A Rhodium-Grafted Hydrotalcite as an Efficient Heterogeneous Catalyst

Significance

A rhodium-grafted hydrotalcite catalyst (Rh/HT) for heterogeneous 1,4-addition of organoboronic acids to α,β-unsaturated carbonyl compounds was developed. The hydrotalcite (HT) was added to an aqueous solution of RhCl₃·nH₂O (Rh; 2.0 x 10^-3 M), and the heterogeneous mixture was stirred at room temperature for 30 minutes. The solid product was separated by filtration, washed with deionized water and dried to give rhodium-grafted hydrotalcite (Rh/HT) (Rh content: 2.0 wt%). Rh/HT catalyzed the 1,4-addition reaction of organoboron reagents to various α,β-unsaturated carbonyl compounds in the presence of 1,5-cyclooctadiene. Thus, for example, the reaction of 2-cyclohexen-1-one and phenylboronic acid was carried out in 1,4-dioxane at 100 °C for 4 hours to give 3-phenylcyclohexanone in 98% yield. The recovered Rh/HT was readily reused twice (over 90% yield).