Spectroscopic Identification of Diphosphene HPPH and Isomeric Diphosphinyldene PPH 2 .

The simplest diphosphene HPPH and isomeric diphosphinyldene PPH 2 features prototype phosphorus-phosphorus multiple bonding properties that have been of long-standing interest in main-group chemistry. Herein, we report the observation of cis-HPPH, trans-HPPH, and PPH 2 among the respective laser photolysis products of phosphine (PH 3 ) and diphosphine (P 2 H 4 ) in solid N 2 - and Ar-matrices at 10 K. The identification of these P 2 H 2 isomers with matrix-isolation IR and UV/Vis spectroscopy is supported by D-isotope labeling and the quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction theory (VCI). Bonding analyses suggest that the two conformers of HPPH contain standard PP double bonds, whereas, PPH 2 resembles P 2 in having partial PP triple bond due to the H 2 P←P π bonding interaction.