Reductive Coupling of (Fluoro)pyridines by Linear 3d‐Metal(I) Silylamides of Cr–Co: A Tale of C−C Bond Formation, C−F Bond Cleavage and a Pyridyl Radical Anion

Abstract

Herein, we disclose the facile reduction of pyridine (and its derivatives) by linear 3d‐metal(I) silylamides (M=Cr–Co). This reaction resulted in intermolecular C−C coupling to give dinuclear metal(II) complexes bearing a bridging 4,4′‐dihydrobipyridyl ligand. For iron, we demonstrated that the C−C coupling is reversible in solution, either directly or by reaction with substrates, via a presumed monomeric metal(II) complex bearing a pyridyl radical anion. In the course of this investigation, we also observed that the dinuclear metal(II) complex incorporating iron facilitated the isomerisation of 1,4‐cyclohexadiene to 1,3‐cyclohexadiene as well as equimolar amounts of benzene and cyclohexene. Furthermore, we synthesised and structurally characterised a non‐3d‐metal‐bound pyridyl radical anion. The reactions of the silylamides with perfluoropyridine led to C−F bond cleavage with the formation of metal(II) fluoride complexes of manganese, iron and cobalt along with the homocoupling or reductive degradation of the substrate. In the case of cobalt, the use of lesser fluorinated pyridines led to C−F bond cleavage but no homocoupling. Overall, in this paper we provide insights into the multifaceted behaviour of simple (fluoro)pyridines in the presence of moderately to highly reducing metal complexes.

On the Synthesis of a T‐Shaped Imido Nickel Complex and Trigonal Amido Nickel Complexes

“…This does not point to a hydrogen transfer to the transient nickel(amide) but a disproportionation reaction, mediated by the in situ formed K{18c6}[NiL 2 ]. This type of disproportionation of CHD was already observed in case of the iron(I) complex [Fe(hmds) 2 ] − , [55] and was confirmed by reacting CHD directly with K{18c6}[ NiL 2 ].…”

Intricate Road to Linear Anionic Nickel(I) Hexamethyldisilazanide [Ni(N(SiMe3)2)2]−

“…They are highly reactive, as expected from thefor these metalslow oxidation state in conjunction with the low-coordinate environment. As such, they have been exploited for a number of different reactivities such as C–F bond cleavage, , C–C multiple bond transformation, − reduction, , and a platform for either low-coordinate π-acceptor adducts (CO or alkynes), ,, imido, or chalcogenido complexes . Given the multifaceted use of these linear compounds, we were naturally interested in the respective nickel­(I) complex, which constitutes the heaviest open-shell linear metal­(I) hexamethyldisilazanide.…”

On the Synthesis and Reduction of Trigonal Halido Bis(silylamido) Metalates of Chromium to Cobalt

“…In recent reports it was also shown that such divalent 3d‐metal silylamides can be reduced giving linear, monovalent complex anions [22,25–29] . These were employed in bond activation and substrate reduction [19,24,27,29–34] . Here, the unique role of the low‐coordinate environment of the low‐valent metal as well as the weak field of silylamide ligands became evident, causing unusual higher‐spin imido cobalt complexes or metal bound alkyne radical anions [31,33,34] .…”

“…In this case, the required iron bromide complex was obtained via oxidation of the quasilinear iron(I) silylamide [M{N(SiMe 3 ) 2 } 2 ] − with benzyl bromide. A few other trigonal halido bis(silylamido) metalates were obtained by us in an analogous fashion using perfluoropyridine (Mn−Co) [19,32] or I 2 [27] as oxidants, all starting from the respective linear metal(I) silylamide. Apart from this approach, the direct introduction of organic functional groups was also shown by us via reaction of [Fe{N(SiMe 3 ) 2 } 2 ] with benzyl potassium (BnK) [19] …”