NHC‐Copper(I)‐Mediated Functionalization of White Phosphorus

Abstract

ABSTRACT We report a method for converting white phosphorus (P 4 ) directly into tetra‐ and pentaphosphanes using N ‐heterocyclic carbene (NHC) copper(I) complexes. The insertion of P 4 into the metal‐element bonds of the NHC complexes (6Dipp)Cu(Nu) [Nu = O t Bu and N( i Pr) 2 ] affords [(6Dipp)Cu( κ 2 ‐P 4 O t Bu)] ( 1 ) and [(6Dipp)Cu{ κ 2 ‐P 4 N( i Pr) 2 }] ( 3 ), which exhibit rotation of the [P 4 Nu] − ligand around the copper center in solution. This fluxional process is suppressed at low temperature, as shown by variable‐temperature 31 P{ 1 H} NMR spectroscopy. Treatment of 1 with W(CO) 5 (thf) resulted in the formation of the bimetallic complex [(6Dipp)Cu(μ, κ 2 : κ 1 ‐P 4 O t Bu){W(CO) 5 }] ( 2 ) which does not show fluxional behavior. Reactions of 1 and 3 with p‐block element halides release metal‐free asymmetrically substituted bicyclo[1.1.0]tetraphosphabutane ‘butterfly’ compounds. The polyphosphanes P 4 (PMes 2 )(O t Bu) ( 4a ), P 4 [P{N( i Pr) 2 } 2 ](O t Bu) ( 4b ), P 4 [P{N( i Pr) 2 } 2 ]{N( i Pr) 2 } ( 4c ), and P 4 (BPh 2 ){N( i Pr) 2 } ( 5 ) were isolated as stable compounds. Treatment of 4c with the NHC IMes induces further phosphorus–phosphorus bond cleavage and rearrangement to give NHC‐phosphinidene adduct [ cyclo ‐P 3 {N( i Pr) 2 }(P{N( i Pr) 2 } 2 )(P═IMes)] ( 6 ). Compound 4c also reacts with W(CO) 5 (thf) and CuBr·SMe 2 to give coordination complexes [W(CO) 5 { κ 1 ‐P 4 (P{N( i Pr) 2 } 2 )(N{ i Pr} 2 )}] ( 7 ) and [Cu(Br){ κ 2 ‐P 4 (P{N( i Pr) 2 } 2 )(N{ i Pr} 2 )}] ( 8 ), respectively, demonstrating the ability of 4c to serve as a mono‐ and bidentate ligand for transition metals. All compounds were characterized crystallographically and spectroscopically.