Electrides are ionic compounds thus far appearing in the solid state, where the anionic part is constituted by isolated electrons. We herein provide an unambiguous computational means to distinguish electrides from similar species, proving the existence of some electrides in the gas phase. We also put forward a recipe to design new electrides.

A detailed mechanistic study of the hydroxylation of alkane C-H bonds using H2O2 by a family of mononuclear non heme iron catalysts with the formula [Fe(II)(CF3SO3)2(L)] is described, in which L is a tetradentate ligand containing a triazacyclononane tripod and a pyridine ring bearing different substituents at the α and γ positions, which tune the electronic or steric properties of the corresponding iron complexes. Two inequivalent cis-labile exchangeable sites, occupied by triflate ions, complete the octahedral iron coordination sphere. The C-H hydroxylation mediated by this family of complexes takes place with retention of configuration. Oxygen atoms from water are incorporated into hydroxylated products and the extent of this incorporation depends in a systematic manner on the nature of the catalyst, and the substrate. Mechanistic probes and isotopic analyses, in combination with detailed density functional theory (DFT) calculations, provide strong evidence that C-H hydroxylation is performed by highly electrophilic [Fe(V)(O)(OH)L] species through a concerted asynchronous mechanism, involving homolytic breakage of the C-H bond, followed by rebound of the hydroxyl ligand. The [Fe(V)(O)(OH)L] species can exist in two tautomeric forms, differing in the position of oxo and hydroxide ligands. Isotopic-labeling analysis shows that the relative reactivities of the two tautomeric forms are sensitively affected by the α substituent of the pyridine, and this reactivity behavior is rationalized by computational methods.

We introduce a simple and general scheme to derive from wavefuntion analysis the most appropriate atomic/fragment electron configurations in a molecular system, from which oxidation states can be inferred. The method can be applied for any level of theory for which the first-order density matrix is available, and unlike others, it is not restricted to transition metal complexes. The method relies on the so-called spin-resolved effective atomic orbitals which for the present purpose is extended here to deal with molecular fragments/ligands. We describe in detail the most important points of the new scheme, in particular the hierarchical fragment approach devised for practical applications. A number of transition metal complexes with different formal oxidation states and spin states and a set of organic and inorganic compounds are provided as illustrative examples of the new scheme. Challenging systems such as transition state structures are also tackled on equal footing.

Abstract:The cytochromes P450 are versatile enzymes in human physiology that perform substrate hydroxylation reactions extremely efficient. In this work, we present results of a computational study on the reactivity patterns of Compound I, Compound II and protonated Compound II with model substrates and addresses the question, which of those is the most effective oxidant. All calculations, regardless of the substrate, implicate that Compound I is the superior oxidant of the three. However, Compound II and protonated Compound II are found to react with free energies of activation that are only a few kcal mol -1 higher in energy than those obtained with Compound I. Therefore, Compound II and protonated Compound II should be able to react with aliphatic groups with moderate C-H bond strengths. We have analyzed all results in detail and give electronic, thermochemical, valence bond and molecular orbital rationalizations on the reactivity differences and explain experimental product distributions. Overall, the work implies that alternative oxidants could operate alongside Compound I in complex reaction mechanisms of enzymatic and synthetic iron porphyrin complexes.

Electrides are ionic substances containing isolated electrons. These confined electrons are topologically characterised by a quasi-atom, that is, a non-nuclear attractor (NNA) of the electron density. The electronic structure of the octahedral A Li and A Be species shows that these species have a large number of NNAs. These NNAs have highly delocalised electron densities and, as a result, the chemical bonding pattern of these systems is reminiscent of that in solid metals, in which metal cations are surrounded by a "sea" of delocalised valence electrons. We propose the term metal cluster electrides to refer to this new class of compounds. In this study, we establish a computational protocol to identify, characterize, and design metal cluster electrides and we elucidate the intricate bonding patterns of this particular type of species.

The first examples of the direct functionalization of non-activated aryl sp(2) C-H bonds with ethyl diazoacetate (N2 CHCO2 Et) catalyzed by Mn- or Fe-based complexes in a completely selective manner are reported, with no formation of the frequently observed cycloheptatriene derivatives through competing Buchner reaction. The best catalysts are Fe(II) or Mn(II) complexes bearing the tetradentate pytacn ligand (pytacn= 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane). When using alkylbenzenes, the alkylic C(sp(3) )-H bonds of the substituents remained unmodified, thus the reaction being also selective toward functionalization of sp(2) C-H bonds.

The IUPAC has recently clarified the term oxidation state (OS), and provided algorithms for its determination based on the ionic approximation (IA) of the bonds supported by atomic electronegativities (EN). Unfortunately, there are a number of exceptions and ambiguities in IUPAC's algorithms when it comes to practical applications. Our comprehensive study reveals the critical role of the chemical environment on establishing the OS, which cannot always be properly predicted using fix atomic EN values. By identifying what we define here as subsystems of enhanced stability within the molecular system, the OS can be safely assigned in many cases without invoking exceptions. New insights about the effect of local aromaticity upon OS are revealed. Moreover, we prove that there are intrinsic limitations of the IA that cannot be overcome. In this context, the effective oxidation state (EOS) analysis arises as a robust and general scheme to derive an OS without any external guidance.

The complete chemoselective functionalization of aromatic C(sp 2)-H bonds of benzene and alkyl-benzenes by carbene insertion from ethyl diazoacetate was unknown until the recent discovery of an iron-based catalytic system toward such transformation. A Fe(II) complex bearing the pytacn ligand (pytacn=L1=1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane) transferred the CHCO 2 Et unit exclusively to the C(sp 2)-H bond. The cycloheptatriene compound commonly observed through Buchner reaction or, when employing alkyl-benzenes, the corresponding derivatives from C(sp 3)-H functionalization are not formed. We herein present a combined experimental and computational mechanistic study to explain this exceptional selectivity. Our computational study reveals that the key step is the formation of an enol-like substrate, which is the precursor of the final insertion products. Experimental evidences based on substrate probes and isotopic labelling experiments in favor of this mechanistic interpretation are provided. KEYWORDS carbene transfer iron catalysis C-H activation C(sp 2)-H functionalization DFT calculations