Water Reduction and Dihydrogen Addition in Aqueous Conditions With ansa-Phosphinoborane

Ortho-phenylene-bridged phosphinoborane (2,6-Cl₂ Ph)₂ B-C₆ H₄ -PCy₂ 1 was synthesized in three steps from commercially available starting materials. 1 reacts with H₂ or H₂ O under mild conditions to form corresponding zwitterionic phosphonium borates 1-H₂ or 1-H₂ O. NMR studies revealed both reactions to be remarkably reversible. Thus, when exposed to H₂ , 1-H₂ O partially converts to 1-H₂ even in the presence of multiple equivalents of water in the solution. The addition of parahydrogen to 1 leads to nuclear spin hyperpolarization both in dry and hydrous solvents, confirming the dissociation of 1-H₂ O to free 1. These observations were supported by computational studies indicating that the formation of 1-H₂ and 1-H₂ O from 1 are thermodynamically favored. Unexpectedly, 1-H₂ O can release molecular hydrogen to form phosphine oxide 1-O. Kinetic, mechanistic, and computational (DFT) studies were used to elucidate the unique "umpolung" water reduction mechanism.

Controlled Release of Reactive Gases: A Tale of Taming Carbon Monoxide

This Personal Account describes the development of air-stable and solid precursors for on-demand release of carbon monoxide. In combination with the development of a two-chamber reactor, COware®, CO liberation can be achieved under safe working conditions, as well as allowing transition metal-mediated carbonylations with stoichiometric carbon monoxide. Particularly appealing is the adaptability of this chemical technology for the preparation of carbon isotope labeled bioactive compounds.

Aldehydes as Alkylating Agents for Ketones

Common and non-toxic aldehydes are proposed as reagents for alkylation of ketones instead of carcinogenic alkyl halides. The developed reductive alkylation reaction proceeds in the presence of the commercially available ruthenium catalyst [(cymene)RuCl₂ ]₂ (as low as 250 ppm) and carbon monoxide as the reducing agent. The reaction works well for a broad substrate scope, including aromatic and aliphatic aldehydes and ketones. It can be carried out without a solvent and often gives nearly quantitative yields of the products. This straightforward and cost-effective method is promising not only for laboratory application but also for industry, which produces carbon monoxide as a large-scale waste product.

Tuning the nucleophilicity of electron-rich diborane(4) compounds with bridging guanidinate substituents by substitution

The proton affinity, HOMO energy and ionization energy of electron-rich sp³–sp³-hybridized diborane(4) compounds with bridging guanidinate substituents can be varied by substitution.