Bio-based isoprene is converted to a high performance jet fuel blendstock by Fe-catalyzed [4 + 4] cycloaddition and hydrogenation.

A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4f n 5d z 2 1 electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(Cp iPr5 ) 2 (Ln = Tb, Dy; Cp iPr5 = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(Cp iPr5 ) 2 (1-Ln) series (including Y and excluding Pm). The compounds can be synthesized through salt metathesis of LnI 3 and NaCp iPr5 followed by potassium graphite reduction for Ln = Y, La, Ce, Pr, Nd, Gd, Ho, and Er, by in situ reduction during salt metathesis of LnI 3 and NaCp iPr5 for Ln = Tm and Lu, or through salt metathesis from LnI 2 and NaCp iPr5 for Ln = Sm, Eu, and Yb. Single crystal X-ray diffraction analyses of 1-Ln confirm a linear coordination geometry with pseudo-D 5d symmetry for the entire series. Structural and ultraviolet−visible spectroscopy data support a 4f n+1 electron configuration for Ln 2+ = Sm, Eu, Tm, and Yb and a 4f n 5d z 2 1 configuration for the other lanthanides ([Kr]4d z2 1 for Y 2+ ). 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 Ln 2+ compounds suggests that the more pronounced 6s−5d mixing may be associated with weaker 4f−5d spin coupling.

Double deprotonation of bis(2-mercapto-4-methylphenyl)amine ([SNS]H) followed by addition to NiCl(PR) in air-free conditions afforded [SN(H)S]Ni(PR) (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(PR)} 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 = / complex, [SNS]Ni(PCy) (3a), was isolated. When R = Ph, the bimetallic complex {[SNS]Ni(PPh)} ({3b}) was obtained. This bimetallic species is diamagnetic; however, in solution it dissociates to give S = / 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, respectively, using the corresponding p K 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.

The tungsten complex W[SNS]2 ([SNS]H3 = 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]2Ni(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]2Ni(dppe) catalyzes the electrochemical reduction of protons to hydrogen coincident with the first reduction of the complex.