Rigid confined space in frustrated Lewis pair/MOF catalyst: Highly regioselective reduction of α, β-unsaturated carbonyl compounds

The regioselective hydrogenation of α, β-unsaturated carbonyl compounds is an extremely important transformation. However, its development is hampered by a lack of precise and efficient catalysts. In this work, triggered by the steric hindrance and confinement capacity of the catalyst, we designed a novel catalyst FLP/MIL-101(Cr), with the bulky frustrated Lewis pair (FLP) of PPh3 and B(C6F5)3 immobilized in NH2-MIL-101(Cr). In the well-tailored FLP/MIL-101(Cr), the promoted selective reduction behaviors were realized, with cinnamyl alcohol selectivity up to 99 % and the complete substrate conversion in cinnamyl aldehyde reduction. Experimental characterizations and theoretical calculations indicated that the CN bond and π-π stacking interaction between FLP and the organic ligand of MIL-101(Cr) implemented and reinforced a rigid structure. Compared with homogeneous FLP, the special nano-space in FLP/MIL-101(Cr) catalyst benefits the selective reduction behavior towards the unsaturated bond with the smaller steric hindrance in α,β-unsaturated carbonyl compounds. As expected, FLP/MIL-101(Cr) showed good stabilities of skeleton structure and catalytic performance. This contribution provides an ingenious strategy to design FLP heterogeneous catalysts and represents its utilization possibility in selective reduction.