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

A series of unique C(2)P(3)-ring compounds [(ADC(Ar))P(3)] (ADC(Ar) = ArC{(DippN)C}(2); Dipp = 2,6-iPr(2)C(6)H(3); Ar = Ph 4a, 3-MeC(6)H(4)4b, 4-MeC(6)H(4)4c, and 4-Me(2)NC(6)H(4)4d) are readily accessible in an almost quantitative yield by the direct functionalization of white phosphorus (P(4)) with appropriate anionic dicarbenes [Li(ADC(Ar))]. The formation of 1,2,3-triphosphol-2-ides (4a–4d) suggests unprecedented [3 + 1] fragmentation of P(4) into P(3)(+) and P(–). The P(3)(+) cation is trapped by the (ADC(Ar))(–) to give 4, while the putative P(–) anion reacts with additional P(4) to yield the Li(3)P(7) species, a useful reagent in the synthesis of organophosphorus compounds. Remarkably, the P(4) fragmentation is also viable with the related mesoionic carbenes (iMICs(Ar)) (iMIC(Ar) = ArC{(DippN)(2)CCH}, i stands for imidazole-based) giving rise to 4. DFT calculations reveal that both the C(3)N(2) and C(2)P(3)-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 C(2)P(3)-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 [{(ADC(Ar))P(3)}M(CO)(n)] (M = Fe, n = 4, Ar = Ph 5a or 4-Me-C(6)H(4)5b; M = Mo, n = 5, Ar = Ph 6; M = W, n = 5, Ar = 4-Me(2)NC(6)H(4)7).