Synthesis and Reactivity of Sterically Encumbered Diazaferrocenes

Charge-compensated nido-carborane derivatives in the synthesis of iron(II) bis(dicarbollide) complexes

A series of stable iron(II) bis(dicarbollide) derivatives [8,8'-(RNHC(Et)HN)2-3,3'-Fe(1,2-C2B9H10)2] (R = Pr, R = Ph, (CH2)2OH, (CH2)3OH, (CH2)2NMe2) was prepared starting from FeCl2 or [FeCl2(dppe)] and the corresponding nido-carboranyl amidines [10-RNHC(Et)HN-7,8-C2B9H11]. In a similar way, the reactions of the oxonium derivatives of nido-carborane with FeCl2 in tetrahydrofuran in the presence of t-BuOK lead to the corresponding stable oxonium derivatives iron(II) bis(dicarbollide) [8,8'-(RR'O)2-3,3'-Fe(1,2-C2B9H10)2] (RR' = (CH2)4, (CH2)2O(CH2)2, (CH2)5; R = R' = Et), which can be alternatively prepared by the reaction of the parent iron(II) bis(dicarbollide) with tetrahydrofuran or 1,4-dioxane in the presence of Me2SO4. The cyclic voltammetry studies of the synthesized iron(II) bis(dicarbollide) derivatives revealed that the introduction of amidinium and oxonium substituents leads to a significant increase in the Fe2+/Fe3+ redox potential relative to the parent iron(II) bis(dicarbollide). The redox potentials of the oxonium derivatives are close to the redox potential of ferrocene and somewhat lower than redox potentials of sulfonium and phosphonium derivatives of iron(II) bis(dicarbollide).

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.

1,2-Diaza-4-phosphaferrocenes: synthesis, structural characterization, 57Fe Mössbauer spectrum analysis, and DFT calculation

Two 1,2-diaza-4-phosphaferrocenes [(η⁵-3,5-R₂dp)Fe(η⁵-CpMe₅)] (R = tBu (3), Ph (4)) with a single η⁵ ring containing two nitrogen atoms are prepared. Mössbauer spectroscopic, electrochemical, and density functional theory (DFT) studies have provided a more detailed understanding of the electronic structures and stabilities of these complexes.

Reactivity studies on [Cp'Fe(μ-I)]2: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation

Facile pseudohalide activation occurs in the reaction of SCN^–, SeCN^– and N₃^– with the iron half-sandwich [Cp′Fe(μ-I)]₂.

The iron half-sandwich [Cp′Fe(μ-I)]₂ (Cp′ = 1,2,4-(Me₃C)₃C₅H₂, 1) reacts with the pseudohalides NCO^–, SCN^–, SeCN^– and N₃^– to give [Cp′Fe(μ-NCO)]₂ (2), [Cp′Fe(μ-S)]₂ (3), [Cp′Fe(μ-Se₂)]₂ (4) and [Cp′Fe(μ-N)]₂ (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state magnetic susceptibility studies and ⁵⁷Fe Mössbauer spectroscopy were employed in the characterization of these species. Mössbauer spectroscopy shows a decreasing isomer shift with increasing formal oxidation state, ranging from Fe(ii) to Fe(iv), in complexes 1 to 5. The sulfido-bridged dimer 3 exhibits strong antiferromagnetic coupling between the Fe(iii) centers. This leads to temperature-independent paramagnetism (TIP) at low temperature, from which the energy gap between the ground and the excited state can be estimated to be 2J = ca. 700 cm^–1. The iron(iv) nitrido complex [Cp′Fe(μ-N)]₂ (5) shows no reactivity towards H₂ (10 atm), but undergoes clean reactions with CO (5 bar) and XylNC (Xyl = 2,6-Me₂C₆H₃) to form the diamagnetic isocyanate and carbodiimide complexes [Cp′Fe(CO)₂(NCO)] (7) and [Cp′Fe(CNXyl)₂(NCNXyl)] (8), respectively. All compounds were fully characterized, and density functional theory (DFT) computations provide useful insights into their formation and the electronic structures of complexes 3 and 5.

The pyrrole ring η2-hapticity bridged binuclear tricarbonyl Mo(0) and W(0) complexes: catalysis of regioselective hydroamination reactions and DFT calculations

Following the report of the ferrocene structure, metal complexes containing the heteroatom-substituted cyclopentadienyl (Cp) analogue, that is the η⁵ pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in organometallics, the transition metal chemistry of the pyrrolyl ligand is still in the developing stage. In view of this, we carried out the reaction between the multidentate ligand 2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole (LH) and Mo(CO)₆ or [W(CO)₃(CH₃CN)₃] and isolated two new binuclear tricarbonyl Mo(0) and W(0) complexes, [Mo₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (1) and [W₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (2). Their X-ray structural analyses showed that the metal centers are bridged by the double bonds of the central pyrrole ring (μ-η²:η²), a rarely observed coordination mode. Interestingly, complex 1 is a catalyst precursor for the hydroamination reactions of phenylacetylene with a series of secondary amines at room temperature offering the regioselectively formed anti-Markovnikov product in excellent yields. In addition, DFT calculations were performed to understand the bonding nature of the pyrrole ring in 1 and 2 and to estimate the energy of six different conformations of LH.