Effective Alkyl-Alkyl Cross-Coupling with an Iron-Xantphos Catalyst: Mechanistic and Structural Insights.

While iron-catalyzed C(sp)-C(sp) cross-couplings have been widely studied and developed in the last decade, alkyl-alkyl cross-coupling systems with iron remain underdeveloped despite the importance of C(sp)-C(sp) bonds in organic synthesis. A major challenge to the development of these reactions is the current lack of fundamental insight into ligand effects and organoiron intermediates that enable effective alkyl-alkyl couplings. The current study addresses this longstanding limitation using a combination of Fe Mössbauer spectroscopy, SC-XRD (single-crystal X-ray diffraction) and reactivity studies of alkyl-alkyl coupling with iron-Xantphos to define the in situ formed iron-Xantphos intermediates in catalysis.

Development and Evolution of Mechanistic Understanding in Iron-Catalyzed Cross-Coupling.

Since the pioneering work of Kochi in the 1970s, iron has attracted great interest for cross-coupling catalysis due to its low cost and toxicity as well as its potential for novel reactivity compared to analogous reactions with precious metals like palladium. Today there are numerous iron-based cross-coupling methodologies available, including challenging alkyl-alkyl and enantioselective methods. Furthermore, cross-couplings with simple ferric salts and additives like NMP and TMEDA ( N-methylpyrrolidone and tetramethylethylenediamine) continue to attract interest in pharmaceutical applications.

Combined Effects of Backbone and N-Substituents on Structure, Bonding, and Reactivity of Alkylated Iron(II)-NHCs.

Iron and -heterocyclic carbenes (NHCs) have proven to be a successful pair in catalysis, with reactivity and selectivity being highly dependent on the nature of the NHC ligand backbone saturation and -substituents. Four (NHC)Fe(1,3-dioxan-2-ylethyl) complexes have been isolated and spectroscopically characterized to correlate their reactivity to steric effects of the NHC from the backbone saturation and -substituents. Only in the extreme case of SIPr where NHC backbone and -substituent steric effects are the largest is there a major structural perturbation observed crystallographically.

A Pseudotetrahedral Uranium(V) Complex.

A series of uranium amides were synthesized from N, N, N-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy] and uranium tetrachloride to give U(NCySiMe) (Cl), where x = 2, 3, or 4. The diamide was isolated as a bimetallic, bridging lithium chloride adduct ((UCl(NCyTMS))-LiCl(THF)), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS)-LiCl(THF)). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron.

NHC and nucleophile chelation effects on reactive iron(ii) species in alkyl-alkyl cross-coupling.

While iron-NHC catalysed cross-couplings have been shown to be effective for a wide variety of reactions ( aryl-aryl, aryl-alkyl, alkyl-alkyl), the nature of the formed and reactive iron species in effective catalytic systems remains largely undefined. In the current study, freeze-trapped Mössbauer spectroscopy, and EPR studies combined with inorganic synthesis and reaction studies are utilised to define the key formed and reactive iron-NHC species in the Kumada alkyl-alkyl cross-coupling of (2-(1,3-dioxan-2-yl)ethyl)magnesium bromide and 1-iodo-3-phenylpropane. The key reactive iron species formed is identified as (IMes)Fe((1,3-dioxan-2-yl)ethyl), whereas the = 1/2 iron species previously identified in this chemistry is found to be only a very minor off-cycle species (<0.

Magnetic circular dichroism of UCl in the ligand-to-metal charge-transfer spectral region.

We present a combined ab initio theoretical and experimental study of the magnetic circular dichroism (MCD) spectrum of the octahedral UCl complex ion in the UV-Vis spectral region. The ground state is an orbitally non-degenerate doublet E and the MCD is a -term spectrum caused by spin-orbit coupling. Calculations of the electronic spectrum at various levels of theory indicate that differential dynamic electron correlation has a strong influence on the energies of the dipole-allowed transitions and the envelope of the MCD spectrum.

High-throughput Screening of Erratic Cell Volume Regulation Using a Hydrogel-based Single-cell Microwell Array.

Here, we report that a single-cell microwell array based on photocrosslinked hydrogel can be used to screen cells exhibiting a defective regulatory volume decrease (RVD) in high-throughput. The RVD is a regulatory function of cells that maintains cell volume homeostasis in a hypotonic medium. Single Madin-Darby canine kidney (MDCK) cells grown in the microwells were loaded with a volume-sensitive fluorescence dye.

Electronic Structure and Bonding in Iron(II) and Iron(I) Complexes Bearing Bisphosphine Ligands of Relevance to Iron-Catalyzed C-C Cross-Coupling.

Chelating phosphines are effective additives and supporting ligands for a wide array of iron-catalyzed cross-coupling reactions. While recent studies have begun to unravel the nature of the in situ-formed iron species in several of these reactions, including the identification of the active iron species, insight into the origin of the differential effectiveness of bisphosphine ligands in catalysis as a function of their backbone and peripheral steric structures remains elusive. Herein, we report a spectroscopic and computational investigation of well-defined FeCl2(bisphosphine) complexes (bisphosphine = SciOPP, dpbz, (tBu)dppe, or Xantphos) and known iron(I) variants to systematically discern the relative effects of bisphosphine backbone character and steric substitution on the overall electronic structure and bonding within their iron complexes across oxidation states implicated to be relevant in catalysis.

An organophosphate sensor based on photo-crosslinked hydrogel-entrapped E. coli.

This paper describes a whole cell sensor using E. coli entrapped within photocrosslinked hydrogel beads. Hydrogel beads containing organophosphorus hydrolase (OPH)-expressed E.