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The electronic structures and contrasting reactivity of [Cu(CF₃)₄]⁻and [Cu(CF₃)₃(CH₃)]⁻were probed using coupled cluster andab initiovalence bond calculations.

 

Nickel K- and L 2,3 -edge X-ray absorption spectra (XAS) are discussed for 16 complexes and complex ions with nickel centers spanning a range of formal oxidation states from II to IV. K-edge XAS alone is shown to be an ambiguous metric of physical oxidation state for these Ni complexes. Meanwhile, L 2,3 -edge XAS reveals that the physical d-counts of the formally Ni IV compounds measured lie well above the d 6 count implied by the oxidation state formalism. The generality of this phenomenon is explored computationally by scrutinizing 8 additional complexes. The extreme case of NiF 6 2− is considered using high-level molecular orbital approaches as well as advanced valence bond methods. The emergent electronic structure picture reveals that even highly electronegative F-donors are incapable of supporting a physical d 6 Ni IV center. The reactivity of Ni IV complexes is then discussed, highlighting the dominant role of the ligands in this chemistry over that of the metal centers. 

We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C–H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe–C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H 2 activation across the Fe( ii ) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe–carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H 2 /hydride-induced loss of the organometallic acyl unit ( i.e. pyCH 2 –CO → pyCH 3 +CO). The known reduced hydride species [HFe(CO) 4 ] − and [HFe 3 (CO) 11 ] − have been observed as products by 1 H/ 2 H NMR and IR spectroscopies, as well as independent syntheses of PNP[HFe(CO) 4 ]. The former species ( i.e. [HFe(CO) 4 ] − ) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate ([ Tol Im](BAr F ) = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase. 

A mononuclear W( iv ) bis-dithiolene complex stabilized by an oxo ligand shows a reductive reactivity toward CO 2 , from which formate and a dinuclear W( v ) complex are generated. An unusual structural rearrangement was observed during the reaction. Structural and spectroscopic characterization for a novel triply bridged dinuclear W( v ) complex is reported. 

Dinitrogen coordination to iron centers underpins industrial and biological fixation in the Haber–Bosch process and by the FeM cofactors in the nitrogenase enzymes. The latter employ local high‐spin metal centers; however, iron–dinitrogen coordination chemistry remains dominated by low‐valent states, contrasting the enzyme systems. Here, we report a high‐spin mixed‐valentcis‐(μ‐1,2‐dinitrogen)diiron(I/II) complex [(FeBr)₂(μ‐N₂)L^bis]⁻(2), where [L^bis]⁻is a bis(β‐diketiminate) cyclophane. Field‐applied Mössbauer spectra, dc and ac magnetic susceptibility measurements, and computational methods support a delocalizedS=⁷/₂Fe₂N₂unit withD=−5.23 cm⁻¹and consequent slow magnetic relaxation.

 

Dinitrogen coordination to iron centers underpins industrial and biological fixation in the Haber–Bosch process and by the FeM cofactors in the nitrogenase enzymes. The latter employ local high‐spin metal centers; however, iron–dinitrogen coordination chemistry remains dominated by low‐valent states, contrasting the enzyme systems. Here, we report a high‐spin mixed‐valentcis‐(μ‐1,2‐dinitrogen)diiron(I/II) complex [(FeBr)₂(μ‐N₂)L^bis]⁻(2), where [L^bis]⁻is a bis(β‐diketiminate) cyclophane. Field‐applied Mössbauer spectra, dc and ac magnetic susceptibility measurements, and computational methods support a delocalizedS=⁷/₂Fe₂N₂unit withD=−5.23 cm⁻¹and consequent slow magnetic relaxation.