Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π‑Donating Imidazolin-2-iminato Ligand

Synthesis and characterization of new P­(III) and P­(V) bis­(azido)­phosphines/phosphoranes supported by an N,N′-bis­(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono­(phosphinimino)­azidophosphines via the Staudinger reaction. The reaction of IPrNP­(N3)2 (2) or IPrNP­(S)­(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP­(N3)­(NPMe3) (7) or IPrNP­(S)­N3(NPR3) (5 R ), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP­(S)­N3[NP­(H)­Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP­(S)­N3[N­(H)­PCy2] form (6b), as confirmed by 31P–31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.