Theoretical elucidation on the mechanism of 1H‐1,2,4‐diazaphospholes synthesis from 1,3‐bis (amino)‐2‐phosphaallyl chlorides with hydrazine

The mechanism of the reaction of 1,3‐bis (amino)‐2‐phosphaallyl chlorides with hydrazine for the synthesis of 1H‐1,2,4‐diazaphospholes in CHCl 3 solvent has been extensively investigated at the B3LYP/6‐311G (d, p) level. The reaction is initiated by the elimination of HCl and formation of a key intermediate A , then A subsequently undergoes H‐migration‐cyclization ( A → B ) and Me 2 NH elimination reactions ( B → C ) to afford carbene intermediate C , and C can transform to F along both single and triplet potential energy surfaces in three steps. H‐migration‐cyclization ( A → B ) step was identified as a proton‐coupled electron transfer (PCET) process, and singlet‐triplet PES crossing should be important in decomposition of C to D1 and D2 . For R═Me, Ph and H, the rate control step should be the decomposition of C , while for R═ t Bu, the first Me 2 NH removal step is the rate control one. Theoretical results suggested that t Bu is a preferable group than Ph, Me, and H in this reaction, which can be attributed to hyperconjugation effects of t Bu, showing good agreement with experimental data.