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The complex [(BDI)VCl(N{SiMe3}2)] (1) (BDI– = [ArNC(CH3)]2CH, Ar = 2,6-iPr2C6H3), a precursor readily prepared from metathesis of [(BDI)VCl2] and Na[N{SiMe3}2], can be reduced with Na/NaCl in the presence of white P4 to form a dinuclear species containing two VIII centers bridged by a tricyclic [P6]2– scaffold, namely, [(BDI)V(N{SiMe3}2)]2(μ-η1:η1-P6) (2). Coordination of [P6]2– involves a unique chairlike μ-η1:η1 binding mode with a contiguous tricyclic hexaphosphorus unit bridging across the two V centers. Complexes 1 and 2 have been structurally characterized, and a pathway toward the formation of the chairlike tricyclic [P6]2– scaffold in 2 is proposed.

Complex (PNP)NbCl 2 (N[ t Bu]Ar) (1) (PNP − = N[2-P i Pr 2 -4-methylphenyl] 2 ; Ar = 3,5-Me 2 C 6 H 3 ) reacts with one equiv. of NaN 3 to form a mixture of (PNPN)NbCl 2 (N[ t Bu]Ar) (2) and (PNP)NbN(N[ t Bu]Ar) (3), both of which have been spectroscopically and crystallographically characterized, including 15 N isotopic labelling studies. Complex 3 represents the first structurally characterized example of a neutral and mononuclear Nb nitride. Independent studies established 3 to form via two-electron reduction of 2, whereas oxidation of 3 by two-electrons reversed the process. Computational studies suggest the transmetallation step to produce the intermediate [(PNP)NbCl(N 3 )(N[ t Bu]Ar)] (A) which extrudes N 2 to form the phosphinimide [(PNPN)NbCl(N[ t Bu]Ar)] (B) followed by disproportionation to 2 and low-valent [(PNPN)Nb(N[ t Bu]Ar)] (C). The latter then undergoes intramolecular N-atom transfer to form the nitride moiety in 3.

The separation and purification of niobium and tantalum, which co-occur in natural sources, is difficult due to their similar physical and chemical properties. The current industrial method for separating Ta/Nb mixtures uses an energy-intensive process with caustic and toxic conditions. It is of interest to develop alternative, fundamental methodologies for the purification of these technologically important metals that improve upon their environmental impact. Herein, we introduce new Ta/Nb imido compounds: M( t BuN)(TriNOx) (1-M) bound by the TriNOx 3− ligand and demonstrate a fundamental, proof-of-concept Ta/Nb separation based on differences in the imido reactivities. Despite the nearly identical structures of 1-M, density functional theory (DFT)-computed electronic structures of 1-M indicate enhanced basic character of the imido group in 1-Ta as compared to 1-Nb. Accordingly, the rate of CO 2 insertion into the MN imido bond of 1-Ta to form a carbamate complex (2-Ta) was selective compared to the analogous, unobserved reaction with 1-Nb. Differences in solubility between the imido and carbamate complexes allowed for separation of the carbamate complex, and led to an efficient Ta/Nb separation ( S Ta/Nb = 404 ± 150) dependent on the kinetic differences in nucleophilicities between the imido moieties in 1-Ta and 1-Nb.

A series of Ca–Mn clusters with the ligand 2-pyridinemethoxide (Py-CH 2 O) have been prepared with varying degrees of topological similarity to the biological oxygen-evolving complex. These clusters activate water as a substrate in the oxidative degradation of propylene carbonate, with activity correlated with topological similarity to the OEC, lowering the onset potential of the oxidation by as much as 700 mV.