“…Full perturbation towards a T‐shape (or C 2 v symmetry) results in a frontier‐orbital arrangement that is highly reminiscent of those found in tetrylenes, albeit with a significantly reduced directionality of the s‐type lone pair situated at the phosphorus center (Figure 1 , top). [ 11 , 12 , 13 , 14 ] Several geometrically constrained phosphines (and phosphenium cations, i. e. PR 2 + species) with ONO,[ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] OON, [30] CCC,[ 31 , 32 , 33 ] NNN,[ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ] NPN,[ 50 , 51 ] SPS,[ 52 , 53 , 54 ] or NNS [55] donor sets have been reported, each showing unusual reactivity towards small molecules and unique spectroscopic and electronic pr...…”