The catalytic reactivity of the high-spin Mn(II) pyridinophane complexes [(Py2NR2)Mn(H2O)2]2+ (R = H, Me, tBu) towards O2 formation is reported. With small macrocycle N-substituents (R = H, Me), the complexes catalytically disproportionate H2O2 in aqueous solution. While this catalysis is shut down with a bulky substituent (R = tBu), the complex becomes active for electrocatalytic H2O oxidation in aqueous solution. Control experiments are in support of a homogeneous molecular catalyst and preliminary mechanistic studies suggest the catalyst is mononuclear. This ligand-controlled switch in catalytic reactivity has implications for the design of new manganese-based water oxidation catalysts.

Iron-catalyzed cross-couplings with simple ferric salts have been known since the 1970s, pioneered by Kochi for cross-coupling using alkylmagnesium nucleophiles including MeMgBr. While Kochi observed the formation of a S = 1/2 iron species in reactions of simple ferric salts with MeMgBr proposed to be an iron(I) species, the identity of this species has remained undefined for nearly 40 years. Herein, we report the isolation and characterization of [MgCl(THF)5][Fe8Me12], which combined with EPR and MCD studies is shown to be consistent with Kochi’s S = 1/2 species. Reaction studies with β-bromostyrene demonstrate that this species alone displays minimal reactivity but, when combined with additional MeMgBr, leads to rapid and selective formation of cross-coupled product.

The use of N-methylpyrrolidone (NMP) as a co-solvent in ferric salt catalyzed cross-coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross-coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP) ][FeMe ] (1), which forms as the major iron species in situ in reactions of Fe(acac) and MeMgBr under catalytically relevant conditions where NMP is employed as a co-solvent. Importantly, combined GC analysis and Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross-coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe Me ] cluster generation, which occurs in the absence of NMP.

Isolation and reactivity of iron–NHCs observed during catalysis demonstrate ligand effects on nucleophile chelation, suppressing β-hydride elimination within alkyl–alkyl cross-coupling.