One-Pot Synthesis of [N(PPh3)2]+ Monoorganoborohydride Salts from Potassium Organotrifluoroborates Yields Unusual Crystalline Compounds for X‑ray Crystallography

• Published in: Organometallics Vol. 41; no. 21; pp. 2933 - 2941
• Main Authors: Yates, James L., Thompson, Brena L., Korchemniy, Eugene P., Rooney-Sailand, Benjamin A., Glasser, Craig M., Allen, Caleb J., Wheeler, Kraig A., Abbey, Eric R.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.11.2022
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.2c00353

This contribution describes the one-pot conversion of potassium organotrifluoroborates (KRBF3s) to their respective metal monoorganoborohydrides (MRBH3s), followed by in situ cation exchange to yield monoorganoborohydrides with PPN+ [N­(PPh3)2]+ cations. A reactivity study comparing PPN+-based borohydrides in CDCl3 and their Na+-containing counterparts in DMSO-d 6 shows enhanced reduction ability toward aldehydes and ketones in the metal-free reactions, as well as greater atmospheric stability. Many of these compounds form crystals suitable for crystallographic assessment. Eight new X-ray structures are analyzed herein, permitting the structural comparison of [PPN]­RBH3 moieties to their metal-containing counterparts in the solid-state. In the absence of metal, cation and anion pack as independent units, with only weak forces contributing to crystal organization, including BH···H–C dihydrogen bonds, C–H···pi interactions, and X···H–C interactions in heteroatom-containing [PPN]­RBH3s. In some instances, supramolecular interactions between RBH3 – units are observed, including pi–pi interactions, and even possible F···F interactions between CF3 units.