Structure of the radical resulting from the addition of H on a P=P bond: A theoretical and single crystal electron spin resonance study

Room temperature ESR spectra of x-irradiated single crystals of bis (2,4,6-tri-tert-butylphenyl) diphosphene provide evidence for the trapping of a R(H)PṖR radical produced by hydrogen addition on the P=P bond. The various experimental hyperfine tensors are compared with those calculated for H2PṖH and CH3(H)PṖCH3 after optimization of the structure of these model radicals by ab initio methods. The barrier to internal rotation about the P–P bond is calculated to be equal to 2.8 kcal/mol for H2PṖH.