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) (5R), 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.

Isolable N-heterocyclic carbene adducts of the elusive diiodophosphine

Reactions of PH-substituted phosphinidene-imidazolylidenes with I₂ afford isolable NHC-adducts of the transient diiodophosphine PHI₂. The products, which show a surprising structural diversity, are according to DFT studies best formulated as charge-transfer complexes of onio-substituted cationic phosphines with I^- and are capable of reaction under formal transfer of an NHC-P⁺ unit.