regioselectivity. [ 14 ] The cobalt complex bearing an iminobipyridine derivative ligand exhibited high catalytic activity along with olefin selective.…”

Base Metal‐terpyridine Complex Immobilized on Stationary Phase Aimed as Reusable Hydrosilylation Catalyst

“…We have been engaged in developing base metal complexes with high catalytic activity and have reported that Fe complexes bearing an appropriately substituted 2,2':6'2"-terpyridine [12] or iminobipyridine ligand [13,14] as a pincer ligand showed high catalytic activity for olefin and ketone hydrosilylation. Co complexes bearing an iminobipyridine ligand [15,16] have been reported to catalyze an unprece-dented switchable chemoselective hydrosilylation between olefin and ketone frameworks, showing olefin-selective hydrosilylation under neat conditions and ketone-selective hydrosilylation in a pyridine medium. [15] In general, suitable metals and ligands are required for the synthesis of transition metal complexes with excellent catalytic activity.…”

“…Co complexes bearing an iminobipyridine ligand [15,16] have been reported to catalyze an unprece-dented switchable chemoselective hydrosilylation between olefin and ketone frameworks, showing olefin-selective hydrosilylation under neat conditions and ketone-selective hydrosilylation in a pyridine medium. [15] In general, suitable metals and ligands are required for the synthesis of transition metal complexes with excellent catalytic activity. In most cases, suitable ligands are not commercially available; therefore, they should be synthesized independently.…”