Organometallics最新文献

The development of Fe-based olefin metathesis has been a long-standing goal for several decades. Research from both experimental and theoretical groups has indicated that suitable Fe alkylidenes should be low-spin complexes with a high bond dissociation energy (BDE) for the Fe═C bond. In this study, we synthesized a series of low-spin Fe complexes featuring IMes (IMes = 1,3-dimesitylimidazol-2-ylidene), CN, and CO ligands, which have potential applications in the synthesis of Fe alkylidenes. We computationally investigated the corresponding Fe benzylidenes in the context of olefin metathesis. Although some of these complexes favor low-spin states and demonstrate high BDE, competing side reactions─such as cyclopropanation and carbene insertions─could impede their effectiveness in olefin metathesis.

In this work, a series of novel germylenes, RN(CH₂CH₂NR’)₂Ge R′ = Ph, R = Et (1); R′ = Ph, R = Bn (2); R′ = Ph, R = t-Bu (3); R′ = R = Ph (4); R′ = Bn, R = Et (5); R′ = Bn, R = Bn (6); R′ = Et, R = Et (7); R′ = Et, R = Bn (8), based on 1,4,7-triazaheptanes have been obtained. The compositions and structures of the novel compounds were established by elemental analysis and ¹H and ¹³C NMR in the solid state by X-ray diffraction analysis (1–4), and it has been shown that germylenes are monomeric. The redox properties of compounds 1–4 and previously obtained germylene 10 (R′ = C₆F₅, R = Bn) in acetonitrile were studied by cyclic voltammetry (CV), and their optoelectronic properties were studied by UV–vis absorption spectroscopy. The easily oxidizing properties of the presented germylenes have been determined. An analysis of frontier molecular orbitals was carried out for compounds 1–8, 10 (R′ = C₆F₅, R = Bn), 11 (R′ = C₆F₅, R = Me), and Lappert’s germylene, Ge[N(SiMe₃)₂]₂. It has been established that the nature of the substituents on the nitrogen atoms covalently bonded to the germanium atom has a significant effect on the energy of the frontier molecular orbitals.

A new unsymmetrical hybrid pincer-type ligand featuring cyclopentadienyl and phosphine donors bridged by a 2,6-dimethylenepyridyl linker has been synthesized. Upon double deprotonation and treatment with [NiCl₂(NCCH₃)₂] in THF, this ligand forms a distorted 18-electron κ²-P,N-η⁵-Cp nickel(II) piano-stool complex. This complex undergoes clean aromatization upon protonation, highlighting the proton-responsive nature of the ligand framework. The same scaffold stabilizes a related reduced κ²-P,N-η⁵-Cp nickel(I) species─an uncommon example of a 19-electron nickel(I) compound─which was characterized by continuous-wave X-band EPR spectroscopy. Crystal structures of the protonated, deprotonated, and reduced complexes were all obtained using single-crystal X-ray diffraction. These results provide entry into a versatile ligand platform that is demonstrated to be both proton-responsive and capable of supporting both Ni(II) and Ni(I) oxidation states.

A one-pot strategy has been applied to access the cyclohexyl-fused 2-arylimino-1,10-phenanthroline-iron(II) complexes, [(L_Ph)₂Fe][FeCl₄] (Fe1) and (L_aryl)FeCl₂ (aryl = 2,6-F₂Ph Fe2, 4-FPh Fe3, 4-MePh Fe4, 2,6-Me₂Ph Fe5, 2,6-Et₂Ph Fe6, 2,6-i-Pr₂Ph Fe7, 2-FPh Fe8, 2-MePh Fe9), that differ in the steric/electronic profile of their N-aryl groups and the number of N,N,N-chelating ligands per iron. Structural characterization of Fe3, Fe5, Fe6, and Fe9, along with the ligand-oxidized species Fe5′ and Fe6′, highlights the distorted square pyramidal geometry about the iron centers and the flexibility/sensitivity of the fused carbocyclic ring. While bis(chelate) Fe1/MAO proved almost inactive for ethylene oligomerization, the majority of the mono(chelate) iron complexes exhibited high to moderate levels of activity under MAO activation. Indeed, the most active system, ortho-methyl Fe9/MAO, attained a level of 3.78 × 10⁶ g oligomer mol^–1 (Fe) h^–1 displaying >99% selectivity for linear α-olefins (C₄–C₁₄+) that follow a Schulz–Flory distribution. When compared to the prototypical 2-imino-1,10-phenanthroline-iron oligomerization catalysts, the current fused systems are less active but are capable of suppressing the formation of polyethylene wax. We attribute this finding to the more open space displayed by the active iron center when compared to that seen in the parent system, leading to more facile β-H elimination.

The reaction of Ni(COD)₂ with [PhC(NtBu)₂SiSi(SiMe₃)₃] (1) in toluene results in the formation of an 18-electron silylene-Ni(0) toluene complex (2). The analogous reaction with 1,3-DFB instead of toluene affords the C–H activation followed by ring walking leading to the allylic cyclooctene adduct, the (η³-C₈H₁₃)Ni(II) complex (3). DFT calculations were carried out to elucidate the mechanism as well as to gain insight into why 1,3-DFB undergoes C–H bond activation instead of C–F bond activation. The use of NiCl₂·DME permits access to 16-electron (tetrylene)₂NiCl₂ (Si(4) and Ge(5)) species, and 4 was later used as a catalyst for the C–N coupling reaction.

Polynuclear complexes of rare earth metals Sc, La, Nd, Sm, Er, Yb with anthracenylboronic acid (AntB(OH)₂) and pyrenylboronic acid (PyrB(OH)₂) as a ligands were synthesized by reactions of cyclopentadienyl metal complexes LnCp₃ with the corresponding arylboronic acid. X-ray structural analysis of Nd, Sm and Er complexes revealed that obtained compounds are dimers, in which each metal atom is coordinated by two terminal Cp ligands and two bridging arylboronic acid fragments. Scandium complex is a tetranuclear compound that contains four anthracenylboronic acid ligands and four Cp-ligands. Lanthanum complex is a trinuclear coordination compound comprising three La³⁺ cations linked by three bridging anthracenylboronate anions. Photoluminescence spectra of Sc and La derivatives in the solid state showed excimer ligand emission in the region 350–650 nm. The Nd, Er and Yb complexes exhibited NIR metal-centered photoluminescence of the corresponding metal ion.

Cyclic alkyl amino iminate (CAAI) phosphines were synthesized in good yields via chlorophosphine/(CAAI)TMS exchange. These ligands adopt a conformation in which the methyl groups on the CAAI unit are oriented toward the metal center, enabling potential weak C–H···metal interactions, as characterized by experimental and computational methods. CAAI phosphines have been applied in Pd-catalyzed ketone arylation, showing promising reactivity with electron-rich substrates. These findings establish CAAI phosphines as a class of flexible ligand for transition-metal-catalyzed transformations.

Chemical reduction of the previously reported Cr(II) chloride dimer supported by a bulky imidazolin-2-iminato ligand, [Cr(μ₂-NIm^Dipp)(Cl)]₂, affords the Cr(I) dimer [Cr(μ₂-NIm^Dipp)]₂ (1) in moderate crystalline yield (NIm^Dipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato, Dipp = 2,6-diisopropylphenyl). Single-crystal X-ray diffractometry analysis of 1 reveals a Cr₂N₂ diamond core structure by two bridging iminato ligands and a strong η⁶ interaction between the Cr(I) ion and one of the flanking Dipp group. A salient feature in 1 is the long Cr···Cr distances of 2.7274(5) and 2.6548(4) Å. Complex 1 is diamagnetic in solution at 300 K, suggesting that the Cr(I) ions have a strong antiferromagnetic interaction. Both unrestricted and broken symmetry density functional theory calculations indicate that 1 has two low-spin (S = ¹/₂) Cr(I) ions with a very large antiferromagnetic exchange coupling constant (J), resulting in a diamagnetic ground state at 300 K.

The chemistry of antimony-based radicals remains significantly less developed in comparison to that of phosphorus radicals. Herein we report the synthesis and characterization of radical anions derived from stibinidene sulfide and selenide via one-electron reduction. Electron paramagnetic resonance spectroscopy combined with density functional theory calculations revealed that the unpaired electron predominantly occupies the π* antibonding orbitals of the Sb═S and Sb═Se double bonds with notable localization on the antimony center.

A series of Ru(L)(X)₂ complexes (L = bidentate ligand; X = OMs, OTs, OTf) was synthesized and characterized. Ru(BINAP)(OMs)₂ showed improved catalytic performance over the established Ru(BINAP)(OAc)₂ catalyst, highlighting the impact of anion variation on catalytic asymmetric hydrogenations.