Hydroxyapatite-supported Rh(CO)2(acac) (acac=acetylacetonate): Structure characterization and catalysis for 1-hexene hydroformylation

A high surface area hydroxyapatite [Ca10(PO4)6(OH)2] was prepared and used as support for Rh(CO)2(acac) (acac = acetylacetonate). The supported catalyst (7270 ppm Rh) was characterized using IR and solid state NMR. The proton in the P–OH group of hydroxyapatite reacts with the acac− ligand forming acetylacetone (acacH); and the Rh dicarbonyl species was anchored on the surface via the resulting P–O− group. It is proposed that acacH stays coordinated with Rh in the supported catalyst. The supported catalyst is active in catalyzing 1-hexene hydroformylation without the need of an auxiliary ligand such as phosphine [1330 turnovers in 17 h; 300 psig syngas (H2/CO = 1); 100 °C]. Activity for the supported Rh catalyst is an order of magnitude higher than that for un-supported Rh(CO)2(acac) homogeneous system. The supported catalyst was separated from the reaction medium and re-used; giving a slightly lower activity. This is the only example of Rh(CO)2(acac) supported on an inorganic material that shows significant activity for olefin hydroformylation without the presence of an auxiliary ligand such as phosphine.