Access to Monomeric Hydridoplumbate(II) Anions with Remarkable Thermostability

We report on the remarkable stability of synthesized monomeric hydridoplumbates M+[LPb(II)H]− (M[1-H]) where L = 2,6-bis(3,5-diphenylpyrrolyl)pyridine and M = (18-crown-6)potassium or ([2.2.2]-cryptand)potassium. The half-life of [K18c6][1-H] is approximately 2 days in tetrahydrofuran at ambient temperature. The presence of a Pb–H bond in the hydridoplumbates was unambiguously identified by performing 1H, 2H (with a lead(II) deuteride analogue), 207Pb{1H}, proton-coupled 207Pb, and 1H-207Pb 2D nuclear magnetic resonance spectroscopy. The experimental observations and theoretical calculations indicated the presence of dihydrogen bonding as a secondary coordination sphere interaction between the protons of the ligand backbone and the hydride ligand that helps stabilize Pb–H bonding. The Pb–H bond readily adds to the C = O bond of benzaldehyde to form a benzyloxy compound. The regeneration of Pb(II)–H moieties was observed by treating pinacolborane with lead(II) benzyloxy compounds, which indicated that lead(II) hydrides can be used as catalysts for hydroelementation reactions involving unsaturated molecules.

Synthesis and Structure of the Bis- and Tris-Polyhedral Hybrid Carboranoclathrochelates with Functionalizing Biorelevant Substituents—The Derivatives of Propargylamine Iron(II) Clathrochelates with Terminal Triple C≡C Bond(s)

A synthetic strategy for obtaining structurally flexible hybrid iron(II) carboranoclatrochelates functionalized with biorelevant groups, based on a combination of a 1,3-dipolar cycloaddition reaction with nucleophilic substitution of an appropriate chloroclathrochelate precursor, was developed. In its first stage, a stepwise substitution of the dichloroclathrochelate precursor with amine N-nucleophiles of different natures in various solvents was performed. One of its two chlorine atoms with morpholine or diethylamine in dichloromethane gave reactive monohalogenoclathrochelate complexes functionalized with abiorelevant substituents. Further nucleophilic substitution of their remaining chlorine atoms with propargylamine in DMF led to morpholine- and diethylamine-functionalized monopropargylamine cage complexes, the molecules of which contain the single terminal C≡C bond. Their “click” 1,3-cycloaddition reactions in toluene with ortho-carborane-(1)-methylazide catalyzed by copper(II) acetate gave spacer-containing di- and tritopic iron(II) carboranoclatrochelates formed by a covalent linking between their different polyhedral(cage) fragments. The obtained complexes were characterized using elemental analysis, MALDI-TOF mass, UV-Vis, 1H, 1H{11B}, 11B, 11B{1H}, 19F{1H} and 13C{1H}-NMR spectra, and by a single crystal synchrotron X-ray diffraction experiment for the diethylamine-functionalized iron(II) carboranoclathrochelate. Its encapsulated iron(II) ion is situated almost in the center of the FeN6-coordination polyhedron possessing a geometry intermediate between a trigonal prism and a trigonal antiprism with a distortion angle φ of approximately 28º. Conformation of this hybrid molecule is strongly affected by its intramolecular dihydrogen bonding: a flexibility of the carborane-terminated ribbed substituent allowed the formation of numerous C–H…H–B intramolecular interactions. The H(C) atom of this carborane core also forms the intermolecular C–H…F–B interaction with an adjacent carboranoclathrochelate molecule. The N–H…N intermolecular interaction between the diethylamine group of one hybrid molecule and the heterocyclic five-membered 1Н-[1,2,3]-triazolyl fragment of the second molecule of this type caused formation of H-bonded carboranoclathrochelate dimers in the X-rayed crystal.

Exploration of Bis(nickelation) of 1,1′-Bis(o-carborane)

The metalation of [Tl]2[1-(1′-3′,1′,2′-closo-TlC2B9H10)-3,1,2-closo-TlC2B9H10], with the smaller {Ni(dmpe)} fragment sourced from [Ni(dmpe)Cl2], is explored. The bis(metalated) products are obtained as a diastereoisomeric mixture. These isomers were separated, fully characterised spectroscopically and crystallographically and identified as rac-[1-(1′-3′-(dmpe)-3′,1′,2′-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (1) and meso-[1-(1′-3′-(dmpe)-3′,1′,2′-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (2). Previously, these 3,1,2-NiC2B9-3′,1′,2′-NiC2B9 architectures (where both cages are not isomerised), were inaccessible, and thus new structures can be achieved during bis(nickelation) with {Ni(dmpe)}. Further, the metalation of the tetra-thallium salt with the bulky {Ni(dppe)} fragment sourced from [Ni(dppe)Cl2] was also studied. These bis(nickelated) products were also fully characterised and are afforded as the stereospecific species rac-[1-(1′-3′-(dppe)-3′,1′,2′-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (3) and [1-(2′-4′-(dppe)-4′,1′,2′-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (4α). In the latter metalation, compound 3 shows intramolecular dihydrogen bonding, contributing to the stereospecificity, whereas isomerisation from 3,1,2 to 4,1,2- in the 4α is related to steric relief.

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes

Ductility, which is a common phenomenon in most metals and metal-based alloys, is hard to achieve in molecular crystals. Organic crystals have been recently shown to deform plastically, but only on one or two faces, and fracture when stressed in any other arbitrary direction. Here, we report an exceptional metal-like ductility in crystals of two globular molecules, BH₃NMe₃ and BF₃NMe₃, with characteristic stretching, necking and thinning with deformations as large as ~ 500%. Surprisingly, the mechanically deformed samples not only retained good long range order, but also allowed structure determination by single crystal X-ray diffraction. Molecules in these high symmetry crystals interact predominantly via electrostatic forces (B^––N⁺) and form columnar structures, thus forming multiple slip planes with weak dispersive forces among columns. While the former interactions hold molecules together, the latter facilitate exceptional malleability. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH₃NHMe₂ negates ductility. We show the possibility to simultaneously achieve both exceptional ductility and crystallinity in solids of certain globular molecules, which may enable designing highly modular, easy-to-cast crystalline functional organics, for applications in barocalorimetry, ferroelectrics and soft-robotics.

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes

Ductility, which is a common phenomenon in most metals and metal-based alloys, is hard to achieve in molecular crystals. Organic crystals have been recently shown to deform plastically, but only on one or two faces, and fracture when stressed in any other arbitrary direction. Here, we report an exceptional metal-like ductility in crystals of two globular molecules, BH₃NMe₃ and BF₃NMe₃, with characteristic stretching, necking and thinning with deformations as large as ~ 500%. Surprisingly, the mechanically deformed samples not only retained good long range order, but also allowed structure determination by single crystal X-ray diffraction. Molecules in these high symmetry crystals interact predominantly via electrostatic forces (B^––N⁺) and form columnar structures, thus forming multiple slip planes with weak dispersive forces among columns. While the former interactions hold molecules together, the latter facilitate exceptional malleability. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH₃NHMe₂ negates ductility. We show the possibility to simultaneously achieve both exceptional ductility and crystallinity in solids of certain globular molecules, which may enable designing highly modular, easy-to-cast crystalline functional organics, for applications in barocalorimetry, ferroelectrics and soft-robotics.