Structural and Spectroscopic Trends in a Series of Half-Sandwich Scorpionate Complexes

[Fe(NCMe)6](BF4)2 is a bifunctional catalyst for styrene aziridination by nitrene transfer and heterocycle expansion by subsequent dipolar insertion

The solvated iron(II) salt [Fe(NCMe)6](BF4)2 (Me = methyl) is shown to be a bifunctional catalyst with respect to aziridination of styrene. The salt serves as an active catalyst for nitrene transfer from PhINTs to styrene to form 2-phenyl-N-tosylaziridine (Ph = phenyl; Ts = tosyl, -S{O}2-p-C6H4Me). The iron(II) salt also acts as a Lewis acid in non-coordinating CH2Cl2 solution, to catalyze heterolytic CN bond cleavage of the aziridine and insertion of dipolarophiles. The 1,3-zwitterionic intermediate is presumably supported by interaction of the metal dication with the anion, and by resonance stabilization of the carbocation. Nucleophilic dipolarophiles then insert to give a five-membered heterocyclic ring. The result is a two-step cycloaddition, formally [2 + 1 + 2], that is typically regiospecific, but not stereospecific. This reaction mechanism was confirmed by conducting a series of one-step, [3 + 2] additions of unsaturated molecules into pre-formed 2-phenyl-N-tosylaziridine, also catalyzed by [Fe(NCMe)6](BF4)2. Relevant substrates include styrenes, carbonyl compounds and alkynes. These yield five-membered heterocylic rings, including pyrrolidines, oxazolidines and dihydropyrroles, respectively. The reaction scope appears limited only by the barrier to formation of the dipolar intermediate, and by the nucleophilicity of the captured dipolarophile. The bifunctionality of an inexpensive, earth-abundant and non-toxic catalyst suggests a general strategy for one-pot construction of heterocyclic rings, as demonstrated specifically for pyrrolidine ring formation.

Expanding the dimensionality of bis(tetrazolyl)alkane-based Fe(II) coordination polymers by the application of dinitrile coligands

Reactions between 1,2-di(tetrazol-2-yl)ethane (ebtz), 1,6-di(tetrazol-2-yl)hexane (hbtz) or 1,1'-di(tetrazol-1-yl)methane (1ditz) and Fe(BF4)2 in the presence of adiponitrile (ADN), glutaronitrile (GLN) or suberonitrile (SUN) resulted in the formation of coordination polymers [Fe(μ-ebtz)2(μ-ADN)](BF4)2 (1), [Fe(μ-hbtz)2(μ-ADN)](BF4)2 (2), [Fe(μ-1ditz)2(GLN)2](BF4)2·GLN (3) and [Fe(μ-1ditz)2(μ-SUN)](BF4)2·SUN (4). It was established that the application of dinitriles allows an increase in the dimensionality of the ebtz and hbtz based systems while maintaining the structure of the polymeric units characteristic of previously studied mononitrile based analogues. In 3 and 4, regardless of the type of dinitrile coligand, the motif of 2D polymeric layers constituted by 1ditz molecules remains preserved. However, the dimensionality of 1ditz based networks is governed by the coordination modes of dinitriles. 3, based on a shorter molecule of glutaronitrile, crystallizes as a two-dimensional (2D) coordination polymer. In this compound, dinitriles coordinate monodentately or play the role of guest molecules. The substitution of glutaronitrile with suberonitrile enables the bridging of neighboring polymeric layers, resulting in a 3D network. The intentional selection of bis(tetrazoles) and dinitriles as building blocks has led, as expected, to obtaining systems with the structure of the first coordination sphere consisting of four tetrazole rings and two axially coordinated nitrile molecules. It created the conditions required for the occurrence of thermally induced spin crossover. Magnetic measurements and single crystal X-ray diffraction studies were used for the characterization of the spin crossover properties of 1-4.

Cationic tetra- and pentacoordinate complexes of nickel based on POCN- and POCOP-type pincer ligands: synthesis, characterization, and ligand exchange studies

The closely related pincer ligands POCN and POCOP display different electron donating properties and different degrees of resistance to ligand exchange reactions proceeding via cationic reaction intermediates.

Cationic tri(ferrocenecarbonitrile)silver(I)

The synthesis of the tri-coordinated ferrocenecarbonitrile silver(I) complex [Ag(N≡CFc)3]OTf (3) is reported. Its electrochemical behavior shows that the three ferrocenyl units are oxidized in a very close potential range. In addition, the molecular structure of 3 in the solid state is discussed, showing that silver(I) is exclusively coordinated by three ferrocenecarbonitrile molecules.

A HPLC-ICP-AES technique for the screening of [XW11NbO40]n− aqueous solutions

In this research combined HPLC-ICP-AES technique was used to study formation of mixed [XW₁₁O₄₀]ⁿ⁻ (X = P, Ge, B) complexes.

Hexahalorhenate(iv) salts of metal oxazolidine nitroxides

Eight coordination compounds of formulae [Fe^II(L˙)₂][Re^IVCl₆] (1a), [Fe^II(L˙)₂][Re^IVBr₆] (1b), [Co^II(L˙)₂][Re^IVCl₆]·CH₃CN (2a), [Co^II(L˙)₂][Re^IVBr₆] (2b), [Ni^II(L˙)(CH₃CN)₃][Re^IVCl₆]·CH₃CN (3a), [Ni^II(L˙)(CH₃CN)₃][Re^IVBr₆]·3CH₃CN (3b), [Cu^II(L˙)₂][Re^IVCl₆] (4a) and [Cu^II(L˙)₂][Re^IVBr₆] (4b), where L˙ is the aminoxyl radical chelating ligand, 4,4'-dimethyl-2,2'-di(2-pyridyl)oxazolidine-N-oxide, have been synthesised. Structural and magnetic studies reveal metal-radical intramolecular antiferromagnetic interactions in the [M^II(L˙)₂]²⁺ cations in the iron, cobalt and copper based compounds (1a, 1b, 2a, 2b, 4a and 4b) with the central metal ion low-spin in the case of iron (1a and 1b) and a gradual, cobalt based, spin-crossover transition present in 2a and 2b. The nickel based compounds, 3a and 3b, were analysed in the dried form (3a(dried) and 3b(dried)) and directly in acetonitrile (3a(solvated) and 3b(solvated)). Microanalysis and IR spectroscopy on 3a(dried) and 3b(dried) suggest that the dried samples are best formulated as [Ni^II(L˙)(H₂O)₃][Re^IVX₆], where X = Cl (3a(dried)) and Br (3b(dried)). All forms of 3a and 3b exhibit cationic metal-radical ferromagnetic interactions resulting in S = 3/2 ground states. In addition, 3a(dried) exhibits spin-canting behaviour with an ordering temperature of 2.7 K, an open hysteresis loop with a coercive field H_c = 580 Oe, and a remanent magnetisation M_r = 0.21μ_B, resulting in a canting angle of ∼1.8°. In contrast, 3b(dried) shows no spin-canting behaviour; a maximum in χ_Mvs. T at T = 3 K suggesting long-range antiferromagnetic ordering. 3a(solvated) and 3b(solvated) show no indication of long-range magnetic ordering, unlike 4a and 4b where anomalies are evident in the low-temperature magnetic susceptibility measurements.

1,2-Dicyanoferrocene: synthesis and characterization

A convenient synthesis of 1,2-dicyanoferrocene (3) was developed by using 2,4-dinitrofluorobenzene as a dehydrating agent for the treatment of 1,2-ferrocenedicarbaldehyde dioxime (2) to give 3 in yields exceeding 80%. Compounds 2 and 3 have been characterized by IR and NMR (1H, 13C{1H}) spectroscopy and by electrochemistry (cyclic voltammetry and square-wave voltammetry). Furthermore, the molecular structures of 2 and 3 in the solid state have been determined by single-crystal X-ray crystallographic studies.