Iron(II) High‐Spin and Low‐Spin Complexes from Pentaisopropylcyclopentadienyliron(II) Bis(trimethylsilyl)amide

Photoactive Fe Catalyst for Light-Triggered Alkyd Paint Curing

Herein, we show that the photoactive complexes [(Cp)Fe(arene)]⁺ (Cp = cyclopentadienyl; arene = C₆H₆, C₆H₅Me) act as latent catalysts that allow for photochemical control over the onset of alkyd paint curing, without the need for antiskinning agents such as the volatile 2-butanone oxime normally used to prevent curing during paint storage. The highly soluble neutral complexes [(Cp)Fe(Ch)] and [(Cp)Fe(Ch')] (Ch = cyclohexadienyl, Ch' = methylcyclohexadienyl) readily convert to the photoactive complexes [(Cp)Fe(arene)]⁺ upon oxidation in alkyd, allowing the latter to be dosed in a wide range of concentrations. Infrared and Raman studies show similar spectral changes of the alkyd paint matrix as have been observed in alkyd curing mediated by well-known, industrially applied cobalt- and manganese-based catalyst Co(neodecanoate)₂ and [(Me₃TACN)₂Mn₂(μ-OOCR)₃](OOCR). The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]⁺ system performs equally well as these cobalt- and manganese-based catalysts in terms of drying time and outperform the manganese catalyst by showing a hardness development (increase) similar to that of the cobalt-based catalyst. Based on electron paramagnetic resonance and light-activity studies, we propose that photolysis of [(Cp)Fe(arene)]⁺ generates short-lived active Fe^II species, explaining the desired latency. The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]⁺ alkyd curing systems presented herein are unique examples of intrinsically latent paint curing catalysts that (1) are based on an abundant and harmless transition metal (Fe), (2) do not require any antiskinning agents, and (3) show favorable performance in terms of drying times and hardness development.

Pogo-Stick Iron and Cobalt Complexes: Synthesis, Structures, and Magnetic Properties

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(μ-I)]₂ (1-M, M = Fe, Co; Cp' = η⁵-1,2,4-tri-tert-butylcyclopentadienyl) with [Im^DippNLi]₂ (Im^DippN = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal half-sandwich compounds [Cp'M(NIm^Dipp)] (2-M, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool. Complex 2-Co can also be prepared by an acid-base reaction between [Cp'Co{N(SiMe₃)₂}] (3-Co) and Im^DippNH. The electronic and magnetic properties of 2-M and 3-Co were probed by ⁵⁷Fe Mössbauer spectroscopy (M = Fe), X-band EPR spectroscopy (M = Co), and solid-state magnetic susceptibility measurements. In particular, the central metal atom adopts a high-spin (S = 2) state in 2-Fe, while the cobalt complex 2-Co represents a rare example of a Co(II) species with a coordination number different from six displaying a low-spin to high-spin spin-crossover (SCO) behavior. The experimental observations are complemented by DFT calculations.

Pentamethylcyclopentadienyl ruthenium “pogo stick” complexes with nitrogen donor ligands

The preparation and reactivity of an imidazolin-2-iminato ruthenium complex with a rare one-legged piano-stool (“pogo stick”) geometry is reported.

Monomeric Fe(iii) half-sandwich complexes [Cp'FeX2] - synthesis, properties and electronic structure

The half-sandwich complex [Cp'Fe(μ-I)]₂ (1; Cp' = η⁵-1,2,4-(Me₃C)₃C₅H₂) is cleaved when heated in toluene to form a cation-anion pair [{Cp'Fe(η⁶-toluene)}⁺{Cp'FeI₂}^-] (2), in which the two Fe(ii) atoms adopt different spin states, i.e., a low-spin (S = 0) and a high-spin (S = 2) configuration. Upon oxidation of 1 with C₂H₄I₂, the thermally stable 15VE species [Cp'FeI₂] (3) can be isolated, in which the Fe(iii) atom adopts an intermediate spin (S = 3/2) configuration. Complex 3 is an excellent starting material for further functionalizations and it reacts with Mg(CH₂SiMe₃)₂ to form the unprecedented Fe(iii) (S = 3/2) bis(alkyl) complex [Cp'Fe(CH₂SiMe₃)₂] (4). The respective spin states of complexes 2-4 are confirmed by single-crystal X-ray crystallography, zero-field ⁵⁷Fe Mössbauer spectroscopy, and solid-state magnetic susceptibility measurements. In contrast to the related 14VE high-spin (S = 2) Fe(ii) alkyl species [Cp'FeCH(SiMe₃)₂], which resists the reaction with H₂ as a consequence of a spin-induced reaction barrier, complex 4 reacts cleanly with H₂ (8 bar) in cyclohexane to yield iron hydrides [{Cp'Fe}₂(μ-H)₃] (5) and [Cp'Fe(μ-H)₂]₂ (6) in a 1 : 4 ratio. However, when the hydrogenation of 4 is carried out in benzene, a green 19VE [Cp'Fe(η⁶-C₆H₆)] (A) intermediate is formed, which dimerizes to the bis(cyclohexadienyl)-bridged product [(Cp'Fe)₂(μ₂-η⁵:η⁵-C₁₂H₁₂)] (7). Further evidence for the intermediacy of [Cp'Fe(η⁶-C₆H₆)] (A) was gathered by X-band EPR and UV/vis spectroscopy. Interestingly, attempts to oxidize 7 with AgSbF₆ proceeded via C-C bond cleavage instead of metal oxidation to form [Cp'Fe(C₆H₆)][SbF₆] (8).