Catalytic Hydrosilylation of Carbonyls via Re(CO)₅Cl Photolysis

Abstract

The hydrosilylation reaction between silanes and various carbonyl substrates such as aldehyde, ketone, ester, and carbonate has been catalyzed by Re(CO) 5 Cl UV photolysis. Kinetic studies have shown that the reaction is favored for the least sterically hindered silanes with aldehydes followed by aliphatic ketones. The IR spectrum of the rhenium carbonyl dimer HRe 2 (CO) 9 (SiR 3 ) has been recorded in the reaction mixture. This complex is believed to be the resting state of the active catalyst Re(CO) 4 SiR 3 , which could be released upon photactivation. A catalytic mechanism involving this species has been proposed and shown to be thermodynamically feasible using computational studies. In addition, the relative hydrosilylation rates among the various carbonyl substrates can be explained using the same mechanism.

Hydrosilylation Reactions Catalyzed by Rhenium

“…The silyl-oxy complex VI-4 could be obtained either from the transfer of a hydride from the silane to the ketone atom or from the oxidative addition of the silane followed by a β-hydride transfer process. Finally, the reductive elimination step produces the siloxy product and regenerates the pre-catalyst VI-1 In 2012, carbonyl rhenium(I) complexes, namely Re(CO)5Cl (C21) and Re2(CO)10 (C22), have been found by Fan and co-workers [48] to be effective catalysts for the hydrosilylation of carbonyl substrates with various silanes and with TOF of 20−25 h −1 for aldehydes (Scheme 9a). In this methodology, 1.0 mol% catalyst and a Et3SiH:carbonyl ratio of 3:1 were used.…”

“…Another silane coordinates to the Re center in VII-5 via a η 2 -silyl complex or a σ-silyl (σH) complex. Migration of a H atom from the silane to the alkyl group yields the silyl ether product and In 2012, carbonyl rhenium(I) complexes, namely Re(CO) 5 Cl (C21) and Re 2 (CO) 10 (C22), have been found by Fan and co-workers [48] to be effective catalysts for the hydrosilylation of carbonyl substrates with various silanes and with TOF of 20−25 h −1 for aldehydes (Scheme 9a). In this methodology, 1.0 mol% catalyst and a Et…”

“…In 2012, carbonyl rhenium(I) complexes, namely Re(CO) 5 Cl ( C21 ) and Re 2 (CO) 10 ( C22 ), have been found by Fan and co-workers [ 48 ] to be effective catalysts for the hydrosilylation of carbonyl substrates with various silanes and with TOF of 20−25 h −1 for aldehydes ( Scheme 9 a). In this methodology, 1.0 mol% catalyst and a Et 3 SiH:carbonyl ratio of 3:1 were used.…”

Syntheses and catalytic application of hydrido iron(ii) complexes with [P,S]-chelating ligands in hydrosilylation of aldehydes and ketones

“…Preliminary studies of the catalytic activity of iron complex 1 were performed to explore its potential in the hydrosilylation reduction of benzaldehyde (eqn (2), Table 1). The studies on the inuence of the reaction conditions were carried out with benzaldehyde as the model substrate by using (EtO) 3 SiH as the hydrogen source in THF at 50 C. The reaction did not occur in the absence of any catalyst (entry 1, Table 1). However, 1 mol% of complex 1 catalyzed the desired transformation and afforded benzyl alcohol in 48% yield (entry 2, Table 1).…”

“…The catalytic properties of hydrido iron(II) complexes 1-4 in hydrosilylation reactions were fully investigated. It was found that the four complexes 1-4 could be used as effective catalysts for hydrosilylation reduction of aldehydes and ketones by using (EtO) 3 SiH as a hydrogen source under mild conditions. Among them 1 is the best catalyst.…”