Synthesis and Reactivity of Zr MOFs Assembled from PNNNP-Ru Pincer Complexes

Abstract

Three isostructural Zr metal-organic frameworks have been synthesized from PNNNP-Ru pincer metallolinkers bearing different combinations of ancillary ligands (1, Zr6O4(OH)4(OAc)4{cis-(PNNNP)RuCl2(CO)}2; 2, Zr6O4(OH)4(O2CH)4{(PNNNP)RuCl(CO)2}2Cl2; 3, Zr6O4(OH)4(OAc)4{cis-/trans-(PNNNP)RuCl2(CO)}2; PNNNP = 2,6-(HNPAr2)2C5H3N; Ar = p-C6H4CO2-). The structure and composition of the PNNNP-Ru pincer MOFs have been determined using synchrotron X-ray powder diffraction, solid- and solution-state NMR spectroscopy, IR spectroscopy, and elemental analysis. Reaction of 2 with KOtBu results in deprotonation of an NH group of the PNNNP-RuCl(CO)2 linkers. Subsequent treatment with Me3NO removes a Ru-coordinated CO ligand, generating 2-b, which proved to be a recyclable catalyst for the hydrosilylation of aryl aldehydes with Et3SiH. A similar postsynthetic treatment of 1 and 3 does not generate active catalysts, highlighting the importance of precatalyst design and activation. A homogeneous analogue of 2-b also showed inferior catalytic performance, demonstrating the benefit of catalyst immobilization.