FeII complexes supported by an iminophosphorane ligand: synthesis and reactivity

The synthesis of iron complexes supported by a mixed phosphine-lutidine-iminophosphorane (PPyNP) ligand was carried out. While bidentate κ2-N,N coordination was observed for FeCl2, pincer coordination modes were adopted at cationic iron centers, either through dechlorination of [LFe(PPyNP)Cl2] (1) or direct coordination of PPyNP to Fe(OTf)2. Reaction with tert-butylisocyanide gave access to the diamagnetic octahedral complex [Fe(PPyNP)(CNtBu)3]X2 (X = OTf (4), Cl (4')). Both 1 and 4 were shown to undergo deprotonation of the phosphinomethyl group, but the resulting complexes were not active for the dehydrogenative coupling of hexan-1-ol. The hydrosilylation of acetophenones was catalyzed at room temperature with 1 mol% of a catalyst generated in situ from cationic PPyNP-supported iron triflate complexes and KHBEt3.

Metal-Ligand Cooperativity in Iron Dinitrogen Complexes: Proton-Coupled Electron Transfer Disproportionation and an Anionic Fe(0)N2 Hydride

Metal-ligand cooperativity and redox-active ligands enable the use of open-shell first-row transition metals in catalysis. However, the fleeting nature of the reactive intermediates prevents direct inspection of the relevant catalytic species. By employing phosphine α-iminopyridine (PNN)-based complexes, we show that chemical and redox metal-ligand cooperativity can be combined in the coordination sphere of iron dinitrogen complexes. These systems show dual activation modes either through deprotonation, which triggers reversible core dearomatization, or through reversibly accepting one electron by reducing the imine functionality. (PNN)Fe(N₂) fragments can be obtained under mildly reducing conditions. Deprotonation of such complexes induces dearomatization of the pyridine core while retaining a terminally coordinated N₂ ligand. This species is nevertheless stable in solution only below -30 °C and undergoes unusual ligand-assisted redox disproportionation through proton-coupled electron transfer at room temperature. The origin of this phenomenon is the significant lability of the α-imine C-H bonds in the dearomatized species, where the calculated bond dissociation free energy is 48.7 kcal mol^-1. The dispropotionation reaction yields an overreduced iron compound, demonstrating that the formation of such species can be triggered by mild bases, and does not require harsh reducing agents. Reaction of the dearomatized species with dihydrogen yields a rare anionic Fe hydride that binds dinitrogen and features a rearomatized core.

Complexation behaviour of LiCl and LiPF6– model studies in the solid-state and in solution using a bidentate picolyl-based ligand

Using a new bulky bidentate ligand and combining various structure elucidation methods, coordination modes of [ligand·LiX] (X = Cl, PF₆) complexes both in solid-state and in solution have been revealed.

Reactivity of a dearomatised pincer CoIIBr complex with PNCNHC donors: alkylation and Si–H bond activation via metal–ligand cooperation

Whereas [Co(^CyP*N_aC^NHC)Br] (1) with dearomatised pincer ^CyP*N_aC^NHC affords the Co^II–alkyl complex 3, uncommon silane reduction yields the Co^I complex 4.

Iron(ii) β-ketiminate complexes as mediators of controlled radical polymerisation

A series of novel iron(ii) β-ketiminate complexes have been prepared and screened in styrene and methyl methacrylate CRP.