Unusual Electronic Features and Reactivity of the Dipyridylazaallyl Ligand: Characterizations of (smif)₂M [M = Fe, Co, Co⁺, Ni; smif = {(2-py)CH}₂N] and [(TMS)₂NFe]₂(smif)₂

Abstract

Application of the dipyridylazaallyl ligand (2-py)CHNCH(2-py) (smif) to a series of first-row transition metals afforded (smif)2M n [n = 0, M = Fe (1), Co (2), Ni (3); n = +1, M = Co (2+)] and {(TMS)2NFe}2(smif)2 (4 2 ) via metathetical procedures. The Mössbauer spectrum of 1 (S = 0) and TDDFT calculations, including a UV−vis spectral simulation, reveal it to be a covalent, strong-field system with Δo estimated as ∼18 000 cm−1 and B ≈ 470 cm−1. (smif)2Co (2) has S = 1/2 according to SQUID data at 10 K. DFT calculations suggest that the odd electron is localized in a smif π* orbital, i.e., smif is redox-active. EPR-silent (smif)2Ni (3) has S = 1 (SQUID), and calculations show that the unpaired spins reside in the d z 2 and d x 2 −y 2 orbitals. X-ray structural parameters suggest that low-spin d6 1 and 2+ are relatively symmetric D 2d species, but 2 and 3 manifest a distortion in which one smif is canted in the plane perpendicular to the other. (smif)FeN(TMS)2 (4) is principally monomeric in solution, but reversibly dimerizes (K eq ≈ 10−4 M−1) via C−C bond formation in the azaallyl backbone to crystallize as {(TMS)2NFe}2(smif)2 (4 2 ). The azaallyl compounds possess extraordinary UV−vis absorptivities (ε ≈ 18000−52000) at 580 ± 15 nm and 406(25) nm that have been identified as intraligand bands with Cnb → smif π* character.

A Theoretical Study of the 3d‐M(smif)2Complexes: Structure, Magnetism, and Oxidation States

“…Motivated by the experimental findings of Wolczanski and coworkers, [1,2] we conducted the present theoretical investigation of the M(smif) 2 electronic structure. We observed many of the features of transition-metal chemistry that are interesting from www.chemphyschem.org a theoretical perspective: complicated potential energy surfaces with near-degenerate stationary structures, competing low-energy (spin-)states, unusual electronic configurations, and redox-active ligands.…”

“…We carry out a theoretical investigation of the recently reported M(smif) 2 series [1,2] and find a number of interesting phenomena. These include complex potential energy surfaces with near-degenerate stationary points, low-lying states, non-trivial electron configurations, as well as non-innocent ligand behavior.…”

“…[9] Wolczanski and co-workers recently synthesized and characterized the homologous first row series from vanadium to nickel, including some of the cations. [1,2] The M(smif) 2 are hexa-coordinated, pseudo-octahedral N-donor complexes ( Figure 1). The tridentate smif ligand coordinates with its anionic aza-nitrogen and the lone pairs of its two pyridyls.…”

Influence of N‐Substitution on the Oxidation of 2‐Pyridylmethylamines with Bis(trimethylsilyl)amides of Iron(III) – Synthesis of Heteroleptic Iron(II) 2‐Pyridylmethylamides

“…[22] As expected from the findings described above, deprotonation of dipicolylamine leads to very reactive iron(II) bis(dipicolylamide) which precipitates from the reaction mixture thus preventing subsequent degradation reactions. [23,24] However, soluble . [23,25] These complexes are stable and also accessible via metalation of N-picolyl-(2-pyridylmethylidene)amine or metathetical via the reaction of lithium [1,3-bis(2-pyridyl)-2-azapropenide] with metal halides.…”

The Instability of Ni{N(SiMe3)2}2: A Fifty Year Old Transition Metal Silylamide Mystery

“…[3] Uniquely, the Ni(II) amide was reported to be unstable, decomposing to a black solid at room temperature. [2] The Mn, Fe, and Co silylamides are thermally stable and have proven to be valuable synthons in diverse applications, [4][5][6][7][8][9][10][11][12][13] but the unstable nature of Ni{N(SiMe3)2}2 has hindered its further use. Its instability is especially striking because several other stable, homoleptic Ni(II) amides are known.…”