Diphosphinoboranes as Intramolecular Frustrated Lewis Pairs: P-B-P Bond Systems for the Activation of Dihydrogen, Carbon Dioxide, and Phenyl Isocyanate

Herein, we present the first example of the activation of small molecules by P-B-P bond systems. The reactivity study involves reactions of two selected diphosphinoboranes, (t-Bu2P)(2)BPh (1') and (Cy2P)(2)BNiPr2 (2), that differ in terms of their structural and electronic properties for the activation of dihydrogen, carbon dioxide, and phenyl isocyanate. Diphosphinoborane 1' activates H-2 under very mild conditions in the absence of a catalyst with the formation of the dimer (t-Bu2PB(Ph)H)(2) and t-Bu2PH. Conversely, diphosphinoborane 2 did not react with H-2 under the same conditions. The reaction of 1' with CO2 led to the formation of a compound with an unusual structure, where two phosphinoformate units were coordinated to the PhBOBPh moiety. In addition, 2 reacted with CO2 to insert two CO2 molecules into the P-B bonds of the parent diphosphinoborane. Both diphosphinoboranes activated PhNCO, yielding products resulting from the addition of two and/or three PhNCO molecules and the formation of new P-C, B-O, B-N, and C-N bonds. The products of the activation of small molecules by diphosphinoboranes were characterized with nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, single-crystal X-ray diffraction, and elemental analysis. Additionally, the reaction mechanisms of the activation of small molecules by diphosphinoboranes were elucidated by theoretical methods.

Automated summary

This study presents the first example of activating small molecules using P-B-P bond systems, involving reactions of two diphosphinoboranes with different properties. Diphosphinoborane 1' successfully activated H-2 and CO2, while diphosphinoborane 2 did not react with H-2 under the same conditions. Both diphosphinoboranes activated PhNCO, forming products with new bonds and structures. The products were characterized using various analytical techniques, and the reaction mechanisms were elucidated using theoretical methods.