Amination of 2,2″-dibromo-p-terphenyl with 2,6-diisopropylaniline, through Pd mediated cross coupling, yields the p-terphenyl bis­(aniline) ligand H2LAr. Deprotonation of H2LAr with excess KH generates the dianion [K­(DME)2]2LAr as a dark red solid. Treatment of [K­(DME)2]2LAr with UI3(dioxane)1.5 produces the mononuclear U­(III) complex LArU­(I)­(DME) (1). Subsequent addition of the nucleophilic metal anion [CpFe­(CO)2]− (Fp–) gives the bimetallic U­(III) compound LArU­(Fp) (2) in modest yield which features a rare instance of an unsupported U–M bond. Inspection of the metrical parameters of the solid-state structures of 1·DME and 2·0.5DME from X-ray crystallographic analyses show a seemingly η6-interaction between the uranium and the terphenyl ligand (1: U1–Ccentroid = 2.56 Å; 2: U1–Ccentroid = 2.45 Å), spatially imposed as a consequence of the anilide N-donor atom coordination. Furthermore, the U–Fe bond length in 2 (U1–Fe1 = 2.9462(3) Å) is consistent with a metal–metal single bond. Notably, electronic structure analyses by CASPT2 calculations instead suggest that electrostatic, and not covalent, interactions dominate between the U–arene systems in 1 and 2 and between the U–Fe bond in the latter.

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H-bonds between neutral tyrosine and arginine in nonpolar environments are modeled by small-molecule phenol/guanidine complexes. From the temperature and concentration dependence of UV spectra, a value of Δ H ° = −74 ± 4 kJ mol –1 is deduced for the formation of H-bonded p -cresol/dodecylguanidine in hexane. Δ E = −71 kJ mol –1 is computed with density functional theory (in vacuo). In dimethyl sulfoxide or crystals, ( p -phenolyl)alkylguanidines form head-to-tail homodimers with two strong H-bonding interactions, as evidenced by UV, IR, and NMR spectral shifts, strong IR continuum absorbance bands, and short O···N distances in X-ray crystal structures. Phenol/alkylguanidine H-bonded complexes consist of polarizable rapidly interconverting tautomers, with the proton shift from phenol to guanidine increasing with increase in the polarity of the aprotic solvent. As measured by NMR, both groups in these strongly H-bonded neutral complexes can simultaneously appear to be predominantly protonated. These systems serve as models for the hypothetical hydrogen-Bonded Uncharged (aRginine + tYrosine), or “BU(RY)”, motifs in membrane proteins.

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The organometallic chemistry of the alkaline‐earth metals has undergone a renaissance during the last 20 years with heavy organoalkaline‐earth metal compounds becoming recognized as an area of organometallic chemistry with significant potential. Intense research efforts have provided a series of synthetic methodologies that provided access to a rapidly growing family of compounds not thought possible only recently. As a result, this improved insight did not only provide the basis for a more detailed understanding of the metal‐ligand bonding characteristics but also paved the way toward a number of applications including uses as diverse as in polymerization initiation, organic synthetic chemistry, catalysis, and materials chemistry. This article summarizes some of the recent, exciting developments in regards to alkaline‐earth organometallics.