Zn–Co Double Metal Cyanides as Heterogeneous Catalysts for Hydroamination: A Structure–Activity Relationship

Abstract

Zn–Co double metal cyanide (DMC) materials are effective heterogeneous catalysts for intermolecular hydroaminations. Using the reaction of 4-isopropylaniline with phenylacetylene as a test, the effect of different catalyst synthesis procedures on the catalytic performance is examined. The best activities are observed for double metal cyanides with a cubic structure and prepared with a Zn2+ excess, and for nanosized particles prepared via a reverse emulsion synthesis. Detailed study of the active Zn2+ sites in the cubic material by EXAFS gives evidence for coordinative vacancies around the Zn, with four cyanide ligands in close proximity of the Zn. The substrate scope of the hydroaminations was successfully expanded to both aromatic and aliphatic alkynes and other aromatic and aliphatic amines. Even with styrenes the reaction proceeded with aromatic amines. The DMC catalysts are truly heterogeneous, possess a high thermal stability and are perfectly reusable.

New Cubic Phases for T2M[CN]6·xH2O with T = Ni, Cu and M = Ru, Os: Improving the Robustness and Modulating the Electron Density at the Cavity Surfaces

“…Both, the catalytic and gas storage performance of PBAs are positively correlated with the number of anionic block vacancies (i.e. the number of available coordination sites at the external metal after water removal),[3a] but also requires the preservation of the porous structure. Particularly, for adsorption applications, when the adsorbates are H 2 , CO 2 or CH 4 (which do not have a dipolar moment), the pores should be small enough to favor short‐range interactions but sufficiently big to adsorb significant quantities of gas .…”

“…For both applications, Cu 2+ containing PBAs have shown an interesting behavior derived from the Cu 2+ tendency to adopt an electron configuration close to 3d 10 . [3b], This comprises a remarkable electron withdrawing ability to remove charge from the inner metal through the Cu–NC bond, but also from the substrates when these metal centers participate as active sites in, for example, catalytic oxidation reactions. In H 2 adsorption, evidence for the H 2 coordination to the copper atoms has been documented …”

Zinc-modulated Fe–Co Prussian blue analogues with well-controlled morphologies for the efficient sorption of cesium

“…Zn-Co PBA is a 3D double metal cyanide with an excellent catalytic performance in ring-opening polymerization reactions and the adsorption of organic pollutants. [32][33][34][35][36] However, its application in Cs sorption requires further investigation.…”

Hidden diversity of vacancy networks in Prussian blue analogues

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Prussian blue analogues (PBAs) are a broad and important family of microporous inorganic solids, famous for their gas storage (1,2,3,4,5), metal-ion immobilisation (6,7), proton conduction (8,9), and stimuli-dependent magnetic (10, 11, 12), electronic (13) and optical (14) properties. The family also includes the widely-used double-metal cyanide (DMC) catalysts (15,16,17) and the topical hexacyanoferrate/hexacyanomanganate arXiv:1908.10596v1 [cond-mat.mtrl-sci] PBAs is the ability to transport mass reversibly, a process made possible by structural vacancies. Normally presumed random (21,22,23), vacancy arrangements are actually crucially important because they control the connectivity of the micropore network, and hence diffusivity and adsorption profiles (24,25).

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