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(N 3 ) 2 ( 2 ) or IPrNP(S)(N 3 ) 2 ( 4S ) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N 3 )(NPMe 3 ) ( 7 ) or IPrNP(S)N 3 (NPR 3 ) ( 5 R ), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy 2 ) to produce IPrNP(S)N 3 [NP(H)Cy 2 ] ( 6a ), which exists in equilibrium with a tautomeric IPrNP(S)N 3 [N(H)PCy 2 ] form ( 6b ), as confirmed by 31 P- 31 P 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.