Direct functionalization of white phosphorus with anionic dicarbenes and mesoionic carbenes: facile access to 1,2,3-triphosphol-2-ides.

A series of unique C2P3-ring compounds [(ADCAr)P3] (ADCAr = ArC{(DippN)C}2; Dipp = 2,6-iPr2C6H3; Ar = Ph 4a, 3-MeC6H4 4b, 4-MeC6H4 4c, and 4-Me2NC6H4 4d) are readily accessible in an almost quantitative yield by the direct functionalization of white phosphorus (P4) with appropriate anionic dicarbenes [Li(ADCAr)]. The formation of 1,2,3-triphosphol-2-ides (4a-4d) suggests unprecedented [3 + 1] fragmentation of P4 into P3 + and P-. The P3 + cation is trapped by the (ADCAr)- to give 4, while the putative P- anion reacts with additional P4 to yield the Li3P7 species, a useful reagent in the synthesis of organophosphorus compounds. Remarkably, the P4 fragmentation is also viable with the related mesoionic carbenes (iMICsAr) (iMICAr = ArC{(DippN)2CCH}, i stands for imidazole-based) giving rise to 4. DFT calculations reveal that both the C3N2 and C2P3-rings of 4 are 6π-electron aromatic systems. The natural bonding orbital (NBO) analyses indicate that compounds 4 are mesoionic species featuring a negatively polarized C2P3-ring. The HOMO-3 of 4 is mainly the lone-pair at the central phosphorus atom that undergoes σ-bond formation with a variety of metal-electrophiles to yield complexes [{(ADCAr)P3}M(CO) n ] (M = Fe, n = 4, Ar = Ph 5a or 4-Me-C6H4 5b; M = Mo, n = 5, Ar = Ph 6; M = W, n = 5, Ar = 4-Me2NC6H4 7).