Versatile and Efficient Synthesis of a New Class of Aza‐Based Phosphinic Amide Ligands via Unusual PC Cleavage

A new class of bidentate, aza‐based phosphinic amide ligands of the type RN(H)P(O)(2‐py) 2 (2‐py = 2‐pyridyl) was synthesized within minutes via a one‐pot process including Staudinger reaction of an organic azide (RN 3 ) with 2‐pyridylphosphines, followed by partial, unprecedented hydrolysis under loss of one aromatic substituent. The structure of the unusual‐hydrolysis product H 2 CCH(CH 2 ) 9 N(H)P(O)(2‐py) 2 ( 5a ) was characterized by IR, 1 H‐ and 31 P‐NMR, as well as by X‐ray crystal‐structure analysis ( Figure ). The tetrahedral P‐atom was found to be surrounded by a trigonal‐pyramidal arrangement of the substituents. To gain insight into the formation of these novel phosphinic amides, a series of intermediate iminophosphoranes, H 2 CCH(CH 2 ) 9 NP(Ar) n (2‐py) 3 −  n ( n  = 0–3), compounds 1a – 1f , were synthesized, and their hydrolyses were studied. All tested compounds followed the classical hydrolysis route of PN cleavage under acidic conditions. Sequential hydrolysis to 5a – 5d only occurred under either basic conditions or in wet MeCN as solvent. Notably, H 2 CCH(CH 2 ) 9 NP(C 6 H 5 )(4‐MeO‐2‐py) 2 ( 1c ) was hydrolyzed at a much slower rate compared to its analogue 1b lacking the MeO group. On the contrary, the halogenated compounds H 2 CCH(CH 2 ) 9 NP(4‐X‐C 6 H 4 ) 3 ( 1f,g ) (X = F, Cl) were hydrolyzed at a notably faster rate relative to the non‐halogenated congener 1e (X = H).