Most state-of-art transition-metal catalysts usually require organic ligands, which are essential for controlling the reactivity and selectivity of reactions catalyzed by transition metals. However, organic ligands often suffer from severe problems including cost, toxicity, air/moisture sensitivity, and being commercially unavailable. Herein, we show a simple, mild, and efficient aerobic oxidation procedure of amines using inorganic ligand-supported non-precious metal catalysts 1, (NH ) [MMo O (OH) ] (M=Cu ; Fe ; Co ; Ni ; Zn , n=3 or 4), synthesized by a simple one-step method in water at 100 °C, demonstrating that the catalytic activity and selectivity can be significantly improved by changing the central metal atom. In the presence of these catalysts, the catalytic oxidation of primary and secondary amines, as well as the coupling of alcohols and amines, can smoothly proceed to afford various imines with O (1 atm) as the sole oxidant. In particular, the catalysts 1 have transition-metal ion core, and the planar arrangement of the six Mo centers at their highest oxidation states around the central heterometal can greatly enhance the Lewis acidity of catalytically active sites, and also enable the electrons in the center to delocalize onto the six edge-sharing MO units, in the same way as ligands in traditional organometallic complexes. The versatility of this methodology maybe opens a path to catalytic oxidation through inorganic ligand-coordinated metal catalysis.

Formamides represent an abundant class of compounds in organic synthesis. They can be made efficiently by the direct catalytic coupling of methanol with amines in the presence of metal-based catalysts. However, these catalysts require complicated organic ligands, susceptible to oxidative self-degradation, restricting their practical applications. Here, we describe an inorganic ligand-supported chromium (III) catalyst, (NH 4) 3 [CrMo 6 O 18 (OH) 6 ], which consists of a central chromium (III) single-atomic core supported by a cycle-shaped inorganic ligand consisting of six Mo VI O 6 octahedra, shows excellent activity and selectivity. Various primary amines and secondary amines are successfully transformed into the corresponding formamides under mild conditions, and the formylation of primary diamines is also achieved. The chromium catalyst can be reused several times with little loss of the activity. Mechanistic insight is provided based on the observation of an intermediate and control experiments.

Engineering photoredox-triggered chemical transformation via visible light has been an emerging area in organic synthesis. However, most of the well-established photocatalysts are based upon either transition metal complexes involved with noble metals and organic ligands or photosensitive organic dyes, the development of pure inorganic molecular photocatalysts that could provide better stability and durability is greatly retarded. Herein we discover that the Anderson polyoxometalate (POM) Na 4 [NiMo 6 O 18 (OH) 6 ] (1), which consists of pure inorganic framework built from a central Ni II core supported by six Mo VI O 6 inorganic scaffold/ligands, can be used as a powerful photocatalyst. Upon irradiation with visible light (> 400 nm), the compound can catalyze, in high efficiency, a wide range of reactions, including the oxidative cross-coupling reaction of chlorides with amines, as well as oxidation of chlorides using molecular oxygen, affording various imines, aldehydes, and ketones, respectively in high selectivity and good yields. Owing to the robust inorganic framework, this catalyst exhibits excellent stability during the catalysis and reusability with little loss of the catalytic activity, thus providing an alternative without use of complicated organic ligands and expensive noble metal-based photosensitizers.The utilization of solar energy as a clean and renewable energy resource for driving synthetic transformations has become a surgent thrust in green chemistry. [1] During the last two decades, organo-Ni complexes [2] in combination with photosensitizers [1a] (e. g. Ru and Ir-based polypyridyl complexes) have been explored extensively for various chemical transformations in organic synthesis (Figure 1b). In general, this catalytic system relies on the ability of metal-complexes and noble metal photosensitizers to engage in electron transfer processes with organic substrates upon photoexcitation with visible light. [3] Despite remarkable advantages of this system, [4] shortcomings such as poor stability of the organometallic compounds derived from the delicate organic ligands, use of precious metals and the difficulty to recover and reuse these homogeneous photocatalysts restrict their practical applications. [5] Polyoxometalates (POMs), [6] a class of discrete metal-oxo clusters analogous to semiconductor photocatalysts such as [a] Dr.Figure 1. Imines synthesis systems: (a) Organic-ligand supported metal catalysis systems. (b) Organic-nickel photoredox catalysis system. (c) Inorganic-ligand supported nickel catalysis system.

Herein, we divulge an efficient protocol for aerobic oxidation of alcohols with an inorganic-ligand supported iodine catalyst, (NH4)5[IMo6O24]. The catalyst system is compatible with a wide range of groups and exhibits high selectivity, and shows excellent stability and reusability, thus serving as a potentially greener alternative to the classical transformations.

A green and highly efficient N-formylation of amines using formic acid as the acylating agent by iron catalysis with excellent selectivity and yields.