Air-stable iron carbonyl compounds bearing cyclopentadienone ligands with varying substitution were explored as catalysts in dehydrogenative diol lactonization reactions using acetone as both the solvent and hydrogen acceptor. Two catalysts with trimethylsilyl groups in the 2-and 5-positions, [2,5- 2), were found to be the most active, with 2 being the most selective in the lactonization of diols containing both primary and secondary alcohols. Lactones containing five-, six-, and seven-membered rings were successfully synthesized, and no over-oxidations to carboxylic acids were detected. The lactonization of unsymmetrical diols containing two primary alcohols occurred with catalyst 1, but selectivity was low based on alcohol electronics and modest based on alcohol sterics. Evidence for a transfer dehydrogenation mechanism was found, and insight into the origin of selectivity in the lactonization of 1°/2°diols was obtained. Additionally, spectroscopic evidence for a trimethylamine-ligated iron species formed in solution during the reaction was discovered.

Facile reduction of aryl halides with a combination of 5% Pd/C, B2(OH)4, and 4‐methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N‐Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B2(OD)4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4‐Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4‐methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N,N‐bis(methyl‐d3)pyridin‐4‐amine (DMAP‐d6) and B2(OD)4 as an effective combination for full aromatic deuteriation.

The inside cover picture, designed by Lakshman and co‐workers, illustrates a diverse set of hydrogenations that can be conducted without use of external hydrogen gas (compressed gas). 4‐Methylmorpholine (NMM), tetrahydroxydiboron [B2(OH)4], and 5% Pd on charcoal work in concert to cause reductions of aryl halides and triflates, alkenes, alkynes, aldehydes, and azides, as well as cleavage of benzylic ethers and N‐Cbz groups. Based on the mechanistic knowledge gained in the study, aromatic deuteriations have also been accomplished using N,N‐bis(methyl‐d3)pyridin‐4‐amine (DMAP‐d6) and B2(OD)4. H2 gas appears to be formed in these reactions and this has been observed by 1H NMR and GC analysis. Details of this work can in found in the full paper on pages 166–176 (K. A. Korvinson, H. K. Akula, C. T. Malinchak, D. Sebastian, W. Wei, T. A. Khandaker, M. R. Andrzejewska, B. Zajc, M. K. Lakshman, Adv. Synth. Catal. 2020, 362, 166–176; DOI: 10.1002/adsc.201901099).