Investigations of a highly crowded phosphino-substituted biphenyl: A precursor for a λ3, λ5-diphosphaphenanthrene

The synthesis of 2,2′‐bis(bis(dimethylamino)‐phosphino)‐3,3′5,5′‐tetra‐tert‐butylbiphennyl (5) is described. It was extensively studied by 1H, 13C, and 31P NMR spectroscopy. Furthermore, the X‐ray analysis of 5 is reported. Crystals of 5 are tetragonal, space group P¯421c, a = b = 24.770 (3) Å, c = 12.658 (4) Å, Z = 8. The surprising reaction of 5 with proton acids leading to the formation of various phosphorus containing five‐ and six‐membered ring compounds is discussed. On reaction of one of the six‐membered ring compounds (9) with magnesium in THF, a λ3, λ5‐diphosphaphenanthrene (19) was obtained.