Three-Dimensional Phosphine Metal-Organic Frameworks Assembled from Cu(I) and Pyridyl Diphosphine

Metal-organic frameworks (MOFs) with phosphine based ligands are extremely attractive for catalysis. In this paper, phosphine has been successfully incorporated for the first time into three-dimensional (3D) MOFs. The MOFs are based on rigid L2M2 dimeric secondary building blocks assembled from Cu(I) and a pyridyl diphosphine ligand, 4-(3,5-bis(diphenylphosphino)phenyl)pyridine, with Br- (CuL-Br), Cl- (CuL-Br), or PF6- (CuL-PF6) as counteranions. The structures have a 4.12(2) net topology, which can be further simplified to 6(4).8(2)-qtz. The MOFs contain 1D homochiral channels. The PF6- anions hosted in the ID channel of CuL-PF6 can be readily exchanged with Br- or cr(-) while keeping the framework intact. The materials show anion-tunable flexible porosity. CuL-Br reveals gradual uptake of MeOH, while CuL-PF6 exhibits stepwise sorption for MeOH. The heterogeneous Lewis acid catalytic activity of the MOFs has been shown in ketalization reaction. CuL-Br and CuL-PF6 are active in the reactions between ethylene glycol and 2-butanone/cyclohexanone, up to 93% yield with 0.2 mol 96 catalyst loading. In contrast, no reaction happens between ethylene glycol and bulky benzophenone, suggesting profound size selectivity. The catalysts can be reused with the framework left intact for three runs without loss of activity.