The acid-base switching of complexes formed from anti-electrostatic anion-anion homodimers of organophosphates and cyanostar macrocycles was investigated for the first time. High-fidelity 2:2 complexes were selected by using suitably sized organo substituents. Reversible and direct switching occurs with triflic acid and hydroxide base. An unexpected acid⋅⋅⋅anion heterodimer was discovered with weaker picric acid, which helped reveal some of the elementary steps. Switching can also proceed in a cooperative (strong anion then weak acid) or stepwise manner (weak acid then strong anion).

The divalent cobalt complex of the diprotic pincer ligand bis-pyrazolylpyridine, (H L)CoCl , is dehydrohalogenated twice by LiN(SiMe ) in the presence of PEt to give monomeric S=1/2 LCo(PEt ) (1), fully characterized in the solid-state and solution as a square pyramidal monomer with a long axial Co-P bond. This 17-electron species reacts in time of mixing with N O to form L Co (μ-OPEt ) (2)+3 OPEt , the former the first example of phosphine oxide bridging two transition metals. The same products are formed from O , and divalent cobalt persists even in the presence of excess oxidant. Species (2) catalyzes oxygen atom transfer (OAT) for generation of O=PEt from PEt from either N O or O . Bridging and terminal cobalt oxo intermediates are suggested, and the electron donor power, and potential redox activity of the dianionic pincer ligand is emphasized.

The process of removal of protons and chloride, dehydrohalogenation, from [(H2L)FeCl2] is investigated systematically, to understand the reactivity of the implied transient LFeII. Reaction of [(H2L)FeCl2] with 2 equiv. of LiN(SiMe3)2 yields the “‐ate” complex LiClFe2L2, as its dimer with every iron five‐coordinate in an FeN4Cl environment. To avoid Li+ cation derived from LiN(SiMe3)2, reaction of Na2L with FeCl2 gives a product from addition of water, paramagnetic Na2[NaFe(HL)(L)]2(LFeO), which reveals Na/pyrazolate Nβ interactions and a five coordinate oxo group in the OFe3Na2 core of this aggregate. Abstraction of chloride in [(H2L)FeCl2] with NaBArF4 in THF gives paramagnetic [(H2L)Fe(THF)3]2+, which fails to react with CO. Dehydrohalogenation in the presence of Ph2PC2H4PPh2, dppe, gives both [LFe(κ2‐dppe)]2(µ‐dppe)] and [LFe(κ2‐dppe)(κ1‐dppe)], diamagnetic saturated species, which can be separated by pentane extraction. Dehydrohalogenation in the presence of tBuNC gives diamagnetic [LFe(CNtBu)3]. This is selectively methylated at both pyrazolate β‐nitrogen atom to give [LMeFe(tBuNC)3]2+ which shows rich cyclic voltammetry, and which is reduced, with KC8, to diamagnetic [LMeFe(tBuNC)2]. Structure determination of some of these, together with IR data on isocyanide stretching frequencies, show L2– to be a stronger donor than LMe. First installing triflate (to avoid the more persistent chloride ligand) facilitates access to [LFe(Lewis base)3]2+ complexes, but this cation still shows relatively weak binding of CO to LFeII, which implicates weak π basicity of that d6 species. Production of paramagnetic bis‐pincer complexes [(H2L)2Fe]2+ and [(LMe)2Fe]2+ in the presence of abundant Lewis base in polar medium is demonstrated, which illustrates a pincer ligand redistribution challenge to be kept in mind when trying to maintain a 1:1 Fe:pincer ratio, for highest reactivity.

Redox inert cations are increasingly featuring participating in non-innocent structural aggregation roles. The six-coordinate bis-pyrazolate pyridine pincer (L) complex LFe II (DMAP) 3 (DMAP = 4-dimethylaminopyridine) is oxidized, to Fe III , by excess silver triflate. All beta nitrogen atoms of the pyrazolate rings bind Ag + , to create a species with two linear N-Ag-N units parallel to the linear Fe-O-Fe unit, in [LFe(DMAP) 2 Ag] 2 O 2+ . Excess silver triflate oxidizes LCo II (PEt 3 ) 2 to form CoL 2 Ag 4 (OTf ) 2 -(PEt 3 ) 2 + as its triflate salt, and this has a bis-pincer Co III center where two pyrazolate nitrogen atoms carry Ag(PEt 3 ) + groups and the other two carry AgOTf groups. Finally, deprotonation [a]