![]() The theoretical defect-free crystal structure of the Cu-Co DMC is shown in Fig. Depending on the valences of the metal ions, n can be 4, 6, or 8, with 6 being the most common for materials crystallizing in the cubic phase. M 1 typically is a divalent metal ( v = 2), like Zn(II) or Cu(II), and M 2 is a trivalent metal ( u = 3), like Co(III) or Fe(III) however, other u- v combinations are also possible, such as 1–1, 4–3 20. DMCs have the general formula M 1 u v (sometimes expressed as M 1-M 2 DMC for simplicity). Inspired by these reports we envisioned a system that includes all the attractive features of the metal-catalyzed oxidative coupling, while also introducing the benefits of a heterogeneously catalyzed system.ĭouble metal cyanides (DMCs) are coordination polymers in which two different metals are linked through a cyanide group (C≡N). ![]() Furthermore, similar homogeneously catalyzed aerobic oxidative cross-coupling systems for P-N bond formation have been investigated, with Cu emerging as the metal of choice for this transformation 18, 19. 17 proposed a mild and atom-efficient synthesis of phosphoramidates starting from phosphites and amines using CuI as catalyst however, this approach suffered from the formation of oxidation side products 17. In this sense, homogeneous Cu salts have shown very promising results 15, 16. While these methods are well-established, they all suffer from either dependency on non-desired precursors or poor atom/step economy.Ī more environmentally friendly approach to the phosphoramidate synthesis is the use of metals for the aerobic oxidative coupling of phosphites and amines. 1d) 13 and the ZnI 2 triggered catalytic oxidative coupling of P(O)-H compounds and amines using an organic oxidant (Fig. 1c) 11, the direct electrochemical oxidation of phosphites and amines 12, the selenite-catalyzed Atherton–Todd-like reaction of phosphites and amines (Fig. ![]() More recent alternatives for phosphoramidate synthesis include the formation of phosphoryl azide precursors (Fig. However, the use of stoichiometric amounts of CCl 4 is highly undesired from an industrial point of view. For example, in the Atherton–Todd reaction a phosphoryl chloride is generated by the halogenation of phosphites using CCl 4 as a chlorine donor (Fig. An alternative to the direct use of halogenated phosphor substrates can be their in situ formation. These straightforward methodologies often use highly toxic reagents, such as the phosphoryl halide itself, and unpractical conditions, such as pre-cooling and fuming reactions 8, 9. Such is the interest in these products that several synthetic methodologies to obtain them have been developed during the last decade 3, 4, 5, 6, 7.Įarly strategies for phosphoramidate synthesis relied on the direct reaction of amines with the corresponding phosphoryl halides (Fig. The phosphoramidate moiety is present in a wide variety of high-value natural and synthetic compounds, ranging from biologically active natural products, such as nucleotides 1, to ligands in metal catalysis and environmentally friendly flame retardant additives 2. ![]() Preliminary mechanism studies suggest that the reaction proceeds by a continuous change in the oxidation state of the Cu metal, induced by a O 2/I − redox cycle. While the detailed study of the catalyst structure and of the metal centers by PXRD, FTIR, EXAFS and XANES revealed changes in their coordination environment, the catalyst maintained its high activity for at least 5 consecutive iterations of the reaction. This strategy successfully provides an efficient, environmentally friendly alternative to the synthesis of these valuable compounds in high yields and it is, to the best of our knowledge, the first heterogeneous approach to this protocol. Here we report the coupling of phosphites and amines promoted by a Cu 3 2-based double metal cyanide heterogeneous catalyst using I 2 as additive for the synthesis of phosphoramidates. Conventional approaches to their synthesis make use of toxic chlorinated reagents and intermediates, which are sought to be avoided at an industrial scale. Phosphoramidates are common and widespread backbones of a great variety of fine chemicals, pharmaceuticals, additives and natural products.
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