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We report on the synthesis and characterization of Mn(III) chloride (MnIIICl3) complexes coordinated with N-oxide ylide ligands, namely trimethyl-N-oxide (Me3NO) and pyridine-N-oxide (PyNO). The compounds are reactive and, while isolable in the solid-state at room temperature, readily decompose into Mn(II). For example, "[MnIIICl3(ONMe3)n]" decomposes into the 2D polymeric network compound complex salt [MnII(µ-Cl)3MnII(µ-ONMe3)]n[MnII(µ-Cl)3]n·(Me3NO·HCl)3n (4). The reaction of MnIIICl3 with PyNO forms varied Mn(III) compounds with PyNO coordination and these react with hexamethylbenzene (HMB) to form the chlorinated organic product 1-cloromethyl-2,3,4,5,6-pentamethylbenzene (8). In contrast to N-oxide coordination to Mn(III), the reaction between [MnIIICl3(OPPh3)2] and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) resulted in electron transfer-forming d5 manganate of the [TEMPO] cation instead of TEMPO–Mn(III) adducts. The reactivity affected by N-oxide coordination is discussed through comparisons with other L–MnIIICl3 complexes within the context of reduction potential. [ABSTRACT FROM AUTHOR]

High-valent Fe-OH species are often invoked as key intermediates but have only been observed in Compound II of cytochrome P450s. To further address the properties of non-heme FeIV-OH complexes, we demonstrate the reversible protonation of a synthetic FeIV-oxo species containing a tris-urea tripodal ligand. The same protonated FeIV-oxo species can be prepared via oxidation, suggesting that a putative FeV-oxo species was initially generated. Computational, Mössbauer, XAS, and NRVS studies indicate that protonation of the FeIV-oxo complex most likely occurs on the tripodal ligand, which undergoes a structural change that results in the formation of a new intramolecular H-bond with the oxido ligand that aids in stabilizing the protonated adduct. We suggest that similar protonated high-valent Fe-oxo species may occur in the active sites of proteins. This finding further argues for caution when assigning unverified high-valent Fe-OH species to mechanisms.

[((Ar) PMI)Mo(CO)4 ] complexes (PMI=pyridine monoimine; Ar=Ph, 2,6-di-iso-propylphenyl) were synthesized and their electrochemical properties were probed with cyclic voltammetry and infrared spectroelectrochemistry (IR-SEC). The complexes undergo a reduction at more positive potentials than the related [(bipyridine)Mo(CO)4 ] complex, which is ligand based according to IR-SEC and DFT data. To probe the reaction product in more detail, stoichiometric chemical reduction and subsequent treatment with CO2 resulted in the formation of a new product that is assigned as a ligand-bound carboxylate, [( iPr 2PhPMI)Mo(CO)3 (CO2 )](2-) , by NMR spectroscopic methods. The CO2 adduct [( iPr 2PhPMI)Mo(CO)3 (CO2 )](2-) could not be isolated and fully characterized. However, the C-C coupling between the CO2 molecule and the PDI ligand was confirmed by X-ray crystallographic characterization of one of the decomposition products of [( iPr 2PhPMI)Mo(CO)3 (CO2 )](2-) .

In situ FT-IR measurements and electronic structure calculations are reported for the reduction of CO2 catalyzed by the macrocyclic complex [CoIIN4H]2+ (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene). Beginning from the [CoIIN4H]2+ resting state of the complex in wet acetonitrile solution, two different visible light sensitizers with substantially different reducing power are employed to access reduced states. Accessing reduced states of the complex with a [Ru(bpy)3]2+ sensitizer yields an infrared band at 1670 cm-1 attributed to carboxylate, which is also observed for an authentic sample of the one-electron reduced complex [CoN4H(MeCN)]+ in CO2 saturated acetonitrile solution. The results are interpreted based on calculations using the pure BP86 functional that correctly reproduces experimental geometries. Continuum solvation effects are also included. The calculations show that Co is reduced to CoI in the first reduction, which is consistent with experimental d-d spectra of square Co(I) macrocycle complexes. The energy of the CO2 adduct of the one-electron reduced catalyst complex is essentially the same as for [CoN4H(MeCN)]+, which implies that only a fraction of the latter forms an adduct with CO2. By contrast, the calculations indicate a crucial role for redox noninnocence of the macrocyclic ligand in the doubly reduced state, [CoI(N4H) -•], and show that [CoI(N4H) -•] binds partially reduced CO2 fairly strongly. Experimentally accessing [CoI(N4H) -•] with an Ir(bpy)3 sensitizer with greater reducing power closes the catalytic cycle as FT-IR spectroscopy shows CO production. Use of isotopically substituted C18O2 also shows clear evidence for 18O-substituted byproducts from CO2 reduction to CO.

Neutral three‐coordinate iron alkylidenes of the form PN−Fe=CHR have been proposed as viable candidates for alkene metathesis. Indeed, during the final stages of preparing this current study, a separate report disclosed that dearomatized PN−Fe‐alkyl complexes are active precatalysts for ring‐opening metathesis polymerization (ROMP) of norbornene implicating PN−Fe=CHR species as possible intermediates. In yet another separate report, we prepared Zn analogues of PN−Fe‐alkyl complexes and herein provide an account for the synthesis, characterization, and reactivity of some new iron complexes with the same tBu substituted PN platform. [ABSTRACT FROM AUTHOR]

We describe herein the hydrogen-atom transfer (HAT)/proton-coupled electron-transfer (PCET) reactivity for Fe(IV)-oxo and Fe(III)-oxo complexes (1-4) that activate C-H, N-H, and O-H bonds in 9,10-dihydroanthracene (S1), dimethylformamide (S2), 1,2-diphenylhydrazine (S3), p-methoxyphenol (S4), and 1,4-cyclohexadiene (S5). In 1-3, the iron is pentacoordinated by tris[N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea](3-)) or its derivatives. These complexes are basic, in the order 3 ≫ 1 > 2. Oxidant 4, [Fe(IV)N4Py(O)](2+) (N4Py: N,N-bis(2-pyridylmethyl)bis(2-pyridyl)methylamine), is the least basic oxidant. The DFT results match experimental trends and exhibit a mechanistic spectrum ranging from concerted HAT and PCET reactions to concerted-asynchronous proton transfer (PT)/electron transfer (ET) mechanisms, all the way to PT. The singly occupied orbital along the O···H···X (X = C, N, O) moiety in the TS shows clearly that in the PCET cases, the electron is transferred separately from the proton. The Bell-Evans-Polanyi principle does not account for the observed reactivity pattern, as evidenced by the scatter in the plot of calculated barrier vs reactions driving forces. However, a plot of the deformation energy in the TS vs the respective barrier provides a clear signature of the HAT/PCET dichotomy. Thus, in all C-H bond activations, the barrier derives from the deformation energy required to create the TS, whereas in N-H/O-H bond activations, the deformation energy is much larger than the corresponding barrier, indicating the presence of a stabilizing interaction between the TS fragments. A valence bond model is used to link the observed results with the basicity/acidity of the reactants.

This work details the synthesis, characterization, and catalytic activity of reactive low‐coordinate organozinc complexes. The complexes activate hydrogen and they appear to be more active in hydrogenation of ketones and imines than their tridentate pincer analogs. This is thought, in part, to be due to the lack of trailing third phosphorus arm present in previous work. DFT computations reveal a sigma‐bond metathesis mechanism is comparable to an alternative aromatization/dearomatization metal‐ligand cooperative mechanism. [ABSTRACT FROM AUTHOR]

Methods to prepare a new synthetic high spin oxoiron(IV) complex from a well-characterized oxoiron(III) species and from a hydroxoiron(III) species via a proton-coupled electron transfer process-a first in synthetic chemistry are reported. The obtained oxoiron(IV) complex has a trigonal bipyramidal coordination geometry with the Fe-O unit positioned within a hydrogen bonding cavity and exhibit longest distance for the [Fe.sup.IV]-O unit bond for a monomeric oxoiron(IV) complex.

The encumbering m-terphenyl isocyanide ligand (CN[Ar.sup.Mes2] (Mes = 2,4,6-[Me.sub.3][C.sub.6][H.sub.2])) is used for stabilizing homoleptic tetraisocyanide complexes of cobalt in the 1-, 0 and 1+ charge state. Density functional theory calculations are used for rationalizing the structural modulation in terms of thermal access to low-energy [b.sub.2]-symmetric C-Co-C bending modes.