Carbene insertion into N-H bonds with size-selectivity induced by a microporous ruthenium-porphyrin metal-organic framework

A stable and porous porphyrinic metal-organic framework, Ru-PMOF-1(Hf), has been prepared through the self-assembly of [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato](monocarbonyl)ruthenium (Ru(TCPP)(CO)) and HfCl4. Single-crystal X-ray diffraction analysis reveals that Ru-PMOF-1(Hf) possesses a three-dimensional (3D) structure with orthogonal 1D open channels of 1.9 x 1.9 nm(2). The porous nature has been confirmed by gas adsorption measurements. Its catalytic activity for the carbene insertion into N-H bonds has been investigated. The catalytic results indicate that Ru-PMOF-1(Hf) is efficient for the insertion reactions of ethyl 2-diazoacetate (EDA) into a range of secondary amines with up to 92% yield, 938 TON and 2475 h(-1) TOF. As an excellent heterogeneous catalyst, Ru-PMOF-1(Hf) can be recovered and reused for at least ten runs with negligible loss of catalytic activity. Due to its uniform microporosity in three orthogonal directions, Ru-PMOF-1(Hf), of which the particle sizes were carefully controlled by sieving, can induce size selectivity regarding the amine substrates. The reactivities of different unbranched dialkylamines, such as diethylamine (NHEt2), dibutylamine (NHBu2) and dipentylamine (NHPent(2)), have been compared, and the results display an apparent decreasing trend along the chain lengthening. For comparison, the corresponding nonporous and homogeneous catalyst Ru(TMCPP)(CO) (TMCPP = tetrakis(4-methoxycarbonylphenyl)porphyrin) displays negligible difference towards the reactions with these three amines.