Unusual Formation of an Azaphospholene from 1,3,4,5-Tetramethylimidazol-2-ylidene and Di(isopropyl)aminophosphaalkyne

Abstract

Intramolecular C−H insertion into the methyl group of the amino substituent of 1 is shown by density functional theory calculations to stabilize this intermediate in the formation of the novel 1:1 carbene–phosphaalkyne adduct 2. Compound 2 is formed in near quantitative yield by reaction of 1,3,4,5‐tetramethylimidazol‐2‐ylidene with P≡CNiPr2.

Application of Imidazole‐2‐thione Substituents in Low‐Coordinate Phosphorus Chemistry – Probing the Scope

“…of BH 3 · thf afforded the dinuclear phosphanido borane complex 11a (Scheme ). Upon complexation, the P signal of 11a appears downfield at δ = –34.8 ppm compared to that of 10a ( δ = –110.5 ppm) in the 31 P{1H} NMR spectra, which is significantly shifted upfield compared that of K[(BH 3 ) 2 PPh 2 ] ( δ = –11.1 ppm) and those of N‐heterocyclic carbene phosphinidene borane complexes ( δ = 4.0 and 2.8 ppm). Remarkably, 10a also reacts with 2 equiv.…”

N‐Heterocyclic Carbene–Phosphinidene Adducts: Synthesis, Properties, and Applications

“…The only example of using phosphaalkynes to produce NHC–phosphinidene adducts comes from Hahn et al, who synthesized the bicyclic adduct ( 2 ‐H) · PCHN( i Pr) 2 ( δ 31 P = –64.8) in almost quantitative yield from aminophosphaalkyne i Pr 2 NCP and N‐heterocyclic carbene 2 (Scheme ) . To date, this remains the only example of an intramolecular carbene‐stabilized phosphinidene.…”

“…Following a similar protocol, the groups of von Hänisch, Bertrand, and Hahn showed that, respectively, 5· PH, 7· PH, and ( 2 ‐H) · PCHN( i Pr) 2 react with two equivalents of BH 3 · THF or BH 3 · SMe 2 to form the corresponding bis(borane) adducts 25 , 26 and 30 (Scheme and Scheme ).…”

“…Hahn and co‐workers applied oxygen from air as oxidant serendipitously. Namely, upon exposure of NHC–phosphinidene adduct ( 2 ‐H) · PCHN( i Pr) 2 ( δ 31 P = –64.8) in benzene to air for several weeks a small amount of bis(oxide) 31 ( δ 31 P = 90.5) was obtained and crystallographically characterized (Scheme ) . Recently, the group of Tamm has demonstrated that 2· PPh, 5· PPh and 6· PPh can also form the corresponding bis(oxides) in the reaction with dioxygen, whereas the heavier sulfur and selenium analogues are selectively obtained only in the reaction of the sterically accessible 2· PPh with elemental sulfur or selenium, respectively …”

N‐Heterocyclic Carbene Adducts of Phenyldioxophosphorane and Its Heavier Sulfur and Selenium Analogues

“…With oxygen, such reactivity has been observed for related phosphaalkenes of the type (Me 2 N) 2 C=PAr upon reaction with ozone (for Ar = Ph) or air (for Ar = 2,4,6‐tri‐ tert ‐butylphenyl) . Similarly, “carbene‐stabilised diphosphorus” (IPr) 2 P 2 [IPr = 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene] reacts with dry O 2 to form the diphosphorus tetroxide (IPr) 2 P 2 O 4 ( IV ), and other NHC–phosphorus(I) compounds have also been shown to react slowly with dioxygen , . In contrast, we are unaware of any study dealing with the oxidation of NHC–phosphinidene adducts with sulfur or selenium, whereas the reaction of cationic dicarbene–phosphorus(I) species afforded bromide salts of the type [(NHC) 2 PS 2 ]Br ( V ) .…”