Molecular-level design of efficient microporous materials containing metal carboxylates: inclusion complex formation with organic polymer, gas-occlusion properties, and catalytic activities for hydrogenation of olefins

Abstract

A new series of microporous materials containing infinite chains of mononuclear metal (Cu(II), Zn(II), Ni(II))-pyridine unit bridged by dicarboxylates, copper(II) terephthalate-pyridine, [Cu II(OOCC 6H 4COO)(C 5H 5N) 2(H 2O)] · C 5H 5N · H 2O ( 1), copper(II) terephthalate-4-phenylpyridine, [Cu II(OOCC 6H 4COO)(C 11H 9N) 2(H 2O)] · (MeOH) 2 ( 2), zinc(II) fumarate-pyridine, [Zn II(OOCC 2H 2COO)(C 5H 5N) 3] · C 5H 5N · (H 2O) 0.5 ( 3), zinc(II) terephthalate-pyridine, [Zn II(OOCC 6H 4COO)(C 5H 5N) 2(H 2O) 2] · (C 5H 5N) 2 · (H 2O) 2 ( 4), nickel(II) fumarate-pyridine, [Ni II(OOCC 2H 2COO)(C 5H 5N) 3] · C 5H 5N · (H 2O) 2 ( 5), and nickel(II) terephthalate-pyridine, [Ni II(OOCC 6H 4COO)(C 5H 5N) 3] 6 · (C 5H 5N) 2 · (DMF) 6 · (H 2O) 9 ( 6), have been prepared. A porous structure, which is formed by stacking and self-assembly of the linear metal(II) dicarboxylates, has been determined by X-ray crystallography. When released with guest solvents, these complexes, except for 5, occlude large amounts of gases such as N 2 and Ar. The maximum amount of N 2 gas is 0.7–10.7 mol per mole of metal(II) salt, indicating the presence of a large number of micro- and/or mesopores. The magnetic susceptibilities of 1 and 2 obey the Curie–Weiss law over the range of 70–300 K ( θ=−1.4 K and θ=+5.5 K, respectively); the obtained Weiss constants ( θ) indicate the existence of small antiferromagnetic interactions ( 1), and ferromagnetic interactions ( 2). The different magnetic behaviors between 1 and 2 demonstrate that hydrogen bonding between the carboxylate groups and coordinated water molecules plays an important role in determining the bridge geometries and superexchange interaction between the Cu(II) ions through the Cu–O–C–O–H–O–Cu pathways. In contrast to those of the copper(II) complexes, the magnetic susceptibilities of 5 and 6 obey the Curie law. Novel inclusion complexes between host microporous molybdenum(II) dicarboxylates (fumarate ( 7), terephthalate ( 8), trans– trans-muconate ( 9), and pyridine-2,5-dicarboxylate ( 10)) and guest organic polyethers (poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG)) of various molecular weights have been synthesized. The rate of complex formation depends on the shapes of the micropores and polyethers. The amount of included polyethers increases with their molecular weight, and reaches up to a saturated amount, with the exception that complex 10 does not form complex with bulky PPG. The amount of absorbed argon in the microporous molybdenum(II) dicarboxylates decreases with increase in the amount of include polyethers. The 13C CP/MAS NMR measurement of complex 8 with PEG has demonstrated that PEG chains are included in the capillaries. This is an effective method for synthesizing supramolecular complexes. Three dimensional microporous polymers of Rh fumarate (Rh(f)) ( 11), Rh terephthalate (Rh(t)) ( 12), and a novel porphyrin rhodium coordination polymer, [Rh 2(H 2TCPP)] (H 2TCPP=4,4′,4″,4‴-(21 H,23 H-porohine-5,10,15,20-tetrayl)tetrakis benzoic acid) complexes ( 13) have exhibited high catalytic activities for hydrogen exchange and hydrogenation of olefins (ethylene, propene, and butene) at 200 K. The turnover frequencies of complexes 11, 12, and 13 for hydrogenation of ethylene at 194 K are much higher than those of other published Rh-containing materials. The microwave spectroscopic analyses of the deuterium isotopic distribution of formed propene- d 1 during C 3H 6–C 3D 6 reaction over complexes 11 and 12 reveal that the hydrogen exchange reactions take place only inside the nanopores of complexes 11 and 12 without complete scission of C–H bond of olefin molecule. Such a novel bimolecular pathway may play an important role for development of new heterogeneous hydrogenation catalysts.