A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4fn5dz21 electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(CpiPr5)2 (Ln = Tb, Dy; CpiPr5 = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(CpiPr5)2 (1-Ln) series (including Y and excluding Pm). The compounds can be synthesized through salt metathesis of LnI3 and NaCpiPr5 followed by potassium graphite reduction for Ln = Y, La, Ce, Pr, Nd, Gd, Ho, and Er, by in situ reduction during salt metathesis of LnI3 and NaCpiPr5 for Ln = Tm and Lu, or through salt metathesis from LnI2 and NaCpiPr5 for Ln = Sm, Eu, and Yb. Single crystal X-ray diffraction analyses of 1-Ln confirm a linear coordination geometry with pseudo-D5d symmetry for the entire series. Structural and ultraviolet-visible spectroscopy data support a 4fn+1 electron configuration for Ln2+ = Sm, Eu, Tm, and Yb and a 4fn5dz21 configuration for the other lanthanides ([Kr]4dz21 for Y2+). Characterization of 1-Ln (Ln = Y, La) using electron paramagnetic resonance spectroscopy reveals significant s-d orbital mixing in the highest occupied molecular orbital and hyperfine coupling constants that are the largest reported to date for divalent compounds of yttrium and lanthanum. Evaluation of the room temperature magnetic susceptibilities of 1-Ln and comparison with values previously reported for trigonal Ln2+ compounds suggests that the more pronounced 6s-5d mixing may be associated with weaker 4f-5d spin coupling.

Nitramines (for example RDX, HMX and CL-20) are frequently made by nitrolyzing tertiary amides. While generally high yielding, sometimes the amides can be difficult to remove while keeping any ring systems intact. This study investigates twelve acyl hexahydro-s-triazines for their ease of conversion into nitramines using four common nitration conditions. Several new amide protecting group have been examined and one (cyclopropanecarboxamide) has been found to be better than those amides currently employed. The amide groups have been found to be nitrolyzable in the following order: Cyclopropyl>Ethyl>Propyl>methyl>i-Propyl approximate to t-Butyl approximate to Methoxymethyl >> Hydrogen>Pentafluorophenyl.

Isoprene was efficiently converted to 1,6-dimethyl-1,5-cyclooctadiene (DMCOD) by selective [4+4]-cycloaddition with a catalyst formed by in situ reduction of [(MePI)FeCl(μ-Cl)]2 (MePI = [2-(2,6-(CH3)2-C6H3-N=C(CH3))-C4H5N]). DMCOD was isolated in 92% yield, at the preparative scale, with a catalyst loading of 0.025 mol%, and a TON of 3680. Catalytic hydrogenation of DMCOD yielded 1,4-dimethylcyclooctane (DMCO). The cyclic structure and ring strain of DMCO afforded gravimetric and volumetric net heats of combustion 2.4 and 9.2% higher, respectively, than conventional jet fuel. In addition, the presence of methyl branches at two sites resulted in a -20 °C kinematic viscosity of 4.17 mm2 s-1, 48 % lower than the maximum allowed value for conventional jet fuel. The ability to derive isoprene and related alcohols readily from abundant biomass sources, coupled with the highly efficient [Fe]-catalyzed [4+4]-cycloaddition described herein, suggests that this process holds great promise for the economical production of high-performance, bio-based jet fuel blendstocks.

A heptacyclo[6.6.0.0(2,6).0(3,13).0(4,11).0(5,9).0(10,14)]-tetradecane (HCTD) complex with terminal allylidene groups at the 7- and 12-positions (HCTD-7,12-diallylidene, 2) was generated at the multigram scale from norbornadiene via an efficient six-step synthesis. Thermal polymerization of 2 at temperatures ranging from 160 to 240 degrees C yielded a robust cross-linked material with thermal stability up to 488 degrees C in air, a glass transition temperature of 377 degrees C, and a char yield (600 degrees C) of 56% in air. This degree of thermal stability is remarkable for a nonaromatic hydrocarbon polymer and is likely due to the rigid multicyclic cages that make up the bulk of the material. To elucidate the polymerization mechanism, a model compound, 7-allylidenenorbornane (4), was synthesized and thermally cured. This resulted in the formation of polymeric material, suggesting that the cross-linking reaction of 2 proceeds via a free-radical reaction and not through Diels-Alder cycloaddition. Addition of dibutylhydroxytoluene (BHT) to compound 2 delayed the onset of cure, providing further support for a radical mechanism. On the basis of these results, it can be concluded that exocyclic allylidene groups represent a new class of thermosetting end-cap capable of generating highly cross-linked materials with thermal stabilities that rival those of high temperature polyimides. Applications include heat resistant composites utilized in the aerospace, electronic, automotive, and textile industries.

Alkyl diamondoid fuel mixtures have been prepared under moderate conditions by AlBr3 catalyzed cracking of nonane and heptane in the presence of adamantane. The fuel mixture prepared with heptane as the alkyl source (HA) contains primarily 1-ethyl-3-methyl adamantane and 1-propyladamantane, while the mixture prepared from nonane (NA) contains primarily C-13-C-15 alkyl diamondoids. Both fuel mixtures exhibit densities greater than 0.9 g/mL and volumetric net heats of combustion approximately 10 and 6% higher than conventional jet and diesel fuels, respectively. The structural diversity of the fuel blends and presence of multiple branch sites lead to lower viscosities compared to pure alkyl diamondoid fuels. The lower molecular weight blend, HA, exhibits a 40 degrees C kinematic viscosity of 3.22 mm(2) s(-1) well within the specification for diesel fuel, and both blends have derived cetane numbers of >42, suggesting that they can be used directly in conventional diesel engines.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Double deprotonation of bis(2-mercapto-4-methylphenyl)amine ([SNS]H3) followed by addition to NiCl2(PR3)2 in air-free conditions afforded [SN(H)S]Ni(PR3) (1a, R = Cy; 1b, R = Ph) complexes, characterized as diamagnetic, square-planar nickel(II) complexes. When the same reaction was conducted with 3 equiv of KH, the diamagnetic anions K{[SNS]Ni(PR3)} were obtained (K[2a], R = Cy; K[2b], R = Ph). In the presence of air, the reaction proceeds with a concomitant one-electron oxidation. When R = Cy, a square-planar, S = 1/2 complex, [SNS]Ni(PCy3) (3a), was isolated. When R = Ph, the bimetallic complex {[SNS]Ni(PPh3)}2 ({3b}2) was obtained. This bimetallic species is diamagnetic; however, in solution it dissociates to give S = 1/2 monomers analogous to 3a. Complexes 1-3 represent a hydrogen-atom-transfer series. The bond dissociation free energies (BDFEs) for 1a and 1b were calculated to be 63.9 ± 0.1 and 62.4 ± 0.2 kcal mol-1, respectively, using the corresponding p Ka and E°' values. Consistent with these BDFE values, TEMPO• reacted with 1a and 1b, resulting in the abstraction of a hydrogen atom to afford 3a and 3b, respectively.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Complexes of the general formula W[SNS]2M(dppe) (M = Pd, Pt; [SNS]H3 = bis(2-mercapto-p-tolyl)amine; dppe = 1,2-bis(diphenylphosphino)ethane) were prepared by combining the corresponding (dppe)MCl2 synthon with W[SNS]2 under reducing conditions. X-ray diffraction studies revealed the formation of a heterobimetallic complex supported by a single thiolate bridging ligand and a short metal-metal bond between the tungsten and palladium or platinum. Electrochemical and computational results show that the frontier orbitals lie predominantly on the W[SNS]2 fragment suggesting that it behaves as a redox-active metalloligand in these complexes.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The tungsten complex W[SNS](2) ([SNS]H-3 = bis(2-mercapto-4-methylphenyl)amine) was bound to a Ni(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane] fragment to form the new heterobimetallic complex W[SNS](2)Ni(dppe). Characterization of the complex by single-crystal X-ray diffraction revealed the presence of a short W-Ni bond, which renders the complex diamagnetic despite formal tungsten(V) and nickel(I) oxidation states. The W[SNS](2) unit acts as a redox-active metalloligand in the bimetallic complex, which displays four one-electron redox processes by cyclic voltammetry. In the presence of the organic acid 4-cyanoanilinium tetrafluoroborate, W[SNS](2)Ni(dppe) catalyzes the electrochemical reduction of protons to hydrogen coincident with the first reduction of the complex.

The influence of a single octa repeat expansion on the Cu-II and Zn-II coordination environments within the octarepeat domain of the human prion protein is examined. Using X-ray absorption spectroscopy and diethyl pyrocarbonate labeling studies, we find that at low copper concentrations the "normal" octarepeat domain (four PHGGGWGQ repeats) coordinates Zn-II in an (N/O)(6) coordination environment with two histidine residues and Cu-II in a redox-inactive (N/O)(4) coordination environment using one imidazole residue. Expansion of the octarepeat region by one repeat (five PHGGGWGQ repeats) yields a three-histidine (N/O)(6) coordination environment for Zn-II and a two-histidine (N/O)(4) coordination environment for Cu-II at low copper concentrations. This Cu-II[(N/O)(2)-histidine(2)] coordination motif is redox-active and capable of generating H2O2 under reducing aerobic conditions.