Probing the redox non-innocence of dinuclear, three-coordinate Co(ii) nindigo complexes: not simply β-diketiminate variants

Abstract

Reduction of the dinuclear Co(II) nindigo complex dmp(2)Nin[Co(N{SiMe(3)}(2))](2), with 1 or 2 equiv. of K(0) (or KC(8)), affords the reduced complexes [dmp(2)Nin{Co(N{SiMe(3)}(2))}(2)](-) and [dmp(2)Nin{Co(N{SiMe(3)}(2))}(2)](2-), respectively. Inspection of these reduced species reveals ligand-centered reduction, with each cobalt ion retaining a formal 2+ oxidation state.

A Dinuclear Cobalt Complex Featuring Unprecedented Anodic and Cathodic Redox Switches for Single-Molecule Magnet Activity

“…26,27 Indeed, a similar band has also been observed for the nindigo radical anion [K(DME) 4 ] [1]. 12 The CV of [1(OEt 2 ) 2 ][BAr f ] in THF ( Figure S6, Supporting Information) displays three reversible reduction waves at −0.17, −1.51, and −2.10 V mirroring those observed for 1 and its anionic derivatives. 12 Moreover, addition of 1 equiv of Figure S3, Supporting Information).…”

“…We have recently been investigating the chemistry of late 3d transition metals supported by N,N′-diaryl-β-diketimines. 12 These ligands, better known as "nindigo," are formed by two conjoined iminoindole units creating a molecule with bilateral binding sites. The steric and geometric features of each site approximate the coordination environment provided by the architecture of β-diketiminates, a highly popular class of site-directing, chelating ligands.…”

“…We and others have recently shown through chemical and electro- chemical methods the ability of nindigo to exist in five distinct oxidation states ranging from neutral dehydronindigo to a tetraanionic, closed-shell form on complexation to a metal (Scheme S1, Supporting Information). 12,24 We were attracted to the unique redox activity of the nindigo system for use in coordination compounds with base metals, namely cobalt, to generate complexes capable of effecting multielectron chemical transformations, beyond the Co 2+ /Co 3+ redox couple. 25 Moreover, as high-spin cobalt(II) (S = 3 / 2 ) possesses an intrinsic magnetic anisotropy, 3a,5 we were also interested in using nindigo to synthesize new bimetallic SMMs.…”

“…12 The reported cyclic voltammogram (CV) of 1 displays two reversible cathodic waves corresponding to its isolable one-and twoelectron reduction products [K(DME) 4 + (C1−C1* = 1.410(3) Å) by ca. 0.02 Å over that found in neutral 1.…”

“…The activity of SMMs is distinct from that of classical magnets, as the locus of their magnetic behavior lies completely at the molecular level, independent from that of the bulk material. Since the seminal discovery of SMM activity in the mixed-valence metal cluster [Mn 12 O 12 (OAc) 16 (H 2 O) 4 ]·2HOAc·4H 2 O (HOAc = CH 3 CO 2 H) in 1991, 1 SMMs have been extensively investigated owing to their potential for use in advanced magnetic materials and quantum computing devices. 2 In order for SMM activity to manifest itself, a molecule must display both a large magnetic anisotropy, resulting from molecular uniaxial zero-field splitting (D), and a non-negligible spin (S ≠ 0) ground state.…”